Special Alert: Permafrost-related Abstracts, 2019

2020027617 Abe, Takahiro (Japan Aerospace Exploration Agency, Kanagawa, Japan); Iwahana, Go and Tadono, Takeo. Thermokarst subsidence in central Yakutia revealed by ALOS/ALOS-2 InSAR analysis [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1371, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Surface deformation in Arctic regions underlain by ice-rich permafrost is induced by the melting of massive ground ice, which is known as thermokarst. Thermokarst development can change the local land use and affects the local socio-economy. Central Yakutia in eastern Siberia is one of the regions where ice-rich permafrost is broadly distributed. The remarkable surface subsidence due to thermokarst has been observed in recent years, which causes destruction of infrastructure in this area. In order to better understand landform changes including thermokarst subsidence, inundation, and thermos-hydrological erosions, knowledge about the deformation rates and spatial distribution of the phenomena is essential. Remote sensing technique, especially Interferometric Synthetic Aperture Radar (InSAR), has a possibility to monitor the thermokarst subsidence and seasonal surface displacement over the permafrost regions. Recent studies of permafrost monitoring using SAR data have been reported, and SAR could provide essential information to understand thawing process of ice-rich permafrost. In this study, we used ALOS/PALSAR (2007-2011) and ALOS-2/PALSAR-2 (2015-2019) data to investigate ground subsidence caused by thermokarst development. GAMMA software was used to generate Single Look Complex data from Lv1.0 data in ALOS/PALSAR and Lv1.1 data in ALOS-2/PALSAR-2. We generated some interferograms and applied stacking procedure. Assuming ground displacement is only vertical component, the LOS change was converted to vertical displacement using incidence angle. As a result, we detected ground subsidence with a rate of 0.5-4 cm/yr in Mayya, Amga, and Churapcha from PALSAR and PALSAR-2 InSAR stacking. In Mayya, the subsidence signals are found in numerous open areas (deforested areas), and the PALSAR-2 results clearly show the spatial distribution of the subsidence corresponding to visible observation of thermokarst development in high-resolution optical images.

2020027654 Abolt, Charles (Los Alamos National Laboratory, Los Alamos, NM); Young, Michael; Atchley, Adam L. and Wilson, Cathy J. High-resolution machine-learning-based quantification of spatial heterogeneity in ice wedge polygon geomorphology [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24A-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

It is well known that microtopography associated with ice wedge polygons drives pronounced, meter-scale spatial gradients in hydrologic and ecological processes on the tundra. However, high-resolution maps of polygonal geomorphology are rare, due to the complexity and subtlety of ice wedge polygon relief at landscape scales. Here we present a novel method to rapidly delineate and measure the microtopography associated with individual ice wedge polygons within high-resolution digital elevation models (DEMs). At its core, the method relies on a convolutional neural network paired with a set of common image processing operations to segment a DEM into discrete polygons. The relief at the center relative to the periphery of each polygon is then calculated, placing each instance on a spectrum between low-centered and high-centered endmembers. The flexibility of this method is first demonstrated through application at a set of geomorphically diverse field sites, each 1 km² in area, near Prudhoe Bay and Utqiagvik, Alaska. Subsequently, the robustness of the method at more extensive spatial scales is demonstrated through application across a ~1,200 km² landscape south of Prudhoe Bay, capturing >10⁶ individual polygons. Manual validations suggest that the results at both spatial scales are highly accurate; in general, >90% of polygons extracted by the algorithm are correctly delineated. The resulting maps permit visualization of heterogeneity in ice wedge polygon geomorphology with unprecedented detail, revealing complex patterns in the spatial distribution of low-centered and high-centered polygons across diverse landforms. In the future, we anticipate that the maps will be useful for quantification of spatial heterogeneity in key environmental processes affected by polygonal microtopography, such as mobilization of soil organic carbon. The maps produced using our method are also valuable for providing extensive baseline datasets to quantify contemporary, climate-driven deformation of ice wedge polygon microtopography, through future surveys at the field sites. Through these two applications, the methodology will ultimately help constrain trajectories of land surface evolution in the rapidly changing Arctic environment.

2020032652 Alavoine, Axelle (Ecole des Ponts ParisTech, Champs-sur-Marne, France); Dangla, Patrick and Pereira, Jean-Michel. Numerical modelling using homogenization techniques of gas hydrate bearing sediments [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS34A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Natural gas hydrates represent a potential energy resource and a geohazard that it is essential to control. The study of gas hydrate bearing soils (GHBS), which are usually located in ocean floor or in permafrost regions, represents a major interest. The hydrate formation and dissociation processes in porous sediments change their microstructure and their physical properties with it. Several multi-physical models have already been applied to GHBS but a reliable mechanical constitutive model is difficult to develop due to the complexity and the instability of these soils.

2020027705 Almenningen, Stian (University of Bergen, Bergen, Norway); Gauteplass, Jarand and Ersland, Geir. Demonstrating the potential of CO₂ hydrate self-sealing during geological CO₂ storage [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC31E-1298, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Formation of solid CO₂ hydrates from injected CO₂ and pore water may increase the storage capacity and provide extra sealing during carbon sequestration in the shallow subsurface. Knowledge about the CO₂ flow and hydrate growth pattern within sedimentary pores are needed to assess the integrity of the hydrate seal. Here, we report the potential self-sealing properties of CO₂ hydrate through hydrate formation experiments in different rock core plugs. CO₂ was injected into brine-filled Bentheim sandstone, Edward limestone, sandstone retrieved from the subsurface in Svalbard, Arctic Norway, and unconsolidated sand at realistic reservoir conditions favorable to CO₂ hydrate growth. The effectiveness of the CO₂ hydrate seal that formed during CO₂ injection increased as the permeability of the core material decreased, except for the delayed flow reduction in limestone, which was affected by local grain dissolution. The mechanism of CO₂ hydrate formation was additionally analyzed by direct imaging of the pore space in a micromodel chip analogous to the pore network in a sandstone. The processes of CO₂-water drainage followed by hydrate formation were also visualized at core-scale in Bentheim sandstone using high-field MR imaging. The imaging results verified hydrate nucleation both at the CO₂-water interface and in the water phase alone due to the presence of dissolved CO₂. The combined results from multiple length scales demonstrate the potential of CO₂ hydrate formation as a secondary seal in settings with favorable CO₂ hydrate kinetics in or above the reservoir. The self-sealing nature of CO₂ hydrate should be considered while planning CO₂ storage operations in both shallow marine and permafrost-affected settings.

2020032498 Amini Tabrizi, Roya (University of Arizona, Environmental Science, Tucson, AZ); Wilson, Rachel; Hodgkins, Susanne B.; Rich, Virginia Isabel; Saleska, Scott R.; Chanton, Jeff and Tfaily, Malak M. Controls on organic matter degradation in thawing permafrost peatlands and subsequent greenhouse gas emissions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2569, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Northern peatlands store globally important amount of soil organic carbon. However, global temperature rise promotes periods of thaw in discontinuous permafrost zone, resulting in the shifts in vegetation and water table level and subsequently, change in carbon accumulation rate in peat profiles. This in return would directly impact the organic carbon (OC) pool composition by triggering the microbial activity and metabolic transformations in these regions. Given that the breakdown of soil organic matter (SOM) is often a major pathway for decomposition in peatlands, knowledge of organic matter reactivity under different permafrost regimes is critical for determining future climate feedbacks. Here in this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was utilized to examine the SOM composition gathered from bog and fen sites along a permafrost thaw sequence in Stordalen Mire, a thawing subarctic peatland in northern Sweden. In this study, we tested the hypotheses that organic matter reactivity increases with permafrost thaw due to thaw-induced subsidence and associated shifts in hydrology and plant community which highly affect the organic C sequestration and decomposition rate/processes. Transition from Sphagnum-dominated bogs to more waterlogged, sedge-dominated rich fens shifts the anaerobically produced CO₂ and CH₄ towards higher production potentials and different mechanisms, indicating a major role of plant communities on the available OC via changes in organic matter chemical composition (commonly referred to as organic matter "quality") in a thawing peatland complex.

2020032541 Anderson, Nicholas J. (University of Loughborough, Loughborough, United Kingdom); Osburn, Chris L.; Stedmon, Colin A. and Leng, Melanie J. Organic carbon quality changes in response to altered hydrological regime and rapid climate warming of an arid, permafrost environment (Kangerlussuaq, SW Greenland) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Land-water interactions across arctic landscapes are changing rapidly in response to regional warming, melting permafrost and altered precipitation regimes. The interplay of seasonal active layer dynamics and precipitation type and amount can strongly influence the source, transfer and fate of organic carbon in permafrost landscapes: process interactions that have important implications for regional GHG emissions. Understanding these processes and how they are changing in response to multiple drivers is difficult because of the scarcity of long-term data series. The Kangerlussuaq area of SW Greenland close to the present ice-sheet margin is characterized by continuous permafrost, low annual precipitation (<200 mm/yr) and a strong landscape-morphometric control on surface water movement and availability. The area has thousands of lakes and only began to warm recently, so much so that it has been possible to track hydrological and carbon quality responses to recent warming in real time. Using a 20-year stable isotope dataset (d¹⁸O and d¹³C) from multiple lakes we consider the effect of altered landscape-scale hydrological linkages (increased evaporation, reduced seasonal hydrological connectivity) on surface water dissolved organic carbon (DOC) dynamics. We show that as well as changes in the aquatic storage pools and variable terrestrial carbon inputs, there have also been significant changes in DOC quality as indicated by stable isotope and fluorescence analyses. The results are indicative of the fate of organic carbon in a future, warmer and importantly, drier Arctic.

2020032490 Aronne, Mary (ASRC Federal Holding Company, Beltsville, MD) and Carroll, Mark. The application of machine learning algorithms and Landsat data to calculate lake depth in the Arctic Coastal Plain [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23K-2463, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic Tundra is characterized by low growing vegetation and small bodies of water. These lakes provide ecosystem services including water storage, freshwater for indigenous people, and ice road construction. Deeper lakes will not freeze to the bottom which impacts the ecosystem dynamics with regards to fish habitat, permafrost vulnerability and a deepening talik layer at the lake bottom, and groundwater discharge. Previous research has focused on mapping these water bodies but not as much on their depth or bathymetry due to limited training data. Here we explore four machine learning techniques to measure water storage in small water bodies and model limnology for inclusion in scientific analysis and decision making. Machine learning algorithms are advantageous for estimating depth due to their extensibility to regions outside of the initial training area. The algorithms employed here use training data made up of in situ data points collected from 17 lakes. One set of measurements, used for training, is from depth-gradient transects collected over a few days in late summer 2017. The other set of validation data is from fixed location buoys collecting data over time. The algorithm is trained using spectral values, from Landsat, at the point locations and applied to the full Landsat data to establish the relationship between depth and spectral response. Results from four machine learning techniques (Random Forest, Support Vector Machine, Artificial Neural Network, and Convolutional Neural Network) are analyzed both thematically and statistically to identify the optimal method. Machine learning algorithms can provide inferences not readily apparent to a human interpreter by accounting for varying spectral responses due to water composition and lake bottom type. All results are compared to the linear regression approach that has more commonly been applied to determine depth of water and was previously applied to the 17 lakes in the study area.

2020027652 Bajracharya, Ajay R. (University of Manitoba, Department of Civil Engineering, Winnipeg, MB, Canada); Stadnyk, Tricia A.; Awoye, Oyemonbade H. R. and Asadzadeh, Masoud. Impact of thawing permafrost and frozen soils on Arctic freshwater runoff under changing climate [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23D-1588, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Hydrological models are important tools to analyze the cold regions processes, such as permafrost, seasonally frozen soil and snow cover, which are widely distributed across Canada. In Arctic regions, frozen soil processes and permafrost play a key role in runoff generation by restricting the infiltration during the frozen state, and thawing during the melting phase. Therefore, the representation of such processes in models is critical for model projections under climate change, and hence for reducing the uncertainty associated with freshwater runoff. In this research, the frozen soil infiltration was incorporated in HYPE model, and the output variables such as soil temperature and soil moisture were validated with field observations across Nelson Churchill River Basin (NCRB). The improved HYPE-NCRB model was used to project climate change impacts on soil moisture, soil temperature, and implications on model uncertainty associated with the projection of streamflow. A suite of 14 GCMs and 2 RCP (RCP 4.5 and RCP 8.5) scenarios representing 87% of the variability of 154 climate scenarios were bias corrected at the catchment scale for a baseline period of 1981-2010 and future period of 2020-2070. Average soil temperature across the basin is projected to increase by up to 2.6°C, with only moderately increasing soil moisture (less than 3%). Projected increases in temperature, however, have profound effects on frozen soil, permafrost cover and Arctic freshwater runoff. Our study shows degradation in permafrost cover from 75,000 sq. km to less than 10,000 sq.km. by the 2060s, and projected increases in runoff up to 40% within parts of the basin. The study could be beneficial to further access the impact of climate change and degrading permafrost on infrastructures and ecosystems of the Arctic .

2020032450 Bakian Dogaheh, Kazem (University of Southern California, Ming Hsieh Department of Electrical and Computer Engineering, Los Angeles, CA); Chen, Richard H.; Moghaddam, Mahta and Tabatabaeenejad, Alireza. Enhancement of permafrost soil properties estimation for organic-rich Arctic soils using P-band radar [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B12D-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Polarimetric synthetic aperture radar (PolSAR) observations have demonstrated a strong capability of retrieving surface and subsurface geophysical properties from radar backscattering data acquisition. Radar backscatter is directly sensitive to the surface and subsurface dielectric profile. Dielectric constant is a function of both soil constituents (organic matter content, sand, silt, and clay fractions, bulk density, and porosity) and soil geophysical conditions (moisture content and freeze/thaw state). We have previously estimated the permafrost soil properties in the ABoVE study domain using the radar data acquired in 2014 and 2015 (as part of an Interdisciplinary Research in Earth Science (IDS) Program project), and during the ABoVE Airborne Campaign in 2017. These radar data were collected over several flight lines referred to as the Legacy Lines. Lack of a well-established soil dielectric model for a full range of organic matter content has been a major challenge to the parametrization of the active layer soil properties using radar observation. Therefore, we modeled permafrost soil as a layered dielectric structure and retrieved layer dielectric constants and the active layer thickness (ALT) using a time-series approach to the inverse problem, formulated as an optimization problem. In this work, we first present an overview of our new organic soil dielectric model, which we have developed using a coupled hydraulic-electromagnetic approach. We will also present an overview of our profile model developed to represent the Arctic soil properties (including soil moisture and organic matter content) as a function of depth. The focus of this work will be on integrating these new soil models into our radar scattering inversion algorithm to retrieve the ALT, subsurface organic matter profile, as well as the soil moisture profile over the Legacy Lines. We will present the inversion results for the Legacy Line for which data are available and will compare the accuracy of the retrieval results with our previously reported results from 2014, 2015, and 2017. The new approach is not only more realistic in terms of representation of permafrost soil structure but also expected to increase the inversion accuracy.

2020032573 Baranskaya, Alisa (Lomonosov Moscow State University, Moscow, Russian Federation); Belova, Nataliya; Shabanova, Nataliya N.; Novikova, Anna V.; Aleksyutina, Daria M.; Ogorodov, Stanislav A. and Jones, Benjamin M. Coastal dynamics in the Kara Sea; spatial and temporal variability from small to large scales [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C12B-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Kara sea region is among the best studied in terms of coastal dynamics in the western sector of the Russian Arctic. Long-term monitoring results are available for four key areas and remote sensing data help to extend the spatial and temporal context of these observations. Thermoabrasional coasts of the Kara Sea retreat with average rates up to several meters per year, as they are composed by permafrost. A large variety of drivers determines the dynamics of such coasts: orientation and exposure, wind and wave conditions, sea level changes, lithology and grain size of the cliff sediments, sea ice-free period duration influencing rates of mechanical destruction, or abrasion, but also air and water temperature, ground-ice content, presence of massive ice bodies, provoking faster or slower thawing of permafrost, or thermodenudation. To reveal the relative role of each driver and their interaction, comparison of several sites with varying environmental conditions and well-studied erosion rates is required. Here, we compare the results of observations on five sites on the Kara Sea coasts: the Ural and Yamal coasts of the Baydaratskaya Bay, Marre-Sale, the Gulf of Kruzenstern and Kharasavey. All sites are situated in the southwestern Kara Sea, but the morphologic, geologic, permafrost and climate conditions vary across the region. Because of this, it was possible to compare the reaction of coasts with different exposure, cliff height, permafrost properties, morphology, etc. to changing hydrometeorological parameters. We found that the spatial variability of erosion rates largely depends on the presence of ground ice, especially massive ice bodies that are widespread in the West Siberian north. Another important factor is orientation and exposure of the coastal segments. The temporal variability mostly depends on the changing ice-free period duration with subsequent wind-wave energy variations. Observations from the Kara Sea fill an important role in better understanding arctic coastal dynamics and contribute to an emerging network focused on permafrost coastal systems.

2020027647 Bartsch, Annett (Austrian Polar Research Institute, Vienna, Austria); Grosse, Guido; Westermann, Sebastian; Strozzi, Tazio; Duguay, Claude R.; Seifert, Frank M.; Obu, Jaroslav; Kaab, Andreas; Nitze, Ingmar; Heim, Birgit; Haas, Antoinie; Widhalm, Barbara; Laboor, Sebastian; Muster, Sina; Wiesmann, Andreas; Hugelius, Gustaf; Delaloye, Reynald; Matthes, Heidrun and Leibman, Marina O. Examining environmental gradients in permafrost regions; achievements of the ESA DUE GlobPermafrost project and first results from ESA CCI+ Permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A Permafrost Information System (PerSys) has been setup as part of the GlobPermafrost ESA DUE GlobPermafrost project (2016-2019, www.globpermafrost.info). This includes a data catalog as well as a WebGIS, both linked to the Pangaea repository for easy data access. A Permafrost Information System (PerSys) has been setup as part of the GlobPermafrost ESA DUE GlobPermafrost project (2016-2019, www.globpermafrost.info). The thematic products available include InSAR-based land surface deformation maps, rock glacier velocity fields, spatially distributed permafrost model outputs, land surface properties and changes, and ground-fast lake ice. Extended permafrost modelling (time series) is implemented in the new ESA CCI+ Permafrost project (2018-2021), which will provide the key for our understanding of the changes of surface features over time. Special emphasis in CCI+ Permafrost will be on the evaluation and development of land surface models to gain better understanding of the impact of climate change on permafrost and land-atmosphere exchange. Additional focus will be on documentation of kinematics from rock glaciers in several mountain regions across the world.The thematic products available include InSAR-based land surface deformation maps, rock glacier velocity fields, spatially distributed permafrost model outputs, land surface properties and changes, and ground-fast lake ice. Extended permafrost modeling (time series) is implemented in the new ESA CCI+ Permafrost project (2018-2021), which will provide the key for our understanding of the changes of surface features over time. Special emphasis in CCI+ Permafrost will be on the evaluation and development of land surface models to gain better understanding of the impact of climate change on permafrost and land-atmosphere exchange. Additional focus will be on documentation of kinematics from rock glaciers in several mountain regions across the world. We will present an overview on technical developments made within GlobPermafrost and demonstrate its utility and challenges for an area prone to change of permafrost features. We will focus on the central Yamal Peninsula and the unusually warm years of 2012 and 2016. Conditions of 2012 triggered widespread retrogressive thaw slumps and the development of a gas emission crater. Thaw slumps have been reactivated in 2016, the first year with extensive coverage of Sentinel-1 as well as Sentinel-2 data. We present the documentation of these developments based on InSAR subsidence, Landsat trend analyses, ground fast lake ice, Sentinel-2 landcover information as well as a time series of the first version of ground temperatures from the ESA CCI+ Permafrost project.We will present an overview on technical developments made within GlobPermafrost and demonstrate its utility and challenges for an area prone to change of permafrost features. We will focus on the central Yamal Peninsula and the unusually warm years of 2012 and 2016. Conditions of 2012 triggered widespread retrogressive thaw slumps and the development of a gas emission crater. Thaw slumps have been reactivated in 2016, the first year with extensive coverage of Sentinel-1 as well as Sentinel-2 data. We present the documentation of these developments based on InSAR subsidence, Landsat trend analyses, ground fast lake ice, Sentinel-2 landcover information as well as a time series of the first version of ground temperatures from the ESA CCI+ Permafrost project. While landcover documents the occurrence of disturbances, InSAR provides insight into soil properties and impacts of unusually warm conditions during the unfrozen period. These space-based observations have been evaluated by in situ measurements at the long-term monitoring site Vaskiny Datchi. Ground fast lake ice and ground temperature modeling results provide additional insight into interannual variability. While landcover documents the occurrence of disturbances, InSAR provides insight into soil properties and impacts of unusually warm conditions during the unfrozen period. These space-based observations have been evaluated by in situ measurements at the long-term monitoring site Vaskiny Datchi. Ground fast lake ice and ground temperature modeling results provide additional insight into interannual variability.

2020032600 Baskaran, Latha (Jet Propulsion Laboratory, Pasadena, CA); Elder, Clayton; Thompson, David R.; Miller, Charles E. and Thorpe, Andrew K. Environmental drivers of Arctic methane emissions hot spots determined from remote sensing datasets [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51E-1115, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane emissions from the Arctic are a critical part of the global carbon cycle, particularly due to the positive feedback associated with melting of the permafrost. Some of the factors influencing Arctic methane emissions include local environmental and climatic factors, such as microtopography, geology, soils, hydrologic conditions, and vegetation. Understanding the occurrence of methane hotspots with respect to the spatial variation and heterogeneity of the environmental factors is important for upscaling methane emissions and for improved estimation of methane emissions across the pan-Arctic. We studied methane hotspots over the Kuparuk River basin, North Slope Alaska, and the Mackenzie Delta in northern Canada using airborne imaging spectroscopy collected as part of the Arctic Boreal Vulnerability Experiment (ABoVE). Methane hotspots, defined here as column integrated enhancements greater more than 3000 ppm-m, were derived from NASA's Next-Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG) flown in 2017. We correlated data from various remote sensing products with methane hotspots to identify the environmental drivers of methane emissions in the study regions. Vegetation indices (such as the Normalized Difference Vegetation Index) derived from imaging spectroscopy data and existing vegetation classifications were used as vegetation community indicators. The influence of hydrologic features on methane hotspots was studied using datasets indicating the presence of lake features and the proximity to waterbodies derived from AVIRIS-NG data. Using high resolution Digital Elevation Models (DEM) of the Arctic, we studied the influence of changes in elevation and slope on the spatial distribution of methane hotspots. Preliminary results over the Kuparuk river basin indicate the presence positive correlations between methane hotspot emissions and elevation, and negative correlations with shrub biomass. We also identified spatial clusters among the hotspots in Mackenzie Basin, possibly indicating the presence of underlying geological factors and/or the effects of exploratory activities influencing the hotspots. We will further study these correlations and present results on spatial patterns and differences among vegetation communities.

2020032547 Beel, Casey Robert (Wilfrid Laurier University, Waterloo, ON, Canada); Lamoureux, Scott F.; Orwin, John F. and Lafreniere, Melissa J. Disturbed High Arctic permafrost watersheds; a decade of impact on fluvial organic carbon fluxes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost exerts an important control on lateral carbon fluxes from High Arctic watersheds. Recent climate warming and changing precipitation patterns have thermally and physically disturbed circum-Arctic permafrost watersheds, increasing the mobility of dissolved organic carbon (DOC) and particulate organic carbon (POC) across the terrestrial-aquatic interface. However, few studies have investigated the spatial and temporal persistence of DOC changes in runoff associated with permafrost disturbances, and fewer have investigated the potential for permafrost disturbances to significantly alter the longer-term export of POC. We present the first decadal, multi-year record (2006-2017) of fluvial DOC and POC fluxes at multiple spatial scales during a period of substantial hydrometeorological change and ensuing permafrost disturbances at the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian High Arctic (~75°N). Thermal disturbances (2007, 2012) are a catchment-wide process that have no discernible impact on DOC export in this environment, unless it triggers a localized physical disturbance (2007), leading to a fundamental shift in the export of carbon from small, headwater-slope streams (~0.2 km²). The physical disturbance of active layer soils results in a general decrease in the concentration and flux of DOC (including export downstream of disturbances), and a substantial increase in the flux of POC (consistent linear relationships). Fluxes of POC respond immediately and recover rapidly (exponential decline within five years), but remain elevated ten-years post-disturbance. Although physical disturbance increases POC mobility across the terrestrial-aquatic interface, localized disturbances have not increased the downstream, watershed-scale (~10 km²) export of POC in this environment due to contemporary fluvial energy limitations and geomorphic controls. These findings strongly suggest that the importance of POC mobilization is likely to increase in the near future, particularly in watersheds with increased sediment erosion resulting from physical permafrost disturbance.

2020032470 Behnke, Megan Irene (Florida State University, Department of Earth, Ocean, and Atmospheric Science, Tallahassee, FL); Holmes, Robert Max; McClelland, James W.; Tank, Suzanne and Spencer, Robert G. Pan-Arctic molecular fingerprints; multi-year FT-ICR MS data from the major Arctic rivers reveal unique seasonal- and river-specific molecular formulae [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23A-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate change has caused rapid warming in the Arctic, which in turn is leading to permafrost degradation, shifts in vegetation and hydrology, and changes in the quantity and composition of dissolved organic matter (DOM) in riverine ecosystems. Since the Arctic Ocean receives a disproportionately large amount of the world's riverine runoff, Arctic riverine DOM composition is important to Arctic Ocean ecosystem functioning. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides an ultrahigh resolution tool for fingerprinting DOM and elucidating its chemical nature. In this study we present an extensive time series of Arctic riverine FT-ICR MS data (2012-2018) from the Arctic Great Rivers Observatory. We demonstrate the molecular formulae that are common to DOM in the six largest Arctic rivers (the Yenisey, Lena, Ob', Mackenzie, Yukon, and Kolyma), along with the unique fingerprints of each river. We show how both common and unique Arctic river molecular formulae compare to previously identified DOM compositional regions such as the "Island of Stability," and relate FT-ICR MS data to watershed characteristics such as land cover. We further highlight seasonal trends in DOM chemistry, link optical properties of DOM to FT-ICR MS data, and demonstrate the unique seasonal fingerprints of DOM across the major Arctic rivers. This work highlights that while there is an assemblage of molecular formulae common to all large Arctic rivers and all seasons, each river and each season is prone to discharging molecular formulae with unique formulae, implying that the presence of such molecular formulae in the Arctic Ocean could be suggestive of riverine and temporal DOM source.

2020027633 Beisman, James (Los Alamos National Laboratory, Los Alamos, NM); Harp, Dylan R.; Jafarov, Elchin E.; Wilson, Cathy J.; Coon, Ethan; Chen, Min and Dann, Julian B. Insights from integrated thermal hydrology simulations of an Arctic watershed with isolated permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1388, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Continued warming of the Arctic system is currently driving rapid and transformative change in high-latitude landscapes. These ice-rich ecosystems are particularly sensitive to perturbations, and many of the processes that dictate system behavior are inextricably linked. For example, water and energy fluxes ultimately determine patterns of soil moisture, which in turn exert a strong control on rates and pathways of organic carbon decomposition. To better understand the complex process interactions occurring as these systems change, we are simulating integrated hydrology and permafrost dynamics in the NGEE Arctic Teller field site (Teller watershed) with the Advanced Terrestrial Simulator (ATS). Teller watershed contains areas with near-surface, deep, and no permafrost, and can be considered to be representative of discontinuous permafrost systems. Observations suggest the watershed has an active and well-connected subsurface hydrologic system. This work utilizes many streams of observational data in a single integrated framework, providing the opportunity to refine our understanding of system behavior under current or past climatological conditions. Hydrological mass balance calculations will be presented, providing insight into rates of permafrost melt. Planned future activities include the integration of observed isotopic data to better constrain our model, and the use of reactive transport simulations to investigate pertinent biogeochemical cycling questions.

2020032575 Belova, Nataliya (Russian Academy of Sciences, Siberian Branch, Earth Cryosphere Institute, Tyumen, Russian Federation); Baranskaya, Alisa; Ogorodov, Stanislav A.; Shabanova, Nataliya N. and Novikova, Anna V. Coastal erosion at Western Yamal, Russia, under climate changes and anthropogenic impact [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1335, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The coasts of the Kara Sea at a quarter of the coastline length are represented by the retreating thermoabrasional coasts composed by permafrost. Their dynamics is determined by hydrometeorological conditions (duration of the ice-free period, wave fetch, air and water temperature, wind direction and strength, etc.) and parameters of the coast (coastal sediments composition and ice content, the relief of the coastline and shallow waters area). The maximum rate of destruction of thermoabrasional coasts is typical for the Western coast of the Yamal Peninsula. Here in the area of the polar station Marre-Sale, the mean multiyear rates are 1.7-2 m per year, and in the area of Kharasavey settlement -0.5-2.5 m per year. The rates of coastal retreat in the key areas of Western Yamal, obtained by different teams of researchers, were recalculated using a single method as for correct comparison of the retreat rates it is necessary to average the results of calculations for similar periods of time and for coastal segments of similar length along the coast. Analysis of coastal retreat rates allows us to identify both the contribution of climate change and anthropogenic impact. The Yamal Peninsula is home to Russia's largest natural gas fields, the development of which is reflected in the dynamics of the coastline. Analysis of multi-temporal aerial photos and space images on the coast near the Kharasavey gas condensate field allowed to trace the dynamics of the shores since 1972, both in undisturbed conditions and after the beginning of construction of the field infrastructure. The role of the technogenic factor at the rapidly retreating coastal segments has turned to be higher than the impact of changes in climatic parameters.

2020032612 Benabderrahmane, Abdelhakim (ANDRA National Radioactive Waste Management Agency, Chatenay-Malabri Cedex, France); Holmen, Johan and Stab, Olivier. Hydrogeological issues associated with nuclear wastes geological repository in clay rocks; example of Cigéo project-France [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H21H-1836, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Nuclear wastes geological repository research activities were conducted, during the last decades, in different types of potential host rock in many countries. Crystalline or granitic rock were the focus of nuclear industry in Sweden, Finland, China while clay as host formation was mainly studied in Belgium, France and Switzerland. An overview of hydrogeology and hydrogeological modelling implication on geological repository development in sedimentary formations environment gives an insight of advances in site characterization and hydrogeological performance assessment made by the French National Agency for Radioactive Wastes Management. Several factors make, particularly challenging, the study of the flow and the transport for the evaluation of the site performance, which involves long-term predictions of hundreds of thousands or millions of years. Development of subsurface flow and transport prediction models includes present time hydrogeological model and geodynamic evolution through the next millions of years covering safety time scale. Performance and safety assessment of a deep geological repository for intermediate high level long lived (IHLL) radioactive wastes requires identification of potential flow paths and the associated travel times for radionuclides originating at repository depth. The planned French repository (Cigéo Project) will be located at great depth of 500 m in the Callovo-Oxfordian claystone formation (160 Ma) of the multi-layered system of Paris Basin. Numerical simulations coupling internal and external geodynamic evolutions with groundwater flow describe how the tectonic uplift, erosion/sedimentation and permafrost genesis, expansion and retreat processes affect (i) long-term transient flow and transport behaviour and (ii) hydrogeological performance measures. Performance is then analysed by the use of Lagrangian transport approach using a 3D transient flow fields induced by: (i) deformation of the multi-layered aquifer system resulting from differential tectonic uplift, (ii) evolution of the outcrop zones governed by erosion and incision of the geological layers and (iii) climate changes.

2020032518 Bennett, Kathryn A. (University of New Hampshire, Earth Sciences, Durham, NH); Burke, Sophia A.; McCalley, Carmody K.; DelGreco, Jessica; Palace, Michael W.; Crill, Patrick M. and Varner, Ruth K. Using stable isotopes to determine dominant methane production pathways of thaw ponds in a subarctic peatland [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2589, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic and subarctic ecosystems are currently warming faster than any other region of the globe, leading to changes such as seasonal permafrost thaw. As thaw progresses, small water bodies form due to slumping of the peatland surface. These ponds emit methane (CH₄), a potent greenhouse gas, predominantly through ebullition (bubbling). Microbes present in these systems produce CH₄ through two primary pathways: acetoclastic and hydrogenotrophic methanogenesis. The acetoclastic pathway forms CH₄ using CH₃COOH, an organic carbon (C) source while hydrogenotrophic uses CO₂, an inorganic C source. Stable isotopes can be used to characterize the relative importance of these two pathways for overall CH4 production, providing information that can improve modeling of current and future CH4 emissions. We used stable isotopes, carbon-13 (¹³C) and deuterium (D), to determine the dominance of acetoclastic versus hydrogenotrophic methanogenesis in a subarctic peatland located in the discontinuous permafrost region of northern Sweden. Isotopic analysis was performed on porewater samples and captured gas from ebullition. Samples were collected from seven ponds over six years during the summer. The ponds varied in physical attributes related to their formation, allowing for identification of the relationship between these attributes and CH₄ production pathways. The relative importance of the two CH₄ production pathways differed significantly between ponds. Some ponds appear to be dominated by either acetoclastic or hydrogenotrophic production with more enriched or depleted signatures respectively, while others appear to have a mixed methanogen community that remains constant across years. High between pond variability in d¹³C-CH₄ signatures (-48.9 ppm to -93.0 ppm) highlights the need for further research on the drivers of CH₄ production pathways. Vegetation surveys, unmanned aerial vehicle imagery, and additional satellite imagery allow for the determination of pond size and seasonal variation in size, as well as vegetation cover. This allows for comparison with isotopic characteristics. Minimal literature exists on the types of microbes and metabolic pathways present in subarctic ponds, therefore, conclusions drawn from this unique multi-year study will inform how ponds contribute to the global CH4 budget.

2020032599 Bergstedt, Helena (University of Salzburg, Salzburg, Austria); Bartsch, Annett; Kroisleitner, Christine; Duguay, Claude R. and Jones, Benjamin M. Accounting for spatial heterogeneity of freeze/thaw cycles in surface state retrieval for permafrost landscapes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1369, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost covers large areas of the high latitudes and significant parts of alpine regions. Landscapes underlain by permafrost undergo annual thawing and refreezing of the ground surface. These freeze/thaw cycles occur at different time scales from daily to seasonal variations. Freezing and thawing has been linked to processes like greenhouse gas release and slope stability. The data collection using traditional in situ methods in those remote areas still is a time and manpower consuming task. Microwave remote sensing approaches have shown to be able to detect surface status changes for large areas. Scatterometer sensors have been used to retrieve surface state information on the circumpolar scale but with coarse spatial resolution. As an alternative, the higher resolution Synthetic Aperture Radar (SAR) has previously been applied to retrieve freeze/thaw information on a regional level. Currently, available data sets on land surface state lack either sufficient temporal or spatial resolution to adequately characterize the complexity of freeze/thaw transition period dynamics. This work focuses on spatial heterogeneity within grid cells of scatterometer data in highly complex terrain in cold regions. Microwave scattering mechanisms negatively influencing the accuracy of surface state information derived from satellite based microwave sensors are identified and quantified. We address findings concerning landscape type specific differences between surface state information derived from different scales as well as dependencies of frozen and thawed season backscatter variations negatively influencing threshold based surface state retrieval. Possibilities of deriving mean annual ground temperature and permafrost extent from freeze/thaw information and the accuracy of the resulting coarse scale data set are discussed. We propose a frozen fraction capable of describing gradual freeze-up and thaw processes on a landscape scale. Validation of the frozen fraction with in situ near surface ground temperature data sets collected in alpine and subarctic areas revealed accuracies of 84.7% to 94%. This work contributes to the improvement of accurate representation of freeze/thaw processes in complex landscapes within future surface state data sets, especially with respect to permafrost applications.

2020027620 Bhuiyan, M. Abul E. (University of Connecticut, Natural Resources and the Environment, Groton, CT); Witharana, Chandi and Liljedahl, Anna K. Big Imagery as a resource to understand patterns, dynamics, and vulnerability of Arctic polygonal tundra [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1374, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw has been observed at several locations across the Arctic tundra in recent decades; however, the spatiotemporal pan-Arctic extent of thaw remains poorly quantified. Thaw-induced differential ground subsidence and dramatic microtopographic transitions, such as transformation of low-centered ice-wedge polygons (IWPs) into high-centered IWPs can be characterized using very high spatial resolution (VHSR) commercial satellite imagery. The entire Arctic has been imaged in 0.5m resolution by commercial satellite sensors on average four times in the last six years. However, the imagery is still largely underutilized, mainly limited to local assessments, with the ArcticDEM as the only derived pan-Arctic science product. Knowledge discovery through artificial intelligence, big imagery, and high performance computing (HPC) resources is just starting to be realized in Arctic science. Large-scale deployment of VHSR imagery resources requires sophisticated computational approaches to automated image interpretation coupled with efficient use of HPC resources. Our ongoing efforts involve a high performance image analysis framework that uses deep learning (DL) convolutional neural net (CNN) algorithms on HPCs to automatically extract ice-wedge polygons from VHSR commercial satellite imagery across large geographic regions. We trained and tasked a DLCNN object instance segmentation algorithm on the Extreme Science and Engineering Discovery Environment's (XSEDE) HPC resources to automatically classify IWPs from VHSR satellite imagery. We systematically experimented the DL model interoperability across varying tundra types and image scene complexities to understand the opportunities and challenges of circumpolar IWP mapping applications. The DL model exhibited promising performances across different tundra types in Alaska and produced noticeably high classification accuracies in imagery comprising wet sedge tundra than tussock tundra. Overall, our findings demonstrate the robust performances of IWP mapping algorithm in diverse tundra landscapes and lay a firm foundation for its operational-level application in mapping ice-rich permafrost and repeated documentation of permafrost disturbances at the sub-meter scale across the pan-Arctic.

2020027665 Bolch, Tobias (University of Saint Andrews, School of Geography and Sustainable Development, Saint Andrews, United Kingdom); Bhattacharya, Atanu; King, Owen and Allen, Simon. Characteristics and changes of glaciers, rock glaciers and glacial lakes in high mountain Asia since the 1960s [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C43A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

High Mountain Asia contains large area and volume of ice and shows great climatic diversity. Large parts are moreover influenced by permafrost and numerous rock glaciers exist. Previous studies showed that the glaciers lost on average significant amount of mass but with large variability and even areas with predominantly positive mass glacier mass budgets. While the general trends are meanwhile well known, several important factors and processes the evolution of debris-covered glaciers and rock glaciers and the influence of lakes on mass loss are less well understood. One reason is the lack of long-term observations. To overcome these obstacles we use declassified high resolution stereo Corona data from the 1960s, stereo Hexagon data from the 1970s and recent high-resolution stereo satellite data. Results show that many large rock glaciers evolved from moraines and debris-covered glaciers under permafrost conditions. Investigated rock glaciers in the Tien Shan and Himalaya showed on average no significant surface elevation changes but typically surface lowering in the upper reaches and elevation gain at the front indicating the downslope creep. Preliminary results of glacier mass balances revealed on average increasing mass loss and with the highest mass loss in northern Tien Shan and Nyainqentanglha and balanced budgets in eastern Pamir since the 1960s. The debris-covered glaciers at Mt. Everest showed significant lowering of partly more than 100m. The highest lowering occurred at Imja Glacier where the proglacial Imja Lake expanded rapidly since the 1960s. The increased mass loss of glaciers with pro-glacial lakes could be confirmed for the whole Himalaya, but no substantial difference in the mass loss of debris-covered and clean-ice glaciers since the 1970s could found. Glacial lakes do not only influence glacier mass loss but prose also a serious threat to the society. Analysis of the lakes in Tibet showed partly rapid growth with 16% of all glacial lakes threaten human settlements a hotspot of GLOF danger identified in central Himalaya. These results are important for stakeholders either directly for planning hazard mitigation measures or indirectly as they provide important baseline data to improve glacio-hydrological models. High Mountain Asia contains large area and volume of ice and shows great climatic diversity. Large parts are moreover influenced by permafrost and numerous rock glaciers exist. Previous studies showed that the glaciers lost on average significant amount of mass but with large variability and even areas with predominantly positive mass glacier mass budgets. While the general trends are meanwhile well known, several important factors and processes the evolution of debris-covered glaciers and rock glaciers and the influence of lakes on mass loss are less well understood. One reason is the lack of long-term observations. To overcome these obstacles we use declassified high resolution stereo Corona data from the 1960s, stereo Hexagon data from the 1970s and recent high-resolution stereo satellite data. Results show that many large rock glaciers evolved from moraines and debris-covered glaciers under permafrost conditions. Investigated rock glaciers in the Tien Shan and Himalaya showed on average no significant surface elevation changes but typically surface lowering in the upper reaches and elevation gain at the front indicating the downslope creep. Preliminary results of glacier mass balances revealed on average increasing mass loss and with the highest mass loss in northern Tien Shan and Nyainqentanglha and balanced budgets in eastern Pamir since the 1960s. The debris-covered glaciers at Mt. Everest showed significant lowering of partly more than 100m. The highest lowering occurred at Imja Glacier where the proglacial Imja Lake expanded rapidly since the 1960s. The increased mass loss of glaciers with pro-glacial lakes could be confirmed for the whole Himalaya, but no substantial difference in the mass loss of debris-covered and clean-ice glaciers since the 1970s could found. Glacial lakes do not only influence glacier mass loss but prose also a serious threat to the society. Analysis of the lakes in Tibet showed partly rapid growth with 16% of all glacial lakes threaten human settlements a hotspot of GLOF danger identified in central Himalaya. These results are important for stakeholders either directly for planning hazard mitigation measures or indirectly as they provide important baseline data to improve glacio-hydrological models.

2020027642 Bolton, Bob (University of Alaska Fairbanks, Fairbanks, AK); Spicer, Rawser; Genet, Helene and Breen, Amy L. Identification of regions susceptible to thermokarst initiation due to "climate priming" on the Alaskan Arctic Coastal Plain [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Landscape change in permafrost regions, caused by thermokarst, can result in profound impacts on the energy and water balance; carbon fluxes; wildlife habitat; and infrastructure. The Alaska Thermokarst Model (ATM) is an intermediate-scale, state-and-transition model designed to simulate landscape evolution in polygonal tundra due to thermokarst. The logical rule set considers factors such as climate, wildfire, land use, hydrologic and soil properties. A number of studies have shown the following sequence of events regarding polygonal tundra evolution: 1) a relatively stable landscape; 2) a "pulse" or extreme climate event that initiates the thermokarst process; 3) rapid landscape evolution; and 4) stabilization of the landscape. Jorgenson (2006) reported that initial and advanced degradation of these ice-wedge dominated landscapes can occur a 20-year period (and quickly as 10-years) and advanced stabilization within a 20-30 year period. Stabilization of the landscape occurs when the seasonal thaw layer depth is unable to penetrate the protective layer (surface soil layer that buffers surface processes from underlying ice-rich permafrost). This study specifically focuses on the initiation of thermokarst. In this study, we explore the concept of "climatic priming" of the landscape. At our Seward Peninsula field sites, the 2017-2019 period has been characterized by near record snow pack and above normal temperatures (both winter and summer). At many of our permafrost field sites, the ground did not completely refreeze, potentially priming the landscape for thermokarst initiation. One of our current focus areas is identifying the thresholds (or conditions) required for the thermokarst process to initiate on the Arctic Coastal Plain of Alaska. In this study, we explore potential regions that have been primed for thermokarst in the past century. Following our Seward Peninsula field observations, we identify regions that are susceptible to thermokarst if the following conditions (compared to the 1901-1950 average) are met: 1) high early winter snow precipitation; 2) high total winter precipitation; 3) above normal winter air temperature; and 4) subsequent above average summer air temperature. We further refine our results to areas physically predisposed to thermokarst.

2020032658 Bove, Livia E. (Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland); Ranieri, Umberto L.; Koza, Michael M.; Kuhs, Werner F.; Klotz, Stefan; Falenty, Andrezji and Gillet, Philippe. Fast methane diffusion at the interface of two clathrate structures [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract P41C-3451, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane hydrates naturally form on Earth and in the interiors of some other planets and moons of the solar system. Diffusion of methane in the structure is important in the gas exchange and release process. By quasielastic neutron scattering we have observed extremely fast methane diffusion at the interface of the two most common clathrate hydrate structures, I and II, faster than that expected in pure supercritical methane at comparable pressure and temperature. Our observations can possibly explain the observed rapid kinetics of gas exchange if accompanied by structural transition, or the methane bursts seen on the surface of Titan and might even have some implication on the methane release rate of the thawing permafrost.

2020032623 Bowden, William B. (University of Vermont, Burlington, VT); Cory, Rose M.; Emerson, David; Giblin, Anne E.; Herndon, Elizabeth; Kling, George W.; Michaud, Alexander B. and Record, Nicholas. The fundamental roles of iron as a mediator of land-water interactions in Arctic catchments [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H42A-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Compared to research on carbon, nitrogen, and phosphorus dynamics at whole-catchment scales, the behavior and roles of iron have received considerably less attention. Iron may be particularly important as a moderator of large-scale, biogeochemical dynamics in Arctic tundra ecosystems because this biome is essentially one, large aquatic interface, with sharp redox gradients between the largely hypoxic tundra soils and generally well-aerated open waters of streams and lakes. Research in the vicinity of the Toolik Field Station (Alaska, USA) has shown that reduced iron (Fe(II)) can serve as an electron donor to O₂ to produce hydroxyl radical (·OH) that can oxidize DOC to CO₂ in dark soils and in sunlit surface waters. The magnitude of these iron-mediated fluxes of CO₂ from aquatic systems is currently unknown and potentially large, accounting for as much CO₂ as bacterial respiration on a landscape scale. Other research has shown that biogenic Fe(III) (oxyhdr)oxides produced by extensive communities of lithotrophic Fe-oxidizing bacteria accumulate in shallow, low-lying areas with neutral pH; conditions common in Arctic soils. The presence of short-ordered Fe oxyhydroxides promotes high phosphate sorption capacities and maintains low phosphate concentrations. The phosphorus bound in this way is susceptible to dissolution under anoxic conditions and may serve as a source of phosphate for terrestrial plants, but an impediment to downslope movement of phosphorus to aquatic ecosystems, which tend to be phosphorus limited in this region. In current research we are investigating whether iron interacts with the carbon cycle to interfere with methane production. Little is known about this interaction in Arctic soils where the potential for methane production from permafrost degradation is particularly high. Together, this research suggests that biotic and abiotic reactions with iron may have important and largely unquantified influences on the movement of important forms of carbon, nitrogen, and phosphorus from terrestrial to aquatic environments in the Arctic. Furthermore, Arctic climate change - notably, longer periods of non-frozen conditions--may influence the intensity, duration, and location of iron redox activity and thus alter the delivery of key nutrients from terrestrial to aquatic environments.

2020032673 Bowden, William B. (University of Vermont, Burlington, VT); Rastetter, Edward B.; Griffin, Kevin L.; Budy, Phaedra; Crump, Byron C.; Giblin, Anne E.; Gough, Laura and Kling, George W. Catchment research in the Arctic long term ecological research program; North Slope, Alaska, USA [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA13B-0995, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Catchment-level research near Toolik Lake (N68°38', W149°36') began in the mid-1970s and was organized into the U.S. National Science Foundation funded Arctic Long-Term Ecological Research program (ARC-LTER) in 1987. The goal of the ARC-LTER was to understand ecosystem interactions in the Toolik landscape, from biogeochemical and community perspectives. This area is typical of the northern foothills of the Brooks Range, with no trees, complete snow cover for 7-9 months, deep ice cover on lakes and streams, and no stream flow during the winter. Mean annual air temperature is about -8.6°C with low precipitation of ~320 mm/yr, about half of which falls as snow. During the summer, daily average air temperature is 7-12°C with the sun continuously above the horizon from mid-May to late July. The area is underlain by spatially continuous permafrost to a depth of ~200 m, has a variety of stream and river morphologies, and is dotted by both deep and shallow lakes, some of which are connected by streams and rivers and others that are isolated on the landscape. Research associated with the ARC-LTER has used a variety of perspectives, from small-plot to large watershed and the research frameworks of the project have evolved continuously, underpinned by the long-term records from a variety of sentinel watersheds and experimental plots. The ARC-LTER manages several of the longest, continuous, biogeochemical and ecological catchment records in the U.S. Arctic, including the Kuparuk River, Oksrukuyik Creek, Imnavait Creek, and Toolik Lake Inlet-Series catchments. New catchments series have been added to explore emerging research topics; e.g., the Anaktuvuk River (wildfire), Trevor Creek (mountain influences), and most recently the NEON-funded Oksrukuyik Creek site. Knowledge based on data collected from these watersheds has transformed our thinking about nutrient-species interactions, hillslope-stream flowpaths, DOM processing, thermokarst impacts, wildfire responses, and the potential consequences of climate change in this region of the Arctic. Research and monitoring of the ARC LTER sentinel catchments has informed science beyond the Arctic region, through collaborative research efforts including the LINX-1, LINX-2, and SCALER projects. Image of sentinel watersheds utilized by the ARC-LTER.

2020032456 Bowen, Jennifer C. (University of Michigan Ann Arbor, Ann Arbor, MI); Ward, Collin P.; Kling, George W. and Cory, Rose Merin. Sunlight and iron control the oxidation of DOC leached from permafrost soils [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13G-2562, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Tremendous stores of organic carbon (C) in permanently frozen permafrost soils in the Arctic are thawing as the planet warms. Once thawed, this organic C can be oxidized to carbon dioxide (CO₂, a greenhouse gas) and reinforce global warming. A current, critical knowledge gap is whether dissolved organic carbon (DOC) draining from permafrost soils to sunlit surface waters is labile to photochemical oxidation to CO₂ (i.e., photomineralization), a process currently accounting for up to 30% of CO₂ emitted from arctic surface waters. Here we characterize for the first time the spectral (wavelength) dependence of the apparent quantum yield for photomineralization, and show that old ¹⁴CO₂ (4000 to 6200 y BP) is produced upon exposure of DOC leached from permafrost soils to UV and visible light. The lability of permafrost DOC to photomineralization increased with the abundance of iron. Nuclear magnetic resonance and isotopic evidence suggest that carboxyl C associated with old DOC derived from lignin and tannin was preferentially photomineralized. Using the measured spectral slope of the apparent quantum yield, we show that water column rates of permafrost DOC photomineralization are 1.3- to 2-fold higher than previously estimated. Together these findings demonstrate that sunlight exposure will contribute to arctic amplification of climate change by oxidizing old DOC to CO₂ in arctic surface waters.

2020032580 Bristol, Emily M. (University of Texas at Austin, Austin, TX); Connolly, Craig T.; McClelland, James W.; Lorenson, Thomas D.; Richmond, Bruce M.; Ilgen, Anastasia; Choens, R.; Bull, Diana L.; Kanevskiy, Mikhail Z.; Iwahana, Go and Jones, Benjamin M. Geochemical characterization of eroding coastal permafrost and organic matter fluxes to the Beaufort Sea near Drew Point, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1343, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Coastal erosion is accelerating along the Alaska Beaufort Sea due to decreases in sea ice cover during the summer, increases in wave action, and warming permafrost. Enhanced erosion increases the transport of important biogeochemical materials, such as organic matter and inorganic nutrients, from land to the Arctic Ocean. Improved geochemical characterization and updated estimates of organic matter fluxes from eroding coastal permafrost is needed to anticipate the fate of this material in coastal environments as a fuel for biological production as well as CO₂ emissions. Three permafrost cores (4.5-7.5 m long) were collected along a geomorphic gradient near Drew Point, Alaska, where recent erosion rates average 17.2 m yr^-1. Organic carbon (C) content in these cores was 12-45% at the ground surface and decreased sharply to ~1% at 3 meters above local sea level. Low C content, low C:N ratios, and d¹³C enrichment below the 3 meter elevation suggest that these sediments were deposited during a marine transgression circa 40,000 yBP or earlier. Porewater salinity throughout the cores increased with depth, with salinities greater than 20 psu within a cryopeg (permafrost in a liquid state at temperatures as low as -8°C). The geochemistry data is being used in combination with remote sensing data to estimate historical fluxes of organic matter and other geochemical constituents on decadal (1955-2019) to annual (2007-2019) timescales for a 9 km stretch of coastline near Drew Point, AK. Our analyses highlights the need to consider landscape geomorphology and organic matter stocks at depth when quantifying fluxes of eroding permafrost.

2020032640 Brunetti, Carlotta (Lawrence Berkeley National Laboratory, Berkeley, CA); Dafflon, Baptiste; Lamb, Jack; Shirley, Ian; Uhlemann, Sebastian and Hubbard, Susan. Improved quantification of soil thermal and physical properties from time-series of soil temperature in permafrost environment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS11B-0628, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Improving the quantification and monitoring of soil and permafrost properties is important to make better predictions of Arctic ecosystem feedbacks to climate under warming temperatures. In particular, investigating the relationships between soil hydro-thermal behavior and soil physical properties (including the fraction of soil constituents) could greatly improve our predictive understanding of the subsurface storage and fluxes of water, carbon and nutrients in permafrost environments. However, obtaining such information is extremely challenging using conventional measurement approaches. The present study aims at investigating and extracting the information and patterns contained in time-series of vertically-resolved profiles of soil temperature. Such measurements are becoming increasingly available due to the development and application of low-cost Distributed Temperature Profiling (DTP) systems. The DTP monitoring system used here can provide up to 10 measurements in the top 1 meter of soil at numerous locations. We describe the development of a Bayesian inversion approach based on a Markov chain Monte Carlo algorithm to estimate soil thermal properties (e.g., thermal diffusivity, thermal conductivity) and the fraction of soil components such as mineral, organic matter, water, ice and air from the DTP soil temperature time-series. We perform synthetic studies to investigate how much natural variability in soil temperature is required for a successful estimation of the fraction of soil components at various depths and compare results using different hydro-thermal models. We then present an application to the DOE Next Generation Ecosystem Experiment (NGEE) field site located on the Seward Peninsula (Alaska), which is characterized by discontinuous permafrost and high spatial variability of soil thermal and physical properties.

2020032574 Bull, Diana L. (Sandia National Laboratories, Albuquerque, NM); Frederick, Jennifer; Mota, Alejandro; Thomas, Matthew A.; Jones, Benjamin M.; Jones, Craig Alexander; Flanary, Chris; Kasper, Jeremy; Choens, R.; Bristol, Emily; McClelland, James W. and Namachivayam, Siddarth. Development of a tightly coupled multi-physics numerical model for an event-based understanding of Arctic coastal erosion [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C12B-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Accelerating Arctic coastal erosion rates have put critical infrastructure and native communities at risk due to several coincident changes in the Arctic environment: increased wave power and storm frequency due to declining sea ice and increased length of open-water season, and increased ocean and permafrost temperatures. Although the Arctic comprises one-third of the global coastline, current tools for quantifying permafrost erosion are unable to explain the episodic, storm-driven events. This presentation will detail a numerical modeling and validation campaign to mechanistically couple oceanographic conditions with a terrestrial Arctic coastline capable of capturing the thermo-chemo-mechanical dynamics of erosion. This local, event-based simulation framework facilitates an ensemble assessment of Alaskan coastline futures unencumbered by the limitations of traditional, empirically-based approaches. In the Arctic Coastal Erosion (ACE) Model, oceanographic boundary conditions are provided by a numerical modeling suite comprised of a circum-Arctic Wave Watch III model forcing a two-way coupled SWAN-Delft3D-FM local model. Combined with atmospheric conditions, this suite produces time-dependent surge and run-up output to force the terrestrial model developed in Albany. The multi-physics based finite element terrestrial model includes: development of 3D stress/strain fields via a frozen water content dependent plasticity model, and thermal evolution of the permafrost bluff via a 3D heat conduction model incorporating phase change. A major advance in the ACE Model is that the failure mechanism of the coastal permafrost bluffs is not pre-determined or empirical, but results from any allowable deformation (block erosion, slumping, etc.). A parallel field campaign (summers of 2018 & 2019) at Drew Point, Alaska will (summers of 2018 & 2019) at Drew Point, Alaska will validate and calibrate ACE Model parameters. The ACE Model will inform our scientific understanding of coastal erosion processes, contribute to estimates of biogeochemical and sediment loading, and facilitate infrastructure susceptibility assessments.

2020032549 Burke, Sophia A. (University of New Hampshire, Department of Earth Sciences, Durham, NH); Perry, Apryl Lee; Padilla, Alexandra Michelle; Palace, Michael W.; Weber, Tom; Persson, Andreas; Crill, Patrick M. and Varner, Ruth K. Listen for the pop; the capture and quantification of ebullitive methane from thaw ponds using a high frequency acoustic bubble trap system [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic regions are showing responses of atmospheric warming related to climate change. This includes the development of small waterbodies in permafrost peatland areas. These small water bodies, or thaw ponds, emit a significant amount of methane (CH₄) to the atmosphere via ebullition (bubbling). However, the rate of ebullitive emission from thaw ponds is unconstrained due to a lack of long-term studies and even fewer, high temporal resolution (sub-minute) studies. Our previous work, using daily to sub-weekly measurements, found that thaw ponds from Stordalen Mire, Abisko, Sweden emit 20 mg CH₄ m^-2 d^-1 during the ice-free season. Ebullitive flux was found to be very weakly correlated with measured meteorological variables which could be attributed in part to the low frequency of the measurements. This study incorporates seven years of growing season measurements of very high resolution (sub-second) acoustic data identifying the release of bubbles from two thaw ponds at Stordalen Mire. Each pond was equipped with two bubble traps containing a continuously recording hydrophone, that captured the sound as bubbles rose and hit the hydrophone, while passing through the traps. Using a bubble finding algorithm, we determined the timing of bubbles as they entered the funnel over the sampling period. To determine bubble size, we used a lab-developed calibration curve consisting of four bubbles of known size. We compared high resolution (sub-hourly) meteorological data (incoming shortwave radiation, air temperature, atmospheric pressure, water table depth) to our acoustic data to identify timing and environmental controls on destabilization events that lead to ebullitive emission from thaw ponds. These high resolution acoustic data used in combination with a measured daily ebullitive flux estimate allows us to better determine characteristics of emission that may be applied to modeling and scaling of these important hotspots in the permafrost landscape.

2020027618 Busey, Robert (University of Alaska Fairbanks, Fairbanks, AK); Iwahana, Go; Bolton, Bob and Breen, Amy L. Evaluation of wildfire initiated thermokarst degradation using in-situ and remotely sensed data at a site on the Seward Peninsula of Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1372, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In a remote part of the Kougarok River drainage, located on Alaska's Seward Peninsula in western Alaska, four tundra fires of varying severity have modified the landscape over the last twenty five years. The fires have triggered thermokarst, resulting in large volume mass wasting of ice-rich permafrost as well as small deformation of the ground surface affecting just local microtopography. The disturbance has resulted in an ecosystem composition shift in many of the burned areas as well as changes to the carbon content within the active layer. Within the perimeter of these multiple fires, the University of Alaska Fairbanks established several micrometeorological and a one kilometer square Circumpolar Active Layer Monitoring site in 1999. We use these data sets in combination with a variety of remote sensing imagery such as differential inSAR to track thermokarst development and restabilization of the landscape.

2020032462 Buursink, Mark L. (U. S. Geological Survey, Reston, VA). Mapping and cataloging geologic sources of greenhouse gases across the United States [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13L-2473, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Carbon dioxide (CO₂) and methane (CH₄), along with associated natural gas mixtures (e.g., nitrogen and helium) may be emitted to the atmosphere from geologic sources contributing to greenhouse gases (GHG). Geologic sources of GHG emissions may include volcanic and geothermal systems, along with seeps from sedimentary basins. Similar to anthropogenic (e.g., fossil fuel exploitation) and biogenic (e.g., wetlands and permafrost) emissions, geologic GHG emissions are relatively widespread and remain poorly characterized. Therefore, characterizing these natural sources of GHG in terms of geologic setting, gas geochemistry, and ultimately flux rate is important for understanding emissions budgets. The United States (U.S.) Geological Survey Utilization of Carbon and other Energy Gases Project is conducting studies of geologic CO₂ reservoirs (with samples containing >10% CO₂) to determine available resources, and document long-term geophysical and geochemical effects of storing CO₂. Included in this study are GHG-rich springs and seeps located within or near sedimentary basins. Our studies include: 1) characterization of natural gas (including noble gases) by geochemical and isotopic analyses to help determine the origin (mantle, thermal carbonate alteration, or other) and migration pathways; 2) characterization of spring water; and 3) geologic characterization and occurrence of GHG reservoir leaks or natural seeps. To put our work in context, we are mapping and cataloging geologic GHG sources, which number into the hundreds, starting in California and extending across the U.S. We are including data points from previous investigations (e.g., volcanic and hydrocarbon systems related) that are supplemented by locations of our ongoing fieldwork in multiple geologic provinces. Specifically, domestic geologic GHG sources are inventoried in a GIS database for interactive map display. It is anticipated that these maps foster discussion on additional sampling efforts, missing datasets, and collaboration on future work.

2020032682 Calderón, Mauricio (Universidad Andres Bello, Carrera de Geología, Santiago, Chile); Henriquez, Carolina; Pérez-Donoso, José M.; Cury, Leonardo F. and Bahniuk Rumbelsperger, Anelize M. Microbial communities in the sedimentary substrate of the Laguna Timone maar, southern Patagonia (52°S) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PP41C-1559, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Laguna Timone corresponds to a lake-filled maar of the Pali Aike Volcanic Field (PAVF), located at an elevation of ca. 110 m.a.s.l., produced by late Pleistocene phreatomagmatic eruptions, involving melt water from streams and permafrost. Surficial waters of Laguna Timone are characterized by saline and alkaline brines. As in many crater-lakes off the PAVF stationary inorganic carbonate precipitation occurs in the flood zone of the lakes. In order to establish or discard the hypothesis of biogenically induced carbonate precipitation two samples from the lake sediments were studied for identifying the microbial communities through 16S rRNA Gene Sequencing. Samples of laminated silts and very fine sands were extracted at 50 cm and 100 cm depth in the substrate in the eastern shore of Laguna Timone maar. The identified bacterial genera are known for their role in biogenic processes such as nitrification of decomposed organic matter (ammonia) and methane oxidation at shallow and deep levels, respectively. Rhodoferax and Sideroxydans have been related to the redox-cycle of Fe which is a key factor in the carbon flux, speciation and mobility of elements in aqueous fluids in a wide spectrum of natural environments. The preliminary results reveal the nonexistence of bacteria capable to induce the carbonate precipitation in the shallow sediments near the shore of the lagoon. This work was funded by LAMIR/UFPR/PETROBRAS Research Project N° 2016/00141-1 and FONDECYT Grant 1161818.

2020032674 Carey, Sean K. (McMaster University, School of Geography and Earth Sciences, Hamilton, ON, Canada); Pomeroy, John W. and Janowicz, J. Richard. The Wolf Creek research basin; 25+ years of subarctic research [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA13B-0999, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Wolf Creek Research Basin (WCRB) lies in the southern mountainous headwaters of the Yukon River basin in the subarctic region of northwestern Canada. Established in 1993 as a research watershed to enhance our understanding of cold regions hydroclimatic processes, it has provided long-term data on hydrology, climate and ecosystem change and guided the development of conceptual and numerical models. WCRB is situated within Boreal Cordillera ecozone and consists of three principal ecosystems: boreal forest, subalpine taiga and alpine tundra with portions of 22, 58 and 20% respectively. Permafrost is sporadic on north-facing slopes and at high elevation. Long-term hydrometeorological stations exist within each ecozone and operate year-round. There are four long-term hydrometric stations. Through the history of WCRB, research has been supported by a variety of agencies including the Yukon Territorial Government, Environment Canada, Natural Sciences and Engineering Research Council of Canada, Canadian Foundation for Climate and Atmospheric Sciences, NERC (UK), ERC (EU), and most recently the Global Water Futures Program. Examples of graduate student led projects include topics such as runoff processes, groundwater, evapotranspiration, snow transport, snow-shrub interactions and vegetation change. There have been over 100 peer-reviewed papers generated from research in WCRB. Due to a commitment to sharing and open-data, WCRB also serves as a node for many international initiatives and inter-comparison programs. Since its establishment, WCRB has changed dramatically. Temperatures have warmed, precipitation timing and patterns have changed, flow regimes have shifted and most notably shrub vegetation has increased dramatically. Wolf Creek is now a sentinel for change, and continued research and monitoring is critical to understand the impacts of global change on this sparsely studied region.

2020032552 Carpenter, Courtlyn (University of Colorado at Boulder, Boulder, CO); Wickland, Kimberly; Clow, David W.; Dornblaser, Mark; Koch, Joshua C.; Striegl, Robert G. and Kasprzyk, Joseph R. Aquatic carbon exports from alpine and boreal wetlands to headwater streams [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43I-2602, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wetlands are significant contributors to the global carbon budget, however there are significant gaps in our understanding of their role in the aquatic carbon cycle. Specifically, lateral exports of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), dissolved carbon dioxide (CO₂), and dissolved methane (CH₄) from wetlands are poorly constrained. We conducted a study of lateral dissolved carbon exports in headwater streams draining wetlands in two ecoregions where snowmelt is a significant hydrologic event: alpine and boreal wetlands. To advance our understanding of carbon processing in and exports from wetlands, we explore 1)the variability in lateral dissolved carbon exports and yields from wetlands at different latitudes and elevations, and 2) the relative DOC/DIC ratio in alpine and boreal wetland stream complexes. Three alpine sites in Rocky Mountain National Park, Colorado, and one boreal site in the White Mountains National Recreation Area, Alaska, were analyzed for this study. The alpine sites are at high elevations (2,400-2,600 meters) and the boreal site is in interior Alaska, partially above the treeline and underlain by permafrost. We calculate DOC, DIC, dissolved CO₂ and dissolved CH₄ exports and yields over seasonal and annual timescales at each site and examine changes in lateral DOC and DIC fluxes with varying discharge. We compare these fluxes against one another over multiple years to quantify the relative importance of lateral organic and inorganic carbon fluxes from wetlands to surface waters. Preliminary results suggest that organic and inorganic carbon fluxes respond differently to seasonal precipitation. Our examination of diverse sites offers novel and broad insights into carbon exports from wetlands through the aquatic pathway.

2020032538 Chanton, Jeff (Florida State University, Department of Earth, Ocean, & Atmospheric Science, Tallahassee, FL); Verbeke, Brittany Aiello; Sparrow, Katy J.; Wilson, Rachel M.; Spencer, Robert G.; Hanson, Paul J.; Dommain, Rene; Hodgkins, Susanne B.; Tfaily, Malak M.; Sebestyen, Stephen D.; Griffiths, Natalie; Holmes, Marjorie Elizabeth; Lilleskov, Erik; Lamit, Louis J.; Rich, Virginia Isabel; Bridgham, Scott D.; Saleska, Scott R.; Crill, Patrick M.; Varner, Ruth K.; Hopple, Anya and Kostka, Joel E. Isotopic and high resolution analytical techniques to investigate the stability of peat soils across gradients in latitude and altitude [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

High latitude soils bank large quantities of organic carbon. The fate of this carbon is of interest on a planet with elemental cycles responding to the activities a large ever-more-robust population. While organic-mineral interactions may result in some degree of stabilization of these carbon stores, peat soils with little mineral content may be particularly vulnerable to decomposition stressors associated with changes in temperature regime and water table. Our team has employed isotopic approaches and two high resolution analytical techniques to investigate the stability of peat soils across gradients in latitude and altitude, and the release of carbon associated with permafrost and peat decomposition under varying climatic regimes. Organic carbon across these gradients exhibits qualitative differences, particularly in carbohydrate (O-alkyl carbon) which is associated with greater lability and susceptibility to decomposition. We will present evidence that anaerobic decomposition results in the production of reduced aliphatic compounds due to decarboxylation and bio-hydrogenation which are thermodynamically more stable under anaerobic conditions. These compounds, released to oxygenated inland water following anthropogenic or climatic disturbance are then particularly labile. Under current conditions, anaerobic microbial respiration of peat is dominated by modern surface production but there is evidence from the "SPRUCE" (Spruce and Peatland Responses under Changing Environments) climate manipulation study that older peat reservoirs are mobilized with increasing temperature.

2020032453 Chen, Richard H. (University of Southern California, Los Angeles, CA); Michaelides, Roger J.; Sullivan, Taylor D.; Parsekian, Andy; Zebker, Howard A.; Schaefer, Kevin M. and Moghaddam, Mahta. Simultaneous retrieval of soil moisture profiles and permafrost active layer thickness using P-band polarimetric backscatter and seasonal subsidence derived from L-band interferometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B12D-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The technique of using seasonal subsidence measured by interferometric synthetic aperture radar (InSAR) to estimate permafrost active layer thickness (ALT) is based on a key assumption that the active layer is entirely saturated at all times between the thaw onset and the maximum thaw. The thaw depth that this InSAR approach can measure is theoretically not limited; however, the estimated ALT can be biased if the actual soil moisture profile is below saturation. The method also assumes the same soil porosity profile for the active layer in permafrost regions, which could also introduce extra biases and uncertainty in ALT estimates. The polarimetric synthetic aperture radar (PolSAR) approach, on the other hand, has been used to estimate soil moisture and ALT simultaneously using time-series P-band radar backscatter observations. Soil moisture profiles can be accurately retrieved by this PolSAR approach, but its limitation on ALT estimation is that the P-band radar sensing depth is about 50 cm, which is not adequate to cover the full range of possible ALT in the Arctic-boreal region. To fully exploit the complementary strengths of both methods, we have developed a soil profile parametrization scheme to harmonize the hydraulic and dielectric properties of permafrost soils and implemented a joint retrieval algorithm to estimate soil moisture profiles and ALT simultaneously. The synergistic use of InSAR and PolSAR techniques can greatly improve the ALT estimation accuracy without sensing depth limitations. The retrieved profiles of soil moisture are also more accurate because the porosity profiles are estimated during the inversion process. This joint approach is applied to the L-band InSAR and P-band PolSAR data collected during the 2017 Arctic-Boreal Vulnerability Experiment (ABoVE) airborne campaign. In this presentation, we will detail the technical aspects of the method, as well as the sensitivity and uncertainty analyses for the soil moisture and ALT retrievals in the ABoVE domain.

2020027689 Chen, Yaping (University of Illinois at Urbana Champaign, Urbana, IL); Lara, Mark J. and Hu, Fengsheng. Decadal impacts of wildfire and climate change on permafrost degradation in Arctic Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP43E-2407, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Tundra fires are projected to increase with implications for landscape reorganization and biogeophysical processes. However, the interactive effects of wildfire and climate change on thermokarst (e.g., subsidence due to degrading ground ice) is poorly understood. We used a high-resolution time-series image analysis to evaluate the impacts of fire and climate change on thermokarst dynamics over the past 65+ years in northern Alaska. We assessed change in 276 study sites (25-hectare) in the Noatak National Preserve, representing unburned (n = 56) and burned (n = 220) tundra with variable fire severity (high, moderate and low), fire return intervals (FRI, 6 to 38 yrs), and ground ice content (i.e. surficial geology). A Spatial Boosted Regression Tree (BRT) model was used to simulate potential thermokarst formation across the tundra of northern Alaska. Results suggest that both fire severity and ground ice content significantly (p < 0.01) influenced thermokarst formation, where the greatest increase was observed in ice-rich sites (i.e. alluvium) burned in high severity. Abrupt increases in thermokarst were observed 3 years after fire (81.6 ± 7.2 m² ha^-1 yr^-1), and the rate of thermokarst declined exponentially to more than an order of magnitude lower during the 2^nd to 3^rd decade (3.2 ± 0.2 m² ha^-1 yr^-1). Thermokarst rates steadily decreased in burned areas (2.1 ± 0.2 m² ha^-1 yr^-1) yet still significantly higher (p < 0.05) than unburned controls (1.2 ± 0.2 m² ha^-1 yr^-1) by the end of 4^th decade. The net increase of thermokarst within burn scars over the course of 40 years was on average 8.3 (5.5~17.4) times that of unburned area. We failed to find evidence (p = 0.72) linking repeated burns with an acceleration/deceleration of thermokarst, and no statistic difference (p = 0.69) was detected between short (6-13 yrs) and long FRIs (34-38 yrs). On a regional scale, however, the spatial BRT model (r² = 0.77, p < 0.001) identified climate change outpacing fire disturbance as the predominant driver for thermokarst formation over past 50 yrs, due to the pervasiveness of climatic effects contrary to a small amount of area burned (<1%) in tundra ecosystems. This study suggests that the synergistic effects of tundra fire and climate change accelerated permafrost degradation over decades with potentially large consequences on Arctic carbon stocks.

2020032472 Christensen, Torben R. R. (Aarhus University, Arctic Research Center, Aarhus, Denmark); Lund, Magnus; Skov, Kirstine; Abermann, Jakob; López Blanco, Efren; Scheller, Johan; Scheel, Maria; Jackowicz-Korczynski, Marcin; Langley, Kirsty; Murphy, Melissa J. and Mastepanov, Mikhail. Hydrological intensification causes multiple ecosystem effects in the Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23G-2490, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Predictions of the future Arctic climate point towards overarching warming, but also towards more precipitation and an intensified hydrological cycle. Here we document how synoptic conditions causing special extreme weather patterns translate into hydrological intensification with severe implications within a high arctic ecosystem. The connection documented between the large-scale weather pattern and local consequences of the intense precipitation events is rarely seen with solid observational data. Here we focus in detail on two recent events: an episode with extreme summer rain (in 2015) and on one with extreme snow conditions (in 2018). These observations are from long time-series of data from Zackenberg, NE Greenland, providing a basis for comprehensive analyses of changes in weather patterns and their subsequent consequences for biogeochemical dynamics and ecosystem functioning. In the first event, during August 2015, one-quarter of the average annual precipitation fell during a nine-day intensive rain event. This extreme event ranked number one for daily sums during the 1996-2018 period and it had large impacts on the radiation, surface energy balance and fluvial sediment transport. The strong and prolonged reduction in solar radiation decreased CO₂ uptake in the order of 18-23 g C m^-2 in a wetland ecosystem, a reduction comparable to typical annual C budgets in Arctic tundra. The second event in 2018 represents a consequence of an extreme melt season that triggered a rapid thermokarst development (permafrost vulnerable due to warming trend). This caused a dramatic transformation in the ecosystem trace gas exchange within a few weeks. A grassy heathland ecosystem in homogenous flat terrain with a known small, but consistent annual CO₂ uptake and very low methane exchange became collapsed scars with highly elevated methane concentrations in the cracks and a substantial wash-away of soil organic material towards downstream riverine and coastal carbon input. Predicted more frequent occurrence of such extreme snow conditions and heavy, persistent, rain events in the future will have large implications for both biotic and abiotic components of otherwise undisturbed tundra ecosystems as well as their climate greenhouse gas and carbon interactions with the atmosphere and the ocean.

2020032510 Conaway, Christopher H. (U. S. Geological Survey, Menlo Park, CA); Johnson, Cordell D.; Lorenson, Thomas D.; Turetsky, Merritt R.; Euskirchen, Eugenie Susanne; Waldrop, Mark P. and Swarzenski, Peter W. Permafrost mapping with electrical resistivity tomography in two wetland systems North of the Tanana River, interior Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2581, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Surface-based 2D electrical resistivity tomography (ERT) surveys were used to investigate the distribution of permafrost at wetland sites on the alluvial plain north of the Tanana River, 20 km southwest of Fairbanks, Alaska, in June and September 2014. The sites contained landscape features characteristic of interior Alaska, including thermokarst bog, forested permafrost plateau, and a rich fen. These sites range from treed to open and vary in groundcover vegetation and peat thickness. At a bog site, two profiles of roughly 200 m distance were surveyed across a thermokarst bog bordered by spruce forest and forested permafrost plateau. At a fen site, a 180 m profile was run from a mixed spruce forest (Picea mariana and Betula papyrifera) across a vegetation gradient into an open fen. Different electrode array types, including dipole-dipole, extended dipole-dipole, and Wenner-Schlumberger, were compared and showed similar profile results. Overall, the results highlight the relationships between vegetation type and permafrost occurrence, and the results demonstrate the utility of ERT in characterizing thaw features in a lowland permafrost setting. The depth of thaw and thermal influence from the surface shown in the results are important in understanding the depth to which permafrost degradation may affect carbon storage and biogeochemical phenomena.

2020032475 Contreras, Adela (University of California, Davis, Davis, CA); Webster, Alex; Willis, Rachel L. and Harms, Tamara. Stream chemistry indicates catchment response to disturbance and regional warming in the boreal forest [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23H-2518, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Fire can alter exports of carbon (C) and nutrients from catchments by reducing capacity for nutrient retention by vegetation and combusting soil organic layers. In regions underlain by permafrost, fire additionally thaws permafrost, potentially increasing the depths of flowpaths draining catchments, and concomitantly the contributions of ions derived from mineral soils. Thus, stream chemistry might serve as an indicator of catchments' ability to recover from fire. As fire frequency and intensity are increasing in high latitude ecosystems, quantifying catchments' ability to recover from fire is critical to understand long-term consequences for carbon storage, nutrient exports, and permafrost stability. A spatially extensive survey of more than 50 streams draining boreal forest in Interior Alaska revealed that dissolved organic C concentration declined 200 mM, on average, in extensively burned compared to unburned catchments. Though previous research in the boreal forest and other regions has highlighted increased concentration of nitrate in individual streams following fire, we found that catchment attributes such as slope superseded the influence of fire on stream nitrogen export at a broad spatial extent. Repeated observations of a subset of the sampled streams over 17 years indicated a significant increase in specific conductivity of stream water (~75 mS cm-1). We attribute this effect to increased contribution of ions derived from mineral soils and hypothesize that regional permafrost thaw is rerouting catchment flowpaths through deeper soils. Thus, co-occurring changes in the fire and thermal regimes of the boreal forest are expected to result in changes to stream chemistry, including declining dissolved organic C concentration and increasing conductivity, providing spatially integrative indicators of ecosystem response to disturbance.

2020027670 Cory, Rose M. (University of Michigan Ann Arbor, Earth and Environmental Sciences, Ann Arbor, MI); Taterka, Bruce; Walker, David; Kling, George W. and Crump, Byron C. Including K-12 teachers in field research; progress and lessons learned on communicating climate change science to a broader audience [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract ED11A-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Given the goal of climate treaties to limit CO₂ emissions to stabilize at 450 ppm CO₂ in the atmosphere (a ~ 3°C increase), the world can emit another 45 Gt of C. This amount could easily come from the C stored in permafrost soils in the Arctic (i.e., Arctic amplification of climate warming). Thus, nations who share Arctic territory may be severely constrained in their emissions and energy policies. Because all generations and societies will share this burden, engaging a broader audience than scientists is critical for a cross-cultural appeal to take on the tasks of discovering and applying solutions to climate change. Our approach to engage a broader audience in understanding the Arctic's role in climate change is to partner with K-12 teachers committed to using cutting-edge science on climate change as the means to achieve learning goals in their classrooms. PolarTREC, a National Science Foundation funded program has allowed us to bring K-12 teachers to the field and participate directly in our research. Interactions between our team of scientists and K-12 teachers in the field since 2013 has resulted in the development of peer-reviewed curricula in earth and environmental science that is integrated with our research and grounded in core education principles. Our curriculum telescopes in age-context and difficulty from K-12 to undergraduate to adult outreach levels. We've established a network of scientists and K-12 teachers that helps new teachers improve on and expand the curriculum and lessons learned from the prior experiences of former teachers. We've learned that including K-12 teachers in our field work capitalizes on the multiplicative effect of making their experiences as field scientists accessible to many more K-12 students and their parents than scientists could reach alone. Thus, we expect that collaboration with K-12 teachers is preparing society to both understand the role of the Arctic in global climate change and to think about possible solutions.

2020032501 Coward, Elizabeth K. (University of Delaware, Delaware Environmental Institute, Newark, DE); Sowers, Tyler D.; Wani, Rucha and Sparks, Donald L. Fraction modern; molecular carbon dynamics across a yedoma permafrost thaw chronosequence [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2572, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost soils contain vast stocks of organic carbon (C) stabilized during Pleistocene glaciation that are increasingly susceptible to mineralization and export as dissolved organic matter (DOM) under ongoing climate warming. Over 25% of permafrost C is stored in deep Yedoma deposits preserved below the oxic threshold, vulnerable to anaerobic decomposition but not well characterized. Thawing of these ancient C stocks poses a great threat to climate forcing, yet the molecular composition, bioavailability and chemical reactivity of C in deep permafrost soils remains unknown. Deep permafrost thaw may also simultaneously alter the speciation of abundant redox-active iron (Fe) phases, documented to stabilize C in surface active-layer horizons, and solubilize mineral-associated DOM. To explore the coupling between C speciation, organomineral association and temporal persistence in permafrost systems, thaw- and mineral-associated DOM samples collected from a thaw chronosequence in Fox, Alaska were characterized via FTICR-MS, NEXAFS spectroscopy, and bulk analyses. The chronosequence encompasses modern fully-thawed, actively freeze-thawing and cemented Yedoma deposits from the Cold Regions and Research and Engineering Laboratory (CRREL) tunnel dating to 19, 27 and 33 ka. Distinct molecular signatures were detected across thaw and age gradients. In the oldest permafrost DOM characterized, 33 ka samples were comprised of a highly microbial signature of amino acids, lipids, and lignin-like moeities. With decreasing age in tunnel deposits, aliphatic structures increased in abundance. In contrast, actively freeze-thawing permafrost was dominated by lignin-like and condensed aromatic compounds, suggesting dynamic oscillations are reducing DOM complexity. Congruently, fully-thawed soils contained a diverse assemblage of hydrocarbons, lipids, proteins, and carbohydrate compounds. Throughout the chronosequence, mineral-associated compounds were preferentially aromatic, and decreased in aromaticity and saturation with age and thaw frequency. Observed variance in bound and unbound organic speciation across this thaw chronosequence suggests the extent of thaw may mobilize discrete DOM populations, fractionated in lability and reactivity, throughout the warming Arctic.

2020032625 Crawford, John T. (University of Colorado at Boulder, INSTAAR and Department of Environmental Studies, Boulder, CO); Hinckley, Eve-Lyn S.; Neff, Jason C.; Brahney, Janice and Litaor, Iggy. Evidence for accelerated climate-driven weathering and sulfate export in high alpine environments [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H43G-2081, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

High elevation alpine ecosystems--the "water towers of the world"--are warming at rates that far exceed those of lower elevations. Active geomorphic features, such as glaciers and permafrost, leave alpine ecosystems susceptible to climate-induced alteration. We examined recent changes in high-elevation stream chemistry in an alpine catchment of Colorado, USA and found strong evidence of increasing sulfate and base cation fluxes. To better understand these recent changes and to examine the potential causes of increased sulfur and base cation fluxes in surface waters, we present a high resolution 33-year record of atmospheric deposition (NADP site: CO02) to evaluate what factors may be driving this shift in stream chemistry. Our mass balance analysis and additional sulfur isotopic data suggests that recent warming is stimulating changes to hydrology and/or geomorphic processes, which in turn lead to accelerated weathering of bedrock. There is no evidence to suggest that atmospheric deposition is responsible for elevated stream export. This trend is also represented globally including in the Rocky Mountains of the United States, western Canada, the European Alps, the Icelandic Shield, and the Himalayas in Asia. All of these locations have experienced rapid increases in temperature during recent years, suggesting a climate-controlled change in sulfur and base cation export from mountainous regions via mineral weathering.

2020032672 Crawford, John T. (University of Colorado at Boulder, Ecology and Environmental Biology, Boulder, CO); Suding, Katharine; Neff, Jason C.; Wright, Anna and Hinckley, Eve-Lyn S. The Niwot Ridge Long Term Ecological Research Site; over 30 years of alpine observations [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA11C-0956, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Niwot Ridge Long Term Ecological Research (LTER) site (40°3'N, 105°36'W.) has been a focal study area for research on climate and ecological change for the last 40 years. It is located approximately 35 km west of Boulder, Colorado, with the entire study site lying above 3000 m elevation. The site contains extensive alpine tundra, a variety of glacial landforms, glacial lakes and moraines, cirques and talus slopes, patterned ground, and permafrost. Niwot Ridge, including the main alpine study site, is part of the Roosevelt National Forest and has been designated as a UNESCO Biosphere Reserve and a USDA Experimental Ecology Reserve. It is also the only LTER that is co-located with a Critical Zone Observatory and National Ecological Observation Network site. The site was formally established in 1980, yet climatological data reach back to 1952. Core datasets collected by the Niwot Ridge LTER include: air temperature, precipitation, relative humidity, wind speed and direction, solar radiation, stream discharge, snowpack ablation, snow water equivalent, soil moisture, atmospheric deposition, snowpack chemistry, and surface water quality. The eddy covariance dataset at Niwot Ridge is among the longest for forest sites. Research objectives include understanding the patterns and controls of alpine ecology; carbon and nutrient cycling; plant primary productivity and species composition; geomorphology, alpine limnology, and paleoecology. Important and significant, but less routine research at Niwot Ridge has included lake-ice clearance and freeze-up, monitoring of soil temperature and moisture, atmospheric N loading, soil physical and chemical properties, decomposition, microbial N transformations, microbial respiration, methane and nitrous oxide emissions, above-ground phytomass, plant phenology, plant species composition, small mammal surveys, soil microarthropod densities, and fossil insect assemblages. The Niwot Ridge LTER openly welcomes engagement by researchers who seek to use its multi-decadal records or conduct focused studies.

2020032546 Czimczik, Claudia I. (University of California Irvine, Earth System Science, Irvine, CA); Pedron, Shawn; Xu, Xiaomei; Walker, Jennifer Clare; Klein, Eric S.; Euskirchen, Eugenie Susanne and Welker, Jeffrey M. Closing the winter gap; year-round measurements of soil respiration sources in Arctic tussock tundra [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In Arctic tundra ecosystems, rapid warming and the extension of the frost-free period is expected to result in significant carbon (C) emissions that may overwhelm their ability to sequester C during the growing season. Such emissions have the potential to accelerate climate change, since tundra soils contain vast amounts of C, particularly in permafrost. However, it is currently not known what proportion of tundra C emissions during the fall and winter originate from the decomposition of recent plant matter vs. older soil C pools. These different C pools can be differentiated by measuring the radiocarbon (¹⁴C) content of soil-respired carbon dioxide (CO₂). Here, we present two years of continuous measurements of the ¹⁴C content of soil CO₂ respired from a moist acidic tundra soil near Toolik Field Station, AK, USA. We used a novel, passive sampling system, capable of trapping diffusive CO₂ within the active layer (n=4, from mineral soil to air/snowpack) over periods of 2-6 weeks. CO₂ was sorbed to 13X zeolite molecular sieve in the field, and thermally desorbed and analyzed at UC Irvine's KCCAMS facility. To evaluate the system's efficiency and quantify the temporal and spatial variability of respiration sources, we also monitored the soil's CO₂ concentration, temperature, and moisture content. In addition, we performed laboratory incubations to estimate the activity and C sources of the microbial community. We found that portions of the soil were thawed during May through January, with frost onset in October and complete freeze-up in early January. As expected, our results show that soil emissions are dominated by modern C sources in the organic horizons (mean D¹⁴C±sd=10±23 ppm, min=-60 ppm, max=111 ppm) and older C sources in the mineral soil (mean D¹⁴C±sd=-44±71 ppm, min=-299 ppm, max=3 ppm). Soil CO₂ during the growing season originates predominantly from modern C sources (mean D¹⁴C±sd=6±19 ppm, min=-39 ppm, max=34 ppm), indicating that C emissions represent mostly plant respiration and microbial decomposition of C recently assimilated by plants. During the non-growing season, we observed older CO₂ at all depth, with the oldest CO₂ captured in the mineral soil in March (-299 ppm). Our data also confirmed previous work showing rapid C emission during freeze-thaw cycles in the spring (and fall). Our comprehensive data set highlights the potential for C emission during the fall period (late August-early October) that might result in a depletion of active layer C stocks and a positive feedback to climate change.

2020027637 Daanen, Ronald P. (Department of Natural Resources Fairbanks, Fairbanks, AK); Emond, Abraham; Liljedahl, Anna K.; Romanovsky, Vladimir E.; Minsley, Burke J.; Walter Anthony, Katey M. and Barnes, David L. Goldstream Valley permafrost map [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1392, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Airborne Electromagnetic (EM) resistivity was used together with thermal modeling to define regions of frozen and unfrozen sediments in Goldstream Valley near Fairbanks, Alaska. This study was conducted in an area of partial development with modifications to the landscape due to road construction, houses, gravel pits and drainage. Gold exploration a century ago has caused disturbance to the valley, but also contributed to subsurface data that was used by Pewe who published a permafrost map for a large portion of the Goldstream Valley in 1957. Despite the development and proximity to Fairbanks very little is known about the surficial geology and especially the thickness of sediment over bedrock. We assembled borehole data and systematically extrapolated these data over the valley to recreate the layered structure of silt, gravel and bedrock that can be expected in this valley, which was never glaciated. The layered surficial geology was then used with the resistivity calculated from the airborne EM survey to find likely boundaries between frozen and unfrozen sediment. The valley was first mapped based on resistivity values, which was verified using borehole data and LiDAR elevation data for areas of ice wedge degradation. It was found that thawing permafrost has a resistivity very close to unfrozen sediments and determining the exact boundary is difficult. One of the problems is that fine grained sediments, at below freezing temperature have liquid water that can support electric currents and small scale variability of temperature and ice content cause those currents to flow around resistive bodies such as massive ice. Combining our map with thermal modeling provided further insights into the structure of permafrost distribution. However the complexity of ground ice distribution, fire extent and severity, beaver activity and human construction are all temporal changes in the surface conditions that is hard to simulate. Further analysis with higher resolution remote sensing devices may provide further insights into the presence of ground ice and the potential future collapse of the surface with infrastructure and houses that are built on permafrost in Goldstream Valley.

2020027657 Dafflon, Baptiste (Earth and Environmental Sciences, Lawrence Berkeley National Laboratory, Berkeley, CA); Uhlemann, Sebastian; Shirley, I.; Akins, H.; Lamb, J.; Ulrich, C.; Peterson, J. E.; Brunetti, C.; Biraud, S.; Andresen, C. G.; Wilson, C. J.; Romanovsky, V. E. and Hubbard, S. Quantifying the influence of soil, snowpack, topography and vegetation properties on soil hydro-thermal behavior across an Arctic watershed in a discontinuous permafrost environment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In Arctic regions, understanding the link between soil physical properties, soil thermal behavior and landscape properties is particularly challenging yet is critical for predicting the storage and flux of carbon and water in a changing climate. This study aims at improving the understanding of the various subsurface hydro-thermal behaviors and the multi-dimensional relationships between subsurface and surface properties in discontinuous permafrost environments. Our work takes place in a watershed near Nome (Alaska) that shows significant heterogeneity in vegetation, snowpack, geomorphic and subsurface characteristics. We use a variety of aerial and ground-based measurements, including a novel Distributed Temperature Profiling (DTP) system that provides unprecedented vertical and horizontal distribution of soil temperature. These measurements complement electrical imaging, seismic refraction, CO₂ efflux and water content measurements, soil sample analysis and UAV-based mapping of snow thickness and vegetation characteristics. Data integration and analysis is supported by numerical approaches that simulate hydrological, thermal and biogeochemical processes. Overall, this study enables the identification of watershed structure and associated subsurface and landscape properties. Our unique dataset has highlighted significant relationships between above- and belowground characteristics including: (1) the effects of topographic lows and tall shrubs on thick snowpack, and with subsurface characteristics on the distribution of taliks (year-round unfrozen soil); (2) the significant spatial co-variability between permafrost characteristics, vegetation, and geomorphology, with graminoid covered areas corresponding to zones having the shallowest permafrost table; and (3) the significant influence of soil hydrological and thermal behavior on soil CO₂ efflux. We are also using numerical models with adequate level of process representation to improve our understanding of how near-surface permafrost transition to talik and absence of permafrost. The obtained information is expected to be useful for improving predictions of Arctic ecosystem feedbacks to climate.

2020032451 Dann, Julian (Los Alamos National Laboratory, Los Alamos, NM); Wilson, Cathy Jean; Lathrop, Emma; Chen, Richard H.; Bolton, Robert W.; Moghaddam, Mahta; Charsley-Groffman, Lauren; Musa, Dea and Wullschleger, Stan. Factors influencing the spatial distribution of soil moisture derived from airborne SAR in watersheds near Nome and in Utguiavik, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B12D-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Researchers in the DOE Office of Science Next-Generation Ecosystem Experiments, NGEE-Arctic, and NASA Arctic Boreal Vulnerability Experiment (ABoVE) projects are collaborating on the development of regional soil moisture data products to improve and assess Earth System Models. Here we present our analysis of in-situ measurements of soil moisture, soil physical properties,and thaw depth collected during the summer of 2017 coincident with NASA ABoVE airborne overflights of L and P-band SAR instruments. New analyses show that the spatial distribution of soil moisture and active layer depth derived from Airborne SAR- using a two-layer dielectric structure (Chen et al. 2019)- differ based on local geomorphology, topography, climate and vegetation properties across a range of field sites and settings near Utqiagvik, AK and Nome, AK. In Utqiagvik, in-situ data were collected at high-center, flat-center, and low-center polygons during the June SAR P-band and September L-band overflights. At all sites on the Seward Peninsula, in-situ data were collected in May and August, coincident with P-band overflights. At each field site the same measurement techniques were used including the establishment of multiple 100m by 100 m plots designated for SAR ground-truthing. Within each SAR plot two 60 meter transects were established along which both soil moisture and thaw depth measurements were taken. This configuration is consistent with the ABoVE protocols which enables proper averaging of multiple pixels for airborne or spaceborne SAR data. In-situ volumetric soil water content (VWC) data were collected during SAR overflights using Hydrosense-II soil-water sensors and data loggers (VWC). The in-situ Hydrosense VWC values corresponded well with laboratory analyses of soil samples collected at the sites. Soil moisture and thaw depth are key factors controlling subsurface biogeochemistry and surface ecosystem type and function. These observations and analyses provide a unique benchmark dataset with which to test predictions of spatial variation and temporal evolution of soil moisture in local and regional permafrost models.

2020032445 Debolskiy, Matvey Vladimirovich (University of Alaska Fairbanks, Fairbanks, AK); Alexeev, Vladimir A.; Hock, Regine; Nicolsky, Dmitry; Romanovsky, Vladimir E.; Schulla, Jorg; Shiklomanov, Alexander I. and Lammers, Richard B. Modeling millennial time scale changes in water balance of mesoscale watersheds within permafrost regions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract A21N-2756, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Physical processes in mesoscale watersheds in the Arctic operate on different characteristic time scales than elsewhere. Inter-annual fluctuations in air temperature and precipitation are attenuated while propagating through the unsaturated zone. Nonlinear relationship between the near-surface air temperature, runoff, evapotranspiration and groundwater recharge depends on the ground temperature dynamics in the active layer, permafrost and unsaturated zone. In this study, we apply the distributed water-balance model WaSiM to investigate how ground temperature,soil moisture fields and the water balance of a homogeneous, synthetic mesoscale watershed respond to changes in air temperature on a millennial timescale. We analyze the sensitivity of the watershed in an equilibrium to changes in air temperature for a range of potential hydraulic conductivity values corresponding to various subsurface conditions. Starting from a thawed equilibrium state we force the model with a negative step change in mean annual air temperature (seasonal cycle is preserved) to estimate the amount of water that can be stored in the ground through epigenetic ice formation. Then we apply a positive change in air temperature to the watershed in a new 'frozen' equilibrium to capture the dynamics of different water balance components of the watershed on the path to a new equilibrium through permafrost degradation. Preliminary results suggest that after a positive step change in air temperature total annual runoff and its components of the watershed experience oscillatory behavior on a centennial time scale in the first couple of millennia before a new equilibrium is reached. The characteristics of these oscillations depend on hydraulic conductivity and the amplitude of the step change.

2020027687 Del Vecchio, Joanmarie (Pennsylvania State University Main Campus, Department of Geosciences, University Park, PA); Fratkin, Mulu M.; Lathrop, Emma; Andresen, Christian G.; Collins, Adam; Crawford, Brandon; Dann, Julian B.; Wilson, Cathy J.; Adams, Jordan M. and Rowland, Joel C. Measuring and modeling periglacial hillslope processes, Seward Peninsula, western Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP43E-2405, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Sediment flux from seasonally thawing Arctic hillslopes results in deposition, burial, and sequestration of soil organic carbon (SOC) in hollows and toeslopes. The vulnerability of these sediments and SOC to erosion represents a significant knowledge gap in predicting the rate, magnitude, and timing of physical SOC release from permafrost landscapes under a warming climate. To better constrain how soil movement, burial, and erosion may control rates and patterns of sediment and SOC fluxes in permafrost landscapes we conducted field investigations on a small first-order watershed on the Seward Peninsula, AK. We used repeat GPS surveys, high-resolution imagery, Sediment flux from seasonally thawing Arctic hillslopes results in deposition, burial, and sequestration of soil organic carbon (SOC) in hollows and toeslopes. The vulnerability of these sediments and SOC to erosion represents a significant knowledge gap in predicting the rate, magnitude, and timing of physical SOC release from permafrost landscapes under a warming climate. To better constrain how soil movement, burial, and erosion may control rates and patterns of sediment and SOC fluxes in permafrost landscapes we conducted field investigations on a small first-order watershed on the Seward Peninsula, AK. We used repeat GPS surveys, high-resolution imagery, elevation data, and soil sampling to investigate how periglacial hillslope processes vary across a present-day hillslope and may have varied over the Holocene. We then use numerical simulations of hillslopes to infer the geomorphic feedbacks to climatic variations that may control the observed timing and patterns of hillslope storage and erosion. elevation data, and soil sampling to investigate how periglacial hillslope processes vary across a present-day hillslope and may have varied over the Holocene. We then use numerical simulations of hillslopes to infer the geomorphic feedbacks to climatic variations that may control the observed timing and patterns of hillslope storage and erosion. Modern surface sediment flux occurs at a rate of ~2 cm/yr, and the style of sediment transport (diffusive versus solifluction) varies with underlying lithology, hydrology and aspect. We used UAV-based photogrammetry to map and measure slope disturbances to estimate recent rates of sediment flux. In hollows and toeslopes, initial radiocarbon dates imply sedimentation rate has decreased over the past 5 ka, coinciding with Neoglacial cooling and subsequent permafrost aggradation, which followed warmer temperatures from 10-5 ka. Modern surface sediment flux occurs at a rate of ~2 cm/yr, and the style of sediment transport (diffusive versus solifluction) varies with underlying lithology, hydrology and aspect. We used UAV-based photogrammetry to map and measure slope disturbances to estimate recent rates of sediment flux. In hollows and toeslopes, initial radiocarbon dates imply sedimentation rate has decreased over the past 5 ka, coinciding with Neoglacial cooling and subsequent permafrost aggradation, which followed warmer temperatures from 10-5 ka. However, this trend is reversed in the Anthropocene, when erosion appears to have accelerated. However, this trend is reversed in the Anthropocene, when erosion appears to have accelerated. To explore how climate may influence sediment flux and hollow dynamics, we used numerical models of landscape evolution that incorporate periglacial processes. We employed sediment transport rules that account for active layer thickness and solifluction to explore what depth-velocity profiles and diffusion rates would reasonably explain our field observations. Process-specific geomorphic models such as these are necessary to predict the sediment and carbon flux from arctic watersheds as climate change creates hydroclimate conditions beyond historic observations. Additionally, these models may help us to better understand landscape evolution during past cold-climate periods.

2020032592 Demir, Cansu (University of Texas at Austin, Department of Geological Sciences, Jackson School of Geosciences, Austin, TX); Cardenas, M. Bayeni; McClelland, James W. and Pedrazas, Micaela Nicole. Groundwater discharge in the lagoons of Alaskan Beaufort Sea [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1362, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Thawing permafrost due to climate change results in severe environmental consequences, such as impacting ecological processes and trajectories, accelerating nutrient and carbon cycling including the production and release of greenhouse gases, and modifying hydrologic flows and storage that impact connectivity between terrestrial, aquatic, and marine environments. In the case of the latter, groundwater plays an important role in the delivery of material to surface water bodies which include not only lakes, rivers, and wetlands but also coastal waters such as the lagoons lining the Beaufort Sea coast of Alaska. However, the groundwater flow regimes in seasonally thawed continuous coastal permafrost areas are still not well understood. Salinity and temperature, which are related by phase relationships at the ice-water boundaries, are vital parameters to comprehend the properties of subsea permafrost and the submarine groundwater discharge (SGD). In this study, we investigate the active layer (seasonally thawing/freezing) distribution, and saline-fresh groundwater mixing zone under Kaktovik Lagoon, one of the shallow lagoons surrounded by barrier islands in the Alaskan Beaufort Sea. This location is a good representative of the lagoon systems of the region. The field campaign includes measurements of hydraulic head, water salinity and temperature of the beach and lagoon substrate collected along a shore-perpendicular and -parallel transects at a sampling interval ranging between 1 m and 10 m horizontally, and 0.1 to 1 m vertically. This is done in conjunction with direct and indirect probing for the permafrost table, if it is present. We hypothesize that coastal lagoons have mostly thawed substrate reaching great depths. This implies that groundwater discharge and transport might be a prominent process. Furthermore, climate warming will enlarge the SGD pathways in the permafrost, and result in connected flow patterns which will result in higher organic loads to the lagoons. Our results have important implications for predicting the driving forces and quantifying the related fluxes of organic matter and gases between groundwater and lagoon in these environments. Our goal is not only to quantify these but also to improve process understanding of groundwater flow and transport in Arctic lagoons.

2020032521 Dieleman, Catherine M. (University of Guelph, Department of Integrative Biology, Guelph, ON, Canada); Gibson, Carolyn; Kane, Evan S.; Rogers, Brendan M. and Turetsky, Merritt R. Fire and ice; the impacts of changing boreal fire regimes and permafrost loss on carbon stocks and stability [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24C-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Boreal ecosystems are experiencing an increase in wildfire extent, and frequency, directly modifying vegetation structure and ecosystem carbon pools. Fire consumption of insulating organic soils also initiates permafrost thaw, rendering old permafrost carbon susceptible to decomposition. Changes in fire and permafrost disturbance regimes each have the potential to transition northern boreal ecosystems from net carbon sinks to notable sources, but few studies have examined the potential for these disturbances to interact. To address this knowledge gap, we evaluated the impacts of contemporary fire regimes and associated permafrost thaw dynamics on carbon stocks and emissions in the North American boreal. To discern fire impacts, we conducted a multi-regional analysis of carbon stocks and combustion rates, contrasting the high frequency fire regimes of the southern boreal (Saskatchewan, Canada) with regions in the north (Alaska, USA, Northwest Territories, Canada). We furthered this work by quantifying the effect of fire on permafrost thaw throughout the discontinuous permafrost zone in Western Canada, using field and GIS techniques. We characterized carbon loss triggered by permafrost thaw using long-term soil incubations paired with in-situ measures across an Alaskan permafrost thaw gradient. Our results show that high frequency fires of the southern boreal generate predominately (>70%) young stands, which store ~2-7 kg C m^-2 less than the mature stands that characterize the north. When these fires occurred on permafrost soils they accounted for ~20% of the permafrost loss over the past 30 years. These permafrost thaw events are associated with sustained CO₂ production as well as significant increases in CH₄ release depending on soil moisture conditions. Taken together this research provides first-order mechanistic knowledge needed to identify generalizable effects of changing fire and permafrost thaw regimes on the fate of boreal carbon storage and emissions.

2020032485 Dillon, Megan (Lawrence Berkeley National Laboratory, Berkeley, CA); Xue, Yaxin and Tas, Neslihan. Arctic permafrost microbiomes; a meta-analysis [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23J-2553, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate change is a complex problem that will bring a multitude of consequences for both human populations and plant and animal ecosystems. The Arctic is particularly vulnerable to these effects because the rate at which temperatures are rising in Arctic regions is 2.5X Earth's average. Much of the Arctic's underlying soils are permanently frozen (permafrost). Permafrost soils hold more carbon than other regions, and as the soils warm, they emit GHGs that further warm soils, accelerating permafrost thaw. Warming experiments and field observations have provided evidence that as temperatures rise, Arctic soils will be a net source of the GHGs carbon dioxide (CO2) and methane (CH4), exacerbating climate change. Microbes contribute substantially to permafrost GHG emission. Recent studies suggest that permafrost types and features vary greatly across the Arctic, but knowledge of their geospatial variation or connectivity is limited. Linking permafrost and landscape features to microbial community structure will help us to understand what the likely constraining habitat features are and their distribution across the Arctic will help us predict what microbial communities are found where. Genome resolution allows microbial ecologists to constrain variation in metabolic capacity within species as well as estimate growth temperature and growth rate, crucial features for understanding ecosystem dynamics in icy habitats. This meta-analysis of permafrost metagenomes across the Arctic quantifies soil characteristics and microbial community composition and metabolic potential. We obtained metagenomes from Alaska, Sweden, Canada, Russia, and Antarctica to compare the correlations among environmental drivers with Arctic microbiomes. The microbial communities inhabiting these soils have common members and metabolic capacity but differ in the extent to which Eukaryotic and viral populations were represented and in the abundance and biochemistry of methanogens. These results contribute to an understanding of global variation in the microbial ecology of permafrost. Recognizing geospatial patterns in soil properties and microbiome characteristics across Arctic permafrost landscapes will allow us to better assess how permafrost responds to global climate change.

2020027648 Ding Yongjian (CAREERI/CAS Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China). Some advances in the study of the effect of cryosphere change in China [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23C-1560, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The cryosphere change has influenced on water resources, ecology and disasters in China. In the past 50 years, glacier meltwater runoff has increased by 54% and snowmelt runoff has advanced by nearly one month in China. Winter runoff in permafrost regions has generally increased. The hydrological changes of the cryosphere at watershed scale caused runoff increasing and extended runoff yield period. Under different RCPs scenarios in the future, glacier runoff will be reduced by 20%~100% by the end of the century. The impacts of cryosphere changes on farmer's net income, oasis area and industry in the Inland River Basin depends on its scale. Under the influence of hydrological changes in the cryosphere, the vulnerability of the Inland Rivers will generally increase. It is necessary to adjust the industrial structure with agriculture as the main part in order to adapt its impact. The observational experiments on the relationship between permafrost and ecology showed that climate change increased the vegetation productivity in stable permafrost regions, and decreased the vegetation productivity in unstable and seasonal permafrost regions. The active layer thickness of 2.0-3.0 m is the threshold of response of alpine grassland vegetation to permafrost degradation. On regional scale, the alpine vegetation in the stable and extremely stable permafrost regions in the Tibetan Plateau tend to be better, while the vegetation are getting better in the continuous permafrost regions and worse in the patchy permafrost regions of northeast China. The permafrost changes has generally weakened carbon sink in the Tibetan Plateau. The carrying capacity of grassland has increased with the thickening of frozen soil active layer, and will be stable in permafrost regions. Based on the comprehensive risk assessment system of cryospheric disasters, the comprehensive risk grades of glacier lake outburst disaster and snow disaster in pastoral area in the Tibetan Plateau were systematically evaluated zoned. The area of potential dangerous glacier lake is the key hazard factor affecting glacier lake outburst disaster. The overloading rate is the key factor of snow disaster in pastoral area. In the initial stage of the change of snow disaster intensity, the effect of animal shelter intervention is better.

2020032486 Doherty, Stacey Jarvis (University of New Hampshire, Molecular, Cellular, and Biomedical Sciences, Durham, NH); Barbato, Robyn A.; Dorrepaal, Ellen; Johansson, Margareta; Monteux, Sylvain; Bennett, Kathryn A.; Ernakovich, Andrew; Mackay, Jessica and Ernakovich, Jessica Gilman. Assembly of microbial communities in thawed permafrost and implications for carbon processing [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23J-2555, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Northern high latitudes are warming twice as fast as the global average and permafrost has become vulnerable to thaw leading to physical, chemical, and biological changes across the landscape. Of particular interest is the change in soil microbial communities and the potential effect on ecosystem functions, such as increased carbon emissions. Changes to the environment during thaw can lead to shifts in microbial communities, the assembly of which is heavily influenced by biotic and abiotic factors. Little is known regarding permafrost microbial assembly both in situ or post-thaw including how assembly might influence ecosystem function post-thaw. We hypothesize that (i) microbial communities residing in well-established active layer and intact permafrost are the result of niche-based assembly and (ii) the assembly of microbial communities in newly formed active layer (i.e. the permafrost-active layer interface) is a result of neutral processes. We tested these hypotheses by determining the microbial community structure through 16S and ITS amplicon sequencing along replicate soil depth profiles from a fourteen-year field thaw experiment at the Storflaket Mire, Sweden. A null modeling approach was used to determine the dominant assembly processes at eight depths, encompassing both active layer, transition zone, and permafrost soils. We also compared the post-thaw carbon processing potential at each depth to determine the link between community assembly and function. Preliminary results show a four-fold decrease in CO₂ respiration along the depth profile with active layer soils exhibiting higher respiration rates compared to permafrost soils. This trend holds true at both 15°C and 4°C with a significant difference in respiration observed between the uppermost active layer and permafrost soil at 15°C (p=0.03). This suggests active layer microbes process carbon faster than permafrost microbes regardless of temperature. Identification of dominant microbial community assembly processes and insights of the functional implications of assembly (e.g., carbon processing rates) will improve our understanding of the ecological impact of permafrost thaw and the permafrost-climate feedback.

2020027685 Douglas, Madison (California Institute of Technology, Pasadena, CA); Lamb, Michael P.; Rowland, Joel C.; Li, Gen; Kemeny, Preston C.; West, A. Joshua; Piliouras, Anastasia; Schwenk, Jon; Chadwick, Austin J. and Fischer, Woodward W. Quantifying organic carbon mobilization and storage due to bank erosion in permafrost-dominated river floodplains [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP42A-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic permafrost soils store approximately twice the carbon currently present in Earth's atmosphere, and are particularly vulnerable to climate change due to the polar amplification of increasing global temperatures. Many organic-rich permafrost sediments are located on large river floodplains, where river channel migration can source, as well as deposit, organic carbon from many meters below the depth of annual thaw. In order to constrain carbon cycling driven by permafrost riverbank erosion, we conducted a field expedition to the Koyukuk River, a large tributary of the Yukon River in Alaska meandering through discontinuous permafrost. We used Landsat and WorldView imagery to measure channel migration rates and map multiple generations of levee and point bar deposits across the floodplain of the Koyukuk. During field work, we sampled and described the sedimentology of both permafrost and non-permafrost cores and banks, as well as bed and suspended sediment in transport in the river. We measured total organic carbon (TOC) content, grain sizes, bulk density, and the radiocarbon content of sediment samples and woody debris. We observed that permafrost occurs only on older, relict point bar and floodplain deposits overlain by horizons of peat, while recent floodplain deposits have little peat and only seasonal frost. Therefore, as the Koyukuk River migrates and reworks its floodplain, older permafrost deposits are predicted to be replaced by younger, permafrost-free deposits. However, our results show that the permafrost and non-permafrost deposits contain similar TOC when integrated to the river channel depth, implying that OC is being eroded from cutbanks and deposited in bars at similar rates with no apparent net carbon flux, despite the loss of permafrost with river migration. Sediment radiocarbon content is variable, and may reflect mixtures of petrogenic, modern biogenic and aged biogenic carbon preserved in permafrost. However, radiocarbon ages of the sediment mud fraction range from 1-3 ka and are similar between cutbank and point bar deposits, regardless of permafrost content. Therefore, any enhanced river migration due to thawing permafrost may not significantly increase carbon mobilization in Arctic landscapes such as the Koyukuk Flats.

2020032637 Draebing, Daniel (University of Bayreuth, Chair of Geomorphology, Bayreuth, Germany); Mayer, Till; Jacobs, Benjamin and McColl, Samuel T. The interaction between permafrost, frost cracking and paraglacial processes and their link to rockfalls [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NH53A-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rockfall is characteristic of deglaciated alpine rockwalls. Small (<5 km²) to very small (<0.5 km²) alpine glaciers are located at altitudes where periglacial and paraglacial processes jointly influence rockfall processes. In this study, we (i) quantify rock fracture damage, (ii) model permafrost distribution, (iii) quantify frost weathering stresses, (iv) model patterns of frost weathering, and (v) assess how these may combine to influence rockfall processes around a small alpine glacier in the Hungerli Valley (Swiss Alps). To achieve this, we use geomorphic, geophysical, geotechnical and remote sensing techniques on three rockwalls (RW1-3) with different glacial retreat history and elevation. (i) Rockwall fracture damage is quantified in the field using laboratory-calibrated seismic refraction tomography and our results demonstrate that rockwall fracture density increases with proximity to the glacier. Therefore, suggesting that rockwalls in proximity to the glacier are still experiencing paraglacial stress-release jointing and that rockfall is yet to remove these fractured blocks. (ii) Local permafrost modelling based on temperature logger data indicates that areas with likely permafrost occurrence (Mean Annual Rock Surface Temperature, MARST <-3°C) are limited to the peaks and upper cirque walls (>3000 m). Possible permafrost (MARST <0°C) areas extend to elevations as low as 2700 m. (iii-iv) Lab simulations show that most frost cracking occurs at subcritical stresses. Ice segregation causes stresses up to 1 MPa in the range of subcritical cracking. Volumetric expansion can generate stresses up to 10 MPa, exceeding critical cracking thresholds, but conditions allowing this are rare. Temperature-driven frost cracking modelling and physical rock fracture modeling both indicate a maxima of frost cracking at 2700 m elevations. (v) Terrestrial laserscanning of the rockwalls shows that rockfall activity is increasing with proximity to the glacier and is enhanced in areas affected by ongoing glacier retreat, permafrost and intense frost cracking. In conclusion, our data suggest a synergy of paraglacial processes, frost cracking and permafrost thaw in preparing and triggering rockfalls. This synergy follows an altitudinal gradient that moves upwards with glacier retreat, permafrost thaw and frost cracking trajectories.

2020032616 Ebel, Brian A. (U. S. Geological Survey, Earth System Processes Division, Lakewood, CO); Koch, Joshua C.; Walvoord, Michelle A.; Minsley, Burke J. and Rey, David. Contrasting wildfire impacts on hydrologic properties and processes in boreal forest in Alaska and coniferous forest in the Southern Rocky Mountains, USA [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H32G-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wildfire is a common disturbance in boreal forest in Alaska and coniferous forest in the Southern Rocky Mountains in the USA. Forest canopy fire severity can be high in both of these environments, but the fire effects at the land surface can be manifested quite differently. Boreal forests tend to have partially combusted, thick organic layers with less visible mineral soil impacts whereas coniferous forest in the Southern Rocky Mountains tends to have fully combusted litter/duff layers and clear effects on mineral soil. Contrasting changes on surface and subsurface hydrologic properties and processes result from many factors, including disparities in tree density and fuel load, precipitation regimes, organic layer thickness and composition, ground cover, antecedent soil moisture, topography, soil properties, and permafrost presence. This presentation will discuss field and laboratory measurements, geophysical characterization, and hydrologic modeling results from fire-affected sites in boreal forest vegetation in interior Alaska where permafrost is discontinuous. The focus for the Alaska work is on mineral soil properties, permafrost conditions, and inferences regarding potential hydrologic controls on permafrost dynamics. Comparisons between Alaska measurements and post-fire conditions and responses in coniferous forest in the Southern Rocky Mountains, USA indicate major differences in the timescales of change with implications for hazards and water supply. Wildfire in boreal forests promotes permafrost thaw likely attributable to shifts in the surface energy balance with potential advective thaw contributions from enhanced groundwater flow, becoming substantial a decade after the fire. By contrast, hydrologic hazards in the Southern Rocky Mountains can be ascribed to losses of tree canopy interception, ground cover, and reductions in infiltration rates, driving flood and water supply risks commonly concentrated in the first three years post-fire.

2020032515 Ebert, Christopher (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Pegoraro, Elaine; Mauritz, Marguerite; Natali, Susan; Hicks Pries, Caitlin and Schuur, Edward. Soil CO₂ profile measurements reveal an increase in the proportion of old soil carbon over a thirteen year study at a permafrost site in interior Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2586, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost degradation is a primary driver of the global atmosphere-ecosystem carbon (C) cycle, with 1300-1500 Pg of stored permafrost C potentially thawing and becoming vulnerable to decomposition. The release of old permafrost C is a particular concern for climate feedback loops, because a large loss of ancient C is not expected to be countered by an increase in Arctic plant productivity. We have collected soil carbon dioxide (CO₂) from two field sites near Healy, Alaska over thirteen years and determined their radiocarbon signature (D14C), a valuable measurement for determining the source and age of the C. A two-pool mixture model was used to distinguish sporadic pulses of old C release from modern samples. A linear model used environmental data to predict which samples were old and which were modern. D14C of modern samples exhibit a yearly decrease of 5.4 ± 1.0 permil. This is a larger drop than the change of atmospheric D14C at the site (4.0 permil/year), so a turnover of modern carbon in the soil does not fully explain the observation. Our conclusion is that a growing proportion of soil CO₂ is ancient C, originating from deep in the permafrost where it was frozen until recent degradation. We also observed pulses of old C release at some sampling dates that appear to be driven by recent precipitation events: precipitation within the last five days was an effective predictor of these pulses, while precipitation within the last fourteen days was not a significant predictor. Two important conclusions from this work are: 1) Precipitation and soil moisture dynamics play an important role in old C release, and permafrost soil C age can be highly impacted by the recent and immediate conditions at the time of sampling 2) Even outside sporadic pulses of old C release, we found evidence that permafrost degradation is accelerating the release of old C.

2020032641 Egorova, Angelina (Australian National University, Canberra, Australia); Tkalcic, Hrvoje; Tauzin, Benoit and Pham, Thanh-Son. Passive seismic monitoring of Arctic environment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS11B-0633, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Global warming is the main environmental threat facing everyone in the world. Most affected region is Arctic: permafrost is thawing, Greenland, Antarctic ice sheets and glaciers are melting dramatically fast today. Thus monitoring temporal variation of ice sheets properties is a straight tool to understand the process of melting and its behaviour. We study shallow Greenland Ice sheet structure and ice elastic properties using environmentally friendly and cost effective seismic passive methods. This provides alternative data source from seismic records, in addition to extensive GPS and ICEsat data. We use data from 12 three-component broadband stations from GLISN and UPPA-GL on the Greenland Ice Sheet. Standard receiver function techniques fail to give interpretable results due to strong reverberations of energy caused by sharp contrast of elastic properties at the ice-bedrock interface that hide useful reflections. So we follow previous successful application of a novel P wave coda autocorrelation method to Antarctic stations, and apply the method to seismic receivers deployed over Greenland Ice sheet. Our results show clear advantage of the method over the receiver function method. Reflection delays of P waves from teleseismic P wave coda autocorrelation are used to estimate the ice thickness. P over S wave speed ratio are obtained from the ratio of S wave and P wave reflection times. We also process one day long seismic ambient noise records and compare the accuracy of the autocorrelation method with the well established H/V spectral ratio method. The results are in good agreement with ice thickness data collected using a coherent ice-penetrating radar system and comply with our synthetic models. We will further investigate the link between event- and noise-data autocorrelation method.

2020032621 Eickmeyer, David (University of Ottawa, Ottawa, ON, Canada); Thienpont, Joshua R.; Korosi, Jennifer B.; Chin, Krista S. and Blais, Jules. Assessing baseline stream metal concentrations in the cumulative impact monitoring program for hydrocarbon extraction by hydraulic fracturing of the Canol shale play, central Mackenzie Valley, NT, Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H41J-1818, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In ecologically sensitive and remote northern locations, environmental monitoring programs often face challenging logistical considerations to provide oversight on natural resource exploration and extraction, especially for regions that are already susceptible to terrain instability by permafrost erosion. However, effective monitoring for the cumulative impacts of these development activities is reliant upon comprehensive assessments of ecological conditions prior to disturbances from resource exploitation. In the Sahtu region, western Canada, accessing the hydrocarbon-rich deposits of the Canol Shale Play would require widespread application of hydraulic fracturing extraction techniques, potentially having unforeseen consequences such as further hydrological and landform alterations by permafrost degradation, compounded with concerns of increased contaminant burdens in aquatic ecosystems. To determine the natural variability in this region, we conducted a spatial survey of metal(loid) concentrations in sediment and benthic macroinvertebrates from streams of the Central Mackenzie Valley, south of Norman Wells, NT. Biota-sediment accumulation factors (BSAFs) were also calculated where both invertebrates and sediment were available. Here we focused on elements either included in the Canadian Council of Ministers of the Environment Sediment Quality Guidelines for the Protection of Aquatic Life (i.e. As, Cd, Cr, Cu, Pb and Zn), or reported enriched in other shale/hydrocarbon deposits (i.e. Mo, Ni, V). Concentrations were variable, but generally low, in sediment and biota, and often below guidelines (where existent). Isolated, distributed sites were noted above probable effect levels for As (> 17 mg g^-1), and Zn (> 315 mg g^-1), however BSAFs for As were < 1 suggesting limited bioavailability. Several elements (e.g. Cd, Cr, Cu, Mo, Ni, Zn) show elevated BSAFs, demonstrating the potential bioaccumulation if resource development were to contribute contaminants to the ecosystem. These findings emphasize the necessity of gathering data on baseline environmental conditions and natural system variability prior to resource extraction disturbances, thereby providing the framework for monitoring potential cumulative impacts as a result of hydrocarbon development in northern landscapes.

2020032596 Eklof, Joel (University of Washington, Civil and Environmental Engineering, Seattle, WA); Waldrop, Mark P.; Jones, Benjamin M. and Neumann, Rebecca Bergquist. Thaw dynamics of a rapidly degrading isolated permafrost plateau in south-central Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1366, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Northern high latitudes are projected to get warmer and wetter in the future which will affect rates of permafrost thaw and the mechanisms by which thaw occurs. To better understand these changing thaw dynamics, we instrumented an isolated permafrost plateau in south-central Alaska with climate conditions that currently mirror those expected in more northern permafrost regions in the future. Using preliminary 2019 measurements of temperature from the soil surface into permafrost, depth to frost table, water level, groundwater temperature, and meteorological variables, we tracked soil and permafrost warming throughout the season, and identified how environmental factors, such as water table elevation, microtopography, and warm rain events, affected rates of warming and thaw. Additionally, we present the extent of permafrost degradation since the last observations at this site in 2015. Permafrost thaw and resultant landscape change has a net warming effect on the climate. Understanding of the environmental factors that lead to thaw and rates at which permafrost will thaw under future climate conditions will allow for better preparation, modeling, and policy making for the future.

2020032535 Elder, Clayton (California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA); Thompson, David R.; Thorpe, Andrew K.; Baskaran, Latha; Walter Anthony, Katey M. and Miller, Charles E. Broad-scale airborne mapping detects widespread methane emission hotspots associated with thermokarst [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane (CH₄) emissions from Arctic and Boreal permafrost contribute significantly to global natural CH₄ emissions. As permafrost degrades under warming rates twice global average, additional CH₄ emissions have the potential to reinforce a warming climate. Despite these concerns, incomplete process-based understanding of CH₄ emissions continually hampers budget estimates and renders model forecasts highly uncertain. Here, we report the results of an orchestrated ground and airborne survey confirming a thermokarst-related CH₄ emission hotspot originally detected on multiple overflights from July 2018 to July 2019 using airborne imaging spectroscopy from NASA's Next-Generation Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-NG). AVIRIS-NG has imaged over one billion pixels at 5-meter resolution across broad regions in Alaska and western Canada. Analysis from the 2017, 2018, and 2019 Arctic Boreal Vulnerability Experiment (ABoVE) showed that CH₄ hotspot occurrence grows exponentially with proximity to ponds, lakes, streams, rivers, and various other wetland features, mirroring flux patterns observed at the site level. Furthermore, hotspots were frequently associated with areas of known thermokarst, including a lake-thermokarst feature near Fairbanks, AK that was identified in 2018 overflights. Repeat detection during summer 2019 enabled a ground team to locate and confirm the CH₄ hotspot in less than 24 hours. On the ground, enhancements ranging from 50 to 200 ppm CH₄, and diffusive fluxes as high as 65±5 mmol CH₄ m^-2 hr^-1 were observed within the remotely-identified hotspot feature; fluxes which are among the highest non-ebullitive flux magnitudes observed from natural northern wetland systems. Given the widespread detection of similar hotspots across the domain-wide ABoVE survey, this work can dramatically improve understanding of CH₄ emissions associated with thermokarst. These advances represent early steps in revolutionizing remote CH₄ observations at scales simultaneously relevant for process-level understanding of permafrost CH₄ dynamics and regional-scale emission budgeting. This new dataset also provides key scaling metrics for optimizing CH₄ emissions in land surface models and for validating new and upcoming satellite remote sensing approaches.

2020032530 Enakovich, Jessica Gilman (University of New Hampshire, Natural Resources and the Environment, Durham, NH); Hewitt, Rebecca E.; Abbott, Benjamin W.; Barbato, Robyn; Barta, Jiri; Biasi, Christina; Chabot, Chris; Dillon, Megan; Doherty, Stacey Jarvis; Hultman, Jenni; Knoblauch, Christian; Lau, Chui Yim Maggie; Leewis, Mary-Cathrine; Liebner, Susanne; Mackelprang, Rachel; Sullivan, Matt; Onstott, Tullis C.; Rich, Virginia Isabel; Richter, Andreas; Schaedel, Christina; Schuette, Ursel; Siljanen, Henri; Tas, Neslihan; Timling, Ina; Vishnivetskaya, Tatiana A.; Waldrop, Mark P.; Whalen, Emily and Winkel, Matthias. Microbiome re-assembly after permafrost thaw; how time, space, history and disturbance fundamentally differentiate permafrost microbial communities [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41E-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Microorganisms entrained in permafrost sustain life in an environment like no other-frozen, salty, and resource limited. Rapidly increasing arctic temperatures are resulting in permafrost thaw. Permafrost thaw represents a dramatic change in the physical and chemical environment for resident microorganisms, resulting in large shifts in the structure of the microbial communities. Furthermore, permafrost contains vast stores of organic matter that are vulnerable to decomposition following thaw, making the permafrost microbiome an important component of the permafrost-climate feedback. We have assembled the Permafrost Microbiome Working Group-whose expertise spans continents, permafrost-associated systems (pingos to polygons to thermokarst wetlands), and methodology (functional assays to microscopy to meta-omics)-to synthesize the state of knowledge of microbiome "re-assembly" in thawing permafrost. We identified four open research areas to address the role of the permafrost microbiome in the global permafrost-climate feedback: i. Time: Does the time that microbes are entrained in permafrost affect their composition, resources, and response to thaw? Are short-term shifts in microbiome composition and function indicative of long-term responses? ii. Space: Does the spatial architecture of brine channels and cracks in permafrost make it a master variable dictating community structure and response to thaw? iii. History: What methods best address the outsized role of landscape history on permafrost microbiomes? Does the composition of the community entrained in permafrost affect the trajectory of permafrost microbiome re-assembly after thaw? iv. Disturbance: How might microbial responses vary in the face of myriad forms of thaw, such as fire, rapid vertical thaw, rapid lateral thaw (i.e. thermokarst), slow warming, coastal erosion, and so on? Do different disturbance regimes promote a different mix of fungi, bacteria, archaea, and viruses? While a handful of studies have observed changes in permafrost microbial community structure, activity, and function after thaw, no framework has been created to understand-much less predict-how permafrost microbiomes assemble following thaw. framework has been created to understand-much less predict-how permafrost microbiomes assemble following thaw. As such, the permafrost microbiome is a large unknown in the global climate change equation.

2020032622 Erkabu, Bekalu (University of Manitoba, Civil Engineering, Winnipeg, MB, Canada); Maghoul, Pooneh and Hollaender, Hartmut M. Evaluation of permafrost changes due to climate change in northern Manitoba [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H41S-2007, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A critical factor in permafrost degradation are the changes in the hydrological processes which results from free flowing water, such as soil and groundwater, and their associated flow paths. Hydrological models calibrated under current climate conditions are less likely to accurately predict the water budget of a catchment under permafrost degradation in future climate conditions. However, such models are used to manage large watersheds in Northern Canada which are used for hydro power generation. The hydrological models are a key for strategic planning on the future supply of energy. The research was conducted aiming to understand and identify the potential impact of permafrost thawing on the hydrological regime of the Nelson-Churchill River Basin (NCRB) due to climate change. Records for 27 borehole soil temperature data were gathered from Manitoba Hydro's record for Conawapa site, about 13 of the boreholes exhibited continuous records of temperature below 0°C at different depth. A numerical model was developed using HYDRUS-1D, to analyze potential changes in ground temperature due to climate change so that a detailed physical-based understanding of the changes in the active layer is being developed. The calibration process was carried out by comparison of measured and simulated soil temperature parameters using the multi-objective calibration algorithm PA-DDS. Data from two GCMs (Global Circulation Models) namely, CanESM2 (Canadian Center for Climate Modelling Second Generation Earth System Model) and GISS-E2-H (Goddard Institute for Space Studies) were downscaled and used to analyze potential changes due to climate change in the future. Two climate change scenarios (RCP8.5 and RCP4.5) were selected to predict the impact for the future on the soil temperature and therefore, on the stability of permafrost. The results show that the permafrost was more or less stable in the past but that it will degrade with time due to the increasing temperatures. A critical parameter in the evaluation is the impact of an organic layer at the surface. We found substantial differences in locations with and without peat coverage.

2020032595 Evans, Sarah G. (Appalachian State University, Department of Geological and Environmental Sciences, Boone, NC); Yokeley, Brandon and Stephens, Connor. Potential mechanistic causes of increased baseflow across northern Eurasia rivers underlain by permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1365, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Warming in the Arctic is occurring at twice the rate of the global average, resulting in permafrost thaw and a restructuring of the Arctic hydrologic cycle as indicated by increased river discharge. In these cold regions, warming increases active layer depths, which is postulated to increase groundwater discharge to streams, or baseflow, through either: (a) increases in subsurface transmissivity, if the water table elevation is maintained in the thickening active layer, or (b) long-term increases in regional groundwater circulation due to extensive permafrost loss over decades. While increasing baseflow has been observed throughout northern Eurasia, the mechanistic causes remain elusive. n this study, we estimate changes in baseflow in concert with changes in active layer thickness by computing minimum stream discharge and performing a baseflow recession analysis using daily streamflow records from 1912-2002 for 139 stations in northern Eurasia underlain by varying permafrost types. Results indicate that there is an increase in baseflow from 1912 to 2002 for the low-flow months of September and October across all permafrost types. However, areas underlain by continuous permafrost have positive recession flow intercepts (a proxy for increasing active layer thickness) while areas underlain by discontinuous, sporadic, isolated, and no permafrost have negative recession flow intercepts, indicating confounding changes in aquifer thicknesses. This may indicate that in regions underlain by continuous permafrost, active layer thickening correlates with increases in baseflow whereas in other permafrost regions, increases in baseflow may be caused by wholesale permafrost loss and enhanced regional groundwater circulation. The results of this work may inform our understanding of the changing Arctic hydrologic cycle which influences terrestrial and aquatic responses to warming temperatures throughout the Arctic.

2020032540 Ewing, Stephanie A. (Montana State University, Department of Land Resources and Environmental Sciences, Bozeman, MT); Wologo, Ethan; O'Donnell, Jonathan A.; Paces, James B.; Striegl, Robert G.; Froese, Duane G. and Koch, Joshua. Groundwater connection and DOC transport in the Yukon River basin inferred from uranium and strontium isotopes in permafrost catchments [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw is expected to result in both profound ecological change and a large positive feedback to Earth's warming climate through release of carbon to the atmosphere. This feedback will be mediated in part by mobilization of C by liquid water. Here we use ²³⁴U/²³⁸U activity ratios ([²³⁴U/²³⁸U]) and ⁸⁷Sr/⁸⁶Sr ratios with measures of dissolved organic carbon (DOC) as tracers of groundwater-surface water connection in permafrost landscapes now subject to thaw. We focus on the largely unglaciated region of interior Alaska and western Yukon Territory, where Holocene to middle Pleistocene reworked loess deposits can influence freezing dynamics of regolith overlying bedrock. In stream and river samples collected over a 10-year period (2008-2018), we observe elevated DOC concentrations (~10-40 mg C L^-1) in intermediate watersheds with thick ice-rich loess deposits influenced by recent thaw. In surface waters draining loess-mantled areas, [²³⁴U/²³⁸U] values are higher (average 1.3) than meteoric values (<1.1). Elevated [²³⁴U/²³⁸U] values (~1.5-3.0) likely reflect contributions from more deeply circulating groundwater in low-order streams draining areas with limited loess cover or pronounced disturbance (wildfire, mining), and in higher-order streams across the region. Drainages underlain by older schist confer higher ⁸⁷Sr/⁸⁶Sr values (~0.740) to surface water. Elsewhere, we observed lower ⁸⁷Sr/⁸⁶Sr values (~0.707-0.712) in streams draining frozen silts, reflecting mixtures of locally- to regionally-derived eolian materials, and higher ⁸⁷Sr/⁸⁶Sr values (~0.713-0.715) in higher-order and gravel-bedded streams, indicating connection to deeper groundwater from older rock units. Ultimately the U and Sr isotopic signals in surface waters across the Yukon River Basin vary systematically as a function of lithologic substrate and permafrost thaw dynamics associated with surface disturbance. Lower concentrations (~1-10 mg C L^-1) of less aromatic DOC in higher order tributaries reflect enhanced connections to sub-permafrost groundwater with older DOC, rather than release of aged, labile DOC from recent permafrost thaw. Our results suggest a transient feedback response to thaw, with a magnitude set by geomorphic response times to warming temperatures, fire, and human activity.

2020032567 Fahnestock, Maria Florencia (University of New Hampshire, Department of Earth Sciences, Durham, NH); Bryce, Julia G.; Driscoll, Charles T.; Garvey, Brendan; Rich, Virginia Isabel and Varner, Ruth K. Mercury isotopic constraints on mercury cycling across a permafrost thaw gradient in Stordalen Mire, Sweden [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51I-2354, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Warming global temperatures, particularly in the Arctic, are accelerating permafrost thaw and releasing previously sequestered mercury (Hg). Limited constraints on the size of Arctic terrestrial Hg pools, coupled with uncertainties in our knowledge of the responses of ecosystem Hg dynamics to climate change, complicate long-term forecasts of Hg impacts on ecosystem health and adaptability. Isotopes of Hg afford a means of deciphering the major pathways controlling elemental biogeochemical cycling and may provide insight into key mechanisms controlling Hg cycling across the permafrost thaw gradient. Stordalen Mire in Abisko, Sweden (68°21'N, 19°02'E) a thawing peatland, contains a permafrost thaw sequence represented by three habitats across the mire including: (i) permafrost-dominated, well-drained palsas occupied by Betula Nana, Eriophorum Vaginatum, Rubus Chamaemorus and Empetrum hermaphroditum, (ii) Sphagnum spp.-dominated semi-thawed sites with variable water table depths, and (iii) fully thawed fen sites containing vegetation dominated by Eriophorum angustifolium. Three lake sites, chosen for their varying total Hg contents and proximity to the thawing mire sites, include: Villasjon <1.5 m water depth), Mellarsta Harrsjon a stream-fed lake (max depth <7 m), and Inre Harrsjon, connected to Mellarsta Harrsjon, (max depth <5 m). Mercury isotope results from peat and lake sediment cores showed both variations in mass-dependent fractionation given by d²⁰²Hg and in mass independent fractionation given by D²⁰¹Hg and D¹⁹⁹Hg across all sites and varying with depth. The d²⁰²Hg values for all samples ranged from -2.22 ppm to -0.65 ppm and D¹⁹⁹Hg varied from -0.58 ppm to 0.09 ppm. Several sites showed a marked decrease in D¹⁹⁹Hg with depth. The D¹⁹⁹Hg/D²⁰¹Hg of 1.34 for lake sediments from the shallow lake Villasjon, together with low surface water methyl Hg contents, suggest that the paired chemical signatures may be explained by photochemical demethylation of MeHg being an important control on Hg cycling in this lake but less so for the other two lakes in this study.

2020032676 Farquharson, Louise M. (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, Vladimir E.; Jones, Benjamin M.; Grosse, Guido; Sergeev, Dmitry and Xiao, Ming. Importance of cross-border team science in permafrost research for risk mitigation [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA24A-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost degradation has already begun to cause damage to infrastructure across the Pan-Arctic and is increasing the potential for climate change related disasters for numerous Arctic nations. Permafrost degradation can pose a risk to the stability and function of Arctic infrastructure in three key ways: 1) where ground-ice is present, permafrost degradation will initiate thermokarst development causing the ground surface to subside, 2) in coastal regions permafrost degradation can increase the rate of coastal erosion and lead to more impactful storm surges, and 3) an increase in ground temperature can change the structural integrity and cohesiveness of the underlying ground surface leading to lateral and vertical ground movement, and a decrease in infrastructure foundation bearing capacity. In addition, recent infrastructure development and associated construction in northern regions has caused disturbance to the ground thermal regime. The combined effects of permafrost degradation from climate warming across the Arctic is likely to cause damage to and the loss of infrastructure critical to the function of Arctic industry and communities. As such, permafrost degradation-related disaster poses a major threat to national and international security across the Pan-Arctic. Successful preparation, response, recovery, and mitigation from permafrost-related disasters will require coordinated cross-border disaster diplomacy efforts and effective dissemination of findings. Critical to these efforts is the co-production of knowledge with indigenous communities and the development of cross-border research and monitoring networks that involve collaborators from a wide-range of backgrounds. We present several examples of such collaborative efforts including: an emerging international network of networks focused on better understanding permafrost affected coastal change across the pan-Arctic; the formation of transdisciplinary research teams involving scientists, stakeholders, community members, and policy makers, to prevent and mitigate permafrost-related disasters in northern communities; the development of a pan-Arctic long-term permafrost monitoring network; and the effective distribution of urgent permafrost research tasks across international multi-institutional teams.

2020027643 Farquharson, Louise M. (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, Vladimir E.; Kholodov, Alexander L.; Nicolsky, Dmitriy; Cable, William; Walker, Donald A. and Kokelj, Steven V. Long-term monitoring of permafrost degradation documents two forms of landscape response [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost temperatures across the sub-Arctic and Arctic are increasing, in some regions by as much as 1°C per decade. Long-term monitoring at sites across Alaska and northern Canada highlight two key mechanisms of permafrost degradation: thermokarst development and talik development. A comparison between the Canadian High-Arctic (~80°N) and Interior of Alaska (~60°N) show that the geomorphological impact of permafrost degradation varies primarily due to differences in summer and winter heat flux, ecosystem conditions, and ground ice distribution. At three High-Arctic monitoring sites in the Canadian Archipelago, ground ice lies close to the surface and there is limited ecosystem protection. The mean annual ground temperature at 1 m depth is near -13°C. Between 2003 and 2016 we observed thawing degree days up to 240% above historical normals. This caused an increase in depth of thaw, ground ice melting, and up to 0.9 m of subsidence over a few years. In the sub-Arctic, across the Seward Peninsula and Interior Alaska, we have observed the initial stages of talik development at over 20 monitoring sites spanning the distance over 1000 km. These sites are characterized by warm permafrost where the mean annual ground temperature ranges from -1 to -0.3° C. At these sites, an increase in thaw depth caused by combined effect of increasing of air temperature and heavy winter snow fall has, in some years, led to incomplete freeze up and the intermittent formation of a talik. Despite our observations being associated with specific locations, both mechanisms described can occur across a range of environmental settings as well as at similar latitudes. The physical, hydrological and geochemical consequences of the two processes we observe have drastically different implications for infrastructure and natural environment.

2020027693 Fedorova, Irina (Saint Petersburg State University, Saint Petersburg, Russian Federation); Shestakova, Elena; Bobrov, Nikita; Guzeva, Alina; Alekseeva, Nataliya; Pashovkina, Anastasiya and Dvornikov, Yury A. Adaptation of the Arctic limnosystems to the climate change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC11L-1101, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Under current rapid climate change in the Arctic, especially lakes have important parameters for the ecosystems safety. Hydrological regime of a lacustrine catchment mostly is a result of talik-lake body thermic and water interaction. Flat big lake can form a new hydrographical system consisting of small lakes chain. The level of initial lake surface can be declined by thermokarst cracks; but during long time water income will be saved due to thawing permafrost and ground water inflow. Talik stores a sufficient water temperature of deep lake layers for ecosystems. So, in lakes of the Lena River delta the water temperature under 2 meters of ice thickness was 0,1-2°C and reached 23°C in summer, although hydrochemical parameters changed in a big value especially in winter. DOC, that is significant for the limnosystems, values from 4.6 to 33.7 mg/l under ice and 3.5-6.6--in summer. aCDOM(440) in April 2018 differs in the rate of 0.91-11.16 nm^-1 in winter and 0.42-5.12--in summer. Electrical conductivity of water had value from 23 to 120 mS/cm--in summer and 140-277--in winter. Radio dating of the top layer of lacustrine sediments gives age 2810±240 cal. kyr BP on the 35 cm of core of thermokarst lake in the Lena River delta; the deposition rate is 0.13 mm per year. The Yamal Lake had quick deposition rate of sediments: the age 145.64 ± 9.98 years (²¹⁰Pb) was on the 14 cm of a core; a deposition rate--0.89 ± 0.06 mm/year. Talik depth is about 25 m under Yakutian Lake and 10 m--under Yamal Lake. Therefore, in consideration of the dating and deposition rate results talik can be recognized as one of the main factors of a high resilience of Arctic lakes and is a buffer of an ecosystem: it saves a lake thermic regime, biogeochemical elements exchange as well as water income. The projects have been supported by RFBR 18-05-60291 and 19-05-00683, Resource educational center Chemistry and Scientific program 1 of SPBU. DOC, CDOM, nutrience analyses were done in OSL AARI.

2020032606 Feng Min (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China); Xu Jinhao; Wang Jianbang; Ran Youhua and Li Xin. Identifying rock glacier in western China using deep learning and satellite data [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC53G-1249, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A rock glacier is a geomorphological landform composed of rock fragments that move slowly down a mountain as a result of gravity. Rock glaciers play an important role in the high-altitude mountain regions. They serve as a transport mechanism and a sink for material and were found to be an indicator of climate changes. Investigating the distribution of rock glaciers is of great significance for assessing the hydrological contribution of permafrost regions and studying their response to climate change.A rock glacier is a geomorphological landform composed of rock fragments that move slowly down a mountain as a result of gravity. Rock glaciers play an important role in the high-altitude mountain regions. They serve as a transport mechanism and a sink for material and were found to be an indicator of climate changes. Investigating the distribution of rock glaciers is of great significance for assessing the hydrological contribution of permafrost regions and studying their response to climate change. However, the identification of rock glacier is extremely challenging. Earlier studies concluded that it is not possible to separate the origin of rock glaciers into purely glacial or periglacial without taking into account the permafrost-glacier interactions that explain these landforms. The ground survey has been the main approach for identifying rock glacier, but it is costly, time-consuming, and difficult to cover a large area. Due to the similarity between rock glacier and its surroundings in spectral surface reflectance and its relatively small spatial extent, the identification of rock glacier from satellite data mainly relied on human interpretation of high-resolution satellite images, and lack of capability on automated rock glacier identification from satellite data.However, the identification of rock glacier is extremely challenging. Earlier studies concluded that it is not possible to separate the origin of rock glaciers into purely glacial or periglacial without taking into account the permafrost-glacier interactions that explain these landforms. The ground survey has been the main approach for identifying rock glacier, but it is costly, time-consuming, and difficult to cover a large area. Due to the similarity between rock glacier and its surroundings in spectral surface reflectance and its relatively small spatial extent, the identification of rock glacier from satellite data mainly relied on human interpretation of high-resolution satellite images, and lack of capability on automated rock glacier identification from satellite data. The deep learning methods, e.g., Convolutional Neural Networks (CNN), has been developed recently to provide the capability of recognizing object structure characteristics. We have developed an approach for identifying rock glacier in high-resolution satellite images by integrating deep learning methods. Other datasets, such as terrain variables, surface temperature, and existing glacier extent maps, have been included in the approach for detecting possible rock glacier activity areas. The pilot study has been carried out in northern Qilian and Nyainqentanglha Mountains in China. More than 200 samples for both positive and negative groups were created and applied for building the VGG and ResNet network models. The preliminary validation indicates that the accuracy is >80%, suggesting a promising approach for rock glacier identification. Several satellite datasets (e.g., GaoFen, Quickbird, Sentinel-2, and Landsat) have also been applied to evaluate the sensitivity of the method to the spatial resolutions of the satellite data. The deep learning methods, e.g., Convolutional Neural Networks (CNN), has been developed recently to provide the capability of recognizing object structure characteristics. We have developed an approach for identifying rock glacier in high-resolution satellite images by integrating deep learning methods. Other datasets, such as terrain variables, surface temperature, and existing glacier extent maps, have been included in the approach for detecting possible rock glacier activity areas. The pilot study has been carried out in northern Qilian and Nyainqentanglha Mountains in China. More than 200 samples for both positive and negative groups were created and applied for building the VGG and ResNet network models. The preliminary validation indicates that the accuracy is >80%, suggesting a promising approach for rock glacier identification. Several satellite datasets (e.g., GaoFen, Quickbird, Sentinel-2, and Landsat) have also been applied to evaluate the sensitivity of the method to the spatial resolutions of the satellite data.

2020032492 Finkelstein, Sarah A. (University of Toronto, Department of Earth Sciences, Toronto, ON, Canada); Packalen, Maara S.; McLaughlin, James; Davies, Marissa A.; Bysouth, David and Da Silva, Kristina. Stability of fen and bog peatland types over the Holocene Epoch in the Hudson Bay Lowlands, Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23L-2504, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Hudson Bay Lowlands (HBL) is a vast continuous peatland in northern Canada, some of which occurs as discontinuous and continuous permafrost peat. The landscape is a mosaic of mostly bogs and fens, with more limited swamp, marsh, forest and open water. Owing to rapid rates of isostatic uplift, younger peats are found closer to the coasts of Hudson and James Bays, with fen-type peatlands somewhat more prevalent on these younger surfaces. More than 30 Pg of carbon have accumulated in the HBL over the Holocene. The rates of Holocene carbon accumulation vary considerably both spatially and temporally, with some sites showing more rapid rates of carbon accumulation in the first two to three millennia following peatland initiation. We evaluate here the hypothesis that vegetation changes over the course of the Holocene, including fen-to-bog transitions, partially explain the variability in carbon accumulation. We find that in some cases, more rapid rates of C accumulation in the middle Holocene (5000-8000 yrs before present) are associated with early successional minerotrophic fens with higher carbon densities. Fen-to-bog transitions are recorded in many peat cores collected from present day bogs; however, these transitions are time transgressive, and can depend on the time since initiation, suggesting that climate changes may play a secondary role, relative to hydrological changes and local ecological processes. Fens are highly prevalent in the HBL landscape (accounting for about 38% of land cover). Cores taken from present day fens and analyzed for carbon accumulation and vegetation change indicate that many fen sites have remained fens since peat initiation. Variability in rates of Holocene carbon accumulation within fen records which have not been subject to any major vegetation change may more closely reflect climate drivers.

2020032480 Franssen, Jan (University of Montreal, Geography, Montreal, QC, Canada); Chiasson-Poirier, Gabriel; Lafreniere, Melissa J.; Fortier, Daniel and Lamoureux, Scott F. Seasonal evolution of active-layer thaw depth and streamflow chemistry in a permafrost catchment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2535, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In permafrost environments, hillslope and catchment scale hydrological and biogeochemical dynamics remain difficult to predict due to uncertainties about the spatiotemporal patterns of active layer thaw. The extent of active-layer thaw varies spatially and temporally in response to atmospheric and environmental conditions and as a function of the physical characteristics of the surface and shallow subsurface. Here we present the results of a hillslope and subcatchment scale study aimed at advancing our understanding of permafrost hillslope drainage dynamics and its influence on streamflow hydrochemistry. We instrumented a hillslope-stream sequence located in the headwaters of the Niaqunguk River watershed, Nunavut, Canada (63°N, 68°W), and combined high spatial resolution field measurements of water and frost tables across the hillslope with semi-weekly measurements of groundwater and streamflow chemistry to track the evolution of surface and subsurface water chemistry during active layer thaw. Interestingly, localized differential thaw patterns emerged under near saturation conditions across the instrumented hillslope; the result of historically high summer rainfall. Hillslope structure and uneven active layer thaw created two distinct fill-and-spill domains. A subsurface-domain defined by frost table microtopography and a surface-domain defined by surface topography. Immediately downstream of the hillslope we observed a seasonal shift in streamflow chemistry with an increased influence of water flowing through the underlying mineral soils as that active layer thawed. As thaw progressed streamflow chemistry began to most closely match that of the riparian groundwater; a mixture of hillslope surface and subsurface water. Hillslope-stream surface connections were punctual and occurred when rainfall, and saturation conditions across the lower portion of the hillslope, were sufficient for water to spill out of mid-slope surface depressions and across a saturated riparian zone and into the stream. Our research shows how hillslope structure and thaw processes influence hillslope-stream connectivity and streamflow chemistry in permafrost environments.

2020027625 Fraser, Rob (Natural Resources Canada, Ottawa, ON, Canada); Kokelj, Steve; McFarlane-Winchester, Morgan; Lantz, Trevor C. and Olthof, Ian. Recent thaw and ponding of upland ice-wedge polygons across the Canadian Arctic Archipelago [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1379, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wedge ice is the most widespread ground ice type in Arctic permafrost. Tundra polygons are the surface manifestation of underlying ice-wedge networks, which develop over millennia due to thermal contraction cracking of the ground and infilling by snowmelt. Wedge ice is often encountered at the top of permafrost, so near-surface thawing can result in subsidence of the terrain surface, ponding, and the development of high centered polygons. Local-scale observations and high resolution remote sensing have demonstrated that recent ice-wedge thaw is a pan-Arctic phenomenon. In our analysis, we used a combination of the 1985-2017 Landsat satellite image archive, high resolution WorldView satellite images, historical air photos, detailed digital elevation models, and field surveys to show that upland ice-wedge thermokarst has been extensive over a 419 000 km² region within the Canadian Arctic Archipelago. We show that newly formed ice-wedge melt ponds are larger (avg. ~ 100 m²) and more widespread than those previously characterized in most other Arctic regions, which have resulted from several anomalously warm summers since 1998. We also observed that upland polygonal terrain in the lower Arctic, NWT and Yukon coastlands has shown more limited ice-wedge ponding over the same period under similar warming. The contrasting landscape responses highlight the inherent sensitivity of higher Arctic, formerly glaciated permafrost environments with high massive ground ice content that is being truncated by an active layer lacking ecosystem protection from summer warming. Increasing evidence suggests that ongoing temperatures increases are likely to most rapidly alter these landscapes.

2020027688 Fratkin, Mulu M. (Los Alamos National Laboratory, Los Alamos, NM); Rowland, Joel C.; Del Vecchio, Joanmarie; Lathrop, Emma; Piliouras, Anastasia; Schwenk, Jon and Shelef, Eitan. The distribution and occurrence of solifluction lobes and their role in mediating hillslope biogeochemistry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP43E-2406, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Solifluction lobes, the downslope transport of soil in discrete lobes, are ubiquitous features of periglacial and alpine landscapes throughout the world. From the fjords of Norway to the Alaskan Arctic, the creep of soil driven by freezing and thawing cycles creates patterned roughness elements that can dominant entire hill-slopes. The impact of solifluction on the microtopography of hillslopes can result in feedbacks between vegetation, snow-cover, and hillslope hydrology. The formation of lobes can also act to redistribute carbon by continually burying vegetation, altering flow pathways, and transporting organic rich mats of sediment towards colluvial hollows and valley bottoms. However, the occurrence of solifluction is highly sporadic due to the strong dependencies on local climate, geology, and hydrology conditions. In this study we investigate solifluction at the regional and hillslope scale. At the regional-scale we seek to understand the controls on the occurrence and spatial variations in the morphology and patterns of lobes. For this analysis, we used the readily-available high resolution (1m) LiDAR derived digital terrain models of Norway. Spectral analysis of the DTM allowed us to quantify the spacing and orientation of lobes. On the Seward Peninsula, AK, we used hillslope-scale field observations, soil and water samples, and UAS-derived imagery and topographic data to investigate the role of solifluction lobes in soil organic carbon storage, soil moisture distributions, local variations in active layer geochemistry, and shrub distributions. Across the southern Seward Peninsula, there is a strong association with shrub occurrence and soliflucation lobes. Through our field studies, we seek to understand whether and how solifluction lobes may facilitate and potentially accelerate shrub expansion on Arctic hillslopes. By connecting the hillslope-scale work with the regional-scale analysis we seek to better estimate where in the Arctic landscape shrub expansion may be strongly associated with hillslope microtopography.

2020027630 Frauenfeld, Oliver W. (Texas A&M University, College Station, TX); Peng, X. and Zhang, T. New estimates of future permafrost extent and corresponding carbon feedbacks [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1385, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Approximately 24% of the Northern Hemisphere's exposed land surface is currently underlain by permafrost. These permafrost environments in the high latitudes and altitudes are also experiencing amplified climate warming, leading to the degradation of frozen ground. Loss of permafrost not only impacts ecosystems, hydrology, and infrastructure, but it can also lead to positive climate feedbacks due to the release of large amounts of greenhouse gases to the atmosphere. Depending on the anthropogenic forcing scenario, directly diagnosed projections from earth system models indicate a 37-80% reduction in the area of permafrost near the surface by the end of the 21st century. Given this extremely large range and potential model shortcomings, we instead derive future permafrost extent based on active layer thicknesses calculated using air temperature projections combined with the Stephan equation and gridded edaphic factors. Rather than an 80% decrease, we find that the most drastic anthropogenic forcing scenario results in only a 14% reduction in near-surface (3.5 m depth) permafrost area extent, and a reduction of only 1.3% at a depth of 6.0 m. Depending on the forcing scenario, the corresponding carbon release from this permafrost degradation ranges 10.2-22.4 Pg C by the year 2040 and 88.7-140.5 Pg C by 2100, which is approximately 1.2%-7.5% of the total soil organic carbon pool. Our findings therefore suggest a substantially smaller 21st century reduction in near-surface permafrost area than directly diagnosed by climate models, with a correspondingly smaller permafrost carbon feedback.

2020027656 Frost, Gerald V. (Alaska Biological Research, Fairbanks, AK); Saperstein, Lisa B.; Loehman, Rachel; Schaefer, Kevin M.; Michaelides, Roger J.; Macander, Matthew J. and Dissing, Dorte. Does tundra fire accelerate drainage of lakes in discontinuous permafrost? Evidence from the Yukon-Kuskokwim Delta, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Alaska's Yukon-Kuskokwim Delta (YKD) is one of the warmest parts of the Arctic tundra biome and YKD upland landscapes experience an active tundra fire regime. Permafrost is currently widespread and strongly influences terrestrial and aquatic landscape properties, but is sensitive to climate change and disturbance because ground temperatures are near freezing. Here we combine field-based and remotely sensed metrics to determine patterns of correspondence between pond drainage and tundra fire history in the YKD's Izaviknek-Kingaglia Uplands (IKU), where the landscape is studded with ponds with small catchments. Extensive fires occurred in the IKU in 1971-1972, 1985, 2006-2007, and 2015. Over the period 1975-2014, pond extent has decreased by ~12% in unburned uplands, consistent with changes elsewhere in the discontinuous permafrost zone. Surface water decreases over this period were similar in recent burn scars (2015, 2005-2007), but decreased 22-58% in historical burns (1985, 1971-1972, 1953). Analysis of seasonal water frequency products (e.g., USGS Dynamic Surface Water Extent) indicate that changes relate to persistent terrestrial-aquatic transitions rather than seasonal water frequency. These observations, coupled with field measurements of tundra active-layer thickness (ALT) and modeling of ALT using Synthetic Aperture Radar (SAR) and ground penetrating radar (GPR) indicate similar time lags (~30 years) between peak ALT and pond drainage rates post-fire. The correspondence in timing suggests that progressive increase in active-layer thickness impacts pond water balance, likely through increased hydrologic connectivity and seepage into thickened active layers. Although tundra vegetation recovers after fire relatively quickly, secondary impacts of fire related to aquatic-terrestrial habitat transitions represent permanent changes with broad implications for fish and wildlife on the YKD. Counterintuitively, the most dramatic impacts of tundra fire in this region appear to be related to aquatic rather than terrestrial ecosystems.

2020027682 Fuchs, Matthias (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Sachs, Torsten; Hugelius, Gustaf; Frost, Gerald; Grigoriev, Mikhail; Jones, Benjamin M.; Nitze, Ingmar; Palmtag, Juri; Overduin, Pier P.; Ping, Chien-Lu; Rivkina, Elizaveta; Schirrmeister, Lutz; Schwamborn, Georg; Siewert, Mattias B.; Strauss, Jens; Veremeeva, Alexandra; Zubrzycki, Sebastian and Grosse, Guido. Arctic deltas; carbon and nitrogen rich deposits in a dynamic permafrost landscape [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP32A-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic river deltas are sensitive polar landscapes at the land-ocean interface. In contrast to lower latitude deltas, Arctic deltas are characterized by low temperatures, a strong seasonality and the presence of permafrost. Seasonal freezing conditions and underlying permafrost hinders runoff for most of the year and leads to typical land forms such as ice wedge polygons, frost mounds and thermokarst lakes. However, compared to other permafrost dominated landscapes, Arctic deltas are more dynamic. The surface morphology is changing constantly due to river ice break up and subsequent spring flooding, coastal and shoreline erosion, thaw slumping, and degradation of ice rich deposits. Deltaic sediments also tend to be highly susceptible to ground-ice aggradation, making them more ice-rich than adjacent nondeltaic landscapes. In addition, Arctic deltas will be severely affected by global climate change through sea level rise, lengthened thaw season, changing river discharge, storm surge flooding and thawing permafrost. We are therefore at risk, to face reactivation of millennia-old soil carbon and nitrogen deposits by the degradation of previously permanently frozen river delta deposits. However, there is a lack of studies on Arctic deltas and only very coarse estimates on Arctic delta carbon and nitrogen stocks exist. Here we present a new data-set of 140 soil cores, including more than 1400 samples from 17 different deltas spread across the Arctic. We combine new and legacy soil core data to estimate for the first time pan-Arctic deltaic carbon and nitrogen stocks and close a knowledge gap for deep permafrost stock estimations. We found that Arctic deltas present a significant pool for organic carbon and nitrogen, thus their change poses risks far beyond the Arctic. Permafrost thaw in such dynamic landscapes will increase nutrient transport from land to ocean with implications on Arctic near-shore zones (e.g. affecting foodwebs and biogeochemical processes) as well as increased greenhouse gas release due to large amounts of carbon and nitrogen becoming available from previously frozen ground. Our study highlights the need to better understand dynamic processes in Arctic deltas, since these vulnerable carbon and nitrogen rich deposits will be severely affected by the effects of global climate change.

2020027616 Furuya, Masato (Hokkaido University, Sapporo, Japan); Yanagiya, Kazuki; Iwahana, Go and Fedorov, Alexander. Post-wildfire surface deformation at Batagay, eastern Siberia; detection by L- and C-band InSAR and preliminary report of field observations [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1370, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Thawing permafrost may release soil organic carbon as greenhouse gases, which can lead to further global warming through positive feedback (Shuur et al. 2015). To estimate terrestrial carbon budget precisely, permafrost degradation should be monitored in the entire circumpolar region. However, it is impractical to perform field observations over all the permafrost areas. Therefore, remote sensing techniques to cover wide areas are indispensable. Observing thaw-induced ground subsidence by InSAR (Interferometric Synthetic Aperture Radar) can tell us the state of permafrost with high spatiotemporal resolution. Some previous studies have been conducted in a part of Alaska, Canada and lowland Siberia where it is relatively easy to compare with field observations (Liu et al. 2010; Short et al. 2011; Iwahana et al. 2016; Antonova et al. 2018). We focused on Eastern Siberia, where no previous studies by InSAR were conducted. Our study area is around Batagay town (67'39N, 134'39E), Sakha Republic, Russia. At ~10 km southeast of Batagay, there is a well-known and one of the largest slump terrain caused by thawing of permafrost (Murton et al. 2017). Processing ALOS and ALOS2 InSAR images, we detected deformation signals due to a wildfire occurred in 2014 at the hill to the 20 km northwest of Batagay. Loss of surficial vegetation layer by wildfire accelerates permafrost thawing, and the degradation continues for several years to decades after a fire (Yoshikawa et al. 2002). Furthermore, given the fact that the frequency and intensity of wildfires are increasing in the Arctic region with global warming (Alexander et al. 2018; Gibson et al. 2018; Masrur et al. 2018), it is important to reveal the spatiotemporal variation of the ground deformation in the post-wildfire area. Besides L-band ALOS2 SAR images, we also used C-band Sentinel-1 images to examine short-term deformation. Seasonal deformation from 2017 to 2018 is detected from both satellites data, whose magnitude and spatial patterns of subsidence and uplift were consistent in both satellites. In particular, Sentinel-1 short-term InSAR images revealed detailed temporal changes from the start of thawing to the end of freezing. Long-term deformation was detected by ALOS2 data. Although some data were affected by ionospheric and topography-correlated tropospheric phase delay, we corrected them by removing long-wavelength phase trend and fitting with DEM on the assumption that the deformation signal over the post-wildfire area is uncorrelated with other noises. The results indicated that thawing subsidence reached up to 15cm in the satellite line of sight direction and were continuing even 2-3 years after the fire. InSAR-based quality deformation maps can contribute to our understanding of thermokarst processes. In September 2019, we will perform our first field-observations at the post-wildfire area. A part of the InSAR data reveal some incoherent pixels over the post-wildfire area, which are systematically distributed along the slope of nearly identical elevations. As those incoherent pixels could represent active-layer detachment or some other thermokarst processes, we plan to confirm what's going on in the field.

2020032468 Gehlot, Swati (Max Planck Institute for Meteorology, Hamburg, Germany); Hagemann, Stefan and Brovkin, Victor. Modelling lateral transport of riverine organic carbon as a link of terrestrial carbon and hydrology within MPI-ESM [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B21G-2420, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The current state of the art Earth System Models (ESMs) do not consider the effects of lateral transport of terrestrial carbon to oceans via the global river network, and hence the carbon cycle is primarily evaluated based only on vertical gas exchange processes between atmosphere and land. Particularly in high latitudes, the interaction between permafrost and lateral hydrology is a substantial factor impacting the organic carbon inflow to the Arctic Ocean and its associated atmospheric exchange. With this study, we aim to quantify the lateral riverine transport (dissolved organic matter or DOM) of terrestrial origin to the oceans using the hydrological discharge scheme (HD Model) of MPI-ESM (Max-Planck Institute for Meteorology Earth System Model). The transported DOM is comprised of slow and fast decaying litter as well as the water soluble organic carbon. The terrestrial carbon source is based on the JSBACH land surface model including the YASSO soil carbon scheme. The water-soluble fraction of the soil carbon pools is attributed to DOM flushing into the rivers via runoff (fast carbon pool, above ground) and base-flow (slow carbon pool, below ground). Additionally, the carbon flux from vegetation to litter (green and woody litter) is considered also as riverine DOM component along with the water-soluble carbon contributing to the surface runoff. The HD model, which simulates the river discharge for all land areas at a resolution of 0.5 degree, is extended with the DOM transport scheme as passive/active tracer. The carbon source is transported as a tracer following the flow properties of rivers depending on terrain slope and reservoir storage. The fraction of available soil carbon (water-soluble and litter) as a source for transport into the river stream is evaluated by model sensitivity tests in comparison to observations and previous studies over selected river basins. The simulation of carbon transfers along the terrestrial-aquatic continuum in high-latitudes will be evaluated based on observations (Arctic Great Rivers Observatory data) as well as on similar studies by other ESMs.

2020032476 Genet, Helene (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Jorgenson, Torre; Douglas, Thomas A.; Greaves, Heather; Hiemstra, Christopher A.; Marcot, Bruce G. and Turetsky, Merriee R. Assessing land cover change and lowland vulnerability to permafrost thaw, altered fire regime, and hydrologic changes on interior Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23H-2519, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate warming and altered precipitation and fire regimes are driving rapid permafrost degradation, especially in the discontinuous permafrost zone of boreal Alaska. Abrupt thaw of ice-rich permafrost can trigger ground subsidence and thermokarst disturbance resulting in landscape transition with dramatic ecological consequences for permafrost stability, vegetation composition, wetland distribution, and local hydrology. We developed a state and transition model with the goal to assess historical and projected vulnerability to land cover change in boreal Alaska in response to climate change, permafrost thaw and altered disturbance regimes. To inform this spatially and temporally explicit model, we synthesized field observations (including regional survey of land cover and permafrost characteristics in burned and unburned sites) and remote sensing data (including repeated imagery analysis) documenting 60 years of land cover change and permafrost dynamic in the Tanana Flats, a major lowland complex in boreal Alaska. This model was then applied to assess land cover dynamic from 2000 to 2050 at a 30 m resolution. Preliminary results from these simulations suggest that wildfire, paludification, and thermokarst are the main drivers of land cover change across lowland landscape in boreal Alaska, affecting a total of 32%, 16% and 15% of the landscape respectively between 2000 and 2050. Altered disturbance regimes in lowland complexes in boreal Alaska are likely to result in an increase in wetlands extent in the first half of the 21st century. These changes in land cover will result in shifts in abundance and distributions of habitats for most wildlife species of the region.

2020032458 Genovese, Vanessa B. (California State University Monterey Bay, Seaside, CA); Matthews, Elaine and Johnson, Matthew S. New global datasets for methane modeling; natural wetlands, lakes and reservoirs [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13J-2420, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Natural wetlands, lakes and reservoirs (WLR) are the major natural sources of global methane (CH4) emissions. Most methane emission models are applied to externally-defined distributions of these sources. To define wetlands, current methane models rely on surface inundation data which captures not only flooded wetlands but also lakes and other surface-waters while missing non-flooded wetlands. It has been shown that methane emissions vary between these different sources as well as among the sources with different characteristics. For example, observations confirm that per unit area CH4 fluxes are higher in carex-dominated wetlands than in shrub tundra, and higher for small, shallow lakes than for large, deep lakes. However, often lake and reservoir datasets are incomplete, do not include depth information and ignore small lakes which we estimate may add 40% to the total global lake area. In addition, few CH4 models include wetland or lake types consistent with those represented in the flux literature which makes validation difficult. These findings confirm the critical need for source data that describe CH4-relevant classes within WLRs, in addition to accurate and mutually exclusive spatial distributions of each source. We have developed new spatially explicit 0.25° global datasets of natural wetlands, lakes and reservoirs critical to methane emission models. For each new dataset, we developed and applied hierarchical methane-centric classification systems: wetland criteria include vegetation, flooding/non-flooding, permafrost state, and soil organic carbon content; lake and reservoir criteria comprise permafrost state, ground-ice content, organic substrate, size and depth. Each source-specific classification yielded classes that can be used to stratify the methane-flux measurements thus enabling all flux measurements to be used for model development and evaluation. Our new suite of data constitutes a unique framework for modeling methane emissions by identifying methane-relevant WLR types and creating mutually exclusive datasets enabling emissions from each source to be modeled and evaluated individually and in combination.

2020032551 Genxu Wang (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Song Chunlin; Mao Tianxu; Huang Kewei; Sun Xiangyang; Hu Zhaoyong; Chang Ruiying; Chen Xiaopeng and Raymond, Peter A. DIC spatiotemporal variability and sources in permafrost catchments of the Yangtze River source region; insights from stable carbon isotope and water chemistry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43I-2587, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Riverine dissolved inorganic carbon (DIC) export plays central roles in the regional and global carbon cycles. Here we investigated DIC spatiotemporal variability and sources of 8 catchments in Yangtze River source region (YRSR) with variable permafrost coverage and the seasonally thawed active layer. The YRSR catchments were DIC-rich and exported 3.51 g m^-2 of DIC per year. The seasonal change of temperature, active layer, and flow path can shift the DIC sources composition and stable carbon isotope of DIC (d¹³C-DIC). The most depleted d¹³C-DIC values were found in the thawed period, suggesting the soil respired CO₂ during the active layer thaw period can promote bicarbonate production via H₂CO₃ weathering. Spatial d¹³C-DIC increased with basin size, likely due to higher permafrost coverage, discharge, and CO₂ degassing rate. We found that evaporite carbonates and silicate weathering contributed 44.2% and 30.9% of stream bicarbonate, respectively; while groundwater and rainwater contributed 16.7% and 7.3% of bicarbonate, respectively. Pure carbonate rock weathering played a negligible role in DIC production. These source contribution results were compatible with Miller-Tans plot d¹³C-DIC source approximation results. Silicate weathering increased from initial thaw to thawed period, reflecting the active layer thaw and subsequent hydrology change impacts. Silicate weathering consumed 1.3´10¹⁰ mol of CO₂ annually, which represent a carbon sink for atmospheric CO₂. This study provided new understandings of the riverine DIC export mechanisms of the YRSR. As permafrost degrades, not only the quantity of riverine exported DIC change, the sources and sinks of DIC may also change spatiotemporally.

2020032576 Gibbs, Anne (U. S. Geological Survey, Pacific Coastal and Marine Science Center, Santa Cruz, CA); Snyder, Alex and Richmond, Bruce M. Rates and patterns of shoreline change along the Arctic coast of Alaska; Bering Strait to the U.S. Canadian border [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1336, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The U.S. Geological Survey has assembled and analyzed rates of historical shoreline change along more than 2500 km of the Alaskan Arctic coast from the Bering Strait to the U.S. Canadian border. Using shoreline positions from 4 eras (1950s, 1980s, 2000s, and 2010), shoreline change rates were calculated every 50 m over 3 time periods: long-term (LT:1950s to 2010s), early short-term (MT; 1950s to 1980s), and late short-term (ST; 1980s-2010s) and summarized by geographic region and shoreline type (exposed, sheltered, mainland, and barrier coast). Results show that the Arctic coast of Alaska was dominantly erosional from the 1950s to 2010s with 76 percent of transects measuring shoreline retreat. Mean long-term shoreline change rates of -0.8±0.1 m/yr were not significantly different than the short-term: MT: -0.7±0.1 m/yr and ST -0.8±0.1 m/yr. Rates were highly variable, however, ranging from -25 m/yr to +20 m/yr, with extreme rates associated with migration of barrier islands and limited sections of the mainland coast. Shoreline change rates along the Beaufort Sea coast were considerably higher (7 to 15%) and more variable compared to the Chukchi Sea Coast. Shorelines were generally more erosional during the ST compared to the MT along the Beaufort Sea Coast, however, along the Chukchi coast the trend was opposite, with highest mean erosion rates measured during the MT. Increases in mean erosion and accretion rates through time, along with an increase in the percent of the coast accreting, indicate that the coast is eroding more rapidly. This is particularly important on the exposed mainland coast where loss of the permafrost bluff and tundra landscape is permanent and the eroded material is entrained into the littoral system, redistributed, and deposited as more ephemeral and dynamic beach, spit, and barrier island landforms.

2020032466 Gibson, Carolyn (University of Guelph, Guelph, ON, Canada); Turetsky, Merritt R.; Brinkman, Todd Jared; Spring, Andrew and Baltzer, Jennifer Lynn. Causes of lowland thermokarst formation and its impacts on carbon cycling and provisioning of ecosystem services [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B21D-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw in Boreal and Arctic regions is causing widespread changes to ecosystems and the services they provide at local, regional, and global scales. Recent empirical and modeling studies have shown that rates of thermokarst initiation and spread is increasing with rising mean annual air temperatures and changes in wildfire severity and extent. Here, we provide detail into both the extent and scope of thermokarst formation in northwestern Canada as well as the consequences of widespread thermokarst formation on carbon cycling and the provisioning of ecosystem services. Using a gridded mapping approach, we developed a spatial understanding of the distribution and degree of thaw to date in permafrost peatlands across the Taiga Plains ecoregion, an area that covers >300,000 km² in the Northwest Territories. We are using these data to test hypotheses about climatic, ecological, and Quaternary controls on thermokarst rates. Near the southern limit of permafrost, wildfire is responsible for 25% of thermokarst expansion rates but it is unclear whether this patterns holds in more expansive peat plateaus further north. By understanding the causes and extent/magnitude of thermokarst formation, we are better able to understand the risks associated with thermokarst formation. Our literature review shows that >50% of published permafrost thaw papers focus on carbon cycling or climate regulation. Synthesis work led by the Permafrost Carbon Network shows that thermokarst or abrupt thaw is likely to impact <20% of frozen ground but will impact more than 50% of permafrost carbon. Inventory modeling shows that thermokarst in both upland and lowland ecosystems release 40% of carbon emissions associated with gradual active layer thickening. However, due to high methane fluxes, thermokarst emissions will double the climate impacts of the permafrost carbon feedback. Thermokarst also impacts a suite of other ecosystems services including access to hunting grounds and safe drinking water. We are conducting community-participatory research to understand how thermokarst impacts these varied ecosystem services in permafrost landscapes with the goal of developing community-driven risk assessment systems related to permafrost change. Here, we will present a case study on the impacts of thermokarst formation on land access.

2020032482 Gibson, John J. (University of Victoria, Victoria, BC, Canada). Permafrost thaw as a mechanism for widespread pH increase in boreal lakes; isotopic and geochemical evidence [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2538, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Surveys of stable isotopes of water in 50 boreal lakes were conducted between 2002 and 2017 in the Oil Sands region, northeastern Alberta, as a component of Alberta's acid sensitivity program. Situated near the southern limit of the discontinuous permafrost zone, lakes in the region were being monitored mainly to detect potential acidification due to oil sands emissions loadings. Unexpectedly, widespread pH increase has occurred in many of the lakes during the past 2 decades. Using an isotope mass balance approach, watershed, climatic and isotopic data (oxygen-18, deuterium, carbon-13, tritium, radon-222) were applied to investigate drivers of water balance and linkages to water chemistry in the lakes and their watersheds. Site-specific differences in runoff to lakes were found to be driven by latitudinal gradients in climate, lake/watershed configuration, substrate, as well as wetland type, and permafrost extent. 14 of 50 lakes, most located northeast of Fort McMurray, and in the Birch and Caribou Mountains, show evidence of being active thaw lakes, receiving up to several hundred millimetres of additional runoff attributed to permafrost thaw, often producing annual runoff in excess of annual precipitation. Concurrent changes in water chemistry (especially pH) are largely attributed to thawing of bogs and/or fens, a process which has led to enhancement of groundwater inflow to lakes, and likely corresponds to a systematic shift from shallow peat-dominated flowpaths to deeper flowpaths through calcareous mineral soils. The mechanism can be viewed as a reversal in wetland succession, whereby wetlands transition from ombrogenous (rain-fed) bogs to geogenous fens.

2020032675 Gokturk, Hal (Ecoken, San Francsico, CA). Reducing methane leakages by filtering contaminated air [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA21D-1146, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane, which is classified as a greenhouse gas, is increasing in the atmosphere as a result of both human activities and natural processes. Methane leakages occur during exploration, production, storage and distribution of the gas. Organic materials decaying in nature in an oxygen poor environment, such as wetlands or the permafrost also generate methane that leaks out. Unlike carbon dioxide, methane is burnable carbon which has commercial value. If it can be recovered from contaminated air at low cost, it can be fed back into the methane distribution system. Such an approach creates a profit motive to reduce the contaminant. The objective of this research is to explore the interaction of methane with various gases in air, to find out whether any of them might be of help in the filtering process. Gases under consideration are (a) main constituents of air such as oxygen (O2), nitrogen (N2), water vapor (H2O), (b) impurities such as nitrogen dioxide (NO2), sulfur dioxide (SO2), and (c) negative ions of those gases which have positive electron affinity such as O2-, NO2-, SO2-. The interaction is investigated by first principle calculations using DFT method with B3LYP functional and Pople type basis sets. An interaction energy (IE) is determined for each gas listed above. IE values for the neutral gases are 4 meV for N2, 3 meV for O2, 18 meV for H2O, 5 meV for NO2, and 4 meV for SO2. IE values for the ions are 105 meV for O2-, 95 meV for NO2-, and 94 meV for SO2-. Results indicate that IE values for neutral gas molecules are small as compared to the ambient thermal energy. IE values for the ions are an order of magnitude greater than those of the neutral counterparts and about 4 times greater than the thermal energy at 25°C. Methane can be recovered from contaminated air with the help of gases such as O2 provided that those gases are converted to negative ions first. A method of generating the negative ions using solar energy will be described in the presentation.

2020032512 Gonzalez Moguel, Regina (McGill University, Earth and Planetary Sciences, Canada); Douglas, Peter M.; Bass, Adrian; Pilote, Martin and Garnett, M. Radiocarbon data from permafrost peatland lakes indicate dissolved methane is dominantly modern while particulate matter and ebullition methane contain older carbon [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2583, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

As a result of permafrost thaw, old carbon could be exported to lakes, decomposed to methane, and emitted to the atmosphere, constituting a positive feedback to global warming. Thus, quantifying the extent to which mobilized old carbon is 1) transported to lakes and 2) transformed to methane are critical questions. To address them, we measured radiocarbon (¹⁴C) content in dissolved organic and inorganic carbon (DOC and DIC), particulate organic carbon (POC), sedimentary carbon (top 10-40 cm), and dissolved and ebullition methane from five thermokarst lakes in northern Quebec near Kuujjuarapik-Whapmagoostui, in summer. Three of the five lakes, draining peatland catchments and yielding high diffusive methane fluxes were also sampled in winter. In the peatland lakes the sediments (3632±444 yrs BP), POC (1360±401 yrs BP), and DOC (881±232 yrs BP) contained significant amounts of old carbon in summer, and the ages of POC (2526±237 yrs BP) and DOC (1136±268 yrs BP) increased in winter. These results suggest that pre-aged carbon from deep peat deposits is a substantial source of sedimentary carbon and POC, and to a lesser extent DOC. This pattern is more strongly expressed in winter when the lakes are ice covered, there is no photosynthesis, and shallow peat layers are frozen. On the other hand, dissolved methane contained younger carbon in summer (252±106 yrs BP) and winter (217±140 yrs BP) whereas ebullition methane was considerably older (1395±243 yrs BP). These differences could be related to the production of methane in different sediment depths. Dissolved methane is likely produced near the sediment surface, or even in the water column, where younger material is available. In contrast, ebullition methane is probably produced in deeper sediments with older carbon. Conversely, these trends were not observed in the non-peatland lakes, where all fractions except the sediments (996±6 yrs BP) and POC (631±71 yrs BP) were derived from modern carbon. The young age of dissolved methane in the peatland lakes, relative to POC and DOC, indicates that high rates of diffusive methane fluxes in these systems are primarily fuelled by contemporary primary productivity, despite the presence of substantial amounts of older carbon in the lakes.

2020032536 Grant, Robert F. (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Mekonnen, Zelalem Amdie and Riley, William J. Changes in CO₂ and CH₄ exchange with climate change in an Arctic polygonal tundra depend on rates of permafrost thaw as affected by changes in vegetation and drainage [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Model projections of future CO₂ and CH₄ exchange in Arctic tundra diverge widely. Here we used ecosys to examine how climate change will affect CO₂ and CH₄ exchange in troughs, rims and centers of a coastal polygonal tundra landscape at Barrow AK. The model was shown to simulate diurnal and seasonal variation in CO₂ and CH₄ fluxes associated with those in air and soil temperatures (T_a and T_s) and soil water contents (q) under current climate in 2014 and 2015. During RCP 8.5 climate change from 2015 to 2085, rising T_a, atmospheric CO₂ concentrations (C_a) and precipitation (P) increased net primary productivity (NPP) from 50-150 g C m^-2 y^-1, consistent with current biometric estimates, to 200-250 g C m^-2 y^-1. Concurrent increases in heterotrophic respiration (R_h) were slightly smaller, so that net CO₂ exchange rose from values of -25 (net emission) to +50 (net uptake) g C m^-2 y^-1 to ones of -10 to +65 g C m^-2 y^-1. Increases in net CO₂ uptake were largely offset by increases in CH₄ emissions from 0-6 g C m^-2 y^-1 to 1-20 g C m^-2 y^-1, reducing gains in net ecosystem productivity (NEP). These increases in net CO₂ uptake and CH₄ emissions were modelled with hydrological boundary conditions that were assumed not to change with climate. Both these increases were smaller if boundary conditions were gradually altered to increase landscape drainage during model runs with climate change. More rapid nutrient cycling modelled with climate change favored dominance of deciduous sedge over evergreen moss which in turn affected the modelled responses of CO₂ and CH₄ exchange to climate change in the polygonal tundra. At a larger spatial scale, accelerated nutrient cycling modelled with climate change drove modelled shrub expansion across the North American Arctic tundra during the 21st Century. Faster-growing deciduous shrubs modeled with less efficient nutrient conservation dominated much of the low Arctic by 2100 where nutrient cycling became more rapid, while the slower-growing evergreen shrubs modeled with more efficient nutrient conservation dominated a wider latitudinal range that extended to the high Arctic where nutrient cycling remained slower.

2020027695 Grebenets, Valery I. (Lomonosov Moscow State University, Geographical Faculty, Moscow, Russian Federation); Tolmanov, Vasiliy A. and Iurov, Fedor D. Influence of engineering-cryogenic processes on the infrastructure of the Arctic due to climatic changes and increasing anthropogenic impact [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1276, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

There has been a noticeable deterioration of the permafrost-ecological and engineering-geocryological situation in recent decades.This retrogression is associated with changes in the natural environment and man-made impact. The data of long-term monitoring observations of the permafrost temperature indicate a tendency towards an increase in temperature. It leads to instabilities of the upper, icy horizons of permafrost, which is the reason for the intensification of engineering-cryogenic processes. Cryogenic processes developing in urban areas of the permafrost zone often differ from those who develop under natural conditions: they proceed more intensively or fade out under the influence of anthropogenic factors. Sometimes, new cryogenic processes and phenomena occur in place where it has not previously been observed. Taken together, these processes can be called engineering-cryogenic. We organized field studies of engineering cryogenic processes at urbanized centers on permafrost, such as: Vorkuta, Norilsk, Salekhard, Labytnangi, Yakutsk, etc. According to the results of the research, was created a map of engineering-cryogenic processes developing in the settlements of the Russian cryolithozone. It was revealed that increasing snowiness of winters activates dangerous processes that adversely affect the infrastructure: man-made warming and flooding of soils. It caused by the formation of man-made snow dumps (located at the same places every year) and leak in the city communications. Field studies revealed that about 200 dumps in Norilsk have height of 2.5 m and more. It extremely reduces the winter cooling of these local areas, adversely affects temperature of the frozen soils and lower bearing capacity of frozen piles. The development of engineering-cryogenic processes in the cryolithozone results in deformations of buildings and infrastructure: about 60% of the facilities in Vorkuta, Igarka, more than 30% in Dudinka, almost 25% in Norilsk, 80-90% of buildings and structures in the Far Eastern national settlements of the North, almost 90% of small dams of the frozen type on river objects. This work was supported by the RFBR project 18-05-60080 Dangerous nival-glacial and cryogenic processes and their impact on the infrastructure in the Arctic.

2020032588 Griffin, Claire (University of Virginia, Charlottesville, VA); Kent, Kelcy; Liljedahl, Anna K.; Daanen, Ronald P.; Jorgenson, Torre; Kanevskiy, Mikhail Z. and Epstein, Howard E. Dissolved organic matter dynamics across a gradient of ice-wedge degradation and stabilization, northern Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1358, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Aquatic dissolved organic matter (DOM) represents a major pathway of carbon removal in Arctic ecosystems, through both lateral transport and mineralization. The massive stores of organic carbon held within permafrost soils make it imperative to understand the sources of aquatic DOM, and its potential bioavailability. In an ice-wedge polygon permafrost landscape, DOM may be sourced from relatively modern terrestrial vegetation, ancient soil carbon, or peats. The release of inorganic nutrients and labile organic matter from permafrost thaw also represents a potential feedback that could stimulate primary production in both aquatic ecosystems and adjacent terrestrial vegetation. Here, we collected water from ponds, soil porewaters, and ice wedges across sequences of ice-wedge polygon degradation and stabilization in northern Alaska in order to refine the understanding how organic matter is transported and transformed in a dynamic, heterogenous landscape. In addition to measuring nutrients, dissolved organic carbon (DOC), and chromophoric dissolved organic matter (CDOM), we incubated a subset of samples for 28 days in the dark, to understand microbial transformations of DOM. Preliminary data from Jago River in 2018 showed ice-wedge polygons at the advanced degradation stage had elevated inorganic nitrogen relative to other stages of degradation and stabilization. DON was elevated at both advanced degradation sites and stabilizing sites, relative to undegraded or initial degradation sites. As climate warming continues, inorganic nitrogen released from frozen soils or re-mineralized organic matter may lead to non-linear responses in local ecosystem functioning.

2020032519 Guo, Mingyang (Purdue University, Department of Earth, Atmospheric, and Planetary Sciences, West Lafayette, IN); Zhuang, Qianlai; Tan, Zeli; Shurpali, Narasimha J.; Juutinen, Sari and Martikainen, Pertti J. Boreal lakes are continuous methane sources in the 21st century; an analysis using a process-based lake biogeochemistry model [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24B-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Lakes are important landscape components in Arctic and subarctic regions, accounting for 11.9-24.2 Tg CH₄ yr^-1methane emissions. More than 90% of the lakes in the boreal zone are less than 0.1 km² which are especially productive in methane emissions due to their high loads of terrestrial carbon and low oxidation conditions. Recent studies have found that boreal lakes are taking in more dissolved organic carbon (DOC), indicating more substrates for potential methanogenesis in the sediments. Here we use an extent lake biogeochemistry model to quantify the methane emissions of 214,995 lakes in Finland. Those lakes range in surface area from 0.15 m² to 1393 km². The model is first calibrated using field measurements of 207 lakes in the country. The simulations are then conducted from 1980 to 2018 and from 2015 to the end of this century under four RCP scenarios. We find there was a substantial increase of annual methane emissions over the past 40 years: the emission in the 2010s (1.35±0.36 Tg CH4 yr^-1) was more than tripled than that in the 1990s. The increasing length of ice-free season allows more methane diffusive emissions beginning two months earlier and ending two months later in comparison with 40 years ago. Our simulations for the 21st century suggest these lakes are continuous methane sources. In this presentation, we will also show our revised methane emission estimates for all Arctic lakes based on lake distribution databases considering the impacts of a several important processes including potential increasing sediment substrates due to labile carbon mobilization and thawing permafrost, and enhanced microbial activities in warmer lakes.

2020032545 Heffernan, Liam (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Cavaco, Maria; Estop Aragones, Cristian; Bhatia, Maya; Jassey, Vincent E. and Olefeldt, David. The effect of permafrost thaw on the controls and pathways of decomposition that regulate the carbon balance of Boreal peatlands [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Boreal peatlands are important carbon (C) sinks while emitting a significant proportion of CH₄. Recent warming in permafrost regions has accelerated thaw rates of permafrost peat plateaus, causing thermokarst bog formation and exposing previously frozen peat to microbial decomposition and mineralization into greenhouse gases. The rate at which peat initially degrades and substrates becomes available for microbial metabolism is controlled by hydrolytic enzyme activity. Most mineralized peat is released at the surface as CO₂ however CH₄ emissions are also important in thermokarst bogs where anaerobic conditions favour growth of methanogens. Using three years of measured CO₂ and CH₄ surface fluxes we present an estimated annual C balance of a thawing peatland in western Canada. We provide evidence of how the controls and pathways of decomposition regulate the annual C balance following thaw. Modelled gas fluxes for a three-year period indicate recently thawed areas are net C sources with a high proportion lost as CH-₄. Hydrolytic enzyme activity suggests that most microbial decomposition occurs in the initial decades following thaw on peat that accumulated post-thaw, despite waterlogged conditions. We show using measured d¹³C-CH₄ that in recently thawed areas a greater proportion of CH₄ production at depth, and CH₄ surface emissions, is due to acetoclastic methanogenesis. There, we observed greater diversity of the microbial community which supports the occurrence of acetoclastic methanogenesis at depth. Previous studies at this site have indicated that following thaw there are small losses of old C but this is not lost as CO₂. Our results suggest that most decomposition occurs on peat which accumulated post thaw, but that loss of old C may be driven by enhanced acetoclastic methanogenesis at depth in the initial decades following thaw. Our findings highlight the importance of CH₄ production in the contribution of thawing peatlands to the permafrost C feedback.

2020027696 Heim, Birgit (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Shevtsova, Iuliia; Kruse, Stefan; Morgenstern, Anne; Lashchinskiy, Nikolay; Kartoziia, Andrei; Buchwal, Agata and Rachlewicz, Grzegorz. Remote sensing approaches for assessing vegetation stocks and short-term fluxes in the sub-Arctic permafrost landscape of the Lena River delta (Siberia) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1278, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Uncertainty in describing processes that control carbon outputs and their cycling rates in terrestrial ecosystems is a major contributor to overall uncertainty in Earth System Models. Here, we focus on remote sensing approaches to understand the status and dynamics of above-ground carbon related to vegetation as primary producers for the central Lena Delta, Siberia. In ongoing and future Russian-German cooperation on Lena Delta expeditions and with the opportunity of the modern Samoylov research station and new spaceborne satellite missions we evaluate the applicability of remote sensing for assessing vegetation stocks and short-term fluxes in the Lena River delta. i) Synoptic mapping of above-ground vegetation biomass for the Lena Delta region: We plan to upscale vegetation cover plot information and in-situ biomass estimates from harvesting to above ground carbon stocks. We use Landsat-8 OLI and Sentinel-2 data for the spatial upscaling. ii) Synoptic monitoring of vegetative regrowth offsetting losses of carbon by spring floods and thermo-erosion using in situ data on vegetation community, biomass, stand age and remote sensing data. iii) Photosynthesis is the starting point of the carbon cycle. Can we assess landscape-scale inherent dynamics of photosynthetic activity for the central Lena Delta region using remote sensing? Remote Sensing vegetation indices, most commonly NDVI are widely used to model the fraction of photosynthetically active radiation absorbed by vegetation, fPAR, for estimating gross primary productivity, GPP, from remotely sensed data. We investigate the applicability of MODIS NDVI for the tundra landscape of the Lena Delta region. Assessments of the applicability of the remote sensing products will be done using upscaling: UAV-based imagery, higher spatial resolution Rapid Eye and assessing the leaf development, plant shooting and greening by phenological monitoring from time lapse cameras.

2020032548 Heimann, Martin (Max Planck Institute for Biogeochemistry, Biogeochemical Systems, Jena, Germany); Goeckede, Mathias; Zimov, Sergei A. and Zimov, Nikita. Arctic permafrost soil hydrology and snow cover depth critically determine CO₂ and CH₄ emissions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The vulnerability of the large carbon reservoir locked up in Arctic permafrost soils under global warming is largely unknown. Soil properties, in particular soil wetness as well as snow cover critically control the thermal regime of the active layer of permafrost soils, and through this also the processes which govern exchanges of carbon dioxide (CO₂) and emissions of methane (CH₄). Here we present results from a long-term drainage experiment conducted on permafrost soils in north-eastern Siberia. Lowering of the water table through drainage changes the surface ecosystem composition and increases the summer time insulation of the underlying permafrost, hence tends to keep it cooler than in the prevailing water logged surrounding. An increase of soil degradation and fragmentation by thermokarst processes, as expected in a warming climate, may therefore lead to more dryer soil patches with reduced greenhouse gas emissions and may thus constitute a negative climate feedback process. On the other hand, higher snow depth in winter provides an important insulation which delays or even prevents the refreezing of the active surface soil layer. Higher snow depths thus lead to warmer soil temperatures and correspondingly to higher emissions of respired carbon as CO₂ and CH₄. Given that a future warmer Arctic most certainly implies increases in precipitation, also as snow in fall and winter, this process might represent a positive climate feedback process. Which one of these two Arctic climate feedbacks will dominate in a warming world is very much unknown. Long-term studies of in situ measurements and high-resolution remote sensing of surface structures complemented with advanced high-resolution modelling are urgently needed to robustly predict the fate of Arctic permafrost carbon within this century. The vulnerability of the large carbon reservoir locked up in Arctic permafrost soils under global warming is largely unknown. Soil properties, in particular soil wetness as well as snow cover critically control the thermal regime of the active layer of permafrost soils, and through this also the processes which govern exchanges of carbon dioxide (CO₂) and emissions of methane (CH₄). Here we present results from a long-term drainage experiment conducted on permafrost soils in north-eastern Siberia. Lowering of the water table through drainage changes the surface ecosystem composition and increases the summer time insulation of the underlying permafrost, hence tends to keep it cooler than in the prevailing water logged surrounding. An increase of soil degradation and fragmentation by thermokarst processes, as expected in a warming climate, may therefore lead to more dryer soil patches with reduced greenhouse gas emissions and may thus constitute a negative climate feedback process. On the other hand, higher snow depth in winter provides an important insulation which delays or even prevents the refreezing of the active surface soil layer. Higher snow depths thus lead to warmer soil temperatures and correspondingly to higher emissions of respired carbon as CO₂ and CH₄. Given that a future warmer Arctic most certainly implies increases in precipitation, also as snow in fall and winter, this process might represent a positive climate feedback process. Which one of these two Arctic climate feedbacks will dominate in a warming world is very much unknown. Long-term studies of in situ measurements and high-resolution remote sensing of surface structures complemented with advanced high-resolution modelling are urgently needed to robustly predict the fate of Arctic permafrost carbon within this century.

2020032619 Heinze, Markus (Technical University of Munich, Chair of Landslide Research, Munich, Germany); Scandroglio, Riccardo; Pail, Roland and Krautblatter, Michael. Relative gravimetry in alpine permafrost-affected tunnel; a first attempt to reveal changes in hydrostatic pressure [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H41B-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Failure of rock faces in periglacial environments is mainly controlled by rock and ice mechanics. The contribution of hydrostatic pressure has been often registered but never quantified (e.g. Piz Cengalo in 2017), which makes of water the most important unknown weakening/triggering factor. Infiltration from rainfall or snow/ice melting can create crucial pressure peaks crucial pressure peaks. Climate change consequences like increase of air temperature and intensification of precipitations amplify the magnitude of this factor and pose a high risk for humans and infrastructures. We present here a new unique approach to the problem, correlating electrical resistivity tomography (ERT) and relative gravimetry measurements. ERT allows to precisely determine permafrost extension. Changes in the local gravity field are attributed to the water content of the surrounding rocks, that for low-porosity rocks means water in its fractures. With permafrost sealing fractured rock, the possibilities for building up hydrostatic pressure are enhanced.sealing fractured rock, the possibilities for building up hydrostatic pressure are enhanced. On monthly base we conduct relative gravimetry and ERT measurements since 2014 at the very touristic Mount Zugspitze (Germany, Wetterstein limestone), in a tunnel located at 2750 m asl (about 9020 ft). At each campaign relative gravimetry was measured at 20 stations with a Scintrex CG-5, while 1200 resistivity values were obtained with a ABEM LS. Additional continuous information from 30 rock- and air-temperature sensors, weather stations, snowpack simulations and discharge measurements in the tunnel and in the valley has been collected. The influence of these external factors on gravimetric measurements has been quantified in detail allowing us, for the first time, to describe the dynamic of water inside the massive and consequently estimate hydrostatic pressure. Here we present the methodology used to detect hydrostatic pressure changes in permafrost-affected rock, the dataset obtained at our fully instrumented test site Mount Zugspitze and we evaluate the feasibility of the gravimetric approach and its potential of a joint interpretation with ERT and complementary data.

2020032487 Henson, Henry Churchill (St. Olaf College, Northfield, MN); Mann, Paul James; Sanders, Aquanette; Natali, Susan; Schade, John D.; Ludwig, Sarah and Sistla, Seeta. Influence of land slumping from permafrost thaw on lake methane emissions in the Yukon-Kuskokwim delta, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23K-2450, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rising temperatures and increasing fire frequency across the Arctic are accelerating permafrost thaw, which can lead to substantial ground slumping in areas of high ice content. When these processes occur near lakeshores, deposition of recently-thawed organic matter into anoxic lake sediments has large potential to increase methane emissions. Specifically, this erosion may fuel methane release in the form of ebullition (bubbling from bottom sediments). High spatial and temporal variability in ebullition rates has made this type of gas emission difficult to quantify, and therefore it is often challenging to incorporate into Earth System Models. Ebullitive fluxes can be substantial, in some cases contributing the majority of methane emissions from lakes, as compared to diffusive fluxes. By studying ebullition in conjunction with ground slumping, we can better understand the factors influencing this source of CH₄ emissions. We measured both lake ebullitive and diffusive methane emissions in the Yukon-Kuskokwim Delta, AK, comparing rates between control sites that lacked ground slumping to sites with adjacent ground slumping. Diffusive fluxes were measured using a Los Gatos gas analyzer connected to a floating chamber. Bubble traps deployed above the sediment allowed us to measure sediment ebullition rates. Both were measured over a two week period in July 2019. We also collected gas bubbles to estimate methane concentrations in the gas being released. In order to determine the factors driving ebullition rates, intact sediment cores were collected, returned to the laboratory, and incubated anaerobically to estimate methane production. Sediments were also analyzed for C:N and composition of dissolved organic matter was analyzed using FTIR. Our findings show that ebullition rates were higher where ground slumping was high, yet diffusive CH4 flux was comparable in control and slumped areas. Methane production from sediment incubations was higher in the slumped areas and production rates were positively correlated with ebullition rates. Overall, our data suggest that ebullition is the major pathway of CH4 emissions from this lake. In addition, our findings may illustrate a positive climate feedback between permafrost thaw, erosion and lake methane emissions.

2020027623 Hiemstra, Christopher A. (Cold Regions Research and Engineering Laboratory Alaska, Fort Wainwright, AK); Douglas, Thomas; Gelvin, Arthur; Liddle Broberg, Kate; Cook, Bruce and Vas, Dragos A. Time series analyses of interior Alaska thermokarst using airborne and terrestrial lidar [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1377, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost in Interior Alaska, with a mean annual temperature of -1C, is ecosystem protected by thick organic mats, moss, and high moisture content vegetation and soils. Projections indicate increasingly warm high-latitude conditions with a greater fraction of liquid to solid precipitation. Recently, consecutive years of above-average summer precipitation has led to substantial changes in ice-rich Interior Alaska boreal permafrost landscapes. Both upland and lowland landscapes are exhibiting rapid changes in surface characteristics. Thermokarst pits, gullies, and collapse features have expanded, stream silt loads have increased, and undercut and tilted Picea mariana trees are common. A time series of aerial and terrestrial lidar measurements have been collected on interior upland and lowland Alaska research sites from 2014 to 2018. These years include the highest (2014) and third highest (2016) summer precipitation totals in Fairbanks' 91-year record. Our survey dataset, aggregated and corrected, allows us to identify and calculate changes in surface elevation and identify where and when landscape changes occurred. Coincidentally, a rich dataset of high-resolution optical imagery allows us to examine relationships among lidar-detected surface changes and imagery. In uplands, surface subsidence and increased inundation are apparent in localized areas such as streams and lakes. In some places, subsidence and elevation loss is on the order of meters over a few years. Other areas on the landscape show increased elevations from silt deposition and lingering aufeis. Lowland subsidence is primarily adjacent to stream and bog edges, but is most pronounced and expansive on lake margins. Our goal is to identify, and eventually predict, permafrost landscape changes due to projected increases in summer precipitation.

2020032522 Higuera, Philip E. (University of Montana, Missoula, MT); Hoecker, Tyler J.; Young, Adam M.; Chipman, Melissa L. and Hu, Fengsheng. Increasing fire frequency and short-interval fires in the boreal forest; precedence and context from Alaskan paleoecological records [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24C-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The combination of climate warming and increasing fire activity is raising concerns about the potential for widespread, fire-catalyzed ecosystem change in the boreal forest, including forest loss, permafrost degradation, and altered biogeochemical cycling. A possible precursor to fire-catalyzed change is an increase in fire frequencies, and thus an increase in "short-interval fires"--when two fires burn the same area within an unusually short time period (e.g., <25-50 yr in boreal forests). Short-interval fires can lead to structural or compositional changes--and potentially forest loss--if forests cannot establish and develop to reproductive ages prior to burning. In any fire regime, there is a non-zero probability of a short-interval fire, so small areas of a landscape are expected to experience this phenomenon. Assessing if currently observed short-interval fires are unusual inherently requires a long-term perspective. We evaluate recent trends in fire frequency and the precedence of short-intervals fires in boreal forests of Alaska by comparing fire activity over the past 60 years, documented through observational records, to fire activity spanning the past 750-5000 years, from 30 previously published sediment-charcoal-based paleofire records from four boreal forest ecoregions. Based on over 450 fire-return intervals (FRIs) from the paleo records, approximately 25% of all FRIs were <=50 yr. Modeling a distribution of FRIs based on these data, we expect approximately 10% of all fires to burn with an interval of 25 years, and only 2.5% to burn with intervals as short as 10 years. These values will be compared to proportions (probabilities) of short-interval fires from the past several decades, from the observational record, on a ecoregion-specific basis. The paleo records also highlight that fire activity over the last century in boreal Alaska, through proxies of biomass burning and fire frequency, is higher than at any time over the Holocene. To the extent that ongoing fire activity, characterized by fire frequency and the frequency of short-interval fires, is outside the range of Holocene reconstructions, then the longstanding resilience of boreal forest to wildfires and environmental change is increasingly called into question.

2020032591 Hinkel, Kenneth M. (Michigan Technological University, Houghton, MI); Jones, Benjamin M.; Ohara, Noriaki; Arp, Christopher D.; Parsekian, Andy; Breen, Amy Lynn; Farquharson, Louise Melanie; Kanevskiy, Mikhail Z.; Gaglioti, Benjamin; Larsen, Chris; Rangel, Rodrigo Correa and Nichols, Ian. Causes and consequences of catastrophic lake drainage in an evolving Arctic system; first year activities and initial results [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1361, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Lakes and drained lake basins (DLBs) are ubiquitous in arctic lowlands, together covering ~80% of the area and making these features the dominate landscape elements. Catastrophic lake drainage and subsequent ecosystem succession in the resultant DLBs are of interest to scientists studying landscape evolution, carbon storage, and hydrology. Lake drainage events are relatively infrequent but are likely to increase in response to enhanced snowfall and warmer temperatures in arctic Alaska. A combination of historic and contemporary remote sensing, paleoecological and geophysical techniques, vegetation and permafrost investigations of DLB soil chronosequences, and models representing blowing snow and hydroclimate will provide understanding of water, soil, vegetation and climate systems so as to improve our understanding of watershed and regional hydrology, identifying flood and ground stability hazards, and evaluating the changing dynamics of terrestrial and aquatic habitat and carbon cycling. In April and May 2019 the interdisciplinary research team performed field work in arctic Alaska. Activities from the first field season included instrumenting 23 lakes with a high potential for drainage and 26 drained lake basins for water level studies associated with snow dam outburst floods, establishing 7 meteorological stations, coring permafrost in 22 DLBs to assess permafrost aggradation following lake drainage, conducting near-surface geophysics to quantify snowpacks and upper permafrost characteristics, and UAV-surveys to construct 3-d models of snow-covered lakes, drained lakes, and interstitial tundra environments. The August 2019 field campaign entailed downloading field instrumentation, conducting vegetation surveys in DLBs, collecting shallow permafrost cores and basal peat samples from DLBs, acquiring high-resolution imagery to develop summertime digital surface models of the study sites, and ground-truthing a lake drainage-susceptibility product developed using GIS and remote sensing datasets. The team also focused on two lakes that drained in late 2018, and collected baseline data for a lake drainage manipulation experiment planned for summer 2020. An overview of methodologies and initial results will be presented here with greater detail provided in related presentations.

2020027701 Hiyama, Tetsuya (Nagoya University, Nagoya, Japan); Ichii, Kazuhito; Iijima, Yoshihiro; Park, Hotaek and Sato, Tomonori. Pan-Arctic Water-Carbon Cycles (PAWCs); a new research project focusing on environmental changes in northern Eurasia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC24C-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Recent global warming accelerates Arctic sea ice retreat, which derives significant changes in atmospheric-terrestrial water cycle in the Arctic and pan-Arctic regions. Because spatiotemporal variations in emission (or absorption) of greenhouse gases are largely dependent on surface water and vegetation conditions, for better understanding and for better future projection of water-carbon cycles in the pan-Arctic region, it is necessary to conduct an integrated study on atmospheric-terrestrial water-carbon cycles in the region. Based on these backgrounds and motivations, we newly launched a research project focusing on environmental changes in northern Eurasia in which very limited data on the fluxes of greenhouse gases exist. The purpose of the research is to integrate atmospheric-terrestrial water and carbon cycles across atmosphere - biosphere - hydrosphere - cryosphere in the region. To achieve this goal, we firstly develop a water traceable integrated model (WTIM), which can calculate spatiotemporal variations in the atmospheric moisture transport, moisture flux convergence, precipitation, vegetation condition, permafrost degradation, and river discharge, with important boundary conditions of the Arctic sea ice extent. Then we estimate spatiotemporal variations of water-covered area and vegetation condition in northern Eurasia, using satellite remote sensing data and WTIM products with the help of spatiotemporal data fusion techniques. Finally, we derive spatiotemporal variations and the driving mechanisms on the fluxes of greenhouse gases over northern Eurasia, using a biogeochemical model. To validate these results, we will continuously measure fluxes of greenhouse gases at eastern Siberia and northern Mongolia. The study consists of four groups: terrestrial observation group, terrestrial modeling group, atmospheric research group, and integration group. The four groups strongly collaborate each other. We also organize international scientific workshops in the research period, and will co-produce our scientific outcomes with Siberian and Mongolian researchers.

2020032505 Holl, David (Universität Hamburg, Center for Earth System Research and Sustainability, Institute of Soil Science, Hamburg, Germany); Wille, Christian; Sachs, Torsten; Boike, Julia; Grigoriev, M.; Fedorova, I. and Kutzbach, Lars. Inter-annual variability of CO₂ and CH₄ fluxes of a polygonal tundra landscape in the siberian arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2576, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost-affected soils in the Arctic have been accumulating organic matter for thousands of years and form a carbon storage of global relevance. Large fractions of this carbon pool may, however, be remobilized in the form of the greenhouse gases CO₂ and CH₄ through the effects of Arctic warming and permafrost degradation. Within several Russian-German cooperation projects, we have been investigating the inter-annual variability of CO₂ and CH₄ exchange fluxes of lowland polygonal tundra on Samoylov Island in the Lena River Delta in the Siberian Arctic (72°N, 126°E) with the eddy covariance technique. The 16-year flux dataset from the polygonal tundra shows that this ecosystem is still a robust carbon sink. Cumulative net ecosystem CO₂ exchange flux (NEE) during the late summer overlap period (15 July to 31 August) is rather consistent with -1.5±0.6 mol m^-2 (n=15). The relationship between soil temperature and late summer NEE could be best fitted with a quadratic function (r²=0.44), which suggests the existence of a temperature optimum, where the difference between photosynthesis and ecosystem respiration leads to maximum net CO₂ uptake. Probably, both photosynthesis and ecosystem respiration initially benefit from higher temperatures. In the highest temperature range, however, ecosystem respiration exceeds photosynthesis. Median CH₄ fluxes during late summer ranged between 30 and 56 mmol m^-2 hr^-1 and were positively linearly correlated (r²=0.79, n=11) with soil temperature at 7 cm depth in wet polygon centers. This result suggests that the enhancement of CH₄ production by higher soil temperatures dominates over the enhancement of CH₄ oxidation by higher soil temperatures in the studied polygonal tundra ecosystem. A longer and warmer thaw period may allow for a stronger accumulation of CH₄ in soil pore space by methanogens and thus enhance transport processes which bypass oxidation (ebullition, plant-mediated transport).

2020032680 Holland, Kira M. (University of Toronto Mississauga, Department of Geography, Mississauga, ON, Canada); Porter, Trevor J.; Froese, Duane G. and Kokelj, Steve. A Holocene record of winter temperatures from ice wedges in the northwestern Canadian Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PP34A-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A majority of Arctic paleoclimate reconstructions demonstrate a long-term cooling trend from the mid to late Holocene following early Holocene warmth, a trend that is largely explained by decreasing summer insolation in northern high latitude regions. However, this cooling trend is predominantly associated with summer-sensitive climate proxies, reflecting a warm-season bias in the Arctic proxy network. Few proxy archives capture cold-season conditions, leaving a gap in our understanding of Arctic seasonal climate dynamics over the Holocene. Ice wedges, a type of ground ice in permafrost regions that form from the thermal contraction of the ground and subsequent infilling of the crack with snowmelt, provide a unique opportunity to constrain winter paleotemperatures based on precipitation isotope ratios (A majority of Arctic paleoclimate reconstructions demonstrate a long-term cooling trend from the mid to late-Holocene following early Holocene warmth, a trend that is largely explained by decreasing summer insolation in northern high latitude regions. However, this cooling trend is predominantly associated with summer-sensitive climate proxies, reflecting a warm-season bias in the Arctic proxy network. Few proxy archives capture cold-season conditions, leaving a gap in our understanding of Arctic seasonal climate dynamics over the Holocene. Ice wedges, a type of ground ice in permafrost regions that form from the thermal contraction of the ground and subsequent infilling of the crack with snowmelt, provide a unique opportunity to constrain winter paleotemperatures based on precipitation isotope ratios (d¹⁸¹⁸O and O and dD) preserved in ice wedge veins. Here we present a mid- to late Holocene record of winter temperatures from ice-wedge water isotopes for the northwestern Canadian Arctic. Four ice wedges from the Tuktoyaktuk Coastlands were analyzed for water isotope ratios (N = 750) and radiocarbon (¹⁴C) dated using dissolved organic carbon (N = 36). Our composite record suggests a long-term increase in D) preserved in ice wedge veins. Here we present a mid- to late Holocene record of winter temperatures from ice-wedge water isotopes for the northwestern Canadian Arctic. Four ice wedges from the Tuktoyaktuk Coastlands were analyzed for water isotope ratios (N = 750) and radiocarbon (¹⁴C) dated using dissolved organic carbon (N = 36). Our composite record suggests a long-term increase in d¹⁸¹⁸O O (+0.14 ppm·ka^-1) over the last 7.4 ka, indicating a winter warming trend since the mid-Holocene. Notably, this trend is consistent with increasing winter insolation at 69°N over the same period, and is corroborated by a similar trend observed in ice wedges from the Siberian Arctic. Winter warming contrasts long-term summer cooling inferred from summer-sensitive proxies. Our record provides evidence that insolation played a major role in forcing winter climate dynamics in the Arctic, and highlights the significance of understanding the seasonality of climate proxy archives in paleoclimate reconstructions.

2020032537 Holmes, Marjorie Elizabeth (Tallahassee Community College, Tallahassee, FL); Crill, Patrick M.; Burnett, William C.; McCalley, Carmody K.; Wilson, Rachel M.; Frolking, Steve E.; Chang, Kuang-Yu; Riley, William J.; Varner, Ruth K.; Hodgkins, Susanne B.; Rich, Virginia Isabel; Saleska, Scott R. and Chanton, Jeff. Carbon accumulation, flux, and fate in Stordalen mire [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Northern peatlands store vast amounts of carbon and changes in apparent carbon accumulation rate (aCAR) in these areas, which include thawing permafrost, can provide information on how carbon uptake and emission are being affected by climate change. aCAR across a permafrost thaw gradient in Stordalen Mire complex in arctic Sweden was assessed by direct semi-continuous measurement of CO₂ and CH₄ exchanges, and ²¹⁰Pb and radiocarbon peat profiles, in unsaturated palsa underlain by permafrost, partially thawed bog, and fully thawed fen. Taken together, these three metrics reflect C balance over different time scales--from this decade to >3000 years BP. Current auto chamber-measured gas fluxes reflect the inundation state, with highest carbon uptake and CH₄ emissions in the fen, and lowest in the palsa. aCAR rates from ²¹⁰Pb profiles have increased during the past century in both the bog and fen. ¹⁴C-based aCAR rates at palsa, bog, and fen sites were low for most of the past 3700 years. Around 40 years ago, aCAR in the bog and fen sites began increasing and by 2016 was more than twice as high as the average palsa aCAR for the past century. Northern peatlands have historically exerted a cooling force on the climate due to the removal of carbon from the atmosphere and its sequestration in soils. As permafrost has thawed recently, shifts in the vegetation and inundation of the Mire, and resulting changes in CO₂ uptake and CH₄ emissions, indicate that now the radiative forcing of this Mire and systems like it may exert a warming influence on climate for the next several hundred years.

2020032449 Hopkinson, Chris (University of Lethbridge, Geography, Lethbridge, AB, Canada); Chasmer, Laura; Quinton, William L.; Flade, Linda F.; Okhrimenko, Maxim and Castilla, Guillermo. Permafrost loss, forest succession and mortality influences on NDVI greening and browning trends in a taiga plains watershed [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B11D-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

There is uncertainty over the nature of ecosystem processes and trajectories that underlie NDVI 'greening' and 'browning' trends in sub-Arctic environments. In extreme cases, such as landcover change due to wildfire, there is justification for equating 'greening' (increasing NDVI) to an increase in biomass, and 'browning' (decreasing NDVI) to a loss of biomass. However, for more subtle changes in VI, such as are occurring in comparatively undisturbed landscapes, the land surface processes are complex and not well understood. At the Scotty Creek Watershed (~138 km²) south of Ft Simpson, NWT, we embarked on a time-series field and airborne lidar campaign to monitor biomass changes from 2007 to 2019. This allowed us to map changes in vegetation height and cover, diminution of individual permafrost plateaus and scale up to the watershed. For the 2010 to 2018 period, we have compared biomass change to trends in eMODIS NDVI to identify correlations across the watershed and with land surface types. No significant correlations between biomass change and NDVI trend were established at watershed-scale. However, when the rate of biomass loss (tree mortality) was mapped across the watershed, higher magnitudes were observed in uplands and riparian zones around permafrost plateaus. While biomass accumulation was the dominant trend across the watershed, it was found to be most prevalent in areas of short vegetation in and around wetlands. Mortality of forest vegetation is visibly widespread and systematic but changes in canopy height and modeled biomass accumulation during the study period exceed loss by >50%. This work suggests that in the Taiga Plains ecozone, satellite vegetation index trajectories over regions not recently influenced by wildfire are not proxy observations for net changes in ecosystem-level biomass accumulation, loss or productivity.

2020027626 Huang Lingcao (Chinese University of Hong Kong, Earth System Science Programme, Hong Kong, China) and Liu Lin. Mapping retrogressive thaw slumps on the Tibetan Plateau using Sentinel-2 images and deep learning [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1380, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Retrogressive thaw slumps (RTSs), resulting from the thawing of ice-rich permafrost, are one of the most dynamic landforms in permafrost areas. As reported by a few studies focused on local areas, their number has increased in recent years. However, their spatial distribution remains poorly quantified. To obtain RTS spatial distribution on the Tibetan Plateau, we map RTSs from Sentinel-2 images using a cutting-edge deep learning algorithm for semantic segmentation. Firstly, we trained a model of Deeplab using training data collected in a local area (i.e., Beiluhe, in the hinterland of the Tibetan Plateau). Secondly, we predicted the RTSs on the entire Tibetan Plateau using the trained model. Lastly, we removed mapped polygons if a polygon cannot meet any of the pre-set criteria. These criteria include (1) on a slope steeper than two degrees but gentler than 15 degrees, (2) inside the permafrost extent, and (3) its area greater than 0.3 ha. We obtained 8263 mapped polygons of RTSs on the entire Tibetan Plateau. Their spatial distribution and the statistics on their geometries as well as topography provide valuable information for scientific communities. This is a very first study mapping RTSs at a large scale, and the same method can be applied to the Arctic regions.

2020032528 Hutchins, Ryan H. S. (University of Alberta, Biological Sciences, Edmonton, AB, Canada); Tank, Suzanne; Olefeldt, David; Quinton, William L.; Spence, Christopher; Dion, Nicole and Mengistu, Samson G. Wildfires in subarctic Canada have no impact on downstream mercury transport but cause decreased delivery of dissolved carbon and nutrients [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41A-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The boreal biome is currently experiencing rapid change, with warming substantially in excess of the global average and wildfires increasing in frequency and severity alongside thawing permafrost. These disturbances could, in turn, engender significant change in the export of carbon, nutrients and metals to aquatic systems, with consequent implications for food webs and ecosystem processes. Here, we examine chemical data from a series of 52 streams and rivers that were sampled across a 250,000 km² expanse of the Taiga Plains and Taiga Shield ecozones of the Northwest Territories (Canada). Samples were collected immediately after and for three years following a 'megafire' that occurred in this region in 2014, and span wildfire-affected and non-affected catchments. Given the large variability in concentrations and runoff, we use Bayesian analysis to provide robust estimates of yields (export per unit area) and their uncertainty. Runoff generation was extremely variable and generally higher in the Plains than in the Shield; which had a large effect on yields, for example, carbon yields were higher in the Plains ecozone despite similar concentrations in the Shield. Watershed yields of carbon and nutrients showed responses to wildfire whereas mercury did not. Both ecozones showed a similar pattern in dissolved organic carbon (DOC) concentration, with burned watersheds exhibiting concentrations that averaged 2 mg/L lower than unburned sites; corresponding to 0.2-0.3 g m² yr^-1 lower annual yields (10% lower). Nutrient yields declined with wildfire on the Shield but were similar across burn status on the Plains. These observed changes in yields following wildfire may have important implications for aquatic food webs and downstream ecosystem function. However, in the past 30 years annual runoff generation had a 15-fold variation and potential future changes in hydrology will have a disproportional impact on yields compared with any wildfire changes in concentrations. Given the unprecedented increases in wildfires, permafrost thaw and altered hydrology in this rapidly changing region the future impacts on aquatic systems could be substantial.

2020027702 Iijima, Yoshihiro (Mie University, Graduate School of Bioresources, Tsu, Japan); Hiyama, Tetsuya; Sato, Tomonori; Iwahana, Go; Kotani, Ayumi; Park, Hotaek; Takakura, Hiroki; Fedorov, Alexander and Maximov, Trofim C. Regional impacts of water cycle changes on permafrost eco-hydrological environment in north-eastern Eurasia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC24C-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic is transformed: the sentence was highlighted in the Arctic Research Report, Snow, water, ice and permafrost in the Arctic. This implies that sea ice extent in the Arctic Ocean has remarkably declined over the last couple of decades. In particular, sea ice reduction with more than 30% in summer in interannually along the Siberian coast has been dramatically modifying the hydroclimate system along Arctic and subarctic region in high-latitudes of Eurasia. Water cycle response over high-latitudes of Eurasia in relation to Arctic change has been investigated integrating multiple methods, field observation, permafrost-ecohydrological modeling and hydro-climatic data analyses under international collaborative researches during the decades. Based on those results, we have found the large increase in precipitation amount over high-latitudes of Eurasia during both summer and early winter causes changes in terrestrial water storage affecting rapid permafrost thaw and boreal forest mortality in the Eastern Siberia during the last decade. This also resulted in the extreme years with increase of river runoff of the major Arctic rivers, causing not only floods during snow-melt season but that occurred late summer with much more severe influences for local inhabitants not to use pasture production. These water cycle changes may potentially alter natural environment through geophysical-biological interactions. However our knowledge is still limited due to remaining uncertain processes in all components, such as precipitation, evaporation and evapotranspiration, river runoff and atmospheric moisture transports. In addition, subsequent actions are needed to cope with water cycle change impacts on human dimensions. The imminence of challenges for environmental sustainability which responds to water cycle changes requires a holistic understanding between researchers and stakeholder communities, which in turn depends on a comprehensive assessment of the dynamic interaction of physical and social drivers of change.Arctic is transformed: the sentence was highlighted in the Arctic Research Report, Snow, water, ice and permafrost in the Arctic. This implies that sea ice extent in the Arctic Ocean has remarkably declined over the last couple of decades. In particular, sea ice reduction with more than 30% in summer in interannually along the Siberian coast has been dramatically modifying the hydroclimate system along Arctic and subarctic region in high-latitudes of Eurasia. Water cycle response over high-latitudes of Eurasia in relation to Arctic change has been investigated integrating multiple methods, field observation, permafrost-ecohydrological modeling and hydro-climatic data analyses under international collaborative researches during the decades. Based on those results, we have found the large increase in precipitation amount over high-latitudes of Eurasia during both summer and early winter causes changes in terrestrial water storage affecting rapid permafrost thaw and boreal forest mortality in eastern Siberia during the last decade. This also resulted in the extreme years with increase of river runoff of the major Arctic rivers, causing not only floods during snow-melt season but that occurred late summer with much more severe influences for local inhabitants not to use pasture production. These water cycle changes may potentially alter natural environment through geophysical-biological interactions. However our knowledge is still limited due to remaining uncertain processes in all components, such as precipitation, evaporation and evapotranspiration, river runoff and atmospheric moisture transports. In addition, subsequent actions are needed to cope with water cycle change impacts on human dimensions. The imminence of challenges for environmental sustainability which responds to water cycle changes requires a holistic understanding between researchers and stakeholder communities, which in turn depends on a comprehensive assessment of the dynamic interaction of physical and social drivers of change. This work is supported by JST SICORP Grant Number JPMJSC1902 and JSPS KAKENHI Grant Number JP19H05668 and JP19H00556, Japan.

2020032584 Irrgang, Anna M. (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Permafrost Research, Potsdam, Germany); Lantuit, Hugues; Overduin, Paul P. and Fritz, Michael. NUNATARYUK; permafrost thaw and the changing Arctic coast; science for socio-economic adaptation [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1352, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost coasts represent a key interface for human-environmental interactions. They provide essential ecosystem services, exhibit high biodiversity and productivity, and support indigenous lifestyles but are also a dynamic and vulnerable zone of expanding infrastructure investment and growing health concerns. Permafrost thaw, in combination with increasing sea level and changing sea-ice cover, expose the Arctic coastal zone to rapid changes (Fritz et al. 2017). The release of previously frozen organic carbon and its transformation into greenhouse gases may push the global climate warming above the 1.5°C targeted in the COP21 Paris Agreement (Schuur et al., 2015). The pressing challenge is to quantify and project organic matter, sediment and contaminant fluxes from thawing coastal and subsea permafrost and to assess the implications of permafrost thaw for the indigenous populations, the local communities and the local environment in the Arctic coastal areas. The Nunataryuk project is an EU Horizon 2020 funded collaborative project. Its main objectives are to determine the impacts of thawing land, coast and subsea permafrost on the global climate and on humans in the Arctic, as well as to develop targeted and co-designed adaptation and mitigation strategies. These objectives are targeted by: (1) developing a quantitative understanding of the fluxes and fates of organic matter released from thawing coastal and subsea permafrost; (2) assessing what risks are posed by thawing coastal permafrost and pollution, to infrastructure, indigenous and local communities and people's health; and (3) using this understanding to estimate the long-term impacts of permafrost thaw on the global climate and economy.

2020027700 Iurov, Fedor D. (Lomonosov Moscow State University, Faculty of Geography, Moscow, Russian Federation); Grebenets, Valery I. and Tolmanov, Vasiliy A. Waste storage problems in the permafrost zone of Eurasia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1293, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The problem of storage of solid waste in the permafrost is particularly acute. It is associated with severe climatic conditions and permafrost, which is quite responsive to man-made impact.Causes of solid wastestoring problems in permafrost zone are following: weakness of ecosystems, waterproof properties of frozen rocks, and development of cryogenic processes. Many pollutant accumulators turn into a frozen (relatively stable) state, but the situation is complicated by climate warming trends. It is especially important for regions where hundred million m³of ore and coal wastes are stored in a sanned (frozen) state. We organized field studies dedicated to the waste accumulation problems and their negative impact on the environment in Norilsk Industrial Area, Vorkuta Industrial Center, Igarka, settlements in the lower reaches of the Ob River, national villages of Taimyr, etc. Field observations included assessment of the area of cluttering and the type of waste, in many cases--sampling for chemical analyses, thermometry, mapping of hazardous processes. 5 main types of waste storage were identified, each of which has specific features of the impact on permafrost soils and northern ecosystems as a whole: landfills of municipal solid waste, present in all settlements without exception; abandoned and littered areas, resulting from the reduction in the population of northern settlements; wood landfills (sawdust, bark, etc.) in the centers of the forest industry; industrial waste storage (slag dumps) in the industrial centers of the north; waste rocks in areas of ore mining, can be transformed into man-made rock glaciers in cold climate and mountainous terrains. The use of imperfect technologies for the extraction and processing of raw materials, the "legacy" of past years with disregard of the ecological situation, the lack of special standards for storing waste and industrial products, the undeveloped methods of waste disposal in harsh climatic conditions have led to pollution of vast areas, to the destruction of many ecosystems. This work was supported by the RFBR grant 18-05-60080 Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic.

2020032523 Iwahana, Go (University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK); Busey, Robert; Muskett, Reginald R.; Ohno, Hiroshi; Yang, Ji-Woong; Ahn, Jinho; LaDouceur, Elizabeth and Saito, Kazuyuki. Spatial variations in seasonal and inter-annual surface displacement after the Anaktuvuk River fire (ARF) measured by field surveys and L-band SAR interferometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24F-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Both inter-annual and seasonal ground displacements are closely related to surface carbon/hydrological cycle and spatio-temporal variation in thermokarst subsidence after surface disturbances, and their variations are critical information to estimate rate of permafrost loss. We investigated surface displacement related to frozen ground dynamics and thermokarst development triggered by a tundra wildfire in Alaska, and estimated potential carbon loss caused by the permafrost disturbance. The Anaktuvuk River Fire (ARF) combusted surface vegetation and organic mat of the tundra region underlain by ice-rich permafrost in 2002. We studied the surface displacement using optical and L-band microwave remote sensing (2006-2018) as well as in-situ field measurements (2014-2019). In addition to the measurements of the surface displacement, we collected permafrost samples to be analyzed for greenhouse gas, organic matter, and ice contents together with cryostructure at multiple locations in the area of ARF. Both inter-annual (thermokarst) and seasonal subsidence were measured by the differential SAR interferometry (DInSAR) using ALOS2-PALSAR and UAVSAR data, and validated by the field measurements. Significantly large amounts of subsidence (up to 6.2 cm/year as spatial average) were measured by the DInSAR using ALOS-PALSAR exclusively within burned areas relative to unburned nearby in the first three years after the fire (2008-2010). The spatial variation in thermokarst subsidence measured during 2015-2018 (from 8th to 11th years after the fire) by ALOS2-PALSAR2 shows a markedly different pattern from the period just after the fire (1st to 3rd years) although overall spatial average in subsidence decreased to about 2 cm/year. The distribution shift indicates recent enhancement of natural thermokarst development by climate warming. This was thought to be reflected by spatial variations in sedimentation history, active layer thickness, and location relative to burned areas in addition to burned or unburned status of the site. Based on the measurements of permafrost loss and carbon content in the thawing permafrost, we made a preliminary estimation of the potential carbon loss caused by thermokarst after the ARF.

2020027662 James, Stephanie R. (U. S. Geological Survey, Geology, Geophysics, and Geochemistry Science Center, Denver, CO); Minsley, Burke J.; Waldrop, Mark P. and Mcfarland, Jack W. Understanding the importance of water and ice dynamics at a thermokarst site with novel geophysical observations [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The impact of permafrost thaw on hydrologic, thermal, and biotic processes in arctic and subarctic ecosystems remains uncertain, in part due to limitations in subsurface measurement capabilities. Application of new technologies and integration of multidisciplinary observations has the potential to offer new insights into subsurface biophysical processes during thermokarst development. In an ongoing field experiment, we combine novel geophysical and biogeochemical measurements to better understand the importance of subsurface water and ice dynamics on soil carbon loss and permafrost thaw. Co-located seismic, nuclear magnetic resonance seismic, nuclear magnetic resonance (NMR) (NMR), temperature, soil moisture, temperature, soil moisture, and, and permafrost gas permafrost gas data data are collected collected along a transect between forested permafrost and two collapse-scar bogs at a lowland thermokarst site near Fairbanks, AK. Ambient seismic noise monitoring provides continuous high-temporal resolution measurements of near surface near surface changes in water and ice saturation across the thaw gradient. Velocity variations show a strong seasonal pattern corresponding to active layer freeze, thaw, freeze, thaw, and soil moisture changes. Stations show different rates and timing of velocity decrease in the summer and increase through the fall and winter, suggesting potential preferential zones of infiltration, subsurface water movement, and variable refreeze rates across the site. Maps of velocity change change identify key areas of large summertime velocity reductions nearest the younger bog, indicating potential thaw and expansion at the bog margin. These results correspond well with borehole NMR measurements of unfrozen water content, which show the largest water concentrations nearest the bog-edges where permafrost soils contain up to 25% liquid water, by volume. Comparison with in-situ measurements of greenhouse gases within permafrost soils show significantly higher methane concentrations at these bog-edge locations. Furthermore, thin talik zones above permafrost have been observed adjacent to the younger bog; suggesting talik formation and sustained liquid water concentrations may be a strong driver of lateral bog expansion. Overall, this multidisciplinary approach shows great promise for providing valuable new insights into the subsurface physical controls on carbon cycling and thermokarst development.

2020027632 Jan, Ahmad (Oak Ridge National Laboratory, Oak Ridge, TN); Painter, Scott L. and Coon, Ethan T. Evaluating integrated surface/subsurface permafrost thermal hydrology models against field data in polygonal tundra [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1387, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Numerical simulations are essential tools for understanding the complex hydrological response of Arctic regions to a warming climate. However, strong coupling among thermal and hydrologic processes on the surface and in the subsurface and the significant role that subtle variations in surface topography have in regulating flow direction and surface storage lead to significant uncertainties. Careful model evaluation against field observations is thus important to build confidence.Here, we evaluate the integrated surface/subsurface permafrost thermal hydrology models in the Advanced Terrestrial Simulator (ATS) against field observations in polygonal tundra at the Barrow Environmental Observatory. ATS represents important physical process such as lateral surface and subsurface flows, advective heat transport, cryosuction, and coupled surface energy balance. We simulated thermal hydrology of three-dimensional ice-wedge polygons with generic but broadly representative surface microtopography. We drove the simulations with meteorological data and observed water table elevations in ice-wedge polygon troughs, and compared simulated water table elevations in the polygon centers to observed values. The simulated soil temperatures at several depths were also compared with multiyear high-frequency observed data. The simulations were found to be sensitive to parameters in the bare soil evaporation model, snowpack, and the soil horizontal hydraulic conductivity. With limited calibration of the soil properties and evaporation model parameters, the simulations were found to be consistent with observed water tables, active layer thickness, snowpack depth, evaporation, and observed soil temperatures at several depths in trough, rim, and center. The study builds confidence in the emerging class of integrated surface/subsurface permafrost simulators and provides a optimized set of model parameters for use in projections of permafrost dynamics in a warming climate.

2020032495 Jastrow, Julie D. (Argonne National Laboratory, Argonne, IL); Matamala, Roser; Hofmann, Scott M.; Vugteveen, Timothy W.; Lederhouse, Jeremy S.; Michaelson, Gary J. and Ping, Chien-Lu. Assessing the degradation state of soil organic matter in the permafrost region [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2565, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Estimates of soil organic matter (SOM) stocks in the permafrost region and their susceptibility to mineralization or mobilization in response to environmental change are improving but remain highly uncertain. Throughout the permafrost region, SOM commonly exists in a poorly degraded state due to the cold, often wet, conditions and cryoturbation. Impacts of climatic change on the fate of SOM are likely to depend, at least initially, on its existing degradation state and association with soil minerals. Physical size fractionation is a frequently used method for characterizing the relative degradation state of peats and organic soils, with decreasing size indicating greater decomposition. Similarly, for mineral soils, size fractionation is used to isolate relatively undecomposed particulate organic matter (POM) from mineral-associated SOM. Given that permafrost-region soils range from peats to low-carbon mineral soils and environmental conditions constrain the rate of plant residue decomposition, we are exploring size fractionation as an indicator of the relative degradation state of SOM for this region. Further, we are investigating whether mid infrared (MIR) spectra of un-fractionated bulk soils can be used to predict the distribution of SOM among size fractions. Thus, we size-fractionated over 500 soils representing a range of carbon contents, genetic horizons, vegetation types, and parent materials from a latitudinal transect across Alaska. A large proportion of bulk SOM was found in POM pools for all soil horizon types. Even for mineral horizons, over 40% (on average) of bulk soil organic carbon occurred as POM, indicating that SOM was relatively undecomposed compared to mineral soils typical of more temperate regions. Calibration models derived from the MIR spectra of bulk soils were able to reasonably predict the distribution of SOM among size fractions, including soils from independent permafrost-region locations. Our findings indicate MIR calibration models can enable widespread, high-throughput estimates of the relative degradation state of SOM stocks across the circumpolar permafrost region, which are needed to benchmark and constrain local, regional, and earth system models.

2020027634 Jeong, Dae I. (Environment and Climate Change Canada, Toronto, ON, Canada) and Cannon, Alex J. Projected near-surface permafrost degradation over northern North America based on Canadian regional climate model simulations [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1389, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

This study investigates future near-surface permafrost degradation over northern North America (NA), using outputs from two Canadian regional climate models (RCMs), i.e., four CRCM5 simulations driven by two global climate models (CanESM2 and MPI-ESM) under RCP 4.5 and 8.5 scenarios and 50 initial condition simulations of CanRCM4 driven by CanESM2 under RCP 8.5 scenario. Near-surface permafrost status is diagnosed by (i) a direct approach using soil temperature at 3-m depth for CRCM5 and (ii) an indirect approach using surface temperature and surface frost index for both RCMs. Based on the direct approach, the reanalysis-driven CRCM5 simulation yields 44% smaller permafrost extent than observations, due to overestimated soil temperature. However, based on the indirect approach, reanalysis-driven CRCM5 and CanRCM4 simulations show similar permafrost extent with observations. All CRCM5 simulations and the CanRCM4 ensemble are consistent in projecting significant decreases in future near-surface permafrost extent over northern NA using both direct and indirect approaches. These projected changes are highly dependent on future RCP emission levels and associated increases in regional soil and surface temperatures, rather than to structural difference between the two RCMs or sensitivity of the RCMs to different emission scenarios. Internal variability of projected changes in near-surface permafrost extent is small, as near-surface permafrost is highly dependent on long-term warming trends over the region. Nevertheless, modeling errors in the simulations, such as overestimated soil temperature in CRCM5 and a cool surface temperature bias imposed by boundary forcing errors in MPI-ESM-driven CRCM5, result in substantial uncertainty in projected absolute changes. When considering relative changes estimated using the indirect approach, CanESM2-driven CRCM5 and CanRCM4 simulations are consistent in projecting around 13% degradation of near-surface permafrost per 1°C increase in global mean temperature over northern NA.

2020027706 Ji, D. (Beijing Normal University, College of Global Change and Earth System Science, Beijing, China). Northern high-latitude permafrost response to solar geoengineering [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC33G-1421, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The northern high-latitude frozen ground contains large stores of organic carbon that have been locked in the permafrost for thousands of years. As global temperatures rise, that melting permafrost raises much concerns about its impact on the climate as organic carbon becomes decomposed. The solar geoengineering is a theoretical approach to reduce some of impacts of climate change by reflecting a small amount of inbound sunlight back out into space. It is expected that solar geoengineering leads to lower temperatures at higher latitudes, and tends to mitigate the northern high-latitude permafrost degradation and permafrost carbon loss. We use climate system models with sophisticated representation of permafrost thermodynamics and soil carbon dynamics to conduct a model-based assessment of changes in permafrost extent and permafrost carbon stores under varying solar geoengineering scenarios. This study answers questions that how the high-latitude permafrost response under solar geoengineering, and potential counteracting effects due to permafrost carbon feedback under solar geoengineering.

2020032583 Jones, Benjamin M. (University of Alaska Fairbanks, Fairbanks, AK); Tweedie, Craig E.; Xiao, Ming; Alexeev, Vladimir A.; Baranskaya, Alisa; Belova, Nataliya; Bristol, Emily; Bull, Diana L.; Chi, Guangqing; Dallimore, Scott; Erikson, Li H.; Farquharson, Louise Melanie; Flanary, Chris; Frederick, Jennifer; Fuchs, Matthias; Gibbs, Ann; Graybill, Jessica; Grigoriev, Mikhail; Grosse, Guido; Günther, Frank; Halvorsen, Kathleen E.; Isaev, Vladimir; Irrgang, Anna M.; Iwahana, Go; Jensen, Anne M.; Jones, Craig Alexander; Kanevskiy, Mikhail Z.; Kasper, Jeremy L.; Kinsman, Nicole; Kokin, Osip; Kroon, Aart; Lantuit, Hugues; Lantz, Trevor C.; Liljedahl, Anna K.; Lubbad, Raed; Maio, Chris V.; Maslakov, Alexey; McClelland, James W.; Mota, Alejandro; Nitze, Ingmar; Novikova, Anna V.; Ogorodov, Stanislav A.; Overbeck, Jacquelyn; Overduin, Paul P.; Petrov, Andrey N.; Richmond, Bruce M.; Romanovsky, Vladimir E.; Rowland, Joel C.; Sachs, Torsten; Schuur, Edward; Shabanova, Nataliya N.; Sinitsyn, Anatoly; Shiklomanov, Nikolay I.; Streletskiy, Dmitry A.; Strzelecki, Matt C.; Swanson, David K. and Thomas, Matthew A. An emerging international network focused on permafrost coastal systems in transition [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1351, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Perennially frozen ground and sea ice are key constituents of permafrost coastal systems, and their presence is the primary difference between temperate and high-latitude coastal processes. These systems are some of the most rapidly changing landscapes on Earth and, in the Arctic, are representative of the challenges being faced at the intersection between natural and anthropogenic systems. Permafrost thaw, in combination with increasing sea level and decreasing sea-ice cover, exposes arctic coastal and nearshore areas to rapid environmental and social changes. Based on decadal timescales, observations in the Arctic indicate an increase in permafrost coastal bluff erosion and storm surge flooding of low-lying ice-rich permafrost terrain. However, circum-arctic observations remain limited and the factors responsible for the apparent increase in arctic coastal dynamics are poorly constrained. A better understanding of permafrost coastal systems and how they are responding to changes in the Arctic is important since a high proportion of Arctic residents live on or near coastlines, and many derive their livelihood from terrestrial and nearshore marine resources. An expanding industrial, scientific, and commercial presence in the Arctic Ocean will also require advanced knowledge about permafrost coastlines as terrestrial access points. Since the issues involved span political, cultural, geographical, and disciplinary borders, an international network focused on permafrost coastal systems in transition is needed. An integrative network focused on permafrost coastal systems is required to realize and address the scale and complexity of the processes, dynamics, and responses of this system to physical, ecological, and social change. A primary focus of such an effort would be guided by the fact that the issues and impacts associated with permafrost coastal systems in transition are far greater than any single institution or discipline is capable of addressing alone. Future permafrost coastal system dynamics will challenge conventional wisdom as the system enters a new state impacting human decision making and adaptation planning, cultural heritage resources and ecosystems, and likely resulting in unforeseen challenges across the Arctic.

2020027624 Kaiser, Soraya (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Permafrost Research, Potsdam, Germany); Grosse, Guido; Boike, Julia and Langer, Moritz. Lateral thermokarst lake dynamics; a remote sensing based analysis of spatial variabilities and erosion processes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1378, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Thermokarst lakes are one of the most abundant landforms in periglacial landscapes. They develop in regions underlain by permafrost as a consequence of soil subsidence triggered by the melting of excess ground ice. As a result of further permafrost degradation and shoreline erosion, thermokarst lakes increase in size, expanding vertically and laterally. This growth process has strong impacts on local to regional hydrological networks and ecological functions of the surrounding landscape. Previous research on the lateral growth of thermokarst lakes usually focused on decadal time scales which results in averaged expansion rates. These averages mask the temporal and spatial variations of lateral thermokarst expansion that occur over shorter time periods of only a few years. The short-term variability results from complex interactions between local erosion processes and meteorological and permafrost conditions. The aim of our study is to quantify these short-term changes of lake shorelines to provide a better understanding of permafrost landscape processes using multi-temporal high-resolution satellite imagery. The images are in the visible and near-infrared spectrum with a resolution of 0.3 to 0.7 m. They cover the period from 2006 to 2017 with acquisitions every 2 to 4 years. In order to map the lake shoreline changes we developed a fully-automated, open-source workflow for analyzing the changes of waterbodies larger than 1000 m². First, all necessary pre-processing steps are implemented such as pansharpening and smoothing of any speckle over waterbodies. Then, the normalized difference water index (NDWI) is applied to extract waterbodies from the imagery and derive their shoreline geometry. After filtering for potentially misclassified elements that originate from infrastructure, shoreline movement rates are calculated using a nearest point analysis. The workflow is independent of scale, image spatial resolution, and waterbody geometry. Preliminary findings demonstrate that the approach provides reliable shoreline recognition for every time step in the different study areas even under difficult light conditions. Changes can be detected on a sub-meter scale. Finally, we discuss the influence of the waterbody's size and geometry on the shoreline change processes.

2020032507 Kallmeyer, Jens (German Research Centre for Geosciences, Helmholtz Centre Potsdam, Potsdam, Germany); Schindler, Maria; Liebner, Susanne; Knoblauch, Christian; Strauss, Jens and Biskaborn, Boris K. Microbial carbon degradation processes in thermokarst lake sediments from Bykovsky Peninsula, northern Siberia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2578, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost is increasingly affected by rising temperatures. The associated thawing processes are responsible for the development of thermokarst lakes which cover ~20% of the permafrost region of the Northern Hemisphere today. Thermokarst lakes are considered large sources of CH₄ contributing to the permafrost carbon feedback and thus, potentially, to climate change. Once thermokarst development is initiated, the organic carbon becomes available for microbial degradation and conversion to CH₄ and CO₂. Our study provides a first approach to quantify microbial process rates involved in the anaerobic oxidation of methane (AOM), which potentially mitigates CH₄ emissions from thermokarst lake sediments. We retrieved sediment cores of up to 6.1 m length from three lakes situated on the Bykovsky Peninsula, Northeast Siberia, of which each lake represents a different stage of thermokarst development. We produced a large biogeochemical data set to characterize the sediment and its pore water constituents. Using radiotracers, we quantified rates of AOM and sulfate reduction (SR) that are often synthrophically coupled to each other. The sediment of all three lakes is characterized by anoxia and high organic carbon content. Organic matter quality showed no correlation to the biogeochemical data, possibly caused by the complex evolution of the thermokarst systems on Bykovsky Peninsula. However, we suggest that there is an active community mediating AOM throughout the sediment column of all three lakes as we were able to detect potential AOM in all samples. Due to the fact that microbial SR could also be detected throughout the cores, we consider sulfate reducers to be the most probable syntrophic partners for the methane oxidizers. Our study shows that AOM is much more widely distributed in thermokarst lake sediments than previously thought and could play a role as a natural methane filter.

2020027641 Karjalainen, Olli (University of Oulu, Oulu, Finland); Luoto, Miska; Aalto, Juha A.; Etzelmuller, Bernd; Grosse, Guido; Jones, Benjamin M.; Lilleoren, Karianne S. and Hjort, Jan. High potential for loss of circumpolar pingos, ice-wedge polygons and rock glaciers due to climate change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Ground ice dynamics bear crucial importance in the hydrologic and ecologic development of permafrost landscapes, but also create characteristic landforms. So far, spatial distributions and sensitivities of these landforms under changing climates have not been assessed at a circumpolar scale. We integrated pingo (n = 9,709), ice-wedge polygon (n = 861) and rock glacier (n = 4,035) observations and geospatial data on environmental conditions into a statistical modelling framework to produce high-resolution (~1km²) distribution maps of permafrost landform occurrence across the Northern Hemisphere in current and future climates. We found that on average more than one-fifth of the potential environmental spaces might be lost by mid-century under a moderate human-induced greenhouse emission forcing (representative concentration pathway, RCP4.5). Thereon, environmental spaces continue to shrink to less than 50% of the current coverage by 2061-2080, given a business-as-usual (RPC8.5) climate-forcing scenario. Forecasted losses of suitable regions for pingos and ice-wedge polygons were attributed to increases in precipitation and thawing-season air temperatures. Rock glaciers were dominantly air temperature-driven. Our results are congruent with the site- and regional-scale observations of rapid geomorphic responses to ongoing climate change, and for the first time demonstrate large regional shifts in potential landform distributions at a circumpolar scale. These findings suggest that extensive regions are undergoing drastic changes in Earth surface processes, e.g. ground ice thaw, which are prone to cause thermokarst and threats to infrastructure development. Despite sophisticated modeling frameworks and increased data availability, circumpolar-scale geomorphological distribution modelling is still highly dependent on the quality of used geospatial data and the completeness of sampling, especially in heterogeneous environments. Based on the magnitude of climatic sensitivities of permafrost landforms, we suggest that geomorphic responses should be closely integrated into assessments of climate change impacts on natural and human systems.

2020032587 Kent, Kelcy (University of Virginia, Environmental Sciences, Charlottesville, VA); Epstein, Howard E.; Jorgenson, Torre; Liljedahl, Anna K.; Griffin, Claire G.; Kanevskiy, Mikhail Z.; Daanen, Ronald P. and Shur, Yuri. Assessment of nitrogen dynamics in soil, vegetation, and surface water across successional stages of ice-wedge degradation and stabilization in the tundra of northern Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1357, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Nitrogen availability affects plant productivity, plant distribution, and feedback loops in Arctic environments. Recent warming has resulted in permafrost thaw in northern Alaska, leading to the release and transport of nitrogen and thereby affecting future vegetation distribution. In ice-wedge polygon permafrost systems, nutrient cycling and availability can vary substantially across ice-wedge polygon successional stages of degradation and stabilization. An improved understanding of fine-scale spatial and temporal nitrogen dynamics among these ice-wedge polygon trajectories will enhance our ability to predict Arctic response to warming. This study aims to identify and quantify plant-available inorganic nitrogen and total dissolved nitrogen in the soil and surface water of various successional stages of degradation in ice-wedge polygons, and to quantify how plant carbon and nitrogen content respond to ice wedge stages across functional groups. NO3- and NH4+ uptake in each site type were assessed with buried bag experiments and AgWestern ion probes. Biomass was clipped from each successional stage to compare functional group composition, and clippings of Eriophorum angustifolium was collected from each successional stage to use as a benchmark species for comparing C:N ratios across site types. Preliminary results from Jago River, Alaska, in 2018 show that though there are relatively small concentrations of NH4+, and especially NO3-, at all sites sampled, there is greater availability of NH4+ and total dissolved nitrogen (TDN) in sites that are experiencing some degree of ice-wedge degradation. A one-way ANOVA found significant differences in NH4+ (p=0.0046), TDN (p=0.00026), and dissolved organic nitrogen (DON) (p=0.0002) among sites. Data from the AgWestern soil ion probes suggest greater N uptake at sites that have experienced some degree of degradation. Further, the %N by weight of plant tissue from E. angustifolium increases slightly with increased ice-wedge degradation, and sedges bordering degraded wedges exhibited an increased "greenness". This preliminary data suggests that ice-wedge polygon degradation results in increased nitrogen availability and transport, and may play a key role in vegetation response to climate warming in dynamic, heterogeneous Arctic ecosystems.

2020027698 Kholodov, Alexander L. (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, Vladimir E.; Spektor, Valentin; Fedorov-Davydov, Dmitry; Andreeva, Varvara; Natali, Susan and Loranty, Michael M. Response of permafrost temperature regime in the northeastern Yakutia to the recent climate changes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1280, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Data of recent observations show that permafrost experiences significant warming during the last decades in entire Northern Hemisphere. The trends of this warming depends on regional climate dynamics as well as local environmental conditions and can be as high as 0.2 degree Celsius per year. Results of our studies demonstrate that extremely high snow accumulation in northeastern Siberia and Alaska during the winter seasons of 2017-18 and 2018-19 lead to significant increasing of the ground warming in these regions. At the same time response of the permafrost temperature to the changes of air temperature and winter precipitations is very variable across the observation sites. We analyzed data from 6 points of monitoring located in northeastern Siberia (two within the tundra natural zone, three in the boreal forest and one in the floodplain of the Kolyma River). Results of the observations show that maximal warming effect was recorded at the sites located at the lower geomorphological levels within the boreal forest ecotype and at the floodplain. At the later one increasing of the permafrost temperature at the depth of 21 meters was recorded first time for the period of observations since the year of 2007. Insulating effect of the higher snow accumulation initiated increasing of the ground warming. On the contrary, at the sites located within the well-drained areas of high geomorphological levels in the boreal forest and both of tundra sites we do not see significant amplification of the permafrost temperature rising. Such effect can be explained by the better efficiency of the snow cover at the wet areas in comparison with dry, because snow can hold up the higher amount of latent heat released after soil moisture freezing within the wet areas.

2020027694 Kicklighter, David W. (Marine Biological Laboratory, Woods Hole, MA); Melillo, Jerry M.; Monier, Erwan; Sokolov, Andrei P. and Zhuang, Qiantai. Future nitrogen availability and its effect on carbon sequestration in northern Eurasia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1274, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

With roughly 70% of the Earth's boreal forests and more than two-thirds of the Earth's permafrost, Northern Eurasia plays a significant role in the planet's carbon cycle. The availability of soil inorganic nitrogen is a critical controller of plant productivity and carbon sequestration in the forests of Northern Eurasia. However, human activities have been altering nitrogen availability in forests, with likely major impacts on carbon sequestration in the region. Understanding the future availability of nitrogen and its effect on carbon sequestration in Northern Eurasia is key to developing effective regional and sub-regional strategies for addressing global change (climate and land-use change) impacts. In this study, we explore how changes in nitrogen availability associated with permafrost degradation, atmospheric nitrogen deposition, and the abandonment of agricultural land to forest regrowth influence carbon storage in the region's forest vegetation over the 21st century. We use a process-based terrestrial ecosystem model that represents carbon-nitrogen interactions under two scenarios of global change. We find that enhanced nitrogen availability increases carbon sequestration in forest vegetation and accounts for 30-50% of the future net carbon sinks estimated for northern Eurasia. We further find that under a high warming and timber forest harvesting scenario, enhanced nitrogen availability increases carbon storage in trees by 13.4 Pg C, mainly caused by permafrost degradation. Meanwhile, under a low warming and forest regrowth scenario, achieved by climate mitigation and forest restoration efforts, enhanced nitrogen availability increases tree carbon storage by 27.8 Pg C or double that under the large warming scenario. In that case, the main driver is the abandonment of agricultural land to forest regrowth. We also find complex regional dynamics among climate change, land-use change and the carbon cycle. This study provides new insight into the role of human activity on future nitrogen availability and its influence on carbon sequestration in northern Eurasia forests. This study further highlights the importance of accounting for carbon-nitrogen interactions when assessing the regional and sub-regional impacts of climate and land-use change policies.

2020032447 Kikuchi, Nobuhiro (Japan Aerospace Exploration Agency, Tsukuba, Japan); Kuze, Akihiko; Kataoka, Fumie; Shiomi, Kei; Hashimoto, Makiko; Suto, Hiroshi; DiGangi, Joshua P.; Kawa, Stephan R. and Mao, Jianping. Monitoring of greenhouse gas emission from permafrost regions by the GOSAT observations of tropospheric CO₂ and CH₄ [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract A41S-2639, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

TANSO-FTS onboard GOSAT has spectral windows in both SWIR and TIR, which enable us to simultaneously observe the Earth's surface reflected sunlight and the thermal emission at the exact same footprint. SWIR spectra have information on the total column amount of CO₂ and CH₄, while TIR spectra are sensitive to these gases mainly in the upper troposphere. Combining these two windows, GOSAT is capable of retrieving mixing ratios of CO₂ and CH₄ in the lower troposphere, which helps the surface flux estimate of these greenhouse gases. It is widely accepted that a large amount of organic carbon is stored in permafrost, which can be released as a result of warming in high-latitude regions (Schuur et al., 2015, Nature). This additional emission of greenhouse gases may accelerate global warming. Therefore, monitoring of the greenhouse gas emissions in permafrost regions is one of the important roles of satellite observations. In this study, we applied our JAXA/EORC experimental retrieval algorithm to derive CO₂ and CH₄ mixing ratios in the troposphere over the permafrost regions (Figure 1), using both GOSAT SWIR and TIR spectra. In our retrieval algorithm, the entire atmosphere is divided into 5 vertical layers, 2 of which are assigned to the lower and upper troposphere. Our retrieval algorithm was validated by comparing retrieved CO₂ and CH₄ mixing ratios in the troposphere with the in situ measurements of the ASCENDS/ABoVE airborne science campaign conducted in the summer of 2017 in Alaska. There are 7 in situ vertical profiles of CO₂ and CH₄ mixing ratios that can be directly compared with the co-located GOSAT observations. We found that the GOSAT retrievals are in agreement with the in situ airborne measurements, except a few cases in which the GOSAT retrievals of CH₄ are somewhat underestimated (Figure 2). Further improvement of the algorithm is underway that includes spectroscopic parameters.

2020032532 Kim, Mincheol (Korea Polar Research Institute, Incheon, South Korea); Kwon, MingJung; Tripathi, Binu Mani and Goeckede, Mathias. Microbial community responses to decadal drainage on a Siberian floodplain [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41I-2437, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Drainage induced by permafrost thaw considerably transforms terrestrial landscapes and ecosystem characteristics in the Arctic. There have been continuous studies on the effects of drainage on greenhouse gas (GHG) flux and soil geochemistry, but the mechanistic links of microbial processes to GHG dynamics have not been well elucidated. We examined changes in microbial communities using shotgun metagenomics on an Arctic floodplain subject to decadal drainage, and linked microbial metabolism to GHG flux (CO₂ and CH₄) and soil geochemistry. The study site is located near Chersky, Russia, and consists of two sites - one that has been drained since 2004 and the other that has not received any treatment. Decadal drainage lowered water tables by ca. 20 cm at the peak of the growing season, and it has changed dominant plant species from Eriophorum angustifolium to Carex spp and shrubs. During the growing season in 2014, CO₂ and CH₄ fluxes were measured, and 5 soil cores up to the permafrost table were taken from each control and drained site. There were no discernible differences in microbial richness; however, microbial taxa and functions shifted due to changes in soil environment from anoxic to oxic conditions in response to drainage. In the drained site, the relative abundance of Alphaproteobacteria and Acidobacteria as well as fungal:bacterial ratios increased. Genes involved in methanogenesis, methane oxidation, and fermentation decreased in the drained site. In particular, Methanoregula and Methanoflorens, which play key roles in methanogenesis under saturated conditions, markedly decreased following drainage. In addition, higher Type I:Type II methanotrophs ratios in wet conditions were reversed due to drainage. These modifications were well aligned with reduced CH₄ emissions in the drained site. Genes related to organic matter degradation became more abundant following drainage, and this can be associated with slightly increased heterotrophic respiration, i.e., CO₂ emissions by microorganisms. Collectively, these results demonstrate that permafrost thaw-induced drainage result in noticeable shifts in microbial communities, and these modifications well explained changes in CO₂ and CH₄ emissions, enabling us to gain a mechanistic understanding of microbial processes regulating GHG dynamics.

2020027663 Kizyakov, Alexander I. (Lomonosov Moscow State University, Geographical Faculty, Moscow, Russian Federation); Streletskaya, Irina D. and Grebenets, Valery I. Hazardous permafrost processes in areas with massive ground ice occurrence in the western Russian Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C41D-1490, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Massive ground ice, includes polygonal-wedge ice, ice-core of pingos and tabular ground ice, are less common than structure-forming ice, but their influence on the surface dynamics is enormous, since their thawing leads to the activation of dangerous permafrost processes such as thermokarst, thermoerosion, complex of slope processes and so on. The dynamics and nature of changes in permafrost state under natural conditions (without anthropogenic impact) for a certain period of time can lead to activation of permafrost processes, making them dangerous and catastrophic in relation to already existing infrastructure facilities. Dangerous permafrost processes and phenomena are mainly due to the reaction of the upper layers to new formations (aggradation) or the degradation of permafrost as a result of changes in heat transfer conditions on the surface. The growth of annual sums of positive temperatures leads to the activation of thermal denudation in areas with subsurface ground ice occurrence. These processes lead to formation of vast thermokarst depressions, themocirques (or retrogressive thaw slumps) and erosion ravines. Over the past decades, due to the imposition of climatic fluctuations of different durations, the average air temperature in Western Siberia has increased by several tenths of a degree. Modern climate warming leads to an increase of permafrost temperature, and growth of active layer thickness. In Central Yamal, in recent years, an increase in the growth of themocirques has been observed, associated with the thawing of tabular ground ice. New themocirques appear, as well as a new cycle of activation appeared of previously stabilized forms. Studies of the dynamics of the coastal dynamics of Kolguev Island with tabular ground ice exposures show high retreat rates of themocirques in recent years (up to 15 m/year). High retreat rates are also revealed on the coasts of Yugorskiy Peninsula. Supported by RFBR grants # 18-05-60080 (destruction rates estimation) and 18-05-60221 (methods of remote sensing data analyses).

2020032544 Kling, George W. (University of Michigan Ann Arbor, Ann Arbor, MI); Euskirchen, Eugenie Susanne; Bret-Harte, Marion Syndonia; Edgar, Colin and Stuefer, Svetlana L. The net aquatic and terrestrial carbon balances are linked by weather events in a headwater Arctic catchment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Determining how carbon, water, and energy balance are changing in the Arctic is a key issue with major implications for feedbacks to further global climate change. Since 2007 we have maintained an NSF-AON network of year-round micrometeorological eddy flux towers arrayed along a hillslope-moisture gradient, as well as measurements of stream discharge and carbon chemistry in a headwater arctic catchment, Imnavait Creek on the North Slope of Alaska (continuous permafrost). Over the period of our observations we have detected a change in the net terrestrial carbon balance and an increase in the average depth of thaw in the catchment. These catchment-level changes are possibly nearing an acceleration of permafrost thaw and carbon release to the atmosphere that cannot be easily reversed. The measurement network allows for direct comparison and integration of both terrestrial and aquatic carbon fluxes at a catchment scale. Our co-located measurements of carbon flux in Imnavait indicate that the terrestrial carbon flux between land and atmosphere is typically about an order of magnitude larger than the carbon exported in stream water from the catchment (chemical concentrations times discharge plus gaseous flux to the atmosphere). Seasonal dynamics in fluxes show that in the shoulder seasons May and September the landscape is losing carbon to the atmosphere (positive NEE, Net Ecosystem Exchange), while during summer months the landscape is usually a sink for carbon (negative NEE). The aquatic fluxes show a different pattern, driven predominantly by snowmelt and storm events that increase channel discharge and carbon export. Increased aquatic export can be related to increased terrestrial carbon flux to the atmosphere during certain periods when storm intensity is greatest. This correlation of aquatic and terrestrial fluxes suggests that future changes in storm frequency or intensity will strongly affect the loss of carbon from catchments; in years of low NEE (near zero), aquatic fluxes can dominate the overall carbon loss from the landscape. Such analyses of the controls and dynamics of integrated aquatic and terrestrial carbon fluxes may be useful in understanding landscape-level carbon balances in the Arctic.

2020032483 Koch, Joshua C. (U. S. Geological Survey, Anchorage, AK); Ebel, Brian A.; Bogard, Matthew; Wickland, Kimberly; Toohey, Ryan; Reeves, Donald Matthew; Butman, David E.; Striegl, Robert G. and Walvoord, Michelle A. Preferential flow mechanisms and implications for carbon transport and cycling in permafrost systems [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2539, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The boreal forest is a major biome that stores much of the Earth's carbon and is undergoing rapid change related to warming air temperatures, permafrost thaw, and altered fire regimes. Ground disturbance from permafrost thaw and wildfire are changing soil morphology, hydrology, and thermal state, with implications for the release of carbon to ecosystems. These changes are often manifest through preferential flow pathways, which allow rapid drainage of hillslopes and rapid transport of water and carbon to surface waters. Here we characterize preferential pathway types, distributions, and flow rates, and connections to surface waters in various headwater streams in boreal Alaska. We identified several types of preferential flow mechanisms, associated with features including erosional gullies and seeps that formed with the collapse of thawed grounds, macropores and pipes that formed within mineral soils, and horizontal soil boundaries such as the transition from organic to mineral, and thawed to frozen soils. These preferential flow mechanisms allow the transport of water and solutes up to several magnitudes faster than flow through the soil matrix in some cases, and can be linked to permafrost thaw through 14C and uranium isotope ratios. Thus, we argue that accounting for preferential flow will improve our ability to identify the appropriate spatial and temporal scales for observing the movement and utilization of permafrost-derived carbon in boreal forest ecosystems.

2020032635 Koh, C. (Colorado School of Mines, Golden, CO); Majid, A. A. A.; Wells, J. and Creek, J. Thermophysical & rheological properties of natural gas hydrates [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract MR13D-0098, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Gas clathrate hydrates are crystalline compounds comprised of a hydrogen-bonded network of water cages that trap small organic molecules, such as methane, ethane, and carbon dioxide. The vast amount of energy trapped in naturally occurring gas hydrate deposits has been estimated to be greater than all other fossil fuel resources available worldwide. In order to realize the potential of the energy trapped in gas hydrates found in oceanic sediments or sediments under the permafrost, key scientific questions need to be addressed on the thermophysical properties of gas hydrates. Gas hydrate thermophysical properties are also important to control the formation of gas hydrates in offshore petroleum pipelines, that can lead to plugging of the pipelines with subsequent severe risks to personnel and the environment. Critical to mitigating gas hydrate plug formation during energy production from gas hydrate or conventional petroleum reservoirs is the ability to predict the thermodynamic and rheological properties of gas hydrate-fluid systems at subsea conditions. This paper will review the state-of-the-art of gas hydrate thermophysical and rheological properties determined from model predictions and experiment. In-situ measurements of gas hydrate phase behavior and viscosity trends will be presented using a range of measurements techniques, including high pressure differential scanning calorimetry, confocal Raman spectroscopy, and slurry rheology.

2020032686 Koppes, Michele N. (University of British Columbia, Vancouver, BC, Canada). Impacts of dwindling glaciers and ice sheets in the Earth system [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Freshwater stores in glaciers and ice sheets worldwide are rapidly declining, a trend that is only expected to accelerate due to progressive warming. A cascade of effects are the result, extending from the mountains to the ocean, with impacts on human livelihoods, economy and habitability. The timing and magnitude of meltwater streamflows are shifting, and sediment and nutrient fluxes are increasing, influencing water quality and aquatic habitat. Slope failures and outburst floods due to thawing alpine permafrost and glacier shrinkage results in rapid, stochastic transfers of mass, threatening downstream populations. The mass transfer of both water and sediment from land to sea drives regional and global sea level rise and isostatic adjustments. Cataloging, monitoring and quantifying these cascading effects are key to understanding the evolving role of glaciers and ice sheets on people and the Earth system.

2020032463 Kou Dan (Chinese Academy of Sciences, Institute of Botany, Beijing, China) and Yang Yuanhe. Spatially-explicit estimate of Tibetan permafrost nitrogen stock and its implication for land model [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13N-2528, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost soils store a large amount of nitrogen (N) which could be activated under the continuous climate warming. However, compared with carbon (C) stock, little is known about the size and spatial distribution of permafrost N stock. By combining measurements from 519 pedons with two machine learning models (supporting vector machine (SVM) and random forest (RF)), we estimated the size and spatial distribution of N stock across the Tibetan alpine permafrost region. We then compared these spatially-explicit N estimates with simulated N stocks from the Community Land Model (CLM). We found that N density (N amount per area) in the top three meters was 1.58 kg N m^-2 (interquartile range: 1.40-1.76) across the study area, constituting a total of 1802 Tg N (interquartile range: 1605-2008), decreasing from the southeast to the northwest of the plateau. N stored below one meter accounted for 48% of the total N stock in the top three meters. CLM4.5 significantly underestimated the N stock on the Tibetan Plateau, primarily in areas with arid/semi-arid climate. The process of biological N fixation played a key role in the underestimation of N stock prediction. Overall, our study highlights that it is imperative to improve the simulation of N processes and permafrost N stocks in land models to better predict ecological consequences induced by rapid and widespread permafrost degradation.

2020032653 Kumar, Priyadarshi (National Geophysical Research Institute, Seismics, Hyderabad, India) and Sain, Kalachand. Gas-hydrates; Indian scenario [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS41B-1677, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Gas-hydrates, ice-like crystalline substances of methane (99.9%) and water, have attracted the scientific community because of their natural occurrences along the outer continental margins and permafrost regions, and huge potential as viable major future energy resources. Successful test productions in Canada, USA, Japan and China during the last decade have provided great hopes to Indian national gas-hydrates programs. The bathymetry, seafloor temperature, total organic carbon content, sediment-thickness, rate of sedimentation, geothermal gradient imply that the shallow sediments in deep water along the Indian margin are good hosts for gas-hydrates. The methane within gas-hydrates has been prognosticated to be >1500 times of country's present natural gas reserve, which can make India energy self-sufficient. Even 10% production from this gigantic reserve can meet India's overwhelming energy requirement for many decades. Thus, it was felt necessary to map the prospective zones of gas-hydrates and evaluate the resource potential. The gas-hydrates stability thickness map of India has been prepared, which provides the maximum depth of gas-hydrates occurrences and helps in identifying the bottom simulating reflectors or BSRs, main marker for gas-hydrates. Analysis and scrutinizing available seismic data reveal the signatures of gas-hydrates in the Krishna-Godavari (KG), Mahanadi and Andaman basins. Various seismic attributes like the reflection strength, blanking, attenuation and instantaneous frequency have been computed to characterize the gas-hydrate reservoirs. Several approaches based on seismic traveltime tomography, full-waveform inversion, amplitude versus offset modeling, impedance inversion, coupled with rock-physics modeling have been developed, and applied to the field seismic data. All these will be presented for the delineation and assessment of gas-hydrates in the eastern Indian margin.

2020032613 Langhorst, Theodore (University of North Carolina at Chapel Hill, Chapel Hill, NC); Pavelsky, Tamlin; Topp, Simon; Ross, Matthew; Dai, Chunli; Durand, Michael T.; Frasson, Renato P. M. and Howat, Ian. Remotely sensed discharge and sediment flux of the Sagavanirktok River [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H21N-1954, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Changes in freshwater runoff and sediment transport to the Arctic Ocean reflect watershed-wide climatic changes, affect ecological habitats, and potentially alter ocean circulation patterns. In this light, monitoring Arctic rivers is important both as an indicator and a feedback to climate change. Arctic rivers have shown steadily increasing discharge and changing seasonal patterns due to increases in precipitation, humidity, permafrost degradation, and forest fires. Sediment transport has shown similar shifts in recent decades. Current discharge and sediment flux data have poor spatial and temporal coverage, and models that fill these gaps have few observational constraints. We use water surface elevation and river width data extracted from ArcticDEM to estimate discharge and establish a width-discharge rating curve on the Sagavanirktok River in Alaska as a test case. We then use optical satellite imagery to apply this rating curve and estimate discharge for hundreds of days over several decades. Last, we train a model with global water quality measurements and optical imagery in order to estimate total suspended solids using the same images used to estimate discharge. The combination of these methods represents multitemporal estimates of discharge and sediment flux, separate from gage data or in situ measurements, and provides a new means to constrain and evaluate global models.

2020032558 Lanoil, Brian D. (University of Alberta, Biological Sciences, Edmonton, AB, Canada); Neuberger, Patrick; Saidi-Mehrabad, Alireza and Froese, Duane G. Bacterial community composition changes independently of soil edaphic parameters with anthropogenic permafrost thaw [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost is a major reservoir of organic carbon that becomes vulnerable to microbial biodegradation upon thaw, resulting in increased flux of the greenhouse gasses CO₂ and CH₄. Although shifts in microbial communities occur rapidly upon thaw in laboratory conditions, such shifts are less clear in the field, and it is unclear whether observed changes in the edaphic parameters of these soils precede, co-vary, or follow these shifts. Further, it is unclear whether the microbial communities in thawed permafrost are derived from the underlying permafrost, are sourced from nearby undisturbed soils, or are a novel microbial community. To assess these questions, we examined the microbial diversity of soils near a gold mine at Dominion Creek, Yukon, Canada where thaw was induced by removal of vegetation and topsoil for road building. These soils were on a disturbance gradient, from undisturbed forest soils underlain by permafrost, through devegetated soils, to recently thawed permafrost adjacent to a small thermokarst pond. We analyzed the 16S rRNA gene diversity in three cores and eight surface samples across the disturbance transect. While soil edaphic parameters did not change six weeks after disturbance, microbial communities showed significant changes. Cluster analysis of the bacterial assemblage identified three distinct groups within the dataset: (1) undisturbed active layer, (2) lower active layer, disturbed active layer, and disturbed permafrost, and (3) intact permafrost. Community shifts were correlated with pH and Zn concentrations, in addition to community interaction metrics, suggesting that these shifting communities are primarily controlled by internal forcing factors. This study suggests a strong microbial community response to permafrost disturbance under field conditions and that this response occurs prior to shifts in the measured soil edaphic parameters. Furthermore, it appears that disturbance such as devegetation leads the soil microbial communities to resemble those of the lower active layer of undisturbed soil, and that either of these may be the source of the community in thawed permafrost soils. Anthropogenic disturbances may therefore impact microbial biodiversity in permafrost-affected soils, with possible implications for ecosystem functioning and stability.

2020032598 Lara, Mark J. (University of Illinois at Urbana Champaign, Urbana, IL); Chipman, Melissa L. and Chen, Yaping. Navigating disturbance regimes in the new Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1368, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic regions have experienced unprecedented climate warming over the past several decades, as well as record-setting rates of disturbance processes such as wildfires, permafrost degradation, and shrub expansion. A growing body of evidence suggests dynamic interactions and feedbacks exist Arctic disturbance regimes. However, the interdependence of these disturbances over space and time makes quantifying their impact challenging, yet paramount for improving our predictive capacity as climate change and disturbance regimes intensify. We present preliminary results from northern Alaskan tundra detailing decadal patterns of thermokarst formation (70+ years) in response to fire and climate change, decadal patterns of lake drainage (50+ years) in response to climate and environment, decadal patterns of thaw slump activity/lake expansion (40+ years) in response to climate change, decadal patterns of shrub expansion (50+ years) in response to climate and environment (Seward Peninsula), and describe progress linking decadal patterns of change to paleoecologial lake sediment cores for extending these observations of disturbance over centennial time-scales. I will outline recent findings, research directions, and potential opportunities for collaboration in our newly funded NSF project, where we evaluate the vulnerability of Arctic tundra regions in northern Alaska to multiple interacting disturbances over the longest time-horizon (decadal to centennial-time scales) ever evaluated in the Arctic.

2020032478 Lathrop, Emma (Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM); Newman, Brent D.; Wilson, Cathy Jean; Musa, Dea; Arendt, Carli A.; Charsley-Groffman, Lauren; Conroy, Nathan Alec; Heikoop, Jeremy M.; Marina, Oana; Perkins, George and Wales, Nathan A. Comparing soil moisture and geochemistry in continuous versus discontinuous permafrost watersheds in the Seward Peninsula, Alaska, USA. [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2533, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Carbon storage and release of emissions from degrading permafrost is linked to hydrologic and geochemical conditions in a landscape. The Next Generation Ecosystem Experiments (NGEE) Arctic project aims to improve understanding of the association between permafrost thaw and the carbon cycle. A key challenge is to understand how different permafrost watersheds behave. We analyzed intra-and inter-site variations in hydrologic and geochemical data in a discontinuous permafrost watershed (Teller) and continuous permafrost watershed (Kougarok). Soil moisture data were collected using time-domain reflectometry (TDR) probes. Water samples were collected using passive wicks (PCAPs), macro-rhizons, and as surface grabs, and analyzed for major geochemical species. Key intra-site variations at Teller include wetter soils in areas with mossy vegetation and highly variable redox chemistry over small scales, as indicated by wide ranges of Fe and NO₃ concentrations. Significantly higher concentrations of NO₃ are observed within willow stands. At Kougarok, intra-site variations are driven by a hillslope gradient. On the toe slope, increases in soil moisture correspond with higher concentrations in reduced species, such as Fe₂⁺. Higher concentrations of oxyanions such as NO₃, PO₄, and SO₄ are observed in alder stands on the ridge. Inter-site differences are affected by the range of and controls on soil moisture and the absence of permafrost. At Teller, the association between willows and taliks affects soil moisture content and NO₃ concentrations. At Kougarok, a hillslope gradient keeps sites on the ridge relatively dry, driving a larger intra-site range in soil water content than is observed at Teller. Both sites have elevated concentrations of NO₃ in shrub areas, but water from alder stands at Kougarok are significantly higher in NO₃ than the willow stands at Teller. Our data highlight the importance of landscape heterogeneity in controlling soil moisture and geochemistry, and will be used to better understand factors controlling carbon and nutrient cycling in Arctic landscapes and the impact of climate change and permafrost thaw on changes in carbon emissions.

2020027664 Li, Dongfeng (National University of Singapore, Department of Geography, Singapore, Singapore); Xixi, Lu and Li Zhiwei. Impact of climate change on water and sediment fluxes in cold region; an example from the source region of the Yangtze River, high mountain Asia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C43A-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Quantifying fluxes of water and sediment in cold region rivers is important for linking the glacial, fluvial channels and coastal ecosystems and to assess the impact of a globally warming climate. However, few studies have documented the changes in sediment fluxes of cold regions based on long-term measurements, especially in the Tibetan Plateau (TP). This study uses a long-term monthly runoff and sediment load dataset from a TP headwater river basin, the source-region of the Yangtze River (SYR), to quantify the changes in runoff and sediment load and evaluate the impact of climate change. Results show a radical increase in annual runoff and sediment load from 1986-1997 to 1998-2016 at the upstream Tuotuohe (TTH, a main tributary of the SYR with larger proportions of glaciers) station primarily due to an increase in temperature and also because of enhanced precipitation. At the Zhimenda station, the outlet control station of the entire SYR with much lower proportions of glaciers, there was a moderate increase in annual runoff and sediment load primarily due to an increase in precipitation. The discrepancy of the increases in sediment load between TTH and ZMD was probably due to the large amounts of sediment deposited in the wide braided channels (1-3 km wide, ~300 km long) along the reach from TTH to ZMD. Monthly analysis shows consistent findings with the annual results, with the increases occurring mostly in melting season from May to October. A sediment yield framework was developed for the high-altitude cold regions, explaining the driving processes of glacial erosion, permafrost freeze-thaw erosion, snow melt erosion, and rainfall erosion, which jointly led to the increase in sediment load with climate change. The increases in sediment load may have significant fluvial geomorphic and ecological implications for the TP and its downstream parts.

2020027635 Li Ruichao (Chinese Academy of Sciences, LASG, Institute of Atmospheric Physics, Beijing, China); Xie, Z.; Gao Junqiang; Xie Jinbo; Wang Longhuan and Wang Yan. Simulated the spatial and temporal distribution of freeze and thaw fronts [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1390, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost and seasonally frozen ground are an important part of the cryosphere. It is widely distributed, and the cycle of freezing and thawing of frozen ground has an important influence on water and energy and water exchanges between the land surface and the atmosphere. The dynamic change of freeze and thaw fronts is a key variable in the process of freezing and thawing. In this study, we investigated.

2020032597 Li Xiaoying (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Laboratory of Frozen Soils Engineering, Lanzhou, China); Jin Huijun; He Ruixia; Huang Yadong; Wang Hongwei and Lu Lanzhi. Impacts of forest fires on the active layer thickness and near-surface permafrost temperatures in the northern Da Xing'anling (Hinggan) Mountains, NE China [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1367, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Under a warming and drying climate and with increasing anthropic activities, the occurrences of wild and human-induced fires have been increasingly more frequent in boreal forests during the last few decades. They could result in an irreversible degradation of permafrost, physical and chemical properties of soils, and subsequent hazardous periglacial landform changes. In the northern Da Xing'anling (Hinggan) Mountains, NE China, forest fires have important impacts on the thermal regimes of soils in the active layer and near-surface permafrost. Four burnover areas were selected to study the impacts of forest fires on the thermal regimes of near-surface permafrost. The fires occurred in 1987 (F1), 2002 (F2), 2009 (F3) and 2015 (F4) in larch (Larix gemileni) woodland in the continuous permafrost zone, respectively. Results show that changes of the active layer thickness (ALT) and ground temperatures are obvious, and they enlarge with the increasing fire severity. The temperature difference between the severely burned and unburned sites reached 3.7°C at the depth of 0.2 m in the F2 area 15 years after the burn. Seven years after the fire, the thermal impacts of the severe burn reached 20 m, with a maximum temperature difference of 2.1°C between the severely burned and unburned sites. Moreover, 30 years after fire, in F1, the thermal impacts of the severe burn reached more than 20 m in depth. The temperature difference between the lightly burned and unburned sites was minor. After the forest fires, the ALT increased with increasing fire severity. For example, at F3, the ALT was 0.5 m at the unburned site, 1.0 m at the site of light burn, and 3.5 m at the site of severe burn, with a 6 folds increase in the ALT in comparison with that of the unburned site. With the elapsing post-fire years, the ALT at the burned sites increased first and then decreased, then gradually returned to the pre-fire level after the severe burn. This process took 30 years, or longer. Overall, after the forest fire, ground temperature and ALT increased obviously, and evidently higher in the severely burned area than that of unburned areas.

2020032531 Liang, Renxing (Princeton University, Department of Geosciences, Princeton, NJ); Li, Zhou; Lau, Maggie; Vishnivetskaya, Tatiana A.; Lloyd, Karen G.; Pfiffner, Susan M.; Rivkina, Elizaveta; Wang, Wei; Wiggins, Jessica; Miller, Jennifer; Hettich, Robert and Onstott, Tullis C. Reconstruction of metagenome-assembled genomes from past and extant microbial populations in ancient Siberian permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41E-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Total DNA (intracellular, iDNA and extracellular, eDNA) preserved in ancient permafrost represents a mixed genetic repository of the past and contemporary microbial populations. When coupled with metaproteomics and DNA repair, metagenomic sequencing of iDNA and eDNA fractions allowed us to reconstruct and differentiate metagenome-assembled genomes (MAGs) from past and contemporary microbial populations preserved in perennially frozen marine sediment (100-120 kyr) from various depths (3.4, 5.8 and 14.8 m) on the East Siberian Sea coast. The MAGs from the youngest sample at 3.4 m likely originated from the contemporary, active microbial species based on the converging evidence of minimal DNA damage, negligible impact of DNA repair on MAGs completeness and expressed proteins from most MAGs. For the older, deeper samples at 5.8 and 14.8 m that exhibited greater DNA damage and aspartic acid racemization, the PreCR repair enzymes corrected DNA damage and thus dramatically increased the completeness of MAGs from both iDNA and eDNA fractions mostly belonging to aerobic lineages affiliated with the phyla Actinobacteria and Proteobacteria. The smaller number of proteins that mapped to these improved MAGs further suggested that they might represent past microbial species that have died upon deposition and freezing over time. By contrast, MAGs affiliated with facultative and obligate anaerobic lineages from Spirochaetales and Clostridiales, Chloroflexi and the Asgard archaea showed similar completeness in both iDNA and eDNA fractions irrespective of DNA repair. Moreover, most expressed proteins that were associated with these MAGs are related to multiple mechanisms for coping with different stresses and metabolism of various carbohydrates and peptides. Therefore, these groups of anaerobic microbes have become adapted to the cryogenic and anoxic environments in this ancient frozen marine horizon. With the aid of DNA repair enzymes to reconstruct fossil MAGs and metaproteomics insights can be gained into adaptive strategies and long-term survivability of indigenous microbes and biogeochemical cycling through geological time in ancient permafrost and potentially other environments.

2020027619 Liljedahl, Anna K. (University of Alaska, Water and Environmental Research Center, Fairbanks, AK); Jones, Benjamin M.; Brubaker, Michael; Budden, Amber E.; Cervenec, Jason M.; Grosse, Guido; Jones, Matthew B.; Marini, Luigi; McHenry, Kenton; Moss, Jennifer; Morin, Paul J.; Nitze, Ingmar; Soliman, Aiman; Wind, Galina and Witharana, Chandi. Permafrost Discovery Gateway; a Web platform to enable discovery and knowledge-generation of permafrost Big Imagery products [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1373, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw has been observed at several locations across the pan-Arctic in recent decades, yet the pan-Arctic extent and potential spatial-temporal variations in thaw are poorly constrained. Thawing of ice-rich permafrost can be inferred and quantified with satellite imagery due to the subsequent differential ground subsidence and erosion that also affects land surface cover, storage and flow of water, sediment, and nutrients. However, a lack of supporting cyberinfrastructure necessary to harness information from the existing and rapidly growing collection of high-resolution satellite imagery (Big Imagery) has limited our advances in understanding the nature of pan-Arctic permafrost degradation. In the coming four years, we will empower the broader Arctic community with a cyberinfrastructure platform, the Permafrost Discovery Gateway (PDG), aimed at making Big Imagery permafrost information accessible and discoverable through novel visualization and analysis tools designed with input from users of the PDG, e.g. the diverse peoples living, working, and/or studying in the Arctic. From the start of the project, we will engage the user-community through in-person and online meetings to ensure effective development of permafrost Big Imagery products for archiving, processing, analyzing, and visualizing. The framework will utilize existing resources, such as the (1) NSF supported data management resources the Arctic Data Center and Clowder, (2) web application visualization tools (Fluid Earth Viewer, Google Earth, and Gapminder Foundation), (3) high performance computing resources (XSEDE, Google Earth Engine etc.), and (4) and satellite imagery (Polar Geospatial Center, Landsat, Sentinel, and Planet). The PDG will include the management of ingesting remote sensing big data into machine and deep learning models. We welcome collaborations with national and international Native, industry, and academic organizations and individuals to ensure broad community engagement and dissemination. The PDG will enable diverse peoples to contribute to and have access to pan-Arctic permafrost knowledge, which can immediately inform the economy, security, and resilience of the Nation, the Arctic region, and the globe with respect to pan-Arctic change.

2020032585 Lilly, Michael R. (Geo-Watersheds Scientific, Fairbanks, AK); Tahirkheli, Sharon N.; Levine, Kristina; Brown, Jerry and Streletskiy, Dmitry A. The Permafrost Monthly Alert (PMA) program; improving reference searches now and in the future [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1354, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The U.S. Permafrost Association (USPA) and the American Geosciences Institute (AGI) developed the Permafrost Monthly Alert (PMA) program to enhance access and discovery of relevant and professionally reviewed international permafrost science and engineering literature on a regular monthly schedule. Results are made available in multiple locations on the Internet that are regularly indexed by major search engines. The monthly-updates portion of the PMA program are available through the USPA website (www.uspermafrost.org). The current eight-year collection includes over 94 monthly and special updates containing over 6,000 citations. The vast majority of the references have abstracts and are organized in four major categories: journals, conferences, thesis and reports. Monthly accessions are uploaded to the AGI publicly accessible database COLD (developed from the Bibliography of Cold Regions Science and Technology database). COLD is a searchable database with almost 30,000 current and historical permafrost references, and indexed by various search engines. Annual usage of the PMA service exceeded 11,000 inquiries (views by readers) in the last three years, with over 60,000 inquiries since 2012. Special Alerts of permafrost-related conferences are a recent addition to PMA; over 300 abstracts were identified from the 2018 AGU Fall Meeting. More publishers are using continuous publishing, where individual articles are published online before full journal issues are released. We now include the regular use of Google Scholar to find additional references released online, but not yet in a full journal issue. New information is available to a larger number of users in a shorter period of time. By placing references in multiple locations, which are regularly indexed by search engines and are high quality sites, references are more easily found by a wider range of users. Science priorities also change over time with permafrost carbon-related publications serving as one example. PMA search and collaborative efforts are being modified to add more references related to carbon-permafrost research. Information systems will continue to rapidly evolve with continued advances in electronic delivery platforms. Information types will also expand as the key focus of polar science and engineering research topics change.

2020027684 Lininger, Katherine B. (University of Colorado at Boulder, Boulder, CO) and Rowland, Joel C. River corridor dynamics in permafrost regions under a changing climate; detecting signatures of change and assessing implications for geomorphic processes and the carbon cycle [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP34B-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

High-latitude permafrost regions are rapidly warming, resulting in the potential for significant changes to Earth's surface. Floodplains in permafrost regions can store significant organic carbon stocks within floodplain sediment, and these floodplain stocks may be vulnerable to permafrost thaw and degradation, enhanced channel migration rates, and changes to incoming water and sediment. Past climatic changes resulted in significant geomorphic changes in river corridors identified in the sediment record, but we lack a conceptual framework that could be used to identify ongoing and future signatures of change in channel and floodplain processes. We present conceptual models describing likely changes to reach-scale geomorphic dynamics that will influence channel and floodplain process and form and organic carbon storage. Potential changes discussed include changes in permafrost extent, active-layer thickness, vegetation characteristics, bank erosion and channel migration rates, and flow and sediment regimes. We use examples from recent work in the central Yukon River Basin in interior Alaska to illustrate the need to assess geomorphic processes and floodplain storage to better understand the flux and storage of carbon on the landscape. As highlighted from our work on the Yukon River, a critical challenge in identifying signatures of climate change is the detection of long-term trends in systems with large spatial and temporal variations in process rates. Changes in channel and floodplain process and form will likely impact the storage and transport of sediment and associated carbon and nutrients, influencing exports to the Arctic Ocean, the spatial distribution of carbon on the landscape, and the release of carbon to the atmosphere.

2020027639 Liu, F. (Michigan Technological University, School of Forest Resources and Environmental Sciences, Houghton, MI) and Ding, Y. Shift in hydrologic regime and potential impact on services in cold regions with a changing climate [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C21A-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate warming has resulted in glacier retreat, permafrost thawing, less snowfall relative to rainfall, and earlier onset of snowmelt in high altitudes and latitudes, all of which lead to changes in hydrologic regime and subsequent changes in ecological and societal services. Using stable isotopes and geochemical tracers, our study in Binggou and Yakou catchments in the northeastern Tibetan Plateau indicated that streamflow was dominated by new water and near surface runoff during the spring snowmelt season as surface frozen soils prevent from infiltration, but by old water and deeper subsurface flow during the summer rainfall season as surface frozen soils thaw. With a continuous rising of soil temperature in permafrost-covered region, streamflow would shift to a hydrologic regime dominated by deeper flowpaths, which likely causes dampening of peak flows and increasing of baseflow at regional scales. A similar study in the glacier-covered Shule River catchment in the same region found that nearly 20% of streamflow was generated from glacier meltwater at large catchment scales (up to 4210 km²) at present condition. If the glacier retreat continues in the region, the contrition of glacier meltwater to streamflow could be considerably reduced and the downstream water supplies would be negatively impacted. Due to an increase in rainfall relative to snowfall and earlier snowmelt, peak streamflow has been shifting earlier away from summer when water is most needed. This shift is occurring not only in high-elevation regions of the western US but also in the Great Lakes Region of US and Canada. Our data showed that the central mass timing of streamflow from January to May on the leeward side of southern and eastern Lake Superior, where the lake-effect snow is greatest, has come significantly (p < 0.05) earlier since 1980s. Consistent with the mountain catchments of the Western U.S., this result is certainly caused by earlier onset of snowmelt in the Great Lakes region. A continuation of this trend could impact fish and wildlife. Salmonid species are particularly at risk, as cold stream water temperatures associated with spring meltwater plays an important role in spawning. Damage to fish population due to earlier snowmelt will negatively affect the regional food web as well as regional commercial and tourist fishing.

2020032494 Loisel, Julie (Texas A&M University, College Station, TX); Gallego-Sala, Angela V.; Amesbury, Matthew J. and Magnan, Gabriel. Expert assessment suggests global peatlands will switch to a carbon source in near future [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23L-2510, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Using literature reviews and expert opinion surveys, we identify and quantify the leading drivers of change that impact peatland carbon stocks and that may provoke non-linear responses in these ecosystems. We show that the relative importance of each driver of change varies over time and space. The expert surveys revealed that small carbon gains across the high latitudes are expected in the near and far future as a result of warmer temperatures, though they will be offset by carbon losses from permafrost thaw, peat fire, and drought. In the tropics, net carbon losses are already underway and expected to increase, mainly as a result of drought, climate warming, land-use change, and peat fire. The overall global carbon balance is expected to switch from sink to source in the near future, mainly because tropical peatland emissions combined with those from permafrost thaw will surpass the carbon gain expected from enhanced plant production in the high latitudes. In total, the net carbon loss for the near (2020-2100 CE) and far (2100-2300 CE) future combined is estimated at 112 Gt globally (geometric mean), of which 25% is due to land-use change alone. Land management could therefore considerably reduce this figure, if large-scale peatland degradation across the tropics are diminished and restoration efforts are undertaken. While these new results are directly relevant to stakeholders, we note that the spread of values that came out of the expert assessment is at least as important as the trends, in that it helps specifying uncertainties and identifying knowledge gaps among the peatland scientific community. We argue that this expert assessment provides a unique perspective on a complex issue, and that the results therein could not have been provided otherwise.

2020032611 Lonchar, Rachel S. (University of Minnesota Twin Cities, Civil, Environmental, and Geo-Engineering, Minneapolis, MN); Roman, Tyler D.; Sebestyen, Stephen D.; Ng, G. H. Crystal; Liu, Shaoqing; Kolka, Randy and Feng, Xue. Stochastic model of water table depth in snow-dominated and hydrologically connected ecosystems [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H13Q-1989, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate change is warming air temperatures, shifting regional precipitation patterns, and drastically altering ecosystem biogeochemical functioning. This is especially critical in carbon-rich northern peatland and permafrost ecosystems, where climate change-induced shifts in soil temperature and hydrological dynamics will likely dictate the direction, magnitude, and spatial extent of carbon emissions (CO

2020032601 Lu Ping (Tongji University, Shanghai, China); Hao Tong; Li, R. and Qiao Gang. Permafrost ALT estimation along the Qinghai-Tibet railway through InSAR and modeling [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51P-1006, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost, as one of the largest elements of the terrestrial cryosphere, is very sensitive to global climate change. Changes of permafrost not only affect regional and global water circulation, carbon deposit and climate warming, but also influence ground ecological, geophysical, and biogeochemical processes in cold regions. The permafrost region of the Qinghai-Tibet Plateau is the highest and largest permafrost area in the middle and low latitudes of the world. The Qinghai-Tibet Railway, from Xining to Lhasa, is 1956 kilometers long, including a total length of 550 kilometers over the permafrost region. The active region along Qinghai-Tibet Railway is selected as the study area. In order to monitor the active layer thickness (ALT), the surface deformation pattern was be analysed by the C-band Sentinel-1 and the L-band ALOS satellites, using the processing techniques of D-InSAR, PS-InSAR and SBAS. The Stefan model was then applied to estimate ATL based on the land surface temperatures (LSTs) data acquired from MODIS and soil thermal parameters. Surface deformation and ground temperature data from the in-situ borehole monitoring along the railway were used to validate the simulated results. The estimations from InSAR are in agreement with the in-situ measurements.

2020032560 Luo, Yiqi (Northern Arizona University, Flagstaff, AZ); Lu Xingie; Schuur, Edward; Mauritz, Marguerite; Taylor, Meghan; Rodenhizer, Heidi; Schaedel, Christina; Ebert, Christopher; Garnello, Anthony; Pegoraro, Elaine; Ma, Shuang and Huang, Xin. Significant C source driven by elevated water table but sink by increasing thaw depth in Alaska tundra under experimental warming; a data assimilation study [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The permafrost region is more vulnerable than any other region on the Earth under climate change. Gradual changes in thaw depth and water table in tundra ecosystem have been widely observed in response to on-going climate warming. However, how ecosystem carbon cycle is affected by changing thaw depth and water table has not been comprehensively estimated. In this study, we applied the data assimilation technique to a snow-fence soil warming experiment, which has been established at a subarctic tundra ecosystem in Alaska since 2009. We optimized parameterization of the Terrestrial ecosystem model (TECO) against 8-year observation data sets, including water table depth, thaw depth, carbon flux, carbon pool sizes, snow depth, soil moisture, and soil temperature. The optimized TECO generated response functions of net ecosystem exchange (NEE), gross primary production (GPP), and ecosystem respiration (ER) to thaw depth and water table depth gross primary production (GPP), and ecosystem respiration (ER) to thaw depth and water table depth. Our results showed that ecosystem changed towards carbon sink by about 80 g C m^-2 yr^-1 with thaw depth increasing from 0.5 to 1.2 meter because modeled GPP increased much more than does ER. In contrast, water table depth rising from -0.35 to 0.15 m shifted the system to a carbon source of about 160 g C m^-2 yr^-1because GPP suppression was much stronger than ER suppression. Overall, changing water table depth plays a more important role in regulation of the carbon cycle-climate change feedback in this permafrost ecosystem than changing thaw depth. However, most terrestrial ecosystem models do not consider thaw-driven subsidence processes nor the flood effects on ecosystem C cycle. Our study indicates that developing subsidence and flood modules in terrestrial ecosystem models is crucial to accurately predict carbon cycle feedback from the permafrost ecosystems to climate warming.

2020027651 Luo Zhicheng (Beijing Normal University, College of Global Change and Earth System Science, Beijing, China) and Ji Duoying. Improve and evaluate the common land model at Samoylov permafrost site [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23D-1587, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Circumpolar permafrost in Northern Hemisphere contains substantial amount of organic matters. The soil organic matters influence the thermal and hydraulic properties in most permafrost regions, insulating the soil especially in non-snow season. Once thawed, released carbon would enhance the global green-house effect through permafrost carbon feedback. Land surface model is an important tool to study how permafrost responds to climate change. The way hydrothermal conditions are represented in models determines the exchanges of heat and water between land and air as well as among the soil layers. Therefore, it's of great scientific significance to improve the scheme of soil hydrothermal parameterization for simulating soil moisture content and soil temperature. Samoylov Island in Lena River delta, northern Siberia is a typical region of high latitude permafrost containing large amount of frozen soil organic carbon. Observations and measurements of soil and atmosphere have been recorded for more than 16 years at this site. Former studies using data from Samoylov site showed significant improvement of soil temperature simulation by incorporating moss layer, soil organic matter, enhanced snow representation and some other factors. This study aims at improving the Common Land Model's simulation at Samoylov site by explicitly considering moss layer and better representing soil organic matters' properties. Results show that CoLM can reproduce the thermal state and variation of soil temperature at Samoylov site. While poorly simulated soil water content suggests lateral waterflow caused by geomorphic heterogeneity might exert large effects on soil moisture at this site. This study would facilitate further researches of Samoylov site's permafrost carbon dynamics.

2020027658 Lyon, Laura N. (McGill University, Earth and Planetary Sciences, Montreal, QC, Canada); McKenzie, Jeffrey M.; Lamontagne-Halle, Jeffrey; Amyot, Frances and Carey, Sean K. Does sporadic permafrost influence catchment-scale groundwater processes? [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Groundwater processes in subarctic regions are poorly understood, particularly in areas of sporadic permafrost (perennially frozen ground underlying 0-50% of the landscape). Permafrost acts as an impermeable boundary to groundwater flow and can control porewater movement and storage. Our objective is to develop a conceptual understanding of how permafrost thaw will impact groundwater flow in watersheds undergoing climate change. We use field data from Granger Basin, a headwater catchment in the Wolf Creek Research Basin, Yukon, Canada, to develop an archetypal numerical model. Granger Basin is representative of the interior subarctic cordilleran landscape where climate change impacts are already being observed. Extensive datasets of meteorological conditions and stream discharge of this site exist from previous studies. We use capacitive-coupled resistivity and ground penetrating radar to map permafrost and bedrock distribution. The USGS saturated-unsaturated variable-density groundwater flow model with dynamic freeze-thaw functionality (SUTRA-ice) is used to compare cryohydrogeologic processes in the basin. Geophysical surveys show patches of sporadic permafrost 40 meters wide on the north-facing slope of the basin. Based on long-term model results, we predict that permafrost within the basin will thaw within 40-60 years. SUTRA-ice simulations show that the presence of permafrost influences patterns and timing of groundwater discharge (exfiltration) to surface water. Specifically, a fill-and-spill mechanism occurring in late summer where groundwater accumulates behind sporadic permafrost blocks until it is rapidly released upon reaching a threshold water level. As a result of this mechanism, with the presence of permafrost we see an increase in late summer exfiltration as a result of spill events. These events have a positive feedback on the permafrost thaw rate as flow through the active zone enhances lateral heat transport and increases connectivity. As permafrost thaws the fill-and-spill mechanism is diminished, and within decades there are no longer spill events. The net result is that permafrost thaw can lead to a decrease in late summer groundwater exfiltration, with potential impacts on the subarctic hydrologic cycle including changes in ecohydrology function and water resources.

2020032499 MacDonald, Erin (University of Alberta, Biological Sciences, Edmonton, AB, Canada); Tank, Suzanne; Hutchins, Ryan H. S.; Kokelj, Steve; Froese, Duane G. and Lanoil, Brian D. DOM composition and biodegradation from diverse permafrost end-members [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2570, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

As temperatures increase, carbon that was previously sequestered in permafrost soils can enter contemporary biogeochemical cycles and become subject to microbial decomposition (biodegradation). Upon thaw, biodegradation can occur both in situ and along the soil-aquatic continuum. This continuum transports carbon as dissolved organic matter (DOM), but not all DOM is equally susceptible to biodegradation, because climate and ecosystem variability shape substrate composition and the microbial community. Here, we aim to characterize the composition and biodegradability of DOM derived from varying permafrost sources across the western Canadian Arctic. Stratigraphic units within the study area have undergone freeze-thaw cycles which may have important implications for biodegradability. To investigate this, we leached DOM from three stratigraphic layers within the headwall of retrogressive thaw slumps. We measured oxygen consumption to determine biodegradation rates of leachates treated with contrasting sources of microbial inocula. The Paleo-active layer leachates had the greatest consumption of oxygen (39.3%±3.89), followed by ancient Pleistocene tills (35.4%±1.83), and modern active layer leachates (19.3%±1.97). Overall, oxygen consumption was correlated to initial OC concentrations and was not affected by the presence of different microbial inocula sources. These results suggest differences in biodegradability among leachate layers, which may be distinguished by optical characteristics, but further investigation is required. We also completed a detailed characterization of DOM from a variety of permafrost end-members, including yedoma, peat, lacustrine, and till deposits. We used Fourier transform ion cyclotron resonance mass spectrometry and optical metrics to characterize samples leached with both water and methanol. We found wide variation in DOM composition among end-members, but similarity within end-member types across a latitudinal gradient. These results highlight that DOM composition and biodegradability reflect the heterogeneity of permafrost at stratigraphic, landscape, and regional scales. Variability of permafrost-DOM should be considered in future research, especially for estimating and extrapolating the fate of carbon liberated by permafrost thaw.

2020032527 Mack, Michelle C. (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ); Walker, Xanthe J.; Johnstone, Jill F.; Alexander, Heather D.; Melvin, April M. and Miller, Samantha. Impacts of increasing wildfire severity on the long-term carbon dynamics of Alaskan boreal forests [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B33B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate-sensitive disturbances, such as wildfire, can feed back positively to climate warming via the carbon (C) cycle if C released by combustion is not replaced over post-fire succession. In boreal forests on permafrost soils, burning of old carbon in deep organic soils is not only an important determinate of ecosystem element balance over the disturbance cycle, but also sets the conditions that control tree seedling recruitment, species dominance and successional dynamics. Species dominance, in turn, has the potential to exert strong control over the plant-soil-microbial feedbacks that determine C and nutrient coupling, C storage, and ultimately, replacement of combusted C. We examined the consequences of increasing fire severity for C balance and C and nitrogen (N) coupling in Interior Alaska boreal forests. We estimated C and N combustion losses in 80 black spruce (conifer) stands that burned in 2004. Over the next decade, we followed natural tree seedling establishment in these stands to identify conifer versus deciduous successional trajectories. We assembled data from 270 stands that varied in time after fire and successional trajectory, and estimated C and N dynamics across 150 years of post-fire succession for each trajectory. Conifer stands that burned with high severity transitioned to deciduous tree dominance after fire. These stands had smaller ecosystem pools of C and N before fire, lost a larger proportion of these pools during the fire, and began succession with smaller residual pools than stands that returned to conifer dominance after fire. Over secondary succession, deciduous stands accumulated about 10 times more carbon in aboveground biomass than conifer stands. Belowground biomass and soil carbon accumulation, by contrast, was about three times higher in the black spruce stands than in deciduous stands. As a result, net ecosystem C accumulation over the 100 year inter-fire interval was three times higher in deciduous stands than in coniferous stands. Nitrogen accumulation did not differ between the trajectories; high C:N ratio biomass accumulation in deciduous stands balanced low C:N ratio soil organic matter accumulation in conifer stands. The timing of N accumulation, however, differed substantially, supporting the idea that deciduous stands mine N from degrading permafrost after fire.

2020032593 Mack, Mikhail (Wilfrid Laurier University, Geography and Environmental Studies, Waterloo, ON, Canada); Quinton, William L. and McLaughlin, James. Characterizing runoff regimes in subarctic wetland-dominated landscapes; application to the Hudson Bay Lowlands, Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1363, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In the past decades, climate warming has led to widespread permafrost thaw and subsequent land cover change in subarctic wetland-dominated landscapes found in the discontinuous permafrost zone (<90% areal extent). Long-term hydrometric records and extensive field studies in northwestern Canada have demonstrated measurable increases in runoff as a consequence of permafrost-thaw-induced land cover change. Land cover changes are largely attributed to the loss of boreal forest area that is dependent on elevated and dry peat plateaus. As permafrost thaws, the peat plateaus amalgamate with surrounding bogs and fens. This has led to both transient and permanent increases to runoff via peatland drainage and increased hydrological connectivity, respectively. However, it remains unknown whether these land cover and runoff changes are a regional occurrence or applicable to all circumpolar regions. The Hudson Bay Lowlands in central Canadian are the world's third largest contiguous wetland complex (225,000 km²), for which many areas are underlain with permafrost. Unfortunately, the remoteness of the Hudson Bay Lowlands has made it difficult collect long-term hydrometric records and engage in intensive field studies. In this study we attempt to better understand how permafrost-thaw-induced land cover change is affecting the Hudson Bay Lowlands. We suggest that by characterizing runoff regimes across 40 pan-subarctic wetland-dominated catchments where hydrometric records are available and land cover information is discernible using remote sensing classification techniques. We can use runoff regimes as a conceptual framework to better understand land cover controls of runoff in the Hudson Bay Lowlands where land cover information is discernible, but sparse long-term hydrometric records exist. For this study we characterize runoff regimes using runoff ratio and response time trends which reflect the sources and timing of runoff. Those trends are then sorted by land cover type prevalence to designate our proposed runoff regimes. We discuss insights and challenges to understanding the impacts of permafrost thaw on runoff in the ungauged catchments of the Hudson Bay Lowlands.

2020032557 Manies, Kristen (U. S. Geological Survey, Reston, VA); Jones, Miriam; Waldrop, Mark P. and Hoefke, Kristen. Influence of permafrost and site history on losses of permafrost carbon after thaw [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate change is heavily impacting boreal regions. Increases in air and soil temperatures have resulted in widespread permafrost thaw. This thaw often transforms the landscape from forested permafrost plateaus, with large stocks of permafrost carbon (C), to inundated peatlands. Some studies have found large losses of permafrost C (25-60%) after thaw, while others found limited losses. These differences may be related to the form of permafrost aggradation. In sites where permafrost aggrades syngenetically (at the same time as peat accumulation), peat decomposition prior to permafrost formation is minimal, whereas peats associated with epigenetic permafrost (where permafrost forms after peat accumulation) usually has undergone C processing prior to permafrost aggradation. We hypothesized that different amounts of C loss across these studies was mainly due to differences in permafrost history. To help understand post-thaw C dynamics within an Alaskan epigenetic permafrost landscape we studied four landforms, ranging from a small, relatively newly formed thaw feature to a larger thaw feature with late successional vegetation, as well as the surrounding intact permafrost plateau. We measured bulk density, C, nitrogen, macrofossils, and radiometric dates from several peat cores taken from within each landform. Landform age ranged from 1800-2500 cal yr BP. Permafrost aggradation occurred between 125-450 cal yr BP and the majority of permafrost thaw occurred within the last 50 years. We found three types of peat: herbaceous (sedge) peat (always located above the mineral soil), detrital forest-derived peat, and Sphagnum-dominated peat at the surface of the bog cores. We found no significant loss of C between cores from thawed versus frozen sites. This result is likely due to the mechanisms of permafrost formation, as the pre-permafrost peat was already highly decomposed prior to incorporation into the permafrost. High variability in C storage for both the thawed and permafrost plateau cores at this site is likely related to local hydrologic complexity, driven in part by the site's proximity to a major glacial river. We conclude that the impact of permafrost thaw on C dynamics within boreal landscapes depends on landform age as well as the timing and type of permafrost formation.

2020027704 Marchenko, Sergey S. (University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK); Jin Huijun; Jin Xiaoying; Li Xiaoying; Luo Dongliang; He Ruixia; Rupp, Scott T. and Romanovsky, Vladimir E. Wildfire as a driver of permafrost degradation in boreal and tundra ecosystems of Alaska, Siberia and northeast China; implications for environmental and socio-economic impact [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC24C-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The overall goal of this study is to evaluate the vulnerability of permafrost under climate warming and wildfire disturbances in respect of ecosystems stability, socioeconomic impact, and to provide stakeholders with information for better understanding possible future changes. In the discontinuous permafrost zone, the presence of vegetation and organic soil layers strongly affect ground thermal regimes due to thermal insulation and offset. Shur and Jorgenson (2007) classified permafrost into five types according to patterns of formation and degradation of permafrost in relation to climate and ecosystems. For each type, permafrost reacts differently to external disturbances. A major threshold is crossed when permafrost thaws after damage or removal of vegetation and upper soil organic layers, e.g., by wildfires. Measurements of ground temperatures indicate a relatively continual warming in most permafrost regions of northern Hemisphere over the last 3 decades and increasing the vulnerability of permafrost to surface disturbances. We applied the process-based permafrost dynamics model GIPL2 developed in the Geophysical Institute Permafrost Lab, University of Alaska Fairbanks, using a historical climate forcing CRU TS 4.0 data-set for retrospective (1901-2015) and five top-ranked global circulation models from the CMIP5/AR5 models and RCPs (2016-2100), as well as various fire severity scenarios for analysis of permafrost dynamics in the future. For model validation, we have acquired a number of long-term records of permafrost temperature from undisturbed and fire-disturbed field sites. The boreal forest and tundra ecosystems with various surface and sub-surface conditions, across selected permafrost domains were examined with respect to fire severity. In some cases, the modeling result shows the dramatic post-fire permafrost changes, such as rapidly rising ground temperatures and enlarging active layer thickness, which leads to talik formation due to the detachment of the permafrost table from seasonally frozen layer and even termination the permafrost because once disturbed, some permafrost types cannot recover. Since the fires are frequent in arctic and boreal areas, and under a warming climate, impact of wildfires can reshape the zonation of northern permafrost.

2020032533 Marcus, Tamara Sade (University of New Hampshire, Durham, NH); Varner, Ruth K.; Evans, Paul N.; Rich, Virginia Isabel; Ernakovich, Jessica G. and Tyson, Gene W. CH₄ flux from sub-arctic mire lakes; a look at relationships between microbial communities and submerged aquatic vegetation [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41J-2454, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

High latitude ecosystems are warming at a rapid rate, increasing permafrost thaw and thereby providing fresh sources of organic carbon (C) to post-glacial lakes. These lakes are a significant source of methane (CH₄) emissions into the atmosphere, however little is known about the reason for variations in these emissions within and between lakes. Stordalen Mire is a 25-ha hydrologically connected system of lakes and wetlands in the discontinuous permafrost zone in northern Sweden. Strong correlations between methanotroph lineage ANME-2d within lake sediments using 16S rRNA sequence data and sediment CH₄ concentration measurements. Similar trends have also been observed with methanogen lineage M. Stordalen mirensis and sediment d¹³CH₄ measurements as well as relationships between these two microbial lineages. However, previous work has shown no strong relationships between carbon sediment geochemistry and submerged aquatic macrophyte (SAM) vegetation. We have shown strong microbial-microbial relationships and their correlations with CH4 and now ask what microbial-vegetation interactions between SAM vegetation and their associated microbial community exist in these lakes and how does that relate to measured CH₄? The effect of plant species on the CH₄ flux from microbial community was investigated by constructing plant-sediment microcosms and incubating them with CH₄ at an initial concentration of 1% v/v for 32 hours at 25°C. Incubations were each performed with two SAM species (Potamogeton and chara) collected from one of the Abisko lakes (Inre Harrsjon). Furthermore, incubations were performed with sediment from the depths of 0-1 cm, 4-5 cm, and 8-9 cm depths of cores that were taken from both high and low CH₄ emitting areas of the Inre Harrsjon lake to assess sediment geochemistry and microbial community composition. After the incubation period, these geochemical and microbial community analysis were performed on the same samples to identify changes that may have occurred in microcosm based on the different treatment parameters. Preliminary results show variation in CH₄ uptake between the different parts of the incubated plant material as well as between species of plant. These results provide early evidence of the impact of microbial-plant interactions in C cycling in sub-arctic lake sediment systems.

2020032459 Marshall, Adrienne Michelle (University of Idaho, Water Resources Program, Moscow, ID); Link, Timothy E. and Lucash, Melissa Sue. Energy and water balances in boreal forest with discontinuous permafrost: Implementation of a physically-based hydrological model at sites with varying disturbance histories [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13K-2610, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In warming Alaskan boreal forests, changing disturbance regimes are altering permafrost, carbon and vegetation dynamics. Accurately modeling energy and water fluxes is a critical component of understanding and predicting changes to these high-latitude ecosystems. Here, we present the implementation of the physically-based Simultaneous Heat and Water (SHAW) model at the Bonanza Creek Long Term Ecological Research station. At four upland sites in the discontinuous permafrost zone with varying fire histories, vegetation structure, and permafrost presence/absence, SHAW was tested using 7 years of meteorological, vegetation, soil moisture, and soil temperature data. We will present results of model validation against depth profiles of soil moisture and temperature at three boreal forest sites, and depth to permafrost at one site. We will also present a sensitivity analysis to quantify the importance of key site parameters, and how the relative importance of these parameters differs between permafrost and non-permafrost sites. Results of this model implementation will inform the integration of SHAW with a forest simulation (LANDIS-II) and permafrost (Geophysical Institute Permafrost Laboratory (GIPL) model to improve our understanding of the effects of changing fire regimes on permafrost and carbon dynamics across the boreal forests of interior Alaska.

2020032496 Matamala, Roser (Argonne National Laboratory, Argonne, IL); Jelinski, Nicolas; Ping, Chien-Lu and Jastrow, Julie D. Contrasting carbon and nitrogen stocks and ice contents along two Arctic hillslope toposequences [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2567, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Hillslope processes affect rates of transport, deposition, and decomposition, impacting the distribution of soil organic carbon (SOC) stocks in many regions. In the Arctic, hillslope processes are further impacted by the added complexity of permafrost-affected solifluction and other lateral mass movements, cryoturbation, and patterned-ground formation. Despite increasing numbers of studies on permafrost-region SOC stocks, quantitative information across soil toposequences in the continuous permafrost zone remain limited and hill-toe deposits comprise only about 2.5% of existing soil profiles for Alaska. In this study, two toposequences in the Arctic Foothills, north of the Brooks Range of Alaska were investigated. The soils of both toposequences were formed on loess over glacial till and support moist acidic tundra vegetation. Several locations along the toposequence (encompassing summit/shoulder, backslope/footslope, and toeslope/basin positions) were sampled by opening soil pits, taking soil cores, or a combination of both to a depth of 2-3 m. Ice-wedge polygons were present at summit/shoulder and toeslope/basin positions. Ice-wedge polygons in the basins were clearly defined, with deep inundated troughs, while the ice-wedge polygons at the summit/shoulder were marked by surficial soil cracks with drier troughs. The thickness of the surficial organic horizons was greater in the toeslope/basin, and the basin contained deep peat deposits infused with ice. In the backslope/footslope, surficial organic horizons varied depending on frost boil features. Both hillslopes contained large C and N stocks across all positions to 1 m depth. Burial of surface organic horizons into the mineral subsoil through cryoturbation was prevalent in all positions. Ice content was high in all positions but it was greater in the basin. While C and N stocks to 1 m in the basin were less compared to other positions due to the massive amount of ice, peat deposits continued below 1 m depth while mineral horizons were already found at this depth in the other positions. A better understanding of the distribution of soil genetic horizons, and ice content along toposequences in hilly permafrost terrains is critical for determining C and N stocks in the Arctic and for informing and improving modeling efforts.

2020032464 Matthews, Elaine (NASA, Ames Research Center, Moffett Field, CA). Natural wetlands and the global methane cycle; five decades of research presents interesting and surprising challenges for the future [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B14B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The first estimate of methane emission from wetlands, 131-273 Tg CH₄/yr, was published by Dieter Ehhalt in 1974 using a wetland area of 2.6´10⁶ km² from the 1926 Principles of Sedimentation authored by Twenhofel and two spot measurements of August fluxes in temperate wetlands; several subsequent estimates using the same area yielded emissions of 11-300 Tg CH₄. Empirical wetland-methane (W-M) models appeared in the 1980s; spatially-explicit application of models was made possible using the static global wetland data set Matthews and Fung (1987) after which W-M models expanded in number and complexity to include, inter alia, dynamics of soil moisture (including water-table position and saturation) and temperature; explicit simulation of CH₄ production, transport by diffusion, ebullition and plants, rhizopheric and soil oxidation, and emission; incorporation of peat, permafrost and moss; and microbial activity. Since 2010, most wetland-methane modelers have used monthly data on surface inundation (Prigent et al., 2007; Papa et al., 2010) to define potential methane-producing 'wetlands'. Surface inundation successfully captures flooded wetlands but most of the flooding comprises non-wetland features such as lakes, while non-flooded wetlands, accounting for ~75% of the world's wetlands, are not reliably detected. Challenges and recommendations to better understand and model natural wetlands and their role in the global methane cycle include: - defining what are where wetlands are in a methane-centric context which has mostly been ignored or vaguely answered; - developing comprehensive and exclusive wetland data sets to model emissions; - incorporating hydrological and biogeochemical exchanges among wetlands, lakes and rivers; - modeling wetland distribution and types; - improving flood simulation especially for tropical wetlands that are primarily flooded by rivers; - building carbon models that simulate both CO₂ and CH₄ carbon stores, transformations and fluxes.

2020032514 Mauritz, Marguerite (University of Texas at El Paso, El Paso, TX); Celis, Gerardo; Commane, Roisin; Euskirchen, Eugenie Susanne; Goeckede, Mathias; Humphreys, Elyn; Kwon, Min Jun; Minions, Christina; Natali, Susan; Oberbauer, Steven F.; Parmentier, Frans-Jan W.; Rogers, Brendan M.; Schildhauer, Mark; Sonnentag, Oliver; Torn, Margaret S.; Ueyama, Masahito; Virkkala, Anna-Maria; Watts, Jennifer and Schuur, Edward. Reconciling historical and contemporary trends in terrestrial carbon exchange of the high-latitude permafrost-zone [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2585, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rapid warming across the Arctic and Boreal region is causing wide-spread permafrost thaw, putting vast quantities of soil carbon (C) at risk of decomposition. Concurrent increases in plant-productivity may offset soil C losses in the short-term, but ultimately, soil C reserves vastly outweigh the sequestration potential of plants. Despite the urgency of understanding high-latitude permafrost zone C dynamics, it remains unclear over what spatial and temporal scales the region could become a C source to the atmosphere. In the past decade, the Arctic has experienced a string of record-high temperatures and record-low sea ice extent. Yet, the last regional, ground-based assessment of high-latitude zone C dynamics lags by a decade. There is an urgent need for a synthesized and updatable repository of site-based net ecosystem C exchange (NEE) measurements that allows for assessment of the Arctic C balance trajectory at time scales relevant to climate and model projections. Here, we present the foundations for a synthesis of high-latitude permafrost zone NEE data. This effort should produce an updatable time series of ecosystem-atmosphere C exchange and a benchmark for the recent PCN model inter-comparison experiment. We have merged historic NEE data from two previous syntheses, updated with recent observations, to produce a comprehensive synthesis of chamber and tower NEE measurements at 290 sites. Observations range from 1980 to 2018 and include both summer and winter seasons. Spatial coverage spans 45 to 82 degrees latitude across North America and Europe with the potential for data from even more sites, if they were made publicly available. Preliminary analysis of NEE trends suggests increases in summer C uptake and winter C loss and an overall neutral annual C balance. This dataset provides a foundation to integrate with existing flux data repositories (e.g., Ameriflux, ICOS, INTAROS), focusing on synthesis rather than new data repositories. The aggregated NEE data will also complement an ongoing high-latitude methane synthesis. Ultimately, an aggregated, updateable dataset will allow regional upscaling, model bench-marking, and more rapid insights into the high-latitude C balance.

2020032554 McClelland, James W. (University of Texas at Austin, Marine Science Institute, Austin, TX); Bonsell, Christina Elisa; Bristol, Emily; Dunton, Kenneth H.; Hardison, Amber and McTigue, Nathan. Organic matter dynamics in Arctic lagoons; linking seasonal and spatial patterns to terrestrial inputs and ocean exchange [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43J-2613, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Terrestrial, freshwater, and marine scientists have a shared interest in organic matter transport and cycling in the Arctic. This is, in part, driven by a need to understand how climate change is impacting stocks of carbon that are currently stored in permafrost. As this permafrost carbon thaws, it may be decomposed in the terrestrial environment and/or mobilized to freshwater and marine ecosystems. Data collected by the Beaufort Lagoon Ecosystems Long Term Ecological Research (BLE-LTER) program is being used to investigate sources and fates of organic matter in coastal waters of northern Alaska. This presentation will focus on seasonal and spatial patterns in dissolved and particulate organic matter characteristics (e.g. concentrations, stable isotope ratios, optical properties) in lagoons along the Alaska Beaufort Sea coast as a first step toward evaluating potential changes in inputs and organic matter processing. Previous work in lagoons along the eastern Alaska Beaufort Sea coast has documented strong seasonal variations in organic matter characteristics that are linked to interactions between terrestrial inputs and ocean exchange. This presentation will explore organic matter dynamics over a larger spatial domain that includes lagoons along central and western portions of Alaska's Beaufort Sea coastline. East-west gradients in the properties of freshwater and ocean inputs are expected to contribute to changes in lagoon organic matter characteristics across the larger domain. For example, concentrations of dissolved organic carbon increase between the ice covered and ice break-up periods in all three study regions (west, central, eastern), but absolute values and magnitudes of seasonal variation differ among regions. These regional differences may influence trajectories of change and the roles that different lagoons play in organic matter processing as the Arctic warms.

2020032525 McIntosh Marcek, Hadley (University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, MD); Lapham, Laura; Lesack, Lance; Dallimore, Scott Raymond; Orcutt, Beth; Wheat, Charles Geoffrey and Prestegaard, K. L. Spatial heterogeneity in groundwater and evaporative fluxes and their influence on lakes with varying methane dynamics within Mackenzie River Delta (Canada) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B32B-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Hydrologic processes affecting Arctic lakes are sensitive to permafrost thaw depths and climate change. Lake water balances reflect changes in air temperature, precipitation, permafrost connectivity, and groundwater transport. The Mackenzie River Delta (MRD), one of the great river deltas of the Arctic coast, contains over 45,000 freshwater lakes. It is an essential place to explore lake hydrologic and biogeochemical processes. The MRD has discontinuous permafrost and previous studies indicate that the delta lakes have negative summer-time water balances, with evaporation greater than annual precipitation. Lake levels are replenished in the spring by the Mackenzie River flood. Three lakes in the middle MRD near Inuvik, Northwest Territories, Canada were selected for study. The lakes are near one another and the Mackenzie River; they are small (0.2 ha-3.1 ha), but have variable depths (1.5 m-3.1 m). We measured lake level using pressure transducers deployed continuously over a two-year time period (August 2015 to August 2017). Deep lake water (25 cm from sediment surface) was collected from two lakes using autonomous, continuous samplers (OsmoSamplers) and integrated samples of 1-2 weeks of lake water were analyzed for their methane (CH₄), Cl, Ca, Mg, Sr, Ba, and Li concentrations. All three lakes exhibited overall lake level decline by the end of the open-water period, but they were influenced by different hydrologic processes. Summer evaporation was the major hydrologic process affecting lake level for one of the three lakes. The shallowest lake exhibited lake level decline consistent with evaporation and low open-water dissolved CH₄, but the two deeper lakes had groundwater influx during the same time-period and variable dissolved CH-₄. Ion concentration due to summer lake evaporation was minimal compared to the much greater concentration in winter due to solute exclusion during ice formation. Surprisingly, in all three lakes, despite the expected groundwater connection to permafrost in two lakes, microbial activity produced modern methane. Taken together, these results indicate that lakes in delta systems should not be assumed to have similar hydrologic or biogeochemical behavior, especially if there are differences in lake geomorphology and permafrost site characteristics.

2020032502 Mekonnen, Zelalem Amdie (Lawrence Berkeley National Laboratory, Berkeley, CA); Riley, William J. and Grant, Robert F. Heat transfer from precipitation hastens permafrost degradation and decreases carbon-climate feedbacks [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2573, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The surface energy budget of high-latitude permafrost systems is poorly represented in Earth System Models (ESMs), yet permafrost is rapidly degrading and these dynamics are critical to future carbon-climate feedback predictions. A potentially important factor in permafrost degradation neglected by ESMs is heat transfer from precipitation. We show here that this process hastens active layer development and soil carbon and nutrient cycling in the Arctic beyond that caused by surface air warming under recent and 21st century climate (RCP8.5). We applied a well-tested ecosystem model, ecosys, with and without heat transfer from precipitation, to analyze these dynamics across the North Slope of Alaska (NSA), a continuous permafrost zone. Modeled active layer depth (ALD) in runs with heat advection from precipitation agreed well with NSA observations from 28 Circumpolar Active Layer Monitoring sites. Simulations that ignored advective heat transfer from precipitation resulted in lower soil temperatures and a 35% reduction in modeled ALD by 2100. The biased low soil temperature and shallower ALD resulted in lower rates of plant N uptake, net primary productivity, and heterotrophic respiration. Overall, the biased ALD caused a 44% reduction in net ecosystem productivity, resulting in a weaker carbon sink to 2100. We conclude that ESMs that do not account for heat transfer from precipitation are likely to underestimate ALD rates of change, and thus may predict biased strong permafrost carbon feedbacks.

2020027621 Miller, Diana M. (University of South Florida Tampa, Tampa, FL) and Dixon, Timothy H. Assessing the utility of three calibration methods for digital elevation models (DEMs) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1375, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost degradation in the Arctic is negatively affecting the environment, structures, and livelihoods of residents in Arctic areas. Melting of permafrost from increased global temperatures causes inconsistent land subsidence and compromises infrastructure, including buildings, roads, and energy pipelines. ArcticDEM data, created by the Polar Geospatial Center from DigitalGlobe, Inc. imagery, is being used to study permafrost degradation, including long-term change, in the North Slope Borough, Alaska. To utilize Arctic DEM for this purpose, it must be calibrated. This study examines the utility of three methods of calibration of ArcticDEM data from each year of 2010, 2011, 2012, 2015, 2016, and 2017. The first method is to calibrate the data using internal referencing, assuming the majority of the area has not changed in elevation and adjusting subsequent years to the first data strip collected in 2010. The second method identifies rock outcrops within the study area and assumes that these outcrops do not change in elevation. The DEMs are all adjusted so the rock outcrops are consistently the same elevation throughout the time series. The third method utilizes an extraneous data source, e.g. LiDAR data from the 2010 USGS North Slope of Alaska LiDAR project, obtained through the NOAA Data Access Viewer. The LiDAR data is compared with the ArcticDEM data strips, and the ArcticDEM are shifted to match the elevation of the LiDAR data. The results of all three calibration methods are compared for precision and accuracy.

2020032448 Moffett, Claire E. (Baylor University, Department of Environmental Science, Waco, TX); Barrett, Tate Edward; Yoon, Subin and Sheesley, Rebecca J. Terrestrial biogenic secondary organic aerosol composition on the North Slope of Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract A53A-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic has warmed almost twice as fast as the rest of the planet resulting in drastic changes to the ecosystem including warming, wetting, loss of sea ice, and thawing of permafrost. Plant life on the tundra has also become greener and shrubbier. Biogenic emissions resulting from these changes have the potential to affect regional chemistry and climate through the release of biogenic volatile organic compounds (BVOCs). Previous biogenic studies indicate that BVOCs such as isoprene and pinene are emitted at higher concentrations and plant growth is increased during periods of warming. These BVOCs are important for the production of secondary organic aerosol (SOA) which can have affects on the Earth's radiation budget. With conditions varying drastically from year to year, a long-term study of SOA from terrestrial BVOCs is necessary to fully understand impacts of warming in the Arctic. Filter based samples were collected at Utqiagvik (Barrow), AK, and Oliktok Point, AK, over three years from 2015 - 2017. The ecosystem surrounding the sites is primarily sedge/grass, moss wetland. The primary focus of this study was to investigate the composition of terrestrial SOA and how it may change over time. Samples were analyzed using gas chromatography-mass spectrometry for the SOA products of isoprene, pinene, and limonene. Preliminary chemical tracer analysis shows that terrestrial SOA varies over time with summers with higher average temperatures having higher concentrations. The results highlight a need to understand concentrations and driving factors of biogenic SOA production in the Arctic.

2020032479 Mzobe, Pearl (Lund University, Lund, Sweden); Crill, Patrick M.; Roulet, Nigel T. and Persson, Andreas. Near-decadal changes in active layer depth in Stordalen mire, Sweden [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2534, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Active layer deepening, a result of precipitation and temperature changes, in the discontinuous permafrost zone (at northern latitudes) is a source of increasing CO₂ and CH₄ emissions. The reintroduction of old carbon is not limited to atmospheric interactions as the lateral flux of carbon from terrestrial systems to river networks is important. Specifically, northern peatlands (which have a large C store) are shifting their function from net carbon sinks to carbon sources. In this study we present an eight year response of peatland permafrost thaw at 30 sites in Stordalen mire, focusing on active layer (ALD) and water table depth (WTD) changes using geospatial analysis and remote sensing techniques. We further use changes in ALD and WTD in the mire to show, through hydrological modelling, the expansion of the stream network in the catchment. Preliminary annual comparison of seasonal inverse distance weighted surfaces shows that there is a progressive increase in ALD starting at sites in the south east of the catchment. This corresponds to a median of 52 cm for sites on the NW-SE axis and 64 cm for sites on the NNW-WSW axis. Results of hydrological modelling on the permafrost table (PFT) indicate that drainage network entrenchment is most dominant in the NE-SW direction with an emergent channel in the E-W direction (mostly fen sites). We use our findings together with hydrological export and efflux data to report the influence that ALD and WTD changes have in Stordalen. Permafrost degradation is ongoing across sites at northern latitudes; applying geospatial techniques provides a first step spatio-temporal approach to present phase shifts in the broader scale of catchment carbon cycling.

2020032542 Neilson, Bethany T. (Utah State University, Logan, UT); Cardenas, M. Bayani; O'Connor, Michael; King, Tyler; Rasmussen, Mitchell T.; Cory, Rose Merin and Kling, George W. The role of groundwater dynamics on carbon export from continuous permafrost watersheds [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Groundwater flow regimes in the seasonally thawed soils in areas of continuous permafrost are relatively unknown despite their potential role in delivering water, carbon, and nutrients to streams. Using numerical groundwater flow models informed by observations from a headwater catchment in arctic Alaska, we identify several mechanisms that result in substantial surface-subsurface water exchanges across the land surface during downslope transport that are a primary control on dissolved organic carbon (DOC) loading to streams and rivers. Based on these mechanisms, headwater streams have high DOC concentrations, as indicated by field-based measurements showing similar DOC concentrations in the streams and groundwater across large discharge ranges. However, at larger scales, river concentrations of DOC are generally lower and have a different composition than groundwater, suggesting instream processes that remove and alter DOC occur during transit. We found up to ~10% of the DOC is converted to CO₂, mostly by sunlight and about 30% of the DOC is partially photo-oxidized (and altered in chemical composition) during transport in rivers. The implication is that several mechanisms control the delivery of DOC laden-groundwater into streams and rivers which then facilitate the transformation of this highly labile DOC during transport to the Arctic Ocean. These results demonstrate the importance of integrating the controls on groundwater delivery with controls on in-stream carbon processing in determining eventual export to the Arctic Ocean.

2020027653 Nicolsky, Dmitry (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, Vladimir E.; Debolskiy, Matvey V. and Bailey, Chris. Incorporation of observations into regional high-resolution permafrost modeling and mapping in Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23D-1589, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

We incorporate various in-situ measurements of the ground temperature dynamics into the thermal model and develop high resolution ecotype-based models for the Alaska North Slope, Seward Peninsula and Selawik National Wildlife Refuge regions. The developed models allow computations of the mean annual ground temperature, active layer thickness and talik thickness projections into the future for various climate scenarios. Custom simulations could be performed for ground different conditions. We demonstrated that the projections with the IPCC Representative Concentration Pathway 4.5 and 8.5 scenarios will result in a drastic difference in the future near-surface ground temperature regimes in 2050s and 2090s. Development of the taliks will have serious implications for ecosystems, human activities, and potential feedbacks to climate change. We are increasing the spatial resolution of all developed models to 30-m in order for the community planners and engineers to understand potential hazards related to the permafrost degradation on the local scale near the relevant infrastructure. The permafrost thaw projections and other related products are posted at the permamap.gi.alaska.edu in order to help to visualize results at the fine scale and transfer projection to the selected communities. In order to conduct the public outreach more effectively, we designed a publically-downloadable application for iPhone to show how permafrost temperature might response to changes in air temperature, snow thickness and ground moisture.

2020032634 Nwigboji, Ifeanyi H. (University of Texas at El Paso, El Paso, TX); Barba, Mauricio; Vargas Zesati, Sergio A.; Mauritz, Marguerite; Ruiz, Sebastian; Huemmrich, Karl F. and Tweedie, Craig E. rSpectral & ASTRAL; interactive tools for analysis of hyperspectral reflectance data acquired through the NASA ABoVE campaign [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract IN33B-0817, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Changes in climate variability over the past decades have exacerbated many Arctic ecosystem changes such as coastal erosion, permafrost thaw and degradation, air temperature rise, snow cover and sea ice loss. To better understand these vulnerable ecosystems, NASA created the Arctic-Boreal Vulnerability Experiment (ABoVE) program to investigate links between changing land surface conditions and the vulnerability and resilience of the Arctic and Boreal ecosystems. To monitor changing Arctic landscapes, detailed field measurements of vegetation optical properties along with corresponding airborne and satellite remote sensing observations, particularly, hyperspectral reflectance measurements have been widely used by NASA investigators. However, due to the size and complexity of data produced by such approaches, managing, analyzing, data sharing, and visualization has posed a great challenge for most of the ABoVE projects. Here, we present web based analytic tools capable of integrating spectral reflectance data from multiple investigators working in the ABoVE region using an open source software--R shiny. ASTRAL, currently maps over 8,000 spectra spanning nearly 10 observation sites across the ABoVE domain pertaining to multiple tundra vegetation species and communities. In combination, ASTRAL and rSpectral will combine to dynamically view, interact and discover optical properties of boreal and tundra plant communities. Users can view the hyperspectral reflectance scans and explore common spectral indices at multiple spatio-temporal scales. The overall goal is a tool that integrates diverse hyperspectral data streams and acts as a growing community database where PIs can easily submit data and access data to improve rapid change detection across the ABoVE domain.

2020032655 Obelcz, Jeffrey (U.S. Naval Research Laboratory, Stennis, MS); Wood, Warren T.; Phrampus, Benjamin J. and Lee, Taylor R. Predicting submarine slope instability along Arctic continental margins [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS53A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The increasingly large and long ice-free season in the Arctic has put previously unavailable resources in play, such as oil and gas reserves and submarine telecommunication routes. With these new opportunities come challenges, including high latitude-unique geohazards. Submarine slope instabilities (SSIs) occur globally, but the spatially and temporally complex movement of fluids and gases from submerged permafrost and gas hydrates make high latitude SSIs pervasive and multivariate. Here, machine learning (ML) is used on a relatively well-studied Arctic continental margin, the Canadian Beaufort Margin (CBM) to 1) geospatially predict the location and magnitude of SSIs, and 2) quantify the importance of various SSI predictors in this environment. Predictors used include those common to all SSI occurrence, such as slope, sedimentation rate, and seismicity, and Arctic-specific variables such as submerged permafrost depth/thickness, water bottom temperature, and geothermal gradient. Observational data used to train and validate ML algorithms are derived from multibeam bathymetric surveys through which past SSI occurrence is quantified based on morphologic evidence (e.g. scarps). Depth changes attributed to SSIs from repeat multibeam surveys are also used where available. Predictions are initially conducted on the CBM, but can also be performed to locate instability hotspots on other Arctic margins once important predictors of SSI in high latitudes are identified.

2020027660 O'Connor, Michael (University of Texas at Austin, Geological Sciences, Austin, TX); Cardenas, M. Bayani; Nicholaides, Kindra D.; Mungia, Zach; Ferencz, Stephen B.; Neilson, Bethany T.; Wu, Yue; Chen, Jingyi and Kling, George W. Predictable soil stratigraphy of the upper thawed layer in permafrost terrain controls hydrological flows and dynamics [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The heating of the Arctic is thawing shallow permafrost and exposing vast amounts of soil carbon to biogeochemical and hydrologic processes. The fate of this carbon is uncertain because there is a lack of information on the spatial variability of hydraulic and thermal properties of the thawed zone (active layer) above permafrost. These properties control all water flow and element transport processes. Through analysis of samples distributed across major topographic and glacial units of the North Slope of Alaska, we show that active layer soils are consistently represented by three hydrostratigraphic horizons (acrotelm, catotelm, and mineral soil) whose thicknesses are predictable based on vegetation cover and land surface slope (e.g., hilltops, hillslopes, valley bottoms). Each horizon has predictable saturation-dependent hydraulic and thermal properties that control hydrological flows. In addition, the physical properties can be predicted solely from substrate bulk density independent of hydrostratigraphic unit. These findings will help advance the prediction of coupled hydrologic, thermal, and biogeochemical processes in permafrost terrain, both at the scale of local flow and transport models and at larger regional scales used in Earth system models.

2020032650 Okinaka, Norihiro (Japan Oil, Gas and Metals National Corporation, Chiba, Japan); Boswell, Ray; Collett, Timothy S.; Yamamoto, Koji and Anderson, Brian. Progress toward the establishment of an extended-duration gas hydrate reservoir response test on the Alaska North Slope [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS33A-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Major challenges that need to be addressed before gas hydrates can be commercialized include concerns associated with accurately characterizing the occurrence of gas hydrates in nature and the development and testing of production technologies required to safely and efficiently produce gas hydrates. Short duration Arctic permafrost and deep marine gas hydrate production tests have confirmed that gas hydrate can be produced by depressurizing the hydrate-bearing reservoir, thus allowing gas released from the solid hydrate structure to be produced using the same types of systems used for existing natural gas production The most important need at this time is to establish gas hydrate field production testing projects at the scale required to address the remaining unknowns associated with production of gas hydrates. Most notably, these include the processes that control the rates at which gas might be produced and the well systems designs that will be needed to optimize and sustain production.Major challenges that need to be addressed before gas hydrates can be commercialized include concerns associated with accurately characterizing the occurrence of gas hydrates in nature and the development and testing of production technologies required to safely and efficiently produce gas hydrates. Short duration Arctic permafrost and deep marine gas hydrate production tests have confirmed that gas hydrate can be produced by depressurizing the hydrate-bearing reservoir, thus allowing gas released from the solid hydrate structure to be produced using the same types of systems used for existing natural gas production The most important need at this time is to establish gas hydrate field production testing projects at the scale required to address the remaining unknowns associated with production of gas hydrates. Most notably, these include the processes that control the rates at which gas might be produced and the well systems designs that will be needed to optimize and sustain production. In 2014, The National Energy Technology Laboratory (NETL), and the Japan Oil, Gas and Metals National Corporation (JOGMEC) signed a Memorandum of Understanding (MOU) toward developing a gas hydrate onshore production test in Alaska. Based on the MOU, NETL, JOGMEC and the U.S. Geological Survey (USGS), have collaboratively conducted studies and selected a potential site for production testing. In order to confirm the occurrence of gas hydrate at the selected site, a Stratigraphic Test Well (STW) was drilled in December 2018 by NETL, working in partnership with JOGMEC, the USGS, and Petrotechnical Resources of Alaska, and in cooperation with the Prudhoe Bay Unit owners. The STW drilling confirmed the occurrence of gas hydrate in two reservoirs suitable for future long-term production testing. The success of the STW has advanced the project toward planning for two additional wells, which will include a geoscience data well that will be converted to a second monitoring well, and the production test well. This presentation will provide an overview of the planned testing program with project structure, including Japan's Methane Hydrate R&D program.

2020032460 Olson, Kristin (University of Colorado Denver, Department of Integrative Biology, Denver, CO); Buma, Brian and Hayes, Katherine. Fine-scale observations of permafrost after repeat fires in interior Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13K-2611, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost in the boreal forest contains large amounts of carbon that is released as the permafrost thaws. Warming temperatures have led to both an increase in permafrost melt and an increase in the frequency of wildfires, as shown in the recent 2019 fire season. Wildfires have been thought to accelerate permafrost melt, but there has been little fine-scale research done on the relationship between frequency of forest fires and the specific resulting amount of permafrost thaw. Understanding this interaction is crucial to understanding both the role of the boreal forest in contributing to atmospheric carbon dioxide levels and how permafrost levels influence forest recovery post-fire. In order to understand this relationship at a fine scale, we investigated the effect of forest fires on permafrost thaw by comparing the depth of permafrost active layer at locations in boreal forest that remain unburned to locations that have burned one, two, or three times within the last 70 years. Specific depth to active layer was evaluated at more than 30 sampling sites ranging in burn frequency using a soil probe at a minimum of 10 points in each plot. Our results provide us with a distribution map of permafrost patterns in burned areas, and a detailed inventory of the effects of postfire fine-scale (meter scale) ground cover heterogeneity on relative differences in active layer depth. Preliminary results indicate a strong relationship between multiple fires and amplification of permafrost thaw as insulating layers of ground cover and tree canopy are reduced according to local variations in fire intensity. Furthermore, spatial heterogeneity in ground cover, woody debris, and standing dead influence the spatial distribution of depths within each burn frequency treatment. Results of this study indicate the importance of evaluating fine-scale variations in topography when examining postfire permafrost thaw in boreal Interior Alaska.

2020032684 Oti, Emma (Ohio State University Main Campus, Columbus, OH); Cook, Ann; Phillips, Steve and Holland, Melanie E. Using X-ray computed tomography (XCT) to estimate hydrate saturation in sediment cores from UT-GOM2-1 H005, Green Canyon 955 [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract U11C-17, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Gas hydrates form at low temperatures and high pressures and are found in marine and permafrost environments. Due the high concentration of methane in gas hydrates, they are considered to be a possible energy source, a significant player in the global carbon cycle, and a submarine geohazard. To better understand gas hydrate production potential, in May of 2017, the University of Texas led a hydrate pressure coring expedition that drilled holes in the northern Gulf of Mexico (Green Canyon Block 955), where previous logging-while drilling data had identified a sand-rich reservoir with high gas hydrate saturations. As quantifying the amount of gas hydrate in a reservoir is an important aspect in assessing its production potential, we estimated hydrate saturation from XCT scans of pressure cores from this reservoir and calibrated these estimates with grain density and quantitative degassing measurements from the same intervals. We use 3D XCT scans of the pressured cores collected from a Geotek Pressure Core Analysis and Transfer System (PCATS). This scanner noninvasively imaged pressure cores at a 0.112 mm voxel size, producing density-sensitive images with denser objects absorbing more photons and having higher CT units than less dense objects. We hypothesize that the presence of lower-density gas hydrate replacing water in the sediment pores affects the cores' CT units thus allowing for estimates of hydrate saturation. We select core sections from sandy silt sediments in two pressure cores (H005-3FB and H005-4FB) that have relatively constant grain density which allows us to treat the gas hydrate reservoir sediment as a constant. By linearly comparing density difference and CT unit value difference between sections of interest and a predetermined background section we derive hydrate saturation. Overall, the hydrate saturations from the quantitative degassing and the CT calculations generally agree (Table 1). These results are encouraging as they suggest that nondestructive means can be used to estimate hydrate saturation, thus preserving the sample for future analysis Table 1: Quantitative degassing hydrate saturations compared to CT derived hydrate saturations

2020032534 Pallandt, Martijn (Max Planck Institute for Biogeochemistry, Department of Biogeochemical Integration, Jena, Germany); Jung, Martin and Goeckede, Mathias. Evolution and optimized extension of the high Northern latitude eddy covariance network [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41L-2456, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

With climate change affecting the high Northern latitude regions severely, related degradation of the large stocks of carbon sequestered in the Arctic permafrost is expected to alter the Arctic carbon budget. A true and tested method to monitor these fluxes is through the eddy covariance (EC) method. However, (wintertime) weather and remoteness make it difficult to setup and keep these EC station running in the Arctic, and accordingly the past and current data coverage is comparatively sparse. In this study, we aim to evaluate the coverage of the existing network of high latitude EC stations, and quantify uncertainties in our understanding of regional-scale vertical carbon exchange processes. Our intention is to indicate where the limits of the network are, and how existing gaps could best be filled. For this purpose, we applied and extended a network representativeness metric used for FLUXCOM, which consist of two parts: The first calculates an extrapolation index which indicates the relative error when predicting fluxes at increasing distances from the existing sites in the network. This method has a k nearest neighbors algorithm at its basis. The second part generates an expected mean absolute error of prediction which for a large part indicates the expected size of the fluxes and their errors. Combining the two into an extrapolation severity index allows to highlight regions that are least represented, and impactful. These indices in turn are applied to predict optimal locations for network extension. As the database of high latitude EC sites in this study, in a previous study we generated a comprehensive survey of high latitude EC sites, which is also available as an online mapping tool. This database facilitates e.g. to visualize the growth in network coverage in 8 day time steps since the first towers were established in 1993. Nowadays, coverage is quite extensive, but larger gaps in Russia and Canada remain, and seasonal differences exists that show large gaps of coverage throughout the Arctic in wintertime. Year-round coverage is most strongly present in Alaska and Europe. Our study identifies ideal locations for overall network extension, and also gives an indication where upgrades of existing sites to e.g. include methane flux monitoring would be most efficient.

2020032631 Pan Zhao (China University of Geosciences, School of Environmental Studies, Wuhan, China); Sun Ziyong; Ma Rui; Chang Qixin and Hu Yalu. Tracing to sources of river water by using environmental isotopes and hydrogeochemical methods in a cold alpine catchment with seasonally frozen ground [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H53J-1897, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Hydrological process in alpine catchments containing seasonally frozen ground is complex, as soil freeze-thaw cycle have a significant impact on the generation of streamflow. However, few studies have been undergone on the processes and mechanisms that control runoff generation in the cold alpine where seasonally frozen ground is dominant. We use environmental isotopes and hydrogeochemical methods to trace to sources of river water in the Hongnigou catchment (1.12 km2), a cold alpine catchment covered with seasonally frozen soil in the northeastern Qinghai-Tibet Plateau, China. Samples including stream water, groundwater, spring water, rainwater and ground ice were collected and then were analyzed for isotopic and hydrogeochemical composition in laboratory. Based on the analysis of isotopic date, hydrogeochemical date and the monitored data of hydrologic factors in the catchment, the influence of soil freeze-thaw cycle on river was assessed. Our results indicate that the value of dD in stream water showed different characteristics in different periods. The saturated shallow-thawed soil layer was an important contributor to the generation of streamflow between March and mid-May which occurred at early March. The stream water was mainly supplied by frozen soil thawing water and precipitation, and the contribution of the former decreases gradually from mid-May to early June. During the rainy season (from early June to mid-September), precipitation indirectly recharged stream water by recharging groundwater or forming slope flow in saturated riparian zones. Groundwater in riparian zone became the main source of rivers from mid-September to early November, when surface soil began to freeze to the depth of 75 cm. Finally, by the end of November when the river was basically dry, the water mainly came from the recharge of deep groundwater. In addition, the groundwater in the deep unfrozen aquifer presents the characteristics of confined aquifer in cold season and diving aquifer in warm season. The above results show that the process of soil freezing and thawing controls the process of groundwater recharge to rivers. Result from this research could improve our understanding of source waters in cold alpine catchments which were affected by seasonally frozen soil.

2020032629 Pardo, R. (University of Guelph, Guelph, ON, Canada); Berg, A. A.; Rowlandson, T. L.; Roy, Alexandre and Toose, Peter. Comparing L-band radiometry and in situ permittivity at 50 MHz of agricultural soils during a freeze/thaw validation campaign [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H51S-1751, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Up to a third of Earth's land surface experiences a transition between seasonally thawed conditions, like the surface of permafrost's active layer, or seasonally frozen conditions with even more regions experiencing short-term diurnal freeze/thaw (F/T) events. Freezing and thawing of the land surface plays an important role in local, regional and global weather and climate, affects the geotechnical properties of soil and slope stability, and influences critical processes such as the land surface energy balance, biogeochemical dynamics, and hydrological partitioning between surface runoff and infiltration. Although it is imperative, monitoring F/T state is difficult given its enormous extent and prevalence in places where access is limited, and climate is extreme. The most viable option at continental scales is through the use of microwave satellite observations. These observations must be validated against ground observations for accurate and credible usage. The SLAPEx F/T field campaign was conducted during the first two weeks of November 2015 to capture transient F/T events at various scales over agricultural land in Manitoba, Canada.

2020032638 Parsekian, Andy (University of Wyoming, Laramie, WY); Rangel, Rodrigo C.; Jones, Benjamin M.; Arp, Christopher D.; Ohara, Noriaki; Kanevskiy, Mikhail Z. and Creighton, Andrea. Geophysical observations of drained permafrost lake taliks, North Slope, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS11B-0626, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Lakes and drained lake basins in total cover approximately 80% of arctic lowland regions. Lake drainage, subsequent ecosystem succession in drained lake basins, and refreeze of the remnant talik has implications for carbon storage, landscape evolution, and hydrology. In some cases, taliks are thought to refreeze over the course of decades associated with top down and bottom up permafrost aggradation. However given the wide variety of drained lake basin sizes, locations, and ages, and the paucity of direct measurements, we are motivated to gain a more complete understanding of where taliks exist below drained lake basins. In order to answer the more general question of how quickly taliks refreeze after lake drainage, we first seek to understand the unique geophysical response of taliks measured using either transient electromagnetic (TEM) or surface nuclear magnetic resonance (NMR) methods. We surveyed a total of nine drained lake basins on the North Slope of Alaska ranging from near the coast of the Beaufort Sea to the silt (Yedoma) foothills of Oumalik. Relative time of drainage of each lake was estimated either by ecological or geomorphological characteristics or by radiocarbon dating of basal peat. Surface nuclear magnetic resonance soundings were most valuable due to the unambiguous ability to detect liquid water, however the bulky nature of the instrumentation prevented measurement at all sites. Transient electromagnetic soundings are interpreted either in conjunction with nearby surface NMR soundings, or through comparison with TEM soundings on nearby permafrost primary surfaces presumed to have not experienced lake formation and drainage. Through these measurements, clear evidence of a remnant talik in drained lake basins was observed at depth at several sites, while at other sites permafrost had aggraded and the material appeared to be refrozen. Due to the resistive properties and very low liquid water content of permafrost in our study region, refrozen taliks are interpreted based on the absence of TEM or surface NMR signal.

2020032628 Pastick, Neal J. (KBR, contractor to the USGS Earth Resources Observation Science Center, Sioux Falls, SD); Jorgenson, Torre; Cooley, Sarah W.; Trochim, Erin; Jones, Benjamin M.; Wylie, Bruce K.; Genet, Helene; Minsley, Burke J. and Walvoord, Michelle A. Artificial intelligence/machine learning and remote sensing reveals over six decades of surface-water dynamics in Alaska with connections to climate change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H43N-2259, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Approximately 38% of global surface water bodies are found in permafrost environments that are currently undergoing dramatic shifts in ecosystem structure and function as the result of climate change. Despite the prevalence of surface waters in permafrost-affected landscapes, and numerous ecosystem services affected by water-permafrost interactions, few studies have leveraged historic and emerging remote sensing technologies to provide a holistic characterization of heterogeneous surface-water dynamics across high latitudes. Here we couple remote sensing data (i.e. aerial photography, Landsat, CubeSats, DigitalGlobe) with signal processing and machine learning/deep learning techniques to determine: (1) The extent of surface water changes across Alaska over the last ~65 years; (2) If the rate of surface water expansion and contraction events have increased in recent decades; (3) What environmental (e.g. climate, permafrost, surficial geology) and allometric factors are associated with long-term directional, cyclical, and seasonal surface-water dynamics, and; (4) How climate warming and changing disturbance regimes might impact lakes and rivers in Alaska in the future. Developing a comprehensive understanding of where and why rapid surface water changes are occurring in permafrost-affected regions requires traversing multiple spatial and temporal scales using Earth observations acquired from field studies and suborbital and orbital platforms as presented here.

2020027673 Paull, Charles K. (Monterey Bay Aquarium Research Institute, Moss Landing, CA); Dallimore, Scott; Jin, Yong Keun; Caress, David W.; Lundsten, Eve M.; Anderson, Krystle; Gwiazda, Roberto; Riedel, Michael; Melling, Humfrey; Duchesne, Mathieu J. and King, Edward L. Submarine permafrost dynamics along the Arctic Shelf edge [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP11B-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Exploration in the Canadian Beaufort Sea, offshore of the Tuktoyaktuk Peninsula, has revealed a remarkable a zone of rugose morphology at the shelf edge and upper slope. This morphology is especially common in 100 to 200 m water depths where seafloor features include topographic mounds, pockmarks, slope parallel ridges, and slide scars. This area occurs at the seaward edge of a sub-sea ~600 m thick relict permafrost zone and geothermal modelling suggests that the lower 100 m of the permafrost zone has decomposed during the Holocene. Sediment cores show escaping brackish waters with pore water chloride content indicating widespread down core freshening, especially near the shelf edge on the upper slope. chloride content indicating widespread down core freshening, especially near the shelf edge on the upper slope. Bottom waters corresponding with this band have a mean annual temperature of less than -1.4°C, cold enough to freeze escaping brackish pore waters. Positive relief mound features are up to 10 m high circular to oval shaped and ~50 m in diameter, occurring at a density of ~6 per km². Pore and lense ice has been observed in sediment cores and we interpret these features as offshore pingos. Pore and lense ice has been observed in sediment cores and we interpret these features as offshore pingos. Intermixed are circular topographic depressions up to 20 m deep. Detailed investigations utilizing a mapping Autonomous Underwater Vehicle (AUV) to provide 1-m grid bathymetric and Chirp profiles, and Remotely Operated Vehicle observations, were made to provide insights as to the origin and age of these features. AUV surveys of one 8 km² area first conducted in 2013 were repeated in 2017. Repeat mapping shows significant changes within this 4-year period. Multiple circular or elongated depressions have developed which are up to 10 m deep and 100 m long. A corresponding volume of newly accreted material around the depressions equal to the missing volume was not detected. No evidence for high methane concentrations were found within this survey area as pore waters sulfate gradients indicate the sulfate-methane transition zone is >8 m below seafloor in most sediment cores and no chemosynthetic seep fauna or authigenic carbonates were seen. We attribute the concentrated band of features to be related to the on-going degradation of relict permafrost, the expulsion of brackish waters, and formation of ground ice within the near seafloor sediments. These observations have significant geohazard implications, which may be characteristic of Arctic settings.

2020027629 Pedrazas, Michelle N. (University of Texas at Austin, Austin, TX); Cardenas, M. Bayani; McClelland, James W. and Connolly, Craig T. Electrical resistivity imaging reveals thawed substrate beneath and across an entire Arctic lagoon within continuous permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1384, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rapid warming's concomitant changes to Arctic coastal environments are incompletely documented and seldom monitored, particularly relating to the degradation of subsea permafrost. Permafrost degradation accelerates coastal erosion and releases formerly frozen and trapped stores of organic carbon, which directly impact local communities and ecosystems and constitute a positive feedback to Arctic warming. Yet the depth and extent of subsea permafrost is still unknown, making it challenging to determine its role in the exchange of water and nutrients with lagoon waters as well as its degradation. Electrical resistivity imaging (ERI) is a promising but largely untested method for acquiring this information. Here we tested ERI by using boat-towed floating electrodes, fixed submerged, and on-land electrodes within a shallow lagoon system in northeastern Alaska to detect and map coastal subsea permafrost. We interpreted the observations through synthetic forward modeling. The analyses show that the lagoon substrate is ice-free down to the full depth of the profiles--7.5 m in the lagoon and 18 m along and across the shoreline. This coastal talik or thaw bulb suggests that the beach and lagoon substrate are an active component of the Arctic coastal system and that the exchange of water and released nutrients and organic matter from sediments are significant for the biogeochemistry of the lagoons.

2020032556 Pedron, Shawn (University of California Irvine, Irvine, CA); Welker, Jeffrey M.; Jespersen, Robert G.; Xu, Xiaomei; Holden, Sandra R.; Natasha, Anna and Czimczik, Claudia I. Accessibility of permafrost carbon in a changing Arctic; assessing the influence of experimentally-increased snowpack height on microbial carbon sources [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In addition to rapid warming, the Arctic is experiencing increases in precipitation due to diminishing sea ice cover and moisture transport from lower latitudes. In the near future and at higher latitudes much of this additional precipitation is expected to fall as snow. Snowpack height and snow cover duration strongly influence the biogeochemistry and structure of tundra systems, with greater snowpack height resulting in warmer soil temperatures and greater rates of carbon (C) and nutrient cycling in winter, and shifts in plant community composition. Here we investigate how long-term increases in snowpack height and subsequent active layer deepening and a shift from graminoid- to shrub-dominated vegetation influence the stability of permafrost C near Toolik Field Station, Alaska, USA. To estimate the loss of permafrost C in response to increasing snow, we compared the amount and composition of soil organic matter under ambient and experimentally-increased snowpack height. We also used laboratory incubations and in situ measurements of the rate and isotopic composition of ecosystem respiration to quantify the activity and C sources of the microbial community. We found that bulk soils under deeper snow are depleted in radiocarbon (¹⁴C) compared to those under ambient snow. For example, at 50 cm depth, D¹⁴C of bulk soil beneath deeper snow is ~-430 ppm, compared to ~-220 ppm under ambient snow. The expected cause is subsidence from loss of ground ice, bringing older C closer to the surface. Incubations of soil under ambient snow produce microbial respiration which is a mixture of young and old C, mostly modern in the surface (organic) layer, and more aged with depth, and we expect that microbes respired older C under deeper snow. The age difference in microbially-accessible C was not evident in seasonal measurements of ecosystem respiration during the growing season (deeper snow=37±12 ppm, ambient=29±9 ppm D¹⁴C±sd) - indicating that plant respiration and decomposition of recent plant assimilates are important microbial C sources in summer. Together, our results show that long-term increases in snowpack height increase the vulnerability of permafrost C to microbial decomposition and combustion by fire both by temperature-induced active layer deepening and subsidence.

2020032526 Pegoraro, Elaine (Northern Arizona University, Center for Ecosystem Science and Society (ECOSS), Flagstaff, AZ); Mauritz, Marguerite; Ogle, Kiona; Ebert, Christopher and Schuur, Edward. Partitioning ecosystem respiration using d¹³C and D¹⁴C to determine sources of permafrost C loss after 10 years of experimental warming [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B32D-02, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Anthropocene epoch is characterized by a 0.8-1.2°C increase in air and sea surface temperatures relative to pre-industrial levels. Warming is especially pronounced in high latitudes, where air temperatures are increasing two times faster than the global average. Permafrost-ground that is frozen for two or more consecutive years-becomes vulnerable to higher microbial decomposition as climate warms. This permafrost feedback to climate change will be pronounced if net primary production cannot offset enhanced C losses due to higher rates of plant and microbial respiration (i.e., ecosystem respiration, R_eco). Plant and microbial respiration respond differently to biological and environmental drivers; consequently, the proportional contribution of each source to R_eco must be considered. If increases in R_eco are dominated by plant respiration, C losses are likely to be offset by C sequestration due to increased plant productivity. If higher R_eco is driven by greater microbial decomposition of soil organic C, especially of old C, the system will exacerbate the effects of climate change. Here, we investigated the effects of 10 years of experimental soil warming on R_eco by disentangling plant and microbial responses to environmental changes associated with long-term permafrost degradation. To provide more robust information on permafrost soil C cycling, natural abundance d¹³C and D¹⁴C from plant above- and belowground respiration, and surface (0-25 cm) and deep (>25 cm) soil respiration were used to partition R_eco from 2016 to 2018. We found that gross primary productivity (GPP), deep soil temperature, and the interaction of soil moisture and GPP led to more positive R_eco D¹⁴C, while soil moisture and surface temperatures contribute to more negative R_eco D¹⁴C. In 2018, when R_eco D¹⁴C was on average more negative, the proportional contribution of old soil C to R_eco ranged from 25-54%. Soil volumetric water content was significantly lower in 2018, averaging 48%, and the water table was also significantly lower relative to 2016 and 2017. This indicates that when soil is less saturated, a higher proportion of old C can be released to the atmosphere. Partitioning source contributions to R_ecois crucial to understanding which environmental drivers may lead to periods of old C release to better predict permafrost C dynamics.

2020032685 Pellerin, Louise (Green Geophysics, Berkeley, CA). Near-surface geophysics; shallow but broad [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Near-surface geophysics has great breadth in terms of its methodologies and applications. Traditional geophysical methods have been adapted and refined for the high-resolution demands of precision agriculture, archeological investigations, geotechnical engineering as well as for conventional resource exploration. However, as this is a session on Fluids in the Earth, I will focus on the use of near-surface geophysics with regard to hydrological structures and processes. Using modern instruments, processing tools and interpretational methods we can answer many practical questions: How much water is down there? How deep is it? Is it potable? Such practical questions lead to significant scientific questions with respect to physical properties and rock physics: Is the water accessible through a porous, permeable medium or through fractures? Is subsurface storage viable? Can we monitor contamination remediation? Near-surface geophysical methods have an important role to play in not only mapping the extent but also adding to a better understanding of underlying processes such as those important to the formation and devastation of permafrost and peatlands--keys in the carbon cycle.

2020032679 Pendleton, Simon (University of Colorado at Boulder, Boulder, CO); Miller, Gifford H.; Lifton, Nathaniel A.; Young, Nicolas E. and Anderson, Robert S. Just how unprecedented is modern warming in the Arctic? [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PP33A-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Over recent decades, the accelerated warming of the Arctic has become dramatically apparent in receding ice caps and glaciers, reductions in sea ice extent, thawing of permafrost, and ecosystem changes. However, just how unprecedented the current warming is beyond instrumental records remains poorly constrained. Using radiocarbon ages from plants preserved beneath now-retreating ice caps on Baffin Island, Arctic Canada, and inventories of in situ cosmogenic radiocarbon (in situ ¹⁴C) from adjacent rock surfaces, we provide a paleo context for modern warming. Ice caps on Baffin Island respond dominantly to summer warmth, making records of past ice cap extent excellent indicators of relative summer warmth. A subset of 14 plant radiocarbon ages obtained on preserved mosses in growth position exposed by retreating ice margins cluster around ~9.3 cal ka. Since recently exposed plants are efficiently removed from the landscape and are unlikely to survive multiple episodes of burial and exposure, the plant ages are interpreted as the most recent time that ice expanded over, and remained over, that location until being exposed by modern warming and associated ice margin retreat. The exposure of these plants today tells us that 1) these landscapes must have been exposed prior to ~9.3 ka and thus experienced similar summer warmth to today, and 2) that subsequent summer warmth was never sufficient to re-expose the plants until the modern warming. Inventories of in situ ¹⁴C in preserved rock surfaces adjacent to plant collection sites indicate centuries to a few millennia of exposure prior to ~9.3 ka. An additional subset of 44 plant radiocarbon ages from 30 different ice caps all returned radiocarbon ages at or beyond the limit of the method, suggesting that these surfaces have be continuously ice covered for at least the past ~40 ka. Co-located in situ ¹⁴C inventories are compatible with a continuous, thin ice cover over the same time period. When viewed in the context of longer regional paleo-temperature records from Greenland, the combined evidence from the plant and cosmogenic radiocarbon suggests that the past century of warmth is likely greater than any century over the past ~115 ka, or since late in the last interglacial period.

2020032477 Philben, Michael J. (Hope College, Geology and Environmental Science, Holland, MI); Tas, Neslihan; Wullschleger, Stan; Kholodov, Alexander L.; Graham, David E. and Gu, Baohua. Influences of hillslope biogeochemistry on anaerobic soil organic matter decomposition in a tundra watershed [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2532, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

We investigated rates and controls on greenhouse gas (CO₂ and CH₄) production in two contrasting water-saturated tundra soils within a watershed near Nome, Alaska. Three years of field sample analyses have shown that soil from a fen-like area at the base of the hillslope had higher pH and higher porewater ion concentrations than soil collected from a bog-like peat plateau at the top of the hillslope. The influence of these contrasting geochemical environments on CO₂ and CH₄ production was tested in microcosms by incubating both the organic- and mineral-layer soils anaerobically for 55 days. NH₄Cl was added to half of the microcosms to test the effects of N limitation on microbial greenhouse gas production. We found that total CO₂ and CH₄ production were higher in the soils from the bottom of the hillslope. Dissolved organic C (DOC) was also higher in these soils, and fermentation of this C pool resulted in an increasing supply of low-molecular weight organic acids (e.g., acetate and propionate) throughout the incubations. Higher availability of labile DOC, in addition to higher pH, likely contributed to the more rapid CO₂ and CH₄ production at the bottom of the hillslope. Our results also indicate that inorganic N concentrations were lower and soil C decomposition was more N-limited in the peat plateau soils than the toeslope soils, which exhibited net N mineralization while the peat plateau soils had net N immobilization. N addition increased CO₂ production in the peat plateau soils, but not the toeslope soils, consistent with greater N limitation. Microbial community compositions changed substantially in incubations of organic soils with added N, compared to smaller changes in mineral soils. Our results suggest that the movement of water, ions, and nutrients down the tundra hillslope can increase the rate of anaerobic soil organic matter decomposition by (1) increasing the pH of soil porewater; (2) providing bioavailable DOC and fermentation products such as acetate; and (3) relieving microbial N limitation through nutrient runoff. We suggest that the soil geochemistry as mediated by landscape position could be an important predictor of the fate of soil organic matter liberated from thawing permafrost.

2020027678 Piliouras, Anastasia (Los Alamos National Laboratory, Los Alamos, NM); Lauzon, Rebecca and Rowland, Joel C. Ice covered delta dynamics [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP23B-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

River delta dynamics and depositional patterns are strongly influenced by a suite of upstream and downstream boundary conditions. In the Arctic, ice and permafrost also play a large role in governing delta dynamics. Here, we present results from remote sensing analyses and numerical modeling of Arctic deltas aimed at characterizing Arctic delta morphologies and understanding how ice influences the form and function of river deltas. We show that thick ice cover limits channel mobility and encourages preservation of channels by limiting in-channel sedimentation. Ice also enhances overbank flooding and aggradation, as well as incision of channels under the ice that transport more sediment offshore. In natural systems, these effects may result in a shift in the population of island sizes towards smaller islands, owing to the preservation of small channels in ice-covered environments. Deltas with higher channel density tend to be more resilient to sea level rise, as the small land-channel distances make for increased overbank sediment delivery to all areas. Thus, ice cover may have an amplified effect in that it both encourages overbank flooding directly by increasing water surface elevations upstream of ice and helps maintain higher channel density that increases ease of aggradation on delta islands. However, this also indicates that decreased ice thickness in a warming Arctic is likely to have a drastic effect on delta aggradation, making Arctic deltas especially vulnerable to rising sea levels. Finally, we show that Arctic deltas are characterized by an uneven distribution of channels nearshore, such that they convey riverine fluxes to only a small portion of their coastlines. We suggest that ice cover is responsible for the large variability in channel size due to a feedback between channel size, river discharge, and ice retreat that maintains small channels and widens large channels over long timescales. These results indicate that ice cover affects delta morphology and dynamics that influence the transport of water, sediment, nutrients, and heat, as well as delta resilience in a warming Arctic.

2020032609 Pon, Andy (3vGeomatics, Vancouver, BC, Canada); Mackenzie, David; Leighton, Jon; Alipour, Samira; Pichierri, Manuele and Ghuman, Parwant. A landslide inventory for British Columbia (Canada) using SAR interferometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H11H-1574, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Interferometric Synthetic Aperture Radar (InSAR) data from SAR space-borne sensors at different resolutions (Sentinel-1, RADARSAT-2 and ALOS-1) have been used to generate a landslide inventory for the entirety of the Canadian province of British Columbia (BC), a roughly 1-million-square-kilometer area containing numerous different topographical areas including mountain ranges, dry valleys and discontinuous permafrost. An historical landslide inventory of BC (from 2006 to 2011) was created using ALOS-1 data. A total of 6675 individual ALOS images were automatically processed at 18-meter resolution and more than 3500 motion areas were detected with sizes greater than 6500 square meters. Moreover, Sentinel-1 data for 2016 and 2017 were downloaded and separated into almost 400 stacks. Using a fully automated chain, all descending data were then processed at 15-meter spatial resolution, resulting in 48 Terabytes of data. This produced a database of over 80,000 candidate displacement regions in the province. To provide greater detail in targeted displacement regions, higher resolution SAR satellites such as RADARSAT-2 were also used to further investigate motion areas detected by the Sentinel-1 processing chain. To demonstrate this capability, RADARSAT-2 stacks with 4-meter resolution were processed over 4 confirmed motion areas within BC. By ensuring full coverage of BC with a relatively short (12-day) repeat time, Sentinel-1 provides the opportunity to not only detect historically moving areas but to also provide rapid detection of new moving areas and accelerating motion areas. The synergy between Sentinel-1 and other higher resolution InSAR sensors (e.g. RADARSAT-2, ALOS-2, TerraSAR-X) can be successfully exploited to develop an automated landslide alerting system capable of detecting the potential risk of landslide anywhere in the province, with minimal turnaround time from data acquisition.

2020032559 Prater, Isabel (Technical University of Munich, Soil Science, Munich, Germany); Zubrzycki, Sebastian; Buegger, Franz; Mueller, Carsten W. and Zoor-Füllgraff, Lena. Undecomposed organic particles dominate the carbon storage in permafrost soils of the Lena River delta, arctic Russia [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

As major terrestrial carbon reservoirs, permafrost-affected soils of the northern hemisphere play a crucial role in the global carbon cycle. Yet, these soils face tremendous alterations due to enhanced warming. Especially the increased deepening of the active thermal layer is assumed to increase the biovailability of the soil organic matter (SOM) for microorganisms. Although an increasing number of studies report on the overall carbon cycling in the Arctic, only little is known about the distribution of carbon among differently stabilized SOM fractions together with their chemical composition. We aimed to elucidate the molecular composition and distribution of SOM fractions in permafrost affected soils in the High Arctic. Therefore we physically fractionated soils from Samoylov Island, located in the Lena River Delta in the Russian Arctic according to density and to grain size. The regions climate is polar and the underlying continuous permafrost up to 600 m thick. Carbon and nitrogen contents of all fractions were determined and SOM fractions objected to ¹³C CP-MAS NMR spectroscopy. The OC stocks were clearly dominated by the light particulate OM (POM), whereas a minor part was also sequestered in organo-mineral associations. The larger POM fractions were clearly dominated by O/N-alkyl carbon as depicted by NMR spectroscopy. This points to the fact that OC storage is dominated by rather fresh and not yet decomposed OM. Small occluded POM (oPOMs) was demonstrated to have a specific role in the OC storage with a composition that relates to the microbial dominated low C/N ratio organo-mineral associated OC of the clay sized fraction. Thus, the oPOMs fraction connects the large POM fractions that are mainly constituted by easily decomposable chemical compounds with the mineral-bound OM in the clay-sized fractions. Thus, the high amount of rather fresh large POM together with a high amount of N in the smaller POM and mineral-associated fractions might support microbial SOM mineralization with increased active layer deepening.

2020032571 Propster, Jeffrey Ryan (Northern Arizona University, Flagstaff, AZ); Schwartz, Egbert; Hayer, Michaela; Mack, Michelle C. and Hungate, Bruce A. Quantifying the effects of warming and ecosystem change on Arctic soil microbial communities [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B53G-2476, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Increases in arctic temperatures have accelerated microbial activity and thawed permafrost, liberating long-frozen substrates that result in positive soil-climate feedbacks. Additionally, above ground changes in the tundra such as shrub encroachment and altered litter quality have led to changes in soil microbial processes. Quantifying the response of each microbial taxon to increased temperature and ecosystem change can offer a more detailed ecological understanding of how climate change alters these processes. To do this, quantitative stable isotope probing (qSIP) incubations using 18O water were conducted at the Toolik Field Station in Alaska. To uncouple the effects of warming and ecosystem change, active layer soil was incubated in situ for 10 and 30 days in each of the following treatments: 3 months warming, 29 years warming (warming and ecosystem change), and unwarmed controls. Native water was removed through desiccation and then rewetted to match the original water content with either 98.5 atom percent 18O oxygen water or natural abundance water. This is one of the first attempts to perform a qSIP experiment in the field, and the first from arctic soil. Over 90% of the native water was removed and replaced, achieving exceptional 18O enrichment in all samples. Total density curves of 16S gene copies shifted in 18O-labelled samples, but weighted average density was not significantly different in warming treatments. Our results suggest either that tundra soil prokaryotic communities are unaffected by warming and ecosystem treatments, even after 30 days of incubation, or that effects are not detectable on the community scale. Only a small portion of community members may have been affected by the treatments. Identification of labelled taxa reveals how much these microbes respond to warming and warming-associated ecosystem changes. Overall, our research offers a glimpse into which soil microbes will thrive in a warming arctic.

2020027649 Qin Jia (Chinese Academy of Sciences, State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Han Tianding; Yang Qin and Shangguan Donghui. The characteristic of runoff variation and its responses to climate change in the Shule River basin [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23C-1564, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The recharge of runoff in the Shule River Basin includes snow melt, precipitation and groundwater. Global warming leads the increase of snow melt, permafrost degradation and the change of underlying surface; these changes have a certain impact on runoff. Based on the measured and hydrological survey data of the Changmabao, Yulinhe Reservoir and Yumen Hydrological Station in the Shule River basin, the methods of tendency analysis, Mann-Kendall mutation test and cross wavelet transform are used to analyze the trends, mutations and variation periods of the runoff of Changmahe River, Yulinhe River and Shiyouhe River in the Shule River basin. Through combining the meteorological data of Tuole, Guazhou and Yumen stations to explore the response of the runoff to climate change. The results show that the seasonal runoff distribution of the Yulinhe River is relatively uniform, while the Changmahe River and the Shiyouhe River are mainly concentrated in the summer, accounting for 58.44% and 70.38% of the annual runoff, respectively. The average annual runoff shows an upward trend, except for the Changmahe River, the upward trend of the Yulinhe River and the Shiyouhe River is not significant, and the variation rates of tendency are 1.04´10⁸m³/10a, 0.00071´10⁸m³/10a and 0.0071´10⁸m³/10a, respectively. The average annual runoff of the Yulinhe River and the Shiyouhe River reached the maximum and minimum in the 1990s, respectively. The runoff of Changmahe River has a turning point in 1997, and after 1997, the runoff has shown a significant upward trend, the Yulinhe River and the Shiyouhe River have not changed suddenly, but there are multiple turning points. Wavelet analysis shows that there are small variation period of 2-4a in all three rivers, and there is also a long period of 32a, but it has not passed the significance test. The correlation between annual average precipitation and runoff in three rivers is stronger than temperature, and runoff changes are more sensitive to precipitation, the runoff lags behind precipitation. Due to the change of underlying surfaces and the distribution of glacier and permafrost, the response of runoff to precipitation and temperature changes is also different.

2020032508 Qin Shuqi (Chinese Academy of Sciences, Institute of Botany, Beijing, China) and Yang Yuanhe. Mineral controls over permafrost carbon stability and decomposition [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2579, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw induced by climate warming makes large fraction of soil organic matter (SOM) available to microbial decomposition. However, SOM interactions with mineral soil matrix protect it from decomposition and could control long-term SOM stabilization. It is still unknown how much carbon is associated with mineral in permafrost soil, and the role of mineral protection in permafrost carbon decomposition are not well understood. Here, based on soil samples from permafrost deposits along a ~1000 km permafrost transect on the Tibetan Plateau, we quantified the proportion of SOM associated with mineral. Our results showed that 14% of SOM was bound to calcium, and 9% of SOM was associated with iron oxides, demonstrating the importance of soil minerals in SOM stability, especially calcium in the alkaline permafrost. In combination with a laboratory incubation, we further found that the rate of SOM decomposition upon permafrost thaw was negatively associated with the amounts of mineral-bound carbon. Overall, our results indicate the vital control of mineral protection over permafrost carbon stability, which should be considered in projecting permafrost carbon-climate feedback.

2020032581 Rahman, Shaily (University of Florida, Geological Sciences, Ft. Walton Beach, FL); Martin, Jonathan B.; Martin, Ellen E.; Pain, Andrea and Ackerman, Philip B. Nutrient fluxes from deglaciated versus proglacial Greenlandic watersheds [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1344, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Assessments of dissolved nutrient fluxes from Greenland tend to focus on proglacial watersheds that deliver glacial meltwater to the oceans. However, Greenlandic streams also exist in deglaciated watersheds separated from the Greenland Ice Sheet by hydrologic divides that drain only local precipitation and permafrost meltwater. Here, we compare select nutrient concentrations in the dissolved (<0.45 mm) fractions from streams draining two proglacial and four deglaciated watersheds in western and southern Greenland. Samples were collected during three field seasons: spring 2017, late summer/early fall 2017, and summer 2018. Average dissolved Si (DSi), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN) concentrations were generally 1.5-2X higher in non-glacial than proglacial streams, whereas soluble reactive phosphorous (SRP) and Fe concentrations were ~3-4X lower. Typical mean annual specific discharge in gauged non-glacial streams ranged from 410-640 mm/y compared to 340 mm/y in the proglacial stream with reliable discharge data. Combining concentration and specific discharge data indicates that specific yields of DSi, DOC, and TDN were ~2-4X greater in non-glacial than the proglacial stream, likely due to enhanced organic matter production and silicate mineral weathering in the presence of terrestrial vegetation in deglaciated watersheds. However, specific yields of Fe and SRP were ~2-100X lower in non-glacial compared to the proglacial stream, likely from sequestration in Fe-oxyhydroxide minerals and assimilation by microbial biomass and vegetation in non-glacial streams. Our data suggest that as the region transitioned from the Last Glacial Maxima to the current interglacial, fluxes of DSi, DOC, and TDN to the coastal Arctic Ocean increased, while fluxes of SRP and Fe decreased. Thus, the ratios, and possibly limitation of these nutrients with respect to marine phytoplankton uptake, varied with decreasing proportion of proglacial relative to non-glacial drainages. These changes in nutrient delivery are likely to be amplified during continued ice retreat as the Arctic warms.

2020032646 Rangel, Rodrigo C. (University of Wyoming, Laramie, WY); Parsekian, Andy; Engram, Melanie J.; Ohara, Noriaki; Jones, Benjamin M.; Arp, Christopher D. and Walter Anthony, Katey M. Arctic thermokarst lake carbon gas emission estimates and scaling [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS14A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost is estimated to store about 20% of the total terrestrial carbon (C) stock. Permafrost thawing releases C in part as methane (CH₄), however, there are large uncertainties in the global CH₄ budget that limit the accuracy of climate change projections. Estimating how much C is released from permafrost as ebullition through lakes is critical to overcome this knowledge gap. Previous studies have estimated thermokarst lake gas fluxes based on direct observations of gas bubbles trapped on lake ice, however, this approach can be limited because the gas bubbles must be visible on the lake ice surface, which can be difficult if there is snow cover or white ice. To overcome this limitation, we demonstrate a new measurement and scaling approach combining direct observations, geophysical measurement, and leverage previous research which correlates space-borne synthetic aperture radar (SAR) backscatter to ebullitive flux to estimate C gas fluxes emitted from Arctic thermokarst lakes. Ground-penetrating radar (GPR) can be applied to estimate the volumetric gas content (VGC) trapped in lake ice, enabling detection of gas bubbles even with snow cover or white ice on the lake surface. Gas flux rates are estimated by combining the VGC with an ice growth model. L-band SAR can remotely-sense gas trapped by lake ice allowing gas flux estimates on local or regional scales. GPR measurements were conducted in 13 thermokarst lakes on the North Slope, Alaska, including four regions: Barrow, Teshekpuk, Oumalik, and Atqasuk. L-band SAR results with low, medium, and high backscatter helped to guide GPR acquisition locations. Ice thicknesses in drill holes were measured in order to calibrate GPR for ice properties. The results suggest variable regional gas fluxes, in part controlled by the location of C-rich Yedoma permafrost. This study contributes to an improved understanding of C fluxes from Arctic thermokarst lakes that could be used to refine atmospheric C models. Furthermore, a better estimation of CH₄ emissions is essential to project the impacts of climate warming and determine the best management strategies.

2020032579 Ravens, Thomas (University of Alaska Anchorage, Civil Engineering, Anchorage, AK); Ulmgren, Michael; Berry, Kevin and Ford, Kristopher. Forecasting coastal hazards, risks, and impacts in Arctic Alaska; to promote sustainable adaptation [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1342, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rapid environmental change in Arctic Alaska is exposing coastal communities to intensifying hazards like coastal erosion, flooding, permafrost thaw, and salinity intrusion. These hazards have social and economic impacts such as the cost of protecting or relocating infrastructure subject to erosion. Because the severity and character of the hazards in the future is uncertain, communities have difficulty planning and investing for the future. In this presentation, we describe a collaborative effort to forecast and communicate hazards and risks, as well as their social and economic impacts, using the communities of Hooper Bay and Utqiagvik (Barrow) Alaska as case studies. Community members and researchers work together to monitor the coastal environment (e.g., monitor beach profiles and storm surge) and to generate data for calibrating and validating models of coastal hazards (e.g., coastal erosion, flooding). Communities also assist with identifying and acquiring data on the social and economic impacts of these coastal hazards. Working together, communities and scientists share their knowledge and experience of coastal hazards and their impacts. Hazard forecasts enable the development of tools for communicating risk, like flood maps that communicate frequency and intensity of flooding for the remainder of the century. Data on the social and economic costs/impacts of hazards in the past--along with hazard forecasts-- nable the forecasting of social and economic impacts in the future. Forecasts of future hazards and associated impacts are critical data for planning, and implementing sustainable adaptation strategies.

2020027650 Rawlins, Michael A. (University of Massachusetts Amherst, Amherst, MA); Stuefer, Svetlana L.; Nicolsky, Dmitry; Cai, Lei and Afshari, Shahab. Changing characteristics of runoff and freshwater export from watersheds draining northern Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C23D-1582, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The quantity and quality of river discharge in arctic regions is influenced by many processes including climate, watershed attributes and, increasingly, hydrological cycle intensification and permafrost thaw. We used a hydrological model to quantify baseline conditions and investigate the changing character of hydrological elements for Arctic watersheds between Point Barrow and just west of Mackenzie River over the period 1981-2010. A synthesis of measurements and model simulations shows that the region exports 31.9 km³

2020027644 Revil, Andre (CNRS, Université Savoie Mont Blanc, France); Coperey, Antoine; Duvillard, Pierre A.; Magnin, Florence; Ravanel, Ludovic and Soueid Ahmed, Abdellahi. Induced polarization as a new tool to monitor the degradation of permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Spectral Induced Polarization is a geophysical method studying the ability of porous rocks to store reversibly electrical charges under the influence of a primary electrical field. In this presentation we discuss the influence of permafrost on induced polarization and how induced polarization can be used as an efficient tool to monitor the degradation of permafrost. First we establish the theory which is combined to a freezing model establishing the relationship between the liquid water content and temperature during freezing and thaw and accounting for the segregation of salt in the liquid water phase. We show that the model unifies electrical conductivity and induced polarization of rocks. Then the model was validated using a large dataset of laboratory experiments in well-controlled conditions in the temperature range +20°C to -16°C with 15 samples including soils, crystalline rocks, sandstones, and graphitic schists. Finally, we applied this model to at two test sites in the Alps and one field experiment in which permafrost was created using a geothermal heat exchanger. The model shows its ability not only to detect permafrost and to estimate its temperature and liquid water content but also to monitor its degradation thanks to a new generation of time-lapse algorithms.

2020032645 Rey, David (Colorado School of Mines, Golden, CO); Walvoord, Michelle A.; Minsley, Burke J.; Ebel, Brian A.; Voss, Cliff and Singha, Kamini. Measurement and modeling of perennial thaw zone development in boreal Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS14A-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Vulnerable boreal ecosystems are experiencing high rates of environmental change. Permafrost thaw associated with these changes will continue to increase the importance of groundwater flow and storage in permafrost environments. Locally, perennial thaw zones (PTZs) have formed in boreal hillslopes as the depth to permafrost increases and the depth of seasonal freezing decreases. PTZs may accelerate permafrost degradation and enhance seasonal connectivity between hillslopes and streams, facilitating the transport of permafrost carbon, nitrogen, and mercury. Previous field observations of PTZs have been primarily limited to areas of discontinuous or sporadic permafrost with mean annual air temperatures less than 3 Celsius. Recent geophysical observations including borehole nuclear magnetic resonance (NMR) and ground penetrating radar (GPR) have shown PTZ development and rapid spatial expansion near the discontinuous/continuous permafrost boundary, in an area with mean annual air temperatures of approximatley-6 C. Perennial thaw appears localized in an area that burned in 2004, while no PTZs have been observed in adjacent unburned areas. In the winter of 2019, volumetric water content profiles measured using down borehole NMR indicate roughly 50-55% volumetric liquid water content from 0.5m to the bottom of the boreholes in the burned area at approximately 2.25m. Co-located GPR measurements suggest that the PTZ likely extends deeper than the NMR borehole depths. Geophysical observations over several years and multiple seasons were combined with direct field measurements (i.e. measurements of active layer thickness and soil temperature) to guide the creation of thermo-hydrologic models. Models were used to simulate the disturbance and model results were compared to the collected field data (i.e. temperature, active layer thickness, volumetric water content profiles). Models that compared favorably to collected data were used to explore key variables thought to drive PTZ initiation. Using a rich field dataset spanning multiple years and seasons to constrain thermo-hydrologic models provides insight into the importance of PTZs in an ecosystem moving towards higher groundwater storage and contribution to streams.

2020032636 Robert, Zena V. (University of Alaska Fairbanks, Geosciences, Fairbanks, AK); Mann, Daniel H.; Farquharson, Louise M.; Romanovsky, Vladimir E.; Capps, Denny; Meyer, Franz J. and Maio, Chris. Impacts of rapid climate changes on mass movements in Denali National Park and Preserve, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NH33E-0964, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Denali National Park and Preserve (DENA) is a crown jewel within the US National Park system. It receives over 600,000 visitors a year, most of whom travel the 140-km road that crosses the northern flank of the park. This road is threatened by mass movements of diverse genesis, some of which are related to the thawing of permafrost (perennially frozen ground). Landslides along the DENA road corridor are both an urgent management issue and an interesting case study into how climate change affects the hillslope geomorphology of a subarctic mountain range. An ongoing mass movement near mile marker 35, referred to as the Mile 35 Slide, is representative of other landslides along the road corridor. The Mile 35 Slide is polygenetic, having begun as an active-layer detachment slide in the summer of 2016 and then developing into a retrogressive thaw slump in the summer of 2019 that is deflating frozen talus deposits of mid-Holocene age. Retreat of the head scarp has recently triggered a rock rotational slide in incompetent bedrock higher on the hillslope. Like the Mile 35 Slide, many ongoing mass movements in DENA are polygenetic reactivations of older landslides and rock glaciers that were active sometime earlier during the Holocene. In addition to investigating the timing of earlier episodes of widespread mass movement, we are testing two hypotheses using remote sensing and lichenometric dating: 1) Mass movements in DENA have increased in frequency since the end of the Little Ice Age (ca. AD 1900) because of warming temperatures and changing precipitation regimes; and, 2) Mass movements are more frequent on north-facing slopes because active layers (depth of seasonal freeze-thaw) are thinnest there and have been less affected by past climatic fluctuations. We will show how preliminary results confirm that landslide frequency has increased over the last several decades, corroborate observations that permafrost thaw is frequently involved in landslide initiation, and suggest that slope aspect is a useful predictor of landslide occurrence.

2020032513 Rogers, Jennifer Anastasia (Florida State University, Tallahassee, FL); Galy, Valier; Chanton, Jeff and Spencer, Robert G. Ramped PyrOx and ultrahigh resolution mass spectrometry insights into the age and composition of Arctic river dissolved organic matter [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2584, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

With extensive and ongoing warming in the Arctic, long frozen permafrost soils are thawing and releasing organic carbon in atmospherically significant quantities that remain poorly constrained. The Kolyma River in North Eastern Siberia is the largest watershed completely underlain by continuous permafrost. In this study we aimed to better constrain release of permafrost derived organic carbon to the Kolyma River and to further our understanding of its fate to better constrain how much may be been released to the atmosphere. Despite permafrost's highly aliphatic (high H/C) and ¹⁴C depleted (~20,000 ¹⁴C years old) signature, evidence of this signature has been shown not to persist downstream to the mouth of the Kolyma River. This suggests either: (i) extensive mineralization of permafrost derived dissolved organic matter (DOM); or (ii) the unique permafrost signature is overwhelmed by modern organic material inputs (i.e. permafrost thaw remains a relatively small portion of DOM released). In this study, samples from a permafrost dominated thaw stream and the Kolyma River were collected and incubated for 28 days. Samples before and after incubation were analyzed via Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) as well as stable and radiocarbon isotopes linked to thermostability- a technique called ramped pyrolysis/oxidation isotopic analysis (RPO). With this we were able to see a shift in the permafrost DOM distribution to higher activation energies indicating more thermally stable degradation products. Preliminary results from this study reveal the lack of a degraded permafrost signature within the Kolyma River mainstem, suggesting either limited permafrost inputs relative to modern inputs or the rapid loss of this material higher in the watershed.

2020027692 Romanovskaya, Maria A. (Lomonosov Moscow State University, Moscow, Russian Federation); Romanovsky, Vladimir E. and Kuznetsova, Tatyana V. Warming-induced release of greenhouse gases from the soil into the atmosphere; how consequential can it be? [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC11G-1135, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

It is no secret that the permafrost and overlaying seasonally thawing horizon contain an enormous amount of sequestered organic carbon. According to some estimates, this amount is equivalent, in carbon terms, to more than twice the carbon dioxide in the Earth's atmosphere. Significant amounts of greenhouse gases, mostly methane, are already contained in watery glacier beds. Accordingly, fears arise that permafrost meltdown and glacier retreat as the Earth warms will lead to new greenhouse burps into the atmosphere. To gain an insight into the matter, we are conducting a program of paleoclimatic research in the Russian region of Voronezh southeast of Moscow. The study area was experienced several Quaternary-period glaciations. Results of our comprehensive geological and geomorphological exploration of the area have clearly shown the presence of features brought about by the Don, Dnepr, Moscow and, Valdai glaciations. These features include stratigraphy indicative of several successive periods of permafrost build-up and degradation during the Late Pleistocene and the Holocene. Importantly, on the map of the Last Permafrost Maximum (LPM) this area is located within the equilibrium permafrost zone. Our finest and most detailed study of a cross-section of Quaternary deposits was carried out at the multilevel archaeological site Divnogorie-9 (50°36'49"N, 39°30'31"E), which is known for numerous finds of fossilized equestrian remains. This section exposed several paleosol layers. Radiocarbon dating of fossils and paleosol layers estimates of 14-12 ka BP. Just 30 km north of Divnogorie (51°23'40"N, 39°30'31"E), lies the world-famous Borshchevo-Kostenki mammoth cemetery (38-18 ka BP). The presence of mammoth suggests a landscape of lush periglacial grassland with organic-rich soil. At the same time, our measurements of organic carbon content in paleosol layers returned infinitesimally low figures, which fall within the error margins of our measurement methods. This means that in Central Russia at least, the Quaternary Period has seen multiple warming-induced massive releases of carboniferous greenhouse gases from rotting vegetation-rich marshlands, from degrading permafrost and from under retreating glaciers. Remarkably, none of these events appears to have resulted in catastrophic consequences

2020027659 Rooney, Erin (Oregon State University, Corvallis, OR); Lybrand, Rebecca; Dragila, Maria I.; Gallo, Adrian; Hatten, Jeff A.; Reno, Loren R.; Sanclements, Michael R.; Varga, Tamas and Qafoku, Odeta. The impact of freeze-thaw cycles on soil porosity in permafrost-affected soils [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Freeze-thaw cycles deform soil pores through cryosuction and water expansion, reducing the stability of permafrost in Arctic landscapes. Warming winter temperatures alter microscale processes that retain permafrost, including reshaping pore connectivity, pore size distribution, and subsequent soil ice-richness. The objective of our work is to quantify how an increased frequency of freeze-thaw cycles in the active layer of permafrost-affected soils in Alaska will influence soil porosity at multiple scales. We conducted our study by subsampling aggregates from permafrost cores collected from Toolik, AK in partnership with the National Ecological Observatory Network (NEON). We performed freeze/thaw incubation experiments on selected soil aggregates that spanned 5 freeze-thaw cycle treatments for a total of 20 days. Aggregates were exposed to -10°C for 2 days (freeze) followed by 2 days of 25°C (thaw) to allow for total freezing and thawing of each sample. Aggregates were scanned using x-ray computer tomography (XCT) and imaged with scanning electron microscopy (SEM). We compared pore connectivity, size, and volume before and after the freeze-thaw treatments. Two pore size ranges (1 to 20 microns and 20+ microns) were analyzed, and two moisture treatments (15% and 30%) were examined through XCT scans of the 20+ micron size range to compare how water content influenced pore deformations. Our examination of pores greater than 20 microns indicated a significant reduction in total porosity volume and a significant increase in the average pore size following five freeze-thaw cycles. Pores less than 20 microns exhibited contractions and expansions following five freeze-thaw cycles using imagery captured by Focus Ion Beam/SEM. Following ten freeze-thaw cycles, morphological changes in the <20 micron pores were not observed, suggesting that pores in this size fraction are not continuously impacted by freeze-thaw cycles after initial changes have occurred. Our findings indicate that greater frequencies of freeze-thaw in the active layer of permafrost under warming climate conditions may reduce soil porosity and diminish ice richness, reducing permafrost retention in cold region soils and contributing to higher carbon emissions, shifts in ecosystems and vegetation communities, and landscape collapse.

2020027645 Rouyet, Line (NORCE Norwegian Research Centre, Tromso, Norway); Liu Lin; Lauknes, Tom R.; Christiansen, Hanne H.; Strand, Sarah M.; Larsen, Yngvar; Stendardi, Laura; Karlsen, Stein-Rune; Johansen, Bernt and Malnes, Erik. Seasonal dynamics of permafrost landscapes; InSAR ground displacements and controlling factors documented by in situ and Sentinel-1/-2 remote sensing data [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In permafrost landscapes, the seasonal ground freeze and thaw induce heave and subsidence due to the phase change of the water within the active layer. On slopes, an additional downslope component of displacement is present over creeping landforms. Changes of the ground thermal regime in a context of climate change can lead to modification in the distribution, amplitude and timing of displacements. In this context, it is paramount to develop large-scale measurement techniques able to monitor periglacial environments and explore the relations between ground dynamics and environmental variables. Synthetic Aperture Radar Interferometry (InSAR) allows for detection of millimetric displacements over large areas. Based of Sentinel-1 and TerraSAR-X InSAR results in and around Adventdalen (Spitsbergen, Svalbard), we showed that 1) subsidence/heave can be measured with a 6-day sampling and the temporal patterns of the displacement match the variation of ground temperature; 2) the spatial variability of the seasonal ground displacements is largely related to topographical and geomorphological factors; 3) the time series over flat areas can be well described by the Stefan equation with a composite model that combines thawing and freezing degree-day indices. However, the model does not account for a downslope component of displacement and the spatial variability of environmental factors. In this study, we complexify the composite model to account for complex topographies and environments, and to improve the characterization of the displacement time series over the study area. We consider locations in the valleys where displacement patterns are dominated by subsidence/heave and on solifluction sheets combining vertical and horizontal components of movement. The InSAR results are compared with in-situ measurements (ground temperature/moisture, displacements) and complementary remote sensing data documenting ground freeze/thaw cycles, snow coverage (based on Sentinel-1 SAR backscatter analysis), vegetation types and phenology (based on Sentinel-2 multi-spectral imagery). The study shows that integration of radar and optical remote sensing provides new insights on the relations between the timing of ground freeze/thaw and biotic/abiotic characteristics of the surface.

2020027661 Rush, Michael (Institute of Arctic and Alpine Research, Boulder, CO) and Rajaram, Harihar. Incorporating the seasonal snowpack into thermo-hydrologic modeling of frozen ground at Niwot Ridge, CO [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Niwot Ridge, CO is one of the most intensely-studied alpine sites in the world and, with long-term climate and ground temperature observations, serves as an ideal location for analyzing the occurrence of frozen ground and its hydrologic effects under a changing climate. While there is little field evidence of permafrost at present, it is unclear to what extent permafrost existed in the past: permafrost was observed at high-elevation, wind-scoured sites in the 1970's, but recent empirical and physical modeling suggests that permafrost was not present at those sites in the 1970's. Frozen ground is important for understanding changes in hydrology: recent work has attributed increasing autumn streamflow in this watershed to permafrost thaw and suggested that frozen ground plays a role in determining the timing of groundwater discharge to streams. It is well known, however, that a seasonal snowpack strongly influences the occurrence of frozen ground: a deep snowpack decouples the ground from the atmosphere. Thus, retrospective and future assessment of the hydrologic influence of frozen ground at Niwot Ridge will benefit from physical representation of the snowpack. We have coupled surface energy balance calculations and a physical snowpack model based on the Utah Energy Balance with PFLOTRAN-ICE, a subsurface thermo-hydrologic model that simulates water and energy transport in the subsurface, including freeze-thaw processes. We present results from modeling seasonally frozen ground during 2000-2014 at the alpine D1 (3740 m), Saddle (3530 m), and subalpine C1 site (3020 m) that features a deep snowpack (maximum depths 80cm-140cm). Soil temperature observations at Saddle and D1 can be reproduced without representation of the snowpack, while excluding the snowpack at the subalpine C1 site results in modeled soil temperatures that are substantially colder than measured temperatures. Simulations performed at the Saddle with and without soil freezing are used to determine how frozen soils control water table elevations during 2007-2014. In a future with shifting snowpack dynamics (e.g. increases in peak-season snowfall and decreases in late-season snowfall), high-elevation sites like those at Niwot Ridge will likely experience changes in frozen ground occurrence that may drive shifts in streamflow and soil moisture.

2020032569 Sachs, Torsten (German Research Centre for Geosciences, Potsdam, Germany) and Zöllner, Mathias. A new UAS system for airborne eddy covariance measurements of heat and carbon fluxes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51K-2384, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

It has become increasingly clear in the past years that fully understanding greenhouse gas emission from highly complex landscapes such as wetlands and permafrost will benefit from measurements on a variety of scales. Given the scarcity of sites in a vast region with limited access on one hand, and the well-documented spatial and temporal variability of fluxes on the other hand, combining long-term, continuous records from individual sites with larger scale surveys of the spatial variability could help to reduce biases and uncertainties in the bottom-up estimates. Several projects in the past years included aircraft measurements of GHG concentrations or even fluxes and succeeded in mapping permafrost GHG fluxes over large regions at resolutions down to 100 m. However, the cost and complexity of such operations allows for few temporal snapshots only. New UAS and lightweight sensor technology now allows for an increase in aerial survey frequency at a fraction of the cost of aircraft operations.

2020032618 Salehi, Bahram (State University of New York, College of Environmental Science and Forestry, Syracuse, NY); Mahdianpari, Masoud; Mohammadimanesh, Farida and Brisco, Brian. Wetland inventory of Canada using satellite Earth observation data and Google Earth engine cloud [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H34E-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wetlands are important ecosystems such that they are commonly referred to as Nature's Kidney. Wetlands however are in danger of being lost and converted to uplands, particularly in lower latitudes. With approximately ten million square kilometers of land mass, Canada owns approximately 25% of the world's total wetlands. However, Canada, like many other countries, lacks a nation-wide wetland inventory map. In this talk, we present our Canada-wide high resolution wetland inventory map and the method we developed. The method is based on an object-based random forest classification framework utilized in Google Earth Engine cloud computing platform. The input data is some 65000 multi-year optical and synthetic aperture radar (SAR) images, acquired by European Space Agency's Sentinel-1 (SAR) and Sentinel-2 (optical) satellites, and field samples across the country. The map, covering all ten provinces and three northern territories, consists of five major wetland classes of bog, fen, marsh, swamp, and shallow water for all provinces and territories as well as other classes such as forests, cropland, urban, ice/snow depending on the existence of such classes in the specific province/territory. The overall classification accuracy of the entire country is about 80% with individual class accuracies ranging from 74% to 84%. Results show that 19% of Canada's land areas is covered by wetlands, most of which are peatlands. Results demonstrates that the Boreal Shield, Taiga Shield, and Hudson Plains comprise much of Canada's wetlands, whereas wetlands are least common in mountainous ecozones. Bogs and fens are found to be the most dominant wetland classes in Canada, especially in the northern regions. In addition, results indicate an increase to the wetlands extents in Canada, particularly in northern ecozones. This potentially could be due to climate change and its effects on the frozen lands such as thawing permafrost and melting ice and snow. The resulting wetland inventory map of Canada provides unprecedented details on the extent, status, and spatial distribution of wetlands on a national basis over a consistent time-period. Thus, it is useful for many stakeholders including federal and provincial governments and provides a basis for better status and trends analysis of the countries wetlands.

2020032488 Sanders, Aquanette (University of Texas at Austin, Marine Science, Austin, TX); Henson, Henry Churchill; Duran, Gabriel; Mann, Paul J.; Natali, Susan; Schade, John D.; Sistla, Seeta; Ludwig, Sarah; Rodriguez-Cardona, Bianca and MacArthur, Rhys. Determining the effects of thermokarst events on the availability and emissions of CH₄, CO₂ and N₂O in the YK delta, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23K-2459, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Due to the increase in temperature and disturbances, such as wildfire, in the Arctic, thermokarst processes (ground collapse due to thawing of ice rich permafrost) have accelerated. The resulting thermokarst features may alter the soil carbon and nitrogen cycle through thawing of frozen ground, movement of soil as the ground collapses, and changes in soil resource availability and environmental conditions. These changes could alter greenhouse gas emissions to the atmosphere, potentially creating a positive feedback to climate change as more organic materials thaw and become available to microbial decomposers. To study the effects of thermokarst processes on the three major greenhouse gasses (N2O, CH4, and CO2), we collected soil gas samples in sub-arctic tundra in the Yukon Kuskokwim Delta, AK in an area that burned in a 2015 wildfire and an adjacent unburned area. In each site, we sampled along six 30 m transects, which included relatively undisturbed tundra (control areas, no thermokarst) and in the burned site, included areas with ground slumping (extensive ground cracking with exposure of mineral soil) and thaw depressions (subsided ground with saturated soils). We also measured gas fluxes from control areas, and near and inside the thaw slumps at two sites that burned in 2015. N2O concentrations in thaw slump soils reached as high as 600 ppb and were almost two times greater than concentrations in the control and thaw depression soils, which were close to atmospheric concentrations. While CH4 concentrations were lower in the thaw slumps than control areas, CH4 concentrations in saturated soils in the depressions were four times greater than control and slumped soils (38 ppm vs 10 and 3 ppm, respectively). The control areas of the burn site had higher soil CO2 concentrations compared to the unburned site, but they both had low CH4 concentrations. These results suggest that thermokarst processes alter soil conditions and the concentrations of carbon and nitrogen species. Importantly, concentrations of N2O were significantly elevated above atmospheric levels in thaw slumps, demonstrating the potential for strong climate feedbacks as a result of abrupt ground thaw.

2020032493 Sanderson, Nicole K. (Universite du Qubec a Montreal, GEOTOP, Montreal, QC, Canada); Aquino-López, Marco A.; Garneau, Michelle; Blaauw, Maarten and Christen, J. Andres. Rule of Plum; comparison of lead-210 dates derived from Bayesian analysis and the constant rate of supply model using simulated and real datasets [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23L-2508, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

To understand changes in peat accumulation in response to recent and rapid climate or anthropogenic change, accurate ages for the last 100-200 years are essential. Dating this period is often complicated by poor resolution and large errors associated with calibrating radiocarbon (¹⁴C) ages. The use of lead-210 (²¹⁰Pb) is a popular method as it allows for the measurement of absolute and continuous dates for the last 150 years of peat accumulation. In ombrotrophic peatlands, the ²¹⁰Pb dating method has traditionally relied on the Constant Rate of Supply (CRS) model which uses the radioactive decay equation to provide a logarithmic model to approximate dates, resulting in a restrictive model. Key limitations of the CRS model are: (1) the accurate estimation of the supported lead which varies between sites and can be problematic if sampling of the total inventory is not continuous (e.g. interval measurements, lack of samples); (2) the inconsistent assessment of uncertainties. The Plum model was developed in a statistical framework with a Bayesian approach, notably resulting in longer chronologies and more realistic uncertainty estimations, and has the advantage of not double-modelling dates for final age-depth models. Here, we present two thorough tests of Plum. First, we created scenarios using simulated datasets with known age-depth functions in a range of shapes and with varying sampling resolution. These simulations are created using the physical behavior that most ²¹⁰Pb dating models are based on. Plum and CRS model outputs are compared under each scenario. We also take this opportunity to demonstrate the new Plum R package, for use by non-statisticians in palaeoecological studies. Second, we present a comparison of ²¹⁰Pb dates derived from CRS models and from Plum using real peat cores from Eastern Canada with additional independent dating controls. These cores represent a thorough test for Plum, as permafrost thaw during the last 50 years has drastically altered stratigraphy and peat type (e.g. shift from ligneous peat to Sphagnum moss) affecting ²¹⁰Pb retention within the peat. Recent decadal-scale changes are still poorly represented so accurate dating is now essential to quantify changes in carbon accumulation rates and predict future trends.

2020032677 Sanderson, Nicole K. (GEOTOP-UQAM, Montreal, QC, Canada); Green, Sophie M.; Cressey, Elizabeth A.; Quine, Timothy A.; Garneau, Michelle; Hartley, Iain P. and Charman, Dan. Strengthening evidence-based policy for peatlands; potential and pitfalls for quantification of C accumulation and loss using fallout radionuclides [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA43D-1182, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Northern peatlands are globally important carbon sinks. In boreal and subarctic regions, climate change-driven permafrost thaw over the last 50-200 years is rapidly altering peat carbon storage. In temperate regions, projects often focus on the restoration of degraded peatlands by blocking drainage ditches. While rewetting increases methane emissions, rapid peat accumulation also increases C sequestration and climate mitigation. Policies for peatland conservation must be supported by quantitative data on carbon accumulation and loss. To calculate peat accumulation rates, chronologies using the fallout radionuclides lead-210 (²¹⁰Pb) and cesium-137 (¹³⁷Cs) are often used, particularly in areas of rapid change. However, questions remain concerning radionuclide mobility within peatlands and its effect on age-depth models. Spatially integrated inventories of ²¹⁰Pb and ¹³⁷Cs have also been used in soil studies to quantify erosion and deposition. We present two novel approaches for quantifying radionuclide patterns within peatlands. (1) Replicate cores from different permafrost regions in northeastern Canada were dated with a combination of ²¹⁰Pb and radiocarbon (¹⁴C) dates. (2) ¹³⁷Cs inventories were measured in situ at a peat restoration site in Exmoor National Park (UK) using a portable gamma spectrometer (PGS) in dry, intermediate and wet plots. Both replicate-based case studies show that there is a relationship between water table depth and radionuclide inventories, indicating some mobility or preferential deposition which may affect dating. However, as this trend is not significant for ²¹⁰Pb, and ¹⁴C-only age-depth models were found to underestimate accumulation rates due to poor dating resolution and large errors, chronologies should multiple dates to accurately evaluate drivers of decadal to centennial changes. As the PGS rapidly measures relative spatial changes in ¹³⁷Cs at low cost, it has potential wider applications in peatland management, e.g. tracking erosion rates after ditch blocking. National policies and regional land-use planning where peat is important should therefore be incorporating well-dated paleoecological data to target areas for future GHG mitigation potential or to design locally appropriate restoration projects.

2020027703 Sato, Hisashi (Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan) and Kobayashi, Hideki. Interactions between topography, permafrost, and vegetation in Siberian larch forest; a simulation study [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC24C-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In eastern Siberia, larches (Larix spp.) often exist in pure stands, constructing the world's largest coniferous forest, of which changes can significantly affect the earth's albedo and the global carbon balance. Siberian larch area locates on the environmental edge of existence of forest ecosystem, and hence small difference in environmental condition alters existence of larch trees. Indeed, there is a quantitative pattern that topographic properties controls the abundance of larch forest via both drought and flooding stresses in this region; larch abundance appears to be controlled by drought stress in mountainous regions, while controlled by flooding stresses in plain areas. Besides, this region is underlain by permafrost, vegetation productivity is constraint by depth of active layer; plant productivity becomes lower for shallower active layer by reducing liquid-state-water holding capacity. At the same time, active layer depth is a function of soil wetness, because wetland soil has larger ice content in active layer, which facilitates downward heat conduction to the permafrost, resulting in shallow thaw for the active layers. To reconstruct such complicated interactions between topography, permafrost, and vegetation in Siberian larch forest, the TOPMODEL, which is a physically based streamflow and water-table-depth computation scheme was implemented to a dynamic vegetation model SEIB-DGVM, which works with a thermohydrology model. In this presentation, I will talk how this integrated model reasonably works, and how it can be employed for future projection of environmental conditions of the Siberian larch region.

2020032643 Scandroglio, Riccardo (Technical University of Munich, Munich, Germany); Schroeder, Tanja and Krautblatter, Michael. One decade of quantitative temperature-calibrated ERT permafrost monitoring in Alpine rock walls [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS13A-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost degradation is a key factor in understanding and forecasting rock slope failures in high mountain areas, especially in the context of climate change. In the last decade mountain permafrost warmed by circa 0.2 °C, leading to reduction of rock walls stability and increase of active layer thickness. The subsequent increase of instable rock masses poses a severe risk for people and infrastructure in these regions. Resistivity has been proven to be the most accurate permafrost monitoring technique in permafrost areas. Its high sensitivity for frozen vs. unfrozen conditions, together with a laboratory calibration, provides clear quantitative information on site-specific rock wall temperatures. Here we show: (i) the longest series (2007-2019) of ERT in steep bedrock with (ii) a unique temperature calibration¹, (iii) a quantitative inversion scheme and (iv) a direct link to mechanical changes. We do this at two sites at the fringe of permafrost (Zugspitze, Germany/Steintalli, Switzerland), where the susceptibility is crucial. Knowing rock temperature at different depth, water percolation inside the mountain, meteorological forcing and data from neighbor borehole allows us to better understand spatial variations for both long term trends and seasonal anomalies (e.g. warm summers like 2015 & 2018, snow-rich winter like 2019). The mean rock temperature of the entire core section shows phase-shift of circa 2-3 months between solar radiation peaks and thermal rock response. Significant warming periods are especially evident in highly fractured zones, thanks to the contribution of percolating cleft water from precipitation and snowmelt. 2018 marks the year with the smallest areal extent and highest permafrost core temperatures yet recorded, reaching resistivity values of 10^4.5Wm (about -2°C). We further developed a coupled thermo-geophysical model for conductive heat transfer in permafrost rock walls at local scale, to validate the ERT and project future conditions. 1. Krautblatter, M., Verleysdonk, S., Flores-Orozco, A. & Kemna, A. (2010): Temperature-calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps). J. Geophys. Res. 115. DOI:10.1029/2008JF001209

2020027669 Schaedel, Christina (Northern Arizona University, Flagstaff, AZ) and Schuur, Edward. Permafrost carbon network; research synthesis to quantify the permafrost carbon feedback [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C52A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost carbon release to the atmosphere has the potential to amplify climate change. Release of just a fraction of this frozen carbon pool has large consequences for society and a comprehensive understanding of the magnitude and timing of this carbon release is highly needed. The Permafrost Carbon Network (PCN, URL: http://www.permafrostcarbon.org) is a US sponsored but international network that produces new knowledge through research synthesis quantifying the role of permafrost carbon in driving future climate change. Established in 2010, the PCN has been synthesizing emerging data on permafrost carbon pools, carbon quality, thermokarst and abrupt thaw, aerobic and anaerobic issues, as well as upscaling and modeling. Through synthesis, the PCN provided updated parameters in support of model assessment and development, guided development of new research initiatives and contributed knowledge to reports and documents used by decision makers. Recent results from a model intercomparison project suggest that permafrost carbon loss during this century could be offset by increased plant carbon uptake while in the long-term cumulative soil carbon losses would dominate. This implies that effective mitigation efforts during the remainder of this century could attenuate the negative consequences of the permafrost carbon climate feedback. The latest PCN synthesis used data from published studies on abrupt thawing across the permafrost zone and showed that a sudden collapse of thawing soils in the Arctic might double the warming from greenhouse gases released from tundra. Synthesis information created by the PCN also provides a platform for communicating science results to society via news articles, blog posts, and via online communication, which are all meant to increase science impact to non-experts.

2020032452 Schaefer, Kevin M. (University of Colorado at Boulder, Cooperative Institute for Research in the Environmental Sciences, National Snow and Ice Data Center, Boulder, CO); Chen, Richard H.; Michaelides, Roger J.; Moghaddam, Mahta; Parsekian, Andy; Sullivan, Taylor D. and Zebker, Howard A. Remotely sensed active layer thickness and soil moisture using airborne L-band and P-band radar [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B12D-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Active Layer Thickness (ALT) is a key parameter to monitor the status of permafrost. We combined airborne L-band Interferometric Synthetic Aperture Radar (InSAR) with P-band backscatter to simultaneously estimate ALT and soil moisture. The L-Band Remotely Sensed Active Layer Thickness (ReSALT) technique uses InSAR to measure the surface heave and subsidence as the active layer freezes and thaws. In ReSALT, we assume the distribution of water in the soil column to estimate ALT from the seasonal subsidence. The P-Band Airborne Microwave Observatory of Subcanopy and Subsurface (AirMOSS) technique estimates the vertical distribution of water in the soil column. As part of the Arctic Boreal Vulnerability Experiment (ABoVE), we combined ReSALT and AirMOSS to estimate ALT and soil moisture for 76 airborne flight lines in Alaska, Yukon, and Northwest Territories. Here, we summarize our techniques and show results for several flight lines. We relate the remotely sensed ALT and soil moisture to various processes, such as fire and thermokarst.

2020032565 Schaefer, Kevin M. (University of Colorado at Boulder, Cooperative Institute for Research in the Environmental Sciences, National Snow and Ice Data Center, Boulder, CO); Schuster, Paul F.; Elshorbany, Yasin E.; Jafarov, Elchin; Striegl, Robert G. and Wickland, Kimberly. Potential impacts of mercury released from thawing permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51I-2352, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Mercury (Hg) is a naturally occurring neurotoxin that bonds with organic matter. Frozen organic matter in permafrost represents the largest reservoir of Hg on the planet. We modified the Simple Biosphere/Carnegie-Ames-Stanford Approach terrestrial biogeochemistry model (SiBCASA) to include mercury biogeochemistry. We then estimated future releases of Hg from thawing permafrost for a low emissions scenario close to the 2°C target of the Paris Accord and a high emissions scenario of unconstrained fossil fuel burning. The high emissions scenario showed annual atmospheric Hg emissions from thawing permafrost peaking above current anthropogenic emissions. Hg concentration in the Yukon River barely increases for the low emissions scenario, but exceeds the Environmental Protection Agency (EPA) maximum limits for the entire thawed season for the high emissions scenario. Calculated Hg concentration in fish never exceed EPA maximum limits for the low emissions scenario, but for the high emissions scenario, it exceeds EPA limits within a hundred years. Our results indicate minimal risks to water and food supplies for the low emissions scenario, but high risks for the high emissions scenario.

2020032570 Schaepman-Strub, Gabriela (University of Zurich, Zurich, Switzerland); Plekhanova, Elena and Oehri, Jacqueline. Arctic biodiversity and its functions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51L-2387, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic is warming at 2-3x the rate of the globe on average. Vegetation changes are a result of this warming, but feedbacks with the permafrost and atmosphere might enhance or inhibit these changes and related functions. How can plant traits shed light on functions of Arctic vegetation and can they be used to improve predictions of ecosystem functions under future increased temperature and precipitation? We will briefly summarize recent tundra plant trait synthesis results from literature and then relate traits to important functions of tundra vegetation, including energy, water, and carbon fluxes using examples from observational and experimental research. Examples include the shift in the leaf economics spectrum, leaf optical properties and stem traits of Arctic shrubs in response to nutrient addition. Based on detailed trait analysis--as opposed to earlier biomass and plant cover only studies--we challenge the perspective that shrubs protect permafrost from thawing through shadow casting.

2020032568 Scheller, Johan (Aarhus University, Bioscience, Aarhus, Denmark); Christensen, Torben R. R. and Mastepanov, Mikhail. UAV-based mapping of galloping thermokarst; implications for methane emissions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51K-2380, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

In Arctic ecosystems, methane release is highly spatially variable. New generations of methane analyzing instruments makes it possible to explore this variability in detail at ecosystem scales, as the instruments are increasingly portable combined with increasing their accuracy. We have used drone-based mapping techniques combined with micro-portable cavity ring-down laser analysers to analyse the rapid development of a thermokarst that appeared along the bank of the Zackenberg river, NE Greenland, in response to an unusual snowmelt in 2018. The landscape transformed from a net carbon sink with very low surface exchange of methane within a few weeks to one of substantial organic carbon loss and highly elevated methane concentrations appearing in the cracks of the permafrost. This presentation will use UAV-based mapping technology to document the temporal development of the thermokarst in relation to its dynamics of greenhouse gas exchange and the spatial differences in the exposure organic matter to anaerobic decomposition and melt-out of methane-rich ground ice. Until now, observational data of methane release from thermokarst systems is very limited, and typically available in both low temporal and spatial resolution. This study is part of a larger project aiming to improve our understanding of the thermokarst-methane dynamics. These first, ground-based observations will pave way to future UAV-based platforms, which cover larger areas more efficiently, and may become an exciting addition to e.g. eddy flux measurements, as this method can point out where potential point sources of methane and rapidly changing such are located.

2020032465 Schiferl, Luke D. (Harvard University, Cambridge, MA); Powell, Margaret; Biraud, Sebastien; Euskirchen, Eugenie Susanne; Farina, Mary; Henderson, John; Larson, Erik; Munger, J. William; Sweeney, Colm; Watts, Jennifer; Zona, Donatella and Commane, Roisin. Insights into changing regional-scale carbon dioxide and methane fluxes from Arctic tundra ecosystems [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B14D-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic is warming at twice the rate of the global average. Thawing of Arctic permafrost has the potential to release vast stores of carbon-containing gases into the atmosphere, thereby accelerating warming. We aim to understand how tundra ecosystems respond to climate change by quantifying changes in carbon dioxide (CO₂) and methane (CH₄) fluxes on annual and decadal timescales. We use improved ecosystem-resolved flux fields driven by functional relationships, which have been tuned to eddy flux tower observations of CO₂ and CH₄. These relationships have been generalized regionally using meteorological reanalysis to produce spatially and temporally varying flux products. We evaluate our models using the calculated surface influence on airborne (e.g., ACME-V, ArctiCAP) and tower (e.g., Barrow) measurements of CO₂ and CH₄ concentration from a Lagrangian atmospheric transport model (WRF-STILT). Our analysis identifies the spatial areas and source vegetation types which are not accurately represented by the models. We find that an increase in fall respiration over the past 30 years shifts the Alaskan North Slope to a net CO₂ source to the atmosphere. Still, the model underestimates observed biogenic CO₂ enhancements in this area, possibly due to the missing representation of soil moisture. Evaluation of the CH₄ flux field reveals large early winter emissions throughout the North Slope region. This work points to a necessity to collect and incorporate soil moisture information and investigate how changes related to melting impact the partitioning of carbon between CO₂ and CH₄.

2020027640 Schoenemann, Spruce W. (University of Montana Western, Environmental Sciences, Dillon, MT); Nusbaumer, Jesse M.; LeGrande, Allegra N. and Porter, Trevor J. Ice sheet-moderated changes in the precipitation isotope climatology of NW Canada during the late deglacial [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C21E-1494, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A recent 13.6 ka-long summer temperature reconstruction based on precipitation isotopes preserved in syngenetic (aggrading) permafrost below a peatland in central Yukon (DHP174 site) shows that early Holocene summers in NW Canada were consistently warmer than the Holocene mean, and reached a thermal maximum at ~6.6 ka BP that was followed by neoglacial cooling until the onset of Industrial Era warming [Porter et al., 2019]. The early Holocene-to-neoglacial transition (~9-6 ka BP) was accompanied by a marked d_excess shift signaling a change in moisture source evaporative conditions, and putatively linked to changing Holocene boundary conditions. Using the GISS ModelE2.1 GCM, we compare the simulated and observed summer precipitation isotopes and identify a robust atmospheric circulation reorganization driven by the disintegration of the Laurentide Ice Sheet (LIS). This change produces adjustments in both the position of the moisture source region and the mean evaporative conditions at ocean surface. Although the GCM simulations somewhat underestimate the full magnitude of isotopic change, they generally align with the timing and sign of d_excess change. Sensitivity experiments to warmer SSTs and lower albedo (coniferous forest vs. tundra) in the early Holocene (9 ka) vs. mid-Holocene (6 ka) show a better fit to the DHP174 pore ice record, and other marine and terrestrial proxy records. Water isotope records from relict permafrost and ice cores provide unique opportunities to reconstruct changes in d_excess, which offers insights on ocean-atmospheric dynamics that can be investigated using model-data approaches. Our model-data investigation of a summer-biased proxy further supports the need for critical re-examination of model parameterizations and applied boundary conditions of current climate models in order to more closely reproduce the inferred Holocene climate.

2020032491 Schulze, Christopher (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Voigt, Carolina; Sonnentag, Oliver; Hernandez Ramirez, Guillermo; Thompson, Lauren; Kuhn, McKenzie Ann; Heffernan, Liam and Olefeldt, David. Effects of wildfire and permafrost thaw on nitrous oxide fluxes from Boreal peatlands in Western Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23K-2476, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Increasing temperatures in the Taiga Plains in northwestern Canada cause more frequent and intense disturbances in boreal permafrost peatlands which threatens the stability of those globally significant stores of carbon and nitrogen. Resulting increased rates of permafrost thaw affect the greenhouse gas balance of peatlands through a higher frequency and severity of wildfires and the development of thermokarst features where the ice-rich permafrost ground collapses into water-saturated bogs or lakes. The developing landforms are characterized by differences in soil temperature and moisture conditions, thaw depth, pore water chemistry and vegetation composition. While the consequences of these transformations for the two carbon-based greenhouse gases, carbon dioxide and methane, have been investigated intensively, the effects of wildfire and thermokarst on nitrous oxide fluxes from permafrost peatlands are poorly understood. In this study, we carry out flux measurements applying both, ground-mounted and floating, closed static dark chambers to detect differences in soil greenhouse gas exchange from selected post-fire and thermokarst stages compared to intact permafrost peat plateaus. Additionally, we monitor porewater chemistry to reveal the interaction between surface fluxes and belowground nutrient cycling. We expect higher nitrous oxide emissions in burned compared to thermokarst-affected areas, due to the larger disruption in vegetation growth post-fire vs. post-thaw, whereas anaerobic conditions in thermokarst bogs and ponds may further inhibit nitrous oxide emissions. The results of this study will help us understand which of the two disturbance types intensified by increasingly warmer temperatures has a larger impact on the nitrous oxide fluxes of northern permafrost peatlands.

2020032562 Schuur, Edward (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ) and Schaedel, Christina. The vulnerability of permafrost carbon to climate change; key findings from a decade of synthesis [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw and the microbial decomposition of previously frozen organic carbon is considered one of the most likely positive feedbacks from terrestrial ecosystems to the atmosphere in a warmer world. Soils in the northern circumpolar permafrost zone store 1,460 to 1,600 petagrams of organic carbon (Pg C), almost twice the amount contained in the atmosphere and about an order of magnitude more carbon than contained in plant biomass (55 Pg C), woody debris (16 Pg C), and litter (29 Pg C) in the boreal forest and tundra biome combined. This large permafrost zone soil carbon pool has accumulated over hundreds to thousands of years, and there are additional reservoirs in subsea permafrost and regions of deep sediments that are not added to this estimate because of data scarcity. Permafrost temperatures have been increasing over the last 40 years, and disturbance by fire (particularly fire frequency and extreme fire years) is higher now than in the middle of the last century. Near-surface permafrost area is projected to be reduced by 30-99% this century as a result of warming, and fire is also projected to increase across most of the tundra and boreal region. 5% to 15% of the organic soil carbon stored in the northern circumpolar permafrost region (mean 10% value equal to 146 to 160 Pg C) is considered vulnerable to release to the atmosphere by the year 2100. The most recent large-scale modeling suggests that additional plant carbon uptake, growth, and deposition of new carbon into soil would together completely offset any soil carbon loss this century, and that it would take several centuries before cumulative losses from soils would overwhelm new carbon uptake. At the same time, the intercomparison and other studies have indicated that future scenarios with limited human greenhouse gas emissions would reduce changes to high latitude ecosystems. Model projections of permafrost carbon do not always match current empirical measurements or other assessments, suggesting that this issue is still emerging from a state of deep uncertainty as described by the IPCC. Together, the loss of carbon from thawing permafrost soils, disturbance by fire and abrupt thaw, in combination with offsetting plant uptake response, determines the net effect of high latitudes on the global carbon cycle.

2020027686 Schwenk, Jon (Los Alamos National Laboratory, Los Alamos, NM); Piliouras, Anastasia; Zhang, Yu; Fratkin, Mulu; Rowland, Joel C.; Douglas, Madison; Chadwick, Austin J. and Lamb, Michael P. Permafrost control on river migration along the Koyukuk River, AK [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP42B-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic river floodplains contain vast stores of carbon that may be released as river banks erode. A recent study comparing Arctic river migration rates with dozens of temperate and tropical river migration rates found that Arctic rivers tend to erode into their floodplains slower. After normalizing for differences in hydrology, Arctic rivers' slower erosion rates were attributed to the presence of permafrost that adds a thermal control to the bank erosion process. Curiously, although the inter-river comparison showed statistically-significant permafrost influence on erosion rate, attempts to discern this relationship for individual rivers were inconclusive, owing perhaps to the difficulty of precisely determining permafrost presence at river reach scales. The Koyukuk River, AK flows through discontinuous permafrost and thus presents an opportunity to determine if permafrost influence on migration rates can be determined locally, as some of its bends are eroding into permafrost-laden banks while others are permafrost-free. In this work, we generate a permafrost map using a machine learning model trained with permafrost observations from a field campaign. Migration rates are measured from remotely-sensed imagery (2 meters per pixel, 1978-2018). Initial results suggest that curvature-driven hydrodynamics have a first-order control on migration rates, so migration rates are normalized for hydrodynamic effects before assessing permafrost control. We compare local, normalized migration rates between permafrost-present and permafrost-free bends to assess if permafrost provides a thermal limitation on the bank erosion process. This work presents new insights into the role of permafrost control on river erosion processes.

2020032614 Shavers, Ethan J. (U. S. Geological Survey, Center of Excellence for Geospatial Information Science, Rolla, MO) and Stanislawski, Lawrence. Alaskan hydrographic feature extraction using IfSAR and Landsat [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H23O-2116, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The United States Geological Survey is in the process of updating the content of the National Hydrography Dataset (NHD) in Alaska, where the hydrography was originally compiled from 1:63,360-scale source data that are now out of date and inadequate for current resource management needs. Remote sensing strategies are being investigated for use in updating the Alaskan NHD. The surface water features of Alaska pose several challenges to remote delineation and flow network generation. The extensive and remote mountain terrain make high resolution data collection difficult. Surface water dynamics related to glacial, proglacial, permafrost and wetland environments are prevalent and complicate flow path delineation. Here we test the use of conventional and new tools for surface water feature extraction and flow network generation from IfSAR data. Flow accumulation derived channel networks are refined using a new stream cross-section analysis (SCA) method. Waterbodies, greater than 10 meters wide, with open water are extracted from orthorectified images generated from the IfSAR return intensity data (0.6-2.5 meter resolution). Several methods are tested using elevation and image data to delineate boundaries of challenging surface water features such as wetlands and to determine least cost paths to maintain flow networks. Results indicate that accurate stream channel extraction is constrained by the spatial resolution of the elevation data with channels narrower than several meters often undetected by the SCA method. Areas of low relief with an absence of well-defined channels remain a challenge. We test the use of convolutional neural networks (CNN) for constraining the challenging areas. The CNN algorithms are trained using the matching areas between the United States Geological Survey's Landsat Dynamic Surface Water Extent data, existing NHD features and IfSAR orthorectified images. Preliminary results of this work show promise for automated mapping of surface water features in Alaska.

2020027697 Shiklomanov, Alexander I. (University of New Hampshire, Earth Systems Research Center, Durham, NH); Tretiakov, M.; Proussevitch, Alexander A. and Georgiadi, Aleksandr. Understanding changes in river flow to the Arctic Ocean from Eurasia using hydrological modeling [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1279, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

River flow to the Arctic Ocean plays a significant role in the oceanic freshwater budget accounting for about 2/3 of the total freshwater flux to the Arctic Ocean. Ocean salinity and sea ice formation are critically affected by river input and changes in the freshwater and heat fluxes to the ocean can exert significant control over global ocean circulation via the North Atlantic deep water formation. There are mounting evidences that hydrological regime across the pan-Arctic is experiencing an unprecedented degree of change. However, the exact causes of such change are not immediately apparent, as they constitute a complex interplay between climate- and human-induced drivers. We used a new version of University of New Hampshire Water Balance Model (WBM) to quantify major sources of changes in river flux to the Arctic Ocean from Eurasian drainage basin. WBM is a grid based model which simulates the vertical water exchange between the land surface and the atmosphere and the horizontal water transport along a prescribed river networks for both natural and anthropogenic systems. The model accounts for sub-pixel land cover types, glacier and snow-pack accumulation/melt across sub-pixel elevation bands, permafrost dynamics, anthropogenic water use (e.g. domestic and industrial consumption, and irrigation for most of existing crop types), hydro-infrastructure for inter-basin water transfer and reservoir/dam regulations. To identify and quantify contributions of individual drivers/factors to river flow we used a new water source tracking capability recently developed in WBM. It allows "fingerprinting" of water at all steps in the water cycle such as in soils, groundwater pools, lakes, reservoirs, and fluxes such as originated from snowmelt, rain, glacier runoff, and baseflow. By comparing the difference in water component fractions in water storages and fluxes resulting from multiple historical runs we were able to quantify responses of each water source to the changes in climatic drivers and to characterize causes of observed changes in river flow to the Arctic Ocean. This work was mainly supported by Russian Foundation for Basic Research, grants: 18-05-60192 and 18-05-60240.

2020032624 Shogren, Arial (Michigan State University, East Lansing, MI); Zarnetske, Jay P.; Abbott, Benjamin W.; Cairns, Samuel T.; Iannucci, Frances; Duda, Megan J. and Bowden, William B. Seasonal and event-based concentration discharge relationships from contrasting Arctic headwater catchments [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H43G-2078, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate change is predicted to accelerate hydrologic cycle and amplify the release of carbon and nutrients from the permafrost landscapes of the Arctic. However, we have limited understanding of how seasonality and landscape characteristics influence hydrologic mobilization and transport of carbon and nutrients into Arctic river networks, especially during intense precipitation and stream flow events. To fill this knowledge gap, we assess river carbon and nutrient dynamics across three headwater catchments and a range of flow conditions. The three watersheds represent dominant landscape types of the northern Arctic Alaska and are part of the Arctic Long Term Ecological Research (LTER) site: low-gradient tundra, low-gradient but lake-influenced tundra, and high-gradient alpine. In each watershed, we collected high-frequency dissolved organic carbon (DOC) and nitrate (NO₃^-.

2020032461 Shu, Shijie (University of Illinois at Urbana Champaign, Department of Atmospheric Sciences, Urbana, IL); Jain, Atul K. and Kheshgi, Haroon S. Investigating global scale wetland and non-wetland soil methane emissions and sinks using a land surface model [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13L-2472, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wetland and wet soil are the largest natural methane (CH₄) sources accounting for about 45% of global CH₄ emissions, while dryland soil is the second largest CH₄ sink, accounting for about 10% of the total sink in the global CH₄ budget. The effects of global warming on soil CH₄ emissions and sinks are, however, uncertain in current model estimates due to the lack of representation of complicated couplings between biogeophysical (soil hydrology and permafrost dynamics) and biogeochemical (methanogenesis and methanotrophy) processes. We estimate the distribution of CH₄ emissions and sinks from wetland and non-wetland soils (including wet and dry soils) with a newly-developed vertically-resolved soil CH₄ model, integrated into a global land-surface model (ISAM) which includes the coupling of the dynamics of hydrology to CH₄ production, oxidation and transport processes. We calibrate and test this integrated model with CH₄ observations at test sites from permafrost, temperate and the tropical wetlands regions. ISAM is applied at the global scale to estimate CH₄ emissions and sinks given both recent past observed climate and wetland extent, and future climate and wetland extent driven by two scenarios, RCP4.5 and RCP8.5. Our study shows an expansion of the wetland over permafrost and tropical regions, due to 1) increases in temperature and seasonal wetland extent as a results of higher precipitation in the future scenarios which, in turn, increases modeled methanogenic activity more than methanotrophic activity in soils, and 2) altered transport in the soil column and exchange with the atmosphere by modeled transport processes (diffusion, ebullition, and aerenchyma transport). This expansion increases the contribution of soils to CH₄ emissions in these future scenarios. We find that the dry soil CH₄ sink also increases globally due to warmer climate under the future scenarios, but the magnitude is not as large as the increase in CH₄ emissions. By resolving the SOC vertical distribution, water table depth and permafrost affected hydrology, ISAM results suggest a stronger CH₄ - climate feedback than previous modeling studies.

2020032607 Skierszkan, Elliott K. (University of British Columbia, Vancouver, BC, Canada); Dockrey, John W.; Mayer, Ulrich K. and Beckie, Roger D. Geogenic uranium and arsenic release results in water-quality impacts in a subarctic region of granitic and metamorphic geology [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GH22A-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

We present a study of the geological sources and mobilization processes controlling geogenic U and As in a subarctic environment. Concentrations of these elements have been found to exceed regulatory limits in groundwater by orders of magnitude in the Dawson Range (Yukon, northwest Canada) through natural weathering of granitic and metamorphic rocks. This region is also susceptible to environmental changes that may alter baseline water quality resulting from mineral-resource extraction and climate-change-driven permafrost thaw. This study examines the geological sources and mobilization processes controlling baseline U and As in this subarctic environment. To this effect, a large geochemical dataset for the region, comprising >1,200 rock samples, >3,000 surface-water samples, and hundreds of sediment and groundwater samples has been compiled from government and industry sampling initiatives. This dataset reveals widespread but modest U enrichment in granitic and metamorphic rocks at mg/g levels that are slightly above average crustal abundance. However, U is naturally present in groundwater (up to 589 mg/L) and surface water under low flow or baseflow conditions: 39% of groundwater monitoring wells and 5% of surface water sampling locations have median U concentrations above Canadian regulatory guidelines (e.g., for the protection of aquatic life). While U mobilization appears regionally pervasive, it may be promoted around mineral deposits through an indirect process involving sulfide-mineral oxidation and concomitant carbonate mineral dissolution, releasing Ca and increasing alkalinity and solubilizing U through complexation reactions. Naturally elevated As in groundwater, with concentrations of up to 2,190 mg/L, is most likely related to mineral deposits and weathering of arsenian pyrite and arsenopyrite and reducing groundwater geochemistry. Overall, combining large geochemical and government exploration datasets provides a unique opportunity to provide regional baseline metal(loid) distribution in an area of geogenic enrichment and to potentially support mitigation strategies for water-quality concerns that may arise through industrial activity and climate change.

2020032524 Sniderhan, Anastasia (Wilfrid Laurier University, Waterloo, ON, Canada); Spence, Christopher and Baltzer, Jennifer Lynn. Landscape change in Canada's taiga shield on discontinuous permafrost; documenting the influence of 50 years of warming on vegetation, lakes, and watercourses in a subarctic ecosystem [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24F-11, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

As climate warms, high-latitude regions underlain by permafrost (perennially frozen ground) experience landscape change through processes such as ground subsidence, forest loss and shifts in vegetation composition, and transitions from raised permafrost plateaus to wetland features as thaw occurs. In Canada's Northwest Territories, studies quantifying these thaw-induced changes to the landscape have largely been focused on the Taiga Plains ecoregion. In contrast to the Taiga Plains, the Taiga Shield landscape (the westernmost portion of the Canadian Shield) is comprised of sparsely treed or exposed bedrock, a large network of lakes and wetlands, forest patches on glaciolacustrine sediments, and peatlands that have accumulated in bedrock depressions. Landscape change as a result of warming and permafrost thaw may manifest differently in the Taiga Shield, where underlying bedrock could offer greater thaw stability and different patterns of vegetation change than has been observed in the Taiga Plains. In this study, we use high-resolution air photos dating back to the 1970s in conjunction with recent satellite imagery to document landscape change in the Baker Creek watershed, a typical Taiga Shield basin north of Yellowknife NT, through this period of rapid climate warming. We will be addressing questions including: (1) are there changes in forest extent and forest density across the Baker Creek watershed? (2) Are these changes associated with permafrost thaw, and did this lead to the development of waterbodies? In our imagery analysis, we have found that while some areas of the basin have experienced forest loss, there is also evidence of forest encroachment and infilling. This landscape-level investigation will be paired with studies which address process understanding of the biogeophysical system, through quantifying differences in plant water cycling and use of different water stores, and impacts of vegetation change on the water budget within the basin.

2020032553 Song Chunlin (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Raymond, Peter A. and Wang Genxu. Distinct seasonality of river CO₂ partial pressure and efflux in permafrost catchments of the Qinghai-Tibet Plateau [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43I-2607, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Riverine CO₂ evasion plays a pivotal role in carbon cycles but is still uncertain, especially for permafrost rivers. Here we investigate the seasonal CO₂ partial pressure (pCO₂) and CO₂ emission flux (FCO₂) of 8 catchments in Yangtze River source region (YRSR), which have high permafrost coverage and seasonally thawed active layer. The YRSR catchments were supersaturated with CO₂ except some sites exhibited CO₂ undersaturation during initial thaw period. Both pCO₂ and FCO₂ peaked in the thawed period under the influence of active layer thaw and hydrological processes. The lower order streams showed significantly higher pCO₂ and FCO₂ than higher order rivers. The YRSR rivers emitted 2.71 TgC of CO₂ annually, corresponding to 75% of terrestrial C that entered the river networks. High emission/export ratio can be attributed to the large proportion of baseflow and steep topography, while in-steam organic carbon mineralization probably played a negligible role. Annually, half of the horizontal C flux and 70% of the CO₂-C emission were transported during the thaw period. The seasonally thawed active layer over QTP played a more crucial role on riverine carbon export than the Arctic. Warming may increase annual CO₂ emission due to deeper flow path and longer emission window.

2020032506 Song Yutong (Chinese Academy of Sciences, Institude of Botany, Beijing, China) and Yang Yuanhe. Methanogens driving methane production from the active layer and permafrost soils on the Tibetan Plateau [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2577, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Carbon loss as carbon dioxide (CO₂) and methane (CH₄) due to permafrost thaw form a positive feedback to climate change. However, little is known about the magnitude and controlling factors of methane production and methanogenic community from permafrost soils on the Tibetan Plateau. Here, we incubated the active layers and permafrost soils from 12 swamp meadow sites at 4°C under anaerobic conditions and identified their methanogens abundance and community composition and analyzed environmental factors. We revealed that the potential rates of CH4 production in permafrost soils (38.8-812.6 ng CH₄-C g C^-1d^-1) was significantly lower than in active layers soils (12.5-2652.2 ng CH₄-C g C^-1d^-1). The abundance of mcrA gene in permafrost soils was also significantly lower compared with active layers soils(P_0.05). Furthermore, variation partitioning analysis showed that the different rates of CH4 production between the two layers was mainly driven by methanogens abundance, whose pure effect was 11.7%. These results indicated that methanogens may play a crucial role in the feedback of methane to climate change once permafrost thaws.

2020027628 Steiner, Nick (City Uuniversity of New York, City College of New York, New York, NY); McDonald, Kyle C.; Podest, Erika and Davitt, Aaron W. D. Frost degree-day mapping over permafrost soils in the Arctic boreal zone from multifrequency passive microwave radiometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1383, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The terrestrial biomes of the Arctic-Boreal Zone (ABZ) are key feedbacks on sources and sinks of atmospheric carbon--feedbacks that are largely based on seasonal freeze/thaw (F/T) controls. The future trajectory of the ABZ as a carbon (C) sink or source is of global importance due to vast quantities of C stored in permafrost and frozen soils. Substantial emissions of methane are linked to the "zero curtain" period when soil temperatures are poised near 0 °C and freezing progresses downward, and from depth, retaining a thinning thawed and actively metabolizing soil horizon towards the frozen season. Observations of refreeze in the active layer are vital for understanding of greenhouse gas exchange in the ABZ. Common observational records of F/T from remote sensing instruments are binary and representative of a depth and landscape constituents (e.g. vegetation, snow, soil) that is determined by the landcover and frequency of the radar or radiometer. The Soil Moisture Active Passive (SMAP) radiometer operates at L-Band and is optimized for sensitivity to soil conditions, especially in sparsely vegetated ecosystems of the ABZ. Using SMAP along with multi-frequency radiometer observations from Advanced Microwave Scanning Radiometer (AMSR2) we determine the F/T state of upper soil and the start of the "zero curtain" period and the subsequent frost-degree day (FDD) forcing at the surface during refreeze. The spatially-resolved FDD product is directly related to the active layer depth during refreeze. The uncertainty in FDD from SMAP, and corresponding frost depth, are determined at automated weather stations that are part of the Snow Telemetry (SNOTEL) and Circumpolar Active Layer Monitoring (CALM) network as well as from the surface component temperature records along our Alaska Ecological Transect (ALECTRA). The physical basis of FDD observations are demonstrated using radiometric modeling of vegetation, snow and soil. We present observations of FDD timing and progression over permafrost soils in the Arctic Boreal Zone during the SMAP satellite record (2015-2019). Portions of this work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

2020032642 Stemland, Helene M. (University of Bergen, Bergen, Norway); Johansen, Tor A. and Ruud, Bent O. Applications of surface seismic on thawing saline permafrost; examples from the Norwegian Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS13A-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Arctic surface temperatures are increasing more rapidly than the world average due to feedback mechanisms, and an implication of this is thawing of currently frozen ground. Saline permafrost is particularly prone to following geomorphic consequences because saline pore-water gradually changes phase at subzero temperatures, hence even minor subzero temperature variations can lead to significant changes in the degree of freezing in such areas. To detect and monitor permafrost degradation, non-intrusive methods are desirable due to efficiency and environmental constraints. The effective elastic properties of the subsurface depend partly on the degree of freezing of pore-water. Since seismic surface waves are sensitive to changes in shear-wave velocity in particular, thawing of even very thin layers is reflected by changes in surface wave characteristics. We have acquired seismic data in Adventdalen on Svalbard in the Norwegian Arctic during several field seasons using a variety of seismic sources, and we here investigate how the data vary with time and source type. Vertical geophones record surface waves of Rayleigh type. Data acquired with explosives show the strongest surface waves, but are dominated by an air wave. Thawing in the uppermost sediments usually affects high frequencies, but we here observe variation with time even at frequencies <50 Hz, likely related to higher modes of Rayleigh waves. We observe an inversely dispersive trend in frequency-velocity spectra of seismic records from winter, indicating dominant higher modes. This is typical for low-velocity sediments embedded in higher velocity sediments, and Rayleigh wave dispersion curves extracted from synthetic seismograms made for such a geometry provide a good match with observations. Previous studies have suggested that Adventdalen consists of eolian low-salinity sediments overlying raised marine high-salinity sediments. Thus, the upper sediments are more frozen (i.e. higher velocity) than those below during winter. Such an inverse velocity gradient makes traditional refraction seismic methods fail, and our results indicate that seismic surface wave methods are a viable option for monitoring thawing of frozen sediments. However, inversion of surface wave data with higher modes is not straightforward and requires further attention.

2020027666 Straneo, Fiammetta (Scripps Institution of Oceanography, La Jolla, CA); Adusumilli, Susheel; Marzeion, Ben; Shepherd, Andrew and Timmermans, Mary-Louise. Heat needed to melt ice; the cryosphere's contribution to the Earth's energy imbalance [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C43D-1515, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Multiple components of the Earth's cryosphere have undergone rapid change over the last few decades. These include mass loss from the Greenland and Antarctic ice sheets, mass loss from ice caps and glaciers in polar and high-mountain regions, loss in Arctic terrestrial snow and sea-ice, polar and mountain permafrost thaw, and a reduction in the seasonal snow-cover of mountain regions. The reduction in mass of these different cryosphere components implies a supply of heat to melt the ice and thus represents a heat sink for the Earth System which must be accounted for in assessing the Earth's Energy Imbalance and the associated radiative flux imbalance at the top of the atmosphere. Here, we present the most-updated, observational and model based estimates for changes in the major cryosphere components based on recent ice loss synthesis for several periods within the 1960-2017 range. This estimate represents the Climate and Cryosphere Project of the World Climate Research Program's contribution to an updated inventory of EEI under the Global Climate Observing System, and prepared for the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.

2020032594 Stuefer, Svetlana L. (University of Alaska Fairbanks, Fairbanks, AK); Kane, Douglas I.; Arp, Christopher D.; Dean, Kelsey and Gieck, Robert. Changes to streamflow variability observed in continuous permafrost watersheds in remote Arctic location [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1364, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Ongoing streamflow changes in four small to midsize watersheds underlain by continuous permafrost in Arctic Alaska are explored based on historic discharge measurements in Imnavait Creek (1985-2017), Upper Kuparuk River (1993-2017), Putuligayuk River (1999-2017), and Fish Creek (2009-2019). Streamflow response to snowmelt and rainfall in these watersheds is strongly affected by energy balance, active layer dynamics, and permafrost landforms. Our measurements highlight increased range of annual discharge variability; that is high annual discharges (Q) measured in recent decade were not present in earlier records. We observed that combination of precipitation changes coupled with permafrost dynamics triggered much wider Q range than previously measured. This change is especially pronounced at the Putuligayuk River and Fish Creek watersheds located on the Alaska Arctic Coastal Plain, where permafrost landforms such as reticulated-patterned ground, strangmoor ridges, pingos, thermokarst lakes and drained thermokarst lake basins strongly affect hydrologic connectivity and surface storage.

2020032474 Stünzi, Simone Maria (Alfred Wegener Institute, Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Langer, Moritz; Boike, Julia; Kruse, Stefan and Herzschuh, Ulrike. Modeling permafrost sensitivity in Arctic forest [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23G-2492, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Deciduous larch is a weak competitor when growing in mixed stands with evergreen taxa but is dominant in many boreal forest areas of Eastern Siberia. However, it is hypothesized that certain factors such as a shallow active layer thickness and high fire frequency favor larch dominance. Our aim is to understand how thermohydrological interactions between vegetation, permafrost, and atmosphere stabilize the larch forests and the underlying permafrost in Eastern Siberia. A tailored version of a one-dimensional land surface model (CryoGrid) is adapted for the application in vegetated areas and used to reproduce the energy transfer and thermal regime of permafrost ground in typical boreal larch stands. In order to simulate the responds of Arctic trees to local climate and permafrost conditions we have implemented a multilayer canopy parameterization originally developed for the Community Land Model (CLM-ml_v0). The coupled model is capable of calculating the full energy balance above, within and below the canopy including the radiation budget, the turbulent fluxes and the heat budget of the permafrost ground under several forcing scenarios. We will present first results of simulations performed for different study sites in larch-dominated forests of Eastern Siberia and Mongolia under current and future climate conditions. Model performance is thoroughly evaluated based on comprehensive in-situ soil temperature and radiation measurements at our study sites.

2020032639 Sullivan, T. D. (University of Wyoming, Laramie, WY); Parsekian, A.; Douglas, T. A.; Schaefer, K. M.; Michaelides, R. J.; Saari, S.; Liddle Broberg, K.; Westenhoff, J. H. and Schaefer, S. Geophysical observations of organic matter and soil moisture interactions during freezing and thawing of Alaskan boreal permafrost [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS11B-0627, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Organic matter distribution within the soil column of interior Alaska's syngenetic ice-cemented permafrost influences the soil moisture distribution during freeze and thaw processes. Soil moisture behavior, in turn, influences freeze/thaw dynamics within the seasonally thawed permafrost active layer. Here we use geophysical time-lapse measurements of soil moisture and thaw depth to answer the question, How does organic matter distribution affect soil moisture behavior within the active layer of Interior Alaska boreal forest permafrost? In situ measurements of organic matter distribution and thaw depth supplement geophysical observations from borehole nuclear magnetic resonance (NMR), ground-penetrating radar (GPR), and electrical resistivity tomography (ERT) to produce images of soil moisture distribution from August, 2018 to October, 2019. Borehole NMR measurements provide depth-specific soil moisture and pore size distribution observations; GPR soundings yield depth-averaged soil moisture estimates; and ERT identifies areas of frozen versus unfrozen regions from two-dimensional and three-dimensional subsurface assessments. This suite of analyses focused on soil moisture distribution in relation to organic matter concentrations helps to explain the dynamic distribution of liquid water during freezing and thawing. Our improved observations of key processes within the active layer help constrain thaw pattern projections within the boreal forest of interior Alaska.

2020032651 Sun, Xiang (University of California at Berkeley, Berkeley, CA) and Soga, Kenichi. Deformation coupled effective permeability change in hydrate-bearing sediment during depressurization [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS33A-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane hydrates found in sediments of deep sea and permafrost regions have drawn global interest as one of the new energy resources. The depressurization method, which reduces the pore fluid pressure from a wellbore and dissociates hydrate to gas, is a basic technique to extract methane gas from hydrate-bearing sediments in the field. The rate of gas production from a depressurized well is governed by the magnitude of pressure drawdown as well as the permeability of the formation around the wellbore. During depressurization, the effective permeability changes spatially and temporary due to changes in hydrate saturation by hydrate dissociation and in porosity of the host sediment associated with effective stress change. Along with the degradation of soil structure by hydrate dissociation, soil compaction occurs, which in turn results in permeability reduction. On the other hand, depressurization induces hydrate dissociation, which results in the increase in effective permeability. In this study, a simple coupled compressibility-permeability analysis method is proposed to identify the conditions under which the effective permeability increases or decreases after depressurization. An analytical solution of the effective permeability change with pore pressure and temperature considering hydrate dissociation and soil compaction is derived. Results show that, when heat supply is sufficient, hydrate dissociation dominates the effective permeability during hydrate dissociation, but after hydrate dissociation, soil compaction is the governing factor for permeability change. When there is no sufficient heat supply, compaction determines the permeability mainly, and the effect of hydrate dissociation on permeability is limited.

2020032654 Suzuki, Kiyofumi (National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan); Collett, Timothy S.; Boswell, Ray; Tamaki, Machiko; Okinaka, Norihiro and Sato, Daichi. Interpretation of logging data from the hydrate-01 stratigraphic test well drilled in the Prudhoe Bay unit, Alaska North Slope [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract OS41C-1688, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Collaborative studies between gas hydrate researchers in the United States and Japan have progressed since 2014, and have led to the drilling of the Hydrate-01 stratigraphic test well (STW) to characterize the geologic conditions at the site of a future long-term gas hydrate production test in the Prudhoe Bay Unit located on the Alaska North Slope. Logging-while-drilling (LWD) and wireline (WL) side-wall coring were conducted at December 2018 to obtain physical property data of gas hydrate-bearing sedimentary units lying below the permafrost. The LWD and WL logging operations were successfully conducted and the occurrence of gas hydrate-bearing reservoirs suitable for production testing was confirmed.

2020032555 Tanski, George (Vrije Universiteit Amsterdam, Amsterdam, Netherlands); Bröder, Lisa M.; Wagner, Dirk; Knoblauch, Christian; Lantuit, Hugues; Tesi, Tommaso; Strauss, Jens; Fritz, Michael; Sachs, Torsten and Vonk, Jorien E. Carbon degradation and CO₂ production within onshore and nearshore zones of eroding permafrost coasts [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost coasts are a key interface between the terrestrial and marine system in the Arctic. Alongside with major Arctic rivers, erosion transfers large amounts of organic matter and sediment into the ocean. Warmer temperatures, permafrost thaw and sea ice area decrease promote coastal erosion due to a longer open-water season, higher sea surface temperatures, sea-level rise, and wave action. Upon thaw and erosion a massive pool of permafrost organic carbon (OC) is being exposed and OC released into the Arctic Ocean, where it can be metabolized, sequestrated or transported offshore. Although the understanding of biogeochemical processes upon gradual permafrost thaw on land and permafrost OC transport on the shelf are improving, little is known about the immediate biogeochemical response during the abrupt coastal erosion process and associated greenhouse gas production. In this study, we mimicked different modes of coastal erosion onshore and in nearshore waters with incubation experiments by mixing in-situ permafrost and eroded permafrost debris (i.e. mud lobes, cliff toe debris) with ambient seawater. Carbon dioxide (CO2) production was measured over a 2-months period at 4°C and OC, nutrients (N), carbon isotopes (13C, 14C) as well as biomarkers (n-alkanoic acids, n-alkanes) were analysed prior and after incubations to comprehend potential OC degradation and CO2 dynamics within the coastal rim; both onshore and within nearshore waters. Our results show that large amounts of CO2 are produced in all simulated erosion modes and that CO2 production increases with the presence of seawater, especially for in-situ permafrost and cliff toe debris incubated. Although C/N-ratios and stable carbon isotope signatures do not show significant differences prior and after incubation, carbon preference index and high-to-low molecular weight ratios of n-alkanoic acids and n-alkanes indicate ongoing degradation of OC which correlates to the observed CO2 production. Our results show that permafrost OC mobilized by coastal erosion is rapidly degrading upon thaw and that this process is accelerated by the presence of seawater. We conclude that erosion of permafrost coasts, onshore and nearshore, is potentially a major source of CO2 to the atmosphere and an incubator of terrestrial organic matter before release into the offshore marine system. Although the fate of OC upon release into seawater is hard to assess by laboratory experiments, we emphasize the importance of coastal erosion for carbon budgets and models, especially under the Earth's current climate trajectory and the accelerated environmental forcing on Arctic permafrost coasts.

2020032561 Tao, Jing (Lawrence Berkeley National Laboratory, Berkeley, CA); Zhu, Qing; Riley, William J.; Neumann, Rebecca Bergquist and Bisht, Gautam. Improved simulation of cold-season methane emissions over Alaska's permafrost with the E3SM land model (ELM) [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B44E-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Field observations have shown that cold-season methane (CH₄) emissions contribute a substantial portion to annual carbon emissions in permafrost regions. However, current Earth System Model (ESM) land models generally underestimate cold-season CH₄ production and emission. We hypothesize that the biases result from poor representation of coupled biogeochemical and hydrological processes in permafrost soils, the lack of a reasonable lowland/wetland module that can adequately account for inundated hydro-ecological dynamics, underestimation of snow accumulation due to micro-topographic effects and thus the snow insulation to the ground, among others. Here we use the Energy Exascale Earth System Model (E3SM) land model (ELM) to examine how different hydrological and thermal regimes impact cold-season CH₄ emissions and to address the knowledge gap of the relative contribution of seasonal CH₄ emissions to annual totals over permafrost regions. Simulation results are evaluated against CH₄ measurements from the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) (2013-2014) and the Arctic Boreal Vulnerability Experiment (ABoVE) (2015-2017) at Alaskan Arctic tundra sites in the continuous permafrost zone. Enhancements to the simulation of cold-season CH₄ emissions were achieved via improving the representation of coupled water and heat transport with phase change in freezing soils. Specifically, improved simulation of the zero-curtain period (i.e., the period when soil temperatures linger around 0°C) results in better simulation of CH₄ production and emission. In addition, incorporation of a lowland module and microtopographic snow redistribution contributes to the improvement of cold-season CH₄ emission predictions. Sensitivity analysis of the CH₄ flux to critical biogeochemical, hydrological, and thermal variables help quantify the uncertainty in current simulation results. We also use ELM to evaluate how CH₄ emissions across permafrost regions would alter under future (warmer and wetter) climate scenarios.

2020032504 Tayo, Malissa Ann Gueco (University of California Irvine, Irvine, CA); Czimczik, Claudia I.; Fine, Aubrey; Schaeffer, Sean M. and Welker, Jeffrey M. Impact of long-term warming and wetting on carbon sequestration and nitrogen dynamics in High Arctic tundra soils [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2575, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic is undergoing rapid warming and increases in precipitation (wetting) which may lead to significant active layer thawing and decreases in permafrost distribution and carbon (C) storage in soils. Loss of permafrost C has the potential to result in a significant positive feedback to climate change by amplifying rising atmospheric CO2 levels. At the same time, climate change may increase C fixation of tundra plants and increase rates of C inputs to soils. However, we currently have a limited understanding of belowground C allocation and the role organo-mineral interactions play for long-term C sequestration in Arctic soils. Here, we investigated the rate and mechanism of soil C sequestration in High Arctic tundra after 15 years (2004-2018) of climate manipulation in NW Greenland. Soil samples (n=4/treatment) were collected to 30 cm depth (0-2 cm (O/A horizon), 2-10 cm (A/rhizosphere horizon), 20-30 cm (C horizon)) from four treatments: (+4°C summer warming (T2), +50% summer precipitation (W), and +4°C warming ´ +50% summer precipitation (T2W)), and an ambient climate control (C). Each warming/wetting treatment had a surface coverage consisting of native vascular plants (V; Dryas integrifolia M. Vahl., Salix arctica Pall., Carex rupestris All.) and bare ground/cryptogamic crust (B; overlying vegetation removed). Samples were analyzed for bulk C and N content and stable isotope composition, pH, and exchangeable Fe, Al, and Ca. We also determined 14C content of C in the bulk soil and low and high density fractions in surface soils from vegetated plots. Preliminary results show that plant cover significantly affected C and N cycling within the surface horizons (0-10 cm). Vegetated plots had greater C and N contents and C/N ratios and were depleted in d13C and d15N. Both wetting treatments increased C and N in vegetated surface soils. We found no impact of warming alone on soil properties. These results further support previous analyses of land-atmosphere C fluxes indicating that changes in precipitation promote C storage in High Arctic tundra systems. Mineral and 14C analyses will reveal if wetting treatments result in changes to the capacity of these soils to sequester C and offer a unique opportunity to test whether the fraction of organic C retained by reactive minerals in semi-arid soils is vulnerable to climate change.

2020032564 ter Horst, Anneliek (University of California, Davis, Davis, CA); Wilson, Rachel M.; Zinke, Laura Alice; Johnston, Eric; Schadt, Christopher W.; Kostka, Joel E.; Chanton, Jeff and Emerson, Joanne B. Viromes from northern Minnesota reveal peatland habitat endemism of globally distributed viral populations [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51F-2314, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Boreal peatlands are considered to be particularly vulnerable to climate change, with increased atmospheric CO₂ and warming predicted to have substantial impacts on organisms and biogeochemical processes in these carbon-rich ecosystems. Peat microbiota, including methanogens, drive CH₄ and CO₂ emissions from the soil, and early evidence suggests that viruses impact microbial contributions to soil carbon cycling. However, viral diversity, ecology, and impacts on biogeochemical cycling are poorly understood in terrestrial ecosystems. To begin to address this knowledge gap, we recovered 1,852 viral population sequences from five near-surface (top 10 cm) peat samples collected along a 200 m transect in a Sphagnum moss-dominated bog in the Marcell Experimental Forest in Northern Minnesota. Comparisons of viral populations recovered from viral size-fraction metagenomes (viromes) and total soil metagenomes from the same samples revealed that viromes alone were sufficient to recover the vast majority (>98%) of viral population sequences. 52 viral populations from two previous studies of thawing permafrost peatlands in subarctic Sweden and 13 viral populations from other publicly available datasets were recovered in Minnesota peat, indicating a surprising degree of global viral sequence conservation (6% of our dataset) and peatland habitat endemism of soil viral "species." The transect from which our samples were collected is adjacent to the Spruce and Peatlands Under Changing Environments (SPRUCE) experiment, including 10 large, open-top chambers for testing ecosystem responses to increased temperatures and elevated atmospheric CO₂ concentrations. Our ongoing work seeks to leverage peat metagenomes from the SPRUCE experiment, in combination with our transect viromes, to evaluate virus-host dynamics in response to soil warming and increased atmospheric CO₂.

2020032471 Tfaily, Malak M. (University of Arizona, Environmental Science, Tucson, AZ); Gieschen, Hans; Toyoda, Jason; Chu, Rosalie K.; Weitz, Karl K.; Hoyt, David W.; Eder, Elizabeth K. and Wilson, Rachel M. Quantifying biotic and abiotic controls on dissolved organic matter dynamics in natural systems using complementary analytical techniques [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23A-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Unraveling biotic and abiotic processes that control the flux and transformation of DOM in natural systems is essential to parsing the microbial DOM and greenhouse gas signal to improve predictive correlations and understand potential changes resulting from land use and climate change. DOM is an important part of wetland ecosystems as the main energy source for microbial metabolic processes. Changes in sources and sinks of DOM and subsequent microbial activity can have widespread effects on the ecosystem's chemical and biological properties, as well as CO2 production rates. DOM is a carbon sink that can be degraded, either biotically or abiotically, to release carbon into other fluxes. Studying these two processes is essential for predicting how future carbon fluxes will grow or shrink, and to what degree. Sphagnum moss is a prominent source of organic matter in many permafrost peatlands, and permafrost holds 1.5 trillion tons of carbon, almost double what is in the atmosphere right now. Studying the abiotic and biotic mechanisms of the breakdown of sphagnum moss leachate and litter can give a better understanding of wetland chemistry, and C-cycling models by observing the pathways that carbon will take when moving into the atmosphere. In this study we used complimentary and novel analytical tools and approaches coupled with flux analysis for (1) an in-depth investigation and quantification of abiotic and biotic factors that influence the decomposition of sphagnum moss, and (2) identification of chemical markers indicative of biotic vs. abiotic mineralization This study represents a unique attempt to design fundamental science experiments to reveal the mechanisms governing biogeochemical processes in natural systems by quantitatively parsing biotic and abiotic C mineralization for direct integration into large-scale ecosystem models.

2020032497 Thapa, Kiran. Contributions of optical remote sensing to permafrost mapping in Donnelly training area, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2568, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Modern optical remote sensing technology and techniques able to help in the mapping of permafrost hazards in the high latitude and more cold mountains. Change in annual temperature rise and other natural as well as anthropogenic activities directly related to the large increase in the extent of permafrost degradation in the northern Alaska since 1982. Studies conduct from 2014 to 2018, and data used Landsat 8 OLI/TIRS from USGS freely downloaded. The study area is covered 1009 sq. mile in the Donnelly Training Area. Found abrupt decrease in permafrost in the Donnelly Training Area. Probability of permafrost detects by using different remote sensing indices and calculated by regression modal proposed by Wang (2017). The results showed that probabilities of permafrost gives the more indices including map gives the best result in the study area.

2020032681 Thomas, Elizabeth K. (University at Buffalo, Department of Geology, Buffalo, NY); Jensen, Britta J. L.; Hollister, Kayla and Buryak, Serhiy. Exploring biomarkers in Beringian Loess as an archive of orbital-scale Pleistocene climate change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PP41B-1542, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The circumpolar north is a bellwether for climate change, currently warming at least twice as fast as the rest of Earth. This warming drives glacier retreat, while melting permafrost releases additional greenhouse gases. Temperatures reconstructed at Lake El'Gygytgyn in eastern Siberia show several Pleistocene "super-interglacial periods", characterized by extreme warmth, and as such may provide context for ongoing changes. Yet, terrestrial records of pre-Holocene interglacials are rare in the north because ice sheets covered much of this region during glaciations, scouring the landscape and removing sediments. This has led to a critical gap in understanding how the Arctic responds to warmer-than-present conditions. Beringia, comprising Alaska, the Yukon Territory, and eastern Siberia, was not blanketed by ice sheets during glaciations. Throughout Beringia, loess accumulated in thick sections that provide semi-continuous climate archives spanning the past 3 million years. In summer 2019, we sampled loess sections in Alaska that contain sediments from multiple pre-Holocene interglacial periods, constrained in age by key tephras present in these deposits. We will present initial results of tephra and paleomagnetic chronological constraints and preliminary climate reconstructions using lipid biomarkers from these loess sediments. We will focus climate analyses on a well-preserved section spanning Marine Isotope Stage 19, at approximately 800,000 years ago.

2020032577 Thomas, Matthew A. (U. S. Geological Survey, Geologic Hazards Science Center, Golden, CO); Mota, Alejandro; Jones, Benjamin M.; Choens, R.; Frederick, Jennifer and Bull, Diana L. Bluff geometry and material variability influence stress states relevant to coastal permafrost bluff failure [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1339, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Scientific knowledge and engineering tools for predicting coastal erosion are largely confined to geographic regions with temperate climates dominated by non-cohesive sediments. The character of erosion exhibited by the cohesive, permafrost-laden bluffs of the Alaskan Arctic, however, is not well-explained by these tools. Therefore, investigation of the oceanographic, thermal, and mechanical processes that are relevant to permafrost bluff failure along Arctic coastlines is needed. Here, we present results from numerical simulations of linear elastic stress that focus on the impacts of bluff geometry and material variability on permafrost bluff stress states for a coastal region in the Alaskan Arctic that is prone to toppling-mode failures. Our 3D geomechanical boundary-value problems, whose parameterization is constrained by field observation and laboratory testing, outputs steady-state snapshots of compressive and tensile stresses that we use to quantify variability in the location of potential instability. We see that the height and depth of the thermo-erosional niche at the base of bluffs influences the magnitude and location of the simulated maximum tensile stress more strongly than bluff height, permafrost polygon size, ice wedge thickness, ice wedge depth, bulk density, Young's Modulus, or Poisson's Ratio. Our simulations also reveal that tension cracks, which have been observed to form just prior to catastrophic failure in coastal permafrost settings, can induce strain localization near the crack within the potential failure mass. These findings motivate the development of a tightly coupled thermo-mechanical framework for capturing the transient geometric characteristics of the basal erosional niche to resolve the component contributions from sea water/wave setup, water temperature, and air temperature. Our work also encourages an investigation of elastic-plastic finite deformation models for tracking the development of tension cracks to avoid overestimating bluff stability prior to catastrophic failure.

2020032566 Thompson, Lauren (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Kuhn, McKenzie Ann; Sonnentag, Oliver and Olefeldt, David. Mercury patterns in permafrost peatland streams and ponds [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51I-2353, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Peatland ecosystems sequester vast mercury stores, accumulated over millennia from atmospheric deposition and subsequent binding to soil organic matter. Many non-permafrost peatlands are acidic, waterlogged, and rich in dissolved organic carbon (DOC) and thus support the microbial transformation (methylation) of inorganic mercury to the toxic form of methylmercury (MeHg). Northern peatlands with perennially frozen permafrost conditions inhibit microbial transformation of deep mercury stores. Thawing of permafrost may cause the release of mercury from peatlands, to adjacent ponds and streams. Here, we assessed the variation of MeHg concentrations in boreal peatland catchments along a climate gradient. Study sites spanned from permafrost free (55°N) to continuous permafrost (67°N) in northern Alberta and Northwest Territories of Canada. A total of 25 ponds and 50 streams were sampled and analyzed for total mercury, major ions, elements, DOC, and DOC optical properties including absorbance and fluorescence in addition to MeHg. We explored relationships between MeHg and these parameters, and also relationships with catchment characteristics including area and coverage of peatland and pond. Our findings are relevant to project future changes of MeHg in peatland rich catchments following permafrost thaw.

2020027699 Tolmanov, Vasiliy A. (Lomonosov Moscow State University, Moscow, Russian Federation); Grebenets, Valery I. and Iurov, Fedor. Formation of technogenic rock glaciers in mining areas of the Russian cryolithozone [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC21E-1291, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

There is an acute problem of stockpiling waste dumps in mining areas. This problem has its own specifics in the permafrost zone. Cold climate and material, thrown on the slopes can lead to the formation of ice-soil mobile bodies from the mass of waste rock. Its movement results in great danger to the infrastructure of mining areas in the permafrost zone. This research accumulates certain material and assesses the severity of the problem of the rock glaciers moving in permafrost conditions. We carried out field observations in Norilsk industrial region, Vorkuta region, etc. This allows us to obtain an objective picture of the possible cryogenic hazards for buildings and structures in economically developed territories, as well as for natural complexes. Detailed studies (analysis of multi-time satellite images, geodetic data and, tracking of dynamics, etc.) were carried out for the anthropogenic rock glacier near the Medvezhy Ruchey quarry in the Norilsk region. The world's largest glacier was formed as a result of the development of the open pit--close to the POST-1 dump (one out of ten, but located on the outskirts of the southern industrial zone of Norilsk). The volume of "empty" rock reached 65 million m³ with a total mass of about 110 million tons. The movement of this glacier began in the summer of 1992, and in 1999 the active bottom part of the stone glacier rested against the opposite slope of the valley of the Medvezhy Ruchey River, destroying the road bed, buildings, water conduit and other objects. Since 2001, the upper third of the glacier, which had not participated in the movement before, started to move. The maximum displacement was about 700 m by 2014. The reasons of the movement of rock glacier was the change in permafrost conditions at the base of the body, which occurred as a result of natural climate change and man-made impact. It leads to a decrease in the adhesion forces of ice-ground particles and makes the body more ductile and deteriorate the strength properties of the soil base. Obviously, with a further increase in the temperature of the rock, we can await fast and progressive moving, which will cause an avalanche-like sliding of the front part. This work was supported by the RFBR grant 18-05-60080 Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic.

2020027674 Tomczyk, Aleksandra (Adam Mickiewicz University, Poznan, Poland) and Ewertowski, Marek. Annual dynamics of surface morphology of alluvial and colluvial fans in central Svalbard and SE Iceland; application of time-series of UAV images [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP11C-2135, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Landforms, which shape reassembles fans and cones are common elements in many mountain areas in all climatic zones. Some of the low-gradient fans are used for agriculture and human settlement; therefore, fan-related processes (e.g., debris-flow activity) can threaten human life and infrastructure. Fans are also valuable archives of past environmental conditions and, especially in non-vegetated polar areas, offer a useful analog for interpretation of extra-terrestrial landforms genesis. Detailed knowledge about fan morphology and dynamics in various temporal and spatial settings, is crucial for understanding fan evolution and its response to environmental changes. While, the processes within fans in warm, arid areas are relatively well known; our understanding of the short-term dynamics of fans in polar areas is still limited. In this study, we aimed to quantify the annual dynamics of the surface morphology of fans based on multi-temporal UAV surveys. We studied several small fluvial-flow-dominated and debris-flow-dominated fans located in central Spitsbergen, Svalbard, and SE Iceland. For each of the fans, we performed time-series (2015-2019) of UAV-surveys, further processed through the structure-from-motion approach. 3D points cloud from each survey were transformed into gridded DEMs (cell size of 10 x 10 cm). Digital elevation models of differences were produced by subtraction of DEMs from subsequent periods to detect surface changes. Based on the five years of observations, we can distinguish four types of surface transformations of fans. The first group contains fans whose surfaces were mostly stable during the five years. The second scenario includes a fan which was transformed by thermokarst processes. In the first year, a significant collapse of the permafrost in the stream banks occurred. Then, over the next four years, only some minor alterations of the surface were recorded. The third scenario illustrates fans, where older, inactive debris flow channels were re-activated by new debris flows, which caused deepening of the channel and development of new levees. The fourth scenario includes the development of new debris flow channel in the previously smooth (inactive) parts of the fans. This work was supported by National Science Centre, Poland [project: 2016/21/B/ST10/01353] This work was supported by National Science Centre, Poland [project: 2016/21/B/ST10/01353]

2020032457 Toyoda, Jason (Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory, Richland, WA); Chu, Rosalie K.; Tolic, Nikola; Hess, Nancy J.; Robinson, Errol R. and Tfaily, Malak M. Extraction efficiency and molecular characterization of organic matter from soils and sediments using high resolution mass spectrometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13G-2576, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Soil organic matter (SOM) represents a key reservoir for carbon (C) and is comprised of a heterogeneous mixture of plant, animal and microbial detritus. To study SOM and gain a better understanding of microbial communities, rhizosphere interactions, and biogeochemical processes, protocols have been developed using different solvents to extract this OM. Most of these extraction protocols use an aqueous solvent to extract the water soluble OM from the soil. In this study, we calculate the extraction efficiency and compare the molecular composition of the soil after repeated extractions with water. Three soil types; peat, Alaska permafrost, and river sediment, with varying percentages of organic C content were extracted sequentially with water up to 15 times. The organic matter in the extracts was characterized at the molecular level using high resolution mass spectrometry. We found that repeated extractions with smaller volumes of water extracts a higher percentage of dissolved organic carbon (DOC) compared to using one large volume of water. The DOC concentration measured in soil water extracts decreased with extraction number, regardless of soil type. Interestingly, the repeated sequential extractions were able to extract only 4% of total SOM regardless of soil type. These results are important as they suggest that water extractable organic matter (WEOM) accounts for only a small proportion of the total organic matter in the soil. However, even with this small percentage of WEOM, it is very diverse in chemical composition, with thousands of compounds resolved by high resolution mass spectrometry.

2020027671 Truskowski, Conner M. (University of Alaska Fairbanks, Fairbanks, AK); Rudolf, Margaret C.; Phillips, Cassidy and Garron, Jessica. Virtual reality modeling of the CRREL permafrost tunnel for online education on permafrost and climate change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract ED13D-0912, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A virtual reality (VR) model of the CRREL Permafrost Tunnel was created as an undergraduate student project to help educate the public and students on permafrost and climate change. The Permafrost Tunnel, located 16 km north of Fairbanks, Alaska, is a series of tunnels dug into the permafrost owned by the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL). In this facility, research on climate, geology, paleontology, engineering, and permafrost is developed. The Tunnel VR was done as part of a larger NSF project,

2020032454 Turner, Kevin W. (Brock University, Geography, St Catharines, ON, Canada); Thorne, William Brent; McDonald, Ian and Pearce, Michelle. Inventorying climate-induced landscape changes and associated impacts on lakes and rivers in Old Crow Flats, Yukon, Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B13D-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Changing climate conditions have induced widespread responses across northern lake-rich permafrost landscapes including shrub vegetation proliferation, retrogressive thaw slumps (RTSs), and fire. We are inventorying these changes and investigating the associated impacts on lake and river biogeochemistry and geomorphology in Old Crow Flats (OCF), Yukon, Canada. OCF is the traditional territory of the Vuntut Gwitchin First Nation who is concerned about the influence that changing climate and landscape characteristics will have on their traditional lifestyles. Vegetation greening was detected using time-series analysis of Landsat during 1985-2013. Greening has mostly occurred in peripheral areas of OCF along the northern and southern mountain-lowland ecotone. We are evaluating spatial association of these vegetation changes and monitored lake and river hydroecological conditions. Zelma Lake, which has been monitored since draining in 2007, is providing a valuable model showing lake biogeochemical responses to shrub encroachment. The influence of RTSs on downstream conditions is being evaluated along the OCF drainage network. Repeat remotely piloted aerial surveys were conducted over the largest slump since 2016, when it initially exported ~29,174 m³ sediment. It exported 47,509 m³ by August 2018. Downstream DIC and DOC were influenced most during the initial wet thaw season. More sediment was exported during the relatively hot and dry summer 2017 than during the cooler and wetter summer 2018. Ongoing analysis is investigating the utility of LVIS and UAVSAR data for detecting permafrost slump characteristics along the Old Crow River. Fire occurring during 2017 influenced a lake monitored since 2007. Post-burn results show the lake received less snowmelt input and experienced increases in phosphorus and ion concentrations. AVIRIS-NG data is being used to classify catchment pre and post-burn land cover properties. Results being generated here will help anticipate how lakes and rivers will respond in permafrost environments if the frequency and magnitude of climate-induced landscape changes increase.

2020032644 Uhlemann, Sebastian (Lawrence Berkeley National Laboratory, Berkeley, CA); Dafflon, Baptiste; Michail, Sofia; Wagner, Florian M.; Shirley, Ian; Peterson, John E.; Ulrich, Craig and Hubbard, Susan. Imaging spatial and temporal subsurface variability in a discontinuous permafrost environment [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract NS14A-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Predicting the feedback of Arctic environments to warming temperatures remains a challenge. Quantifying and monitoring soil and permafrost thermo-hydrology can improve our understanding of the hydro-biogeochemical processes and can substantially advance modelling of Arctic ecosystems. Particularly in discontinuous permafrost, with a co-existence of active layer, talik, and permafrost, thermal and hydrological properties are highly variable, both spatially and temporarily. Imaging the subsurface dynamics of such system will not only provide a better understanding of its feedback to warming temperatures and the related changes in subsurface storage and flux of water, carbon, and nutrients, but will also enable a predictive understanding of Arctic environments that are yet to undergo a transition from frozen to unfrozen conditions. We focus on the geophysical imaging of permafrost distribution and dynamics within a watershed on the Seward Peninsula, Alaska, which acts as a study site for the Next-Generation Ecosystem Experiments (NGEE). We acquired seismic and geoelectrical data across the watershed. The results highlight the co-existence of shallow and deep permafrost, and taliks, and their potential link to the subsurface geology. By jointly inverting those data sets we estimate the subsurface ice/water/rock fraction, which allows for approximating the base of permafrost. Spatially extensive low-induction electromagnetic data show a good correlation with snow thickness, highlighting the insulating properties of the snow pack. Additionally, geoelectrical, and distributed temperature and moisture data were acquired along a transect for two consecutive years. The data show spatial and temporal variability linked to the vegetation distribution, with rapid responses related to snowmelt and intense rainfall events, and generally decreasing resistivities and increasing temperatures over the monitoring period. Finally, by linking laboratory analysis of soil cores to the field data, we can transform geophysical parameters into thermo-hydraulic quantities, which are suited for integration into ecosystem models.

2020027622 van der Sluijs, Jurjen (Northwest Territories Centre for Geomatics, Yellowknife, NT, Canada); Kokelj, Steve; Tunnicliffe, Jon F. and Rudy, Ashley. High resolution digital terrain models provide multi-dimensional perspective on thaw slump-driven transformation of permafrost terrain in the Canadian western Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1376, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Ice-rich glaciated permafrost environments across northwestern Canada are amongst the most rapidly changing permafrost landscapes of the world. To monitor these dynamic environments, Unmanned Aerial Vehicle (UAV) systems, and Light Detection and Ranging (LiDAR) have enabled highly detailed three-dimensional surface reconstructions (e.g., Digital Elevation Model; DEM) of permafrost thaw features at a scale that bridges the gap between satellite remote-sensing and field-scale observations. Satellite technology now can provide daily-to-weekly observations of mass wasting features such as retrogressive thaw slumps (RTS), but it is primarily limited to two-dimensional size estimations. Our work links two-and three-dimensional measurements of RTS by quantifying area-volume (A/V) relationships to better understand the geomorphic and geochemical implications of rapidly accelerating thaw-driven processes. A LiDAR-derived single-date A/V relationship based on disturbances from fluvial and lake-dominated landscapes across the forest-tundra transition in western Arctic Canada included RTS ranging in size from small slope-side features to mega slumps. The relationship was modeled by a power-law function (R² = 0.90; n = 71) indicating non-linearity in the geomorphic impacts of slump intensification. The capacity of UAVs to derive robust quantitative time-series provides novel insights into permafrost processes that are otherwise challenging to study. Multi-date A/V patterns for individual features track accelerating, linear, and stabilizing RTS change trajectories and provide new insight on thaw-driven processes and feedbacks. The study highlights the importance of exploring A/V relationships to better understand RTS evolution, to predict landscape denudation and ground ice volumes over larger geographic extents, and to back-cast consequences of recent RTS intensification using satellite records.

2020032563 Varner, Ruth K. (University of New Hampshire, Durham, NH). Wetland methane biogeochemistry; can geophysical approaches improve our understanding of these spatially and temporally heterogeneous processes? [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B51D-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Wetlands remain the largest natural source of methane, a strong greenhouse gas. Methane is produced in the anoxic zones of wetlands and transported through diffusion, plant transport and ebullition (bubbling). The net emission of methane from wetlands however is determined by both the production and oxidation rates in these organic rich soils. Understanding the rate at which methane is produced and consumed before it enters the atmosphere is important for future climate predictions and to determine the feedback of warming by these ecosystems. Peatlands specifically in the permafrost regions (high latitude and/or altitude) are already showing impacts of warming and are emitting methane at a faster rates. Determining rates of emission can be challenging as the production, consumption and transport are spatially heterogeneous. Traditional methods to measure emissions are generally at small plot level scales (<1 m) and tend to produce large errors when scaling. Non-invasive geophysical approaches (e.g. ground-penetrating radar, acoustical sensing) could help in scaling these spatially heterogeneous processes to better estimate the environmental and landscape level drivers of emission and to determine the impact that climate change will have on these sensitive ecosystems.

2020032543 Virkkala, Anna-Maria (University of Helsinki, Helsinki, Finland); Aalto, Juha Antero; Tagesson, Torbern; Treat, Claire C.; Lehtonen, Aleksi; Rogers, Brendan M.; Natali, Susan and Luoto, Miska. High-latitude terrestrial regions remain a CO₂ sink over 1990-2015 [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Climate warming is changing the high-latitude (i.e. tundra and boreal biomes) carbon dioxide (CO₂) balance, but our understanding of source-sink dynamics across space and time is highly limited. Here, we upscale high-latitude CO₂ fluxes at high resolution (1 km²) to show the spatial variation of CO₂ fluxes and to estimate the CO₂ budget of the region. We compiled measurements of annual and growing season CO₂ fluxes over the period of 1990-2015 from 162 sites and used an ensemble of statistical models to predict fluxes using a set of climatic, vegetation and soil predictors. Our prediction shows that the CO₂ sink strength decreased with latitude but was associated with a large spatial variability, reflecting the heterogeneity in soil organic carbon stocks, local climate and vegetation productivity. We found that northern Alaska and Canada, and northwestern and central Siberia were the largest net CO₂ sources and southern Canada and southwestern Siberia the strongest net CO₂ sinks, but these regions also lose some accumulated carbon to the atmosphere via forest fires, lateral transport, harvesting and insect outbreaks. Our results suggest that the terrestrial high-latitude region was a net CO₂ sink of -757 (-580 to -1018; 90% uncertainty range) Tg C yr^-1 over 1990-2015 with the tundra biome being a smaller sink with -87 (-153 to +1). Within the region, the northern permafrost zone was a sink of -413 (-623 to -265). We conclude that the high-latitude region is currently a strong CO₂ sink and may not accelerate major atmospheric CO₂ increases.

2020032484 Voigt, Carolina (University of Montreal, Department of Geography, Montreal, QC, Canada); Hould Gosselin, Gabriel; Black, T. Andrew; Chevrier-Dion, Charles; Marquis, Charlotte; Nesic, Zoran; Saarela, Taija; Wilcox, Evan; Marsh, Philip and Sonnentag, Oliver. Resolving spatial and temporal greenhouse gas dynamics across a heterogeneous Arctic tundra landscape in the Western Canadian Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2540, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic region is currently warming twice as fast as the rest of the world. Accelerated permafrost thaw unlocks large pools of currently immobile carbon (C) and nitrogen (N) and ultimately increases the atmospheric burden of the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). However, Arctic GHG dynamics and their hydrological controls are poorly understood. Whether the Arctic acts as a net GHG source or sink depends on the complex and spatially varying interactions between hydrology, active layer thickness, topography, temperature, vegetation, substrate availability and the microbial world. Our study site, Trail Valley Creek (68°44'N, 133°29'W), is an upland tundra site characterized by small-scale (<10 m) land cover type heterogeneity with interspersed shrub, tussock, and lichen patches, polygonal tundra areas, wetlands, lakes, and streams. To understand the large spatial and temporal variability of GHG dynamics across these terrestrial and aquatic landcover types we use a nested observational approach at plot- (<1 m²), ecosystem- (~10 m²), landscape- (~100 m²) and regional (~50 km²) scale. Existing ecosystem- scale eddy covariance (EC) measurements of net CO₂ and CH₄ exchanges are complemented with landscape-scale EC measurements and plot-scale automated and manual chamber measurements within the EC tower footprint and beyond. To constrain the processes governing aboveground GHG exchange we complement these multi-scale GHG flux measurements with a wide array of auxiliary measurements including soil profilce dynamics of CO₂, CH₄ and N₂O, lake and soil pore nutrient concentrations, oxygen, temperature and moisture profiles, thaw depth, leaf area index (LAI), normalized difference vegetation index (NDVI), lake catchment characteristics, and quality and microbial degradability of aquatic dissolved organic matter. Preliminary results indicate that at ecosystem-scale upland tundra is a negligible net source of CH₄. High CH₄ emissions from emission hotspots such as lakes and wetlands in our study region (9.09±2.38 mg CH₄ m^-2 h^-1) are compensated through net CH₄ uptake by uplands. Our study highlights the need to combine belowground, plot-, ecosystem- and landscape-scale measurements to understand biosphere-atmosphere interactions in Arctic ecosystems.

2020032550 Voigt, Carolina (University of Montreal, Department of Geography, Montreal, QC, Canada); Marushchak, Maija E.; Abbott, Benjamin; Biasi, Christina; Christensen, Torben R. R.; Elberling, Bo; Jackowicz-Korczynski, Marcin; Lamprecht, Richard E.; Martikainen, Pertti J.; Mastepanov, Mikhail; Sonnentag, Oliver and Yang Yuanhe. Effects of warming and permafrost thaw on the three important greenhouse gases; carbon dioxide, methane, and nitrous oxide [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B43E-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost soils in the Arctic are thawing, exposing not only C but also large N stocks. The decomposition of this vast pool of long-term immobile C and N results in the release of greenhouse gases (GHGs) to the atmosphere. While gaseous C release from thawing permafrost is known to be substantial, recent studies show that permafrost soils may further be a relevant source of the potent GHG nitrous oxide (N₂O). As N₂O is almost 300 times more powerful in warming our climate than CO₂, the release of N₂O from thawing permafrost could create a significant noncarbon-permafrost feedback to the global climate. We applied climate manipulation experiments to 1) examine the impact of temperature increase on the seasonal GHG balance of all three important GHGs from various tundra surface types (vegetated peat soils, unvegetated peat soils, uplands) in the Russian Arctic (67°03'N 62°55'E), and 2) simulated sequential permafrost thaw on intact plant-soil systems (mesocosms) from a permafrost peatland in Northern Finland (68°52'N, 21°03'E). Air warming (~1.0°C) increased GHG release from all dominant surface types: the GHG budget of vegetated peat and mineral soils shifted from a sink to a source of -300 to 144 g CO₂-eq m^-2 and from -198 to 105 g CO₂-eq m^-2, respectively. While the warming response was governed by CO₂, warming also increased N₂O emissions: warming not only enhanced N₂O fluxes from bare peat, a typical landform previously identified as hot spot for Arctic N₂O emissions, but also from vegetated peat, not emitting N₂O under the present climate. Gradual permafrost thaw, without changes in moisture content, clearly increased N₂O emissions, and we observed the largest post-thaw emissions from bare peat, where permafrost thaw caused a five-fold increase in emissions (0.56 vs. 2.81 mg N₂O m^-2 d^-1). While water-logged conditions suppressed N₂O emissions, the presence of vegetation lowered, but did not prevent post-thaw N₂O release. We show that N₂O emissions from permafrost soils may be larger than previously thought, and that one fourth of the Arctic land area could be subject to increasing N₂O emissions upon permafrost thaw. While permafrost-derived N₂O emissions may add to the atmospheric GHG burden, the N₂O source strength of the Arctic will be crucially governed by moisture conditions and future changes in vegetation cover.

2020027679 Vulis, Lawrence M. (University of California at Irvine, Department of Civil and Environmental Engineering, Irvine, CA); Tejedor, Alejandro; Schwenk, Jon; Piliouras, Anastasia; Rowland, Joel C.; Pease, Gailin and Foufoula-Georgiou, Efi. Revealing channel network control on seasonal lake area dynamics in Arctic deltas [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract EP23E-2262, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Rapid warming and permafrost thaw in the Arctic will impact the formation, expansion, and drainage of lakes, as well as lacustrine methane emissions on Arctic Deltas (ADs). Understanding and quantifying the spatial variability in the seasonal patterns of lake growth and shrinkage, which are driven by springtime snowmelt and riverine flooding, is vital for understanding how these landscapes might respond to future warming. Here we use the Landsat-derived Global Surface Water dataset to study the seasonal "breathing" of water bodies on the Yukon and Colville deltas and document that deltaic water bodies located closer to the Delta Channel Network (DCN) display higher summertime shrinkage rates compared to those farther away. We show that the preferential shrinkage closer to the DCN is consistently observed for 22 years of record, but with substantial interannual variability in the magnitude of relative shrinkage rates, which we attribute to the timing of snow cover disappearance. A targeted analysis of high-resolution data ruled out the possibility that preferential shrinkage close to the DCN is due to narrow surface channels not visible in Landsat images. We hypothesize that increased shrinkage close to the channels is due to a combination of subsurface flow and increased evapotranspiration from near-channel vegetation, and we explore predictive relationships of these relationships under changing forcings. A warming Arctic is projected to cause changes in vegetation coverage and thawing cycles, leading to shifts in seasonal lake shrinkage dynamics which in turn are expected to affect the transport and residence time of water and nutrients on the delta top and their export to the ocean.

2020032529 Waldrop, Mark P. (U. S. Geological Survey, Denver, CO); Mcfarland, Jack W.; James, Stephanie R.; Manies, Kristen; Neumann, Rebecca Bergquist; Minsley, Burke J.; Leewis, Mary-Cathrine and Blazewicz, Steven. Between states; the microbial ecology of biogeochemical processes near the freezing point. [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B41E-04, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Microbial communities control important biogeochemical processes in boreal and arctic environments. The transformation of soils from a frozen to thawed state, which occurs seasonally in active layers soils or during the course of permafrost thaw, produces profound biophysical change resulting in rapid increases in microbial activity and biogeochemical processes. However, a subtler and perhaps more important aspect of the microbial ecology of the cryosphere are those processes that occur when soils might seem frozen, yet significant amounts of liquid water are present. These processes occur in at least two important situations: 1) taliks - unfrozen soils beneath frozen active layers that continue microbial activity over winter- and 2) in near zero permafrost (<1 degree below zero). We examined levels of microbial activity under saturated C conditions slightly above and below 0C at the Alaska Peatland Experiment (APEX), located in Interior Alaska. First, we estimated overwinter microbial activities in taliks between 0.5 and 1.5 m depth using a series of peepers to sample talik waters, dissolved gases, and the isotopes of dissolved CO₂ and CH₄ in late winter and early spring. We used an isotope biogeochemical model to quantify rates of microbial activity within the winter talik and compared it to rates determined for summer. In permafrost we used a series of peepers to measure the concentration of CO₂, CH₄, and N₂0 at 1.2 and 1.8 m depth, as well as in situ Nuclear Magnetic Resonance (NMR) and temperature data to assess the quantity of liquid water in near-zero permafrost. Results showed that wintertime microbial activity in taliks was approximately 10% of the rates determined for summer, but the longer winter season increased the importance of these processes to overall ecosystem biogeochemistry. In permafrost we observed concentration and isotopic patterns that indicated CH₄ production and CO₂ and N₂O reduction are important processes occurring in near-frozen soils. Together, these results indicate that despite being frozen or overlain by ice, both near-frozen permafrost and taliks contribute significantly to microbial processing of C and N.

2020032608 Walvoord, Michelle A. (U. S. Geological Survey, Earth System Processes Division, Denver, CO); Ebel, Brian A.; Minsley, Burke J.; Pastick, Neal J.; Rey, David and Voss, Cliff. Hydrologic impacts of linked disturbances in Boreal Alaska, USA [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H11B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost conditions in boreal regions are responding to gradual "press" (e.g. shifting climate) and punctuated "pulse" (e.g. wildfire) landscape disturbances. The pore ice in permafrost exerts strong controls on thermal, hydrologic, and mechanical soil properties. Thus, phase change from ice to liquid water affects the exchange and flow of energy and water as well as soil strength and slope stability. Coupled dynamics of permafrost thaw and water fluxes driven by individual disturbances are increasingly understood. Disturbances, however, seldom take place in isolation, instead overlapping in space and time and potentially leading to cross-scale interactions. In many cases, disturbances are linked through (i) causal increases in the likelihood of a subsequent, different disturbance because of direct physical or biological process connections, or (ii) indirect increases in ensuing disturbance probability and impacts because of overall reductions in system resilience. Here we examine the role of permafrost dynamics as a catalyst in the chain of linked disturbance responses in boreal Alaska. At the local scale, geophysical investigations in headwater catchments together with thermo-hydrologic modeling provide insight on how permafrost degradation, exacerbated by wildfire and linked changes in vegetation and surface energy balance, may induce changes in baseflow seasonality and magnitude. Intermediate-scale assessments in the Yukon Flats lowlands illustrate how permafrost thaw, accelerated by flooding, can enhance hydrologic connectivity and thereby influence immediate to decadal-scale lake area dynamics. At the regional scale, remote sensing investigations reveal widespread landscape change, including broad shifts in surface water distribution that can be attributed to disturbance, permafrost thaw, and associated thermo-mechanical processes that affect the flow and retention of surface water. Bridging multi-scale studies, such as those presented here, builds comprehensive understanding of the effects of linked disturbances in boreal Alaska and similar environments, catalyzed by ice-to-liquid water phase change in the subsurface.

2020032473 Wang, Jingfeng (Georgia Institute of Technology, Atlanta, GA); Zhu, Modi; El Sharif, Husayn Ahmad; Ivanov, Valeriy Yu. and Sheshukov, Aleksey Yu. Modeling active layer depth of permafrost under changing surface boundary conditions [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23G-2491, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

A new approach is developed for modeling the active layer depth of permafrost under changing boundary conditions without assuming linear temperature profile, which is often assumed in solving the traditional Stefan problems. Time-varying ground heat flux is obtained from net radiation and surface temperature using the Maximum Entropy Production (MEP) model as the driver of the melting process. Conductive heat flux at the melting front is approximated in terms of an analytical function of ground heat flux. The simulated active layer depth is in good agreement with the field observations. Surface energy budget according to the MEP model is also in close agreement with field observations.

2020032604 Wang, L. (Nanjing University of Information Science and Technology, Nanjing, China); Zhao, L.; Zhou Huayun and Liu Shibo. Monitoring permafrost changes in the Yangtze River source region of the Qinghai-Tibetan Plateau using differential SAR interferometry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51P-1026, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Qinghai-Tibet Plateau (QTP) is the largest high-altitude permafrost zone in the mid-latitudes. It is also the source region of major rivers in Southeast and East Asia, referred to as the Water Tower of Asia. Large hydrologic changes have been observed in the Yangtze River source region and adjacent areas in the early 21st century. The contribution of permafrost degradation and loss of ground ice to the hydrologic changes is however still lacking. In permafrost areas, the seasonal freeze-thaw cycle in the active layer causes seasonal upward and downward ground motion because of ice-water phase transition process; under climate warming, thawing of the permafrost causes long-term subsidence. The surface deformation reflects the changes in the permafrost active layer and the ground ice. This study monitors ground deformation in permafrost terrain (1991-now) by applying Small BAseline Subset InSAR (SBAS-InSAR) technique using C-band ERS, ENVISAT, Sentinel-1 and L-band ALOS PALSAR datasets; reveals the spatial and temporal characteristics of the changes in the permafrost active layer and the ground ice. The study provides data support for studying the hydrologic changes in the Yangtze River source region.

2020027672 Wang, Tianlin (University of Michigan Ann Arbor, Ann Arbor, MI); Huang, Huanting and Gu, Weihui. Investigation of methane emission in permafrost using in-situ measurements and satellite remote sensing data for climate change education [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract ED31D-0997, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane is a greenhouse gas with positive global warming feedbacks. Arctic region is warming much faster than the rest of the world, and one major root cause is the increasing atmospheric methane emission. The Arctic region is one of the natural sources of the greenhouse gas methane, with huge amounts of methane-rich organic matter in the Arctic and sub-Arctic permafrost, and of methane hydrates in Arctic lakes and seas. As an educational research project supported by the IEEE Arctic Challenge, our team conducted in-situ measurements of the methane emission over frozen permafrost at the University of Michigan Biological Station (UMBS) at Pellston and Wawa of Ontario, Canada. An extreme high-resolution (1 ppb, 1 second) ultra-portable greenhouse gas analyzer was used to accurately characterize the methane emission. An obvious time lag between the methane emission and ambient temperature is observed. Also, the methane emission decreases when there is snow while the carbon dioxide emission increases. We also study the remote sensing data about methane emission. The remote sensing data has the advantage of the global average over a long period. Base on the in-situ experiment, our team produced a 6-minute educational video named Arctic methane and climate change. It has been officially published by IEEE Geoscience and Remote Sensing Society (GRSS). Our objective is to bring in a new perspective and involve young engineers and scientists to create technical solutions for the climate change challenge.

2020027667 Wang Taihua (Tsinghua University, Beijing, China) and Yang Dawen. Analysis on the responses of the Asian water tower to climate warming and the consequent cryospheric changes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C51B-1264, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Tibetan Plateau contains the headwaters of several major Asian rivers, including the Yellow River, Yangtze River, Brahmaputra River, Salween River, Mekong River, Indus River, and these rivers provide water for more than 1.4 billion people. Therefore, the Tibetan Plateau is also called the Asian water tower, which is of vital importance for the water resources security and food security for the upstream regions as well as the densely populated downstream regions. Almost all of the Tibetan Plateau is underlain by permafrost and seasonally frozen ground because of its high elevation, and the contribution of water from snow melt and glacier melt can be considerably high at some basins. However, due to limited observations and the complicated interactions between hydrological and cryospheric processes, the responses of streamflow to climate change and the consequent cryospheric changes in the TP are not well understood, which has aroused wide concern recently. Here we try to analyze the long-term streamflow changes and their responses to climate warming and the consequent cryospheric changes using statistical approaches as well as process-based modelling approaches for several large river headwater basins over the Tibetan Plateau. We simulate the cryospheric changes including permafrost degradation and glacier retreat and attempt to quantify their impacts on streamflow. For the permafrost-dominated river basins, we explore the interactions between soil freeze-thaw regime and hydrological processes; and for the glacier-dominated river basins, we examine the tipping point of the glacial runoff and assess the water resources security under a changing climate. The results could provide a scientific basis for water resource management and ecological protection under a changing climate in headwater regions The Tibetan Plateau contains the headwaters of several major Asian rivers, including the Yellow River, Yangtze River, Brahmaputra River, Salween River, Mekong River, Indus River, and these rivers provide water for more than 1.4 billion people. Therefore, the Tibetan Plateau is also called the Asian water tower, which is of vital importance for the water resources security and food security for the upstream regions as well as the densely populated downstream regions. Almost all of the Tibetan Plateau is underlain by permafrost and seasonally frozen ground because of its high elevation, and the contribution of water from snow melt and glacier melt can be considerably high at some basins. However, due to limited observations and the complicated interactions between hydrological and cryospheric processes, the responses of streamflow to climate change and the consequent cryospheric changes in the TP are not well understood, which has aroused wide concern recently. Here we try to analyze the long-term streamflow changes and their responses to climate warming and the consequent cryospheric changes using statistical approaches as well as process-based modeling approaches for several large river headwater basins over the Tibetan Plateau. We simulate the cryospheric changes including permafrost degradation and glacier retreat and attempt to quantify their impacts on streamflow. For the permafrost-dominated river basins, we explore the interactions between soil freeze-thaw regime and hydrological processes; and for the glacier-dominated river basins, we examine the tipping point of the glacial runoff and assess the water resources security under a changing climate. The results could provide a scientific basis for water resource management and ecological protection under a changing climate in headwater regions over the Tibetan Plateau.

2020032511 Wani, Rucha (University of Delaware, Delaware Environmental Institute, Newark, DE); Sowers, Tyler D.; Coward, Elizabeth K. and Sparks, Donald L. Probing organomineral associations across a chronosequence of yedoma permafrost deposits in Fox, AK [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2582, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Projected increases in polar temperatures will decrease the stability of terrestrial carbon (C) sinks, which promotes the mobilization of C to the atmosphere in the form of CO₂ and CH₄. Aged C, stored in deep deposits, represents a substantial component of permafrost C currently stabilized below thermodynamic and metabolic thresholds, but the mechanisms governing the fate of deep permafrost C under changing climate conditions remains unknown. Mineral association, one of the most important C stabilization mechanisms in soils, could contribute to stability within deep permafrost. Using a suite of high-resolution analytical techniques, we characterized organomineral associations across a chronosequence of Yedoma permafrost from Fox, Alaska. Core samples were taken from the Cold Regions Research and Engineering Laboratory Permafrost Tunnel, spanning 19, 27, and 36 kya, an active freeze-thaw surface horizon, and a thawed former-permafrost site. Scanning electron microscopic imaging and STXM spectroscopy revealed strong correlations between C and iron (Fe) across all samples and co-precipitation of C-calcium-Fe in some systems. Elemental analysis revealed high C:Fe ratios in soils, and high C concentrations were detected in thaw from the freeze-thaw and 19 kya tunnel soils; both declining with increasing age. Thaw samples were analyzed via FTICR-MS, which displayed a drastic disappearance of proteins and aliphatic groups as well as a steady decrease in lignin-like compounds with increasing sample age. Sequential selective mineral dissolutions were conducted to probe the role of Fe speciation in organomineral stabilization. Across all samples, a majority of the abundant C detected by elemental analysis was sorbed to crystalline Fe phases, whereas very little C was associated with short-range ordered phases. Multi-approach characterization of these soils revealed abundant sorption between C and Fe phases that may play protective roles under unstable conditions. Changes in freeze-thaw regimes can destabilize organomineral associations by oscillating the Eh of the system and solubilizing Fe(III) oxide phases. Understanding the stability of these organomineral linkages in aged, deep permafrost stores under such climate pressures will be important for predicting the rate of C mobilization.

2020032590 Ward, Melissa Karine (McGill University, Montreal, QC, Canada) and Pollard, Wayne H. Environmental interactions and feedbacks of degrading ice wedges and impacts on shallow ground temperatures in a high Arctic polar desert system [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1360, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Recent decadal observations shows ice wedges are degrading rapidly. These periglacial landforms are ubiquitous within the continuous permafrost zone of the Arctic. Ice wedges form polygonal networks that drive environmental changes such as snow distribution, surface hydrology, vegetation and carbon fluxes. Field observations of ice wedge systems, particularly in the high Arctic and in winter are lacking. We present topographic surveys, thaw depths, vegetation cover, soil moisture and annual shallow (12 cm) ground temperature measurements of seven ice wedge troughs of varying dimensions (the largest being 1 m deep and 11 m wide) and two polygon centres in a high centred polygon system. Our field site is located on Ellesmere Island, in the Canadian high Arctic, an area with cold (-16.5°C at the depth of zero amplitude), thick (>500 m) continuous permafrost with a mean annual -19.7°C air temperature. We show that ice wedge degradation at our study site generates micro-topographic changes that creates a mosaic of varying ground temperatures ranging as much as 15.7°C in winter, 2.5°C in summer, and 5.1°C mean annually. It is critical to capture these fine scale details to accurately estimate the impacts of future changes to ice wedge systems.

2020032467 Watts, Jennifer (Woods Hole Science Center, Falmouth, MA); Natali, Susan; Minions, Christina; Ludwig, Sarah; Rogers, Brendan M.; Risk, David A.; Goetz, Scott J.; Sonnentag, Oliver; Rocha, Adrian V.; Euskirchen, Eugenie Susanne; Arndt, Kyle Andreas; Zona, Donatella; Humphreys, Elyn; Celis, Gerardo; Ikawa, Hiroki; Schuur, Edward; Taylor, Meghan; Ueyama, Masahito; Kobayashi, Hideki; Suzuki, Rikie; Lafleur, Peter; Torn, Margaret S.; Dengel, Sigrid; Lee, Bang-Yong; Kim, Yongwon; Helbig, Manuel; Hould Gosselin, Gabriel; Kimball, John S.; Ledman, Justin; Commane, Roisin; Schiferl, Luke D.; Oechel, Walter C.; Parmentier, Frans-Jan W.; Jastrow, Julie D.; Mauritz, Marguerite; Madani, Nima; Miller, Charles E.; Birch, Leah and Wullschleger, Stan. Soil CO2 flux in the permafrost zone; new insight from a year-round chamber network in Alaska and Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B21D-03, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The permafrost affected Arctic-boreal region is increasingly vulnerable to soil thaw and warming, which can enhance root respiration and microbial mineralization. However, the seasonal patterns and magnitudes of belowground CO2 emissions from boreal and tundra remain poorly understood. Also uncertain is how feedbacks and interactions between regulating temperature and moisture conditions, and the influence of ecosystem disturbances including fire, attenuate or enhance CO2 loss. To address these knowledge gaps, we installed a network of Soil Respiration Stations (SRS) in Alaska and Canada. Each SRS is equipped with a gas analyzer, forced diffusion chambers on the soil surface, and soil gas chambers at multiple depths. These systems are capable of running year-round with minimal power requirements. Our SRS records for 2016-2018 showed the highest belowground CO2 fluxes occurring in summer (June through August). Summer fluxes averaged 1.67±0.65 gC-CO2 m² d^-1 in the boreal and 0.78±0.29 in tundra. We also observed considerable emissions in the shoulder seasons, at 0.54±0.33 gC-CO2 m² d^-1 in spring and 0.43±0.18 gC-CO2 m² d^-1 in autumn. In addition, we detected CO2 emissions throughout the snow-covered winter (November-March) season with flux averages ranging from <0.05 to >0.3 gC-CO2 m² d^-1. The legacy effect of fire was also important; we observed lower emissions in the burned tundra and boreal sites, relative to unburned. This was primarily due to drier soils at the unburned sites, whereas wetter soils at burned sites reduced heterotrophic respiration. The SRS observations are now being used to develop regional baseline respiration budgets. We are in the process of extrapolating the SRS fluxes to the greater domain using machine learning, information from satellite remote sensing, and flux data from eddy covariance towers. These monthly estimates are provided at a 100 m spatial resolution. Our results for 2016/2017 indicate annual cold season (September-March) emissions of >140 Tg C-CO2. Ongoing modeling efforts will extend this estimate to include spring and summer periods. These emission maps, in addition to the SRS fluxes, will provide valuable comparisons with ecosystem model estimates and guidance for how soil respiration algorithms can be improved to better account for CO2 loss under cold soil conditions.

2020032481 Webster, Alex J. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Douglas, Thomas; Regier, Peter J. and Harms, Tamara. Detecting catchment-scale permafrost degradation and biogeochemical regime change from high-frequency stream chemistry [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23I-2536, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The biogeochemical regimes of high-latitude ecosystems are shaped by the spatial extent of permafrost and its interaction with vegetation and hydrologic flowpaths. In the boreal forest of Interior Alaska, distinct patterns of stream chemistry reflect the spatial extent of discontinuous permafrost and the carbon and nitrogen cycling regimes of deciduous and coniferous forests. Using stream chemistry as an integrative signal of catchment processes, we analyzed high-frequency (15 min) observations from headwater catchments that contrast in permafrost extent and fire history. We characterized temporal variation at seasonal, storm, and diel time scales toward developing indicators of changing regimes. At the seasonal scale, significant increases in nitrate concentration occurred in a catchment likely undergoing degradation of permafrost, whereas a deciduous-dominated catchment that is permafrost-free showed no seasonal trend. Storms flushed nitrate from the catchment undergoing thaw, whereas nitrate was diluted during storms in the permafrost-free catchment. Increased cumulative precipitation in autumn was also associated with a surprising ~11.5 uM increase in stream nitrate concentration over 1.5 days, likely due to activation of deep flowpaths in the catchment undergoing thaw; this non-linear change may indicate regime shift and would have been difficult to detect with lower frequency sampling. Finally, diel peaks of dissolved organic matter (fDOM) occurred concurrent to midday peaks in light and dissolved oxygen in the permafrost-free catchment, likely due to instream processing. In contrast, maximum daily fDOM concentration occurred at night, coinciding with light and dissolved oxygen minima in the catchment undergoing thaw. These observations suggest that permafrost degradation predictably influences the interactions of biogeochemical regimes with hydrologic flowpaths and stream ecosystems at multiple temporal scales. Deviations from the observed patterns could indicate catchment responses to thawing permafrost, increasing temperature, more frequent and intense fires, and more extreme precipitation events.

2020032489 Wesley, Daniel (St. Francis Xavier University, Antigonish, NS, Canada); Garrison, Billy; Layden, Ronald E.; MacLeod, Roger; Dallimore, Scott and Risk, David A. Landscape-scale variability of methane in the Mackenzie-Beaufort Delta region of northern Canada, during winter and summer. [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23K-2462, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Mackenzie-Beaufort Delta (MBD) in northern Canada is an area rich in hydrocarbon deposits, with known natural geologic methane seeps that are aided by permafrost heterogeneity. A recent airborne Eddy Covariance study found hotspots of activity in which methane was moderately elevated and presumed to be geologic in nature, but researchers have also shown that surface biogenic emissions can be prolific in Arctic landscapes, even in winter. In this study, we investigated landscape-scale methane variability in the MBD region, during late winter and summer. We conducted vehicle-based surveys both on and off the highway, using a portable gas analyzer mounted on a truck or boat, and also characterized known hotspots using geochemical analysis to determine source type (biogenic or thermogenic). Below Inuvik in the south of the MBD, we observed spatially-extensive methane enhancements indicative of soil respiration, including in winter, when biological activity is assumed to be negligible. Often, enhancements were associated with known hydrological networks. We compared winter methane distributions with multiple Landsat-8 data products, and found a correlation between the thermal band, and the magnitude of methane enhancements presumed to be biogenic on the basis of spatial occurrence. The pattern of methane emission was different to the north of Inuvik, with more spatial complexity. Geochemical analysis of known persistent (>6 yr) hotspots confirmed 3 sources of methane, including surface biogenic (surface), biogenic/mixed (likely permafrost base), and thermogenic (deep geologic reservoirs). Emission from all sources and in all areas was hotspot-driven, so future studies should include multiple spatial scales of measurement to create a good understanding of each source in this complex Arctic region.

2020027655 Wilcox, E. (Wilfrid Laurier University, Cold Regions Research Centre, Waterloo, ON, Canada); Walker, B.; Hould Gosselin, Gabriel; Wolfe, Brent B.; Sonnentag, Oliver; Marsh, Philip and Saarela, Taijka. Landscape controls on thermokarst lake water fluxes between Inuvik and Tuktoyaktuk, Northwest Territories, Canada [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C24B-01, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic is warming at twice the rate of the rest of the world, causing precipitation to shift from snowfall to rainfall, longer snow-free and ice-free summers, increased evapotranspiration, and permafrost thaw. It is necessary to understand how thermokarst lake water fluxes will react to these changes if we are to predict future greenhouse gas fluxes from lakes. Greenhouse gas fluxes from lakes are tied to the amount of lateral carbon delivery into the lake, the residence time of lake waters, and the temperature of lake waters, all of which are regulated by lake water fluxes and lake characteristics. The Arctic is warming at twice the rate of the rest of the world, causing precipitation to shift from snowfall to rainfall, longer snow-free and ice-free summers, increased evapotranspiration, and permafrost thaw. It is necessary to understand how thermokarst lake water fluxes will react to these changes if we are to predict future greenhouse gas fluxes from lakes. Greenhouse gas fluxes from lakes are tied to the amount of lateral carbon delivery into the lake, the residence time of lake waters, and the temperature of lake waters, all of which are regulated by lake water fluxes and lake characteristics. We measured lake water flux components at multiple spatial and temporal scales across the 5000 km² boreal-tundra transition zone between Inuvik and Tuktoyaktuk, Northwest Territories, Canada. Lake water flux components were measured at two adjacent thermokarst lakes with different ratios of lake area to catchment area (LACA), from 2017-2019. Also, stable water isotope samples were collected from March-September 2018 from ~100 lakes across 2000 km². From these samples we estimated the ratio of evaporation to inflow, residence time, and the mixture of snowmelt and rainfall runoff in each lake. Catchments of all 7500 lakes in the region were delineated using a high-resolution digital elevation model in order to estimate their LACA, and evaluate connectivity between lakes. Lake temperature, conductivity, dissolved oxygen, pH, DOC, DON, and chlorophyll profiles were also measured from ~50 lakes pre-snowmelt in 2019. We measured lake water flux components at multiple spatial and temporal scales across the 5000 km² boreal-tundra transition zone between Inuvik and Tuktoyaktuk, Northwest Territories, Canada. Lake water flux components were measured at two adjacent thermokarst lakes with different ratios of lake area to catchment area (LACA), from 2017-2019. Also, stable water isotope samples were collected from March-September 2018 from ~100 lakes across 2000 km². From these samples we estimated the ratio of evaporation to inflow, residence time, and the mixture of snowmelt and rainfall runoff in each lake. Catchments of all 7500 lakes in the region were delineated using a high-resolution digital elevation model in order to estimate their LACA, and evaluate connectivity between lakes. Lake temperature, conductivity, dissolved oxygen, pH, DOC, DON, and chlorophyll profiles were also measured from ~50 lakes pre-snowmelt in 2019. Lakes with a smaller LACA had a larger portion of their inflow evaporate, longer residence times, and have less of their water replaced after rainfall events. Coupling isotope samples taken before, during, and after snowmelt with field observations also revealed that the majority of snowmelt runoff flowed overtop of lake ice and through the outlet, as the lake ice stopped snowmelt runoff entering the lake until it had melted sufficiently. LACA and lake connectivity also varied greatly across the 7500 lakes in the region. Further work this year will compare lake limnological properties and greenhouse gas fluxes with LACA and other lake and catchment properties. Lakes with a smaller LACA had a larger portion of their inflow evaporate, longer residence times, and have less of their water replaced after rainfall events. Coupling isotope samples taken before, during, and after snowmelt with field observations also revealed that the majority of snowmelt runoff flowed overtop of lake ice and through the outlet, as the lake ice stopped snowmelt runoff entering the lake until it had melted sufficiently. LACA and lake connectivity also varied greatly across the 7500 lakes in the region. Further work this year will compare lake limnological properties and greenhouse gas fluxes with LACA and other lake and catchment properties.

2020032633 Wilson, Bruce E. (Oak Ridge National Laboratory, Oak Ridge, TN); Dattilo, Hannah; Shrestha, Rupesh; Thornton, Michele; Boyer, Alison and McNelis, John J. Strategies for integrating orbital, airborne, and in situ data; extending a soil moisture visualizer to visualize permafrost data [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract IN23D-0902, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Harmonizing disparate data sources with varying spatial and temporal resolutions is a challenge which directly affects the reusability of data. The Oak Ridge National Laboratory's Distributed Active Archive Center (DAAC) addresses these issues for a specific science domain a web-based tool called the Soil Moisture Visualizer (SMV). The SMV integrates in situ, airborne, and satellite soil moisture data from various sources and scales. Our intent is to build upon the SMV technology to create a more general toolset, which can be configured to do the integration for other science domains, based on our experience that the integration of these disparate data source requires at least some understanding of the target science domain. As a next step, we applied the methods and data harmonization techniques of the Soil Moisture Visualizer to a similar but different scientific domain: permafrost. Generally found in Earth's Arctic regions, permafrost is any kind of ground, including rocks and soil, which has been frozen for at least two years. An application that integrates and visualizes disparate ground, airborne, and satellite permafrost measurements is extremely important to better understanding of the effects of climate change in the Pan-Arctic region. Our project also provides insight into ways to harmonize data in a specific science domain (permafrost) that feeds into a broader science domain (climate change). In this project, we used back-end data manipulation and front-end display tools. Back-end data manipulation includes aggregating the measurements from disparate datasets into a spatially and temporally consistent platform. This aggregation allows for a clear visualization of data for a specific scientific domain from multiple sources. Harmonized data can be aggregated and organized either by points or within a grid. We successfully applied both of these methods to permafrost data. The challenge of creating a meaningful visualization for permafrost data was due to the lack of spatial overlap and low temporal resolution in the datasets.

2020027636 Wilson, Susan (3rd Rock Consulting, Wasilla, AK); Hubbard, Trent and Hoffman, Hans. Geologic terrain unit and geohazards mapping, Arctic Strategic Transportation and Resources (ASTAR) project, North Slope, Alaska [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1391, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Geologic terrain and geohazards mapping was completed as part of the State of Alaska's Arctic Strategic Transportation and Resources (ASTAR) project. The goals of the ASTAR project are to identify, evaluate, and advance opportunities to enhance the quality of life and economic opportunities in North Slope communities through responsible infrastructure development. In partnership with the North Slope Borough (NSB), the State seeks to collaborate with area communities and other stakeholders in an effort to identify community infrastructure and regional connectivity projects that offer the greatest cumulative benefits for the region. The project area is underlain by continuous permafrost, and to date mapping of 21,740 square miles of Alaska's North Slope has been completed extending from the Dalton Highway, across the National Petroleum Reserve-Alaska (NPR-A), to the Chukchi Sea coast. Analyses include definition and mapping of geologic terrain units, potential geologic hazards, and potential materials sources. Terrain units are based on the landforms and geologic units characteristic of a generalized soil profile. Mapped geologic hazards primarily relate to slope instability and permafrost; including thaw slumps along bluffs and banks where ice-rich soils have or are currently experiencing thermal degradation; and pingos, which are conical ice-cored mounds that form in response to hydrostatic pressure of permafrost in former lake basins. Many potential geologic hazards can be avoided, or their effects on planned projects minimized, if identified early in the planning process. Understanding the general physical characteristics of the soils provides an indication of geotechnical characteristics of these materials, including suspected permafrost distribution, erosion potential, frost heave potential, thaw settlement potential, thawed bearing strength, and overall slope stability. Geologic terrain and hazard analyses aid in potential project siting, evaluation of engineering considerations, and identification of potential construction materials sources. These analyses also help inform planning and land use decision-making for the communities of the NSB, as well as other public and private entities. This mapping will be available through Alaska's interactive online database in the future.

2020032620 Winnard, Blaise R. (University College London, Rock and Ice Physics and Seismological Laboratory, London, United Kingdom); Mitchell, Thomas M.; Meredith, Philip G.; Cuss, Robert J. and Norris, Simon. Suitability of bentonite for long-term radioactive waste disposal; consideration of climatic change [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H41G-1758, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Globally, bentonite is the primary candidate to be used as a barrier in concepts for underground radioactive waste disposal. Bentonite blocks will be used to surround waste canisters, and often to backfill construction tunnels. It is widely accepted that bentonite is excellent for this purpose as it has good self-sealing characteristics, very low permeability, and is durable. However, less is known about its functionality on extremely long timescales (up to a million years), and it is essential that all properties of bentonite are thoroughly probed. On these timescales, additional environmental scenarios must be considered, including multiple ice ages. The occurrence of permafrost not only causes frozen ground, but also initiates several subsurface changes, such as salt exclusion which can lead to significant changes in groundwater chemistry. The prospect of multiple ice ages necessitates evaluation of how cyclical temperature and groundwater changes will affect bentonite. Here, we present experimental results demonstrating changes in hydro-mechanical properties of standard MX80 bentonite under a wide range of pressures, temperatures, and fluid chemistry conditions. Samples used in these experiments are compacted to industry standards, with a dry density of 1.7 g/cm³, and bulk density of 2.07 g/cm³, samples have a degree of saturation of 98+%. Uniaxial and triaxial strength tests were performed, under a variety of conditions. Samples that experienced freeze-thaw cycles did not behave differently to untreated samples. The strength and strain accommodated of samples deformed at ambient temperatures of -10 °C also remained unchanged. Use of different saline compaction fluids did have an influence on the stress-strain curves. These experiments have been complemented by further analysis using micro-CT imaging in conjunction with a thermal control stage. Initially, a 20 mm core was imaged using a Nikon 225 CT system, at 98+% saturation. Small desiccation cracks were observed around the edges and surfaces, but no porosity was observable, as expected. We use a Zeiss Versa 520 to achieve a better resolution and implement a sequence of temperature steps to -20 °C to observe the evolution of a saturated sample at sub-zero temperatures. No external pressures were applied as these images were taken.

2020032582 Wiseman, Matthew (Williams College, Williamstown, MA) and Bradley, Alice. Impact of the length of the sea ice-free summer season on Alaskan Arctic coastal erosion rates [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1345, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Erosion along the Arctic Alaskan coastline poses a major threat to local communities and their way of life. While erosional processes are far from new, erosion rates seem to be increasing in response to a changing Arctic climate. In the Arctic, factors such as permafrost degradation, storms, and decreases in sea ice cover all play a large role in determining the severity of the coastal erosion. For this project, we are specifically looking into the effects of the changing length of the sea ice-free summer season and how it is impacting coastal erosion. Coastal erosion rates are measured for study sites along the Alaskan Coastline by analyzing Planet Labs satellite imagery over the 2009-2019 period. The number of ice free days per summer for the area surrounding each of these locations is calculated from SSMI-derived passive microwave ice concentration products. Together, we use the coastal erosion rates and annual sea ice-free day counts to investigate the relationship between the length of the ice-free season and coastal erosion over this period. Historical erosion rates sourced from USGS reports provide additional comparisons in a changing Arctic climate. We expect to find that a warming climate causes the ice free season to lengthen, leaving the shoreline exposed to storms and coastal processes for a greater period of time, leading to an increase in coastal erosion rates. This presentation will cover recent variability in coastal erosion in the Alaskan Arctic and the influence that sea ice-free summers have on the shoreline.

2020027646 Witharana, Chandi (University of Connecticut, Natural Resources and the Environment, Storrs, CT); Bhuiyan, M. Abul E. and Liljedahl, Anna K. Towards first pan-Arctic ice-wedge polygon map; understanding the synergies of data fusion and deep learning in automated ice-wedge polygon detection from high resolution commercial satellite imagery [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C22C-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The utility of sheer volumes of very high spatial resolution (VHSR) commercial imagery in permafrost feature mapping at regional scales is new and actively evolving. Thaw-induced differential ground subsidence and dramatic microtopographic transitions, such as transformation of low-centered ice-wedge polygons (IWPs) into high-centered IWPs can be characterized at pan-Artic scale by using VHSR imagery. However, IWP mapping efforts are yet limited to small scales and confined to manual or semi-automated methods due to prevailing resource gaps among Arctic science community on best available remote sensing methods to deal with the challenge of big imagery. Commercial satellite sensors typically record image data in a low resolution multispectral (MS) mode and high resolution panchromatic (PAN) mode. High spatial resolution is needed to accurately describe feature shapes and textural patterns such as IWPs and other microtopographic features, while high spectral resolution is needed to classify detailed land-use and land-cover types. Data fusion, the process of combining PAN and MS images with complementary characteristics, serves as an integral component of remote sensing mapping workflows and is systematically explored in this study. Fusion process generates spectral and spatial artifacts that may affect the classification accuracies of subsequent automated image analysis algorithms, such as deep learning (DL) convolutional neural nets (CNN). Scene dependency of fusion algorithms impedes the transferability of the knowledge on their performances across application domains. We employed a detailed multidimensional assessment to understand the performances of an array of application-oriented data fusion algorithms when applied to VHSR image scenes of ice-wedge polygonal tundra. A systematic experiment was then conducted to examine the reliance of DLCNN-based IWP classification accuracies on the spectral and spatial fidelity of fused imagery. Big Imagery products has the potential to propel the permafrost science into the next generation of discovery and knowledge-generation if combined with effective visualization and analysis tools.Big Imagery products has the potential to propel the permafrost science into the next generation of discovery and knowledge-generation if combined with effective visualization and analysis tools.

2020027627 Wondolowski, Nicholas A. (University of Pittsburgh, Pittsburgh, PA); Shelef, Eitan and Thomas, Brian F. Influences of topography on permafrost meltwater [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1381, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw caused by changes in climate alters Arctic natural system and promotes decomposition of soil organic carbon (SOC) in thawed soil. Permafrost thaw caused by changes in climate alters Arctic natural system and promotes decomposition of soil organic carbon (SOC) in thawed soil. The natural system, and the rate of permafrost thaw are sensitive to the presence of surface and ground water, and thus the fate of permafrost meltwater influences the future of permafrost regions permafrost thaw are sensitive to the presence of surface and ground water, and thus the fate of permafrost meltwater influences the future of permafrost regions. As surface and ground water flow are related to landscape gradient, topographic roughness (TR) is likely a key influencer of permafrost meltwater movement. Studies that explore the fate of permafrost meltwater at a large spatial scale can identify regional patterns and processes and guide large scale models. However, existing studies mainly focus on the watershed scale or smaller due to sampling limitations the watershed scale or smaller due to sampling limitations. Here, we explore the influence of large scale topographic patterns on the fate of permafrost meltwater . Here, we explore the influence of large scale topographic patterns on the fate of permafrost meltwater using Gravity Recovery and Climate Experiment (GRACE) and remotely sensed topographic and temperature datasets. We test the simple hypothesis that in permafrost regions, dissected terrains of relatively high TR drain meltwater out of areas delineated by a GRACE pixel during times of We test the simple hypothesis that in permafrost regions, dissected terrains of relatively high TR drain meltwater out of areas delineated by a GRACE pixel during times of permafrost thaw, whereas flat terrain does not. To do so, we identified To do so, we identified regions north of 45°N where water storage covaries with air temperature. In permafrost regions we found that the likelihood of having negative relations between air temperature and water storage is higher in areas of high TR compared to low TR. These relations were not apparent in non-permafrost regions. This suggests that in high TR regions, permafrost meltwater may drain into the stream network and flow out of a GRACE pixel, stream network and flow out of a GRACE pixel, thus resulting in a loss of mass from a given area thus resulting in a loss of mass from a given area. In contrast, permafrost meltwater in flat areas remain fairly stagnant, capture the space that used to be occupied by ice, and thus may increase the mass in a GRACE pixel due to the density difference between water and ice and additional water inputs. These results highlight the role of topography in influencing the fate of permafrost meltwater, and hence the associated changes in key factors such as soil characteristics, river discharge, and SOC fate. More generally, these findings demonstrate that GRACE data can be used to capture permafrost meltwater processes across large spatial scales, and may constrain global Earth System models that operate at this scale.

2020032500 Wu, Yue (University of Texas at Austin, Department of Aerospace Engineering & Engineering Mechanics, Austin, TX); Chen, Jingyi; O'Connor, Michael; Ferencz, Stephen Bruce; Cardenas, M. Bayani and Kling, George W. Estimating soil organic carbon in the active layer of the Arctic foothills using spaceborne InSAR surface deformation data [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2571, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Thawing permafrost can fuel large fluxes of carbon from land to the atmosphere, which may further accelerate global warming. Because the Arctic covers continent-sized areas that are mostly inaccessible, remote-sensing has become a critical tool for observing the continuous permafrost. Particularly, the density difference between liquid water and ice causes seasonal ground surface deformation that can be detected over large spatial scales using InSAR. We jointly analyzed the InSAR deformation signal from 12 ALOS PALSAR scenes and the hydraulic properties and stratigraphies of over 200 sites across the Arctic Footslope to determine what factors control seasonal freeze-thaw (FT)-related land surface deformation patterns. We discovered a strong relationship between the seasonal FT deformation signal, land vegetation cover types, and soil organic carbon content. Deformation amplitude increases along a geomorphic-ecohydrologic transect, with the smallest deformation occurring in heath vegetation on the drier ridge-tops, intermediate deformation in tussock-dominated hillslopes, and the largest deformation occurring in lowland valley-bottoms dominated by wet sedge. The strong agreement between the remote sensing and field measurements suggest that InSAR has greater observational capabilities than previously assumed for monitoring changes in hydrological and ecological characteristics above continuous permafrost.

2020032578 Xiao, Ming (Pennsylvania State University, University Park, PA) and Liew, Min. Engineering challenges and options in remediation and prevention of permafrost coastal erosion [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13D-1340, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Erosion along the permafrost coasts has been accelerating, threatening the wellbeing of many Alaskan communities. This research work synthesizes and presents the engineering challenges and the remediation and prevention measures for permafrost coastal erosion through case histories. The review and synthesis of the state-of-the-practice of permafrost coastal erosion controls can be used toidentify measures and construction materials that are proven effective in Arctic coasts.The synthesis shows that revetments built with rocks have the least reported failures and are the most common measures applied along the permafrost coasts. For seawalls, bulkheads, and groin systems, reported failures are mostly associated with displacement, deflection, settlement, vandalism, and material ruptures. No successful case history is reported for the non-engineered expedient measures that are constructed in the event of an emergency. The effectiveness of beach nourishment in the permafrost regions is inconclusive; only one successful beach nourishment project, which is located in the southern region of Alaska, is reported. Soft erosion remediation structures such as dynamically stable beaches are effective in preventing erosion and are observed to experience only minor damages after each storm event.

2020032678 Xiao, Ming (Pennsylvania State University Main Campus, University Park, PA); Romanovsky, Vladimir E.; Jones, Benjamin M.; Farquharson, Louise M.; Halvorsen, Kathleen E. and Chi, Guangqing. Convergence NNA; coordinate a transdisciplinary research network to identify challenges of and solutions to permafrost coastal erosion and its socioecological impacts in the Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract PA51D-0900, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The Arctic is currently subject to major and rapid changes rapid changes in ecosystems, socioeconomic systems, and environmental processes. Since the early 2000s Arctic permafrost coastal erosion has been accelerating, such as from 8.7 m/year (1979 to 2002) to 13.6 m/year (2002 to 2007) and 16 m/year since 2007 along a 60 km segment of the Alaskan Beaufort Sea coast. Coastal erosion along the ocean shore and riverbanks is threatening many Alaskan communities. The challenges related to permafrost coastal erosion are multitude including environmental factors such as climate change, permafrost warming and thawing, sea level rise, change of the physicochemical characteristics of the sea water and permafrost, ecological factors, financial factors, and social including demographical factors, while these factors are interacting and interdependent. This Convergence NNA project is the among the first NNA awards funded by the National Science Foundation. The goal of the 4-year project is to establish a transdisciplinary Permafrost Coastal Erosion Research Coordination Network (PCE-RCN) to identify challenges of and solutions to Arctic permafrost coastal erosion as well as its socioecological impacts. The research team of five lead investigators in civil engineering, geophysics, natural resource policy, and social sciences will serve as a nucleus to bring additional twenty-five researchers, practitioners, policy makers, and Alaska local community representatives to the RCN. This project is in its 2^ndyear. We will present the convergent research and outreach activities we have conducted and plan to engage, including development and facilitation of successful research teams and communities, developing ideas for community-wide strategies that promote equitable and effective collaborations across disciplines and knowledge systems.

2020032517 Yang Yuanhe (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Mao Chao and Kou Dan. Trajectory of topsoil nitrogen transformations along a thermo-erosion gully on the Tibetan Plateau [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2588, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost thaw, especially thermokarst formation, that is, ground collapse due to thawing of ice-rich permafrost, is expected to alter soil gross nitrogen (N) transformations, which can regulate plant productivity and ecosystem carbon cycle. However, it remains unclear how thermokarst formation modifies soil N processes in permafrost ecosystems. Here ¹⁵N pool dilution techniques were used to evaluate changes in topsoil gross N transformations during various thaw stages (early, middle, and late stages) along a thermo-erosion gully on the Tibetan Plateau. Structural equation modeling was then conducted to explore the relative importance of biotic and abiotic factors in affecting soil gross N transformations. The results showed that topsoil gross N mineralization (GNM) decreased at the three stages, reflecting declined inorganic N production after permafrost collapse. In contrast, topsoil gross nitrification increased only during the early stage. Additionally, the ratio of microbial N immobilization to GNM was enhanced during the middle and late stages, indicating a stronger microbial N limitation after thermokarst formation. The structural equation modeling analysis revealed that soil moisture played an important role in modulating gross N transformations. For GNM, decreased soil moisture had inhibiting effects via regulating the microbial biomass, microbial community, and enzyme activities along the thaw sequence. For gross nitrification, declined soil moisture exerted facilitating effects directly by improving oxygen availability and indirectly by modulating the abundances of ammonia-oxidizing archaea and bacteria during the early stage. Overall, these results demonstrated that thermokarst formation altered soil N processes, potentially triggering interactions between ecosystem N and carbon cycles after permafrost thaw.

2020027668 Yao Yingying (Xi'an Jiaotong University, Department of Earth & Environmental Sciences, Xian, China); Zheng Chunmiao; Andrews, Charles and Wu Yiping. Role of permafrost and seasonally frozen ground in groundwater system of northern Himalayan Mountains [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C51B-1277, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost covers about 25% of the land surface of the Northern Hemisphere. Particularly in the mountainous headwater regions of Himalaya, permafrost and seasonally frozen ground (SFG) act as an "aquitard" when frozen but as a more recharged "aquifer" when thawing. Climate warming changes the hydraulic connection of the permafrost and SFG, which has a subsequent effect on water and food security for their downstream regions. The critical scientific gap exists in quantifying how the permafrost and SFG regulate the groundwater flow. This study aims to quantify the extent to which the permafrost and SFG impact mountainous groundwater system and related hydrological processes, respectively, based on experimental observations and integrated surface-groundwater modeling for the Yarlung Zangbo River basin of Northern Himalyan Mountains. Temporal and spatial characteristics of climate variables and hydrological variables were explored and depicted with quantitative methods. The distribution of permafrost, two seasonal freezing-thawing stages (winter and summer period) for SFG were identified, and assigned to the integrated model so as to model changes of groundwater flow. The effects of variation of temperature and precipitation on hydrological processes of headwater mountainous regions were evaluated based on the sensitivity analysis and flow path tracking analysis. This study offers new insights on the mechanism of hydrological responses to climate change, and provide important information to scientific planning, management and utilization of future water resources and ecosystem protection.

2020032446 Ye Wenjuan (University of Science and Technology of China, School of Earth and Space Sciences, Hefei, China) and Zhu Renbin. Potential volatile selenium fluxes from the tundra soils in maritime Antarctica [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract A33J-3072, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Selenium (Se) is an essential trace element for human health, but it is unevenly distributed on the earth. Se biomethylation and volatilization is a major process in the biogeochemical cycle and contribute to its redistribution in the environment. Antarctica tundra area constitute large reservoirs for trace elements (such as Se). However, Se emissions via biomethylation and subsequent volatilization have not virtually studied under the extremely cold Antarctic environments till now. In this paper, penguin colony soils, seal colony soils and normal tundra soils were collected on Ardley Island and the Fildes Peninsula in maritime Antarctica, and incubation experiments and gas trapping method were conducted to investigate the volatilization of gaseous Se and Se species. Results showed that the methylation and volatilization of Se have distinct spatial differences. The mean fluxes of volatile Se was 0.13±0.02 mg Kg^-1 d^-1 from seal colony soils, 0.14±0.02 mgKg^-1 d^-1 from penguin colony soils and 0.11±0.01 mgKg^-1 d^-1 from normal tundra soils. With the thawing of soils, the fluxes of volatile selenium were enhanced by 1.4-4.1 fold. The fluxes of volatile Se from the soils increased with the temperature (ranged from 0°C to 20°C) from 0.005 to 0.56 mg Kg^-1 d^-1, indicating that the emissions of volatile Se might significantly increase with global warming and the melting of permafrost in Antarctica. Different methylated selenium species (DMSe and DMDSe) were observed in all samples and dominated by DMDSe. The biomethylation and volatilization of selenium might play crucial role in the biogeochemical cycle of selenium in Antarctic terrestrial ecosystems.

2020032630 Yi, Yonghong (Jet Propulsion Laboratory, Pasadena, CA); Xu, Xialan; Chen, Richard H.; Bakian Dogaheh, Kazem; Moghaddam, Mahta and Miller, Charles E. Potential applications of SMAP brightness temperature to improve permafrost monitoring in Arctic tundra area [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract H53E-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Surface organic layer thickness and soil moisture represent first order controls on permafrost active layer freeze/thaw (FT) dynamics in the northern high latitudes. However, it remains a significant challenge for models to represent such effects in the northern permafrost area. Satellite microwave remote sensing can capture significant dielectric changes resulting from landscape FT transitions or drying/wetting events, with enhanced sensitivity to soil surface and profile moisture and FT conditions at longer wavelengths such as L-band. Here, we explore the possibilities using SMAP brightness temperature (Tb) to improve regional permafrost monitoring through data analysis and modelling in the Arctic tundra area. Our analysis demonstrated that strong insulation of a very dry organic layer at surface modulates the response of underlying permafrost to surface thermal variations. This is not well represented in current models mostly due to uncertainties in soil moisture inputs or simulations including the SMAP Level 4 system. Model sensitivity analysis shows that different soil organic profiles can have a large impact on the soil moisture distribution along the active layer; SMAP Tb can provide information on surface soil moisture variations, which may help constrain the model representation of organic soil profile. The SMAP Tb also shows sensitivity to active layer refreezing process up to 20 cm below surface, which can be used to improve model representation of FT process. Preliminary simulations using a multi-layer microwave emission model in Alaska North Slope shows that the model can capture the seasonality of L-band Tb reasonably well (R>&eq;0.4, RMSE≤&eq;5K), with largest errors during the transitional season. During spring thaw and summer period, Tb changes are mostly associated with surface wetting and drying events. During the fall and early winter period, Tb follows the changes in active layer liquid water content, with strong sensitivity to deeper (>10 cm) soils after surface soil freezes. Our results highlight the importance of accurately representing active layer soil moisture in regional permafrost monitoring. Future work include using SMAP Tb to evaluate the FT process representation in global land models in Arctic tundra area and model improvement in organic soil representation.

2020027638 Yi Shuhua (Nantong University, Nantong, China). Modeling the carbon dynamics of alpine grassland in the Qinghai-Tibetan Plateau under scenarios of 1.5°C and 2°C global warming [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C21A-06, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Alpine grassland occupies two-thirds of the Qinghai-Tibetan Plateau (QTP). It is vital to project changes of this vulnerable ecosystem under different climate change scenarios before taking any mitigation or adaptation measures. In this study, we used a process-based ecosystem model, driven with output from global circulation models under different representative concentration pathways (RCPs), to project the carbon dynamics of alpine grassland. The results showed the following: 1) Vegetation carbon (C) on the QTP increased by 22-38 gC m^-2 during periods of 1.5 °C and 2°C warming under different RCPs when compared to the baseline period (1981-2006), while soil C increased by 85-122 gCm^-2. 2) The increases of vegetation C and soil C at the period of 1.5°C warming were about 15 gCm^-2 and 40 gCm^-2 smaller than those at the period of 2°C warming, respectively; increase of C was greater for alpine meadow than for alpine steppe. 3) Precipitation, radiation, and permafrost changed significantly and showed heterogeneous spatial patterns, and caused heterogeneous response of C dynamics. For alpine meadow in regions transformed from permafrost to seasonally frozen soil with medium annual precipitation (200-400 mm), vegetation C and net primary production decreased by 18.7 gC m^-2 and 3.1 gCm^-2 per year during 2 °C warming under RCP 4.5, respectively. This decrease can be attributed to the disappearing impermeable permafrost. Different from previous studies that indicated an unfavorable response of alpine grassland to climate warming, this study showed a relatively favorable response, which is mainly attributed to CO₂ fertilization.

2020032586 Yue Yongyu (Peking University, College of Urban and Environmental Sciences, Beijing, China); Liu Hongyan and Guo, Weichao. Ecological indicators of near-surface permafrost habitat at the southern margin of the boreal forest in China [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1356, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The permafrost distribution and degradation is difficult to detect directly on a large scale. Ecological indicators can be used to provide an early signal of changes in terrestrial ecosystems for regional near-surface permafrost habitats and potentially to monitor near-surface permafrost degradation. Carex schmidtii and C. appendiculata in the herb layer and Betula fruticosa in the shrub layer were found to be specific near-surface permafrost plant indicator species at the southern edge of the boreal forest and permafrost in northeastern China, especially for the wetland permafrost. Shrub cover, moss mat thickness and tree canopy cover are also strongly correlated with near-surface permafrost distribution. The active layer thickness (ALT) showed negative correlations with moss thickness and shrub cover because these features may act as buffers for regional climate warming. The results of prediction model for the possible distribution of near-surface permafrost in our study region showed good performance and accuracy which used the cover of each indicator species, near-surface permafrost-specific community features and geographical information as independent variables. which provides an opportunity for us to understand permafrost dynamics on a large spatial scale by obtaining the dynamics of related vegetation features from remote sensing images.

2020032503 Yun, Hanbo (Purdue University, West Lafayette, IN); Wu, Qingbai and Chen, Anping. High thaw lake methane emissions at the permafrost of Qinghai Tibet Plateau [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2574, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The fate of the vast stocks of organic carbon stored in permafrost of the Qinghai Tibet, the world's most high altitude permafrost ecosystem, is uncertain. Specially, the amount of greenhouse gas emissions from thaw lakes in the region is unknown. Here we present estimates of annual CH4 emission from 152 thaw lakes across all permafrost zones of the Qinghai Tibet plateau.We found that emissions peak at permafrost boundary of Xidatan and Anduo, and decrease where permafrost is more prevalent and in drier and colder climatic conditions. We suggest that high emissions are a result of warm temperatures and the permafrost degeneration,especially the winter temperature warming. We show that thaw lakes in the Qinghai Tibet Plateau play an important role in the carbon cycle.

2020032603 Zhang Fan (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China); Zeng Chen; Shi Xiaonan; Wang Guanzing; Xiao Xiong and Wang Li. Response of sediment flux in headwater of the Yangtze River to climate and environment changes [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51P-1018, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Sediment fluxes of headwater areas that are crucial for downstream reservoirs, landscape and aquatic ecology are under the influence of climate and environment changes in high mountain regions. This study investigated the variation of sediment flux in headwater of the Yangtze River in the Tibetan Plateau in response to changes of temperature, precipitation, NDVI, and runoff etc. Temperature, precipitation, runoff, suspended sediment concentration (SSC) and sediment flux all showed increasing trends during 1986-2014, while non uniform seasonal increases of temperature and precipitation introduced altered relationships of runoff vs precipitation and SSC vs runoff after 1997. Partial Least Squares Structural Equation Modeling (PLS-SEM) illustrated the dominant influence of warming and wetting on both runoff and SSC, while warming plays more noteworthy role on the enhanced soil erosion and sediment transport than the boosted runoff generation, potential via changes of glaciers and permafrost.

2020032605 Zhang Jiahua (Chinese University of Hong Kong, Hong Kong, China); Che Tao; Su Lei and Liu Lin. Three-in-one; measuring snow depth, surface soil moisture, and frozen ground elevation changes by GPS Interferometric Reflectometry at a site in northwestern Qinghai-Tibet Plateau [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51P-1061, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

GPS-IR can retrieve snow depth, surface soil moisture, and ground surface elevation changes from reflected GPS signals. However, in previous studies, these three variables were usually estimated separately at different GPS sites. In this study, we retrieve all of them at daily intervals in 2017 and 2018 at a GPS site in Northwestern Qinghai-Tibet Plateau. In situ observations, including snow depth and soil moisture, are available to validate the GPS-IR measurements. We first obtain daily reflector heights (Fig.1a), which are the vertical distances between the GPS antenna and the surface. We then convert the reflector heights in winter to snow depth, and those in summer to ground surface elevation changes. When estimating soil moisture, the default method uses a constant reflector height, which cannot hold in permafrost areas where surface deforms due to thawing and freezing of the active layer. We make a simple but effective modification to the default by using time-varying reflector height. We find that the GPS-IR-measured snow depth and the manual observations during day of year (DOY) 112-156 have a high correlation coefficient of 0.78, but large root mean squared error (RMSE) of 7.19 cm (Fig. 1b). Such a large RMSE could be caused by the inconsistency between the GPS-IR sensing area and manually probing locations and wind-driven snow redistribution. The soil moisture estimated based on time-varying reflector height have a better agreement with the in situ values: their correlation coefficient and RMSE are 0.82 and 1.5%, respectively, whereas those are 0.71 and 1.9% between the soil moisture estimated by default method and in situ values (Fig. 1c). This study presents that snow depth, surface soil moisture, and surface elevation changes are measured by GPS-IR at a permafrost site. It highlights the improvement to the GPS-IR-based soil moisture retrieval method, which can be extended to other GPS stations in permafrost areas.GPS-IR can retrieve snow depth, surface soil moisture, and ground surface elevation changes from reflected GPS signals. However, in previous studies, these three variables were usually estimated separately at different GPS sites. In this study, we retrieve all of them at daily intervals in 2017 and 2018 at a GPS site in northwestern Qinghai-Tibet Plateau. In situ observations, including snow depth and soil moisture, are available to validate the GPS-IR measurements. We first obtain daily reflector heights (Fig. 1a), which are the vertical distances between the GPS antenna and the surface. We then convert the reflector heights in winter to snow depth, and those in summer to ground surface elevation changes. When estimating soil moisture, the default method uses a constant reflector height, which cannot hold in permafrost areas where surface deforms due to thawing and freezing of the active layer. We make a simple but effective modification to the default by using time-varying reflector height. We find that the GPS-IR-measured snow depth and the manual observations during day of year (DOY) 112-156 have a high correlation coefficient of 0.78, but large root mean squared error (RMSE) of 7.19 cm (Fig. 1b). Such a large RMSE could be caused by the inconsistency between the GPS-IR sensing area and manually probing locations and wind-driven snow redistribution. The soil moisture estimated based on time-varying reflector height have a better agreement with the in situ values: their correlation coefficient and RMSE are 0.82 and 1.5%, respectively, whereas those are 0.71 and 1.9% between the soil moisture estimated by default method and in situ values (Fig. 1c). This study presents that snow depth, surface soil moisture, and surface elevation changes are measured by GPS-IR at a permafrost site. It highlights the improvement to the GPS-IR-based soil moisture retrieval method, which can be extended to other GPS stations in permafrost areas.

2020032509 Zhang Qiwen (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Yang Yuanhe and Zhang Dianye. Patterns and drivers of potential methane oxidation and production rates across Tibetan alpine permafrost region [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B23M-2580, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Our knowledge on patterns and drivers of methane (CH₄) oxidation and production potential across permafrost regions is crucial for understanding the magnitude and direction of permafrost carbon (C)-climate feedback. However, current studies were mainly derived from the Arctic area, with limited evidence from other permafrost regions. Here, based on 51 soil samples collected from the Tibetan alpine permafrost region, we conducted large-scale laboratory incubation to determine potential CH₄ oxidation rate in alpine steppe and meadow (CH₄ sink areas) and potential CH₄ production rate in swamp meadow (CH₄ source areas). We then quantified the relative and interactive effects of abiotic (e.g. soil moisture and organic carbon content) and biotic variables (abundance of CH₄-related functional genes by quantitative real-time PCR) on potential CH₄ oxidation and production rates. We further adopted machine learning technique and bootstrap resampling approach to evaluate spatial patterns of CH₄ oxidation and production potentials across the Tibetan alpine permafrost region. Our results showed that potential CH₄ oxidation rate in alpine steppe and alpine meadow was 9.14±0.65 and 9.48±0.42 ng g^-1 dry soil h^-1, and potential CH₄ production rate in swamp meadow was 33.14±12.86 ng g^-1 dry soil h^-1. Our results also revealed that methanotrophs abundance and soil moisture were two dominant factors regulating potential CH₄ oxidation rate in CH₄ sink areas, jointly accounting for 43.6% of the variance. By contrast, potential CH₄ production rate in CH₄ source areas was mainly affected by methanogens abundance and soil organic carbon (SOC) content, which interpreted 92.1% of total variation. Overall, the Tibetan alpine permafrost region exhibited a potential CH₄ sink, suggesting weaker CH₄-climate feedback in Tibetan alpine permafrost region than those reported in Arctic area.

2020027708 Zhang Tingjun (Lanzhou University, Key Laboratory of West China's Environment, Lanzhou, China) and Peng Xiaoqing. Linkages and remote connections of cryospheric extent change between the Third Pole and the Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC41B-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The cryosphere is theoretically defined as the sphere with temperature below the freezing point, but in practice it primarily consists of ice sheets, glaciers, sea ice, snow, lake and river ice, seasonally frozen ground and permafrost. Cryosphere plays a major role in the earth's climate system through its impact on surface energy balance, water cycle, primary productivity, and sea level change. Up-to-date, studies on changes in cryospheric extent mainly focus on single element such as sea ice or snow cover. Here we synthesize multiple data products to reconstruct one global cryospheric extent dataset. We will then evaluate variability of cryospheric extent and response to climate change at regional, hemispheric, and global scales. Preliminary results show that from 1979 to 2016, the daily global cryospheric extent ranged from 46.7 to 89.5´10⁶ km². Over this period, the global cryosphere lost about 80 ´ 10³ km² per year. The first date of cryospheric cover was delayed by 3.6 days or a rate of 0.095 days per year, the last date advanced by 5.7 days or a rate of 0.15 days per year. Both the duration and number of cryospheric cover days declined by 8.7 days and 7.6 days, respectively. We will further investigate how these changes vary with latitudes and latitudes over the Third Pole and the Arctic regions. A full comparison study of changes in cryopshere as a whole and its major component between the Third Pole and the Arctic will be carried out. Finally, we will further investigate response of changes in cryopshere to climate change over these two regions. These variations of global cryospheric extent are correlated with rising air temperatures, and significantly impact sea level.

2020032602 Zhao, L. (Nanjing University of Information Science and Technology, Nanjing, China); Sun Zhe; Hu Guojie and Qiao, Y. Prediction of the thaw settlement and degradation in permafrost in the northern limit permafrost on the Qinghai-Tibetan Plateau in the next 100 years [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC51P-1009, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Permafrost has suffered thawing and disappearance on a large scale in the northern limit of permafrost on the Qinghai-Tibetan Plateau (QTP) in recent decades. Thaw settlement resulted from permafrost degradation is a big threat to buildings and infrastructure, which has caused public concern. Many models have been used to predict permafrost changes on QTP in the future. However, few of them attempted to take the effect of thaw settlement in permafrost degradation into consideration. Here, we offer a 1D moving-boundary heat conduction numerical model of permafrost in order to estimate the impact of thaw settlement processes on permafrost changes. After validation by long-term monitoring of ground temperature data, the simulation results suggest the thaw settlement rate in the study site was about 6.28 mm/a in the past decade which was highly consistent with the filed geodetic leveling (about 4.09mm/y). Then the model is used to predict permafrost degradation and thaw settlement in the discontinuous permafrost zone in the northern limit permafrost on the QTP under different scenarios of climate warming. The simulation predictions show (1) deepening of the permafrost table and thaw settlement is very slight in next 30 years, even under the most radical warming scenario (RCP 8.5); (2) by the end of the 100 years period, thaw settlement and deepening of the permafrost table prediction are 0.04m and 0.35m for RCP 2.6, 0.76m and 6.95m for RCP6.0, 1.55m and 15.45m for RCP8.5, respectively; (3) thaw settlement may accelerate permafrost degradation because it makes permafrost closer to the surface.

2020027709 Zheng Guanheng (Tsinghua University, Department of Hydraulic Engineering, Beijing, China); Yang Yuting; Yang Dawen and Dafflon, Baptiste. Spatiotemporal change of frozen soil and its climate controls over the Tibetan Plateau during 2002~2016 [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract GC41B-07, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

The changing climate is affecting the frozen soil at an unexpected speed in the Northern Hemisphere. However, due to sparse ground measurements, the changes of frozen soil and the climatic controls over the vast cryosphere are still unclear. The process-based model driven by satellite remote sensing data has the potential to retrieve the frozen soil across large space, but its performance at continental scale, such as the Tibetan Plateau (TP), is still unknown. In this study, a satellite-data driven model was employed to simulate the frozen soil over the entire TP (~ 3 million km²) from 2002 to 2016 and was validated using ground-measured frozen ground types at 569 boreholes, soil temperature (T_soil) and frozen depth (D_f) at 109 CMA stations, as well as T_soil over 40 m deep at 4 GTN-P boreholes. In addition to the overall good accuracy, the model also performed well in simulating the thermal dynamics in seasonally frozen ground (with T_soil anomalies R² > 0.55 and D_f anomalies R² of 0.42~0.66) and permafrost (with T_soil anomalies R^2- generally higher than 0.5). Based on the model simulation, we computed the spatiotemporal changes of the frozen soil properties, i.e., permafrost area, the maximum thickness of seasonally frozen ground (MTSFG), and the maximum thickness of active layer (MTAL), over the TP. From 2002 to 2016, the degradation of permafrost is significant with the total area decreased by 4.9% and the MTAL increased at a high speed of +27 cm 10yr^-1, whereas the changes of MTSFG are small and insignificant. Further analysis reveals that the spatiotemporal variations of MTSFG and MTAL over the TP are mainly controlled (> 80% of total area) by the land surface temperature. However, the impacts of initial ground thermal condition before freezing or thawing season and precipitation on the spatial pattern are also evident. In terms of the temporal changes of frozen soil, snowfall controlled the MTSFG near the Nyainqentanglha, Gangdise, and Karakoram Mountains in the southern plateau, and the rainfall controls the MTSFG and MTAL near the permafrost boundaries. This study employed the satellite data and process-based model to increase the knowledge on the spatiotemporal changes of frozen soils over the TP and such research framework would benefit further studies on the global frozen soil and related processes.

2020027631 Zhou, Wenbo (University of Michigan Ann Arbor, Ann Arbor, MI); Ivanov, Valeriy Y.; Sheshukov, Aleksy Y.; Wang, Jingfeng; El Sharif, Husayn A.; Liu, Desheng; Mazepa, Valeriy; Shiyatov, Stepan and Sokolov, Alexander. Coupling of snow and freeze-thaw processes to model permafrost state in a timberline ecotone [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract C13E-1386, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Warmer climate of the past several decades has affected permafrost thermal state in the Arctic and also caused encroachment of tall woody vegetation into tundra areas. It remains to be explored whether the impact of tall vegetation on thermal state of the permafrost has a dampening effect on the climate trend warming the permafrost, or the opposite effect. Specifically, vegetation expansion can affect snow distribution and accumulation and therefore change heat exchange processes in an area with encroached woody species. In this study, we present an empirical analysis based on datasets collected from 11 energy budget stations located in the Polar Urals area (Western Siberia). We analyzed characteristic differences in terms of radiative fluxes, surface and subsurface temperatures, soil moisture, ground heat fluxes, and snow depth. Results demonstrate differences between areas with encroached vegetation and tundra areas. A physically-based ecohydrological model tRIBS-VEGGIE is used in this study. This model includes coupling of a distributed snow model and a 1-D subsurface thermal model based on energy and mass balance formulations. Calibration and validation are conducted using in-situ measurements from our monitoring stations. This model demonstrates simulation of temperature and moisture regimes during subsurface freeze and thaw process as dependent on surface budgets of vegetated snow covered and snow free areas. This study provides insights into mass-energy transfer between surface and subsurface of vegetated areas, the state of the permafrost and its impact on the Arctic hydrologic fluxes. Warmer climate of the past several decades has affected permafrost thermal state in the Arctic and also caused encroachment of tall woody vegetation into tundra areas. It remains to be explored whether the impact of tall vegetation on thermal state of the permafrost has a dampening effect on the climate trend warming the permafrost, or the opposite effect. Specifically, vegetation expansion can affect snow distribution and accumulation and therefore change heat exchange processes in an area with encroached woody species. In this study, we present an empirical analysis based on datasets collected from 11 energy budget stations located in the Polar Urals area (Western Siberia). We analyzed characteristic differences in terms of radiative fluxes, surface and subsurface temperatures, soil moisture, ground heat fluxes, and snow depth. Results demonstrate differences between areas with encroached vegetation and tundra areas. A physically-based ecohydrological model tRIBS-VEGGIE is used in this study. This model includes coupling of a distributed snow model and a 1-D subsurface thermal model based on energy and mass balance formulations. Calibration and validation are conducted using in-situ measurements from our monitoring stations. This model demonstrates simulation of temperature and moisture regimes during subsurface freeze and thaw process as dependent on surface budgets of vegetated snow covered and snow free areas. This study provides insights into mass-energy transfer between surface and subsurface of vegetated areas, the state of the permafrost and its impact on the Arctic hydrologic fluxes.

2020032520 Zhuang, Qianlai (Purdue University, Department of Earth, Atmospheric, and Planetary Sciences, West Lafayette, IN); Oh, Youmi; Liu, Licheng; Welp, Lisa R.; Lau, Maggie; Onstott, Tullis C.; Medvigy, David; Bruhwiler, Lori; Dlugokencky, Edward J.; Hugelius, Gustaf and Elberling, Bo. The role of microbial dynamics of methanogens and high affinity methanotrophs in current and future net land methane emissions in the Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B24B-08, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Methane emissions from arctic soils (north of 50 °N) have been extensively studied due to their potential role as a significant methane source when permafrost thaws. However, this methane source might have been overestimated as high affinity methanotrophs (HAM) identified in arctic mineral soils have not been considered. Previous mechanistically-based methane models were typically parameterized using observed methane emission data from organic soils under anaerobic conditions without considering methane consumption in mineral soils. Here we integrated microbial dynamics, i.e., temporal changes in their active biomass abundance, of both methanogens and HAM into a biogeochemistry model that considers the effects of permafrost dynamics to re-assess the net arctic methane emissions. Here we will report the comparison between the new model estimates and the simulations using a previous model that has not considered microbial and permafrost dynamics for the contemporary period (2000-2016). The revised estimates are also evaluated using site-level, regional, and pan-arctic observations. Moreover, we will also report the new model projections of wetland methane emissions for the 21st century. Our results highlight the urgent need for including HAM and microbial dynamics in mechanistic methane models to better understand and constrain the current and future methane budget in the Arctic.

2020027691 Zinke, Robert W. (NASA Jet Propulsion Laboratory, Pasadena, CA); Peltzer, Gilles; Fielding, Eric J.; Sangha, Simran; Bekaert, David P. and Owen, Susan E. Tectonic deformation and surface processes across the Tibetan Plateau; insights from time series analysis of Sentinel-1 InSAR data [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract G13B-0540, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

We constrain deformation patterns resulting from tectonic motions and surface processes across the Tibetan Plateau (29-45°N, 75-95°E) since late 2014 using ascending and descending passes of the Sentinel-1A and -1B radar satellites. The broad spatial extent of these data (> 10⁶ km²) and high rate of temporal sampling (6-12 day orbit repeat time) offer unprecedented resolution in space and time, but present a processing challenge. To address this challenge, we leverage the Advanced Rapid Imaging and Analysis (ARIA) standardized interferometric synthetic aperture radar (InSAR) products and toolbox. These products are scalable to high capacity computing systems, and will be used to process large volumes of data for the upcoming NASA-ISRO NISAR mission. We construct time series of surface deformation constrained from our Sentinel-1 interferograms using the small baseline subset routine of MintPy software. Our preliminary results from two Sentinel-1 tracks and 10 frames along track allow us to quantify regional deformation in the satellite line of sight (LOS). Combining ascending and descending track measurements will allow for determination of true east-west motions, and help constrain north-south and vertical motions when combined with GPS data. The resulting velocity fields will provide a more complete and accurate picture of interseismic strain accumulation rates across active faults in the region such as the Altyn Tagh Fault, and allow us to study surface processes such as permafrost active layer dynamics and isostatic adjustment due to lake level changes in unparalleled scope and detail.

2020032539 Zolkos, Scott (University of Alberta, Department of Biological Sciences, Edmonton, AB, Canada); Tank, Suzanne; Kokelj, Steve; Striegl, Robert G.; Shakil, Sarah; Estop Aragones, Cristian and Olefeldt, David. Divergent landscape evolution shapes fluvial chemistry and carbon balance in the western Canadian Arctic [abstr.]: in AGU 2019 fall meeting, American Geophysical Union Fall Meeting, 2019, Abstract B42B-05, December 2019. Meeting: American Geophysical Union 2019 fall meeting, Dec. 9-13, 2019, San Francisco, CA.

Global inland waters are a critical nexus in the global carbon (C) cycle because they receive, transport, and transform large amounts of terrestrial C. The fate of fluvial C is of particular interest in northern environments, where C release from thawing permafrost and strengthening land-freshwater linkages are reshaping watershed C cycling. Characterizing fluvial C species balance and export across diverse permafrost landscapes provides an opportunity to constrain the magnitude and drivers of northern C cycling and assess terrain responses to permafrost thaw. Working in a suite of watersheds across permafrost terrains with varying geology, topography, hydrology, vegetation, and thermokarst, we quantified the magnitude and proportions of C species exported in fluvial networks, characterized the hydrochemical and landscape drivers of fluvial C cycling, and estimated fluvial C contributions to ecosystem C balance. Our measurements of stream chemistry and C export (lateral flux and gas efflux to the atmosphere) paired with geospatial analyses revealed gradients of C cycling driven by the contrasting landscape conditions. A primary gradient was coupled to elevation and broadly separated inorganic from organic processes. In higher-elevation watersheds with more exposed bedrock, bicarbonate dominated fluvial C export (70% of total). In lower elevation and low-relief watersheds, lateral DOC flux (50%) and CO₂ efflux to the atmosphere (25%) dominated, reflecting stronger biotic controls on C cycling across the relatively organic-rich terrains. Watersheds underlain by ice-rich permafrost were intermediate in this gradient, except where thermokarst enhanced carbonate weathering and sediment release by mobilizing mineral-rich tills, revealing a strong gradient across a former glacial margin. From an ecosystem C balance perspective, fluvial C export was equivalent to 8% of CO₂ uptake by terrestrial vegetation, except in the watersheds affected by thermokarst (~1% by area), where fluvial C export was equivalent to nearly 40% of CO₂ uptake by vegetation. Constraining the effects of environmental change on the balance and fate of fluvial C species is a priority for refining models of C cycling across the diversity of landscape types that contribute to the variability in the circumpolar permafrost environment.

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