Permafrost Monthly Alerts (PMAs)

2018070223 Evgrafova, Alevtina (University of Bern, Department of Geography, Bern, Switzerland); de la Haye, Tilman René; Haase, Ina; Shibistova, Olga; Guggenberger, Georg; Tananaev, Nikita; Sauheitl, Leopold and Spielvogel, Sandra. Small-scale spatial patterns of soil organic carbon and nitrogen stocks in permafrost-affected soils of northern Siberia: Geoderma, 329, p. 91-107, illus. incl. 5 tables, sketch map, 121 ref., November 2018. Includes appendices.

The vulnerability of soil organic matter (SOM) sequestered in permafrost-affected soils to climate change plays one of the key roles in the global carbon (C) cycle. However, it still remains unclear how changing soil and site-specific factors, associated with the changing depth of the permafrost table due to thawing, influence the spatial distribution and variability of soil organic carbon (SOC) and total nitrogen (N) stocks in high-latitude mineral soils.The relationships between the spatial variation of SOC and N stocks (0-30 cm) and active layer (AL) thickness, thickness of the organic layer (OL), soil acidity, Al and Fe hydroxides as well as plant- and microbial-derived C inputs were studied using ordinary statistics and geostatistics within six landscape patches (16 m²) in the Siberian forest-tundra ecotone underlain by warm and discontinuous permafrost.At deeper permafrost table, SOC and N stocks (0-30 cm) were lower and, according to the semivariogram analysis, an overall homogenization of SOC and N distribution at the analyzed scale occurred. Total N and SOC stocks were spatially independent from root-derived organic matter distribution (i.e. the concentration of suberin-derived monomers) at shallow AL patches, whereas there was a significant positive spatial correlation within deep AL and non-permafrost soils. Hence, the development of root systems and an increase in rooting depth, leading to "hot spots" of SOM accumulation at intensively rooted soil patches, was observed as a result of deeper AL. Total N and SOC stocks within deeper AL and non-permafrost subsoils were also positively spatially correlated with the concentration of Fe and Al hydroxides, demonstrating the importance of organo-mineral associations for SOM stabilization in soils with lower permafrost table. This study confirmed that deepening of the AL in boreal forest ecosystems may lead to an overall homogenization of SOM distribution and simultaneous development of distinct mechanisms of SOM accumulation and stabilization.

DOI: 10.1016/j.geoderma.2018.05.014

2018074920 Grewer, David M. (University of Toronto, Department of Chemistry, Toronto, ON, Canada); Lafrenière, Melissa J.; Lamoureux, Scott F. and Simpson, Myrna J. Spatial and temporal shifts in fluvial sedimentary organic matter composition from a high Arctic watershed impacted by localized slope disturbances: Organic Geochemistry, 123, p. 113-125, illus. incl. 2 tables, sketch map, 63 ref., September 2018. Includes appendices.

Arctic warming may induce slope failure in upland permafrost soils. These landslide-like events, referred to as active layer detachments (ALDs), redistribute soil material into hydrological networks during spring melt and heavy rainfall. In 2011, 2013 and 2014, fluvial sediments from the West River at the Cape Bounty Arctic Watershed Observatory were sampled where ALDs occurred in 2007-2008. Two ALD-impacted subcatchments were examined exhibiting either continuing disturbance or short-term stabilization. Solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy and targeted biomarker analysis via gas chromatography-mass spectrometry were used to investigate shifts in organic matter (OM) composition. Additionally, radiocarbon ages were determined using accelerator mass spectrometry. Biomarker concentrations and O-alkyl carbon assessed via NMR were both lower in sediments nearest the active disturbance and increased in sediments downstream where other aquatic inputs became more dominant. This suggests immobilization of recalcitrant OM near the ALD and the sustained transport of labile ALD-derived OM further downstream. Shifts toward older radiocarbon dates along the river between 2011 and 2014 suggest the continued transport of permafrost-derived OM downstream. The stabilizing subcatchment revealed high O-alkyl carbon via NMR and increased concentrations of unaltered terrestrial-derived biomarkers indicative of enhanced OM accumulation following ALD activity. The relatively young radiocarbon ages from these sediments suggest accumulation from contemporary sources and potential burial of the previously dispersed ALD inputs. Within the broader context of Arctic climate change, these results portray a complex environmental trajectory for thaw-released permafrost-derived OM and highlight uncertainty in the relationship between lability and persistence upon release by permafrost disturbance.

DOI: 10.1016/j.orggeochem.2018.07.004

2018071954 Dublyansky, Yuri (Innsbruck University, Institute of Geology, Innsbruck, Austria); Moselley, Gina E.; Lyakhnitsky, Yuri; Hai Cheng; Edwards, Lawrence R.; Scholz, Denis; Koltai, Gabriella and Spötl, Christoph. Late Palaeolithic cave art and permafrost in the Southern Ural: Scientific Reports, 8(12080), 7 p., illus. incl. sect., 1 table, sketch map, 36 ref., August 13, 2018.

Shulgan-Tash (also known as Kapova) cave located on the western slope of the Ural Mountains (Russia) is the easternmost European cave art monument of late Palaeolithic age. Radiocarbon dates from cultural layers in the cave suggest an age of about 16.3 to 19.6 ka (cal BP), but dates directly on the paintings were not obtained. In order to constrain the age of this art using an independent method, we performed detailed ²³⁰Th-U dating of calcite fowstone underlying and overgrowing the paintings at 22 sites in three halls of the cave. The youngest age for the underlying calcite (i.e., the maximum age of the cave art) is 36.4±0.1ka, and the oldest overlying calcite (constraining the minimum age of the cave art) is 14.5±0.04ka. The ca. 21.9 ka-long hiatus in calcite deposition during which the paintings were made is attributed to regional permafrost conditions and sub-zero temperatures inside the cave during Marine Isotope Stage (MIS) 2. This is supported by samples of cryogenic cave calcite, which document seven episodes of freezing and thawing of permafrost associated with stadials and interstadials of MIS 3, respectively.

DOI: 10.1038/s41598-018-30049-w

2018075047 Muller, Oliver (University of Bergen, Department of Microbiology, Bergen, Norway); Seuthe, Lena; Bratbak, Gunnar and Paulsen, Maria L. Bacterial response to permafrost derived organic matter input in an Arctic fjord: Frontiers in Marine Science, 5(263), 12 p., illus. incl. sketch map, 96 ref., August 6, 2018. WWW.

The warming of the Arctic causes increased riverine discharge, coastal erosion, and the thawing of permafrost. Together, this is leading to an increased wash out of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems. This tDOM may be anticipated to affect both carbon and nutrient flow in the microbial food web and microbial community composition, but there are few studies detailing this in Arctic marine ecosystems. We tested the effects of tDOM on the bacterial community composition and net-growth by extracting DOM from the active layer of permafrost soil and adding the aged tDOM concentrate to a natural microbial fjord community (Kongsfjorden, NW Svalbard). This resulted in an increased carbon load of 128mM DOC in the tDOM treatment relative to the control of 83mM DOC. We observed changes in community composition and activity in incubations already within 12 h where tDOM was added. Flow cytometry revealed that predominantly large bacteria increased in the tDOM treated incubations. The increase of this group correlated with the increase in relative abundance of the genus Glaciecola (Gammaproteobacteria). Glaciecola were initially not abundant in the bacterial community (0.6%), but their subsequent increase up to 47% after 4 days upon tDOM addition compared to 8% in control incubations indicates that they are likely capable of degrading permafrost derived DOM. Further, according to our experimental results we hypothesize that the tDOM addition increased bacterivorous grazing by small protists and thus tDOM might indirectly also effect higher trophic levels of the microbial food web.

DOI: 10.3389/fmars.2018.00263

2018071564 Tran, Anh Phuong (Lawrence Berkeley National Laboratory, Earth and Environmental Sciences Area, Berkeley, CA); Dafflon, Baptiste; Bisht, Gautam and Hubbard, Susan S. Spatial and temporal variations of thaw layer thickness and its controlling factors identified using time-lapse electrical resistivity tomography and hydrothermal modeling: Journal of Hydrology, 561, p. 751-763, illus. incl. 2 tables, sketch map, 38 ref., June 2018. Includes appendices.

Quantitative understanding of controls on thaw layer thickness (TLT) dynamics in the Arctic peninsula is essential for predictive understanding of permafrost degradation feedbacks to global warming and hydrobiochemical processes. This study jointly interprets electrical resistivity tomography (ERT) measurements and hydro-thermal numerical simulation results to assess spatiotemporal variations of TLT and to determine its controlling factors in Barrow, Alaska. Time-lapse ERT measurements along a 35-m transect were autonomously collected from 2013 to 2015 and inverted to obtain soil electrical resistivity. Based on several probe-based TLT measurements and co-located soil electrical resistivity, we estimated the electrical resistivity thresholds associated with the boundary between the thaw layer and permafrost using a grid search optimization algorithm. Then, we used the obtained thresholds to derive the TLT from all soil electrical resistivity images. The spatiotemporal analysis of the ERT-derived TLT shows that the TLT at high-centered polygons (HCPs) is smaller than that at low-centered polygons (LCPs), and that both thawing and freezing occur earlier at the HCPs compared to the LCPs. In order to provide a physical explanation for dynamics in the thaw layer, we performed 1-D hydro-thermal simulations using the community land model (CLM). Simulation results showed that air temperature and precipitation jointly govern the temporal variations of TLT, while the topsoil organic content (SOC) and polygon morphology are responsible for its spatial variations. When the topsoil SOC and its thickness increase, TLT decreases. Meanwhile, at LCPs, a thicker snow layer and saturated soil contribute to a thicker TLT and extend the time needed for TLT to freeze and thaw. This research highlights the importance of combination of measurements and numerical modeling to improve our understanding spatiotemporal variations and key controls of TLT in cold regions.

DOI: 10.1016/j.jhydrol.2018.04.028

2018073293 Knutsson, Roger (Lulea University, Department of Civil, Environmental and Natural Resources Engineering, Lulea, Sweden); Viklander, Peter; Knutsson, Sven and Laue, Jan. Geothermal study to explain man-made permafrost in tailings with raised surface: Environmental Earth Sciences, 77(7), Paper 288, illus. incl. 2 tables, 22 ref., April 2018.

DOI: 10.1007/s12665-018-7465-8

2018074452 Miller, Johanna. Thousands of tons of mercury are trapped in permafrost: Physics Today, 71(4), p. 14-16, illus. incl. sketch map, 6 ref., April 2018.

2018073230 Sarici, Didem Eren (Inonu University, Department of Mining Engineering, Malatya, Turkey) and Ozdemir, Engin. Determining point load strength loss from porosity, Schmidt hardness, and weight of some sedimentary rocks under freeze-thaw conditions: Environmental Earth Sciences, 77(3), Paper 62, illus. incl. 9 tables, sketch map, 25 ref., February 2018.

DOI: 10.1007/s12665-018-7241-9

2018075028 Novikova, Anna (Lomonosov Moscow State University, Faculty of Geography, Moscow, Russian Federation); Belova, Nataliya; Baranskaya, Alisa; Aleksyutina, Daria; Masalakov, Alexey; Zelenin, Egor; Shabanova, Natalia and Ogorodov, Stanislav. Dynamics of permafrost coasts of Baydaratskaya Bay (Kara Sea) based on multi-temporal remote sensing data: Remote Sensing, 10(9), Paper no. 1481, illus. incl. 6 tables, sketch maps, 76 ref., 2018.

Arctic coasts composed of frozen deposits are extremely sensitive to climate change and human impact. They retreat with average rates of 1-2 m per year, depending on climatic and permafrost conditions. In recent decades, retreat rates have shown a tendency to increase. In this paper, we studied the coastal dynamics of two key sites (Ural and Yamal coasts) of Baydaratskaya Bay, Kara Sea, where a gas pipeline had been constructed. Based on multi-temporal aerial and satellite imagery, we identified coastal erosion rates at several time lapses, in natural conditions and under human impact, and discussed their temporal variability. In addition to planimetric (m/yr), we calculated volumetric (m³/m/yr) retreat rates of erosional coasts using ArcticDEM. We also estimated the influence of geomorphology, lithology, and permafrost structure of the coasts on spatial variations of their dynamics. Erosional coasts of the Ural key site retreat with higher mean rates (1.2 m/yr and 8.7 m³/m/yr) as compared to the Yamal key site (0.3 m/yr and 3.7 m³/m/yr) due to their exposure to higher open sea waves, more complex lithology, higher ice content and lower coastal bluffs. Since the 1960s, coastal retreat rates have been growing on both coasts of Baydaratskaya Bay; we relate this effect with Arctic climate warming. From the 1960s to 2005, such growth was moderate, while in 2005-2016 it became rapid, which may be explained by the enhanced wave and thermal action or by the onset of industrial development. The adjacent coastal segments, originally accumulative, remained relatively stable from the 1960s to 2005. After 2005, a considerable part of them began to retreat as a result of changing weather conditions and/or increasing human impact.

DOI: 10.3390/rs10091481

2018075045 Strozzi, Tazio (Gamma Remote Sensing, Switzerland); Antonova, Sofia; Günther, Frank; Mätzler, Eva; Vieira, Goncalo; Wegmüller, Urs; Westermann, Sebastian and Bartsch, Annett. Sentinel-1 SAR interferometry for surface deformation monitoring in low-land permafrost areas: Remote Sensing, 10(9), 20 p., illus. incl. 2 tables, sketch map, 55 ref., 2018.

Low-land permafrost areas are subject to intense freeze-thaw cycles and characterized by remarkable surface displacement. We used Sentinel-1 SAR interferometry (InSAR) in order to analyse the summer surface displacement over four spots in the Arctic and Antarctica since 2015. Choosing floodplain or outcrop areas as the reference for the InSAR relative deformation measurements, we found maximum subsidence of about 3 to 10 cm during the thawing season with generally high spatial variability. Sentinel-1 time-series of interferograms with 6-12 day time intervals highlight that subsidence is often occurring rather quickly within roughly one month in early summer. Intercomparison of summer subsidence from Sentinel-1 in 2017 with TerraSAR-X in 2013 over part of the Lena River Delta (Russia) shows a high spatial agreement between both SAR systems. A comparison with in-situ measurements for the summer of 2014 over the Lena River Delta indicates a pronounced downward movement of several centimetres in both cases but does not reveal a spatial correspondence between InSAR and local in-situ measurements. For the reconstruction of longer time-series of deformation, yearly Sentinel-1 interferograms from the end of the summer were considered. However, in order to infer an effective subsidence of the surface through melting of excess ice layers over multi-annual scales with Sentinel-1, a longer observation time period is necessary.

DOI: 10.3390/rs10091360

2018075027 Zhang, Weixing (University of Connecticut, Department of Natural Resources and the Environment, Storrs, CT); Witharana, Chandi; Liljedahl, Anna K. and Kanevskiyk, Mikhail. Deep convolutional neural networks for automated characterization of Arctic ice-wedge polygons in very high spatial resolution aerial imagery: Remote Sensing, 10(9), Paper no. 1487, illus. incl. 4 tables, sketch map, 109 ref., 2018.

The microtopography associated with ice-wedge polygons governs many aspects of Arctic ecosystem, permafrost, and hydrologic dynamics from local to regional scales owing to the linkages between microtopography and the flow and storage of water, vegetation succession, and permafrost dynamics. Wide-spread ice-wedge degradation is transforming low-centered polygons into high-centered polygons at an alarming rate. Accurate data on spatial distribution of ice-wedge polygons at a pan-Arctic scale are not yet available, despite the availability of sub-meter-scale remote sensing imagery. This is because the necessary spatial detail quickly produces data volumes that hamper both manual and semi-automated mapping approaches across large geographical extents. Accordingly, transforming big imagery into 'science-ready' insightful analytics demands novel image-to-assessment pipelines that are fueled by advanced machine learning techniques and high-performance computational resources. In this exploratory study, we tasked a deep-learning driven object instance segmentation method (i.e., the Mask R-CNN) with delineating and classifying ice-wedge polygons in very high spatial resolution aerial orthoimagery. We conducted a systematic experiment to gauge the performances and interoperability of the Mask R-CNN across spatial resolutions (0.15 m to 1 m) and image scene contents (a total of 134 km²) near Nuiqsut, Northern Alaska. The trained Mask R-CNN reported mean average precisions of 0.70 and 0.60 at thresholds of 0.50 and 0.75, respectively. Manual validations showed that approximately 95% of individual ice-wedge polygons were correctly delineated and classified, with an overall classification accuracy of 79%. Our findings show that the Mask R-CNN is a robust method to automatically identify ice-wedge polygons from fine-resolution optical imagery. Overall, this automated imagery-enabled intense mapping approach can provide a foundational framework that may propel future pan-Arctic studies of permafrost thaw, tundra landscape evolution, and the role of high latitudes in the global climate system.

DOI: 10.3390/rs10091487

2018074161 Docherty, Catherine L. (University of Birmingham, School of Geography, Earth and Environmental Science, Birmingham, United Kingdom); Hannah, David M.; Riis, Tenna; Leth, Simon Rosenhoj and Milner, Alexander M. Large thermo-erosional tunnel for a river in northeast Greenland: Polar Science, 14, p. 83-87, illus. incl. 1 table, sketch map, 22 ref., December 2017.

DOI: 10.1016/j.polar.2017.08.001

2018072522 Wang Huini (Wuhan University of Technology, Intelligent Transport Systems Research Center, Engineering Research Center for Transportation Safety, Wuhan, China); Liu Hongjia and Ni Wankui. Factors influencing thermokarst lake development in Beiluhe Basin, the Qinghai-Tibet Plateau: Environmental Earth Sciences, 76(24), Article 816, illus. incl. 7 tables, geol. sketch maps, 30 ref., December 2017.

Thermokarst lake is a significant indicator of permafrost degradation. However, the evaluation of thermokarst lake development is very difficult through physical mechanism analysis because the development is influenced by many factors. In the present study, the factors influencing thermokarst lake development were investigated from the perspective of frozen soil and the geographical environment. The influences of six factors on thermokarst lake development in Beiluhe basin, located in the hinterland of the Qinghai-Tibet Plateau, were analyzed: permafrost type, ground temperature, vegetation type, soil type, hydrogeological type, and slope. Sensitivity coefficients were calculated for these factors using statistical methods. The results show that thermokarst lake development was influenced by the analyzed factors as follows: permafrost > soil type > ground temperature > hydrogeological type. Furthermore, 80.1% of the study area was highly sensitive to thermokarst lake development. Overall, thermokarst lake development in the Beiluhe basin was thoroughly evaluated based on sensitivity factors and an established statistical evaluation method. The method detailed in this paper provides a reference for evaluating the likelihood and severity of thermokarst lake development. Copyright 2017 Springer-Verlag GmbH Germany, part of Springer Nature

DOI: 10.1007/s12665-017-7143-2

2018073432 Griffiths, J. S. (University of Plymouth, Plymouth, United Kingdom) and Martin, C. J., editors. Engineering geology and geomorphology of glaciated and periglaciated terrains; engineering group working party report: Engineering Geology Special Publication, 28, 953 p., illus., 2017. ISBN: 9781786203021. Individual chapters are cited separately.

DOI: 10.1144/EGSP28

2018073437 Murton, J. B. (University of Sussex, Department of Geography, Sussex, United Kingdom) and Ballantyne, C. K. Periglacial and permafrost ground models for Great Britain: in Engineering geology and geomorphology of glaciated and periglaciated terrains; engineering group working party report (Griffiths, J. S., editor; et al.), Engineering Geology Special Publication, 28, p. 501-597, illus. incl. geol. sketch maps, 1 table, sect., 432 ref., 2017.

Periglacial environments are characterized by cold-climate non-glacial conditions and ground freezing. The coldest periglacial environments in Pleistocene Britain were underlain by permafrost (ground that remains at or below 0°C for two years or more), while many glaciated areas experienced paraglacial modification as the landscape adjusted to non-glacial conditions. The growth and melt of ground ice, supplemented by temperature-induced ground deformation, leads to periglacial disturbance and drives the periglacial debris system. Ice segregation can fracture porous bedrock and sediment, and produce an ice-rich brecciated layer in the upper metres of permafrost. This layer is vulnerable to melting and thaw consolidation, which can release debris into the active layer and, in undrained conditions, result in elevated porewater pressures and sediment deformation. Thus, an important difference arises between ground that is frost-susceptible, and hence prone to ice segregation, and ground that is not. Mass-movement, fluvial and aeolian processes operating under periglacial conditions have also contributed to reworking sediment under cold-climate conditions and the evolution of periglacial landscapes. A fundamental distinction exists between lowland landscapes, which have evolved under periglacial conditions throughout much of the Quaternary, and upland periglacial landscapes, which have largely evolved over the past c. 19 ka following retreat and downwastage of the last British-Irish Ice Sheet. Periglacial landsystems provide a conceptual framework to interpret the imprint of periglacial processes on the British landscape, and to predict the engineering properties of the ground. Landsystems are distinguished according to topography, relief and the presence or absence of a sediment mantle. Four landsystems characterize both lowland and upland periglacial terrains: plateau landsystems, sediment-mantled hillslope landsystems, rock-slope landsystems, and slope-foot landsystems. Two additional landsystems are also identified in lowland terrains, where thick sequences of periglacial deposits are common: valley landsystems and buried landsystems. Finally, submerged landsystems (which may contain more than one of the above) exist on the continental shelf offshore of Great Britain. Individual landsystems contain a rich variety of periglacial, permafrost and paraglacial landforms, sediments and sedimentary structures. Key periglacial lowland landsystems are summarized using ground models for limestone plateau-clay-vale terrain and caprock-mudstone valley terrain. Upland periglacial landsystems are synthesized through ground models of relict and active periglacial landforms, supplemented by maps of upland periglacial features developed on bedrock of differing lithology.

DOI: 10.1144/EGSP28.5

2018071129 Bond-Lamberty, Ben (Department of Energy, Pacific Northwest National Laboratory, Joint Global Change Research Institute, College Park, MD); Smith, A. Peyton and Bailey, Vanessa. Temperature and moisture effects on greenhouse gas emissions from deep active-layer boreal soils: Biogeosciences, 13(24), p. 6669-6681, illus. incl. 3 tables, 82 ref., 2016. Includes appendices.

Rapid climatic changes, rising air temperatures, and increased fires are expected to drive permafrost degradation and alter soil carbon (C) cycling in many high-latitude ecosystems. How these soils will respond to changes in their temperature, moisture, and overlying vegetation is uncertain but critical to understand given the large soil C stocks in these regions. We used a laboratory experiment to examine how temperature and moisture control CO₂ and CH₄ emissions from mineral soils sampled from the bottom of the annual active layer, i.e., directly above permafrost, in an Alaskan boreal forest. Gas emissions from 30 cores, subjected to two temperatures and either field moisture conditions or experimental drought, were tracked over a 100-day incubation; we also measured a variety of physical and chemical characteristics of the cores. Gravimetric water content was 0.31 ± 0.12 (unitless) at the beginning of the incubation; cores at field moisture were unchanged at the end, but drought cores had declined to 0.06 ± 0.04. Daily CO₂ fluxes were positively correlated with incubation chamber temperature, core water content, and percent soil nitrogen. They also had a temperature sensitivity (Q₁₀) of 1.3 and 1.9 for the field moisture and drought treatments, respectively. Daily CH₄ emissions were most strongly correlated with percent nitrogen, but neither temperature nor water content was a significant first-order predictor of CH₄ fluxes. The cumulative production of C from CO₂ was over 6 orders of magnitude higher than that from CH₄; cumulative CO₂ was correlated with incubation temperature and moisture treatment, with drought cores producing 52-73 % lower C. Cumulative CH₄ production was unaffected by any treatment. These results suggest that deep active-layer soils may be sensitive to changes in soil moisture under aerobic conditions, a critical factor as discontinuous permafrost thaws in interior Alaska. Deep but unfrozen high-latitude soils have been shown to be strongly affected by long-term experimental warming, and these results provide insight into their future dynamics and feedback potential with future climate change.

DOI: 10.5194/bg-13-6669-2016

2018072167 Peng, Shushi (Université Joseph Fourier-Grenoble I, Laboratoire de Glaciologie et Géophysique de l'Environnement, Grenoble, France); Ciais, P.; Krinner, G.; Wang, T.; Gouttevin, I.; McGuire, A. D.; Lawrence, D.; Burke, E.; Chen, X.; Decharme, B.; Koven, C.; MacDougall, A.; Rinke, A.; Saito, K.; Zhang, W.; Alkama, R.; Bohn, T. J.; Delire, C.; Hajima, T.; Ji, D.; Lettenmaier, D. P.; Miller, P. A.; Moore, J. C.; Smith, B. and Sueyoshi, T. Simulated high-latitude soil thermal dynamics during the past 4 decades: The Cryosphere (Online), 10(1), p. 179-192, illus. incl. 3 tables, 66 ref., 2016.

Soil temperature (T_s) change is a key indicator of the dynamics of permafrost. On seasonal and interannual timescales, the variability of T_s determines the active-layer depth, which regulates hydrological soil properties and biogeochemical processes. On the multi-decadal scale, increasing T_s not only drives permafrost thaw/retreat but can also trigger and accelerate the decomposition of soil organic carbon. The magnitude of permafrost carbon feedbacks is thus closely linked to the rate of change of soil thermal regimes. In this study, we used nine process-based ecosystem models with permafrost processes, all forced by different observation-based climate forcing during the period 1960-2000, to characterize the warming rate of T_s in permafrost regions. There is a large spread of T_s trends at 20 cm depth across the models, with trend values ranging from 0.010±0.003 to 0.031±0.005°C yr^-1. Most models show smaller increase in T_s with increasing depth. Air temperature (Tsub^a) and longwave downward radiation (LWDR) are the main drivers of T_s trends, but their relative contributions differ amongst the models. Different trends of LWDR used in the forcing of models can explain 61% of their differences in T_s trends, while trends of T_a only explain 5% of the differences in T_s trends. Uncertain climate forcing contributes a larger uncertainty in T_s trends (0.021±0.008°C yr^-1, mean±standard deviation) than the uncertainty of model structure (0.012±0.001°C yr^-1), diagnosed from the range of response between different models, normalized to the same forcing. In addition, the loss rate of near-surface permafrost area, defined as total area where the maximum seasonal active-layer thickness (ALT) is less than 3 m loss rate, is found to be significantly correlated with the magnitude of the trends of T_s at 1 m depth across the models (R=-0.85, P=0.003), but not with the initial total near-surface permafrost area (R=-0.30, P=0.438). The sensitivity of the total boreal near-surface permafrost area to T_s at 1 m is estimated to be of -2.80±0.67 million km² °C^-1. Finally, by using two long-term LWDR data sets and relationships between trends of LWDR and T_s across models, we infer an observation-constrained total boreal near-surface permafrost area decrease comprising between 39±14´10³ and 75±14´10³ km² yr^-1 from 1960 to 2000. This corresponds to 9-18% degradation of the current permafrost area.

DOI: 10.5194/tc-10-179-2016

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2018070251 Campbell, Seth W. (University of Maine at Orono, School of Earth and Climate Sciences, Orono, ME); Liljedahl, Anna; Douglas, Thomas A.; Bernsen, Steve; Gatesman, Tiffany; Gerbi, Christopher C. and Miner, Kimberley. An interdisciplinary approach to assess water resources originating from glaciated watersheds [abstr.]: in Geological Society of America, Northeastern Section, 53rd annual meeting, Abstracts with Programs - Geological Society of America, 50(2), Abstract no. 22-2, March 2018. Meeting: Geological Society of America, Northeastern Section, 53rd annual meeting, March 18-20, 2018, Burlington, VT.

Glacier meltwater contributions to downstream water supply has been increasing in much of the Arctic, likely from higher recent air temperatures. For mountain glaciers that contribute a large portion to downstream discharge, a sustained negative glacier mass balance is concerning to Arctic communities because the water budget will ultimately decline when glacier ice disappears. Glacierized watersheds are complex because the hydrological budget is influenced by precipitation across the entire area, snow melt from both on and off glacier, glacier ice melt, and from water stored at the surface or within the subsurface. In regions where permafrost is prevalent, sub-surface water storage capacity and flow is heavily controlled. This storage capacity and flow is also changing due to thawing permafrost in the rapidly warming Arctic. Unfortunately, glaciological, geological, permafrost, and hydrological studies are typically treated as separate research topics. However, it has become obvious that understanding the complex relationships between these dynamic systems is important for predicting future hydrological budgets, from a water resources perspective. Herein, we discuss the combined use of ground and airborne geophysics, glaciology, meteorology, hydrology, chemistry, and numerical modeling to predict future changes to the water supply originating from a partially glacierized and permafrost-laden watershed. Our study site is Jarvis Creek Watershed in Eastern Alaska which contains a 6-km long glacier that has been in retreat since the 1950's. Despite its retreat, Jarvis accounts for 15% of the annual downstream discharge into Jarvis Creek. Our results suggest that Jarvis Glacier will entirely disappear by 2100. This prediction, combined with observed decreased local precipitation rates and thawing permafrost, suggest that downstream water budgets will be a significant local community concern in the near-future. We propose that this interdisciplinary approach should be considered by other Arctic communities to develop more accurate water resource predictions in the future.

2018072685 Sivak, Tyler (Kutztown University of Pennsylvania, Department of Physical Sciences, Kutztown, PA); Reichard-Flynn, Willow R.; Willever, Heather; Sewall, Jacob O. and Sherrod, Laura A. Potential palsa relicts in eastern Pennsylvania [abstr.]: in Geological Society of America, Northeastern Section, 53rd annual meeting, Abstracts with Programs - Geological Society of America, 50(2), Abstract no. 44-2, March 2018. Meeting: Geological Society of America, Northeastern Section, 53rd annual meeting, March 18-20, 2018, Burlington, VT.

Possible periglacially-derived depressions were found along the floodplain of a small, entrenched, first order stream on the Piedmont of Pennsylvania. If the structures were produced by permafrost during the last glaciation, their preservation over 10 ka implies an anomalously low rate of sediment deposition and surface erosion. To characterize the features, we took ten soil cores across three oblong depressions (5-10 m) on the floodplain and constructed two cross sections, which show undulating sediment layers following the curvature of the depressions. A GPR survey of the site corroborated the continuous nature of the subsurface layers. Palsas are periglacial features formed when a layer of peat or water-logged clay an ice nucleus. This ball of ice expands due to capillary action, compressing underlying layers and expanding overlying layers to form an ovular mound (1-20 m), which frequently occurs with several other palsas. As the ice melts, the structure collapses and forms a shallow depression with a surrounding berm. This morphology closely conforms to the studied depressions. Additionally, the high clay content, nonplanar water table, and periglacial history of the area would render the formation of permafrost structures possible. However, palsa collapse would have occurred over 10 ka ago. For such a small feature to retain its current level of preservation, it would require that virtually no sediment be deposited for more than 10 ka. The possibility that this area is subject to a low rate of sediment transport has been posed in a previous study of the creek. It revealed that the stream is incapable of transporting the sediment in its banks and bed, pointing to probable glacial legacy deposits and indicating near sedimentary stasis since the last glacial maximum. Additionally, relict palsas have been identified in Belgium, Germany, Wales, and Ireland, lending further credibility to the interpretation of the features as periglacial. The subtlety of these features may have led them to be largely overlooked, making it possible that more palsa remnants can be found elsewhere along floodplains in former periglacial regions. If undescribed palsas are indeed prevalent, their presence can be used as a proxy to identify past periglaciation and low post-glacial sedimentation rates.

2018072766 Beerten, Koen (SCK-CEN, Engineered and Geosystems Analysis, Mol, Belgium); Meylemans, Erwin; Mestdagh, Thomas; van Rooij, David; Kasse, Cornelius and Bastiaens, Jan. Morphometric analysis of relict patterned ground in the Campine area, NE Belgium [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-13755, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

The Campine area (NE Belgium) is characterised by soils that mainly developed in Pleistocene sands. It is widely accepted that the region has witnessed several episodes of permafrost build-up during glacial periods. Geomorphological reconstructions applied during the last few decades aimed at determining the duration of and the climate during permafrost episodes. These reconstructions were mainly based on in-situ periglacial deformation phenomena in the shallow subsoil, such as cryoturbations and ice-wedge casts. Recently published high-resolution LiDAR (Light Detection and Ranging) images of the area revealed the presence of soil polygon networks which resemble those that can be observed in permafrost regions today. The topographic signature consists of shallow troughs, several decimeter deep, that are organised into polygons with a diameter of several decameters up to 100 m. The shape and size suggests that the networks consist of relict thermal contraction crack polygons or patterned ground that developed during past permafrost. In this study, we aim at determining the morphometric characteristics of the polygon networks, in order to compare them with modern analogues and ultimately obtain information on past permafrost characteristics. Understanding past permafrost would greatly help to assess the future evolution of geological disposal systems for radioactive waste, because some of these are considered to experience cold climate conditions during the next 1 Ma. Radioactive waste management in Belgium is performed by ONDRAF/NIRAS. An area of ca. 300 km2 was visually surveyed on the DEM (Digital Elevation Model), which led to the selection of a series of networks for further analysis. Individual polygons of each network were digitised using very narrow topographic intervals, and the average area of the polygons and percentage of 4-ray and orthogonal intersections within individual networks were calculated. The results were then compared with pedological and geological properties. Finally, the obtained metrics were evaluated against those of published modern and fossil analogues. The first results suggest that the characteristics of individual networks in the Campine area (mean polygon area and percentage of 4-ray and orthogonal intersections) are not related to subsoil characteristics. Strikingly, the mean polygon area (ca. 3000 m2) is much higher than any of the analogues. In addition, the percentage of 4-ray and orthogonal intersections is fairly low in comparison with the analogues. Several explanations can be put forward to understand this discrepancy between Campine polygon networks and their analogues. One possibility is that the observed networks represent an immature stage of ice-poor permafrost - this explanation is in line with the morphometric analysis. Another explanation would involve the detection method. The analogues, whether modern or fossil, are all systematically mapped using aerial imagery or field observations, whereas the Campine polygons are mapped using LiDAR images. It thus cannot be excluded that the topographic expression of so-called higher order polygons inside the main polygon is obliterated by posterior earth surface processes. We conclude that subsurface imaging is needed to solve this problem, i.e. GPR (Ground Penetrating Radar) profiling followed by trenching as ultimate verification tool. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-13755.pdf

2018072832 Bense, Victor (Wageningen University and Research, Department of Environmental Sciences, Wageningen, Netherlands); Neefjes, Annabelle; Jin Huijun and Sheng Yu. Forecasting the degradation of deep permafrost using temperature-depth observations [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-18960, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Timing of permafrost disappearance in a warming climate is a crucial control on a suite of environmental processes including the reactivation of groundwater flow, landscape development and the associated release of carbon into the atmosphere. Forecasting of permafrost demise has mainly been approached as a near-surface phenomenon from the land-surface modeling perspective, with limited consideration of heat flow processes below a few meters depth. We show, using numerical models and temperature-depth profiles of warm and vulnerable permafrost that the thermal state of deep permafrost during thaw can be obtained using relatively simple measurements of the depth at which thermal gradient is zero, the temperature at this depth and the thickness of permafrost, without the need of repeated measurements. As an example, we demonstrate that across the Source Area of the Yellow River on the Qinghai-Tibet Plateau, China it will take approximately another 80-140 years before permafrost will be fully degraded. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-18960.pdf

2018072770 Blöthe, Jan Henrik (University of Bonn, Department of Geography, Bonn, Germany); Korup, Oliver; Rosenwinkel, Swenja and Höser, Thorsten. Rock-glacier dams in High-Asia [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-17190, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Rock glaciers are especially abundant in the periglacial zone of semiarid mountain belts. Here, they store large amounts of ice and might be important water reservoirs aside from glaciers, lakes, and rivers. Yet whether and how rock glaciers interact with watercourses in mountain valleys remains largely unresolved. In the present study, we examine the potential for rock glaciers to block or disrupt river channels, using a newly compiled inventory of more than 2000 intact rock glaciers that we mapped from remotely sensed imagery in the Karakoram, the Tien Shan, and the Altai mountains. In total, our inventory covers an area of 30,000 km2, which we subdivided into 48 segments of 25´25 km2. Within these subregions, we determined rock glacier density, as well as the area lying upstream of rock glaciers that impact the drainage network. We find that between 5% and 14% of the mapped rock glaciers partly buried, blocked, diverted or constricted at least 95 km of mountain rivers in High Asia, completely disrupting or partly disturbing the sediment delivery from up to 20% and 46% of a segment, respectively. To discern those rock glaciers disrupting mountain rivers from those with no obvious impacts, we use a Bayesian robust logistic regression with multiple topographic (SRTM derived) and climatic variables (WorldClim). We identify elevation and potential incoming solar radiation (PISR), together with the size of feeder basins, as dominant predictors, so that lower-lying and larger rock glaciers from larger basins are more likely to disrupt river channels. Given that elevation and PISR are key inputs for modelling the regional distribution of mountain permafrost from the positions of rock-glacier toes, we infer that river-blocking rock glaciers may be diagnostic of non-equilibrated permafrost. Eliminating the strong correlation between these two and several other topographic and climatic variables with principal component analysis adds low temperature variability and low dry-season precipitation to the controls that characterise rock glaciers impacting on rivers, while accounting for size effects. Clarifying whether rapidly advancing rock glaciers can physically impound rivers, or fortify existing dams instead, deserves future field investigation. We conclude that rock-glacier dams are conspicuous features that may share a polygenetic history and encourage more research on the geomorphic coupling between permafrost lobes, river channels and the sediment cascade. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-17190.pdf

2018072829 Boike, Julia (Alfred-Wegener-Institut, Potsdam, Germany); Ebenhoch, Sabrina; Höfle, Bernhard; Westermann, Sebastian; Maturilli, Marion; Stern, Lielle; Juszak, Inge and Roth, Roth. Warming and thawing trends of permafrost at high Arctic site (Bayelva, Spitsbergen) 1998-2017 [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-8225, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Permafrost around the Arctic is warming and thawing. We report data from the high arctic research site Bayelva (78.551N; 11.571E) located close to Ny-Alesund. Data on meteorology, energy balance components and subsurface observations have been made for the last 20 years (1998-2017; Boike et al. 2017). This study site is underlain by permafrost with current mean permafrost temperature of -2.8 C and is seasonally snow-covered from October to May. Mean annual, summer and winter soil temperature data at all depths have been rising over the period of record with a warming trend of 0.18 0.07 C/year in active layer and top of permafrost. However, interannual to sub-decadal variability is evident in the data and results mostly from differences of the climate during the winter months. The modeled active layer thickness using the Stefan equation has increased continuously from about 1 m in 1998 and is estimated to have surpassed 2 m in 2016. The data show that snow ablation has started earlier, thus extending the snow free season, potentially resulting in more time for soil warming and deepening of active layer. The snow cover onset and ablation, as well as the thermo insulation properties of the snow cover, will be investigated together with active layer and permafrost variables (temperature, volumetric water content) for further understanding of the observed warming and deepening. Boike, J., Juszak, I., Lange, S., Chadburn, S., Burke, E., Overduin, P. P., Roth, K., Ippisch, O., Bornemann, N., Stern, L., Gouttevin, I., Hauber, E., and Westermann, S.: A 20-year record (1998-2017) of permafrost, active layer, and meteorological conditions at a High Arctic permafrost research site (Bayelva, Spitsbergen): an opportunity to validate remote sensing data and land surface, snow, and permafrost models, Earth Syst. Sci. Data Discuss., URL: https://doi.org/10.5194/essd-2017-100, in review, 2017. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-8225.pdf

2018072844 Colombo, Nicola (University of Turin, Department of Earth Sciences); Gruber, Stephan; Martin, Maria; Malandrino, Mery; Magnani, Andrea; Godone, Danilo; Freppaz, Michele; Fratianni, Simona; Williams, Mark; Giardino, Marco and Salerno, Franco. Rainfall as primary driver of discharge and solute export from rock glaciers; the case of the Col d'Olen Rock Glacier (NW Italian Alps) [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-8650, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Permafrost degradation affects hydrochemistry of surface waters. In particular, evidence of modifications of water quality has been collected in mountain headwaters impacted by rock-glacier thawing. Rock glaciers are slowly flowing mixtures of debris and ice-rich permafrost, and melting ice inside them has been reported to affect surface water hydrochemistry, in some cases causing severe ecological damages. Three hypotheses have been formulated to explain how weather and climate drive the export of solute-enriched water from rock glaciers: (1) Warm periods cause increased subsurface ice melt, which releases solutes; (2) rain periods and the melt of long-lasting snow enhance dilution of rock-glacier outflows; and (3) percolation of rain through rock glaciers facilitates the export of solutes, causing an opposite effect as that described in hypothesis (2). This lack of understanding exists because suitable studies of atmospheric parameters, hydrologic processes and physicochemical characteristics of water bodies downstream from rock glaciers are unavailable. In this study, a rock-glacier pond in the North-Western Italian Alps was studied on a weekly basis for the ice-free seasons 2014 and 2015 by observing atmospheric forcing (air temperature, snow cover duration, rainfall) assumed to drive the export of solute-enriched waters from the rock glacier and the physicochemical response of the pond (water temperature as a proxy of rock-glacier discharge, stable water isotopes, major ions and selected trace elements). Results revealed intra-seasonal patterns of increasing solute export associated with higher rock-glacier discharge. Specifically, rainfall (after winter snowpack depletion) was found to be the primary driver of solute export from the rock glacier during the ice-free season, likely through the flushing of stored solutes (SO42-, Mg2+, Ca2+, Ni, Mn, Co) and microbially-active sediments (NO3-) in the rock-glacier interior. With projected reductions in snow cover duration, and increases in air temperature and summer rainfall in the northern hemisphere and in the Alps, an increase in solute flushing from rock glaciers is likely. However, characteristics of rock-glaciers and relative catchments (e.g., ratio of rock-glacier size to catchment area, lithological setting) and characteristics of rock-glacier interior (e.g., frozen core structure and dimensions, hydrological system properties) might influence the timing and magnitude of the impacts of rock-glacier thawing on water quality. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-8650.pdf

2018072756 Draebing, Daniel (Technical University of Munich, Landslide Research, Munich, Germany); McColl, Samuel and Brandschwede, Arne. Identification of periglacial and paraglacial processes and their implications for rockfall [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-5343, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

In alpine environments, rockfall is the primary process shaping deglaciated rockwalls. In addition to periglacial processes, rockwall stability concurrently adjusts to non-glacial conditions, evolving through time according to a suite of time-varying processes, all of which need to be accounted for to accurately model rockwall trajectories. While models exist to explain or simulate permafrost's influence on rockwall stability or frost weathering of rockwalls, few models integrate these processes and there is little field data to verify these models. In this field-based study, we quantify (i) geological controls, (ii) paraglacial stress-release histories, (iii) permafrost distribution, and (iv) the spatial and temporal patterns of frost weathering, and assess how these combine to influence rockfall processes at alpine rockwalls. To achieve this, we use geomorphic, geophysical and geotechnical techniques on three rockwalls (RW1-3) with different glacial history and altitude. All rockwalls are located in the Hungerli Valley (Swiss Alps) and lithology ranges from aplite (RW1) to amphibolite (RW2) and schisty quartz slate (RW3). (i-ii) Laboratory seismics shows that schisty quartz slate is an order of magnitude more anisotropic than aplite or amphibolite due to foliation. Foliation represents planes of weakness where failures can occur. In the field, fractures will additionally control rock slope failures and seismic refraction tomography (SRT) results demonstrate that the fracture density of the rockwalls increases with proximity to the glacier. Therefore, our findings suggest that RW1 in proximity to the glacier is still undergoing paraglacial adjustment to glacier retreat, through active stress-release jointing. Local permafrost modelling based on temperature logger data indicates that areas with likely permafrost occurrence (<-3°C) are limited to the peaks and upper Rothorn cirque walls. Possible permafrost (-2 to -3°C) areas are located in the middle cirque wall section including RW1. However, SRT demonstrate the absence of permafrost within the uppermost 6 m of the rockwall. Crackmeter data were analysed according to the technique developed by Draebing et al. (2017) and resolve thermo-cryogenic movements controlled by altitudinal- and topography-dependent snow cover and temperature. RW1 experienced 191-221 days snow-covered and showed a seasonal thermal-induced opening and closing of 0.55 mm. Ice segregation occurs but permanent fracture widening is minor (<0.1 mm). The snow cover duration was less at RW2 (69-73 days) and the fracture underwent 0.15 mm of cyclic opening from thermal contraction, with ice segregation causing 0.05-0.1 mm widening. At RW3, snow cover was absent and crackmeters showed a high-frequency diurnal cyclic thermal-induced opening of up to 0.2 mm. In conclusion, foliation preconditions rockfall at the low-lying RW3, which can be prepared and triggered by abundant thermal stresses. With increasing altitude, the importance of frost cracking increases as a preparing and triggering factor (RW2). In the highest RW1, permafrost may be limiting frost cracking due to decreased water availability, but increased stress-release and seasonal active layer thawing prepare and trigger rock slope failures. References: Draebing, D., Krautblatter, M. and Hoffmann, T.: Thermo-cryogenic controls of fracture kinematics in permafrost rockwalls. Geophysical Research Letters 44: 3535-3544, 2017. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-5343.pdf

2018072759 Eichel, Jana (Karlsruhe Institute of Technology, Institute of Geography and Geoecology, Karlsruhe, Germany); Draebing, Daniel and Meyer, Nele. Ice, sediments and plants; paraglacial adjustment of lateral moraine slopes in time and space [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-1398, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Worldwide, glaciers are retreating and enlarge glacier foreland areas made up of unstable sediments. A variety of non-glacial processes reworks these sediments, including periglacial processes but also landsliding and water soil erosional processes. Lateral moraines are a hotspot of paraglacial reworking in glacier forelands, however, they have been considerably less studied than glaciofluvial floodplains. Consequently, it is not well understood which factors control paraglacial adjustment of lateral moraine slopes in time and space. Paraglacial adjustment is considered to be completed either once the geological norm of denudation is attained, glacial sediments are exhausted or colonized by vegetation. However, recent research found that paraglacial adjustment can continue below dense vegetation cover of the ecosystem engineer Dryas octopetala with bound solifluction (Draebing and Eichel, 2017; Eichel et al., 2016, 2017). Thus, a new indicator for the completion of paraglacial adjustment is required. We address these research gaps by combining geomorphic and ecologic methods on lateral moraines in the Turtmann glacier foreland (Switzerland), including a permanent plot survey, soil sampling and geomorphic mapping (Eichel et al., in review). Multivariate statistical analysis of permanent plot data showed that ecosystem engineering, material properties and slope geomorphometry are the most important controls for the occurrence of geomorphic processes and landforms. Furthermore, our data demonstrate that geomorphic processes are often absent once vertical vegetation structure and soil horizons develop, which are therefore valuable indicators for completed paraglacial adjustment. Based on our results, we developed a conceptual model of 'paraglacial process and landform succession' in time with four stages: (i) dead ice melt, (ii) gullying, (iii) solifluction and (iv) stabilisation. In space, the geomorphic maps show that paraglacial adjustment is heterogeneous and depends on the identified controls. A diverging paraglacial adjustment was detected for distal and proximal slopes (Draebing and Eichel, minor revisions). On distal slopes, the solifluction stage can occur immediately after deglaciation, while on proximal slopes solifluction can only start once a 'biogeomorphic feedback window' (Eichel et al., 2016) is reached. Hence, our research links para- and periglacial processes and enhances the understanding of present-day landscape development in cold regions. References: Eichel, J., Draebing, D., Meyer, N. in review. What controls paraglacial adjustment of lateral moraine slopes in time and space? Submitted to Land Degradation and Development. Draebing, D., Eichel, J. minor revisions. Divergence, convergence and path-dependency of paraglacial adjustment of alpine lateral moraine slopes. Submitted to Land Degradation and Development. Draebing, D., Eichel, J. 2017. Spatial Controls of Turf-Banked Solifluction Lobes and Their Role for Paraglacial Adjustment in Glacier Forelands. Permafrost and Periglacial Processes 28:446-459. DOI:10.1002/ppp.1930. Eichel, J., Draebing, D., Klingbeil, L., Wieland, M., Eling, C., Schmidtlein, S., Kuhlmann, H., Dikau, R. 2017. Solifluction meets vegetation: the role of biogeomorphic feedbacks for turf-banked solifluction lobe development. Earth Surface Processes and Landforms 42:1623-1635. DOI:10.1002/esp.4102. Eichel, J., Corenblit D., Dikau, R. 2016. Conditions for feedbacks between geomorphic and vegetation dynamics on lateral moraine slopes: a biogeomorphic feedback window. Earth Surface Processes and Landforms 41:406-419. DOI:10.1002/esp.3859 [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-1398.pdf

2018072839 Frampton, Andrew (Stockholm University, Department of Physical Geography, Stockholm, Sweden). Numerical modelling of active layer dynamics, water flow and solute transport subject to seasonal variations and climate change [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-14272, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

There is a need for improved understanding of the mechanisms controlling subsurface solute transport in the active layer in order to better understand permafrost-hydrological-carbon feedbacks, in particular with regards to how dissolved carbon is transported in coupled surface and subsurface terrestrial arctic water systems under climate change. Studying solute transport in arctic systems is also relevant in the context of anthropogenic pollution which may increase due to increased activity in cold region environments. In this contribution subsurface solute transport subject to ground surface warming causing permafrost thaw and active layer change is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in subsurface water flows and solute transport travel times are analysed for different modelled geological configurations during a 100-year warming period. Results show that for all simulated cases, the minimum and mean travel times increase non-linearly with warming irrespective of geological configuration and heterogeneity structure. The timing of the start of increase in travel time depends on heterogeneity structure, combined with the rate of permafrost degradation that also depends on material thermal and hydrogeological properties. These travel time changes are shown to depend on combined warming effects of increase in pathway length due to deepening of the active layer, reduced transport velocities due to a shift from horizontal saturated groundwater flow near the surface to vertical water percolation deeper into the subsurface, and pathway length increase and temporary immobilization caused by cryosuction-induced seasonal freeze cycles. The impact these change mechanisms have on solute and dissolved substance transport is further analysed by integrating pathway analysis with a Lagrangian approach, incorporating considerations for both dissolved organic and inorganic carbon releases. Further model development challenges are also highlighted and discussed, including coupling between subsurface and surface runoff, soil deformations, as well as site applications and larger system scales. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-14272.pdf

2018072757 Gallach, Xavi (CNRS, Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Chambery, France); Ogier, Christophe; Carcaillet, Julien; Ravanel, Ludovic and Deline, Philip. Reconstruction of the rock fall frequency in the Mont Blanc massif since the last glacial maximum using TCN dating and laboratory reflectance spectroscopy; a complete dataset of 72 samples. [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-13919, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Rockfalls and rock avalanches are active processes, including hazards for infrastructures and outdoor activities. Present rockfalls are well surveyed and documented in the Mont Blanc massif thanks to a network of observers set up in 2007, and composed of hut keepers, mountain guides, alpinists and infrastructure workers. Frequency over the past 150 years of massif rockfall, studied by comparison of historical photographs, has strongly increased during the last 30 years, especially during very hot summer (2003 and 2015), likely due to permafrost degradation driven by the climate change. In order to understand at a longer timescale the relationship between rockfall frequency and climate dynamics in the Mont Blanc massif, we use Terrestrial Cosmogenic Nuclide (TCN) dating to obtain the exposure ages of Lateglacial and Holocene rockfall scars and old rockwall surfaces, and glacial and climate proxies to verify the hypothesis that rockfalls were more frequent in warm periods. 55 samples have been collected at 9 sites of the Glacier du Geant basin, at elevation in the range 3300-3800 m a.s.l. These new exposure ages were completed by the 25 others TCN ages sampled during two previous campaigns and recalculated using the newest input parameters. A total of 72 ages were obtained, between 0.04±0.02 and 100.50±8.50 ka. We found four age clusters. Two clusters are related to the Holocene Warm Period (~6.1-7.4 ka) and Roman Warm Period (~1.6-2.3 ka); a cluster of LIA-post-LIA ages is mainly composed by smaller rockfalls, considered as the 'normal' erosion. A forth cluster have been recognized at 4.2-5.0 ka. Data suggest a relationship between the reflectance spectral data of the scar surfaces and exposure ages, mainly in the E-SE-S aspects. Fresh rock surfaces of recent rockfall scars are light grey, whereas long-time exposed weathered rock surfaces range from light orange to dark red. This confirms the initial hypothesis: the redder a rock surface, the older its age. Reflectance spectroscopy is used to quantify the granite surface colour and allow the establishment of a robust relationship between scar exposure ages and colour of the rockwalls in the Mont Blanc massif. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-13919.pdf

2018072843 Halla, Christian (University of Bonn, Department of Geography, Germany); Blöthe, Jan Henrik; Hauck, Christian; Trombotto, Dario and Schrott, Lothar. Potential water storage of rock glacier permafrost derived from geophysical modeling (Central Andes of Argentina) [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-9358, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Active rock glaciers potentially constitute significant reservoirs and sources of water in the dry Central Andes. However, volumetric ice and water contents of Andean rock glaciers are largely unknown. In this study, we apply the so-called four-phase model (4PM) to quantify the material composition of the talus-derived rock glacier Dos Lenguas and the large rock glacier complex Morenas Coloradas in the Central Andes of Argentina. The 4PM is based on different porosity models for ice-rich permafrost bodies and on geoelectric and refraction seismic tomography that were conducted in the root zone, middle part and on the tongues of both rock glaciers. The spatial distributions of ice and water contents show a heterogeneous pattern. Ice-oversaturated permafrost and massive ground ice with ice contents of 50 up to 90 vol% are two to three times higher in root zones of both rock glaciers compared to lower lying rock glacier tongues containing 20 to 30 vol%. High water contents and saturated subsurface conditions are identified underneath surface depression and furrows indicating effective water pathways. Furthermore increased active layer depths, dissected permafrost bodies, and thermokarst show the influence of thermal erosion on the internal hydrologic structure of both rock glaciers. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-9358.pdf

2018072833 Hauck, Christian (University of Fribourg, Department of Geosciences, Fribourg, Switzerland) and Hilbich, Christin. Quantifying ground ice content and its variability in permafrost bodies using geophysical techniques; implications for water release and future water availability [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-10605, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

The cryosphere in mountain regions undergoes currently strong changes due to climate change. Many studies confirm also the impact of enhanced glacier melt on the glacial water contribution during the 21st century. This effect will be strongest for comparatively dry regions, such as Central Asia and the Central Andes. Whereas the effect on glacial melt on long-term water availability and runoff is well investigated, little is known about the contribution of ground ice melt from permafrost regions to total runoff. One reason is the sparseness of ground truth data (ice content) from permafrost regions, both regarding amount and spatial extent. Without this information, regional permafrost, hydrological, and/or hemispheric land-surface models can neither accurately estimate future permafrost extent and temperature, nor assess the impact of thawing permafrost on runoff. As permafrost and especially its ground ice content is invisible from the surface, remote sensing approaches can only be used for specific landforms, i.e. rock glaciers. However, also in this case the ground ice content, its thickness and its potentially heterogeneous spatial distribution within the rock glacier cannot be determined. Geophysical surveying is the only alternative to costly and point-scale borehole information and is now widely used in permafrost research to detect and monitor frozen ground and to quantify the ground ice content. A combination of different methods, such as electric/electromagnetic and seismic methods, is hereby used for ground ice quantification over scales of 10 metres to a few kilometres. In this contribution, we will present geophysical data and subsequently calculated ground ice contents from several survey sites in the Central Andes, where dry conditions increase the importance of thawing permafrost to future runoff. We will focus on the advantages but also the inherent uncertainties of our geophysical approach, including two measurement techniques (electrical resistivity tomography, refraction seismics) and the petrophysical model used to calculate the ice content (Hauck et al. 2011, Mewes et al. 2017). The effect of spatial variability and measurement uncertainty on estimations of future water release from permafrost regions will be discussed. Hauck, C., Bottcher, M. and Maurer, H. 2011. A new model for estimating subsurface ice content based on combined electrical and seismic data sets. The Cryosphere, 5, 453-468. Mewes, B., Hilbich, C., Delaloye, R., and Hauck, C. 2017. Resolution capacity of geophysical monitoring regarding permafrost degradation induced by hydrological processes, The Cryosphere, 11, 2957-2974, URL: https://doi.org/10.5194/tc-11-2957-2017. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-10605.pdf

2018072763 Hilbich, Christin (University of Fribourg, Department of Geosciences, Geography, Fribourg, Switzerland); Hauck, Christian and Hählen, Nils. Establishing a permafrost monitoring network in the Bernese Alps; geophysical characterisation of potential monitoring sites and validation of permafrost distribution models [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-19479, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Permafrost monitoring has a long tradition in Switzerland and is operational since 2000 within the PERMOS network (www.permos.ch). Distribution of monitoring sites is however not homogeneous with an increased concentration of sites towards the Valais Alps in the West and the Grisons in the East, while the Bernese and Central Alps are underrepresented. The canton of Berne therefore recently initiated the establishment of a long-term permafrost monitoring network within the Bernese Alps, with the main goal to detect and map permafrost occurrences, monitor their long-term evolution and evaluate the probability of natural hazards related to degrading permafrost. As a first step, potential monitoring sites are selected based on the modelled permafrost distribution (Alpine permafrost index map by Boeckli et al. 2012, and Map of potential permafrost distribution by BAFU 2005), and promising sites are investigated by means of geophysical measurements (Electrical Resistivity Tomography/Refraction Seismic Tomography), ground surface temperature measurements as well as geomorphological interpretation. From the joint analysis of all data, propositions for new boreholes are made. In this contribution we will present a data set of more than 20 geophysical profiles from more than 10 new locations (without previous information). As many of the sites of interest are located close to the lower boundary of potential permafrost distribution (~2500 m asl), this extensive geophysical data set can further be used for the validation of existing permafrost distribution models for this region. We here present a comparative analysis of geophysical-based characterisation of the permafrost distribution and the modelled permafrost probability for the respective locations. The results confirm that geophysical surveying presents a cost-effective approach to detect permafrost over larger areas and evaluate permafrost distribution models with an independent data set. References: Boeckli, L.; Brenning, A.; Gruber, A.; Noetzli, J. 2012. Alpine permafrost index map. PANGAEA, URL: https://doi.org/10.1594/PANGAEA.784450, Supplement to: Boeckli, L. et al. 2012. Permafrost distribution in the European Alps: calculation and evaluation of an index map and summary statistics. The Cryosphere, 6, 807-820, URL: https://doi.org/10.5194/tc-6-807-2012 Bundesamt fur Umwelt (BAFU) 2005. Hinweiskarte der potentiellen Permafrostverbreitung in der Schweiz. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-19479.pdf

2018072830 Karamichail, Spyridon (University of Hamburg, Institute of Soil Science, Germany); Schreiber, Peter; Wille, Christian; Holl, David; Rüggen, Norman; Sachs, Torsten and Kutzbach, Lars. Cold season CH4 emissions from polygonal tundra in the Lena River delta, Russia [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-18209, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Arctic permafrost-affected wetlands substantially contribute to the global methane emissions. A major reason for large uncertainties of the emission estimates for the Arctic is the scarcity of land-atmosphere flux measurements during the long cold season. This study focusses on the contribution of the cold season (September-May) to the annual methane budget of polygonal tundra in the North-Siberian Lena River Delta (72°22'N, 126°30'E). Furthermore, it aims at identifying the major environmental drivers for the methane emissions during different freeze-thaw-related periods of the year. Methane emissions were measured by the eddy covariance method from September 2010 to September 2011. Time series of hourly methane emissions were related to meteorological variables, i.e. soil and air temperatures, wind speed, barometric pressure, friction velocity, and the time derivative of barometric pressure using a stepwise multiple linear regression analysis. A Monte Carlo method with 50,000 iterations was applied to determine the optimal combination of variables explaining the temporal variability of methane emissions and to create a generalized model for methane emissions for the periods that were not covered by data. We split the year into four freeze-thaw-related periods, namely the refreezing (late September-early December), the frozen (early December-mid-May), the early thawing (mid-May-late June), and the growing period (late June-late September). It was found that barometric pressure, air temperature at 10 m, and friction velocity were the best explanatory variables of the methane emissions during the refreezing period. On the other hand, in the course of the growing period, the corresponding drivers were the soil temperature measured at a water-logged polygon center at 0.15 m depth, the soil temperature measured at the drier soil at a polygon at 0.05 m, and the friction velocity. The results showed that the cold season, consisting of the refreezing and frozen period, contributed to 35% of the annual methane budget. With a climate change scenario and continued warming in the Arctic, a potential increase of the active layer depth may lead to increase of the "zero curtain" period duration. For this reason, measurements and modeling of methane emissions beyond the growing season in the Arctic ecosystems will become an even more important issue in the future. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-18209.pdf

2018072837 Lamontagne-Hallé, Pierrick (McGill University, Department of Earth and Planetary Sciences, Montreal QC, Canada); McKenzie, Jeffrey; Kurylyk, Barret and Zipper, Samuel. How will groundwater discharge patterns in continuous permafrost regions change in a warming climate? [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-10664, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Permafrost strongly influences the storage and movement of groundwater in cold regions by confining ground-water flow to the active zone located above permafrost, to the sub-permafrost aquifer located below permafrost or through perennially unfrozen areas known as taliks. Permafrost thaw due to climate warming modifies hydrological processes by increasing hydraulic conductivity by several orders of magnitude and thereby enhances groundwater storage and hydrological connectivity between aquifers and surface water bodies. While data from previous studies reveal increases in Arctic river baseflow, the hydrogeological processes leading to these changes remain poorly understood. Modelling these changes is a challenge partly due to choices in the design and parameterization of the surface boundary conditions. Herein, we develop an improved set of surface boundary conditions for a coupled heat and groundwater flow numerical model that includes dynamic freezing and thawing processes and to simulate the impacts of climate warming on permafrost distribution and the spatial and seasonal patterns of groundwater discharge. Under a range of conditions simulated, we show a spatial shift in groundwater discharge from upslope to downslope and temporal shift towards the winter season due to the formation of a lateral supra-permafrost talik underlying the active layer. These changes only occur once the lateral talik has reached its full lateral extension therefore suggesting that the thickness of the supra-permafrost aquifer is the main driver of the baseflow variations. Parameters such as subsurface permeability, surface slope, recharge rate and recharge seasonality can influence the timing and the magnitude of the temporal and spatial groundwater discharge variations, but the trajectory of spatial and temporal shifts in groundwater discharge remain the same. These insights help explain observed changes in Arctic baseflow and wetland patterns and are important for water resources and ecosystem management. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-10664-1.pdf

2018072836 Lebedeva, Liudmila (Melnikov Permafrost Institute, Yakutsk, Russian Federation); Makarieva, Olga and Nesterova, Nataliia. Spatial variability of streamflow in continuous permafrost environment in Central Yakutia, Russia [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-16001, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Runoff generation in permafrost environments are controlled by time-variable frozen aquiclude, limited connectivity between surface and ground water, long snow season and period of river ice cover. Although influence of ground thawing/freezing and surface conditions on streamflow generation is not fully understood,both rain and snow are usually assumed to be the main driver of any hydrological events. The study aims at investigation of runoff formation and identification of key hydrological processes at set of close-by watersheds in Central Yakutia, Eastern Siberia, Russia.Nineteen river basins with areas from 40 to 65000 km2, practically all active gauges up to the moment, were chosen for streamflow analysis. Precipitation and air temperature data from 22 meteorological stations were employed for the study.The river basins are characterized by relatively flat topography, dry and cold climate. Mean annual precipitation varies from 240 to 390 mm/year. Mean annual air temperature changes from -7.7 to -11.9 C. Altitude ranges from 60 to 1000 m a.s.l. Permafrost thickness is 200-500 m. Dominant landscape is coniferous taiga. Mean annual flow depth of the studied rivers varies in more than two orders of magnitude from 0.61 to 80 mm/year. High spatial variability of streamflow that far exceeds variability of precipitation suggests that surface conditions could play more important role in runoff generation than rain and snow input. Variation coefficient (Cv) characterizes year-to-year dynamics of streamflow. Cv of rivers with lower flow depth is much higher than "high flow" rivers. Role of different control factors such as geology, permafrost distribution, lakes, contributing areas and others will be discussed. Careful investigation of runoff generation processes is needed for successful modelling strategies and future projections. The study was partially supported by Russian Foundation for Basic Research, projects No 17-05-00926. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-16001.pdf

2018072835 Nesterova, Nataliia (St. Petersburg State University, Institute of Geosciences, Hydrology, St.Petersburg, Russian Federation); Makarieva, Olga; Shikhov, Andrey and Ostashov, Andrey. Aufeis flow and assessment of their role in formation of hydrological regime of North-East Russia [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-603, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Aufeis are an indicator of the complex interconnection of river and groundwater in the permafrost conditions (Sokolov, 1975) and play important hydrological role. The aufeises may cover from 0.4 to 1.3% of basin areas in the Northeast of Russia reaching 4% in the basins of some rivers. In most cases, the share of the aufeis component of annual river flow is about 3-7%. We have chosen for our research three catchments with available runoff data and the information on the location and characteristics of the aufeis within the selected catchments: the Charky river (8290 km2), Suntar river (7680 km2) and Anmangynda river (400 km2) belonging to the Yana, Indigirka and Kolyma River basins respectively. Initial information on aufeis locations within the catchments was adopted from the Cadaster of the aufeis of the North East Siberia of the USSR (1958) and specified by topographic maps and satellite images. Satellite imagery was used also to assess the inter-annual and seasonal dynamics of aufeis within the period of 1999 to 2017. Preliminary comparison of the Cadaster and satellite data at the Charky river basin has shown that some large aufeis are absent in the Cadastre and at the same time there were aufeis which presently are absent in the satellite images. This may indicate the dynamics of aufeis processes in this region which is studied together with meteorological data. There are no complex hydrological models that take into account the role of aufeis in the river runoff generation in an explicit form. We developed and included such algorithm in the Hydrograph model (Vinogradov et al., 2011). The Hydrograph model is suitable for a remote gauged region such as Arctic domain as it allows for a priori assessment of the model parameters. The method of Sokolov to calculate aufeis flow was used and adapted. The method makes it possible to calculate the hydrograph of aufeis-runoff for a long period and individual years. The following initial data are required for calculating the aufeis runoff by this method: the dates of the transition of the mean daily air temperature through 0 in the spring and in the autumn; the sum of positive average daily air temperatures for periods of 10 days; the maximum area of aufeis at the end of winter; the altitude of the aufeis location. The limitations of the method are that the refinement of the values of the parameters of the calculation formulas proposed by Sokolov is practically impossible because of the lack of observational data on the aufeis. As a preliminary result, average calculated values of annual aufeis flow is 13.2% (31.5 mm) at the Charky river and 9.2% (17.4 mm) at the Suntar river which puts aufeis on the one level with such important objects in the runoff formation as the glaciers. We are going to discuss the results of 1) satellite imagery analysis and the assessment of aufeis dynamic and 2) hydrological modelling with the account of aufeis input into runoff generation. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-603.pdf

2018072834 Pohl, Eric (Université Paris-Saclay, LSCE/IPSL, Gif-sur-Yvette, France); Grenier, Christophe; Séjourné, Antoine; Saintenoy, Albane; Fedorov, Alexander and Konstantinov, Pavel. Spatial variability of river thermal imprint on permafrost through combined in situ measurements and 2D hydro-thermal modeling; a case study in Central Yakutia [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-14901, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

A key aspect of global warming in permafrost regions is the associated transport of heat into the ground and its impacts onto permafrost properties, especially in the presence of ground ice. Melting of ground ice in excess induces the formation of thermokarst lakes and their connecting rivers, which, in return, increases the complexity of such natural systems. Such processes primarily affect active layer depth evolution and heat transport into the ground through the presence of water affecting heat transport. Knowledge about these processes is crucial to assess impacts and feedback mechanisms involved in global warming, in particular with respect to carbon transfer. While lakes and related heat transport into the ground have recently gained a lot of attention, the role of river systems and their intricate hydrological characteristics is hardly addressed. However, such river systems play a significant role in the redistribution of heat and water and associated mass transport processes. They also provide a great opportunity to specifically investigate how meteorological variability and resulting river flow, and changes in landscape morphology affect heat transport into the ground and how the river influences the thermal state of a valley. To address these issues, a study site in form of a river valley between two thermokarst lakes was initiated in Central Yakutia in 2012. Measurements include thermal and hydraulic state variables, active layer depths, various soil properties, and were recently complemented by ground penetrating radar and electrical resistivity measurements. We used these data to first calibrate and validate a 2D hydro-thermal model of the soil. In a second step, we investigated how changes in river width, either through variability in meteorological forcing, or in river valley morphology affect the evolution of active layer depths and heat transport into permafrost. The results highlight an intensive spatial variability along the course of the river that could not be assessed by the spatially limited in situ measurements alone. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-14901.pdf

2018072762 Popescu, Razvan (University of Bucharest, GEODAR Research Center for Geomorphology, Geoarchaeology and Paleo-Environments, Bucharest, Romania); Virghileanu, Marina; Vespremeanu-Stroe, Alfred; Savulescu, Ionut; Vasile, Mirela; Cruceru, Nicolae; Mihai, Bogdan and Nedelea, Alexandru. Permafrost distribution modeling in the marginal periglacial environment of Southern Carpathians, Romania [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-1294, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

This study presents the buildup of a high-resolution permafrost distribution model in an attempt to estimate the probable permafrost surfaces in the highest massifs of Southern Carpathians, i.e. Fagaras, Parang and Retezat. Our approach uses accurate land cover maps obtained by NDVI calculation on Sentinel-2 MSI (10 m resolution) and Landsat 8 OLI (pansharpened at 15 m resolution) satellite imagery. Three classes of land cover represented by forest and subalpine shrubs (1), alpine meadows (2) and screes (3) were well delimited. A fourth class (mountain rockwalls) was extracted from the digital elevation model as slopes with declivity above 45°. The field methods applied in the Southern Carpathians in the last decade indicate that permafrost can only possibly occur in rock glaciers, talus slopes and rockwalls and thus we focused on spatially defining these landforms. Debris covered slopes and talus slopes were considered to be scree areas with slope angles between 17°and 45°; they were fairly differentiated using the mean value of surface curvature of each polygon. The former are usually linear or slightly convex in terms of general curvature (-0.03...+0.3) while the latter are more or less concave (<-0.03). It was important to delimit these two landforms because talus slopes present a high permafrost probability due to great thickness and debris sorting (which foster overcooling by chimney circulation and air stratification) while debris covered slopes are permafrost free in Carpathians mainly because of their reduced thickness. We also set the limits for the lower third of the talus slopes which usually contain permafrost by using the 30° slope threshold. The scree areas with slope angles below 17° were considered rock glaciers. The polygons of the three classes (rock glaciers, talus slope base and rock walls) were split upon altitude, aspect and lithology and were assigned to different permafrost probability classes (10-90%) according to the in situ measurements (thermal and geophysical) obtained by our team or from the literature. The results indicate 2D surfaces where permafrost is more or less possible of 5.9 km2 in Retezat, 4.7 km2 in Parang and 2.5 km2 in Fagaras. If we convert the probability classes into a spatial component we can assert that permafrost is more probable on 2.7 km2 in Retezat, 0.9 km2 in Parang and 0.6 km2 in Fagaras. The larger probable permafrost surfaces of Retezat and Parang are attributed to lithology, i.e. the larger occurrence of hard rocks (granodiorites, granites and amphibolites) in comparison to Fagaras, where softer rocks prevail (micaschists and paragneisses, chlorite-sericite schists and crystalline limestones). The largest area of permafrost is found in talus slopes (44-74%) while rock glaciers have a smaller share (20-38%). Probable rockwall permafrost areas are very small in the granitic massif (<2.3%) while it increases to 35% in the crystalline massif of Fagaras. This approach indicated much smaller permafrost areas in comparison to previous studies and we consider it could be applied successfully in other marginal periglacial areas around the world if locally calibrated. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-1294-1.pdf

2018072838 Scheidegger, Johanna (British Geological Survey, Keyworth, United Kingdom); Jackson, Christopher; McEvoy, Fiona and Norris, Simon. Modelling of permafrost and groundwater development in generic geological environments over glacial time-scales [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-18369, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

As part of the safety case for a geological disposal facility for radioactive waste, climate and climatic related processes need to be considered far into the future, which for the United Kingdom is likely to consider a time-scale spanning several glacial cycles. We evaluated the sensitivity of simulated permafrost thickness and dynamics to a variety of climatic, geological and hydrogeological conditions for two generic UK environments, using numerical modelling of coupled heat and fluid flow. The environments considered describe two contrasting geological case studies, consisting of a low permeability basement under a higher permeability sedimentary cover with a high topographic gradient (Case 1), and a low permeability succession with a low topographic gradient (Case 2). Scaling a temperature proxy record to assumed minimum temperatures of 10, 14, 18 and 25°C below present day temperature, the maximum modelled permafrost thickness for Case 1 reached 46, 171, 280, and 528 m, respectively, and for Case 2, 10, 104, 160, and 320 m. Modelled groundwater recharge and discharge decrease considerably during periods of continuous permafrost. Predominantly for Case 1, this results in a drop in hydraulic head beneath the permafrost, and lower groundwater flow rates at depth. The effects of heat advection on maximum permafrost thickness can be significant for Case 1 assuming relatively high permeability of frozen ground, however, for Case 2, no difference in permafrost thickness was found. A constant point source tracer released at depth is simulated and the area affected by this is compared for permafrost and unfrozen conditions. No difference was simulated during permafrost for Case 2, however for Case 1 modelling indicates the discharge of the tracer to the surface stops and the tracer spreads laterally, affecting a larger area than under unfrozen conditions. The tracer concentrates below the permafrost and is then released after the permafrost thaws, resulting then in a higher surface flux than under constantly unfrozen conditions. Heat conduction dominates the temperature regime during permafrost events. The influence of heat advection on local permafrost thickness of a maximum of tens of metres for Case 1 is of minor importance considering the time frame of glacial cycles. However, advective heat flow is important in forming a non-uniform permafrost distribution and the development of taliks. The changing sub-permafrost groundwater regime and discharge locations can fundamentally alter the size and location of an area affected by the flux of a tracer from a point source. The modelling presented here demonstrates that permafrost could extend up to a depth of ~300 m below the surface for the 18°C scenario and, depending on system properties and an exceptionally long cold period, could extend to greater depths. Permafrost formation and related changes to groundwater chemistry could affect the properties of engineered components of a GDF, such as the properties of clay buffer materials, on the longer time-scale; research in this area is continuing. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-18369.pdf

2018072842 Tubini, Niccolo (Universita di Trento, Dipartimento di Ingegneria Civile, Ambientale e Meccanica, Trento, Italy); Rigon, Riccardo; Gruber, Stephan and Casulli, Vincenzo. New insights in modeling coupled surface-subsurface flow in glacial and periglacial catchments [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-13980, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

A challenge in modeling the hydrological response of a glacial and periglacial catchment is represented by a properly land surface scheme (Walvoord, 2016). In this abstract, we focus on the interaction between the surface and ground water flow. The infiltration rate through the ground surface is driven by the meteorological forcing and the soil hydraulic conductivity of the uppermost layer of the soil. The latter, in turn is significantly reduced by the presence of the permafrost and seasonally frozen soil (Bogaart, 2003). This affects the runoff production, and the energy balance of the ground since water flow carries a significant amount of heat. This for its part has a positive feedback on the ice thawing and hence on the soil hydraulic conductivity. Thus, for these reasons the equation for freezing soil mass budget (called generalized Richards equation) based on the freezing equals drying hypothesis (Miller, 1965) has to be extended to couple the surface and subsurface flow. This can be achieved by using the new coupled surface-subsurface model presented in (Casulli, 2017). Finally there is the application of new techniques based on the double nested Newton algorithm (Casulli, 2010) to integrate the coupled equations of water and energy budgets. References: Bogaart, Patrick W., Gregory E. Tucker, and J. J. De Vries. "Channel network morphology and sediment dynamics under alternating periglacial and temperate regimes: a numerical simulation study." Geomorphology 54.3 (2003): 257-277. Casulli, Vincenzo. "A coupled surface-subsurface model for hydrostatic flows under saturated and variably saturated conditions." International Journal for Numerical Methods in Fluids 85.8 (2017): 449-464. Casulli, Vincenzo, and Paola Zanolli. "A nested Newton-type algorithm for finite volume methods solving Richards' equation in mixed form." SIAM Journal on Scientific Computing 32.4 (2010): 2255-2273. Walvoord, Michelle A., and Barret L. Kurylyk. "Hydrologic impacts of thawing permafrost-A review." Vadose Zone Journal 15.6 (2016). Miller, R. "Phase equilibria and soil freezing, in: Permafrost: Proceedings of the Second International Conference." Washington DC: National Academy of Science-National Research Council 287 (1965): 193-197 [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-13980.pdf

2018072831 van Winden, Elise (Wageningen University & Research, Department of Environmental Science, Wageningen, Netherlands); van der Ploeg, Martine and Bense, Victor. Cryohydrogeology and associated carbon transport resulting from deep permafrost degradation [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-18982, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Deep permafrost holds both ice and organic matter, which comes available for transport and degradation when it warms and subsequently thaws. Currently continuous permafrost areas undergo warming with deepening of the active layer and increase in the number and size of taliks in the transition towards a more discontinuous permafrost system. Both processes will propagate deep groundwater flow. As a consequence, it is expected that more organic matter will be available for transport via groundwater flow towards surface water where it can degrade and enhance CO₂ and CH₄ fluxes towards the atmosphere. At the same moment, timing of peak flow and magnitudes of base flow in nearby streams and rivers will shift. This will likely have profound socio-economic consequences when these areas are part of the source areas of important river systems such as the Yellow river or Lena river. Cryohydrogeological processes are central in this process whilst it is not well known how water and solutes are transported through thawing permafrost. Numerical models are hardly constrained by field- and/or laboratory measured parameters that control coupled energy- water-, and solute transport in thawing permafrost. We address the question as to how organic matter will be released and transported by the reactivation of groundwater flow and the consequent deepening of groundwater flow paths that are to be expected in areas of permafrost degradation. Sediment samples with known grain size, organic matter and pore ice content, will be thawed under controlled conditions. The breakthrough of meltwater and dissolved solutes will be monitored which will be related to spatial variation in pressure, moisture content and temperature inside the sample. This laboratory technique will allow to run a series of experiments using a range of sediment types in which the grain size, organic matter content and moisture content is controlled during the preparation of the soil sample. When the effect of these soil variables is known, the second step will be using field samples from different world wide permafrost locations (e.g. North Sweden, Tibetan Plateau) for validation. The project has recently started and the preliminary results will be presented. The outcomes are expected to create insight in parameters which can be used for permafrost hydrogeology modelling of remote field sites to get a better understanding of future climate feedback due to changes in carbon release and degradation. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-18982.pdf

2018072840 Westermann, Sebastian (University of Oslo, Department of Geosciences, Oslo, Norway); Aas, Kjetil; Martin, Leo; Nitzbon, Jan; Kristiansen, Havard; Langer, Moritz; Kaiser, Soraya; von Deimling, Thomas Schneider; Boike, Julia; Lee, Hanna and Etzelmüller, Bernd. Towards representing small-scale changes in permafrost hydrology in Earth System Models [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-9625, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

Field observations from a range of permafrost landscapes convincingly show that melting of ground ice can lead to modifications of the drainage regime so that soil moisture conditions can radically change in short time. This not only leads to significant changes in the carbon turnover, but can also trigger further permafrost thaw through complicated feedback loops. Representation of small-scale interactions between hydrology and ground thermal state are a crucial prerequisite for credible projections on a future permafrost carbon feedback. However, the present generation of Earth System Models, based on single column ground models representing coarse grid cells, can not account for such processes, although spatial heterogeneity is to a certain extent represented by means of tiling. Aiming for structural changes to overcome these challenges, we present the concept of "interacting tiles" developed in the Permanor, COUP and PermaRisk projects: by coupling tiles through lateral fluxes of heat, water and snow, it becomes possible to explicitly represent changes of microtopography, drainage regime and soil water contents triggered by melting ground ice. Simulations with the CryoGrid permafrost model and the Noah-MP land surface scheme suggest that "interacting tiles" is capable of representing a range of thaw phenomena in strongly different permafrost landscapes, ranging from lateral erosion of peat plateaus (sporadic permafrost) to formation of thermokarst ponds and ice-wedge degradation in polygonal tundra (continuous permafrost). Using field observations from permafrost landscapes, we discuss prospects and challenges for application in coupled circulation models, focusing on model architecture and possibilities for model calibration/validation with field and remote sensing data sets. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-9625.pdf

2018072847 Wiehle, Stefan (DLR, Maritime Security Laboratory, Bremen, Germany); Pleskachevsky, Andrey; Frost, Anja and Dobrynin, Mikhail. Geophysical and morphological processes in the Arctic coastal regions and marginal ice zone by using remote sensing data [abstr.]: in European Geosciences Union general assembly 2018, Geophysical Research Abstracts, 20, Abstract EGU2018-17847, 2018. Meeting: European Geosciences Union general assembly 2018, April 8-13, 2018, Vienna, Austria.

The Arctic experiences a significant impact of ongoing climate change resulting in an increase of air and water temperature, sea-ice loss and changes in the ocean and atmospheric circulation, temperature and wind distribution. These lead to changes in factors driving seabed and coastal erosion, likely to its acceleration in the shallow Arctic regions such as the Laptev Sea and East Siberian Sea. In the context of a changing sea ice and wave climate, the build-up of ocean waves in ice-free parts of the Arctic seas and their impact on both the coastline and marginal ice zone gains growing attention. In these regions, the coastline consists to a large extent of permafrost. The increase of the erosion rate of the coastline will increase the release of organic and inorganic matter from permafrost. Automatic methods were developed to distinguish land from water and retrieve the coastline at the time of acquisition based on contrast and brightness of space borne SAR (Synthetic Aperture Radar) images. Due to their high resolution, daylight and weather independency, and global coverage, space borne SAR is particularly suitable for coastal regions in the Arctic. The Copernicus Sentinel-1 A/B SAR satellites cover these latitudes with acquisition strips extending thousand kilometres with 10 m resolution in the Interferometric Wide Swath Mode (IW), each image with an approximate size of 200 km´250 km. All acquisitions are accessible through the Sentinel data archive; this allows monitoring coastal processes retroactively in most areas of the world. Also, a new algorithm and processor for meteo-marine parameter estimation from Sentinel-1 (S1) imagery were developed. Surface wind speed, sea state parameters, and coastline can be estimated simultaneously from the same IW SAR image and used, e.g., for validation of numerical simulations. This study is focused on coastline dynamics with connection to sea state conditions and ice situation both from satellite data and numerical model results. Sentinel-1 acquisitions with processed coastlines of the New Siberian Islands in the Laptev Sea for different seasons are presented. [Copyright Author(s) 2018. CC Attribution 4.0 License: https://creativecommons.org/licenses/by/4.0/legalcode]

URL: http://meetingorganizer.copernicus.org/EGU2018/EGU2018-17847.pdf

2018067746 Cuozzo, Nicolas (University of Washington at Seattle, Department of Earth and Space Sciences, Seattle, WA); Sletten, Ronald S.; Hu, Yan and Teng, Fang-Zhen. Chemical weathering in permafrost assessed using magnesium isotopes [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 338-12, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.

While it is recognized that chemical weathering occurs in permafrost soils, there are few studies that document in-situ weathering of the frozen sediment. This study analyzes the chemical composition, including magnesium isotopes, that have accumulated in the ice phase of a 30-meter permafrost core collected in the Antarctic Dry Valleys. This study reveals that Mg is sourced from two end members with distinct isotopic signatures: (1) marine aerosols that are captured and deposited by snowfall, and (2) chemical weathering of dolerite. Weathering products accumulate in the ice and have Mg isotopic values between the compositions of the two end members. The conditions under which chemical weathering occur is characterized by measured temperatures, soluble salt concentrations, pH, rock-ice ratios, Mg isotopes, and modeled unfrozen water content using the chemical thermodynamic models, PHREEQC and FREZCHEM. The data reveal that Mg isotopic ratios and core composition change abruptly at 7 meters. The Mg isotopic values in the upper 7 meters follow a mixing curve of the two Mg end members. The upper 7 meters are characterized by seasonal temperatures rising above -20°C, with higher soluble salt concentrations, pH values, rock-ice ratios, and percentage of unfrozen water content compared to below 7 meters. Below 7 meters, Mg isotopic values fall within the range of the marine aerosol end member with little deviation. The results show chemical weathering occurring in the upper 7 meters and provide evidence of the degree and potentially the rate of chemical weathering in permafrost. Primary controls on chemical weathering are the rock-ice ratios and the amount of unfrozen water, which is dependent on both temperature and the soluble salt concentrations.

2018069981 Perryman, Clarice R. (University of New Hampshire, Department of Earth Sciences, Durham, NH); Kashi, Natalie N.; McCalley, Carmody K.; Malhotra, Avni and Varner, Ruth K. Methane oxidation kinetics provide insight to methanotrophy in a thawing permafrost peatland [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 157-8, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.

Rising summer temperatures are accelerating permafrost thaw in the subarctic, increasing methane (CH₄) production and emissions from permafrost peatlands. Methanotrophic bacteria in these peatlands can consume CH₄, mitigating total CH₄ emissions. Under anaerobic conditions, CH₄ concentration controls the rate of bacterial CH₄ consumption. The amount of available below ground CH₄ varies across the permafrost landscape, increasing from near-atmospheric level in palsa mounds, where permafrost still exists within 1 m of ground surface, to near-percent level in fully thawed fens. As methane-oxidizing bacteria are the only biological sink of CH₄ it is critical to constrain the kinetic parameters of CH₄ oxidation in thawing permafrost peatlands. Laboratory incubations of peat were employed to measure the uptake rates of CH₄ oxidation in three environments in Stordalen Mire (68°21'N, 18°49'E): palsa, semi-wet sphagnum, and open-water sedge. Peat cores were extracted and incubated at 10°C under a range of headspace CH₄ concentrations from 100 to 10,000 parts per million by volume (ppmv). Headspace samples were collected over a 24-hour period and analyzed for CH₄ concentration using flame ionization detection gas chromatography (GC-FID). Net CH₄ uptake was observed under all experimental treatments. Palsa peat had the lowest potential CH₄ oxidation rates across all treatments and the lowest maximum oxidation potential (V_max=0.00098 umol CH₄/g*hr). Peat from open water sedge locations had the highest potential CH₄ oxidation rates across all treatments as well as the highest V_max (0.0942 umol CH₄/g*hr). Semi-wet sphagnum sites had a larger Michaelis-Menten constant than sedge sites (26148.4 umol CH₄ vs 11156.8 umol CH₄), indicating that sphagnum sites require higher below ground CH₄ concentrations to reach their V_max than sedge sites, despite having a lower V_max. Sphagnum sites also had the highest apparent CH₄ concentration threshold (Th_a) for CH₄ oxidation; palsa and sedge sites had similar Th_a values. These results suggest that communities of low and high affinity methanotrophic bacteria may overlap in permafrost peatlands, allowing CH₄ oxidation at a variety of below ground CH₄ concentrations. Microbial analyses will further elucidate controls on CH₄ oxidation across the thaw gradient.

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