|
14071745 Barker, Amanda J. (U. S. Army Cold Regions Research and Engineering Laboratory, Ft. Wainwright, AK); Douglas, T. A.; Jacobson, A. D.; McClelland, J. W.; Ilgen, A. G.; Khosh, M. S.; Lehn, G. O. and Trainor, T. P. Late season mobilization of trace metals in two small Alaskan Arctic watersheds as a proxy for landscape scale permafrost active layer dynamics: Chemical Geology, 381, p. 180-193, illus. incl. 5 tables, sketch map, 51 ref., August 14, 2014.
Increasing air temperatures in the Arctic have the potential to degrade permafrost and promote the downward migration of the seasonally thawed active layer into previously frozen material. This may expose frozen soils to mineral weathering that could affect the geochemical composition of surface waters. Determining watershed system responses to drivers such as a changing climate relies heavily on understanding seasonal controls on freshwater processes. The majority of studies on elemental concentrations in Arctic river systems have focused on sampling only from spring snowmelt to the summer season. Consequently, there remains a limited understanding of surface water geochemistry, particularly with respect to trace metals, during late fall and early winter. To examine the variability of metal concentrations as a function of seasonality, we measured trace metal concentrations from spring melt to fall freeze-up in 2010 in two high Arctic watersheds: Imnavait Creek, North Slope, Alaska and Roche Mountanee Creek, Brooks Range, Alaska. We focused on aluminum (Al), barium (Ba), iron (Fe), manganese (Mn), nickel (Ni) and zinc (Zn). Concentrations of 'dissolved' (< 0.45 mm) Al, Ba, Fe, and Mn in Imnavait Creek waters and Ba in Roche Mountanee waters were highest in late fall/early winter. To link observed surface water concentrations at Imnavait Creek to parent soil material we analyzed the elemental composition of a soil core from the watershed and tracked the soil temperatures as a function of time and depth. The results from this study show a distinct seasonal signature of trace metal concentrations in late fall that correlates with the depth of the thawed active layer. Abstract Copyright (2014) Elsevier, B.V.
DOI: 10.1016/j.chemgeo.2014.05.012
14071462 Barnhart, Katherine R. (University of Colorado Boulder, Department of Geological Sciences, Boulder, CO); Anderson, Robert S.; Overeem, Irina; Wobus, Cameron; Clow, Gary D. and Urban, Frank E. Modeling erosion of ice-rich permafrost bluffs along the Alaskan Beaufort Sea coast: Journal of Geophysical Research: Earth Surface, 119(F5), p. 1155-1179, illus. incl. 2 tables, May 2014.
The Arctic climate is changing, inducing accelerating retreat of ice-rich permafrost coastal bluffs. Along Alaska's Beaufort Sea coast, erosion rates have increased roughly threefold from 6.8 to 19 m yr-1 since 1955 while the sea ice-free season has increased roughly twofold from 45 to 100 days since 1979. We develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice-free season, sea level, water temperature, nearshore wavefield, and permafrost temperature in controlling erosion rates in this setting. The model captures the processes of erosion observed in short-term monitoring experiments along the Beaufort Sea coast, including evolution of melt notches, topple of ice wedge-bounded blocks, and degradation of these blocks. Model results agree with time-lapse imagery of bluff evolution and time series of ocean-based instrumentation. Erosion is highly episodic with 40% of erosion is accomplished during less than 5% of the sea ice-free season. Among the formulations of the submarine erosion rate we assessed, we advocate those that employ both water temperature and nearshore wavefield. As high water levels are a prerequisite for erosion, any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion. The certain increases in sea level and potential changes in storminess will both contribute to this effect. As water temperature also influences erosion rates, any further expansion of the sea ice-free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates. Abstract Copyright (2014) American Geophysical Union. All Rights Reserved.
DOI: 10.1002/2013JF002845
14071298 Guglielmin, Mauro (Insubria University, Department of Theoretical and Applied Sciences, Varese, Italy); Dalle Fratte, Michele and Cannone, Nicoletta. Permafrost warming and vegetation changes in continental Antarctica: Environmental Research Letters, 9(4), Paper no. 045001, illus. incl. 2 tables, sketch map, 77 ref., April 2014.
Continental Antarctica represents the last pristine environment on Earth and is one of the most suitable contexts to analyze the relations between climate, active layer and vegetation. In 2000 we started long-term monitoring of the climate, permafrost, active layer and vegetation in Victoria Land, continental Antarctica. Our data confirm the stability of mean annual and summer air temperature, of snow cover, and an increasing trend of summer incoming short wave radiation. The active layer thickness is increasing at a rate of 0.3 cm y-1. The active layer is characterized by large annual and spatial differences. The latter are due to scarce vegetation, a patchy and very thin organic layer and large spatial differences in snow accumulation. The active layer thickening, probably due to the increase of incoming short wave radiation, produced a general decrease of the ground water content due to the better drainage of the ground. The resultant drying may be responsible for the decline of mosses in xeric sites, while it provided better conditions for mosses in hydric sites, following the species-specific water requirements. An increase of lichen vegetation was observed where the climate drying occurred. This evidence emphasizes that the Antarctic continent is experiencing changes that are in total contrast to the changes reported from maritime Antarctica. Copyright 2014 IOP Publishing Ltd
DOI: 10.1088/1748-9326/9/4/045001
14071300 Hayes, Daniel J. (Oak Ridge National Laboratory, Climate Change Science Institute and Environmental Sciences Division, Oak Ridge, TN); Kicklighter, David W.; McGuire, A. David; Chen, Min; Zhuang, Qianlai; Yuan, Fengming; Melillo, Jerry M. and Wullschleger, Stan D. The impacts of recent permafrost thaw on land-atmosphere greenhouse gas exchange: Environmental Research Letters, 9(4), Paper no. 045005, illus. incl. 1 table, 60 ref., April 2014.
Permafrost thaw and the subsequent mobilization of carbon (C) stored in previously frozen soil organic matter (SOM) have the potential to be a strong positive feedback to climate. As the northern permafrost region experiences as much as a doubling of the rate of warming as the rest of the Earth, the vast amount of C in permafrost soils is vulnerable to thaw, decomposition and release as atmospheric greenhouse gases. Diagnostic and predictive estimates of high-latitude terrestrial C fluxes vary widely among different models depending on how dynamics in permafrost, and the seasonally thawed "active layer" above it, are represented. Here, we employ a process-based model simulation experiment to assess the net effect of active layer dynamics on this "permafrost carbon feedback" in recent decades, from 1970 to 2006, over the circumpolar domain of continuous and discontinuous permafrost. Over this time period, the model estimates a mean increase of 6.8 cm in active layer thickness across the domain, which exposes a total of 11.6 Pg C of thawed SOM to decomposition. According to our simulation experiment, mobilization of this previously frozen C results in an estimated cumulative net source of 3.7 Pg C to the atmosphere since 1970 directly tied to active layer dynamics. Enhanced decomposition from the newly exposed SOM accounts for the release of both CO2 (4.0 Pg C) and CH4 (0.03 Pg C), but is partially compensated by CO2 uptake (0.3 Pg C) associated with enhanced net primary production of vegetation. This estimated net C transfer to the atmosphere from permafrost thaw represents a significant factor in the overall ecosystem carbon budget of the Pan-Arctic, and a non-trivial additional contribution on top of the combined fossil fuel emissions from the eight Arctic nations over this time period. Copyright (Copyright) 2014 IOP Publishing Ltd
DOI: 10.1088/1748-9326/9/4/045005
14071299 Lamoureux, Scott F. (Queen's University, Department of Geography, Kingston, ON, Canada) and Lafrenière, Melissa J. Seasonal fluxes and age of particulate organic carbon exported from Arctic catchments impacted by localized permafrost slope disturbances: Environmental Research Letters, 9(4), Paper no. 045002, illus. incl. 2 tables, sketch maps, 33 ref., April 2014.
Projected warming is expected to alter the Arctic permafrost regime with potential impacts on hydrological fluxes of particulate organic carbon (POC) and sediment. Previous work has focused on large Arctic basins and revealed the important contribution of old carbon in river POC, but little is known about POC fluxes from smaller coastal watersheds, particularly where widespread postglacial raised marine sediments represent a potential source of old soil carbon that could be mobilized by permafrost disturbance. To evaluate these processes, the characteristics of POC, particulate nitrogen (PN) and suspended sediment transport from paired small coastal Arctic watersheds subject to recent permafrost disturbance were investigated at the Cape Bounty Arctic Watershed Observatory (CBAWO) in the Canadian High Arctic. Approximately 2% of the total suspended sediment load from both watersheds was composed of POC and the majority of the sediment and POC fluxes occurred during the spring snowmelt period. Radiocarbon analysis of POC indicates recent permafrost disturbances deliver substantially older POC to the aquatic system. Localized permafrost slope disturbances have a measurable influence on downstream POC age and dominate (estimated up to 78% of POC) sediment fluxes during summer baseflow. The elevation of disturbances and Holocene emergence data show limited age sensitivity of POC to the location of disturbance and suggest slope failures are likely to deliver carbon with a relatively similar age range to the aquatic system, regardless of landscape location. Copyright 2014 IOP Publishing Ltd
DOI: 10.1088/1748-9326/9/4/045002
14073262 Gresov, A. I. (Russian Academy of Sciences, Far Eastern Division, Il'ichev Oceanological Institute, Vladivostok, Russian Federation); Obzhirov, A. I. and Yatsuk, A. V. Geostrukturnyye zakonomernosti raspredeleniya merzloty v uglenosnykh basseynakh severo-vostoka Rossii [Structural aspects of permafrost distribution in coal basins of northeastern Russia]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 3-11 (English sum.), illus. incl. sect., 1 table, sketch map, 25 ref., March 2014.
The results of cryological researches and study of gas presence in the coal basins of North-East Russia have been summarized and analyzed. The six basic regularities of the distribution of natural gas and permafrost, changeability of heat and methane flows, gas cryological zonality, gas composition and gas permeability of coal formations in permafrost have been determined.
14073509 Hipp, T. (University of Oslo, Department of Geosciences, Oslo, Norway); Etzelmuller, B. and Westermann, S. Permafrost in alpine rock faces from Jotunheimen and Hurrungane, southern Norway: Permafrost and Periglacial Processes, 25(1), p. 1-13, illus. incl. 2 tables, geol. sketch maps, 39 ref., March 2014.
The warming and degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. In the mountains of southern Norway (Jotunheimen), an increase in ground temperatures has been recorded during the last 12 years, and modeling studies suggest the possible degradation of most mountain permafrost during the 21st century. To better estimate the thermal state of permafrost in steep rock walls in Norway, five temperature loggers were installed in 2009 and 2010, measuring the near-surface rock wall temperatures in vertical rock faces. Surface temperatures in rock walls in Norway are on average higher than the ambient air temperature, by about 1 °C in shaded faces to more than 3 °C in faces with other aspects. An aspect dependency of rock wall temperatures is mainly visible during summer, with deviations of up to 4 °C between north- and south-facing walls. Based on a 1D transient heat flow model, the active-layer thickness at the study sites was estimated to be in the range of 3 m to 5 m at 2300 m asl and 1600 m asl, respectively. As a first-order approximation, a spatial regression model based on elevation and potential incoming short-wave radiation was used to estimate the lower limit and distribution of rock wall permafrost under present-day conditions and for a scenario with average air temperatures increased by 2 °C. Today, the lower limit ranges from 1200-1300 m asl to 1600-1700 m asl in north- and south-facing rock walls, respectively. With a warming of 2 °C, the lower limit would increase to about 1700 m and 2100 m, respectively, which corresponds to a loss of 70 per cent of the rock walls underlain by permafrost today in the study area, where more than half of the rock walls potentially containing permafrost are situated below 1800 m asl. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1799
14073510 Kanevskiy, Mikhail (University of Alaska Fairbanks, Fairbanks, AK); Jorgenson, Torre; Shur, Yuri; O'Donnell, Jonathan A.; Harden, Jennifer W.; Zhuang, Qianlai and Fortier, Daniel. Cryostratigraphy and permafrost evolution in the lacustrine lowlands of west-central Alaska: Permafrost and Periglacial Processes, 25(1), p. 14-34, illus. incl. strat. cols., sects., 2 tables, sketch map, 83 ref., March 2014.
The influence of permafrost growth and thaw on the evolution of ice-rich lowland terrain in the Koyukuk-Innoko region of interior Alaska is fundamental but poorly understood. To elucidate this influence, the cryostratigraphy and properties of perennially frozen sediments from three areas in this region are described and interpreted in terms of permafrost history. The upper part of the late Quaternary sediments at the Koyukuk and Innoko Flats comprise frozen organic soils up to 4.5 m thick underlain by ice-rich silt characterized by layered and reticulate cryostructures. The volume of visible segregated ice in silt locally reaches 50 per cent, with ice lenses up to 10 cm thick. A conceptual model of terrain evolution from the late Pleistocene to the present day identifies four stages of yedoma degradation and five stages of subsequent permafrost aggradation-degradation: (1) partial thawing of the upper ice wedges and the formation of small shallow ponds in the troughs above the wedges; (2) formation of shallow thermokarst lakes above the polygons; (3) deepening of thermokarst lakes and yedoma degradation beneath the lakes; (4) complete thawing of yedoma beneath the lakes; (5) lake drainage; (6) peat accumulation; (7) permafrost aggradation in drained lake basins; (8) formation of permafrost plateaus; and (9) formation and expansion of a new generation of thermokarst features. These stages can occur in differing places and times, creating a highly complex mosaic of terrain conditions, complicating predictions of landscape response to future climatic changes or human impact. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1800
14073514 Pan Xicai (Chinese Academy of Sciences, Laboratory of Frozen Soils Engineering, Lanzhou, China); You Yanhui; Roth, Kurt; Guo Lei; Wang Xinbing and Yu Qihao. Mapping permafrost features that influence the hydrological processes of a thermokarst lake on the Qinghai-Tibet Plateau, China: Permafrost and Periglacial Processes, 25(1), p. 60-68, illus. incl. sects., sketch maps, 47 ref., March 2014.
Climate warming has been observed for some time in the permafrost regions on the Qinghai-Tibet Plateau (QTP), China, resulting in active layer thickening, shrinkage or expansion of thermokarst lakes, and reduced permafrost extent. Little is known, however, about the hydrological processes near thermokarst lakes and their influences on lake development. We employed ground-penetrating radar (GPR) profiling, topographic mapping and drilling to explore the interaction between hydrological processes and thermokarst lake development at a site on the QTP. The GPR data and borehole water-level measurements revealed spatio-temporal variation of the frost table and soil water storage, and indicated the main direction of subsurface flow through soil on hillslopes near the lake. The measurements hinted at the self-organized formation of lateral flow channels at the thawing frost table near the lake. The ensuing recharge of the lake is balanced by drainage from the deepest end of the lake, down the topographic gradient, as ascertained by coring and lake bed mapping. Such a process-based qualitative understanding is crucial for assessing the impact of climate change, in conjunction with the local topography and hydrogeology, on the evolution of thermokarst lakes on the QTP. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1797
14073511 Wu Xiaodong (Chinese Academy of Sciences, State Key Laboratory of Cryospheric Sciences, Cryosphere Research Station on the Qinghai-Tibetan Plateau, Lanzhou, China); Fang Hongbing; Zhao Lin; Wu Tonghua; Li Ren; Ren Zhengwei; Pang Qiangqiang and Ding Yongjian. Mineralisation and changes in the fractions of soil organic matter in soils of the permafrost region, Qinghai-Tibet Plateau, China: Permafrost and Periglacial Processes, 25(1), p. 35-44, illus. incl. 3 tables, sketch map, 54 ref., March 2014.
To determine the relationship between soil organic matter (SOM) decomposition and chemistry in the permafrost region of the Qinghai-Tibet Plateau (QTP), 300-day laboratory incubations at 25°C and chemical fractionation were performed to characterize the mineralization dynamics of organic carbon from soils under five vegetation conditions. The respiration rates in wet meadows were the highest, followed by the Kobresia pygmaea meadow and K. robusta meadow. After the incubation period, all four fractions of SOM--non-polarity soluble, water soluble, holocellulose and lignin contents--showed some decline, and the SOM decreased by 16-20 per cent in soils of the steppe, meadow and wet meadow. These results suggest that a large proportion of the organic matter in soils of the permafrost region in the QTP is mineralizable. Based on the changes in chemical fractions of organic matter, it could be determined that soils with higher water-soluble fractions had higher rates of carbon mineralization, while the mechanisms involved in the respiration of different chemical fractions are complicated. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1796
14073776 Sobota, Ireneusz (Nicolaus Copernicus University, Faculty of Earth Sciences, Department of Hydrology and Water Management, Torun, Poland) and Nowak, Marcin. Changes in the dynamics and thermal regime of the permafrost and active layer of the high Arctic coastal area in north-west Spitsbergen, Svalbard: Geografiska Annaler. Series A: Physical Geography, 96(2), p. 227-240, illus. incl. 3 tables, sketch maps, 52 ref., June 2014.
In this paper changes in the active layer of the high arctic coastal area in north-west Spitsbergen, Svalbard are described. Analysis includes both the ground thawing depth and its near-surface thermal structure. The study was conducted on the Kaffioyra Plain (Svalbard) at several fixed sites, which represent places typical of the region: a sandy beach, a tundra plain and a moraine ridge. The results show that in recent years, at two measurement points a significantly deeper thawing was observed. In 1996-2012 on the beach and on the moraine the trend of active layer thickness change was +1.3 cm yr-1 and +2.5 cm yr-1, respectively. Generally, in the years 2008-2012 the mean thickness of the active layer in the Kaffioyra region increased by 3% to 6%. Even at the spatially close sites, within similar environments, there are significant differences in the thickness of the active layer. Measurements show that significant changes also occurred in the thawed ground temperature. Mean values of the observed near-surface temperature in recent years (2007-2011) were higher by more than 1.0°C, in comparison to the mean in the late 1970s. Abstract Copyright (2014), Swedish Society for Anthropology and Geography.
DOI: 10.1111/geoa.12045
14071012 Alonso, Victoria and Liaudat, Darío Trombotto. Mapping and permafrost altitudes in a periglacial environment; the Laguna del Diamante Reserve (Central Andes, Argentina): Zeitschrift für Geomorphologie, 57(2), p. 171-186, 12 ref., June 2013.
DOI: 10.1127/0372-8854/2012/0098
14073740 Pastick, Neal J. (Stinger Ghaffarian Technologies, Sioux Falls, SD); Rigge, Matthew; Wylie, Bruce K.; Jorgenson, M. Torre; Rose, Joshua R.; Johnson, Kristofer D. and Ji, Lei. Distribution and landscape controls of organic layer thickness and carbon within the Alaskan Yukon River basin: Geoderma, 230-231, p. 79-94, illus. incl. 4 tables, sketch maps, 69 ref., October 2014.
Understanding of the organic layer thickness (OLT) and organic layer carbon (OLC) stocks in subarctic ecosystems is critical due to their importance in the global carbon cycle. Moreover, post-fire OLT provides an indicator of long-term successional trajectories and permafrost susceptibility to thaw. To these ends, we 1) mapped OLT and associated uncertainty at 30m resolution in the Yukon River basin (YRB), Alaska, employing decision tree models linking remotely sensed imagery with field and ancillary data, 2) converted OLT to OLC using a non-linear regression, 3) evaluate landscape controls on OLT and OLC, and 4) quantified the post-fire recovery of OLT and OLC. Areas of shallow (<10cm), moderate (>&eq;10cm and <20cm), moderately thick (>&eq;20cm and <30cm), and thick (>&eq;30cm) OLT, composed 34, 20, 14, and 18% of the YRB, respectively; the average OLT was 19.4cm. Total OLC was estimated to be 3.38Pg. A regional chronosequence analysis over 30 years revealed that OLT and OLC increased with stand age (OLT: R2=0.68; OLC: R2=0.66), where an average of 16cm OLT and 5.3kg/m2 OLC were consumed by fires. Strong predictors of OLT included climate, topography, near-surface permafrost distributions, soil wetness, and spectral information. Our modeling approach enabled us to produce regional maps of OLT and OLC, which will be useful in understanding risks and feedbacks associated with fires and climate feedbacks. Abstract Copyright (2014) Elsevier, B.V.
DOI: 10.1016/j.geoderma.2014.04.008
14071940 Mohammed, Aaron A. (University of Western Ontario, Department of Earth Sciences, London, ON, Canada); Schincariol, Robert A.; Nagare, Ranjeet M. and Quinton, William L. Reproducing field-scale active layer thaw in the laboratory: Vadose Zone Journal, 13(8), 9 p., illus., 36 ref., August 2014.
A method to simulate freeze-thaw and permafrost conditions on a large peat-soil column, housed in a biome, was developed. The design limits ambient temperature interference and maintains one-dimensional freezing and thawing. An air circulation system, in a cavity surrounding the active layer, allows manipulation of the lateral temperature boundary by actively maintaining an air temperature matching the average temperature of the soil column. Replicating realistic thermal boundary conditions enabled field-scale rates of active-layer thaw. Radial temperature gradients were small and temperature profiles mimicked those for similar field conditions. The design allows complete control of key hydrologic processes related to heat and water movement in permafrost terrains without scaling requirement; and presents a path forward for the large-scale experimental study of frozen ground processes. Because subarctic ecosystems are very vulnerable to climate and anthropogenic disturbances, the ability to simulate perturbations to natural systems in the laboratory is particularly important.
DOI: 10.2136/vzj2014.01.0008
14073266 Are, F. E. (Russian Academy of Sciences, Siberian Division, Institute of the Cryosphere, Tyumen, Russian Federation). Teplofizicheskiye aspekty printsipa Tsytovicha o ravnovesnom sostoyanii vody i l'da v merzlykh gruntakh [Physical aspects of the Tsytovich's principle of water-ice equilibrium in frozen grounds]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 47-56 (English sum.), illus. incl. 1 table, 42 ref., March 2014.
The applicability of the Stephen problem solutions for permafrost dynamics modeling is discussed using N. A. Tsytovich principle of water and ice equilibrium state in frozen ground. The main external impacts controlling equilibrium, relationships between equilibrium dynamics and thermal processes in ground, possibilities of mathematical modeling of permafrost dynamics reviewed. The dynamics of equilibrium state in saline ground is discussed using results of permafrost investigations on Yamal Peninsula and Laptev Sea shelf. It is revealed that the cryopeg temperature in equilibrium state is equal to its initial freezing point, the ice-bonded permafrost may contain cryopeg and preserve permeability, and the cryopeg boundary may not coincide with the phase boundary. Free-salined permafrost on the shelf flooded by the sea undergoes fast salinization and physicochemical thawing at negative temperature. The thawing is accompanied by temperature lowering due to latent heat absorption. The ice content in salined permafrost on shelf changes in space gradually without a clear phase boundary. It is revealed that the solutions of Stephen problem are unacceptable for shelf permafrost modeling.
14071632 Krautblatter, Michael (Technische Universität München, Chair of Landslide Research, Munich, Germany) and Moore, Jeffrey R. Rock slope instability and erosion; toward improved process understanding: Earth Surface Processes and Landforms, 39(9), p. 1273-1278, illus. incl. 1 table, 73 ref., July 2014.
Rock slopes in a range of environments are among the landscape elements most sensitive to climate change, the latter affecting rock mass properties, altering slope boundary conditions, and changing geosystem configurations. Major climate-dependent influences promoting destabilization include stress redistribution with changing glacial ice extents, degradation of mountain permafrost, altered slope hydrology and weathering environments, loading and unloading due to deposition and erosion, and changes in the spectrum of magnitude and frequency of driving forces. In steep bedrock terrain, erosional processes control slope morphology by modulating rates of: (i) weathering in response to climate and pre-disposition, (ii) rock slope retreat in response to magnitude and frequency of detachment, and (iii) channel incision or valley infilling in response to variable sediment supply. Modelling landscape evolution and anticipating natural hazards in these environments thus requires deeper insights into the processes driving rock slope instability and erosion. This special issue emphasizes new understanding of rock slope processes through a collection of manuscripts at the forefront of research in the field. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/esp.3578
14073772 Ribolini, Adriano (University of Pisa, Dipartimento di Scienze della Terra, Pisa, Italy); Bini, Monica; Consoloni, Ilaria; Isola, Ilaria; Pappalardo, Marta; Zanchetta, Giovanni; Fucks, Enrique; Panzeri, Laura; Martini, Marco and Terrasi, Filippo. Late-Pleistocene wedge structures along the Patagonian coast (Argentina); chronological constraints and palaeo-environmental implications: Geografiska Annaler. Series A: Physical Geography, 96(2), p. 161-176, illus. incl. sect., strat. col., 3 tables, sketch maps, 50 ref., June 2014.
This paper investigates several wedge structures formed in continental deposits covering marine sediments deposited during MIS 5 along the central Patagonian coast of Argentina. The size and surface microtexture characteristics of the infilling sediments are consistent with a depositional environment dominated by aeolian transport. Fragments of Andean volcanic rocks (glass shards) in the wedge-fill suggest long-distance transport via a westerly component of wind direction. The wedges are interpreted as products of deep seasonal frost action in frozen ground, which produced open cracks that filled rapidly with partially non-local aeolian sediments. Many wedges cross cut carbonate crusts that formed under permafrost conditions in coastal Patagonia. The radiocarbon dating of carbonate crusts yielded an age of 25-27 kyr bp, while wedge-fill sediments are OSL dated to 14 670 ± 750 yr bp. This indicates that ground wedge formation occurred during a cold event (the Antarctic Cold Reversal period) that interrupted the permafrost degradation following the Last Glacial Maximum. Abstract Copyright (2014), Swedish Society for Anthropology and Geography.
DOI: 10.1111/geoa.12038
14073294 Thiry, Médard (Mines-Paris Tech, Géosciences, Fontainebleau, France); van Oort, Folkert; Thiesson, Julien and van Vliet-Lanoe, Brigitte. Periglacial morphogenesis in the Paris Basin; insight from geophysical survey and consequences for the fate of soil pollution: Geomorphology, 197, p. 34-44, illus. incl. 1 table, sketch maps, 31 ref., September 1, 2013.
Geophysical survey by Automatic Resistivity Profiling (ARP(C)) system of the Pierrelaye-Bessancourt area revealed remarkable conductive polygon patterns of 20- to 30-m diameter detected between 0.5- and 1.7-m depth. Trenches dug down to the limestone substrate allowed detailing of the pedological and lithological units that compose such polygonal features. The patterns are formed by greenish glauconite and carbonated sand hollows where clay-rich pedological horizons bend downward, forming narrow tongs extending up to 2- to 3-m depth. Such structures were interpreted as a buried polygonal ice-wedge network (thermokarst depressions). Geometrical relationships between the lithological units and consecutive erosional surfaces allowed the identification of successive landscape events and a landscape chronology. The sequence started during the Saalian glaciation with (1) the development of patterned grounds by thermokarstic cryoturbation; (2) the consecutive deflation/erosion during post-permafrost aridity; (3) the loess and eolian sand deposits; (4) the weathering of the former deposits with development of pedogenic horizons during the Eemian interglacial; (5) the recurrent cryoturbation and thermal cracking leading to infolding of the pedogenic horizons during the Pleniglacial optimum (Weichselian); and finally (5) the erosion that levelled the periglacial microreliefs, most probably during the last glacial stage (Weichselian), leading to the modern landscape. In this agricultural area, urban waste water has been spread for more than 100 years by flooding irrigation for food crop production and has led to high levels of metal pollution in the surface horizons of the soils. The polygonal cryogenic structures have major impacts on soil hydrology and dispersion/distribution of heavy metals toward the geological substrate. Such structures are essential to consider when conceiving proposals for future soil management of this polluted area. Abstract Copyright (2013) Elsevier, B.V.
DOI: 10.1016/j.geomorph.2013.04.027
14071459 Balser, Andrew W. (University of Alaska Fairbanks, Department of Biology and Wildlife, Fairbanks, AK); Jones, Jeremy B. and Gens, Rudiger. Timing of retrogressive thaw slump initiation in the Noatak Basin, northwest Alaska, USA: Journal of Geophysical Research: Earth Surface, 119(F5), p. 1106-1120, illus. incl. 4 tables, sketch map, 36 ref., May 2014.
In the North American low arctic, increased retrogressive thaw slump frequency and headwall retreat rates have been linked with climate warming trends since the mid-twentieth century, but specific weather drivers of slump initiation timing are less clear. We examined relationships among retrogressive thaw slump initiation and annual air temperature, precipitation, and snow cover using time series of satellite imagery and weather station data in northwest Alaska. Synthetic aperture RADAR and optical imagery were used to examine retrogressive thaw slump initiation between 1997 and 2010. Over 80% of the slump features examined in this study first appear within a 13 month span from late June 2004 to July 2005. Remote weather station data show that 2004 and 2005 are among several years exhibiting above average thawing indices and average summer temperatures between 1992 and 2011. However, 2004 is distinct from the rest of the record, with unusually warm temperatures primarily occurring early in the thaw season between April and early June, and including two intense precipitation events in May. Regional weather reported by the NOAA National Weather Service also reflects these local findings. Snowmelt timing in 2004 corresponded with warmer air temperatures and precipitation between April and May, exposing the ground surface more than 2 weeks earlier than average for 2001-2012 within the Noatak Basin. Future rates of thaw slump initiation may be linked with changing trends in the timing of weather, in addition to general climate warming. Abstract Copyright (2014) American Geophysical Union. All Rights Reserved.
DOI: 10.1002/2013JF002889
14073267 Gorelik, Ya. B. (Russian Academy of Sciences, Siberian Division, Institute of the Cryosphere, Tyumen, Russian Federation); Romanyuk, S. N. and Seleznev, A. A. Osobennosti rascheta teplovogo sostoyaniya merzlykh gruntov v osnovanii fakel'noy ustanovki [Aspects of thermal regime analysis for frozen grounds in a foundation of gas flare facility]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 57-64 (English sum.), illus., 15 ref., March 2014.
The substantiation of methods for calculating the dynamics of the thermal state of frozen soils in the flare foundation is presented. A distinctive feature of this problem is the presence of the water boiling front higher than the thawing front in the frozen soil. The calculation results show that the depth of thawing of frozen grounds flare for the planned term of its operation is not catastrophic and it can be minimized by using relatively simple technical measures (increasing the height of flare placement, using insulation layer on the surface of the soil etc.).
14073268 Gubin, S. V. (Russian Academy of Sciences, Institute for Physicochemical and Biological Problems of Soil Science, Pushchino, Russian Federation) and Zanina, O. G. Izmeneniye pochvennogo pokrova v khode formirovaniya otlozheniy ledovogo kompleksa na Kolymskoy nizmennosti; Chast' 2 [Variations of soil cover during glacial processes in the Kolyma Lowland; Part 2]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 77-82 (English sum.), 1 table, sketch map, 4 ref., March 2014.
The presence of profiles of one or two types of epigenetic soils of second and third epigenetic stage of the pedogenesis in the ice-complex outcrop of the tundra zone of Kolyma lowland area has been established. The peaty-gley soils and aquatic soils of the flooded polygons are predominant. The comparison of buried soils from the contemporary tundra and the North taiga zones has been made and the existence of the well-determined soil zonality during the second stage of epigenic pedogenesis and the absence of this zonality in the third stage of epigenic pedogenesis has been revealed.
14073512 Kohout, Tomas (University of Helsinki, Department of Physics, Helsinki, Finland); Bucko, Michal S.; Rasmus, Kai; Lepparanta, Matti and Matero, Ilkka. Non-invasive geophysical investigation and thermodynamic analysis of a palsa in Lapland, northwest Finland: Permafrost and Periglacial Processes, 25(1), p. 45-52, illus. incl. sects., sketch map, 25 ref., March 2014.
Non-invasive geophysical prospecting and a thermodynamic model were used to examine the structure, depth and lateral extent of the frozen core of a palsa near Lake Peerajarvi in northwest Finland. A simple thermodynamic model verified that the current climatic conditions in the study area allow sustainable palsa development. A ground penetrating radar (GPR) survey of the palsa under both winter and summer conditions revealed its internal structure and the size of its frozen core. GPR imaging in summer detected the upper peat/core boundary, and imaging in winter detected a deep reflector that probably represents the lower core boundary. This indicates that only a combined summer and winter GPR survey completely reveals the lateral and vertical extent of the frozen core of the palsa. The core underlies the active layer at a depth of ~ 0.6 m and extends to about 4 m depth. Its lateral extent is ~ 15 m ´ ~ 30 m. The presence of the frozen core could also be traced as minima in surface temperature and ground conductivity measurements. These field methods and thermodynamic models can be utilized in studies of climate impact on Arctic wetlands. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1798
14073265 Konovalov, A. A. (Tyumen State University of Oil and Gas, Tyumen, Russian Federation). Fazovyye perekhody i dolgovechnost' merzlogo grunta [Phase transitions and stability of frozen ground]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 31-38 (English sum.), illus. incl. 4 tables, 16 ref., March 2014.
The correlation of the strength of the frozen ground with its temperature, duration of supercooling and temperature of crystallization has been examined. The quantitative evaluation of this correlation has been made.
14073263 Slagoda, E. A. (Russian Academy of Sciences, Siberian Division, Institute of the Cryosphere, Tyumen, Russian Federation); Kurchatova, A. N.; Popov, K. A.; Tomberg, I. V.; Opokina, O. L. and Nikulina, E. L. Kriolitologicheskoye stroyeniye pervoy terrasy ostrova Belyy v Karskom morye; mikrostroyeniye i priznaki kriolitogeneza; Chast' 2 [Cryolithlogical structure on a primary terrace in Belyy Island, Kara Sea; microstructure and cryolithogenic features; Part 2]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 12-22 (English sum.), illus. incl. sect., sketch map, 30 ref., March 2014.
In 2009-2012 the cryological composition of the first marine terrace (Belyy Island, Kara Sea) has been studied. The differences of macro- and microstructure of syncryogenic and epicryogenic saline sediments have been found. The features of taberal sediments (postcryogenic deformation and textures, fragments of pseudomorphoses demonstrating the processes of thawing of syncryogenic sediments) have been identified. According to the peculiarities of freezing, epicryogenic, syncryogenic and parasyncryogenic sequences have been established in the sediments of the first terrace.
14073264 Zabolotnik, S. I. (Russian Academy of Sciences, Siberian Division, Melnikov Permafrost Institute, Yakutsk, Russian Federation) and Zabolotnik, P. S. Usloviya sezonnogo protaivaniya i promerzaniya gruntov v yuzhnoy Yakutii [Conditions of seasonal ground thawing and freezing in southern Yakutia]: Kriosfera Zemli = Earth Cryosphere, 18(1), p. 23-30 (English sum.), illus. incl. sketch maps, 33 ref., March 2014.
Evaluation of geocryological conditions in South Yakutia and analysis of factors controlling the development of seasonally thawing and seasonally freezing layers have been accomplished. Seasonal thaw depth have been computed for four soil types: relatively dry and saturated sands with moisture contents of 5 and 25% and silty loams with moisture contents of 20 and 45%, respectively. The relationships of seasonal thaw depth and latitude/altitude have been revealed. It has been established that the increase in altitude by 1000 m causes a decrease in the depth of seasonal thaw by 0.56-0.68 m in silty loams and by 0.85-1.28 in sands. On the contrary, toward southward, the thaw depth increases per each degree of latitude by 0.064-0.078 m in silty loams and by 0.097-0.143 m in sands. The altitudinal position of the snow line, above which soils never thaws, has been obtained. The rates of seasonal soil thawing are given for different altitudes.
14071094 Zhou Jian (Chinese Academy of Sciecnes, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Pomeroy, John W.; Zhang Wei; Cheng Guodong; Wang Genxu and Chen Chong. Simulating cold regions hydrological processes using a modular model in the west of China: Journal of Hydrology, 509, p. 13-24, illus. incl. 4 tables, sketch maps, 50 ref., February 13, 2014.
The Cold Regions Hydrological Model platform (CRHM), a flexible object-oriented modeling system, was devised to simulate cold regions hydrological processes and predict streamflow by its capability to compile cold regions process modules into purpose-built models. In this study, the cold regions hydrological processes of two basins in western China were evaluated using CRHM models: Binggou basin, a high alpine basin where runoff is mainly caused by snowmelt, and Zuomaokong basin, a steppe basin where the runoff is strongly affected by soil freezing/thawing. The flexibility and modular structure of CRHM permitted model structural intercomparison and process falsification within the same model framework to evaluate the importance of snow energy balance, blowing snow and frozen soil infiltration processes to successful modeling in the cold regions of western China. Snow accumulation and ablation processes were evaluated at Binggou basin by testing and comparing similar models that contained different levels of complexity of snow redistribution and ablation modules. The comparison of simulated snow water equivalent with observations shows that the snow accumulation/ablation processes were simulated much better using an uncalibrated, physically based energy balance snowmelt model rather than with a calibrated temperature index snowmelt model. Simulated seasonal snow sublimation loss was 138mm water equivalent in the alpine region of Binggou basin, which accounts for 47% of 291 mm water equivalent of snowfall, and half of this sublimation loss is attributed to 70mm water equivalent of sublimation from blowing snow particles. Further comparison of simulated results through falsification of different snow processes reveals that estimating blowing snow transport processes and sublimation loss is vital for accurate snowmelt runoff calculations in this region. The model structure with the energy balance snowmelt and blowing snow components performed well in reproducing the measured streamflow using minimal calibration, with R2 of 0.83 and NSE of 0.76. The influence of frozen soil and its thaw on runoff generation was investigated at Zuomaokong basin by comparing streamflow simulated by similar CRHM models with and without an infiltration to frozen soil algorithm. The comparison of simulated streamflow with observation shows that the model which included an algorithm describing frozen soil infiltration simulated the main runoff events for the spring thawing period better than that which used an unfrozen infiltration routine, with R2 of 0.87 and NSE of 0.79. Overall, the test results for the two basins show that hydrological models that use appropriate cold regions algorithms and a flexible spatial structure can predict cold regions hydrological processes and streamflow with minimal calibration and can even perform better than more heavily calibrated models in this region. Given that CRHM and most of its algorithms were developed in western Canada, this is encouraging for predicting hydrology in ungauged cold region basins around the world. Abstract Copyright (2014) Elsevier, B.V.
DOI: 10.1016/j.jhydrol.2013.11.013
14073513 Turner, Kevin W. (Wilfrid Laurier University, Department of Geography and Environmental Studies, Waterloo, ON, Canada); Edwards, Thomas W. D. and Wolfe, Brent B. Characterising runoff generation processes in a lake-rich thermokarst landscape (Old Crow Flats, Yukon, Canada) using d18O, d2H and d-excess measurements: Permafrost and Periglacial Processes, 25(1), p. 53-59, illus. incl. 1 table, sketch map, 31 ref., March 2014.
Application of novel hydrological methods for assessing runoff generation in remote northern landscapes is necessary to identify the consequences of climate variability and change. In Old Crow Flats, a lake-rich thermokarst landscape in northern Yukon Territory (Canada), local land users have concerns over the effects of recent lake drainage and fluctuating river discharge on their traditional way of life. In the absence of hydrometric stations, we evaluate the utility of isotopic monitoring of the lower Old Crow River, which is fed by several tributaries and drains the flats, for tracking runoff generation. Isotopic "snapshots" obtained from 2007, 2008 and 2009 during the recession limb of the spring freshet hydrograph provided characteristic patterns of deuterium excess (d-excess) along the Old Crow River. River sampling in June 2007 captured a pulse of evaporatively enriched lake water originating from a rainfall-triggered catastrophic lake drainage event, identified by decreased d-excess values. June 2008 was marked by negligible variability in d-excess values along the same reach of the river, consistent with minimal export of lake waters after a winter of below-normal snow accumulation. In contrast, rising d-excess values along the study reach in June 2009 indicate enhanced rainfall-generated runoff. River isotope sampling could be used to monitor spatial and temporal variability in runoff generation processes in the Old Crow Flats and other northern lake-rich landscapes drained by rivers. Abstract Copyright (2010), John Wiley & Sons, Ltd.
DOI: 10.1002/ppp.1802
|
|
14073709 Aukes, P. (University of Waterloo, Earth and Environmental Sciences, Waterloo, ON, Canada) and Schiff, S. L. Degradation of dissolved organic carbon from discontinuous permafrost due to photolysis and different inoculants [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0531, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Northern areas with permafrost are very susceptible to a warming climate. Temperature increases can alter hydrologic flow paths, increase the depth and biogeochemistry of the active layer, and degrade and reduce the amount of remaining permafrost. Particularly, loss of permafrost will release large stores of previously unavailable frozen carbon to the environment. Dissolved organic carbon (DOC) plays many important roles that affect both ecosystem health and drinking water quality. Comprised of countless different molecules, DOC absorbs harmful ultra-violet (UV) radiation and controls thermal regimes of lakes, is an important energy and nutrient source for heterotrophic microbes, complexes with and transports heavy metals, and reacts during chlorination of drinking water to form carcinogenic disinfection by-products. Since the ultimate fate of DOC depends on its reactivity with the surrounding environment, the implications of DOC released from permafrost for ecosystems and drinking water quality will vary across the landscape. We used 90-day lab incubations to assess the differences in quality of DOC by observing the susceptibility for DOC to degrade among various discontinuous-permafrost sources. Specifically, UV-photolysis and two surface water inoculants (pond and creek water filtered to 2.0mm) were used to represent the dominant degradation pathways encountered within the environment. Samples were taken in July 2013 from three locations (pond, creek, and wetland porewater) in a region of discontinuous permafrost near Yellowknife, NWT, Canada. We observed changes to the composition and quality of DOC resulting from photolysis and degradation by two inoculants over 90 days, where DOC quality was determined by Liquid Chromatography - Organic Carbon Detection, DOC:DON, UV-absorbance, and changes to other constituents (DIC, d13C-DIC, CO2). We hypothesize that UV-photolysis and microbial degradation will readily degrade easily accessible and reactive components of DOC, leaving behind recalcitrant forms. However, if DOC released from permafrost is of low quality, we hypothesize that the original DOC quality will not significantly change over time. Finally, we hypothesize that photolysis will have the greatest effect upon DOC, regardless of source, while differences from inoculant will be observable in the final DOC composition. These results will allow for a characterization to the quality of DOC released from discontinuous permafrost, and a better understanding to future changes in newly released DOC in the northern environment.
14073676 Bracho, R. G. (University of Florida, Biology, Gainesville, FL); Schuur, E. A.; Pegoraro, E.; Crummer, K. G.; Natali, S.; Zhou, J.; Wu, L.; Luo, Y.; Tiedje, J. M. and Konstantinidis, K. Temperature sensitivity (Q10), and dynamics of soil organic matter (SOM) decomposition in permafrost soils with different carbon quality and under experimental warming [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost soils contain approximately 1700 Pg of carbon (C), twice the amount of C in the atmosphere. Temperatures in higher latitudes are increasing, inducing permafrost thaw and subsequent microbial decomposition of previously frozen C. This process is one of the most likely positive feedbacks to climate change. Understanding the temperature sensitivity (Q10) and dynamics of SOM decomposition under warming is essential to predict the future state of the earth - climate system. Alaskan tundra soils were exposed to two winter warming (WW) seasons in the field, which warmed the soils by 4°C to 40 cm depth. Soils were obtained from three depths (0 - 15, 15 - 25 and 45 - 55 cm) and differed in initial amounts of labile and recalcitrant C. Soils were incubated in the lab under aerobic conditions, at 15 and 25°C over 365 days. Q10 was estimated at 14, 100 & 280 days of incubation (DOI); C fluxes were measured periodically and dynamics of SOM decomposition (C pool sizes and decay rates) were estimated by fitting a two pool C model to cumulative respired C (Ccum, mgC/ginitialC). After two WW seasons, initial C content tended to decrease through the soil profile and C:N ratio was significantly decreased in the top 15 cm. After one year of incubation, Ccum was twice as high at 25°C as at 15°C and significantly decreased with depth. No significant WW field treatment was detected, although Ccum tended to be lower in warmed soils. Labile C accounted for up to 5% of initial soil C content in the top 15 cm and decreased with depth. Soils exposed to WW had smaller labile C pools, and higher labile C decay rates in the top 25 cm. Q10 significantly decreased with time and depth as labile pool decreased, especially for WW. This decrease with time indicates a lower temperature sensitivity of the most recalcitrant C pool. The deepest WW soil layer, where warming was more pronounced, had significantly lower Q10 compared to control soils at the same depth. After two seasons, the warming treatment affected decomposition by reducing labile C pools and increasing its decay rates. Warming also reduced temperature sensitivity, showing acclimation of the most recalcitrant C pool in the tundra ecosystem.
14073694 Delire, C. L. (Centre National de la Recherche Scientifique, Meteó France, Toulouse, France); Decharme, B. and Alkama, R. Simulating the evolution of permafrost in the recent past with the ISBA land surface model [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0515, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
We present here a numerical study of the evolution of permafrost over the N hemisphere land since the 1960s. We used the ISBA land-surface model (Masson et al., 2013). The simulations were done according to a protocol proposed by D. Mc Guire for the "Research Coordination Network on carbon vulnerability in the permafrost. Compared to the estimates of Brown et al., 1998, ISBA represents well the current area of permafrost (defined as the area for which active layer thickness is less than 3 m) with a total area of 22.8 million km2. It also represents reasonably well the distribution of soil organic matter compared to the Harmonised World Soil Database. In the last 40 years, the model simulates a reduction of about 2.8 million km2 while simulating an increase of about 600 gC/m2 of soil organic matter. To understand these changes we performed as suggested by the RCN a few runs keeping one climatic variable (temperature, precipitation or CO2 concentration) at its 1960 levels while allowing the others to change as observed. As expected, the decrease in area is mostly due to the temperature increase since the 1960s. The increase in soil carbon due to a larger increase in NPP than microbial decomposition mostly depends on the atmospheric CO2 increase since 1960 and the lengthening of the growing season. The spinup choice and the way land-use change is treated also play a role in this carbon accumulation.
14073678 Ernakovich, J. G. (Colorado State University, Natural Resource Ecology Laboratory, Fort Collins, CO); Lynch, L. and Wallenstein, M. D. The temperature sensitivity of microbial respiration after permafrost thaw under oxic and anoxic conditions [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-08, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Carbon in permafrost soils may be vulnerable to decomposition under climate warming. The ensuing release of carbon dioxide (CO2) and methane (CH4) into the atmosphere would result in a positive climate feedback. General theory dictates that the activity of biological and chemical reactions doubles for every ten degree increase in temperature. However in Arctic soils, the temperature sensitivity of CO2 production is often larger than two, especially in experiments conducted at field relevant temperatures. Less is known about the temperature sensitivity of microbial CH4 production, which can occur after permafrost thaw if field conditions remain anoxic. We investigated the temperature sensitivity (Q10) of CO2 and CH4 production from thawed permafrost under oxic and anoxic conditions, as well as the effect of the chemical recalcitrance of soil organic matter (SOM) constituents on the Q10 of respiration. We hypothesized that (1) CH4 production under anoxic conditions would be more sensitive to increasing temperature than CO2 production under oxic conditions, and (2) the Q10 of respiration from permafrost with more labile material would be lower than for permafrost with more chemically recalcitrant material. Permafrost soil was collected from Sagwon Hills, Alaska, a region in the continuous permafrost zone. Previously, we found that the top 0-10 cm of the permafrost contained more labile material than "deeper" (16-25 cm) permafrost cores using Fourier-transformed Mid-infrared spectroscopy (FT-IR). The "top" and "deeper" permafrost soils were submitted to oxic and anoxic incubation treatments at 1°C and 15°C for two weeks. CO2 and CH4 were measured and the Q10 was calculated on the cumulative gas flux. After two weeks of incubation, the Q10 of CH4 production was very high (Q10= 25.1+12.7), whereas the Q10 of CO2 production was equal to the theoretical Q10 of 2 (Q10= 2.0+0.3). The depth of the soil affected the Q10 of decomposition, however the results varied by treatment. The oxic process of CO2 production confirmed our hypothesis, such that the deeper permafrost- which contained less labile compounds- had a larger Q10 than the top of the permafrost (p<0.05). Conversely, under anoxic conditions, the top of the permafrost- which contained more labile compounds- had a Q10 seven times larger than the deeper permafrost with less labile compounds (p<0.001). This indicates that some other factor besides chemical recalcitrance governs the Q10 of CH4 production under anoxic conditions. The behavior of the permafrost under anoxic conditions confirms that climate induced permafrost thaw can contribute large amounts of carbon to the atmosphere, and that the mechanisms underlying the temperature sensitivity of respiration need to be explored.
14073699 Harder, S. R. (McGill University, Geography, Montreal, QC, Canada); Roulet, N. T.; Crill, P. M. and Strachan, I. B. Interpreting carbon fluxes in a transient permafrost peatland; scaling from plant scale to ecosystem scale [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0520, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Various microforms make up a heterogeneous peatland complex due to spatial differential thawing of permafrost. This results in significantly different peatland ecosystems across a short distance. Water table level, vegetation cover, ground temperatures and active layer depths vary considerably across the different microforms. We have initiated a series of CO2 fluxes measurements across a heterogeneous peatland complex where we are measuring the fluxes from the scale of plants associations to that of the entire peatland complex. We are examining if it is possible to derive the spatially integrated ecosystem wide fluxes measured from eddy covariance (EC) based on simple light use efficiency (LUE) and ecosystem respiration (ER) models and a knowledge of the spatial variability of the vegetation and water table and active layer depths. The LUE and ER are being developed using several years of continuous autochamber flux measurements for the three major plant functional types (PFTs) in the Stordalen peatland in northern Sweden (68°22'N, 19°03'E). An EC flux measurement system has been measuring the CO2 at the centre of the palsa complex since 2008. Lidar was used to produce a 1 m resolution digital evaluation model of the complex. Continuous water table depths have been measured for four years at over 40 locations in the complex, and peat temperatures and active layer depths in surveyed every 10 days at more than 100 locations. High resolution digital colour air photography is being used to map the various vegetation classes. The EC footprint is calculated for every half-hour and the PFT based models are run with the corresponding environmental variables weighted for the PFTs within the EC footprint. In this poster we will report on the EC flux measurements and the spatial variability of the physical variables in the EC footprint, and will show some preliminary results on the development of the LUE and ER PFT based models.
14073697 Helbig, M. (Université de Montreal, Département de géographie, Montreal, QC, Canada); Detto, M.; Higgins, K.; Wischnewski, K.; Chasmer, L.; Quinton, W. L. and Sonnentag, O. Quantifying carbon, water and energy fluxes under the influence of rapidly degrading discontinuous permafrost in the Northwest Territories, Canada [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0518, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
A large portion of Canada's northern landscapes, including boreal forest, peatland and tundra ecosystems, is affected by permanently cryotic ground (permafrost) that underlies a seasonally-thawed (i.e. active) layer. A widely used classification distinguishes between discontinuous (thickness varies but is typically <10 m at its southern extent) and continuous (thickness usually is >100 m) permafrost zones, consisting of less than 90% and 90-100% of permanently cryotic ground in areal extent, respectively. Recent research indicates rapid degradation of permafrost at its southern limit with associated ground surface subsidence and conversion of forest to wetland. Together these changes might cause a strong net feedback to the climate system of unknown magnitude and direction by altering important land surface characteristics and/or by altering the fluxes of carbon dioxide (CO2) and methane (CH4) between the biosphere and the atmosphere. Large knowledge gaps exist regarding the links between continued permafrost degradation, regional hydrology and topography, vegetation composition and structure, land surface properties, and CO2 and CH4 sink-source strengths. To shed light on these links, we have measured the net exchanges of CH4, CO2, water vapour and heat with an eddy covariance system at Scotty Creek, Northwest Territories, Canada, a hydrologically well-characterized watershed in the discontinuous permafrost zone. The landscape in the vicinity of the eddy covariance tower features forested permafrost peat plateaus (~40%) and permafrost-free bogs (~25%), fens (~25%) and shallow lakes (~10%). These measurements are complemented by repeated surveys of surface and frost table topography and vegetation, and by remote sensing-based footprint analysis. With our contribution, we will present the first growing season of measurements. Preliminary results for May and June 2013 suggest that daily net uptake of atmospheric CO2 at Scotty Creek peaks at 2.5 g C m-2 day-1 and is, therefore, comparable to other permafrost and permafrost-free boreal forest sites. However, given the high proportion of bogs, fens and shallow lakes in the footprint, CH4 emission rates reach >100 nmol CH4 m-2 s-1 in early summer. Thus, CH4 might be an important component of the site's carbon budget.
14073684 Hodgkins, S. B. (Florida State University, Earth, Ocean and Atmospheric Science, Tallahassee, FL); Tfaily, M. M.; McCalley, C. K.; Logan, T.; Crill, P. M.; Saleska, S. R.; Rich, V. I. and Chanton, J. Changes in soil chemistry help drive higher greenhouse gas emissions from thawing permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0505, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Carbon release due to permafrost thaw represents a major potential positive feedback to climate change. The magnitude of this carbon loss and the proportion lost as methane (CH4) vs. carbon dioxide (CO2) depend on many factors including temperature, mobilization of previously-frozen carbon, hydrology, and organic matter chemistry. While the first three of these effects on CH4 release are relatively well understood, the effect of organic matter chemistry remains largely unstudied. To address this gap, we examined the biogeochemical characteristics of peat and dissolved organic matter (DOM) along a permafrost thaw progression from recently- to fully-thawed sites in Stordalen Mire (68° 21' N, 19° 03' E), a thawing peat plateau in northern Sweden. This thaw progression exhibited increasing carbon gas production potentials, with higher CH4/CO2 ratios and a shift in CH4 production pathway from CO2 reduction to acetate cleavage. Underlying these changes in production were changes in organic matter chemistry: peat C/N ratios decreased while humification rates increased, and DOM shifted towards lower molecular weight compounds with lower aromaticity and organic oxygen content and a higher proportion of microbially-produced compounds. Mechanistically, the relative effect of changing plant inputs vs. microbial activity on organic matter chemistry remains unclear. These results imply that thaw-induced increases in organic matter lability cause shifts in biogeochemical processes towards higher decomposition rates with an increasing proportion of carbon released as CH4 vs. CO2. This impact of permafrost thaw on organic matter chemistry could intensify the predicted climate feedbacks of increasing temperatures, permafrost carbon mobilization, and hydrologic changes.
14073671 Hugelius, G. (Stockholm University, Department of Physical Geography and Quaternary Geology, Stockholm, Sweden). Assessing uncertainties in circumpolar permafrost carbon maps by comparing them to local scale studies [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Soils in the northern circumpolar permafrost zone store large amounts of soil organic carbon (SOC). Based on the Northern Circumpolar Soil Carbon Database (NCSCD), the upper 1 m of soil stores ca. 500 Pg of SOC. In this study, the NCSCD is compared to several high-resolution local scale studies to assess the accuracy of the circumpolar estimates for SOC storage. Initial comparisons of the NCSCD to local scale studies have revealed large differences, stressing the need to understand across scale variability of SOC stocks. Increasingly, local scale studies of landscape SOC distribution provide insights into the variability of near surface SOC stocks across the circumpolar region. Comparing these datasets to the NCSCD can inform us on across-scale variability and shed light on how much information is lost when widening the geographical focus of a study. This across scale comparison specifically provides validation of (1) our calculated estimates of uncertainties due to limited pedon data to describe natural soil variability across regions and (2) a first order estimate of uncertainties caused by using small scale maps to estimate SOC storage across the circumpolar region that exhibits great natural spatial variability. We partition the validation into these two uncertainties by comparing local and circumpolar estimates when: (1) calculating what local estimates would be if they were upscaled with the local pedon dataset but using the circumpolar soil map and (2) calculating what local estimates would be if they were upscaled with the circumpolar pedon dataset but using the local soil map. The results of these comparisons are discussed in the context of what pedon and map data is currently available for different regions and how estimates for different regions may be improved.
14073692 Jafarov, E. E. (University of Colorado, Boulder, National Snow and Ice Data Center, Boulder, CO); Schaefer, K. M.; Watts, J. and Zhang, T. Improved estimates of the permafrost carbon feedback [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0513, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The Permafrost Carbon Feedback (PCF) is an amplification of surface warming due to the release of CO2 and CH4 from thawing permafrost. Currently, there is substantial uncertainty in estimates of future CO2 release. Studies show that the extensive northern wetlands (>30N) contribute up to 25% of global CH4 emission, whereas 2.3% of CH4 emissions occurs from thawing permafrost in these regions. To improve estimates of the PCF we added prognostic organic layer to the Simple Bioshpere/Carnegie-Ames-Stanford (SIBCASA) Terrestrial Carbon Cycle Model and quantified CO2 and CH4 fluxes resulting from changes in terrestrial carbon storage in permafrost affected soils. Model simulations spanning 1801 to 2010 were driven using Climatic Research Unit-National Centers for Environmental Prediction (CRUNCEP) reanalysis, atmospheric CO2, and land use change information as modified by the Multi-Scale Terrestrial Model Intercomparison Project (MsTMIP). From 2011 to 2300, multiple projections of CO2 and CH4 emissions and changes in PCF were evaluated by scaling the CRUNCEP data using trends in weather data derived from the Fifth Coupled Model Intercomparison Project (CMIP5) for all Representative Concentration Pathway (RCP) scenarios. Implementation of the dynamic organic layer into the model lowered the effective thermal conductivity between the soil and the atmosphere and increased the resilience of permafrost to climate warming and decreased permafrost seasonal thawing depth. The ensemble mean for each RCP is our best estimate of CO2 and CH4 emissions from degrading permafrost and the standard deviation is a measure of uncertainty.
14073674 Kling, G. W. (University of Michigan, Ecology and Evolutionary Biology, Ann Arbor, MI); Dobkowski, J.; Ward, C. P.; Crump, B. C.; Neilson, B. T. and Cory, R. M. The fate of carbon draining permafrost soils is controlled by photochemical reactions in addition to microbial degradation in arctic surface waters [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Perhaps the unknown of greatest potential consequence in determining the arc of climate change in this century is the role of thawing permafrost carbon. Arctic soil temperatures are increasing and large areas of permafrost have thawed, but not all soils will thaw quietly in place. Destabilization from melting ice has caused an increase in thermokarst failures that expose buried C and release dissolved organic C (DOC) to surface waters. We found that this exposure to sunlight and surface conditions increases the reactivity of permafrost C to microbial attack by 40% compared to soil DOC held in the dark. The range of lability to microbes depends on microbial community composition and especially on prior light exposure, implying that sunlight may act as an amplification factor in converting frozen C to gases in the atmosphere. We also found that photochemical degradation accounted for the majority (up to 80%) of the degradation of DOC in the water column of lakes and streams. This was based on concurrent measurements of (1) respiration of DOM to CO2 by bacteria in the dark, (2) O2 consumed in DOM photo-oxidation, (3) CO2 produced by DOM photo-mineralization, and (4) photo-stimulated bacterial respiration. Using in-situ UV light profiles and surveys of ~70 surface waters on the North Slope of Alaska, we found that depth-integrated water column rates of photochemical DOM degradation equaled or exceeded dark bacterial respiration, by up to 7´ depending on the mean depth of the water column. The total dark and light processing of DOM in these waters was estimated to be roughly 20% of the DOM exported from major rivers on the North Slope of Alaska to the Arctic Ocean. The dominant degradation pathway was the partial photo-oxidation of DOC, which was at least 2´ greater than complete photo-mineralization of DOC to CO2 or than bacterial respiration to CO2. This means that the dominant fate of permafrost C released as DOC is to be partially degraded and transported through rivers to oceans rather than mineralized to CO2 and returned to the atmosphere. In either case, photochemical degradation of DOC is critical to understanding the fate of C that will drain from thawing arctic soils.
14073708 Lawrence, R. D. (University of New Hampshire, Natural Resources and Earth System Science, Durham, NH); McCalley, C. K.; Varner, R. K.; Crill, P. M. and Saleska, S. R. Changes in net ecosystem exchange and the isotopic composition of ecosystem respiration across permafrost thaw gradient in a subarctic mire [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0529, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Subarctic peatlands in zones of discontinuous permafrost are experiencing widespread environmental changes due to climate warming. The increase in temperature in Arctic regions has given rise to permafrost degradation, increasing exposure of once stable soil organic carbon and consequent significant changes in the carbon budget. In this study, we examined net ecosystem (CO2) exchange and d13 C-CO2 from a subarctic mire in northern Sweden. Measurements were made using automatic chambers placed in the three predominant ecosystems (a dry, elevated Palsa; an intermediate thaw regime dominated by Sphagnum spp. and; a completely thawed, inundated site dominated by Eriophorum angustifolium). The isotopic composition of ecosystem respiration was determined using a Quantum Cascade Laser Spectrometer. Measurements of net ecosystem (CO2) exchange (May - October 2012) revealed a shift from a net carbon source to the atmosphere in the Palsa site with intact permafrost (average 4.5 ± 10.7 mg C m-2 h-1) to a carbon sink that increased with thaw, to -21.5 ± 6.1 and -77.6 ± 25.8 mg C m-2 h-1 for the partially thawed Sphagnum and the fully thawed Eriophorum sites respectively. By contrast, the isotopic composition of respiration did not change with thaw averaging -26 ppm, -25.1 ppm, and -25.9 ppm for the Palsa, Sphagnum and Eriophorum sites respectively. Net ecosystem (CO2) exchange rates varied throughout the growing season with max CO2 uptake and nocturnal respiration occurring mid July - August 2012. Although increased warming has resulted in permafrost thaw, and possibly the destabilization and release of old carbon from permafrost, any possible loss of old carbon from thawing or thawed sites was more than offset by a greater net uptake of CO2 occurring in the wetter sites due to increasing dominance of more productive vegetation in these sites.
14073685 Lee, H. (National Center for Atmospheric Research, Climate and Global Dynamics Division, Boulder, CO); Lawrence, D. M.; Swenson, S. C.; Slater, A. G.; Wieder, W. R.; Phillips, C. L. and Risk, D. A. Evaluating methane dynamics under thawing permafrost using CLM4.5BGC [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0506, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost soils characterize the Arctic landscape and are known to contain massive soil carbon (C) pools that are vulnerable to changing climate. The response of permafrost soils to Arctic warming represents a major source of uncertainty in projecting C-cycle climate feedbacks. Permafrost soils are highly heterogeneous, especially related to oxygen availability and redox conditions that govern the C-cycle response to changing soil conditions and the production and consumption of methane (CH4) and carbon dioxide (CO2). Uncertainty in the mechanisms controlling C mineralization is compounded by concurrent changes in soil hydrology associated with permafrost thaw. Until recently, the ESMs that incorporate global C cycle-climate feedbacks lacked sufficient structural completeness to realistically represent permafrost-C feedbacks. Developments in the most recent version of the Community Land Model (CLM4.5, released in June 2013, URL: http://www.cesm.ucar.edu/models/cesm1.2/clm/) target a more complete representation of permafrost soil biogeophysical and biogeochemical processes and provide an exciting tool with which we can scale our understanding of hydrological influences on the C dynamics of thawing Arctic soils. Recent developments in CLM4.5BGC (the biogeochemistry subcomponent of the CLM4.5 that includes simulations of CH4 production and oxidation) aimed to improve representation of the complex biogeophysical and biogeochemical interactions characteristic of permafrost soils. These model development efforts, however, have outpaced collection of data in permafrost systems. To date, model validation efforts have largely relied on surface flux measurements of CO2 and CH4. These surface measurements alone cannot properly evaluate the processes represented in the vertically resolved structure of the model because they represent the net sum of CH4 production and oxidation throughout the soil column and are not directly linked to subsurface drivers that vary across steep vertical gradients. The objective of this study was to present the model structure related to aerobic and anaerobic CO2 and CH4 production and oxidation within the new version of CLM4.5BGC and suggest the types of observations that are necessary to evaluate and enhance the model. In addition, the newly developed excess ice features in the CLM4.5 was tested to show how permafrost-thaw associated land surface subsidence influences future simulations of CH4 from thawing permafrost.
14073688 Li, J. (University of Oklahoma, Norman, OK); Luo, Y.; Natali, S.; Schuur, E. A.; Xia, J.; Pak, B. C.; Kowalczyk, E. and Wang, Y. Modeling ecosystem carbon cycle and permafrost thaw under annual and seasonal warming at a tundra site in Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0509, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost thaw and subsequent ecosystem carbon (C) dynamics are key components for predicting global climate change. This study validated a land surface model, the Community Atmosphere Biosphere Land Exchange (CABLE) model, at an Alaskan tundra site, then used it to simulate ecosystem C flux and growing season thaw depth under 2°C air warming scenarios (annual warming: AW; winter warming: WW; or summer warming: SW) over short-term stepwise warming and 50-year gradual warming. Our results show that (1) AW and WW induced greater plant productivity than respiratory C loss thus leading to ecosystem C accretion over short-term stepwise warming and 50-year gradual warming; (2) SW increased ecosystem C accretion over short-term stepwise warming but decreased ecosystem C (0.6%) over long-term gradual warming; (3) under the short-term stepwise warming, WW resulted in greater permafrost thaw than SW with a change of 2.8-3.4 cm°C-1 on average; (4) WW increased soil temperature by 0.1~0.2°C as modeled, which is one order magnitude lower than that achieved under field experimental warming treatments, 1.5°C. Under this greater soil warming scenario, simulations showed warming induced a shift in ecosystem sink to ecosystem source suggesting a potential positive feedback of tundra to climate change. These results demonstrate the vulnerability of organic C residing in near surface permafrost to climate warming and seasonal warming may be an important factor in long-term projections of climate changes at the tundra region.
14073686 Lieberman-Cribbin, W. (Colgate University, Department of Geography, Hamilton, NY); Loranty, M. M.; Alexander, H. D.; Berner, L. T. and Natali, S. On the distribution of permafrost carbon, plant functional type, and wildfire occurrence in northern high latitudes [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0507, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Multiple lines of evidence indicate that increasing global temperatures have lead to increased permafrost temperatures and the transfer of carbon from permafrost to the atmosphere. However, neither increasing permafrost temperatures nor the release of permafrost carbon are uniform in space or time. Multiple factors, including plant functional type, soil physical properties, hydrology, and disturbance regimes, exert strong influence on the magnitude and direction of change in permafrost temperature, and therefore, carbon release. This study quantifies the distribution of permafrost soil carbon and, wildfire disturbance by plant functional type in northern hemisphere high latitude ecosystems. Utilizing maps of permafrost soil organic carbon and plant functional type we find that arctic tundra and needle leaf coniferous boreal forests contain the vast majority of permafrost soil carbon in the upper 1 m of the soil column. In both discontinuous and continuous permafrost zones, needle-leaf deciduous ecosystems contain the greatest amount of permafrost carbon in comparison to any other single vegetation type. Further, we find that the vast majority of fires since 2000 have occurred in areas classified as needle leaf deciduous forests. Fire rapidly impacts the structure and function of both over- and understory vegetation communities, which have been shown to influence permafrost temperatures via impacts on surface energy partitioning. In this context our results underscore the importance of ecosystem dynamics with regard to the fate of permafrost carbon and indicate that understanding Eurasian needle-leaf deciduous forests will be essential for accurately quantifying the magnitude and timing of the permafrost carbon feedback.
14073663 McGuire, A. D. (University of Alaska, Fairbanks, Fairbanks, AK). The vulnerability of permafrost carbon; a retrospective analysis of changes in permafrost area and carbon storage simulated by process-based models between 1960 and 2009 [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
We conducted a retrospective (1960 - 2009) comparison of how large-scale models represent permafrost carbon dynamics. The models participating in this comparison were those that had joined the model integration team of the Vulnerability of Permafrost Carbon Research Coordination Network (see URL: http://www.biology.ufl.edu/permafrostcarbon/). Each of the 9 models in this comparison conducted simulations over the permafrost land region in the Northern Hemisphere. Among the models, the area of permafrost (defined as the area for which active layer thickness was less than 3 m) ranged between 7.4 and 28.5 million km2 and the density of soil carbon storage ranged an order of magnitude between 9.9 and 85.7 thousand g C m-2. Between 1960 and 2009, models generally indicated loss of permafrost area that ranged between 9.4 thousand km2 and 2.8 million km2. Although the permafrost area decreased, models simulated gains in soil carbon storage that ranged from a gain of 24 g C m-2 to a gain of 1032 g C m-2. All models indicated that both net primary production (NPP) and heterotrophic respiration (RH) increased from 1960, with a mean increase of NPP that was approximately 0.23 g C m-2 yr-1 greater than the increase in RH. However, there are indications among the models that the NPP anomalies are decelerating in magnitude by the end of the analysis period, while the RH anomalies are accelerating. Some of the models are clearly showing a deceleration in the accumulation of soil carbon during the last fifty years. These results suggest that simulated RH may generally overtake simulated NPP in applications of these models driven by future climate projections, a response that would result in net losses of carbon from permafrost zone soils.
14073701 Pelletier, N. (University of Montreal, Department of Geography, Montreal, QC, Canada); Olefeldt, D.; Turetsky, M. R.; Quinton, W. L.; Sonnentag, O. and Talbot, J. Influence of permafrost thaw on carbon cycling and vegetation communities in a northern discontinuous permafrost peatland complex at Scotty Creek, Northwest Territories [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0522, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Globally, peatlands comprise an important proportion of the total belowground carbon pool. Peatlands in permafrost regions are usually considered as particularly important carbon sinks since their decomposition rate is slowed by the effects of low temperatures causing the ground to be frozen year-round. Discontinuous permafrost regions are particularly sensitive to contemporary climate changes causing rapid permafrost degradation with associated changes in land cover from forested permafrost peat plateaus to treeless, permafrost-free bogs. However, only little is known about the impact of these fundamental changes in land cover on peatland carbon cycling. Here we present an analysis based on peat cores collected in the late-winter of 2012 and summer 2013 in a discontinuous permafrost boreal forest-peatland complex located in the Northwest Territories, Canada. This site is known to show signs of rapid permafrost degradation over the last 40 years. Our results suggest that the hydrological changes that follow permafrost thaw might have a beneficial effect on carbon storage via changes in plant functional types. Pollen analyses performed on the same cores provide a comprehensive insight of the regional vegetation and fire dynamics over the Holocene period. Testate Amoebae analyses provide information in regards to local past hydrological conditions. Together, our results allow for a better understanding of the ways hydrology, vegetation and fire affect carbon cycling in a discontinuous permafrost peatland.
14073665 Peng, S. (Laboratoire de Glaciologie et Géophysique de l'Environnement, Grenoble, France); Gouttevin, I.; Krinner, G. and Ciais, P. Simulated permafrost soil thermal dynamics during 1960-2009 in eight offline processed-based models [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-08, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost soil thermal dynamics not only determine the status of permafrost, but also have large impacts on permafrost organic carbon decomposition. Here, we used eight processed based models that participated in the Vulnerability Permafrost Carbon Research Coordination Network (RCN) project to investigate: (1) the trends in soil temperature at different depths over the northern hemisphere permafrost region during the past five decades, and (2) which factors drive trends and inter-annual variability of permafrost soil temperature? The simulated annual soil temperature at 20 cm increases by ~0.02 °C per year from 1960 to 2009 (ranging from 0.00 °C per year in CoLM to 0.04 °C per year in ISBA). Most models simulated more warming of soil in spring and winter than in summer and autumn, although there were different seasonal trends in different models. Trends in soil temperature decrease with soil depth in all models. To quantify the contributions of various factors (air temperature, precipitation, downward longwave radiation etc.) to trends and inter-annual variation in soil temperature, we ran offline models with detrended air temperature, precipitation, downward longwave radiation, respectively. Our results suggest that both annual air temperature and downward longwave radiation significantly correlate with annual soil temperature. Moreover, trend in air temperature and downward longwave radiation contribute 30% and 60% to trends in soil temperature (0 - 200 cm), respectively, during the period 1960-2009.
14073706 Salmon, V. G. (University of Florida, Biology Department, Gainesville, FL); Natali, S.; Crummer, K. Grace; Mack, M. C. and Schuur, E. A. Changes in soil nitrogen availability associated with permafrost thaw [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0527, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The globally significant size of the permafrost carbon (C) pool reflects the balance between soil decomposition and plant growth in high latitude ecosystems. Projected increases in mean annual temperatures in these cold systems are expected to increase rates of both of these processes. As the nutrient limiting plant productivity in high latitude ecosystems, nitrogen (N) is expected to play a key role in determining the future balance between permafrost C losses and increased C sequestration by plants. In this experiment a tundra ecosystem in interior Alaska was subjected to soil and air warming treatments for five years. Soil warming was executed using an insulating snow pack that was removed prior to spring thaw while air warming was achieved using open top chambers deployed during the growing season. Soil warming treatments increased growing season thaw depth by 9 cm and increased soil temperature by 4°C. Air warming treatments raised air temperatures by 0.5°C. To assess N availability across treatments, anion and cation binding resins were deployed during the fourth and fifth years of warming manipulations at a depth of 10 cm. Analysis of resin extracts indicated that inorganic N availability of surface soils increased significantly with soil warming but did not significantly change from control levels when soil and air warming treatments were combined. Resins from control plots had 5.2 mg N per g dry resin in the form of ammonium and nitrate while resins from soil warmed plots had 10.7 mg N per g dry resin. Resins from combined soil and air warming plots had 7.3 mg N per g dry resin. Changes in inorganic N availability were partially explained by changes in environmental variables (active layer depth, soil temperature, and soil moisture). Nondestructive methods were used to survey aboveground plant biomass and are combined with %N analysis of live and senesced plant tissues. The resulting estimates of aboveground plant N pools and fluxes of litter N into surface soils were examined to explain the failure of combined soil and air warming treatments to increase inorganic N availability. N mediated feedbacks between plants and soils are an important factor to consider when making assessments of the future C balance of high latitude ecosystems.
14073695 Schaedel, C. (University of Florida, Department of Biology, Gainesville, FL); Schuur, E. A.; Bracho, R. G.; Elberling, B.; Lupascu, M.; Natali, S.; O'Donnell, J. A. and Waldrop, M. P. Quantifying the effect size of changing environmental controls on C release from permafrost soils [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0516, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Microbial decomposition of soil organic matter is controlled by substrate quality, physical protection of soil minerals and environmental conditions (e.g. temperature, soil moisture). Increasing temperatures in high latitude ecosystems not only increase carbon (C) emissions from previously frozen C in permafrost but also indirectly affect the C cycle through changes in regional and local hydrology. For instance, increasing active layer thickness due to permafrost thaw can cause better drainage in uplands but poorly drained soil conditions in lowlands which both influence the amount and form of C being released. We have compiled a database of more than 40 incubation studies with soils from across the entire permafrost zone to quantify the effect size of increasing temperatures and changes in hydrology on CO2 emissions. The difference in cumulative CO2 release for a temperature increase of 10K over time, ranged initially from less than 1% to up to 48% after one year of incubation. Drier soil incubation conditions stimulated CO2 release by 2-19% relative to saturated treatments, and there was a positive interaction with temperature. These preliminary results show that a 10K increase in temperature and a shift from wetter to drier soil conditions might similarly enhance CO2 release from permafrost. However, near saturated soil conditions likely stimulate C release in form of the more potent greenhouse gas methane (CH4) which needs to be considered to fully estimate changes in C release from permafrost soils under changing environmental conditions.
14073664 Schaefer, K. M. (University of Colorado, Boulder, National Snow and Ice Data Center, Boulder, CO); Jafarov, E. E.; Zhang, T.; Li, Z.; Schwalm, C. R. and Williams, C. A. Potential impacts of the permafrost carbon feedback on global temperature [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-07, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
We estimate potential temperature increases in Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections due to the Permafrost Carbon Feedback (PCF) using published estimates of permafrost emissions and statistical estimates of individual model climate sensitivities. The PCF is the amplification of anthropogenic warming due to carbon dioxide (CO2) and methane (CH4) emissions from thawing permafrost. The average of the eleven published estimates of permafrost emissions is 94±53 Gt C in 2100, but only four of these estimates include impacts on global temperature. None of the CMIP5 climate projections account for impacts of the PCF on global temperature. Adding the PCF to the CMIP5 models and re-running the projections is time consuming and computationally expensive, so we use a statistical analysis of current projections to estimate temperature impacts in 2100. We use linear curve fits to estimate the short-term sensitivities of simulated temperature to changes in atmospheric CO2 for individual CMIP5 models. We estimate changes in atmospheric CO2 concentration due to permafrost emissions using the published estimates, assuming half of the emissions are absorbed by the land and ocean. Multiplying the temperature sensitivities by the changes in atmospheric CO2 provides useful estimates of the temperature impacts of the PCF. We focus on Representative Concentration Pathway (RCP8.5), the scenario used in nearly all published estimates of permafrost emissions. We account for CH4 by converting permafrost CH4 estimates to CO2 equivalents and use Guassian error propagation to estimate uncertainties in estimated temperature impacts. We validate our results by running the CESM4 model with and without permafrost emissions. Our results indicate that the impact of the PCF on global temperature is proportional to the fraction of total carbon emissions that come from thawing permafrost.
14073703 Schuur, E. A. (University of Florida, Gainesville, FL); Bracho, R. G.; Belshe, F.; Crummer, K. Grace; Hicks Pries, C.; Krapek, J.; Natali, S.; Pegoraro, E.; Salmon, V.; Trucco, C.; Vogel, Jason G. and Webb, E. Long term trends of carbon dioxide exchange in a tundra ecosystem affected by permafrost thaw [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0524, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic warming has led to permafrost degradation and ground subsidence as a result of ground ice melting. Frozen soil organic matter that thaws can increase carbon (C) emissions to the atmosphere via respiration, but this can be offset in part by increases in plant growth. The balance of plant and microbial processes, and how they change through time, will determine how permafrost ecosystems influence future climate change via the C cycle. This study addressed this question both on short (interannual) and longer (decadal) time periods by measuring C fluxes over a ten-year period at three sites that represent a gradient of time since permafrost thaw. All three sites are upland tundra ecosystems located in Interior Alaska but differed in the extent of permafrost thaw and ground subsidence. Results showed an increasing growing season (May - September) trend in gross primary productivity, net ecosystem exchange, aboveground net primary productivity, and annual net ecosystem exchange at all sites over the study period from 2004-2013. In contrast, there was no directional change in annual and growing season ecosystem respiration, or mass loss from decomposition of a common cellulose substrate. The increasing trends over time as well as inter site differences most closely followed variation in growing season thaw depth over the same time period. During the study period, sites with more permafrost degradation (deeper seasonal thaw) had significantly greater gross primary productivity compared to where degradation was least, but also greater growing season ecosystem respiration. Adding in winter respiration decreased, in part, the summer C sink and left the site with the most permafrost degradation near C neutral, with the other sites annual C sinks. However, annual C balance was strongly dependent on winter respiration, which, compared to the growing season, was relatively data-poor due to extreme environmental conditions. Measurements of growing season and annual C exchange made with an eddy covariance tower from 2009-2013 had similar interannual variability as chamber-based fluxes, but with more data coverage overall predicted higher winter losses and that this tundra ecosystem as a whole was a C source. This points towards the importance of accurate and sustained winter measurements for understanding the net exchange of C from tundra.
14073680 Stiegler, C. (Lund University, Department of Physical Geography and Ecosystem Science, Lund, Sweden); Lindroth, A. and Johansson, M. Surface energy balance of subarctic lowland palsa mires related to permafrost degradation [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21A-0437, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
During the last decades, an accelerating trend in increasing active-layer thickness and rising permafrost temperatures has been observed in the Nordic area. One region, where permafrost is particularly vulnerable to any further climate change is the Tornetrask area in northern subarctic Sweden. Within the next decades a projected ongoing climate warming and increase in snow cover will most likely lead to the disappearance of lowland permafrost in this region, affecting surface vegetation cover, greenhouse gas emissions and surface energy balance. In this study we link first results of surface energy balance measurements from lowland palsa mires in the Tornetrask region to the current state of permafrost and the degradation of peat plateaus. The study area covers several mires with similar local topographic conditions along an east-west oriented transect. Due to a strong climatic gradient, with maritime climate in the west and a more continental climate in the east, active layer thickness and permafrost temperatures generally increase from east to west while permafrost thickness decreases. In the recent years permafrost has fully disappeared at our westernmost study site while at the other investigated locations the peat plateaus show varying stages of degradation. For our measurements of energy balance components we use both a mobile energy balance tower and a stationary eddy covariance tower. Data has been collected during the growing season in 2013 by measuring all components of the surface energy budget, i.e. net radiation, turbulent fluxes of sensible and latent heat as well as ground heat fluxes. In addition, we measure active layer thickness and both soil moisture and soil temperature at various depths. First results display that the turbulent fluxes of latent heat exceed the fluxes of sensible heat at all investigated sites. The difference is more pronounced at those mires where permafrost degradation is at an advanced stage and therefore more open water is available. Ground heat fluxes show no significant variation among the studied mires whereas albedo is significantly reduced at the site where permafrost has fully disappeared. Further results such as energy flux partitioning and energy balance closure will be presented and discussed at the conference.
14073672 Strauss, J. (Alfred Wegener Institute, Periglacial Research, Potsdam, Germany); Schirrmeister, L.; Grosse, G.; Ulrich, M.; Wetterich, S.; Herzschuh, U. and Hubberten, H. W. The deep permafrost carbon pool of Siberia and Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Estimating the amount of organic carbon stored in Arctic permafrost and its biogeochemical characteristics are important topics in today's permafrost research. While the uppermost cryosoil horizons are reasonably studied and recorded in the Northern Circumpolar Soil Carbon Database (NCSCD), there are large uncertainties concerning the quantity and distribution of permafrost deep organic carbon. We studied the organic carbon content of the Yedoma region of unglaciated Siberia and Alaska. This region is unique because of its long-term accumulation of organic carbon, which was deeply incorporated into permafrost during the late Quaternary. Inclusion of labile organic matter into permafrost halted decomposition and resulted in a deep long-term carbon sink. Organic carbon in the Yedoma region occurs mainly as peat inclusions, twigs and root fragments, other solid and fine detrital plant remains, fossil remains of mammals, insects, aquatic plankton and soil microorganisms, and finally their decompositional and metabolic products in terms of particulate and dissolved organic matter. With our study we show that two major sub-reservoirs compose the Yedoma region deep frozen organic carbon; Yedoma deposits (late Pleistocene ice- and organic-rich silty sediments) and deposits formed in thaw-lake basins (generalised as thermokarst deposits). Thaw-lake basins result when lake formation degrades Yedoma deposits, then the lakes drain and deposits refreeze. Therefore, the deep Yedoma region organic carbon pool is far from homogeneous and strongly linked to depositional and permafrost dynamics as well as the ecological and climatic history. Using of approximately 1000 frozen samples from 23 Siberian and Alaskan study sites and a new approach for upscaling, we find significant differences to former estimates of the Yedoma coverage area, thickness of the relevant frozen deposits, ground ice content and finally in organic carbon content that lead to a reassessment of the deep permafrost carbon pools of the northern high latitude Yedoma region. Because of high inherent (spatial) heterogeneity and non-normal input parameter distributions, we used median values (rather than means) and bootstrapping statistics for carbon budget calculation and error estimation. Based on this approach we quantified the organic carbon pool to 54 +15/-9 Gt for Yedoma deposits and to 80+32/-23 Gt for thermokarst deposits. The total Yedoma region deep organic carbon pool of 134+47/-32 Gt is a substantial amount of thaw-vulnerable organic carbon that must be accounted for in global carbon-cycle models.
14073675 Treat, C. C. (University of New Hampshire, Durham, NH); Natali, S.; Iversen, C. M.; Lupascu, M. and Santruckova, H. The fate of permafrost soil carbon under saturated conditions [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-05, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The effects of permafrost thaw on soil carbon storage remain unclear due to complex interactions between soil temperature, moisture, substrate quality, microbial abundance, and interactions between soils and vegetation. As ice-rich permafrost thaws, ground subsidence often leads to saturated soils (thermokarst), and the anaerobic conditions lead to slower decomposition rates but increased methane (CH4) fluxes. Some field studies have shown higher CH4 fluxes from thermokarst areas than intact permafrost but it is unclear whether similar trends are found across ecosystems, biomes, or soil types. We compiled an extensive dataset consisting of CH4 and CO2 measurements taken during anaerobic incubations of soils from the permafrost region. We synthesized trends in potential methane production from permafrost soils in laboratory incubations, evaluated the effects of substrate quality, in-situ soil environment, and soil properties on methane production and compared the relative contributions of CO2 and CH4 to anaerobic C emissions. We found that anaerobic CO2 and CH4 production rates were dependent upon region, soil depth and incubation temperature. There was significantly higher CH4 production in organic compared to mineral soils on a per gram soil basis but not on a per gram C basis. These results have implications for modeling the fate of permafrost carbon after thaw.
14073707 Wik, M. (Stockholm University, Department of Geological Sciences, Stockholm, Sweden); Bastviken, D.; Walter Anthony, K. M.; Varner, R. K. and MacIntyre, S. Synthesis of methane emission from lakes and ponds across climate sensitive permafrost environments [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0528, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Emission of methane (CH4) from the numerous lakes and ponds across northern permafrost landscapes is highly uncertain but expected to increase with Arctic warming. Our understanding of the role of lakes and ponds within these environments is currently not only limited by lack of measurements, but also by large unknowns in permafrost vulnerability, carbon (C) mobilization and the formation and drainage of water bodies. Until now, no effort has been made that synthesizes available data to investigate and compare CH4 flux magnitudes across lakes and ponds at high latitudes. As part of the Vulnerability of Permafrost Carbon Research Coordination Network, we conducted a synthesis study that investigates different types of water bodies and their CH4 source strength across the various permafrost zones (sporadic, discontinuous and continuous) and in the northernmost boreal zone. Our goal is to stratify lakes and ponds into a handful of categories that reflect their history, formation process, landscape position and physical characteristics (i.e. water depth, area and temperature), which ultimately are going to determine their response to a changing climate. We aim to use new estimates of northern lake distribution along with the Global Wetland Lake Database in order to identify lake morphologies and quantify potential emission magnitudes across regional and pan-Arctic scales. This will allow for increased understanding of northern lakes and ponds and their contribution to atmospheric CH4 and aid biogeochemical process models that predict future landscape interactions with the global C cycle.
14073677 Wu, Y. (Lawrence Berkeley National Laboratory, Berkeley, CA); Kneafsey, T. J.; Nakagawa, S.; Borglin, S. E.; Cook, P.; Tas, N.; Torn, M. S.; Jansson, J. and Hubbard, S. S. Freeze-thaw laboratory column experiments using Arctic permafrost cores; exploring controls of subsurface heterogeneity on greenhouse gas release [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-07, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Although warming induced permafrost thaw and greenhouse gas release to the atmosphere is considered to be one of the largest possible ecosystem feedbacks to climate change in the Arctic, there are significant uncertainties associated with subsurface hydrological, geochemical and microbial controls over the magnitude and rate of the greenhouse gas release. Gaining an understanding of the controls of typically heterogeneous subsurface properties on greenhouse gas release is exacerbated by the difficulty in sufficiently quantifying subsurface dynamics and gas exchange in-situ and in response to freeze-thaw perturbations. As a part of the DOE's Next Generation Ecosystem Experiments (NGEE) in the Arctic, we are performing a series of controlled laboratory freeze-thaw experiments to study CO2, CH4, and N2O gas release in vertical permafrost columns as a function of dynamic and vertically heterogeneous hydrological, geochemical and microbial properties. The column studies are being performed using representative ~ 0.75 m cores collected at the NGEE Barrow, AK site from the ground surface into the permafrost. The experimental apparatus was designed to simulate the seasonal freeze-thaw of the Barrow active layer. The column is equipped with several types of sensors and sampling devices, including thermistors, geophysical (seismic and electrical) sensors, and ports that allow sampling for solids, fluids, and gasses. Our preliminary tests simulated seasonal temperature variation from ~ -20°C to +5°C. Our results demonstrated the success of the freeze-thaw control of the experimental apparatus and the capability of the geophysical methods to monitor the freeze-thaw spatiotemporal dynamics. Samples collected during the experiment also revealed the changes of the hydrological and biogeochemical conditions of the column and its linkage to carbon degradation and release in a vertical permafrost soil column. While our initial experiments were conducted to simulate the seasonal freeze thaw of a fairly homogeneous active layer under current climate conditions, subsequent experiments will be designed to (a) investigate thaw of deeper permafrost and associated hydrological, geochemical and microbiological processes, including greenhouse gas release; (b) quantify the effect of vertical subsurface heterogeneity on the integrated above-ground greenhouse gas response.
14073696 Yasuda, K. P. (Colgate University, Geography, Hamilton, NY); Loranty, M. M.; Natali, S. and Schade, J. D. Investigating variability in carbon and water dynamics along a hill slope in a tundra ecosystem underlain by permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0517, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Understanding interactions between the distributions of soil moisture and vegetation communities is essential to accurately quantify ecosystem carbon and water dynamics. This is particularly true in permafrost ecosystems where relatively large changes in both vegetation and soil hydrologic conditions can occur rapidly as a consequence of climate warming. These changes often occur simultaneously, and so understanding these relationships will be necessary for accurate quantification of associated climate feedbacks. In this regard, research at the hill slope scale may provide useful insight, as relatively small topographic features can be characterized large hydrologic and vegetation gradients in tundra ecosystems underlain by permafrost. In this study we examined variability in ecosystem biological and physical properties along with associated carbon and water dynamics along a hill slope in central Alaska. Vegetation at the bottom of the slope near a stream was characterized by herbaceous vegetation, with woody shrubs increasing in occurrence further up the slope. Measurements of thaw depth, soil organic matter, and carbon and water fluxes were used to characterize differences along the slope. We found that net ecosystem carbon exchange (NEE) and evapotranspiration are strongly correlated with vegetation type. Gross primary productivity (GPP) was higher in areas dominated by shrubs. Although thaw depth decreased and soil moisture increased as we moved down the slope, there appeared to be relatively little variation in ecosystem respiration indicating that early season NEE controlled primarily by differences in photosynthetic activity. We found that less variability in evapotranspiration, likely due to the relatively wet conditions. Our results highlight the potential for topographic gradients to serve as proxies for the effects of ecosystem change on carbon and water dynamics.
14073698 Yuan, F. (Oak Ridge National Laboratory, Climate Change Science Institute and Environmental Science Division, Oak Ridge, TN); Thornton, P. E.; McGuire, A. D.; Oechel, W. C.; Yang, B.; Tweedie, C. E.; Rogers, A. and Norby, R. J. The role of explicitly modeling bryophytes in simulating carbon exchange and permafrost dynamics of an Arctic coastal tundra at Barrow, Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0519, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Bryophyte cover is greater than 50% in many Arctic tundra ecosystems. In regions of the Arctic where shrubs are expanding it is expected that bryophyte cover will be substantially reduced. Such a loss in cover could influence the hydrological, biogeochemical, and permafrost dynamics of Arctic tundra ecosystems. The explicit representation of bryophyte physiological and biophysical processes in large-scale ecological and land surface models is rare, and we hypothesize that the representation of bryophytes has consequences for estimates of the exchange of water, energy, and carbon by these models. This study explicitly represents the effects of bryophyte function and structure on the exchange of carbon (e.g., summer photosynthesis effects) and energy (e.g., summer insulation effects) with the atmosphere in the Community Land Model (CLM-CN). The modified model was evaluated for its ability to simulate C exchange, soil temperature, and soil moisture since the 1970s at Barrow, Alaska through comparison with data from AmeriFlux sites, USDA Soil Climate Networks observation sites at Barrow, and other sources. We also compare the outputs of the CLM-CN simulations with those of the recently developed Dynamical Organic Soil coupled Terrestrial Ecosystem Model (DOS-TEM). Overall, our evaluation indicates that bryophytes are important contributors to land-atmospheric C exchanges in Arctic tundra and that they play an important role to permafrost thermal and hydrological processes which are critical to permafrost stability. Our next step in this study is to examine the climate system effects of explicitly representing bryophyte dynamics in the land surface model.
14073693 Zubrzycki, S. (Institute of Soil Science, Hamburg, Germany); Bolshiyanov, D.; Eliseev, A. V.; Evgrafova, S.; Fedorova, I.; Glagolev, M.; Grigoriev, M.; Hubberten, H. W.; Knoblauch, C.; Kunitsky, V.; Kutzbach, L.; Reichstein, M.; Rethemeyer, J.; Schirrmeister, L.; Wagner, D.; Zimov, S. A. and Pfeiffer, E. CarboPerm; an interdisciplinary Russian-German project on the formation, turnover and release of carbon in Siberian permafrost landscapes [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0514, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost-affected soils of the northern hemisphere have accumulated large pools of organic carbon (OC) since continuous low temperatures in the permafrost prevented organic carbon decomposition. According to recent estimates these soils contain 1670 Pg of OC, or about 2.5-times the carbon within the global vegetation. Rising arctic temperatures will result in increased permafrost thawing resulting in a mobilization of formerly frozen OC. The degradation of the newly available OC will result in an increased formation of trace gases such as methane and carbon dioxide which can be released to the atmosphere. Rising trace gas concentrations due to permafrost thawing would thereby form a positive feedback on climate warming. CarboPerm, is a joint German-Russian research project funded by the German Federal Ministry of Education and Research. It comprises multi-disciplinary investigations on the formation, turnover and release of OC in Siberian permafrost. It aims to gain increased understanding of how permafrost-affected landscapes will respond to global warming and how this response will influence the local, regional and global trace gas balance. Permafrost scientists from Russia and Germany will work together at different key sites in the Siberian Arctic. These sites are: the coast and islands at the Dmitry Laptev Strait, the Lena River Delta, and the Kolyma lowlands close to Cherskii. The scientific work packages comprise studies on (i) the origin, properties, and dynamics of fossil carbon, (ii) the age and quality of organic matter, (iii) the recent carbon dynamics in permafrost landscapes, (iv) the microbial transformation of organic carbon in permafrost, and (v) process-driven modeling of soil carbon dynamics in permafrost areas. The coordination will be at the University of Hamburg (scientific), the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research in Potsdam (logistic) and the Arctic and Antarctic Research Institute in St. Petersburg. CarboPerm will strengthen permafrost research in underrepresented areas which are hardly accessible to international researchers. The obtained results will improve our understanding of the future development of the sensitive and economically relevant arctic permafrost regions.
14073811 Fedorov, Alexander N. (Russian Academy of Sciences, Siberian Branch, Melnikov Permafrost Institute, Yakutsk, Russian Federation); Ivanova, R. N.; Park, H.; Hiyama, T. and Iijima, Y. Recent air temperature changes in the permafrost landscapes of northeastern Eurasia: in The third international symposium on the Arctic research (ISAR-3) (Polyakov, Igor, editor; et al.), Polar Science, 8(2), p. 114-128, illus. incl. 5 tables, sketch map, 38 ref., June 2014. Meeting: Third international symposium on the Arctic research (ISAR-3), Jan. 15-17, 2013, Tokyo, Japan.
DOI: 10.1016/j.polar.2014.02.001
14073810 Iwahana, Go (University of Alaska-Fairbanks, International Arctic Research Center, Fairbanks, AK); Takano, Shinya; Petrov, Roman E.; Tei, Shunsuke; Shingubara, Ryo; Maximov, Trofim C.; Fedorov, Alexander N.; Desyatkin, Alexey R.; Nikolaev, Anatoly N.; Desyatkin, Roman V. and Sugimoto, Atsuko. Geocryological characteristics of the upper permafrost in a tundra-forest transition of the Indigirka River valley, Russia: in The third international symposium on the Arctic research (ISAR-3) (Polyakov, Igor, editor; et al.), Polar Science, 8(2), p. 96-113, illus. incl. sects., 2 tables, sketch maps, 72 ref., June 2014. Meeting: Third international symposium on the Arctic research (ISAR-3), Jan. 15-17, 2013, Tokyo, Japan.
DOI: 10.1016/j.polar.2014.01.005
14073813 Miyazaki, Shin (National Institute of Polar Research, Arctic Environment Research Center, Tachikawa, Japan); Ishikawa, Mamoru; Baatarbileg, Nachin; Damdinsuren, Sodov; Ariuntuya, Nymsambuu and Jambaljav, Yamkhin. Interannual and seasonal variations in energy and carbon exchanges over the larch forests on the permafrost in northeastern Mongolia: in The third international symposium on the Arctic research (ISAR-3) (Polyakov, Igor, editor; et al.), Polar Science, 8(2), p. 166-182, illus. incl. 2 tables, 72 ref., June 2014. Meeting: Third international symposium on the Arctic research (ISAR-3), Jan. 15-17, 2013, Tokyo, Japan.
DOI: 10.1016/j.polar.2013.12.004
14073812 Morishita, Tomoaki (Forestry and Forest Products Research Institute, Shikoku Research Center, Kochi, Japan); Matsuura, Yojiro; Kajimoto, Takuya; Osawa, Akira; Zyryanova, Olga A. and Prokushkin, Anatoly S. CH4 and N2O dynamics of a Larix gmelinii forest in a continuous permafrost region of central Siberia during the growing season: in The third international symposium on the Arctic research (ISAR-3) (Polyakov, Igor, editor; et al.), Polar Science, 8(2), p. 156-165, illus. incl. 3 tables, sketch map, 55 ref., June 2014. Meeting: Third international symposium on the Arctic research (ISAR-3), Jan. 15-17, 2013, Tokyo, Japan.
DOI: 10.1016/j.polar.2014.01.004
14073658 Czimczik, C. I. (University of California, Irvine, Earth System Science, Irvine, CA); Lupascu, M.; Csank, A. Z.; Seibt, U. H.; Maseyk, K. S.; Xu, X. and Welker, J. M. Carbon cycling in a rapidly changing High Arctic; results from long-term climate experiments and observations of interannual variability in NW Greenland [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The High Arctic, a region dominated by polar semi-deserts underlain with continuous permafrost, is experiencing dramatic changes in climate associated with the loss of sea ice, including warming and shifts in precipitation regimes (i.e. wetting and changing snow cover). Here, we present findings from a set of studies that are addressing the sign and strength of the High Arctic's summertime carbon (C) cycle feedback. We explored magnitudes, patterns and sources of C losses through CO2 and CH4 fluxes and via leaching as dissolved organic C (DOC) and particulate organic C (POC) along with measurements of net ecosystem exchange and plant C uptake. From studying long-term summertime experimental warming and/or watering and interannual weather patterns we find that in polar semi-deserts: a) Summer precipitation regime is the key driver of current summertime C budgets. Warming plus wetting results in increased ecosystem C sequestration and reduced losses of older C as CO2, while warming alone decreases C uptake and increases losses of older soil C as CO2. The system is a sink for CH4, but the sink strength will decline with increasing soil moisture. Thus, the High Arctic has the potential to remain a strong summertime C sink even as the rest of the permafrost region transitions to a net C source to the atmosphere as climate continues to warm. b) Old C is diffusing out of the High Arctic landscape into the atmosphere. This C loss is especially evident in the spring before vegetation pumps fresh C into the soil system. Further, loss of older C from the deeper active layer is highly episodic and dominates C emissions during small precipitation events. c) Precipitation regime is also the key driver of that ancient C export from the land surface as DOC, higher precipitation in the later part of the growing season (July-August), when the active layer is deeper, results in a greater fraction of old C transported to the nearshore Arctic Ocean. Collectively these findings represent a comprehensive picture of C cycle-climate interactions in the High Arctic and provide benchmark datasets critically needed to assess simulations of a changing Arctic.
14073659 Dorrepaal, E. (Umea University, Climate Impacts Research Centre, Abisko, Sweden); Hicks Pries, C.; van Logtestijn, R.; Schuur, E. A. and Cornelissen, H. Declines in old soil carbon losses after 11 years of experimental warming in a subarctic peatland [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Warming of ecosystems underlain by permafrost is a potential large positive feedback to climate change. Permafrost stores twice the amount of carbon (C) as is currently in our atmosphere. Warming is causing permafrost to thaw resulting in soil C that had previously been frozen for hundreds to thousands of years to become vulnerable to above-freezing microbial decomposition. We measured and partitioned ecosystem respiration in a subarctic peatland underlain by permafrost in Abisko, Sweden that had undergone experimental warming for 11 years. The warming was achieved with hexagonal ITEX chambers that acted as greenhouses in the summer and collected snow in the winter, which insulated the ecosystem. The experimental plots were set up in a summer warming by winter warming factorial design with five replicates of each treatment combination spread out over five blocks. We partitioned ecosystem respiration into young soil (<50 years old, 0-25 cm), old soil (>50 years old, 25-50 cm), and autotrophic sources using natural abundance radiocarbon at the height of the July 2011 growing season. Summer warming caused greater soil thaw during the growing season and warmer soil temperatures annually, while doubled winter snow thickness had no effects. The summer warming treatment significantly increased the D14C value of ecosystem respiration and the proportion of respiration coming from autotrophs. The proportion of respiration coming from old soil was actually greatest in the ambient plots. As a result, during the month of July, there was a 25% to 45% smaller flux of old soil C being respired from the summer warming plots than from the ambient plots. Previously at this site, after seven years of summer warming, ecosystem respiration had increased about 50% with 69% of that increase coming from old soil. Our contrasting results imply possible depletion of labile substrates in the old soil despite the large amount of SOC available in this pool, or microbial temperature acclimatization after 11 years of warming. The strength of the permafrost climate change feedback may thus be smaller than previously estimated.
14073687 Fisher, J. P. (University of Sheffield, Department of Animal and Plant Sciences, Sheffield, United Kingdom); Estop-Aragones, C.; Xenakis, G.; Hartley, I. P.; Murton, J.; Charman, D.; Williams, M. and Phoenix, G. K. Influence of plant communities on active layer depth in unburned and post-fire forest [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0508, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Vegetation plays a crucial role in determining active layer depth and is thought to be an important control for permafrost persistence in areas where the mean annual air temperature is as high as +2°C. However this critical component of the interface between the soil and atmosphere is often poorly represented in models, and the relative importance of contrasting vegetation communities is not understood. In particular the role of certain vegetation types such as mosses is completely neglected, in spite of their potential to exhibit contrasting thermal properties depending on their moisture content. Furthermore, most models assume steady states and so ignore important dynamic disturbance events such as fires. Given that the frequency of forest fires is predicted to increase due to climate change in boreal regions, the influence of these ecologically important events on active layer thickness must be established. Contrasting rates of vegetation recovery within and between burn sites may strongly impact on the rate of increase of active layer thickness. Using a combination of targeted and cyclic sampling in boreal forests within a discontinuous permafrost zone in Southern Yukon, Canada we have aimed to further our understanding of how key characteristics of the understory and canopy vegetation influence soil physical conditions including soil moisture, temperature and thaw depth throughout the growing season. By undertaking these surveys in sites with contrasting hydrological conditions in both burned and unburned areas we have been able to determine which features of the vegetation control frost table thawing and how this relationship changes after a fire event and on different soil types.
14073691 Kholodov, A. L. (University of Alaska, Fairbanks, Fairbanks, AK); Meyer, H.; Schirrmeister, L.; Zolotareva, B. and Nicolsky, D. Estimation of ancient organic matter transformation due to thermokarst process at the Bykovsky Peninsula on Laptev Sea Coast [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0512, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Organic carbon stored in frozen Quaternary deposits can potentially be released into the modern biogeochemical cycle due to permafrost degradation. This task takes more and more attention recently including one of the important research questions related to the quality of organic matter (OM) in permafrost. The main method of OM liability estimation is the incubation. But it is impossible to reconstruct in the lab all varieties of natural conditions and real time frames of the organics decay process. Our approach is based on the comparison of quality of OM in (1) initial edoma and (2) taberal deposits (i.e. thawed under the lakes, packed and refrozen after lake drainage). Two pairs of boreholes located at the top of edoma and within adjoining thermokarst depressions had been drilled on Bykovsky Peninsula; northern Siberia near the Lena River delta. Samples taken from permafrost cores were analyzed for TOC, C/N ratio, d13C and composition of humus. Results show an overall decrease of the carbon pool due to partial decomposition of OM in talik under the lake. Insignificant differences of C/N ratio in original edoma (10.83 in average) and taberal deposits (11.82) point to relatively low stage of decomposition. The average d13C in edoma is about -24ppm, while in taberal deposits d13C decreases from close to edoma (-24ppm) to the bottom of taberal layer to -26ppm in the upper part with exponential trend. This trend can be explained by the increasing duration of organic decomposition within the talik under the lake at the top of the taberal layer in comparison with the bottom due to the process of talik formation. The humic acid content and the humic/fulvic acids ratio have similar patterns. Average content of humus content in edoma is 20% of TOC and ratio of humic and fulvic acids is 1. In taberal deposits content of humus increasing downward from 10 to 20% of TOC and the ratio of humic and fulvic acids is 0.8. The one-dimensional mathematical model of edoma thaw and subsidence under lake based on Stefan equation shows gradual decreasing of thawing duration from the top to the bottom of taberal layer. It allows us to estimate time rates of organic decomposition due to thermokarst process.
14073704 Lara, M. J. (University of Alaska, Fairbanks, Institute of Arctic Biology, Fairbanks, AK); McGuire, A. D.; Euskirchen, E. S.; Sloan, V. L.; Iversen, C. M.; Norby, R. J.; Genet, H.; Zhang, Y. and Yuan, F. Modeled change in carbon balance between 1970-2100 of a polygonal Arctic tundra ecosystem near Barrow, Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0525, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Northern permafrost regions are estimated to cover 16% of the global soil area and account for approximately 50% of the global belowground organic carbon pool. However, there are considerable uncertainties regarding the fate of this soil carbon pool with projected climate warming over the next century. In northern Alaska, nearly 65% of the terrestrial surface is composed of polygonal tundra, where microtopographic position (i.e. high center, low center, trough) varies surface hydrology, plant community composition, and biogeochemical cycling, over small (<5m) spatial scales. Due to large spatial heterogeneity and other non-linear responses of soil carbon to altered thermal regime, it is difficult to accurately estimate the fate of terrestrial carbon balance over decadal time-scales without explicitly considering the dynamically coupled processes driving permafrost dynamics, community structure, and ecosystem function. We use a new version of the terrestrial ecosystem model (TEM), which couples a dynamic vegetation and dynamic organic soil model (DVM-DOS-TEM). This large-scale ecosystem model is designed to study interactions among carbon and nitrogen cycling, vegetation composition, and soil physical properties, including permafrost and active layer dynamics. The model is parameterized and calibrated using data specific to the local climate, vegetation, and soils within various polygon land cover types (i.e. high center & rim, low center, trough) collected from sites (71.28°N 156.60° W) on the arctic coastal plain near Barrow, Alaska to estimate the likely change in carbon balance between 1970 and 2100 in this landscape. Model outputs are scaled across the Barrow Peninsula using the distribution of polygonal tundra land cover types, described by a land cover classification of 26.9 km2, using a 2008 multi-spectral QuickBird satellite image. The polygonal tundra land cover classification found high center & rims to represent 37.5% of the study area, low centers 19.7%, troughs 9.9%, water bodies (i.e. lakes, ponds, rivers) 17.8%, and non-polygonal tundra (i.e. drainage terraces & graminoid meadows) 15.1%, respectively. The overall accuracy of the map was 86%, based on 250 ground control points, and the Kappa coefficient was 0.77. Preliminary model runs for this region indicated variability in response to specific polygonal tundra land cover type through time. Overall, results suggest that it is important to consider discrete polygonal tundra features in regional estimates of carbon balance in northern Alaska.
14073700 Manies, K. L. (U. S. Geological Survey, Menlo Park, CA); Harden, J. W.; Turetsky, M. R. and Fuller, C. C. A comparison of recent, short-, and long-term carbon accumulation rates for a vegetation gradient in central Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0521, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Information regarding historical rates of carbon (C) accumulation will aid scientists in understanding how climate change may affect biogeochemical cycles in the future. We examined rates of C accumulation for the following three time periods: the last two thousand years (long-term rates), the last 30 years (short-term rates), and the last several years (recent rates). We compared C accumulation rates among these time periods for five different ecosystems found along a ~300-m transect within the Bonanza Creek Long-term Ecological Research (LTER) site. These sites were dominated by black spruce, low shrubs, tussock grass, Carex sp., or brown moss. The black spruce and shrub site are the only ecosystems currently underlain by permafrost. Three soil cores were taken at each site and analyzed for C content. In order to gain a robust understanding of C accumulation rates at each site, 14C measurements and 210Pb chronologies were also obtained, and flux measurements were taken at each site. 14C dates were acquired for the basal horizon of one profile for each ecosystem type, providing estimations of C accumulation rates since organic matter began to form. 210Pb chronologies for each soil profile allowed us to estimate C accumulation rates for the last several decades. Finally, CO2 flux measurements were taken at each site from May - September for five years (2007 - 2011), capturing recent C losses and gains. Although short-term C accumulation rates were lowest in the black spruce ecosystem, rates among ecosystems were not significantly different, due to large variability among soil profiles within each site (coefficient of variations of up to 50%). The long-term C accumulation rate at the black spruce site corresponds well to values measured in an adjacent black spruce forest using eddy covariance. The brown moss site had the highest long-term rates of C accumulation among the five ecosystems. Short-term C accumulation rates were always higher than long-term rates (40-100 gC/m2/yr and 3-30 gC/m2/yr, respectively). This information provides insights into the fate of C over different time scales for ecosystems which comprise important parts the boreal forest.
14073673 Mishra, U. (Argonne National Laboratory, Environmental Science, Argonne, IL); Jastrow, J. D.; Matamala, R.; Hugelius, G.; Ping, C. and Michaelson, G. J. Spatial variability of surface organic horizon thickness across Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B14E-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Surface organic horizon (SOH) thickness regulates water and nutrient availability, active-layer dynamics, thermal conductivity and permafrost stability, and the magnitude of carbon loss due to combustibility in northern circumpolar region. The objective of this study was to predict the fine-scale spatial variability of SOH thickness across Alaska. We used spatially referenced soil forming factors (topographic attributes, land cover types, climate, and surficial geology) and soil profile description data (n=549) in a local regression kriging framework to predict SOH thickness and its variability at 60-m spatial resolution across Alaska. Data trends were modeled by applying a geographically weighted regression approach to environmental variables, and the residuals were interpolated by ordinary kriging. Predicted thickness was validated using independent datasets (n= 80). Predicted SOH thickness across Alaska ranged from 5 to 200 cm, with a spatial average of 24 cm, and a coefficient of variation of 115%. The average prediction error was 15 cm, and the ratio of performance to deviation was 2. Environmental controls of SOH and its relationships with active-layer thickness will be presented. Fine-scale predictions of SOH thickness and variability can be used as a resource to validate and improve upon earth system models, which use modeled SOH thickness to simulate soil thermal conductivity and the consequences of fire in order to predict carbon-climate feedbacks.
14073661 Smith, L. J. (University of California, Berkeley, Energy and Resources Group, Berkeley, CA); Torn, M. S.; Conrad, M. E.; Curtis, J. B. and Hahn, M. S. Soil carbon vulnerability in Arctic coastal tundra; seasonal and spatial variations in 14C-CO2 [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
One reason permafrost soils contain large, old soil organic carbon stores is slow decomposition rates due to cold and waterlogged conditions. If climate change causes high latitude soils to warm and dry, carbon emissions from permafrost soils could be an important atmospheric greenhouse gas source. The vulnerability of global Arctic soil carbon stocks to increased decomposition due to thaw is hard to assess, due to environmental heterogeneity, complex controls on microbial processes, uncertain carbon stocks and flux rates, and poorly understood soil carbon stabilization mechanisms. To address these knowledge gaps, we are using radiocarbon measurements to estimate carbon turnover times in polygonal tundra in Barrow, Alaska. Specifically, we ask: (1) how do old versus recently fixed soil carbon pools contribute to total decomposition, (2) how does this vary seasonally, and (3) how does it vary across a permafrost degradation gradient? Old radiocarbon ages of soil organic matter in perennially frozen soils and deep portions of the seasonally thawed active layer reflect slow historic decomposition rates, and changes in the radiocarbon content of respired CO2 indicate relative mineralization rates of this old, stored carbon. At four time points from June-October 2013, we sample soil organic matter and respired CO2 from low-centered, transitional, and high-centered polygons characteristic of a permafrost degradation cycle. We measure the radiocarbon content of CO2 in surface fluxes and soil pore space from 3 depths in the soil profile, and concurrently incubate active layer soils to resolve the 14C-CO2 signatures of individual soil layers. Preliminary data from 2012 suggest that old soil carbon stores are vulnerable to decomposition. CO2 ages increase with depth in the profile from modern radiocarbon ages to as old as 3115 BP, and high incubation flux rates indicate availability to microbes. As part of the Next Generation Ecosystem Experiment (NGEE-Arctic), we now study the relationships between this carbon's vulnerability and environmental factors throughout the growing season. NGEE-Arctic aims to improve models of Arctic greenhouse gas fluxes by integrating a broad range of measurements from the cm- to the landscape-scale. By combining carbon dynamics measurements with data on geophysics, vegetation, microbiology, micrometeorology, and hydrology, we investigate the biological and environmental controls on greenhouse gas gross fluxes and net emissions.
14073702 Vonk, J. (Utrecht University, Department of Earth Sciences, Utrecht, Netherlands); Tank, S. E.; Spencer, R. G.; Mann, P.; Striegl, R. G.; Treat, C. C. and Wickland, K. Circum-Arctic biodegradability of fluvial dissolved organic carbon; a meta-analysis [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0523, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Circum-arctic frozen soils contain twice as much carbon as is currently present as greenhouse gases in the atmosphere. When frozen soils thaw, the carbon becomes available for microbial degradation. This process will generate greenhouse gases which may occur at the thaw site, but also during lateral transport in inland and coastal waters. Aquatic systems are increasingly recognized as reactive transport systems, but are generally not included in quantitative assessments of the magnitude of the permafrost carbon feedback. Carbon fluxes from lateral transport and aquatic gas emission can however be important components of the total watershed carbon budget. In this meta-analysis, part of the Research Coordination Network on Vulnerability of Permafrost Carbon, we assess the biolability of dissolved organic carbon in aquatic systems (soil leachates, streams, lakes, rivers) of the Arctic Ocean watershed, a region that is about 75% underlain by permafrost. We target dissolved organic matter as it is the most important intermediate in the global carbon cycle, fueling microbial metabolism, and it represents the major proportion (~80%) of the total organic carbon flux from Arctic watersheds. We extracted data from 15 existing literature studies. Additionally, we performed a standardized biodegradability experiment in three major Arctic watersheds. In each watershed (Yukon, Kolyma and Mackenzie River) we assessed the biodegradable fraction of the dissolved organic matter in the main river and an additional, watershed-representative, small stream, during multiple occasions in the summer season. By means of spatial data analyses we will present an estimate of aquatic processing of permafrost carbon in the Arctic Ocean watershed.
14073660 Webb, E. (University of Florida, Biology, Gainesville, FL); Schuur, E. A.; Natali, S. and Bracho, R. G. Wintertime ecosystem respiration shifts tundra from carbon sink to carbon source at tundra warming experiment [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B13N-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Northern latitude ecosystems play a significant role in the global carbon (C) budget due to the roughly 1700 Pg of C stored in permafrost soils. As high latitudes warm, previously frozen C is expected to decompose, thereby increasing CO2 fluxes to the atmosphere and potentially creating a positive feedback to climate warming. While warming has been shown to increase plant C uptake during the growing season, these seasonal C gains may be offset on an annual basis by ecosystem respiration (Reco) during the remaining seven months of the year. Here we present research from the Carbon in Permafrost Experimental Heating Research (CiPEHR) project, a tundra ecosystem warming experiment in interior Alaska. We partitioned the non-growing season into three segments: fall (October 1 until first snow), winter (snow-covered period until spring), and spring (snow depth less than 30 cm until melt out). During fall, we measured net ecosystem exchange and Reco using a static flux chamber. In winter, we measured Reco using chamber measurements and soda lime. For spring, we modeled fluxes based on known relationships between snow depth and photosynthetic rate of arctic evergreen species. We found that ecosystem warming caused plants to photosynthesize later in fall and increased C uptake during spring but also enhanced respiration during the long winter. We combined these off-season estimates with measurements from growing season auto-chamber data and found that despite the C gained during the growing season, ecosystem warming resulted in net annual C loss for the two years measured. This annual C loss was dependent on the magnitude of wintertime Reco. Our results indicate that snow depth, soil temperature, and day of season are the major determinants of wintertime Reco. Some climate models predict that arctic ecosystems will experience warmer winters with more snow. Thus, despite increased plant productivity during the growing season, we document that increased wintertime temperatures and precipitation will likely shift high latitude tundra ecosystems from a historical C sink to a C source.
14073689 Zhang, Y. (University of Alaska, Fairbanks, Institute of Arctic Biology, Fairbanks, AK); McGuire, A. D.; Genet, H.; Bolton, W. R.; Romanovsky, V. E.; Grosse, G.; Jorgenson, T. and Lara, M. Modeling thermokarst dynamics in Alaska ecosystems; description of the predisposition and initiation/expansion sub-models [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0510, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Warming in northern high latitude regions is increasing the vulnerability of permafrost to thawing. In ice-rich soils, permafrost degradation may result in ground surface subsidence and may cause transitions among ecosystems. These transitions are the result of significant changes in the local hydrology and soil thermal regime that impact vegetation composition and nutrient and carbon cycles. The Alaska Thermokarst Model (ATM) is a state-and-transition model that is being developed to predict thermokarst disturbance in response to climate warming. Predicting thermokarst disturbance requires (1) identifying the proportion of the landscape that is predisposed to thermokarst disturbance, and (2) calculating the proportion of the predisposed landscape that will be disturbed by thermokarst. To address these issues, two sub-models are being developed in the ATM: (1) a predisposition sub-model and (2) an initiation/expansion sub-model. The predisposition sub-model uses ground ice content, and lowland and permafrost distributions to determine the area of the landscape that is predisposed to thermokarst disturbance. In areas that are predisposed to thermokarst disturbance, the initiation/expansion model calculates (1) the area of the landscape in which thermokarst is initiated, and (2) and the annual expansion of the existing thermokarst features in the landscape. The ATM model has been designed to be integrated into the Alaska Integrated Ecosystem Model (AIEM), which includes coupled models of fire disturbance, soil thermal dynamics, and ecosystem structure and function at 1km*1km resolution. The initial application of the ATM in a test area located within the Alaskan boreal forest ecosystem is presented as a "proof-of-concept" in this presentation.
14073705 Ziolkowski, L. A. (University of South Carolina Columbia, Department of Earth and Ocean Sciences, Columbia, SC); Slater, G. F.; Onstott, T. C.; Whyte, L. and Townsend-Small, A. Microbes residing in young organic rich Alaskan soils contain older carbon than those residing in old mineral High Arctic soils [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0526, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic soils range from very organic rich to low carbon and mineral-dominated soils. At present, we do not yet fully understand if all carbon in the Arctic is equally vulnerable to mineralization in a warmer climate. Many studies have demonstrated that ancient carbon is respired when permafrost has thawed, yet our understanding of the active layer and permafrost carbon dynamics is still emerging. In an effort to remedy this disconnect between our knowledge of surface fluxes and below ground processes, we used radiocarbon to examine the microbial carbon dynamics in soil cores from organic rich soils near Barrow, Alaska and mineral soils from the Canadian high Arctic. Specifically, we compared the microbial community using lipid biomarkers, the inputs of carbon using n-alkanes and measured the 14C of both the bulk organic carbon and of the microbial lipids. In theory, the microbial lipids (phospholipid fatty acids, PLFA) represent the viable microbial community, as these lipids are hydrolyzed quickly after cell death. Variations in the PLFA distributions suggested that different microbial communities inhabit organic rich Alaskan soils and those of the Canadian high Arctic. When the PLFA concentrations were converted to cellular concentration, they were within the same order of magnitude (1 to 5 ´ 108 cells/g dry soil) with slightly higher cell concentrations in the organic rich Alaskan soils. When these cellular concentrations were normalized to the organic carbon content, the Canadian high Arctic soils contained a greater proportion of microbes. Although bulk organic carbon 14C of Alaskan soils indicated more recent carbon inputs into the soil than the Canadian high Arctic soils, the 14C of the PLFA revealed the opposite. For corresponding depth horizons, microbes in Alaskan soils were consuming carbon 1000 to 1500 years older than those in the Canadian high Arctic. Differences between the 14C content of bulk organic carbon and the microbial lipids were much smaller in Alaskan soil than that of the Canadian high Arctic soil, indicating that Alaskan microbes were interacting with the bulk organic carbon pool and Canadian high Arctic soil microbes were disconnected from the bulk organic carbon pool. Additionally, dissimilarities in the n-alkane distributions suggest vastly different carbon sources to these different soils. Collectively, these results suggest that (a) these Arctic soils contain a comparable abundance of microbes, (b) the organic carbon being accumulated in the Alaskan soil is likely from recent biomass, (c) mineral soil accumulation in the Canadian high Arctic is likely due to erosional inputs of ancient carbon and (d) the carbon stocks in Alaskan soils are more bioavailable to the microbes than those in mineral soils of the Canadian high Arctic. Incubation studies that incorporate gas fluxes and proteomics may tease apart if the observed differences in bioavailability are a function of temperature, substrate availability or some other variable.
14073710 Conrad, M. E. (Lawrence Berkeley National Laboratory, Berkeley, CA); Smith, L. J.; Curtis, J. B.; Hahn, M. S.; Bill, M. and Torn, M. S. Assessment of the effects of longer thaw seasons on subsurface methane production and consumption in the Arctic [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B21D-0533, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Methane is a highly potent greenhouse gas that is produced by microorganisms in anaerobic soil horizons. This methane can escape to the atmosphere or be consumed converted to CO2 by methane oxidizing organisms. The net balance of these two processes in Arctic soils is highly dependent on a complex interaction between factors including the depth of the active layer, soil moisture content, soil organic matter, plant cover and the types of methanogens and methane oxidizers present in the soil. To assess the importance of these factors and quantify production and oxidation rates of methane in Arctic soils, we are monitoring the concentrations and isotopic compositions of methane and dissolved inorganic carbon (DIC)/CO2 in different soil environments at the Barrow Experimental Observatory (BEO) as part of the Next Generation Ecosystem Experiment (NGEE) Arctic project. Gas/water samplers have been installed at depths of ~30 cm, 20 cm and 10 cm in the centers, edges and troughs of polygonal soil features on the BEO. In addition, surface flux samples are collected with each set of soil gas/water samples. During 2012, a limited set of surface flux samples and gas/water samples were collected early in the thaw season (late June/early July) and more complete sets were collected during mid August and late September/early October (at the beginning of freeze up). In general, the early season samples had much lower concentrations of dissolved methane and CO2/DIC than samples taken during the mid and late thaw season (concentrations of dissolved methane as high as 950 mM were measured in deep, water-saturated soils in the latter part of the thaw season). The isotopic compositions of methane indicate that acetoclastic methanogenesis is the dominant mode of microbial methane production in the low-centered, water-saturated polygons whereas CO2 reduction is more common in transitional and high-centered polygons. Increased d13C values of methane at shallower depths in aerobic, unsaturated soils of the transitional and high-centered polygons indicates that oxidation of methane produced at depth is occurring. Similar shifts were smaller to non-existent in the low-centered polygons, which also had the highest surface methane fluxes, suggesting that oxidation is not mediating the flux of methane to the atmosphere. For this year, we are collecting more frequent samples from a higher number of sites in order to quantify the effect of increasing thaw depth during the early part of the season and freeze up at the end of the season.
|
