|
15103008 Côté, Jean and Allard, Michel, chairpersons. 68th Canadian geotechnical conference and 7th Canadian permafrost conference; GEOQuébec 2015: Canadian Geotechnical Conference = Conference Canadienne de Géotechnique, 68, unpaginated, illus., 2015. Meeting: 68th Canadian geotechnical conference and 7th Canadian permafrost conference; GEOQuébec 2015, Sept. 20-23, 2015, Quebec City, QC, Canada. Individual papers within scope are cited separately.
15095619 Baltzer, J. L. (Wilfrid Laurier University, Waterloo, ON, Canada); Quinton, W. L. and Sonnentag, Oliver. Boreal forests in permafrost landscapes; changing structure and function in response to climate warming [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B53F-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Boreal forests occupy latitudes that are experiencing the greatest rates of warming on earth, a pattern that is expected to continue over the coming decades. Much of the Boreal is underlain by permafrost, which can be expected to have important consequences for forest structure, composition and functioning as the climate warms. The southern margin of permafrost is especially susceptible to warming, since in this region, the permafrost is discontinuous, relatively thin, warm and ice-rich. In the discontinuous permafrost zone, permafrost often forms the physical foundation on which trees develop, forming tree-covered peat plateaus where trees contribute to permafrost maintenance and aggradation processes through reductions in radiation load and changes in snow accumulation. Forests are restricted to peat plateaus while wetland communities occupy intervening permafrost-free areas. The extent and distribution of each land cover type is an important determinant of how boreal forest-wetland landscapes in the discontinuous permafrost zone function as part of the climate system. Climate warming is rapidly thawing permafrost leading to ground surface subsidence and transformation of the forests into wetlands, increasing both the areal extent and connectivity of the latter. In this presentation, we will use an integrative framework at the ForestGEO Scotty Creek Forest Dynamics Plot site near Fort Simpson, Northwest Territories, Canada to demonstrate the changes in ecological, hydrological and biosphere-atmosphere interactions within this boreal forest-wetland landscape characterized by rapidly degrading permafrost.
15095655 Bennett, K. E. (University of Alaska Fairbanks, Fairbanks, AK); Cherry, J. E.; Walsh, J. E. and Hinzman, L. D. Understanding future projected changes and historical trends in extreme climate and streamflow events in warm boreal permafrost basins of interior Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0395, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Changes in future and historical extreme events may have disastrous consequences in vulnerable systems such as the warm- permafrost-dominated Interior region of Alaska. This paper presents a study examining extreme hydro-climate events (temperature, precipitation and streamflow) in Interior Alaskan watersheds, focused on results from Fairbanks, Alaska, located within the Chena River basin. Results are presented for an ensemble of global climate models (GCMs) and emission scenarios, run through to 2100. GCMs, selected for performance over the Alaskan domain, project the largest increases in minimum daily minimum temperature (TNn), compared to maximum daily maximum temperature (TXx), in the winter and spring at the Fairbanks Airport station. The increases in TNn and TXx are much larger (two to four times) than the across GCM standard deviations, indicating robustness in the projected changes. Statistically significant increases in five-day maximum precipitation are also projected to occur by the 2080s, with the largest increases expected for the summer and fall seasons. Streamflow projections provided by running the Sacramento Soil Moisture Accounting model, coupled with the SNOW17 snow model, are analyzed using a generalized extreme value (GEV) theorem and nonparametric trend approach. The Chena River basin exhibits linear nonstationary increases in maximum and minimum annual streamflow projected by the 2080s under both the RCP 4.5 and RCP 8.5 scenarios, minimized by the Akaike Information Criteria statistic, corrected for small sample sizes. Changes are indicative of increased flow volumes in the summer and fall, following precipitation changes projected to occur during these seasons. These changes are distinct from trends and GEV analysis performed on the historical streamflow series, which indicate declining flows associated with the loss of snowpack observed as a statistically significant reduction in relative flow volume (-49%, p-value 0.01) during the May-June period for the Chena River. These results paint a compelling picture of shifting ecosystems and future changes to water resources that may pose risks to ecology and infrastructure in the region.
15092709 Bouchard, F. (Centre d'Études Nordiques, Quebec, QC, Canada); Preskienis, V.; Laurion, I. and Fortier, D. Carbon cycling in permafrost aquatic systems of Bylot Island, Eastern Canadian Arctic [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33G-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Aquatic systems are widespread in permafrost environments and play a crucial role in biogeochemical cycles, especially in GHG emissions (CO2, CH4). Amount, rate and age of carbon released from permafrost thawing can be strongly influenced by local geomorphology, which affects the biogeochemical dynamics of ponds and lakes. Bylot Island (Nunavut) is located in the heart of the Eastern Canadian Arctic and comprises numerous glacial and periglacial aquatic landscapes. Several glacial valleys of the island represent highly dynamic biogeosystems rich in permafrost ground ice, peat, and aquatic environments. We aimed at characterizing the influence of geomorphology and permafrost degradation processes on aquatic system biogeochemistry. We sampled gas, water, permafrost and lacustrine sediment in different types of aquatic systems: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes overlying unfrozen soil ("talik"). Preliminary results and field observations indicate a relationship between pond/lake morphology, processes of permafrost degradation, and the age of carbon processed--ultimately released as GHG--in these aquatic systems. Small and shallow ponds produced modern or young (< 500 yr BP) CO2 and CH4, whereas larger and deeper lakes released older (< 2000 yr BP) gases. We also observed a substantial difference in gas fluxes between similar ponds of comparable size and depth. When pond margins were actively eroding (eroded and collapsed peat blocks), fluxes were several orders of magnitude higher than when their margins were stabilized. Such findings underscore the strong impact of local geomorphology and permafrost degradation processes on aquatic system biogeochemistry. Upscaling of GHG emissions at the watershed scale requires a better understanding of the emissions from different types of ecosystems.
15095603 Brown, D. N. (University of Alaska Fairbanks, Fairbanks, AK); Jorgenson, T.; Douglas, Thomas A.; Romanovsky, V. E.; Kielland, K.; Euskirchen, E. S. and Ruess, R. Influence of fire on permafrost in lowland forests of the Tanana Flats, Interior Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B51H-0114, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The degradation of ice-rich permafrost in lowland ecosystems may have particularly strong ecological impacts due to the potential for thaw settlement and subsequent water impoundment. We examined the effects of fire disturbance on permafrost across a chronosequence of fire scars (1930-2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats of Interior Alaska, and utilized a thermal permafrost model (GIPL) to assess the roles of soil physical properties and historic climate. Field-based calculations of potential thaw settlement following the loss of ice-rich permafrost ranged from 0.4 m to 0.9 m. This subsidence would cause the surface elevations of current day forests to drop, on average, to 0.1 m below the surface water level of adjacent collapse-scar bogs, likely resulting in water impoundment. However, the vulnerability of permafrost to deep thawing and talik formation was variable among fire scars due to heterogeneity in organic layer thickness, soil texture, moisture, and associated thermal properties. Simulated reductions in organic layer thickness predicted talik formation in peat and silt loam-dominated soils, but not in sandy loams. The vulnerability of permafrost to talik formation increased under the climatic conditions since 1970, which were characterized by higher air temperatures. Pronounced permafrost thawing occurred during periods of high snow accumulation, whereas periods of low snow accumulation appeared to facilitate permafrost recovery. Simulations of the complete removal of the organic layer (high severity fire) in silt loam-dominated sites suggested the long-term loss of permafrost under the climate of the last century. Overall, the influence of fire on permafrost in these lowland ecosystems appears to be dependent on soil physical properties, fire severity, and climatic conditions.
15095691 Destouni, Georgia (Stockholm University, Stockholm, Sweden). Transformation pathways through the land-water geosphere in permafrost regions [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic land-water undergoes and participates in multiple climate-driven and other (natural and direct human-driven) environmental exchanges and changes. A bits-and-pieces approach to these may miss essential aspects of change propagation and transformation by land-water across its multiple components (soil water, groundwater, hyporheic water, streams/rivers, wetlands and lakes) and from/to other geospheres (atmosphere and its climate change drivers, cryosphere and its permafrost segment, as well as the anthroposphere/technosphere, geosphere/pedosphere, marine hydrosphere and biosphere). This paper synthesizes results from recent modeling and observational studies of land-water flow and dissolved carbon transport in permafrost regions, departing from a new conceptualization of the land-water geosphere as a scale-free catchment-wise organized system (Figure 1), emphasizing several key new system aspects compared to traditional hydrosphere/water cycle view. Among these new aspects, we particularly investigate here the role of land-water flow and transport pathways as system coupling agents, with focus on their variability and change with varying permafrost conditions and permafrost thaw in a warming climate. Utilizing the conceptualization of land-water as a continuous yet structured geosphere, following the proposed flow-transport pathways of change propagation-transformation, we identify patterns of permafrost-related and other changes in Arctic hydrology.
15095654 Endalamaw, A. M. (University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK); Bolton, W. R.; Hinzman, L. D.; Morton, Don and Young, J. M. Meso-scale hydrological modeling using small scale parameterizations in a discontinuous permafrost watershed in the Boreal forest ecosystem [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0394, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The sub-Arctic region lies in the transition zone between the warm temperate region to the south and the cold arctic region to the north. The sub-Arctic hosts sharply contrasting ecosystems that vary over short horizontal spatial scales due to the presence or absence of permafrost. In the discontinuous permafrost zone, the presence or absence of permafrost plays a dominant role to many hydrological processes including stream flow, soil moisture, and water storage dynamics. The distribution of permafrost also has a strong influence on ecosystem composition and function. The land cover and vegetation distribution is also an important parameter affecting the stream flow responses due to the large differences in the transpiration rates between coniferous and deciduous vegetation. As a result, accurate simulation of the hydrology in this region is challenging. The objectives of this study are to improve the parameterization of meso-scale hydrologic simulations in the discontinuous permafrost zone through fine-scale observation and modeling. Slope and aspect, derived from 30 m Digital Elevation Model (DEM), are used as a proxy for permafrost distribution and vegetation composition. Small-scale parameterizations were conducted at the two sub-basins (area ~11 km2 ) of the Caribou-Poker Creeks Research Watershed (CPCRW) using the Variable Infiltration Capacity (VIC) meso-scale hydrological model. The small scale parameterization simulation results indicate that slope and aspect based vegetation cover and soil parameter parameterization improve meso-scale hydrological modeling in these regions. In order to test the extent to which these small-scale parameterizations are valid, the Chena River Basin (area ~5,478 km2), located in Interior Alaska, is being simulated using these small-scale parameterizations. Aspect will be used as the proxy for the parameterization of vegetation cover and soil property. Results from the VIC simulation using the small scale parameterization will be compared with the results of a simulation using a meso-scale parameterization to evaluate the improvement that may be obtained from higher resolution analyses.
15095558 Ernakovich, J. G. (CSIRO, Division of Land and Water, Glen Osmond, Australia); Lynch, L. M.; Calderon, F.; Brewer, P. E. and Wallenstein, M. D. Unraveling the complex drivers of CO2 and CH4 flux in permafrost soils [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41G-0142, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost contains large stocks of organic carbon (C) that are vulnerable to decomposition following thaw, which could increase greenhouse gas (GHG) emissions leading to a potential C-climate feedback. Despite their global importance, GHG emissions from thawing permafrost are difficult to predict due to their complex mechanisms. The objective of this study was to determine the mechanisms controlling GHG flux from permafrost soil, comparing CH4 and CO2 production. We simulated permafrost thaw under drained and anoxic conditions at 1 and 15 °C, and measured CH4 and CO2 production. We also measured soil chemical and biological parameters (e.g. mid-infrared spectroscopy, iron speciation, soil redox, and next generation sequencing of the 16S gene). All treatments produced considerable amounts of CO2 (oxic, 15 °C: 0.3-2.0 mg CO2-C gdws-1). CH4 production was highly variable (anoxic, 15 °C: 0.4-67 mg CH4-C gdws-1), which was not explained by soil C content (2-603 mg CH4 g soil C-1). We explored the reasons behind this seemingly random variability in CH4 production, and found that it can be explained by the activity of non-methanogenic anaerobes and substrate supply. For example, we found that the activity of iron reducers improved the fit of CH4 production model, reducing second order bias correction (AICc) from 80 to 38, as did a gross measure of anaerobic activity (AICc reduced from 80 to 60), however neither was statistically significant (p>0.05). In methanogenesis, the lability, rather than the total chemistry of the dissolved organic matter, was important for determining gas production, but the opposite was found to be important for predicting CO2 production. Differences in methanogen populations likely also contributed to the variability in the CH4 production, and further analysis of the 16S gene abundances will elucidate this. In summary, production of CH4 depends not only on the methanogens themselves, but also on the activity of the non-methanogenic anaerobes and the lability of the DOM. Thus, methanogenesis should be viewed as a process dependent on a consortium of anaerobes. Because the prediction of GHG fluxes is critical to our understanding of the impact of permafrost C on the global C cycle, a more mechanistic understanding of the processes governing anaerobic GHG flux will be crucial.
15095684 Etzelmuller, Bernd (University of Oslo, Department of geosciences, Oslo, Norway); Westermann, Sebastian; Gisnas, Kjersti; Aas, K. S.; Schuler, T. V.; Dunse, Thorben; Ostby, Tornbjorn; Berntsen, T. K.; Kristjansson, J. E. and Stordal, Frode. Towards better integration of climate models and models for the terrestrial cryosphere (permafrost and glaciers) [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C13B-0452, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Predictions of the future climate are based on Earth System Models operating on coarse grids, while the impact of a changing climate on most elements of the terrestrial cryosphere is strongly heterogeneous. This scale discrepancy hampers realistic predictions of the development of permafrost landscapes or glacier mass balances. At the University of Oslo, Norway, meteorologists and glaciologists/permafrost scientists working on the terrestrial cryosphere, have since 2011 collaborated on approaches trying to overcome such scaling problems. For intermediate spatial scales of 1-3 km we use two approaches: First, we apply the Weather Research and Forecasting model (WRF) to dynamically downscale climate parameters for a period of 10 years. The results are validated against continuous energy balance measurements at Ny-Alesund and against meteorological and in-situ mass-balance observations from the Austfonna ice cap, both at Svalbard. Those data sets feed into simple permafrost modelling schemes and glacier mass balance models, respectively. Secondly, for permafrost we combine multi-temporal remote sensing products and thermal ground modeling, compiling maps of permafrost temperatures and thaw depth. Such a "permafrost re-analysis" has significant potential for validation of large-scale models by delivering a statistical distribution of ground parameters for coarse modeling grid cells. However, a spatial scale of 1 km is still too coarse to resolve the spatial heterogeneity of especially permafrost properties because of the large heterogeneity of e.g. snow cover, but also surficial material and/or vegetation cover. For scales below 1 km we propose to describe this variability in a statistical way by distribution functions rather than a deterministic representation on refined grids. We demonstrate that the concept facilitates modeling of the transition from continuous over discontinuous to sporadic permafrost along the climatic gradient from Svalbard to Southern Scandinavia, which is not possible without subgrid representation of snow depths. Finally, we evaluate the possibility to improve simulations of surface energy fluxes also in atmosphere and climate models, through better representation of sub-grid scale variability of variables relevant for atmosphere-cryosphere interactions.
15095648 Frampton, Andrew (Stockholm University, Stockholm, Sweden); Destouni, Georgia and Pannetier, Romain. Changes in travel times in thawing permafrost systems [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0386, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Physically based models for permafrost-hydrological interactions can contribute to improved process understanding and aid in bridging the gap between limited field observations and large scale heat, water and material transport effects. Previous studies have demonstrated the importance of including coupled heat and multiphase flow processes in order to better understand and describe the dynamics of permafrost change and its interactions with temperature and subsurface water conditions in partially frozen ground. In particular, long-term simulation results show that warming trends reduce the temporal and seasonal variability characteristics of groundwater and its discharges into surface waters. A compelling question for waterborne transport of substances relevant for climate feedbacks, biogeochemical cycling and/or water pollution is how different scenarios of hydro-climatic change influence permafrost formation and degradation dynamics and through that also the residence times of subsurface water, from land surface recharge to surface water discharge. In this contribution, heat transport and water flow in permafrost systems which include the active layer are simulated and changes in water fluxes and associated travel times of water parcels through the subsurface are investigated. Initial results indicate that the geological setting can notably impact the spread and change in travel time distributions during warming. Also, for all cases investigated the median and minimum travel times increase, indicating longer flow pathways as permafrost thaws. Potential effects on solute transport and climatic feedbacks are highlighted.
15092447 Gao Hong (Peking University, Beijing, China); Lu, H. and Lu, Z. Pore effect on the occurrence and formation of gas hydrate in permafrost of Qilian Mountain, Qinghai-Tibet Plateau, China [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11B-0024, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Gas hydrates were found in the permafrost of Qilian Mountain, Qinghai- Tibet Plateau, China in 2008. It has been found that gas hydrates occur in Jurassic sedimentary rocks, and the hydrated gases are mainly thermogenic. Different from the gas hydrates existing in loose sands in Mallik, Mackenzie Delta, Canada and North Slope, Alaska, USA, the gas hydrates in Qilian Mountain occurred in hard rocks. For understanding the occurrence and formation mechanism of gas hydrate in hard rock, extensive experimental investigations have been conducted to study the pore features and hydrate formation in the rocks recovered from the hydrate layers in Qilian Mountain. The structures of sedimentary rock were observed by high-resolution X-ray CT, and pore size distribution of a rock specimen was measured with the mercury-injection method. Methane hydrate was synthesized in water-saturated rocks, and the saturations of hydrate in sedimentary rocks of various types were estimated from the amount of gas released from certain volume of rock. X-ray CT observation revealed that fractures were developed in the rocks associated with faults, while those away from faults were generally with massive structure. The mercury-injection analysis of pore features found that the porosities of the hydrate-existing rocks were generally less than 3%, and the pore sizes were generally smaller than 100 nm. The synthesizing experiments found that the saturation of methane hydrate were generally lower than 6% of pore space in rocks, but up to 16% when fractures developed. The low hydrate saturation in Qilian sedimentary rocks has been found mainly due to the small pore size of rock. The low hydrate saturation in the rocks might be the reason for the failure of regional seismic and logging detections of gas hydrates in Qilian Mountain.
15095621 Genet, H. (University of Alaska, Institute of Arctic Biology, Fairbanks, Fairbanks, AK); Zhang, Y.; McGuire, A. D.; He, Y.; Johnson, Kristofer D.; D'Amore, D. V.; Zhou, X.; Bennett, A.; Breen, A. L.; Biles, F. E.; Bliss, N. B.; Euskirchen, E. S.; Kurkowski, T. A.; Pastick, N.; Rupp, S. T.; Wylie, B. K.; Zhu, Z. and Zhuang, Q. The importance of permafrost thaw, fire and logging disturbances as driving factors of historical and projected carbon dynamics in Alaskan ecosystems [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B53H-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Carbon dynamics of natural ecosystems are influenced by disturbance regimes of various frequencies and magnitudes. With global change, these disturbances are projected to increase in frequency and/or magnitude and may have significant effects on future net carbon balance, especially in high latitude ecosystems where carbon stocks are among the largest on Earth and climate change is substantial. In Alaska, permafrost degradation and fire in the boreal and arctic regions and logging in the southern coastal region are the main disturbances that affect ecosystems. Large uncertainties related to the effects of these disturbances on the capacity of these regions to store carbon still exist mainly due to difficulty in representing permafrost degradation in current ecosystem models. We ran the Terrestrial Ecosystem Model (TEM), which explicitly simulates the carbon cycle and permafrost dynamics, coupled with a disturbance model (the Alaska Frame Based Ecosystem Code, ALFRESCO) to assess the relative importance of permafrost thaw, wildfire, and forest management on historical and projected carbon balance and carbon stocks in Alaska, from 1950 to 2100, at a 1-km resolution. Our simulations showed that the increase in plant productivity in response to warming in boreal and arctic regions is offset by soil carbon loss due to permafrost degradation and wildfire combustion during both historical and future simulations. Fire disturbances act as a catalyst accelerating permafrost degradation and associated soil carbon loss. In addition, our preliminary results for south coastal regions of Alaska indicate that logging of second growth forests could influence carbon dynamics in that region. Overall, these results have implications for land management strategies and illustrate the importance of taking into account multiple types of disturbance regimes in ecosystem models for Alaska.
15095553 Goeckede, M. (Max Planck Institute for Biogeochemistry, Jena, Germany); Kwon, M. J.; Kittler, F.; Burjack, I.; Heimann, M.; Zimov, N. and Zimov, S. A. An inter-disciplinary approach to assess adaptation processes resulting from a long-term drainage disturbance of a permafrost ecosystem [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41E-0113, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Hydrology plays a pivotal role for the sustainability of the permafrost carbon reservoir in the northern high latitudes under climate change. Changes in moisture conditions may significantly carbon pools and fluxes, and in addition trigger secondary shifts in biogeochemical and biogeophysical ecosystem properties, with feedbacks to the carbon cycle. The net impact of hydrologic disturbance, e.g. as a result of changes in drainage conditions, on the links between carbon processes and climate is therefore highly uncertain. This study presents findings from an interdisciplinary experiment established on the floodplain of the Kolyma River near Cherskiy, northeast Siberia. Parts of our study site have been artificially drained by ditches since 2004, simulating the formation of a channel system triggered by the thawing of ice wedges in ice-rich permafrost. Observations from this area are directly compared to data from a nearby undisturbed reference site. CO2 and CH4 flux measurements are available from 2 eddy-covariance towers operated year-round, and a distributed array of soil chambers. Additional observations target e.g. microbial and vegetation community structures, radiocarbon signals, nutrient availability and seasonal dynamics in phenology. Drainage has lowered average soil water levels by about 20cm, resulting in systematic shifts in e.g. soil temperature regime and snow cover. These dryer and warmer conditions have shifted the vegetation structure away from the formerly dominating cotton grasses towards tussock-forming sedges and shrubs. Microbial communities were found to have adapted to the new environment, e.g. concerning the dominating orders of methanogenetic archaea. Radiocarbon signals indicate that the drainage has unlocked older carbon pools from deeper layers. The combined effects of these changes reduce the CO2 uptake and significantly lower the CH4 emissions in the drained area, resulting in a higher net carbon sink compared to the reference. Seasonal dynamics of these shifts were found to be complex, particularly concerning the role of the shoulder seasons. Based on the altered functional relationships between environmental drivers and carbon fluxes, we expect that drainage will systematically affect the trajectories of carbon pools and fluxes under future climate change.
15095707 Haghshenas-Haghighi, Mahmud (Deutsches GeoForschungsZentrum, Potsdam, Germany); Motagh, M.; Heim, Birgit; Sachs, Torsten; Kohnert, Katrin and Streletskiy, D. A. Using TerraSAR-X and hyperspectral airborne data to monitor surface deformation and physical properties of the Barrow permafrost landscape, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C21C-0345, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
In this study, we assess seasonal subsidence/heaving due to thawing/freezing of the permafrost in Barrow (71.3N, 156.5W) at the northernmost point of Alaska. The topographic relief in this area is low. Thick Permafrost underlies the entire area, with large ice volumes in its upper layer. With a large collection of field measurements during the past decades at the Barrow Environmental Observatory (BEO), it is an ideal site for permafrost investigation. There are long term systematic geocryological investigations within the Global Terrestrial Network (GTN-P) of the Circumpolar Active Layer Monitoring (CALM) programme. We use 28 TerraSAR-X images, acquired between December 2012 and December 2013 and analyze them using the Small BAseline Subset (SBAS) technique to extract time-series of ground surface deformation. We also analyze hyperspectral images acquired by the airborne AISA sensor over Barrow area, within the AIRMETH2013 programme, to assess physical characteristics such as vegetation biomass and density, surface moisture, and water bodies. Finally, we combine the information derived from both InSAR and hyperspectral analysis, with field measurements to investigate the link between physical characteristics of the permafrost and surface displacement.
15092466 Hammad, A. O. (University of Alberta, Biological Sciences, Edmonton, AB, Canada); Mahony, M.; Froese, Duane G. and Lanoil, Brian D. Microbial community dynamics from permafrost across the Pleistocene-Holocene boundary and response to abrupt climate change [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11H-0132, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Earth is currently undergoing rapid warming similar to that observed about 10,000 years ago at the end of the Pleistocene. We know a considerable amount about the adaptations and extinctions of mammals and plants at the Pleistocene/Holocene (P/H) boundary, but relatively little about changes at the microbial level. Due to permafrost soils' freezing anoxic conditions, they act as microbial diversity archives allowing us to determine how microbial communities adapted to the abrupt warming at the end of P. Since microbial community composition only helps differentiate viable and extant microorganisms in frozen permafrost, microbial activity in thawing permafrost must be investigated to provide a clear understanding of microbial response to climate change. Current increased temperatures will result in warming and potential thaw of permafrost and release of stored organic carbon, freeing it for microbial utilization; turning permafrost into a carbon source. Studying permafrost viable microbial communities' diversity and activity will provide a better understanding of how these microorganisms respond to soil edaphic variability due to climate change across the P/H boundary, providing insight into the changes that the soil community is currently undergoing in this modern era of rapid climate change. Modern soil, H and P permafrost cores were collected from Lucky Lady II site outside Dawson City, Yukon. 16S rRNA high throughput sequencing of permafrost DNA showed the same trends for total and viable community richness and diversity with both decreasing with permafrost depth and only the richness increasing in mid and early P. The modern, H and P soils had 50.9, 33.9, and 27.3% unique viable species and only 14% of the total number of viable species were shared by all soils. Gas flux measurements of thawed permafrost showed metabolic activity in modern and permafrost soils, aerobic CH4 consumption in modern, some H and P soils, and anaerobic CH4 production in one H sample. Soil chemistry analysis showed that older permafrost, P, had higher pH, lower total nitrogen, ammonium, and organic carbon than younger permafrost, H.
15092665 Harder, S. R. (McGill University, Montreal, QC, Canada); Roulet, N. T.; Strachan, I. B.; Crill, P. M.; Persson, A.; Pelletier, L. and Watt, C. Interpreting carbon fluxes from a spatially heterogeneous peatland with thawing permafrost; scaling from plant community scale to ecosystem scale [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Various microforms, created by spatial differential thawing of permafrost, make up the subarctic heterogeneous Stordalen peatland complex (68°22'N, 19°03'E), near Abisko, Sweden. This results in significantly different peatland vegetation communities across short distances, as well as differences in wetness, temperature and peat substrates. We have been measuring the spatially integrated CO2, heat and water vapour fluxes from this peatland complex using eddy covariance and the CO2 exchange from specific plant communities within the EC tower footprint since spring 2008. With this data we are examining if it is possible to derive the spatially integrated ecosystem-wide fluxes from community-level simple light use efficiency (LUE) and ecosystem respiration (ER) models. These models have been developed using several years of continuous autochamber flux measurements for the three major plant functional types (PFTs) as well as knowledge of the spatial variability of the vegetation, water table and active layer depths. LIDAR was used to produce a 1 m resolution digital evaluation model of the complex and the spatial distribution of PFTs was obtained from concurrent high-resolution digital color air photography trained from vegetation surveys. Continuous water table depths have been measured for four years at over 40 locations in the complex, and peat temperatures and active layer depths are surveyed every 10 days at more than 100 locations. 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. Our results show that the Sphagnum, palsa, and sedge PFTs have distinctly different LUE models, and that the tower fluxes are dominated by a blend of the Sphagnum and palsa PFTs. We also see a distinctly different energy partitioning between the fetches containing intact palsa and those with thawed palsa: the evaporative efficiency is higher and the Bowen ration lower for the thawed palsa fetches.
15092493 Hugelius, Gustaf (Stockholm University, Stockholm, Sweden). Estimating soil carbon pools in the northern permafrost region; challenges in adapting datasets to models [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11K-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Current global scale estimates of soil organic carbon (SOC) stocks do not account for pedogenic processes unique to permafrost environments. The Northern Circumpolar Soil Carbon Database (NCSCD) was compiled to address this lack of knowledge of permafrost affected soils. The NCSCD links pedon data in the 0-3 m depth range from the northern permafrost regions to several digitized regional soil classification maps to produce a combined circumpolar coverage. While these different soil classification maps have been harmonized to a common soil classification system, the maps are of different origin and age and they were produced at a range of different scales. The spatial distribution of soil pedon data is also highly uneven with notable data-gaps in central Siberia, the High Arctic and Alpine regions. The NCSCD is thus a dataset with its roots in traditional soil survey and soil map data and with substantial uncertainties and data-gaps. The original maps are subdivided into polygons where soil specialists have mapped different coverages of soil orders. The NCSCD has been gridded and is currently in use for many different model-based studies. This conversion of polygon-based data to the gridded world of spatial or process-based models can affect accuracy, precision and usability of a dataset. There are also inherent difficulties in assessing the uncertainty of stock or process quantifications based on polygon soil maps such as the NCSCD. Soil science is moving into a fully digital world where new maps of soil order distribution or soil properties are based on gridded remote sensing products. Such data can more easily be scaled and adapted for use in grid-based soil models. However, it is argued that the traditional soil maps are still extremely valuable data-sets that contain information that may be lost in fully digital soil mapping approaches. This presentation discusses these issues and gives some examples of how existing pedon databases and soil maps can be made useful for broad scale model applications.
15095620 Iijima, Y. (Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan); Abe, K.; Ise, H.; Masuzawa, T. and Fedorov, A. N. Permafrost and forest degradation after wet climate years in eastern Siberian boreal forest [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B53H-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Unusual precipitation increase during summer through winter had continued since 2004 in the central Lena river basin, eastern Siberia. The precipitation increase led to deepening active layer (permafrost thawing near the surface) accompanying with remarkable increase in soil moisture. The perennially waterlogged conditions had exacerbated the boreal forest habitat; that is, larch trees had widely withered and died in this region. The present study clarified spatial extent of permafrost and forest degradation due to the unexpected hydro-climate-driven damages. We have attempted to extract the degraded boreal forest based on satellite image analyses, along with expansion of the perennially waterlogged surface area. We used ALOS-PALSAR and AVNIR-2 images taken from 2006 to 2009. Classification of waterlogged area was performed by PALSAR images with supervised classification based on a microwave backscattering coefficient. Then, we compared the distribution of the waterlogged area between multi-years. Additional supervised classification of boreal forest change was conducted using AVNIR-2 images. Both classifications produced the multi-years change in degraded boreal forest at the intensive observational sites in both left and right bank of Lena River near Yakutsk. In the right bank area, most of alas lakes expanded and boreal forest on the periphery of lakes turned to waterlogged surface. In the left bank area, in contrast, waterlogged surface expanded at concaved terrain and along valleys in conjunction with forest degradation. Field survey supported that humidified and deepening active layer along slope and near alas lakes correspond with the gradient of forest degradation and enhanced thermokarst activity. Both of increasing precipitation and thawing ice in permafrost might cause the degradation. In brief, the method combining ALOS satellite images has possibility to detect permafrost and forest degradation caused by wet climate in boreal forest.
15095652 Iwahana, G. (University of Alaska Fairbanks, Fairbanks, AK); Harada, K.; Uchida, M.; Kondo, Miyuki; Saito, K.; Narita, K.; Kushida, K.; Hinzman, L. D.; Fukuda, Masami and Tsuyuzaki, S. Permafrost degradation after the 2002 wildfire in Kougarok, Seward Peninsula, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0391, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Geomorphological and thermo-hydrological changes after wildfire were investigated here to clarify the rates of permafrost degradation and impacts on the surrounding environment. Study sites are located in Kougarok on the central Seward Peninsula of northwestern Alaska. This area is classified as zones of either continuous and discontinuous permafrost. In 2002, wildfire burned a large area of this region. We selected an intact area and a burned area as research sites located close to one another and divided by a road. The surface organic layer was either combusted or reduced in thickness during the fire. It is assumed that the vegetation cover and subsurface conditions were similar between both sites before the fire. General vegetation at unburned sites was shrub-tussock tundra with more than 30% evergreen shrubs, about 30% deciduous shrubs and about 20% sedges. Our studies of aerial photography and high-resolution satellite images showed that surface subsidence due to thermokarst developed differentially within some of the burned and vehicle-disturbed areas, exposing the polygonal reliefs on the surface. Within burned areas absent the thermokarst polygonal reliefs, soil moisture was higher at burned areas than unburned, and the active layer thickness was about 1.5-2.0 times deeper at the burned area during the initial stage of the study (2005-2007). In the following years, however, the difference in active layer thickness decreased, and thickness for the burned area seemed to be recovering to pre-fire status. Geophysical surveys demonstrated that there had been no detectable difference in the depth of the permafrost base between the burned and unburned areas. On the other hand, at the burned site with thermokarst polygonal reliefs, we confirmed using differential GPS that the polygonal reliefs actually coincides with depression lines along the subsurface ice wedge network. Near-surface unfrozen and frozen soil cores down to 1.6 m depth were sampled at seven and three points at burned and intact sites, respectively. Our geocryological analysis of cores has added evidence for permafrost disturbance, also suggesting that permafrost could be used for the reconstruction of development and degradation history of the study site.
15095602 Jain, A. K. (University of Illinois at Urbana Champaign, Urbana, IL); El Masri, B.; Barman, R.; Shu, S. and Song, Y. The interactions between biogeophysical and biogeochemical processes and their feedbacks on permafrost soil carbon stocks [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B51H-0113, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
One of the major challenges in more detailed Earth system models (ESMs) is the treatment of the biophysical and biogeochemical processes and feedbacks and their impact on soil organic carbon in the Northern high latitudes (NHL). We use a land surface model, the Integrated Science Assessment Model (ISAM) to investigate the effects of feedbacks between the biogeochemical and biogeophysical processes on the model estimated soil organic carbon (SOC) for the NHL permafrost region. We not only focus on recent model improvements in the biogeophysical processes that are deemed important for the high latitude soils/snow; such as deep soil column, modulation of soil thermal and hydrological properties, wind compaction of snow, and depth hoar formation; on permafrost SOC; but also biogeochemical processes; such as dynamic phenology and root distribution, litter carbon decomposition rates and nitrogen amount remaining; on soil biogeochemistry. We select multiple sites to evaluate the model. We then carried out several model simulations to study the effects of feedbacks between biogeochemical and biogeophysical processes on SOC. Our model analysis shows that including the biogeophysical processes alone could increase modeled NHL permafrost carbon by about 30% compared to measurements. Accounting for the biogeochmical processes further improve the NHL soil carbon.
15092686 Kittler, F. (Max Planck Institute for Biogeochemistry, Jena, Germany); Heimann, M.; Goeckede, M.; Zimov, S. A. and Zimov, N. Assessing the net effect of long-term drainage on a permafrost ecosystem through year-round eddy-covariance flux measurements [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B32B-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost regions in the northern high latitudes play a key role in the carbon budget of the earth system because of their massive carbon reservoir and the uncertain feedback processes with future climate change. For an improved understanding of mechanisms and drivers dominating permafrost carbon cycling, more observations in high-latitude regions are needed. Particularly the contribution of wintertime fluxes to the annual carbon budget and the impact of disturbances on biogeochemical and biogeophysical ecosystem properties, and the resulting modification of the carbon cycle, have rarely been studied to date. In summer of 2013, we established a new eddy-covariance station for continuous, year-round monitoring of carbon fluxes and their environmental drivers near Cherskiy in northeast Siberia (68.75°N, 161.33°E). Parts of the observation area have been disturbed by drainage since 2004, altering the soil water conditions in a way that is expected for degrading ice-rich permafrost under a warming climate. With two eddy-covariance towers running in parallel over the disturbed (drained) area and a reference area nearby, respectively, we can directly infer the disturbance effect on the carbon cycle budgets and the dominating biogeochemical mechanisms. This study presents findings based on 16 months of continuous eddy-covariance CO2 flux measurements (July 2013-October 2014) for both observation areas. At both towers, we observed systematic, non-zero flux contributions outside the growing seasons that significantly altered annual CO2 budgets. A direct comparison of fluxes between the two disturbance regimes indicates a net reduction of the sink strength for CO2 in the disturbed area during the growing season, mostly caused by reduced CO2 uptake with low water levels in late summer. Moreover, shifts in soil temperatures and snow cover caused by reduced soil water levels result in lower net CO2 emissions during the winter at the drained area, which is partly compensated by a pronounced emission peak immediately following the spring flood in June. Based on the composition and weighting of environmental factors dominating the fluxes in different seasons, we demonstrate systematic shifts in the carbon cycle mechanisms as a result of 10 years of disturbance in the drained area.
15095695 Koch, J. C. (U. S. Geological Survey, Alaska Science Center, Anchorage, AK); Schmutz, J. A. and Fondell, T. Supra-permafrost subsurface flow on the Arctic Coastal Plain of Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Subsurface flow is often considered to be a minor component of arctic coastal water budgets due to low land surface slopes and shallow, impermeable permafrost. However, in these landscapes the ground may thaw up to a meter during summer, and microtopography on lake shores and ground ice gradients may promote subsurface flow. Using permeameter and infiltration tests coupled with lake water budgets, we test the hypothesis that subsurface flow may be an important component of arctic lake water budgets after the spring freshet. Water budgets incorporating only evaporation, precipitation, and stream discharge indicated substantial, unmeasured fluxes that varied in direction and magnitude in full and partially-drained lakes. We were able to successfully reproduce the observed fluxes with a model incorporating drainage from thawing soils, storm runoff, and lake edge evapotranspiration. Thaw drainage was the dominant flux in a full lake, and runoff and evapotranspiration became increasingly important in partially drained lake basins. Our results suggest that supra-permafrost flow is an important component of arctic lake water budgets that must be considered to accurately predict water, solute, and heat fluxes in a changing Arctic.
15095552 Loranty, M. M. (Colgate University, Geography, Hamilton, NY); Berner, L. T.; Alexander, H. D. and Davydov, S. P. Variability in canopy transpiration with atmospheric drivers and permafrost thaw depth in an Arctic Siberian larch forest [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41E-0112, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic ecosystems are experiencing rapid change associated with amplified rates of climate warming. A general increase in vegetation productivity has been among the expected responses for terrestrial ecosystems in the Arctic. However, recent evidence from satellite derived productivity metrics has revealed a high degree of spatial heterogeneity in the magnitude, and even the direction, of productivity trends in recent decades. Declines in productivity may seem counterintuitive in what are traditionally thought to be temperature limited ecosystems. However a warmer and drier atmosphere in conjunction with changing permafrost conditions may impose hydrologic stresses on vegetation as well. Many Siberian ecosystems receive annual precipitation inputs characteristics of arid and semiarid regions. Boreal forests persist because permafrost acts as an aquatard trapping water near the surface and because historically cool growing season temperatures have kept atmospheric evaporative demand relatively low. As climate change simultaneously warms the atmosphere and deepens the active layer it is likely that vegetation will experience a higher degree of hydrologic limitation, perhaps necessitating the reallocation of resources. Here we use sap flux observations of canopy transpiration to understand the influence of atmospheric and permafrost conditions on the function of an arctic boreal forest in northeastern Siberia. We find that individual trees exhibit stronger responses to atmospheric vapor pressure deficit (D) as the growing season progresses. Further, the magnitude of this response appears to be positively correlated with changes in the depth of permafrost thaw. These results imply that arctic boreal forests will need to adapt to increasing hydrologic stress in order to benefit from what are typically thought of as increasingly favorable growing conditions with continued climate change.
15095557 Mackelprang, Rachel (California State University Northridge, Northridge, CA); Douglas, Thomas A. and Waldrop, M. P. Frozen in time? Microbial strategies for survival and carbon metabolism over geologic time in a Pleistocene permafrost chronosequence [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41G-0138, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost soils have received tremendous interest due to their importance as a global carbon store with the potential to be thawed over the coming centuries. Instead of being "frozen in time," permafrost contains active microbes. Most metagenomic studies have focused on Holocene aged permafrost. Here, we target Pleistocene aged ice and carbon rich permafrost (Yedoma), which can differ in carbon content and stage of decay. Our aim was to understand how microbes in the permafrost transform organic matter over geologic time and to identify physiological and biochemical adaptations that enable long-term survival. We used next-generation sequencing to characterize microbial communities along a permafrost age gradient. Samples were collected from the Cold Regions Research and Engineering Laboratory (CRREL) Permafrost Tunnel near Fox, AK, which penetrates a hillside providing access to permafrost ranging in age from 12 to 40 kyr. DNA was extracted directly from unthawed samples. 16S rRNA amplicon (16S) and shotgun metagenome sequencing revealed significant age-driven differences. First, microbial diversity declines with permafrost age, likely due to long-term exposure to environmental stresses and a reduction in metabolic resources. Second, we observed taxonomic differences among ages, with an increasing abundance of Firmicutes (endospore-formers) in older samples, suggesting that dormancy is a common survival strategy in older permafrost. Ordination of 16S and metagenome data revealed age-based clustering. Genes differing significantly between age categories included those involved in lipopolysaccharide assembly, cold-response, and carbon processing. These data point to the physiological adaptations to long-term frozen conditions and to the metabolic processes utilized in ancient permafrost. In fact, a gene common in older samples is involved in cadaverine production, which could potentially explain the putrefied smell of Pleistocene aged permafrost. Coupled with soil chemistry analysis, these processes show how a tightly linked microbial food web can survive over geologic time with no influx of new energy or materials. This web may also help to explain differences in Pleistocene carbon chemistry and why this carbon is highly bioavailable for microbial consumption post thaw.
15095708 Marchand, Nicolas (University of Sherbrooke, Sherbrooke, QC, Canada); Royer, Alain; Krinner, G. and Roy, Alexandre R. Monitoring of the ground surface temperature and the active layer in northeastern Canadian permafrost areas using remote sensing data assimilated in a climate land surface scheme [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C21C-0347, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Projected future warming is particularly strong in the Northern high latitudes where increases of temperatures are up to 2 to 6°C. Permafrost is present on 25% of the northern hemisphere lands and contain high quantities of "frozen" carbon, estimated at 1400 Gt (40% of the global terrestrial carbon). The aim of this study is to improve our understanding of the climate evolution in arctic areas, and more specifically of land areas covered by snow. The objective is to describe the ground temperature year round including under snow cover, and to analyse the active layer thickness evolution in relation to the climate variability. We use satellite data (fusion of MODIS land surface temperature "LST" and microwave AMSR-E brightness temperature "Tb" assimilated in the Canadian Land Surface Scheme (CLASS) of the Canadian climate model coupled with a simple radiative transfer model (HUT). This approach benefits from the advantages of each of the data type in order to complete two objectives: 1- build a solid methodology for retrieving the ground temperature, with and without snow cover, in taiga and tundra areas; 2- from those retrieved ground temperatures, derive the summer melt duration and the active layer depth. We describe the coupling of the models and the methodology that adjusts the meteorological input parameters of the CLASS model (mainly air temperature and precipitations derived from the NARR database) in order to minimise the simulated LST and Tb ouputs in comparison with satellite measurements. Using ground-based meteorological data as validation references in NorthEastern Canadian tundra, the results show that the proposed approach improves the soil temperatures estimates when using the MODIS LST and Tb at 10 and 19 GHz to constrain the model in comparison with the model outputs without satellite data. Error analysis is discussed for the summer period (2.5-4 K) and for the snow covered winter period (2-3.5 K). Further steps are described to apply this methodology over a taiga environment, as we have to take into account the vegetation effects in the radiative transfer. A better understanding of the permafrost evolution processes, and particularly the impact of the snow cover should enable us to better apprehend the impact of the global warming on the melt of permafrost and the future of their carbon stock.
15092688 Newman, B. D. (Los Alamos National Laboratory, Los Alamos, NM); Heikoop, J. M.; Throckmorton, H.; Wilson, C. J. and Wullschleger, S. D. Implications of fine-scale geochemical depth trends in the active layer of a continuous permafrost landscape near Barrow, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B32D-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
As part of the US DOE, Office of Science, Next Generation Ecosystem Experiment-Arctic project, we have been using environmental tracers (naturally occurring stable isotopes and geochemical species) to understand hydrological and geochemical processes within polygonal ground in a continuous permafrost area in the Arctic coastal plain. The study site is characterized by a thin zone of active layer development (typically <50 cm). This condition makes it difficult to understand development of geochemical gradients between the near surface and the frost line because traditional sampling using pumping causes mixing which can obscure depth gradients. We have applied a passive approach by using a series of diffusion cells that are installed at different depths within the active zone. The cells are filled with deionized water and over time, they equilibrate with the adjacent active layer water chemistry (ions diffuse into the cell, but the water in the cell does not exchange). Using this approach we have collected a series of fine resolution depth profiles within saturated zones in the active layer. Results over the last three years often show well-developed and sometimes substantial geochemical gradients for multiple analytes. Such gradients imply minimal vertical mixing within the active zone. Reductions in permeability with depth and lack of strong hydrological gradients likely limit vertical mixing. We also noted that the strength of the depth gradients varies across the landscape reflecting differences related to microtopography and drainage conditions. These results suggest that there are likely to be substantial fine-scale depth variations in biogeochemical processes such as methane and carbon dioxide production. Hydrological models should also reflect limited mixing with depth.
15095710 Nyland, K. E. (George Washington University, Washington, DC); Streletskiy, D. A. and Shiklomanov, N. I. Land cover and permafrost change mapping using dense time stacks of Landsat and Quickbird imagery [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C21C-0362, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Climate change is especially pronounced in the Arctic, and regions on permafrost are at the frontier of these changes. Increasing air temperatures affect the extent, type, and characteristics of permafrost which is critical to many natural phenomena and northern infrastructure. In areas of discontinuous permafrost certain land cover types are indicative of permafrost conditions making satellite imagery an important tool for assessing environmental change in these remote areas. In arctic environments remote sensing can be particularly challenging due to consistently high cloud cover, data gaps, and landscape heterogeneity. However, there has been success at dealing with such challenges in lower latitude regions using the emerging dense time stack methodology. In place of using an anniversary date for land cover comparisons from different years, this methodology includes scenes from all seasons in addition to imagery normally rejected due to data gaps and high amounts of cloud cover. The incorporation of all available data creates a "dense time stack" which provides both a more complete dataset and more nuanced spectral signatures for classification. This work applied the dense time stack method to mapping five drainage basins in the close vicinity of the city of Igarka, Russia using both Landsat and Quickbird satellite imagery. The resulting map series proved this method to be effective within the Arctic for multiscalar mapping both temporally (annual and seasonal) and spatially (at the resolutions of Landsat and Quickbird). The time series of observed land cover changes produced allowed areas of permafrost degradation to be identified. These maps will be applied in the future to ongoing hydrological research in the region investigating the sources of increased run off and its relation to permafrost degradation.
15095650 Pannetier, Romain (Stockholm University, Stockholm, Sweden). Modeling permafrost's distribution and prospective development with coupled heat and groundwater flow equation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0388, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
A need for improvements in numerical models for the representation of permafrost and active layer dynamics has been highlighted. Initial efforts to address this have been made, in particular by coupling heat and multiphase flow equations under transient conditions. Implications of honoring the physical representation of such process includes an improved ability to model and analyze effects of projected changes in hydro-climatic variables, as for example the change in thermal regime and the geographic patterns of permafrost degradation. In this contribution the recently developed frozen ground module of PFloTran for fully coupled transient heat and water flow under partially saturated conditions is applied to the subarctic field site of Tarfala in Northern Sweden, where the occurrence of permafrost is sporadic and strongly dependent on snow-depth. Optimizing this model to reproduce subsurface temperature fluctuations in the ground, as recorded in two different boreholes over the last decade, allows to identify the respective roles played by heat diffusion, advection and convection in a changing permafrost environment. The influence of topography is analyzed by applying the model to different domains geometries, where topography is simplified to different degrees. The model has been configured to reproduce temperature observations, providing a estimation of the distribution and thermal regime of permafrost over the entire hill-slope. Based on the configurations that give the most accurate validation against data, changes in permafrost are extrapolated by applying different scenarios of prospective climatic conditions.
15095639 Pastick, N. (University of Minnesota Twin Cities, Department of Forest Resources, Minneapolis, MN); Jorgenson, T.; Wylie, B. K.; Nield, Shawn; Johnson, Kristofer D. and Finley, A. Distribution of near-surface permafrost in Alaska; estimates of present and future conditions [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B54F-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
High-latitude regions are experiencing rapid and extensive changes in ecosystem composition and function as the result of increases in average air temperature. Increasing air temperatures have led to widespread thawing and degradation of permafrost, which in turn has affected ecosystems, socioeconomics, and the carbon cycle of high latitudes. Further warming could lead to increasing ground temperatures, thickening active-layers, and accelerated thawing and degradation of permafrost. Despite permafrost's influence on ecosystem structure and functions, relatively little has been done to quantify permafrost properties across extremely large areas and at high resolutions. Detection and mapping of permafrost are difficult, however, because it is a subsurface condition of the ground, heterogeneous in nature, and largely exists in remote locations. Here we overcome complex interactions among surface and subsurface conditions to map permafrost through empirical modeling approaches that statistically and spatially extend field observations using remotely sensed imagery, climatic data, and thematic maps of a wide range of surface and subsurface biophysical characteristics. The data fusion approach generated high-resolution (30-m pixels) maps of near-surface (within 1 m) permafrost, active-layer thickness, and associated uncertainty estimates throughout most of Alaska. Our calibrated models were then used to quantify changes in permafrost distribution under varying future climate scenarios assuming no other changes in biophysical factors. The mapping of permafrost distribution across Alaska is important for land-use planning, environmental assessments, and a wide-array of geophysical studies.
15092706 Romanovsky, V. E. (University of Alaska Fairbanks, Fairbanks, AK); Cable, W.; Marchenko, S. S. and Panda, S. K. Distributed permafrost observation network in western Alaska; the first results [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33G-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The area of Western Alaska including the Selawik National Wildlife Refuge (SNWR) is generally underrepresented in terms of permafrost thermal monitoring. Thus, the main objective of this study was to establish a permafrost monitoring network in Western Alaska in order to understand the spatial variability in permafrost thermal regime in the area and to have a baseline in order to detect future change. Present and future thawing of permafrost in the region will have a dramatic effect on the ecosystems and infrastructure because the permafrost here generally has a high ice content, as a result of preservation of old ground ice in these relatively cold regions even during the warmer time intervals of the Holocene. Over the summers of 2011 and 2012 a total of 26 automated monitoring stations were established to collect temperature data from the active layer and near-surface permafrost. While most of these stations were basic and only measured the temperature down to 1.5 m at 4 depths, three of the stations had higher vertical temperature resolution down to 3 m. The sites were selected using an ecotype (basic vegetation groups) map of very high resolution (30 m) that had been created for the area in 2009. We found the Upland Dwarf Birch-Tussock Shrub ecotype to be the coldest with a mean annual ground temperature at 1 meter (MAGT1.0) of -3.9 °C during the August 1st, 2012 to July 31st, 2013 measurement period. This is also the most widespread ecotype in the SNWR, covering approximately 28.4% by area. The next widespread ecotype in the SNWR is the Lowland and Upland Birch-Ericaceous Low Shrub. This ecotype had higher ground temperatures with an average MAGT1.0 of -2.4 °C during the same measurement period. We also found that within some ecotypes (White Spruce and Alder-Willow Shrub) the presence or absence of moss on the surface seems to indicate the presence or absence of near surface permafrost. In general, we found good agreement between ecotype classes and permafrost characteristics such as temperature, active layer thickness, and freeze back duration. Thus, we believe it might be possible to translate the ecotype map into a very high spatial resolution (30 m) permafrost map using our measurements. Such a map would be useful in decision making with respect to land use and understanding how the landscape might change under future climate scenarios.
15092540 Sachs, Torsten (Deutsches GeoForschungsZentrum, Potsdam, Germany); Serafimovich, Andrei; Metzger, S.; Kohnert, Katrin and Hartmann, Jorg. Low permafrost methane emissions from Arctic airborne flux measurements [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0256, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
One of the most pressing questions with regard to climate feedback processes in a warming Arctic is the regional-scale greenhouse gas release from Arctic permafrost areas. Ground-based eddy covariance (EC) measurements provide continuous in-situ observations of the surface-atmosphere exchange of energy and matter. However, these observations are rare in the Arctic permafrost zone and site selection is bound by logistical constraints among others. Consequently, these observations cover only small areas that are not necessarily representative of the region of interest. Airborne measurements can overcome this limitation by covering distances of hundreds of kilometers over time periods of a few hours. The Airborne Measurements of Methane Fluxes (AIRMETH) campaigns are designed to quantitatively and spatially explicitly address this question. During the AIRMETH-2012 and AIRMETH-2013 campaigns aboard the research aircraft POLAR 5 we measured turbulent exchange of energy, methane, and (in 2013) carbon dioxide along thousands of kilometers covering the North Slope of Alaska and the Mackenzie Delta, Canada. Time-frequency (wavelet) analysis, footprint modeling, and machine learning techniques are used to (i) determine spatially resolved turbulence statistics, fluxes, and contributions of biophysical surface properties, and (ii) extract regionally valid functional relationships between environmental drivers and the observed fluxes. These environmental response functions (ERF) are used to explain spatial flux patterns and--if drivers are available in temporal resolution--allow for spatio-temporal scaling of the observations. This presentation will focus on 2012 methane fluxes on the North Slope of Alaska and the relevant processes on the regional scale and provide an updated 100 m resolution methane flux map of the North Slope of Alaska.
15095653 Shur, Y. (University of Alaska Fairbanks, Fairbanks, AK); Jorgenson, T. and Kanevskiy, M. Z. Northern peatland shifts under changing climate and their impact on permafrost [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0393, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Formation of peatlands depends primarily on climate and its interactions with hydrology, soil thermal regimes, plant composition, and nutrients. A water balance with precipitation exceeding evaporation is necessary for their formation. The rate of peat accumulation also greatly depends on thermal resources. The prominent impact of the water balance and temperature on peatland formation is evident in the West Siberia Lowland. The rate of peat accumulation steadily increases from arctic tundra to moss tundra, to forest tundra, to northern taiga, and to southern taiga. This increase is a result in increase in air temperature and length of the growing season because all of these zones have water balance favorable for peat formation. Further to south, evaporation prevails over precipitation and peat formation occurs only in isolated areas. Climate change will redefine geographical distribution of climatic and vegetation zones. It is predicted that in arctic and subarctic regions the difference between precipitation and evaporation will increase and as a result these regions will remain favorable to peat accumulation. With increase of thermal resources, the rate of peat accumulation will also increase. The Alaska Arctic Coastal Plain is of a special interest because it has thousands of shallow lakes, which due to warming climate would shift from open waterbodies to peatlands through shoreline paludification and infilling. The accumulation of organic matter will likely turn open water into shore fens and bogs, and eventually to peat plateaus, as is occurring in many boreal landscapes. Expected impact on permafrost in arctic and subarctic regions will include rise of the permafrost table, thickening of the ice-rich intermediate layer with ataxitic (suspended) cryostructure, and replacement of frost boils with earth hummocks. In the contemporary continuous permafrost zone, permafrost formed as climate-driven will be transformed into climate-driven ecosystem protected. Sphagnum mosses, which grow better under warm climates, is a dominant factor in this transformation. Terrestrialization of numerous shallow lakes on the Arctic Coastal Plain of Alaska will lower permafrost temperatures beneath them and in surrounding areas.
15092714 Spencer, R. G. (Florida State University, Department of Earth, Ocean and Atmospheric Science, Tallahassee, FL); Mann, P. J.; Dittmar, T.; Eglinton, T. I. and Stubbins, A. Detecting the signature of permafrost thaw in Arctic rivers [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B34B-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic permafrost soils contain vast quantities of ancient organic matter. Numerous studies have shown extensive permafrost thaw and degradation in the Arctic, but dissolved organic carbon (DOC) exported from the mouths of large Arctic rivers--which are expected to integrate processes and changes occurring through their watersheds--has been shown to be predominantly modern. This raises the question, where is the ancient DOC that is mobilized from permafrost thaw and the deepening of the active layer? This study examines DOC radiocarbon age, biolability and dissolved organic matter (DOM) composition via FT-ICR-MS in permafrost thaw streams and the Kolyma River mainstem (Northeast Siberia). Ancient permafrost thaw stream DOC is observed to be highly biolabile particularly in comparison to modern Kolyma River mainstem DOC. In conjunction with this high biolability the permafrost thaw stream DOM exhibits large changes in molecular structure, loss of hydrogen rich (energy rich) aliphatic molecules, and production of molecules in the classical area in van Krevelen space associated with riverine DOM. Modern Kolyma River mainstem DOM conversely appears very stable in bioincubations in comparison to ancient permafrost thaw DOM. Thus the apparent offset between mobilization of ancient permafrost derived organic matter and the current predominantly modern age of DOC at the mouth of major Arctic rivers may be explained due to microbial degradation of permafrost derived DOC within the river's hydrologic residence time.
15092693 Treat, C. C. (U. S. Geological Survey, University of Alaska Fairbanks, Fairbanks, AK); Jones, M. and Loisel, J. Fen to bog transitions in high latitudes; what conditions lead to permafrost aggradation? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33A-0155, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Northern high-latitude peatlands accumulated an estimated 436 Gt of carbon over the Holocene. Vegetation changes, such as the succession from fen to bog species, are often clearly visible in peat profiles and can be caused by organic matter accumulation or by changes in regional climate. Most peatlands developed during the early Holocene as fens under a climate that was warmer than today due to a summer insolation maximum. Subsequent transition to bogs facilitated permafrost aggradation during the mid- to late Holocene. Teasing out permafrost aggradation in peat cores remains a challenge, as they often resemble dry bogs. However, in many locations permafrost aggradation can be assumed especially if thermokarst is evident later in the peat record (i.e., an abrupt transition from dry bog or plateau peat to wet Sphagnum riparium or even fen peat). We used a database of existing peat core records from around the northern high latitudes to determine transition of fen to bog from plant macrofossils and determined permafrost aggradation from both plant macrofossils and physical peat properties to improve constraints on methane emissions from northern peatlands throughout the Holocene. Here, we examine the spatial and temporal trends of the fen to bog transition and permafrost aggradation in the northern high latitude regions by compiling a database of existing records of macrofossil assemblages and peat properties (carbon, nitrogen, and bulk density). We find that the timing of the fen-to-bog transition varied throughout the northern high latitudes, from 5200 yr BP in Alaska and Western Canada to < 1000 yr BP in Eastern Canada and Siberia. Similarly, the first occurrences of permafrost aggradation varied across the high latitudes, ranging from 4000 yr BP in Western Canada to the Little Ice Age in southern regions and parts of Western Siberia. The spatial and temporal differences in the fen to bog transition and permafrost aggradation suggest that methane emissions differed considerably across northern high latitudes throughout the Holocene. Identifying controls of the fen-to-bog transition and permafrost aggradation in the northern high latitudes has important implications for both carbon sequestration and methane emissions from northern peatlands to the atmosphere throughout the Holocene.
15095678 Vaks, Anton (University of Oxford, Earth Sciences, Oxford, United Kingdom); Mason, Andrew J.; Breitenbach, Sebastian F. M.; Kononov, A. M.; Osintcev, A. V. and Henderson, Gideon M. 1,350 000 year history of Siberian permafrost based on U-Pb chronology of speleothems [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C13B-0444, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost history of the last ~1.35 millions of years (Ma) was reconstructed using chronology of speleothems from a Siberian cave. Rain and snowmelt waters can penetrate into caves only when soil and subsoil temperatures are above 0°C and permafrost above the cave is discontinuous or absent. Speleothems in regions currently affected by permafrost therefore provide a tracer of past permafrost thawing events. Ledyanaya Lenskaya Cave is located at 60°22'N-116°57'E, on the southern boundary of modern continuous permafrost, with no present-day water seepage and a mean annual temperature of -5°C to -6°C. U-Th dating of speleothems from this cave in a previous study showed that the youngest speleothem growth period occurred at 427±23 thousand years ago (ka), during early Marine Isotope Stage (MIS) 11. In this study we dated several horizons of older speleothems from this cave using the U-Pb method. Two high precision ages indicate growth at 1074.2 +6.6/-5.2 ka and 947.8 +3.3/-3.4 ka, while new preliminary data provide strong evidence of an older growth period around 1.35-1.30 Ma. Other preliminary data mostly overlap the high precision ages, but also hint at limited growth at ~860 ka, with one data point suggesting younger, but minor growth at ~560 ka. The timing of these permafrost thawing events apparently correlates with interglacial episodes of exceptionally high Pacific Warm Pool sea surface temperature (~30°C). During these warm episodes the average global temperature was 1.1-1.5°C higher than pre-industrial temperatures. These findings put the threshold of thawing of continuous permafrost at its southern boundary at slightly more than 1.0°C above preindustrial level.
15092544 Verbeke, B. A. (Florida State University, Tallahassee, FL); Clarizia, P. E.; McCalley, Carmody K.; Werner, S. L.; Malhotra, Avni; Burke, S. A.; Crill, Patrick M.; Chanton, J. and Varner, Ruth K. Interannual variation in methane production across a permafrost thaw gradient [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0262, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Methane (CH4) is an important greenhouse gas whose emissions from high-latitude ecosystems are highly sensitive to climate change. Warming and permafrost loss is causing a vegetation shift in northern peatlands from well-drained palsas to graminoid-dominated wetlands, resulting in increased CH4 emissions. Understanding CH4 production patterns across this vegetation transition and under varying environmental conditions is important for improving the accuracy of models used to predict future emissions. We measured CH4 fluxes, porewater profiles of carbon dioxide (CO2) and CH4 concentrations, along with d13C along a permafrost thaw gradient in Stordalen Mire, Sweden spanning a vegetation transition from palsa to Sphagnum and graminoid dominated wetlands. Measurements were made in the summers of 2013 and 2014, which had lower and higher average temperatures, respectively. Across years, CH4 fluxes increased in sites dominated by the graminoid species Eriophorum angustifolium. A change in C isotopes indicates a shift from hydrogenotrophic to increasingly acetoclastic production with thaw. Comparison between years showed considerable interannual variability in both porewater and emitted CH4, likely driven by large differences in temperature and cloud coverage. Porewater CH4 concentrations increased in sites with Eriophorum vaginatum, but decreased for Eriophorum angustifolium and showed almost no variation in Sphagnum sites. Carbon dioxide concentrations were variable in E. vag sites, but increased for E. ang and Sphagnum sites. Methane fluxes showed a different pattern, higher emissions in 2014 were only observed at the wettest graminoid site, while 2014 fluxes were similar or lower in the drier Sphagnum and Eriophorum vaginatum sites. These results show the value of multi-year data sets for understanding interactions between plant communities and environmental conditions in describing CH4 dynamics and will improve our ability to predict and understand future CH4 emissions.
15095694 Voss, C. I. (U. S. Geological Survey, Menlo Park, CA) and McKenzie, Jeffrey M. Groundwater flow impacts on thawing permafrost systems [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Results of numerical simulation analysis indicate that where groundwater flows in permafrost landscapes in a warming climate, advective heat transport enhances permafrost thaw rate, increasing transmissivity and the movement of warmer recharge and deep waters. Enhanced flows further increase the rate at which permafrost margins warm and thaw, resulting in positive feedback. Groundwater flow is a significant control on thaw rate and on local and regional patterns of residual permafrost in the landscape. Results indicate that residual permafrost patterns in landscapes with groundwater flow should differ from those in landscapes with little flow. As permafrost thaws from above, a deeper seasonal active zone (the shallow subsurface layer that freezes and thaws annually) develops and more through-going thawed zones (taliks) develop that connect supra- and sub-permafrost zones. The new taliks host additional groundwater flow. Despite this potential for increasing groundwater movement in warming arctic environments, most predictive models of permafrost thaw generally have considered only subsurface heat conduction, not incorporating advective heat transport. To understand these systems and feedbacks, the USGS-SUTRA numerical groundwater code, which models coupled groundwater flow and heat transport, was modified to include freeze/thaw. When temperatures are below freezing, the modeled permeability and thermal properties are dependent on ice saturation, and latent heat of ice formation is included in the energy balance. Simulations of groundwater flow and permafrost thaw were carried out across a hillslope cross section with undulating topography that is initially underlain by a continuous thick permafrost layer. Climate warming is applied with mean air-temperature increase of 0.5°C per 100 years for 1600 years with constant temperature thereafter. This temperature evolution is superimposed on a seasonal ±10°C variation that drives yearly freeze/thaw cycles in the shallow subsurface. Simulation results compare changes in permafrost distribution over a few thousand years of climate change due to (1) purely conductive heat transport (with essentially no groundwater flow) and (2) advective-conductive heat transport (with significant groundwater flow).
15095693 Walvoord, M. A. (U. S. Geological Survey, Denver, CO); Briggs, M. A.; Day-Lewis, F. D.; Jepsen, S. M.; Lane, J. W., Jr.; McKenzie, Jeffrey M.; Minsley, B. J.; Striegl, R. G.; Voss, C. I. and Wellman, T. P. Hydrogeologic controls on water dynamics in a discontinuous permafrost, lake-rich landscape [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Understanding permafrost distribution, rate of change, and influence on groundwater movement are critical for assessing climate change impacts in northern ecosystems. Lake-rich lowlands in interior Alaska provide important habitat for migratory waterfowl, ungulates, and other wildlife. Despite low annual precipitation, the Yukon Flats area in the north central Yukon River Basin of Alaska (USA) supports over 20,000 lakes, due in part to the presence of permafrost. The fate of this lake-rich lowland and, by proxy, similar circumboreal lowland systems under projected climate warming is the focus of a series of recent studies highlighted here. Lake water chemistry analyses of over 200 lakes in the Yukon Flats reveal a large degree of spatial heterogeneity suggestive of a hydrologically disconnected system, a conclusion also supported by abrupt spatial changes in lake elevation. Airborne geophysical characterization shows a laterally continuous shallow gravel layer (~25-m thick) that would offer good hydraulic connectivity throughout the lowlands. However, the gravel layer is generally frozen (as permafrost) except beneath surface water bodies; thus inhibiting lateral pathways of groundwater flow under current conditions. Ground-based geophysical characterization provides a high resolution of permafrost distribution and relevant hydrogeologic features at several lake study sites. Relatively recent thaw in the gravel layer appears to be associated with lakes that have experienced change in size (area) over the past several decades, whereas lakes with taliks (unfrozen conduits) that fully penetrate the permafrost layer are more likely to be stable. Multi-scale permafrost characterization provides the basis for numerical models that simulate permafrost dynamics, lake-talik evolution, supra-, intra-, and sub-permafrost groundwater flow, lake-groundwater exchange, active layer dynamics, and permafrost aggradation response to lake recession. Collective field and simulation results provide insight into expected alterations in groundwater flowpaths, water budgets, lake distribution, and lake chemistry in discontinuous permafrost lowlands given continued climate and permafrost change.
15092715 Walvoord, M. A. (U. S. Geological Survey, Denver, CO) and Striegl, R. G. Identifying hydrologic vulnerabilities to permafrost change and the effects on carbon transport to aquatic systems [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B34B-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost in northern latitudes serves as a potential source of carbon (C) upon thaw. The fate of this and other sources of C in arctic and subarctic regions depends on several factors. This study focuses on the influence of hydrologic processes on dissolved C transport to aquatic systems in permafrost environments. The spatial distribution and depth to permafrost are changing in response to climate as a result of direct (solar radiation) and indirect (vegetation, snow cover, soil moisture, wildfire) changes. Furthermore, permafrost thaw may be accelerated by heat transfer via groundwater flow. Such alterations to permafrost configuration, and resulting hydrogeologic framework, have the potential to modify pathways, residence times, and fluxes of water and dissolved constituents. Lengthened flow paths and increased residence times of soil water and groundwater promotes increased mineralization of terrestrial organic matter and subsurface weathering of carbonates. Intensification of groundwater circulation enhances baseflow to rivers and streams as suggested by both observations and modeling studies. These aforementioned changes result in a downward shift in the relationship between dissolved organic C (DOC) concentration and water discharge, an upward shift in the dissolved inorganic C (DIC) concentration--discharge relationship, and a likely decrease in the fraction of biodegradable organic C transported to aquatic systems. However, the expected magnitude and timing of shifts in hydrology and C are dependent on a variety of factors. Drawing from examples in the Yukon River basin in Alaska (USA), we offer insight on landscape and hydrogeologic characteristics that influence the vulnerability of northern latitude systems to change with respect to hydrology and aquatic C export.
15095712 Adewuyi, Adeniyi A. (Montana Tech of the University of Montana, Butte, MT) and Zhou, X. Derivation of volumetric liquid water content from the RADARSAT-1 SAR images over a permafrost region in interior Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C21C-0384, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The empirical adopted integral equation model (EA-IEM) is implemented as a promising algorithm for liquid water content from the microwave data over a bare soil and sparsely vegetated conditions. The EA-IEM provides simplified mathematical expressions to calculate the soil dielectric constant. The Newton-Rhapson iteration is used to generate the calibrated rms height and calibrated correlation length by using the absolute difference between the calculated liquid water content (LWC) and the measured liquid water content. The absolute difference is less than the threshold value set to 1e-8. The calibrated rms height shows a constant value of 0.02 m while the calibrated correlation length varies for different sample points. A simple exponential regression model is established between the calibrated correlation length values and the backscattering coefficient observations. In addition, the regression model is incorporated into the EA-IEM as a robust way in determining the roughness parameters for retrieval of LWC over a large area. Liquid water content is then calculated directly from radar backscattering coefficient without iteration. Seven strategies were adopted to calibrate and validate the two NCRS-SCAN sites: Nenana and Ward Farm. A comparison between the predicted LWC and the measurements is performed for each strategy, and the root-mean-square (rms) error is found to be 3.60%, suggesting that the strategy one performs well compared to other strategies. All these strategies indicate that the EA-IEM can be used to retrieve soil moisture under the tested range of model parameters: incidence angles between 10° and 60°, surface rms height from 10 to 25 mm, and correlation length from 30 to 100 mm.
15092664 Gu, B. (Oak Ridge National Laboratory, Oak Ridge, TN) and Mann, B. Molecular profiling of permafrost soil organic carbon composition and degradation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B23K-0134, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Microbial degradation of soil organic matter (SOM) is a key process for terrestrial carbon (C) cycling, though the dynamics of these transformations remain unclear at the molecular level. This study reports the application of ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) to profile molecular components of Arctic SOM collected from the surface water and the mineral horizon of a low-centered polygon soil at Barrow Environmental Observatory (BEO), Barrow, Alaska. Soil samples were subjected to anaerobic warming experiments for a period of 40 days, and the SOM was extracted before and after the incubation to determine the components of organic C that were degraded over the course of the study. A CHO index based on molecular composition data was utilized to codify SOM components according to their observed degradation potential. Carbohydrate- and lignin-like compounds in the water-soluble fraction (WSF) demonstrated a high degradation potential, while structures with similar stoichiometries in the base-soluble fraction (BSF) were not readily degraded. The WSF of SOM also shifted to a wider range of measured molecular masses including an increased prevalence of larger compounds, while the size distribution of compounds in the BSF changed little over the same period. Additionally, the molecular profiling data indicated an apparently ordered incorporation of organic nitrogen in the BSF immobilized as primary and secondary amines, possibly as components of N-heterocycles, which may provide insight into nitrogen immobilization or mobilization processes in SOM. Our study represents an important step forward for studying Arctic SOM with improved understanding of the molecular properties of soil organic C and the ability to represent SOM in climate models that will predict the impact of climate change on soil C and nutrient cycling.
15095643 Kholodov, A. L. (University of Alaska Fairbanks, Fairbanks, AK); Liljedahl, A. K.; Romanovsky, V. E. and Cable, W. Cryostratigraphy and main physical properties of active layer soils and upper horizon of permafrost at the Barrow environmental observatory research site [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0380, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Complete understanding of the results of geophysical survey, microbiological and biogeochemical analyzes of soil cores in the Arctic environment impossible without detail description of the frozen soil and its physical properties determination. Cryostratigraphyc features i.e. total ice content and forms of ice patterns reflects the important processes such as water migration due to freezing in frozen active layer soils and history of sedimentation and freezing in underlying perennially frozen deposits. That plays significant role in biogeochemical processes that take place in the Arctic ecosystem. Current research was based on description and analyzing of 8 cores taken during 2012 and 2013 coring campaign had been done at the Barrow Environmental Observatory research site. Cores were taken from different types of polygons and analyzed on lithological composition, soil density, ice content and thermal conductivity. Volumetric ice content within the active layer composed by organic soil consists of 70 to 80% and within silt one less than 60%. Ice content of underlying syncryogenic perennial frozen deposits is about 70%. No clear evidences of soil moisture redistribution due to freezing of active layer were noticed in the cores composed by the organic soil. Organic soil does not have any clear cryogenic structures. Ice usually fills the pores and follows the plants fibers. Mineral soil has recticulated cryogenic structure (ice forms grid like patterns with vertically oriented cells) with some thin (up to 2 cm thick) layers of soil particles and aggregates suspended in ice. Thermal conductivity of frozen samples varies in the range from 1.5 to 2.8 W/(m*°K). It has a positive correlation with soil density and negative with gravimetric ice content (see figure below). Mineral soils have a higher bulk density and average thermal conductivity in the range 2.15 W/(m*°K), organic soils have a lower density and average thermal conductivity about 2 W/(m*°K). Samples, composed by fibrous has an extremely high ice content and low bulk density. Its average thermal conductivity is close to the values typical for ice (2.3 W/(m*°K)). Current research was supported by US DOE as a part of research project Next Generation of Ecosystem Experiment (NGEE).
15095644 Atchley, Adam L. (Los Alamos National Laboratory, Los Alamos, NM); Harp, Dylan R.; Painter, S. L.; Coon, E.; Wilson, C. J.; Romanovsky, V. E. and Liljedahl, A. K. Using observational data to inform physically based models of subsurface thermal hydrology properties and active layer thickness at the Barrow environmental observatory, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0381, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Climate change is profoundly impacting permafrost regions and reshaping carbon rich tundra ecosystems from carbon sinks to potential carbon sources triggering a positive feedback to climate change. The annual maximum depth of ice-free soil with above 0°C temperatures, which is known as the active-layer thickness (ALT), determines the volume of carbon-rich stores available for decomposition and therefore potential greenhouse gas release into the atmosphere. Despite the increased vulnerability of permafrost regions to climate change, predictive tools and precise parameterization of physical characteristics to estimate projected ALT in tundra ecosystems have been developed slowly and often are not adequately representing natural systems due to the complex nature of corresponding atmospheric-surface-subsurface hydrological and energy interactions undergoing freeze-thaw dynamics. A model-observation-experiment process (ModEx) is employed to generate three 1D models representing characteristic micro-topographical land-formations, which are capable of simulating present ALT from current climate conditions. Observational soil temperature data from a tundra site located near Barrow, AK is used to calibrate thermal properties of moss, peat, and sandy loam soil to be used in the multiphysics Arctic Terrestrial Simulator (ATS) models. In the process of calibration and model formulation key physical processes and appropriate model parameters are identified, which showcases the importance of correctly representing physical processes and reformulating models based on observational data. Iterative execution of the ModEx concept identified key processes that control thermal propagation into the subsurface: 1) physical representation of thermal conduction, 2) liquid, ice, and gas partitioning in the subsurface, 3) snowpack distribution and dynamics, and 4) precipitation delivery of water to the surface/subsurface. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.
15092451 Bigalke, N. (GEOMAR, Helmholtz Centre for Ocean Research, Kiel, Germany); Deusner, C.; Kossel, E.; Schicks, J. M.; Spangenberg, Erik; Priegnitz, Mike; Heeschen, Katja U.; Abendroth, S.; Thaler, Jan and Haeckel, M. Hydraulic and mechanical effects from gas hydrate conversion and secondary gas hydrate formation during injection of CO2 into CH4-hydrate-bearing sediments [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11B-0028, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The injection of CO2 into CH4-hydrate-bearing sediments has the potential to drive natural gas production and simultaneously sequester CO2 by hydrate conversion. The process aims at maintaining the in situ hydrate saturation and structure and causing limited impact on soil hydraulic properties and geomechanical stability. However, to increase hydrate conversion yields and rates it must potentially be assisted by thermal stimulation or depressurization. Further, secondary formation of CO2-rich hydrates from pore water and injected CO2 enhances hydrate conversion and CH4 production yields. Technical stimulation and secondary hydrate formation add significant complexity to the bulk conversion process resulting in spatial and temporal effects on hydraulic and geomechanical properties that cannot be predicted by current reservoir simulation codes. In a combined experimental and numerical approach, it is our objective to elucidate both hydraulic and mechanical effects of CO2 injection and CH4-CO2-hydrate conversion in CH4-hydrate bearing soils. For the experimental approach we used various high-pressure flow-through systems equipped with different online and in situ monitoring tools (e.g. Raman microscopy, MRI and ERT). One particular focus was the design of triaxial cell experimental systems, which enable us to study sample behavior even during large deformations and particle flow. We present results from various flow-through high-pressure experimental studies on different scales, which indicate that hydraulic and geomechanical properties of hydrate-bearing sediments are drastically altered during and after injection of CO2. We discuss the results in light of the competing processes of hydrate dissociation, hydrate conversion and secondary hydrate formation. Our results will also contribute to the understanding of effects of temperature and pressure changes leading to dissociation of gas hydrates in ocean and permafrost systems.
15095698 Bolton, W. R. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Romanovsky, V. E.; McGuire, A. D.; Grosse, Guido and Lara, M. J. Initial conceptualization and simulation of Arctic tundra landscape evolution using the Alaska Thermokarst Model [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thermokarst topography forms whenever ice-rich permafrost thaws and the ground subsides due to the volume loss when excess ground ice transitions to water. The Alaska Thermokarst Model (ATM) is a large-scale, state-and-transition model designed to simulate transitions between [non-]thermokarst landscape units, or cohorts. The ATM uses a frame-based methodology to track transitions and proportion of cohorts within a 1-km2 grid cell. In the arctic tundra environment, the ATM tracks thermokarst-related transitions between wetland tundra, graminoid tundra, shrub tundra, and thermokarst lakes. The transition from one cohort to another due to thermokarst processes can take place if thaw reaches ice-rich ground layers either due to pulse disturbance events such as a large precipitation event or fires or due to gradual active layer deepening that eventually results in penetration of the protective layer. The protective layer buffers the ice-rich soils from the land surface and is critical to determine how susceptible an area is to thermokarst degradation. The rate of terrain transition in our model is determined by the ice-content of the soil, the drainage efficiency (or ability of the landscape to store or transport water), and a cumulative probability of thermokarst initiation. Tundra types are allowed to transition from one type to another (i.e., wetland tundra to a graminoid tundra) under favorable climatic conditions. In this study, we present our conceptualization and initial simulation results from the ATM model for an 1792 km2 area on the Barrow Peninsula, Alaska. The area selected for simulation is located in a polygonal tundra landscape under varying degrees of thermokarst degradation. The goal of this modeling study is to simulate landscape evolution in response to thermokarst disturbance as a result of climate change. The ATM will eventually be incorporated into the Integrated Ecosystem Model (IEM) for Alaska and Northwest Canada for use in management decisions that are influenced by thermokarst dynamics.
15095577 Chasmer, L. (University of Lethbridge, Lethbridge, AB, Canada); Hopkinson, C. and Petrone, R. M. Assessing rates of biological and morphological change in northern ecosystems using remote sensing time series data, LiDAR, and gridded climate records [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41I-0174, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Northern ecosystems are changing at accelerating rates as a result of climate warming in northern latitudes. In many areas, changes in vegetation species and succession may be a response to underlying hydrological and geomorphological changes to the land surface. Others note significant decreases in productivity as a result of drought, but direct linkages and underlying causes remain elusive. Long-term records of satellite imagery have provided proxy indicators of the complex interactions between the terrestrial biosphere and the atmosphere, as well as disturbances over a variety of space and time scales. The following study compares long-term gridded climate patterns with historical remote sensing-based changes in vegetation productivity within a north to south transect of the Canadian boreal forest and into the zone of sporadic permafrost. The objective is to identify significant ecological and morphological changes associated with long-term climate trends. Areas of natural variability are identified within the western boreal plains and parts of the northern boreal forest associated with increased drying. Geomorphological and ecological changes as a result of thawing sporadic permafrost are also assessed.
15092545 Clarizia, P. E. (University of New Hampshire, Durham, NH); Verbeke, B. A.; McCalley, Carmody K.; Werner, S. L.; Malhotra, Avni; Burke, S. A.; Crill, Patrick M. and Varner, Ruth K. Comparison of CH4 emission and CO2 exchange between 2013 and 2014 in a subarctic peatland [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0263, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
One of the major concerns with climate change is the potential feedback from the emission of greenhouse gases, carbon dioxide (CO2) and methane (CH4), from high latitude thawing organic soils. With increasing temperatures in Arctic regions, thawing permafrost palsas transition to wetter sedge-dominated wetlands, which account for 20-39% of global atmospheric CH4 burden. This rapid change in habitat raises the following question: how do CO2 exchange rates and CH4 emissions change along a gradient of permafrost thaw and what is the interannual variability in these fluxes? To address this question, we measured CO2 exchange, CH4 flux, vegetative type and vascular green area (VGA) along a thaw gradient during July of 2013 and 2014 in Stordalen Mire, Sweden. Environmental variables showed that 2013 and 2014 were climatically different; higher photosynthetically active radiation (PAR) and measurements of water table level and temperature showed that 2014 was warmer and drier than 2013. Warmer conditions led to higher rates of respiration and gross primary productivity (GPP), with the largest increases observed in the palsa sites, likely due to an increase in mean temperature. Methane fluxes showed a less consistent response to climate differences between years, fluxes were higher in 2014 in the mostly inundated Eriophorum angustifolium dominated site and lower in the drier Sphagnum and Eriophorum vaginatum dominated sites. Results of this study highlight the need for accounting for interannual variability when predicting greenhouse gas emissions during permafrost thaw.
15095696 Coon, E. (Los Alamos National Laboratory, Los Alamos, NM); Atchley, Adam L.; Painter, S. L.; Karra, S.; Moulton, J. D.; Wilson, C. J. and Liljedahl, A. K. Effects of spatial and temporal resolution on simulated feedbacks from polygonal tundra [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Earth system land models typically resolve permafrost regions at spatial resolutions grossly larger than the scales of topographic variation. This observation leads to two critical questions: How much error is introduced by this lack of resolution, and what is the effect of this approximation on other coupled components of the Earth system, notably the energy balance and carbon cycle? Here we use the Arctic Terrestrial Simulator (ATS) to run micro-topography resolving simulations of polygonal ground, driven by meteorological data from Barrow, AK, to address these questions. ATS couples surface and subsurface processes, including thermal hydrology, surface energy balance, and a snow model. Comparisons are made between one-dimensional "column model" simulations (similar to, for instance, CLM or other land models typically used in Earth System models) and higher-dimensional simulations which resolve micro-topography, allowing for distributed surface runoff, horizontal flow in the subsurface, and uneven snow distribution. Additionally, we drive models with meteorological data averaged over different time scales from daily to weekly moving windows. In each case, we compare fluxes important to the surface energy balance including albedo, latent and sensible heat fluxes, and land-to-atmosphere long-wave radiation. Results indicate that spatial topography variation and temporal variability are important in several ways. Snow distribution greatly affects the surface energy balance, fundamentally changing the partitioning of incoming solar radiation between the subsurface and the atmosphere. This has significant effects on soil moisture and temperature, with implications for vegetation and decomposition. Resolving temporal variability is especially important in spring, when early warm days can alter the onset of snowmelt by days to weeks. We show that high-resolution simulations are valuable in evaluating current land models, especially in areas of polygonal ground. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science. LA-UR-14-26227.
15092542 Corbett, J. E. (NASA, Goddard Institute for Space Studies, New York, NY); Tfaily, Malak; Burdige, D.; Glaser, P. H. and Chanton, J. Quantifying the microbial utilization of methanogenesis and methane loss from northern wetlands [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0258, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The importance of methanogenesis and percent of methane loss from the subsurface porewater in various northern wetland sites was quantified with isotope-mass balance equations. With equimolar amounts of CO2 and CH4 produced from methanogenesis, the amount of dissolved CO2 produced from methanogenesis as compared to other decomposition processes can be calculated and is equivalent to the amount of CH4 before loss due to ebullition, plant-mediated transport, and diffusion. This method was applied to porewater samples collected from various locations within permafrost collapse-scar bogs and northern peatlands. From the peatland sites, bogs produced less CO2-meth than fens (2.9±1.3 mM and 3.7±1.4 mM, respectively). Methanogenesis was a more utilized decomposition process in the bogs than the fens. However, greater amounts of CO2-meth found in fen sites was most likely due to the presence of more labile organic substrates resulting in greater overall production. More CH4 was lost in fens (89±2.8%) than bogs (82±5.3%) from plant-mediated transport as fens are dominated by vascular plants (Carex) while bogs are dominated by Sphagnum mosses. In permafrost sites, mid-bogs produced twice the amount of CO2-meth as bog moats (1.6±0.63 mM and 0.82±0.20 mM, respectively). Less methanogenesis was found in bog moats as recently thawed organic matter is exposed to initial decomposition processes and methane production grows over time. A similar amount of CH4 was lost from bog moats as mid bogs (63±7.0% and 64±9.3%, respectively) likely due to the greater density of vascular plants found within a bog moat.
15095697 Fortier, Daniel (Centre d'Études Nordiques, Quebec City, QC, Canada); Godin, Etienne; Lévesque, Esther and Veillette, Audrey. Subsurface thermal erosion of ice-wedge polygon terrains; implications for arctic geosystem in transition [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-07, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Subsurface thermal erosion is triggered by convective heat transfers between flowing water and permafrost. For inland ice-wedge polygon terrains, heat advection due to infiltration of run-off in the massive ice wedges and the ice-rich upper portion of permafrost creates sink holes and networks of interconnected tunnels in the permafrost. Mass movements such as collapse of tunnel's roof, retrogressive thaw-slumping along exposed permafrost and active layer detachment slides lead to the development of extensive gully networks in the landscape. These gullies drastically change the hydrology of ice-wedge polygon terrains and the fluxes of heat, water, sediment and carbon within the permafrost geosystem. Exportation of sediments by fluvial processes within gullies are positive mechanical feed-back effects that keep gully channels active over decades. Along gully margins, drainage of disturbed polygons and ponds, slope drainage, soil consolidation, plant colonization of disturbed gully slopes and wet to mesic plant succession of drained polygons change the thermal properties of the active layer and create negative feedback effects that stabilize active erosion processes and promote permafrost recovery in gully slopes and adjacent disturbed polygons. On Bylot Island (Nunavut), over 40 gullies were mapped and monitored to characterize gully geomorphology, thermal and mechanical processes of gully erosion, rates of gully erosion over time within different sedimentary deposits, total volume of eroded permafrost at the landscape scale and gully hydrology. We conducted field and laboratory experiments to quantify heat convection processes and speed of ice wedge ablation in order to derive empirical equations to develop a numerical, fully-coupled, heat and mass (water) transfer model of ice-wedge thermal erosion. We used data collected over 10 years of geomorphological gully monitoring, regional climate scenarios, our physics-based numerical thermal erosion model and our field/laboratory-based empirical thermal erosion model to evaluate the potential response of ice-wedge polygon terrains to changes in snow, permafrost thermal regime and hydrological conditions over the coming decades and its implication for the short and long term dynamics of arctic permafrost geosystems.
15095651 Frauenfeld, Oliver W. (Texas A&M University, Geography, College Station, TX) and Ford, T. Surface-atmosphere moisture coupling in Eurasian frozen ground regions [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0389, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost represents an impermeable barrier to moisture, resulting in a saturated or near-saturated surface layer during the warm season in many continuous and discontinuous permafrost zones. These surface conditions could lead to enhanced convection and precipitation during the warm season, and significant local recycling of moisture. In areas underlain by sporadic or isolated permafrost, or in seasonally frozen areas, the moisture can drain away more readily, resulting in much drier soil conditions. As climate change causes frozen ground degradation, this will thus also alter the patterns of atmospheric convection, moisture recycling, and the hydrologic cycle in high-latitude land areas. In this study, we analyze evaporative fraction (EF) as a proxy for evapotranspiration, and precipitation from the Modern-Era Retrospective analysis for Research and Applications (MERRA-land) reanalysis dataset. We focus on 1979-2012 and document patterns and changes in EF over the Eurasian high latitudes. We find strong, positive April EF trends over the study period, particularly in the Lena River Basin, 80% of which is underlain by continuous permafrost. In fact, these significant positive trends in spring EF are strongest over continuous permafrost across the Eurasian high latitudes, but negative for sporadic and isolated permafrost. In addition, we find a strong, statistically significant relationship between EF anomalies and the probability of subsequent precipitation over the Lena Basin during April. This association therefore suggests a potential land-atmosphere coupling between frozen ground and precipitation. As the permafrost and seasonally frozen ground distribution changes in the future, this will likely have repercussions for the Arctic hydrologic cycle.
15092694 Grant, R. F. (University of Alberta, Edmonton, AB, Canada); Humphreys, E. and Lafleur, P. Hydrological controls on ecosystem CO2 and CH4 exchange in a MIXED tundra and a FEN within an arctic landscape UNDER current and future climates [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33A-0156, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Variation in CO2 and CH4 exchange in years with contrasting weather is strongly affected by hydrology in landscapes underlain by permafrost. Hypotheses for this variation were incorporated into the ecosystem model ecosys which simulated CO2 and CH4 fluxes along a topographic gradient within an arctic landscape at Daring Lake, NWT, Canada. Fluxes modelled at mixed tundra and fen sites within the gradient were compared with CO2 fluxes measured at eddy covariance towers from 2006 to 2009, and with CH4 fluxes measured with surface chambers in 2008. Slopes and correlation coefficients from regressions of modeled vs. measured CO2 fluxes were 1.0 ± 0.1 and 0.7-0.8 for both sites in all years. At the mixed tundra site, rises in net CO2 uptake in warmer years with earlier snowmelt were constrained by midafternoon declines in CO2 influxes when vapor pressure deficits (D) exceeded 1.5 kPa, and by rises in CO2 effluxes with greater active layer depth (ALD). Consequently annual net CO2 uptake at this site rose little with warming. At the fen site, CO2 influxes declined less with D and CO2 effluxes rose less with warming, so that rises in net CO2 uptake in warmer years were greater than those at the mixed tundra site. The greater declines in CO2 influxes with warming at the mixed tundra site were modeled from greater soil-plant-atmosphere water potential gradients that developed in drier soil, and the smaller rises in CO2 effluxes with warming at the fen site were modeled from O2 constraints to heterotrophic and below-ground autotrophic respiration that limited their responses to greater ALD. Modeled and measured CH4 exchange during July and August indicated very small influxes at the mixed tundra site, and larger emissions at the fen site. Emissions of CH4 modeled during soil freezing in October-November contributed about one-third of the annual total, and so should be included in estimates of annual emissions. These contrasting responses to warming under current climate modeled and measured at the mixed tundra and fen sites were apparent in their contrasting responses modeled under long-term climate change.
15092563 Johnson, Kristofer D. (U. S. Forest Service, Newtown Square, PA). The distribution and controls of deep mineral soil carbon in Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13N-0074, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Substantial amounts of carbon are currently stored in the mineral and organic soils of Alaska. Frozen carbon in soils, if released through warming, could affect the global carbon balance and climate change. However, their spatial and vertical distributions remain a challenge to explain and map, even with improved spatial datasets. Previous studies revealed the coupling between organic layer depth and permafrost distribution in Alaska, but one knowledge gap remains in the quantity and controls of soil carbon in deeper mineral soils. We gathered together data from more than 700 soil profiles in Alaska and estimated their carbon content in the 0 to 100 cm of mineral soil as well as their organic horizons. The frozen component of the profiles in the Arctic and Boreal regions was strongly correlated with the profile's organic layer depth and mean annual temperature. Differences were also found when the profiles were grouped according to their topographic position, parent material and ground cover. For example Rocky Uplands and Sandy Lowlands generally held the lowest frozen mineral carbon in the Boreal region while Silty landforms held the highest. Understanding the distribution of the mineral soil carbon pool in Alaska helps improve our ability to model processes the impacts of the change in mineral soil carbon at larger scales.
15092495 Koven, C. D. (Lawrence Berkeley National Laboratory, Berkeley, CA); Lawrence, D. M.; Riley, W. J. and Torn, M. S. Zero-D to one-D; challenges and implications of considering vertical soil C profiles in Earth System Models [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11K-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Earth system models have traditionally considered soil biogeochemical transformations as occurring only at the surface, neglecting C and nutrient cycling that occurs below the surface zone. However, much of the world's soil C lies below this surface zone, and the dynamics of this carbon in response to global change may differ considerably from those at the surface. We have implemented a vertically-resolved soil biogeochemistry model into the Community Land Model (CLM4.5), and discuss the uncertainties in adding this level of increased complexity as well as the implications of this representation on the response of C cycle feedbacks. We focus on the uncertainty of how decomposition rates differ between the surface and depth, and show that this uncertainty maps strongly onto the response of soil C to warming, which is primarily due to the response of permafrost soils and their post-thaw decomposition dynamics.
15092660 Laurion, I. (Institut National de la Recherche Scientifique-Eau Terre Environnement, Quebec City, QC, Canada); Bégin, P. N.; Bouchard, F. and Preskienis, V. Greenhouse gas exchange in small Arctic thaw ponds [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B23H-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic lakes and ponds can represent up to one quarter of the land surface in permafrost landscapes, particularly in lowland tundra landscapes characterized by ice wedge organic polygons. Thaw ponds can be defined as the aquatic ecosystems associated to thawing of organic soils, either resulting from active layer processes and located above low-center peat polygons (hereafter low-center polygonal or LCP ponds), or resulting from thermokarst slumping above melting ice wedges linked to the accelerated degradation of permafrost (hereafter ice-wedge trough or IWT ponds). These ponds can merge together forming larger water bodies, but with relatively stable shores (hereafter merged polygonal or MPG ponds), and with limnological characteristics similar to LCP ponds. These aquatic systems are very small and shallow, and present a different physical structure than the larger thermokarst lakes, generated after years of development and land subsidence. In a glacier valley on Bylot Island, Nunavut, Canada, thermokarst and kettle lakes together represent 29% of the aquatic area, with a thermal profile resembling those of more standard arctic lakes (mixed epilimnion). The IWT ponds (44% of the area) are stratified for a large fraction of the summer despite their shallowness, while LCP and MPG ponds (27% of the area) show a more homogeneous water column. This will affect gas exchange in these diverse aquatic systems, in addition to their unique microbiota and organic carbon lability that control the production and consumption rates of greenhouse gases. The stratification in IWT ponds generates hypoxic conditions at the bottom, and together with the larger availability of organic carbon, stimulates methanogenesis and limits the mitigating action of methanotrophs. Overall, thaw ponds are largely supersaturated in methane, with IWT ponds dominating the emissions in this landscape (92% of total aquatic emissions estimated for the same valley), and they present large variations in emission rates. Conventional wind-based models seem inappropriate to simulate GHG exchanges, as seen when comparing with floating chamber estimations. Surface renewal models that consider heat exchanges are used to estimate flux more accurately, and ebullition flux are measured with submerged funnels to compare with diffusive flux estimations.
15095689 Liu Lin (Chinese University of Hong Kong, Earth System Science, Hong Kong, China); Schaefer, Kevin M.; Chen, A. C.; Gusmeroli, Alessio; Zebker, H. A. and Zhang, T. Measuring thermokarst subsidence using InSAR; potential and pitfalls [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C13D-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thawing of ice-rich permafrost results in irregular, depressed landforms known as thermokarst terrain. The significant subsidence leading to thermokarst features can expand lakes, drain lakes, accelerate thaw, disturb the soil column, and promote erosion. Consequently, it affects many permafrost-region processes including vegetation succession, hydrology, and carbon storage and cycling. Many remote sensing studies identify thermokarst landforms and catalog their ever-changing areas. Yet the intrinsic dynamic thermokarst process, namely surface subsidence, remains a challenge to map and is seldom examined using remote sensing methods. Interferometric Synthetic Aperture Radar (InSAR) is a remote sensing technique that uses a time-series of satellite SAR images to measure cm-level land surface deformation. We demonstrate the capabilities and limitations of space-borne InSAR data to map thermokarst subsidence at a site located near Prudhoe Bay, on the North Slope of Alaska. A pipeline access road was constructed at this site in the 1970s, and is likely to have triggered the thawing of the region's permafrost, causing subsequent expansion of thermokarst-landform terrain. Our InSAR analysis using ALOS PALSAR images reveals that the thermokarst landforms in this region have undergone up to 10 cm of surface subsidence each summer from 2007 to 2010. This pilot study demonstrates the application of InSAR to map localized mass movement in permafrost terrain. We also illustrate how the effectiveness and accuracy of InSAR measurements are limited by several factors such as loss of interferometric coherence due to fast changes of ground surface conditions, spatial and temporal resolutions of InSAR data, and difficulty separating long-term and seasonal deformation signals.
15092552 Logozzo, L. A. (CUNY City College, New York, NY); Perry, A. L.; Wik, Martin; Thornton, Brett F.; Crill, Patrick M.; Johnson, Joel E. and Varner, Ruth K. Linking sediment characteristics to methane emission potential in Subarctic lakes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0275, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
High latitudes are experiencing warmer average annual temperatures, resulting in the thawing of permafrost, and possibly, the increased emission of methane (CH4) from lakes and ponds. One potential impact of permafrost thaw is increased runoff of organic matter into streams, lakes and ponds. Warming can also potentially increase lake sediment temperatures, resulting in a lower methane (CH4) storage capacity and increased CH4 production. We focused our study on six lakes of varying size, location, and characteristics, located in the Stordalen Mire area in northernmost Sweden. We collected sediment cores in each lake and analyzed the dissolved CH4 in the sediment at various depths in the core. The sediment CH4 concentrations were compared to the grain sizes and compositions (total organic carbon (TOC), total sulfur (S), and total nitrogen) of the sediment at the corresponding depths. We also measured dissolved CH4 concentrations in the lake water and compared them to those of the sediment. We found that on average, the CH4 concentration was higher (16.7 mgCH4 gds-1 ±16.4) in sediments with more TOC (31.4 wt% ±10.8). There was also a strong positive correlation between sediment CH4 and total S (r2=0.37, p=0.165), between sediment CH4 and TOC (r2=0.53, p=0.101), and between TOC and total S (r2=0.64, p=0.066). This indicates in situ production of CH4- in the lake sediment at depths of peak CH4 concentrations in at least two of the lakes. The peak of dissolved CH4 was located deeper in the cores although this depth varied among the lakes. In four lakes, we found high CH4 concentrations in the sediment, as well as high CH4 concentrations in the water, indicating little oxidation in the water column or persistent CH4 production in the sediment. This suggests that at least four of our studied lakes have great potential to release a substantial amount of their produced CH4 to the atmosphere.
15095551 Loisel, J. (University of California at Los Angeles, Los Angeles, CA); Yu, Z.; Beilman, D. and Kaiser, K. Developmental history of an intriguing peat-forming community along the West Antarctic Peninsula [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41E-0107, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost peatbanks along the West Antarctic Peninsula (WAP) have become valuable high-resolution archives for late Holocene climatic conditions recently. We recently observed and studied a few water-saturated peatlands that had formed in rocky depressions near Vernadskiy Station and in mainland Antarctica (~ 65°S, 64°W). Remarkably, we seem to be the very first ones to analyze these systems for environmental reconstructions. The similarity between these peatlands and fens from the lower latitudes is striking, and the rarity of these systems along the WAP is intriguing. We present a high-resolution, multi-proxy record of ecosystem development and paleoenvironmental conditions for Rasmussen peatland. The ecosystem is ~100 m2 in size and is characterized by a shallow water table depth at 7 cm below the surface. Surface vegetation is dominated by Calliergon spp., a wet-adapted moss found along the WAP. The studied moss deposit is 50 cm thick and has a high organic matter content (> 90% dry weight). Plant macrofossil analysis reveals that the peatland was initially a wet Sanionia spp. carpet and that a sharp transition to Calliergon spp. occurred about half way through the deposit. A distinct layer of highly decomposed organic matter was observed from 32 to 40 cm and could indicate a period of slowed peat formation, potentially due to dry conditions (enhanced peat decay) or perennial snow cover (limited plant growth). Biochemical decomposition indicators such as carbohydrate yields, acid:aldehyde ratios of lignin phenols, and hydroxyproline yields are being determined to better understand the extent of peat decay that has occurred at this site throughout its development, particularly to further address the nature of the observed stratigraphic changes. Preliminary results indicate that carbohydrate yields of the bottom half of the core are about 1/3 smaller than those of the top half, indicating substantial carbon loss due to decomposition. Overall, these peatlands may represent a transition from wet and thin Sanionia carpets to waterlogged peatlands, which would be an important ecosystem transformation along the WAP that could be promoted in a warmer and wetter climate.
15095554 Monteux, S. (Umea University, Abisko, Sweden); Krab, E. J.; Rönnefarth, J.; Becher, M.; Blume-Werry, G.; Kreyling, J.; Keuper, F.; Klaminder, J.; Kobayashi, M.; Lundin, E. J.; Milbau, A.; Teuber, L. M.; Weedon, J. and Dorrepaal, E. Effects of winter climate change on plant and soil ecology of cryoturbated non-sorted circles tundra [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41E-0114, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Cryoturbation is the movement of soil particles through repeated freeze-thaw events, resulting in the burial of large amounts of soil organic carbon (SOC). Non-sorted circles are a common type of cryoturbated ground in arctic and alpine areas underlain by permafrost. They appear as sparsely vegetated areas surrounded by denser tundra vegetation. Climate change in arctic environments will likely increase winter precipitation in large parts of the Arctic in Europe, Asia and America, resulting in deeper snow cover. Snow is a good thermal insulator and modifications in freezing intensity and freeze-thaw cycles are therefore likely, which could affect the burial of organic matter. Moreover, vegetation, soil fauna and soil microbial communities, which are important drivers of SOC dynamics, may be impacted directly by the altered winter conditions and indirectly by reduced cryoturbation. We aimed to investigate this, and therefore subjected non-sorted circles in North-Swedish subarctic alpine tundra to two years of increased thermal insulation in winter and spring, using snow fences or fiber cloth (Figure 1). Both snow fences and fiber cloth manipulations increased surface soil temperatures, especially daily minimum temperatures, and strongly reduced freeze-thaw frequency. We compared the impacts of these manipulations on plant performance, soil chemistry, soil fauna and soil microbial communities between the centre of the circles and the dense tundra heath just outside. Directly after snowmelt, the extra winter insulation decreased plant leaf damage, both in the center and in adjacent tundra, but responses differed between species. We will further present the responses of plant phenology and growth, soil pH and dissolved organic carbon content, soil fauna activity, Collembola community composition and body size distribution, as well as fungal and bacterial diversity profiles and functional groups abundance. We expect that winter warming due to increased snow cover and its effects on cryoturbation will stimulate the biotic components of non-sorted circles, but may change the interactions between organisms at different trophic levels of this ecosystem. The resulting new balance between increased productivity and decomposer activity might have large implications for this important carbon pool.
15095692 Morton, Don (Boreal Scientific Computing, Fairbanks, AK); Bolton, W. R.; Endalamaw, A. M.; Young, J. M. and Hinzman, L. D. Hydrological parameter estimation (HYPE) system for Bayesian exploration of parameter sensitivities in an Arctic watershed [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C14A-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
As part of a study on how vegetation water use and permafrost dynamics impact stream flow in the boreal forest discontinuous permafrost zone, a Bayesian modeling framework has been developed to assess the effect of parameter uncertainties in an integrated vegetation water use and simple, first-order, non-linear hydrological model. Composed of a front-end Bayes driver and a backend interactive hydrological model, the system is meant to facilitate rapid execution of seasonal simulations driven by hundreds to thousands of parameter variations to analyze the sensitivity of the system to a varying parameter space in order to derive more effective parameterizations for larger-scale simulations. The backend modeling component provides an Application Programming Interface (API) for introducing parameters in the form of constant or time-varying scalars or spatially distributed grids. In this work, we describe the basic structure of the flexible, object-oriented modeling system and test its performance against collected basin data from headwater catchments of varying permafrost extent and ecosystem structure (deciduous versus coniferous vegetation). We will also analyze model and sub-model (evaporation, transpiration, precipitation and streamflow) sensitivity to parameters through application of the system to two catchment basins of the Caribou-Poker Creeks Research Watershed (CPCRW) located in Interior Alaska. The C2 basin is a mostly permafrost-free, south facing catchment dominated by deciduous vegetation. The C3 basin is underlain by more than 50% permafrost and is dominated by coniferous vegetation. The ultimate goal of the modeling system is to improve parameterizations in mesoscale hydrologic models, and application of the HYPE system to the well-instrumented CPCRW provides a valuable opportunity for experimentation.
15092814 Petrenko, V. V. (University of Rochester, Earth and Environmental Sciences, Rochester, NY); Severinghaus, J. P.; Smith, A.; Riedel, K.; Brook, E.; Schaefer, Hinrich; Baggenstos, D.; Harth, C. M.; Hua, Q.; Buizert, C.; Schilt, A.; Fain, Xavier; Mitchell, Logan E.; Bauska, T. K.; Orsi, A. J. and Weiss, R. F. New measurements of 14C provide constraints on sources of a large atmospheric methane increase during the Younger Dryas - Preboreal abrupt warming event [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract PP51D-1154, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thawing permafrost and marine methane hydrate destabilization have been proposed as large sources of methane to the atmosphere in the future warming world. To evaluate this hypothesis it is useful to ask whether such methane releases happened during past warming events. The two major abrupt warming events of the last deglaciation, Oldest Dryas-Bolling (OD-B) and Younger Dryas-Preboreal (YD-PB), were associated with large (up to 50%) increases in atmospheric methane (CH4) concentrations. The sources of these large warming-driven CH4 increases remain incompletely understood, with possible contributions from tropical and boreal wetlands, thawing permafrost as well as marine CH4 hydrates. We present new measurements of 14C of paleoatmospheric CH4 over the YD-PB transition from ancient ice outcropping at Taylor Glacier, Antarctica. 14C can unambiguously identify CH4 emissions from "old carbon" sources, such as permafrost and CH4 hydrates. The only prior study of paleoatmospheric 14CH4 (from Greenland ice) suggested that wetlands were the main driver of the YD-PB CH4 increase, but the results were weakened by an unexpected and poorly understood 14CH4 component from in situ cosmogenic production directly in near-surface ice. In this new study, we have been able to accurately characterize and correct for the cosmogenic 14CH4 component. Preliminary analysis of the results indicates that ~10% of the overall CH4 source to the atmosphere during the nearly-constant climate of the YD was attributable to 14C-free sources. This 14C-free source fraction increased slightly over the YD-PB transition, however, wetlands were nonetheless the main driver of the CH4 increase. Final analysis and interpretation of the 14CH4 data are currently in progress.
15095649 Pradhan, Nawa R. (Engineer Research and Development Center, Coastal and Hydraulic Laboratory, Hydrologic Systems Branch, Vicksburg, MS); Downer, Charles W.; Wahl, Mark; Marchenko, S. S. and Liljedahl, A. K. Simulating interactive effects of frozen soil hydrological dynamics in the Caribou-Poker Creek research watershed, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0387, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Degradation of permafrost due to increased global warming has the potential to dramatically affect soil thermal, hydrological, and vegetation regimes. To explicitly simulate the soil moisture effects of soil thermal conductivity and heat capacity and its effects on hydrological response, we included the capability to simulate the soil thermal regime, frozen soil and permafrost in the Geophysical Institute Permafrost Laboratory (GIPL) model in the physically based, distributed watershed model Gridded Surface Subsurface Hydrologic Analysis (GSSHA). The GIPL model simulates soil temperature dynamics, the depth of seasonal freezing and thawing, and the permafrost location by numerically solving a one-dimensional nonlinear heat equation with phase change. The GSSHA model is a spatially explicit hydrological model that simulates two dimensional groundwater flow and one-dimensional vadose zone flow. The GIPL model is used to compute a soil temperature profile in every two-dimensional GSSHA grid. GSSHA uses this information to adjust hydraulic conductivities for both the vertical unsaturated soil flow and lateral saturated groundwater flow. The newly coupled system was applied in the Caribou-Poker Creek Research Watershed (CPCRW), a 104 km2 basin north of Fairbanks, Alaska. The watershed lies in the zone of discontinuous permafrost and is reserved for ecological, hydrological, and climatic research with no current human influence (other than scientific research). In the application we calibrate the hydrologic model to sub-watersheds and then apply the model to the larger ungaged watershed to assess the impacts of frozen soil and permafrost on the watershed response. Initial simulation result indicates that freezing temperatures reduces soil storage capacity thereby producing higher peak discharges and lower base flow.
15095647 Raz Yaseef, N. (Lawrence Berkeley National Laboratory, Berkeley, CA); Young, J. M.; Rahn, T. A.; Newman, B. D. and Torn, M. S. Variations in evapotranspiration fluxes across geomorphological units and plant functional types in a polygonal-structure tundra in Barrow, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0385, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Although the landscape in tundra ecosystems is relatively flat, and the vegetation is typically shorter than 10 cm, micro-topographical changes within the polygonal structure produce spatial heterogeneity in the form of permafrost depth, soil temperature, soil moisture, and wind speed. Plants react to these conditions and form linkages with the landscape. For example, mosses occupy the wet troughs and lichens are more abundant in the drier high-centred polygons. We conducted measurements in a polygonal-structure tundra site at Barrow, Alaska, to investigate the interconnections between evapotranspiration fluxes, geomorphology and plant cover, during two consecutive years. Fluxes were measured at three spatial and temporal scales: (1) Eddy covariance flux tower, (2) Continuous, fixed, surface clear chamber, and (3) Discontinuous measurements with mobile chambers in approximately 60 locations across the landscape. Our results indicate that different environmental conditions (soil moisture, soil temperature, wind speed, and thaw depth) and plant community composition, driven by microtopographical features, have significant influences on soil greenhouse gas and energy fluxes. Among plant types, evapotranspiration fluxes from moss-covered and inundated areas were more than twice those from other plant types. Continuous chamber measurements were similar in trend and values to eddy-covariance measurements, implying on the high contribution of surface fluxes to atmospheric concentrations. However, wind direction influenced the upscaling of fluxes from chamber to tower, because maritime winds had different moisture content and temperature than terrestrial winds. Microclimate was also affected by microtopography, and wind speed was higher on polygon ridges, and lower in the more protected trough areas, affecting evapotranspiration fluxes. In addition, we observed a strong seasonal trend in fluxes. During peak summer, although 24-hour daylight occurs, our results indicated substantial diurnal variations, despite constant daylight conditions. Information gathered in this research has advance our understanding of coupled processes in Arctic terrestrial ecosystems, and will be used to improve climate model predictions for this already rapidly changing ecosystem.
15092751 Samartin, Stephanie V. (University of Bern, Bern, Switzerland); Heiri, Oliver; Boltshauser-Kaltenrieder, Petra and Tinner, Willy. Reconstruction of full glacial environments and summer air temperatures from Lago della Costa, a refugial site in northeastern Italy [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract PP11A-1319, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Vegetation and climate during the Last Glacial Maximum (LGM) were considerably different than during the current interglacial (Holocene). In Europe large areas north of 40°N were entirely covered by continental ice-sheets and widespread permafrost, with temperatures around 10-20°C lower than at present, whereas further south aridity and temperatures 7-10°C cooler than today occurred. Cool climatic conditions and growing ice-sheets during the LGM radically reduced forest extent and diversity in Europe to a restricted number of so-called "refugia", mostly located in the southern part of the continent. The Euganian Hills in northeastern Italy are supposed to be one of the northernmost refugia of thermophilous mixed oak forest species (e.g. deciduous Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Carpinus, Castanea) as well of some temperate mesophilous species (e.g. Fagus sylvatica, Abies alba) in Europe. In this study we present the first European chironomid-based quantitative temperature reconstruction for the LGM and address the question whether climate conditions were warm enough to permit the local survival of Quercetum mixtum species between ca. 31'000-17'000 cal yr BP. Chironomids preserved in a lake sediment core from Lago della Costa (7 m a.s.l.), a lake on the border of the Euganean Hills in northeastern Italy, allowed quantitative reconstruction of Full and Late Glacial July air temperatures using a combined Swiss-Norwegian temperature inference model based on chironomid assemblages from 274 lakes. Our results suggest that July air temperatures never fell below 10°C which are considered necessary for forest growth. In general, mild climatic conditions prevailed between ca. 31'000-17'000 cal yr BP with temperatures ranging from ca. 11°C to 15.7°C. The expansion of thermophilous trees such as Quercus, Tilia, Ulmus, Fraxinus excelsior, Acer, Carpinus, Castanea (Quercetum mixtum) between ca. 30'000-23'000 cal yr BP can most likely be explained by climate warming (ca. 14°C), conversely, the local contraction of these taxa between ca. 23'000-18'500 cal yr BP was possibly triggered by cooler summer air temperatures (ca. 13.4°C) and a significant moisture decline during the LGM.
15092443 Sanchez, M. J. (Texas A&M University, College Station, TX); Gai, X., Sr.; Shastri, A. and Santamarina, J. C. Coupled THCM modeling of gas hydrate bearing sediments [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11B-0020, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Gas hydrates are crystalline clathrate compounds made of water and a low molecular gas, like methane. Gas hydrates are generally present in oil-producing areas and in permafrost regions. Methane hydrate deposits can lead to large-scale submarine slope failures, blowouts, platform foundation failures, and borehole instability. Gas hydrates constitute also an attractive source of energy as they are estimated to contain very large reserves of methane. Hydrate formation, dissociation and methane production from hydrate bearing sediments are coupled Thermo-Hydro-Mechanical (THM) processes that involve, amongst other, exothermic formation and endothermic dissociation of hydrate and ice phases, mixed fluid flow and large changes in fluid pressure. A comprehensive THM formulation is briefly presented here. Momentum balance, mass balance and energy balance equations take into consideration the interaction among all phases (i.e. solid, liquid, gas, hydrates and ice) and mechanical equilibrium. Constitutive equations describe the intrinsic THM behavior of the sediment. Simulation results conducted for hydrate bearing sediments subjected to boundary conditions highlight the complex interaction among THM processes in hydrate bearing sediments.
15092631 Santamarina, J. C. (Georgia Institute of Technology, Atlanta, GA). Pressure core characterization [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B22B-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Natural gas hydrates form under high fluid pressure and low temperature, and are found in permafrost, deep lakes or ocean sediments. Hydrate dissociation by depressurization and/or heating is accompanied by a multifold hydrate volume expansion and host sediments with low permeability experience massive destructuration. Proper characterization requires coring, recovery, manipulation and testing under P-T conditions within the stability field. Pressure core technology allows for the reliable characterization of hydrate bearing sediments within the stability field in order to address scientific and engineering needs, including the measurement of parameters used in hydro-thermo-mechanical analyses, and the monitoring of hydrate dissociation under controlled pressure, temperature, effective stress and chemical conditions. Inherent sampling effects remain and need to be addressed in test protocols and data interpretation. Pressure core technology has been deployed to study hydrate bearing sediments at several locations around the world. In addition to pressure core testing, a comprehensive characterization program should include sediment analysis, testing of reconstituted specimens (with and without synthetic hydrate), and in situ testing. Pressure core characterization technology can be used to study other gas-charged formations such as deep sea sediments, coal bed methane and gas shales.
15092504 Schreiner, K. M. (University of Minnesota Duluth, Duluth, MN); Bianchi, T. S. and Rosenheim, B. E. Sources and reactivity of terrestrial organic carbon to the Colville River delta, Beaufort Sea, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B12B-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Terrestrial particulate organic carbon (tPOC) delivery to nearshore deltaic regions is an important mechanism of OC storage and burial, and continental margins worldwide account for approximately 90% of the carbon burial in the ocean. Increasing warming in the Arctic is leading to an acceleration of the hydrologic cycle, warming of permafrost, and broad shifts in vegetation. All of these changes are likely to affect the delivery, reactivity, and burial of tPOC in nearshore Arctic regions, making the Arctic an ideal place to study the effects of climate change on tPOC delivery. However, to date, most studies of tPOC delivery from North America to the Arctic Ocean have focused on large Arctic rivers like the Mackenzie and Yukon, and a significant portion of those watersheds lie in sub-Arctic latitudes, meaning that their tPOC delivery is likely not uniquely representative of the high Arctic tundra. Here, we focus on tPOC delivery by the Colville River, the largest North American river with a watershed that does not include sub-Arctic latitudes. Sediment samples from the river delta and nearby Simpson's Lagoon were taken in August of 2010 and subsequently fractionated by density, in order to study the delivery of both discrete and sediment-sorbed tPOC. Samples were analyzed for stable carbon isotopes, bulk radiocarbon, terrestrial biomarkers (including lignin-phenols, and other CuO reaction products), and aquatic biomarkers (algal pigments), and additionally a subset of the samples were analyzed by ramped pyrolysis-14C. Results show that tPOC delivery near the river mouth is sourced from coastal plain tundra, with additional delivery of tPOC from peat released into the lagoon from the seaward limit of the tundra by coastal erosion. Ramped pyrolysis-14C analysis also shows a clear differentiation between tPOC delivered by the river and tPOC delivered by coastal retreat in the lagoon. Additionally, a significant portion of the OC released by the Colville River is relatively thermochemically reactive and sourced from Pleistocene-aged yedoma-like deposits, and could contribute to increased OC mineralization in the Beaufort shelf. These results are the first to combine biomarker and ramped pyrolysis-14C analyses in an Arctic setting.
15092553 Stilson, K. (Elizabeth City State University, Elizabeth City, NC); Sampson, J. M.; Wik, Martin; Crill, Patrick M.; Varner, Ruth K. and Crawford, M. Correlating the presence of Sparganium angustifolium with methane ebullition in a subarctic Swedish lake [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0276, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Methane (CH4) is a greenhouse gas more potent than carbon dioxide. It is released in the Arctic from the seafloor and sediments in melting permafrost regions. Lakes and ponds also emit methane to the atmosphere. Methane production in anoxic lake sediments is often controlled by the amount of available organic material and temperature. It is speculated that the amount and type of submerged aquatic vegetation (SAV) in lakes can also affect methane production in two ways; by either providing a source of carbon (C) for methane production and/or releasing oxygen into the sediment through the roots to hinder production. We sampled SAV at 63 locations on Mellan Harrsjon, a small post-glacial lake in a permafrost setting in sub-arctic Sweden (N68°21', E19°02'). We also measured percent cover of the vegetation, dissolved oxygen, temperature, depth and other variables. We found that the most abundant species, Sparganium angustifolium, occurred in areas with high ebullitive methane emissions from previous studies and therefore provides a carbon source for CH4 production. We also found that over a ten day period percent cover of Sparganium angustifolium increased, with increasing water temperatures, from 37 to 49%. With Arctic warming, high latitude lakes are likely to experience an earlier ice-out and later freeze-up. Because of this, SAV growth is likely to increase and provide a more stable carbon source for CH4 production.
15092550 Tan, Z. (Purdue University, West Lafayette, IN) and Zhuang, Q. Quantifying the variability of CH4 emissions from Pan-Arctic lakes with lake biogeochemical and landscape evolution models [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13G-0272, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Recent studies in the arctic and subarctic show that CH4 emissions from pan-arctic lakes are playing much more significant roles in the regional carbon cycling than previously estimated. Permafrost thawing due to pronounced warming at northern high latitudes affects lake morphology, changing its CH4 emissions. Thermokarst can enlarge the extent of artic lakes, exposing stable ancient carbon buried in the permafrost zone for degradation and changing a previously known carbon sink to a large carbon source. In some areas, the thawing of subarctic discontinuous and isolated permafrost can diminish thermokarst lakes. To date, few models have considered these important hydrological and biogeochemical processes to provide adequate estimation of CH4 emissions from these lakes. To fill this gap, we have developed a process-based climate-sensitive lake biogeochemical model and a landscape evolution model, which have been applied to quantify the state and variability of CH4 emissions from this freshwater system. Site-level experiments show the models are capable to capture the spatial and temporal variability of CH4 emissions from lakes across Siberia and Alaska. With the lake biogeochemical model solely, we estimate that the magnitude of CH4 emissions from lakes is 13.2 Tg yr-1 in the north of 60°N at present, which is on the same order of CH4 emissions from northern high-latitude wetlands. The maximum increment is 11.8 Tg CH4 yr-1 by the end of the 21st century when the worst warming scenario is assumed. We expect the landscape evolution model will improve the existing estimates.
15092716 Tank, S. E. (University of Alberta, Edmonton, AB, Canada); Striegl, R. G.; McClelland, J. W. and Kokelj, S. V. Decadal-scale increases in dissolved carbon flux from the Western Canadian Arctic to the Arctic Ocean [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B34B-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The chemical signature of large rivers has a clear effect on the chemistry and biology of the nearshore ocean. At the same time, the flux of riverine constituents to coastal environments can be used to understand changes occurring over broad terrestrial landscapes. This is particularly relevant in the Arctic, where rivers have a disproportionate impact on nearshore ocean function. Additionally, change is playing out rapidly in Arctic regions, as permafrost thaw and changes in temperature and hydrology are exposing previously frozen soils, changing the nature of hydrological linkages between land and water, and affecting the seasonality of riverine chemistry and flux. Here, we examine a 40-year dataset of point-measurement alkalinity (largely dissolved inorganic carbon) and dissolved organic carbon (DOC) concentrations near the mouth of the Mackenzie River, in addition to similar data from four of the Mackenzie's major sub-catchments. These datasets are coupled with continuous discharge records, and capture flow from the fourth largest river discharging to the Arctic Ocean. Trends near the Mackenzie mouth show that annual fluxes of both alkalinity and DOC are increasing over time, with the proportional changes in DOC (approximately 16% per decade) being much greater than those for alkalinity (approximately 4% per decade). Seasonally, this increase in total flux occurs largely in the winter and late summer, for both constituents. Sub-catchment datasets indicate that these fluxes are increasing in northern, but not southern, sub-catchment regions. These results have clear implications for nearshore ocean function in the Western Canadian Arctic. Increases in DOC may fuel increased bacterial metabolism, while differences in the magnitude of change in alkalinity and DOC flux may modify coastal aragonite saturation. Overall, the changing flux of dissolved carbon near the mouth of the Mackenzie River documents broad-scale changes in the carbon cycle of this region, both on land and in the nearshore ocean.
15092707 Townsend-Small, A. (University of Cincinnati, Cincinnati, OH); Akerstrom, F.; Hinkel, K. M.; Arp, C. D.; Beck, R. A.; Grosse, G.; Jones, B. M.; Kim, C.; Lenters, J. D.; Liu, H. and Eisner, W. R. Sources and fluxes of atmospheric methane from lakes in the Alaskan arctic [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33G-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Climate warming in the Arctic may result in release of carbon dioxide and/or methane from thawing permafrost soils, resulting in a positive feedback to warming. Permafrost thaw may also result in release of methane from previously trapped natural gas. The Arctic landscape is approximately 50% covered by shallow permafrost lakes, and these environments may serve as bellwethers for climate change-carbon cycle feedbacks, since permafrost thaw is generally deeper under lakes than tundra soils. Since 2011, the Circum-Arctic Lakes Observation Network (CALON) project has documented landscape-scale variability in physical and biogeochemical processes of Arctic lakes in permafrost terrain, including carbon cycle feedbacks to climate warming. Here we present a dataset of concentrations, isotope ratios (13C and 2H), and atmospheric fluxes of methane from lakes in Arctic Alaska. Concentrations of methane in lake water ranged from 0.3 to 43 micrograms per liter, or between 6 and 750 times supersaturated with respect to air. Isotopic measurements of dissolved methane indicated that most of the lakes had methane derived from anaerobic organic matter decomposition, but that some lakes may have a small source of methane from fossil fuel sources such as natural gas or coal beds. Concurrent measurements of methane fluxes and dissolved methane concentrations in summer of 2014 will aid in translating routine dissolved measurements into fluxes, and will also elucidate the relative importance of diffusive versus ebulliative fluxes. It is essential that measurements of methane emissions from Arctic lakes be continued long-term to determine whether methane emissions are on the rise, and whether warming of the lakes leads to increased venting of fossil fuel methane from enhanced thaw of permafrost beneath the lakes.
15092661 Turetsky, M. R. (University of Guelph, Guelph, ON, Canada); Euskirchen, E. S.; Czimczik, C. I.; Waldrop, M. P.; Olefeldt, D.; Fan, Z.; Kane, E. S.; McGuire, A. D. and Harden, J. W. Controls on northern wetland methane emissions; insights from regional synthesis studies and the Alaska Peatland Experiment (APEX) [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B23H-07, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Wetlands are the largest natural source of atmospheric methane. Static chambers have been used to quantify variation in wetland CH4 flux for many decades. Regional to global scale synthesis studies of static chamber measurements show that relationships between temperature, water availability and CH4 emissions depend on wetland type (bog, fen, swamp), region (tropical, temperate, arctic) and disturbance. For example, while water table position and temperature serve as the dominant controls on bog and swamp CH4 flux, vegetation is an important control on emissions from fens. These studies highlight the fact that wetland types have distinct controls on CH4 emissions; however, it is unlikely that modeling of wetland CH4 flux will improve without a better mechanistic understanding of the processes underlying CH4 production, transport, and oxidation. At the Alaska Peatland Experiment, we are quantifying CH4 emission using static chambers, automated chambers, and towers. Our sites vary in permafrost regime, including groundwater fens without permafrost, forested peat plateaus with intact permafrost, and collapse scar bogs formed through permafrost thaw. Experimental studies that examine plant and microbial responses to altered water table position and soil temperature are complemented by a gradient approach, where we use a space-for-time substitutions to examine the consequences of thaw on time-scales of decades to centuries. Our results thus far have documented the importance of soil rewetting in governing large CH4 fluxes from northern wetland soils. Accounting for CH4, our collapse scar bog significantly contributed to the global warming potential of the landscape. A major objective of our work is to explore the role of permafrost C release in greenhouse gas fluxes from wetland soils, which we are assessing using radiocarbon as a natural tracer. We have shown, for example, that ebullition of CH4 is dominated by recently fixed C, but a significant fraction of CH4 in bubbles is derived from old C released during thaw. The APEX time series datasets are being used in a variety of modeling studies, from small-scale soil pore and microbial controls on gas production and transport to regional scale assessments of how carbon cycle feedbacks to climate vary with wetland type and abundance.
15095720 Vieira, G. (Universidade de Lisboa, Lisbon, Portugal); Mora, Carla; Pina, P.; Bandeira, L. and Hong, S. G. Geomorphology and vegetation mapping the ice-free terrains of the western Antarctic Peninsula region using very high resolution imagery from an UAV [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C31A-0274, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The West Antarctic Peninsula (WAP) is one of the Earth's regions with a fastest warming signal since the 1950's with an increase of over +2.5°C in MAAT. Significant changes have been reported for glaciers, ice-shelves, sea-ice and also for the permafrost environment. Mapping and monitoring the ice-free areas of the WAP has been until recently limited by the available aerial photo surveys, but also by the scarce high resolution satellite imagery (e.g. QuickBird, WorldView, etc.) that are seriously constrained by the high cloudiness of the region. Recent developments in Unmanned Aerial Vehicles (UAV's), which have seen significant technological advances and price reduction in the last few years, allow for its systematical use for mapping and monitoring in remote environments. In the framework of projects PERMANTAR-3 (PTDC/AAG-GLO/3908/2012 - FCT) and 3DAntartida (Ciencia Viva), we complement traditional terrain surveying and mapping, satellite remote sensing (SAR and optical) and D-GPS deformation monitoring, with the application of an UAV. In this communication, we present the results from the application of a Sensefly ebee UAV in mapping the vegetation and geomorphological processes (e.g. sorted circles), as well as for digital elevation model generation in a test site in Barton Pen., King George Isl. The UAV is a lightweight (ci. 700 g) aircraft, with a 96 cm wingspan, which is portable and easy to transport. It allows for up to 40 min flight time, with application of RGB or NIR cameras. We have tested the ebee successfully with winds up to 10 m/s and obtained aerial photos with a ground resolution of 4 cm/pixel. The digital orthophotomaps, high resolution DEM's together with field observations have allowed for deriving geomorphological maps with unprecedented detail and accuracy, providing new insight into the controls on the spatial distribution of geomorphological processes. The talk will focus on the first results from the field surveys of February and March 2014 and will also include some test data from the mountains of Serra da Estrela, Portugal. New surveying is planned for the season of 2014-15 with mapping to be conducted in Livingston and King George Islands.
15092708 Walter Anthony, K. M. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Sepulveda-Jauregui, A.; Anthony, P.; Grosse, G. and Chanton, J. Methane and carbon dioxide emissions from 40 lakes along a north-south latitudinal transect in Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B33G-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
We assessed the relationship between CH4 and CO2 emission modes in 40 lakes along a latitudinal transect in Alaska to physicochemical limnology, geographic characteristics and permafrost soil types and carbon stocks surrounding lakes. We found that all lakes were net sources of atmospheric CH4 and CO2 but that the climate warming impact of lake CH4 emissions was two times higher than that of CO2. Ebullition and Diffusion were the dominant modes of CH4 and CO2 emissions respectively. Geographically, CH4 emissions from stratified, dystrophic interior Alaska thermokarst (thaw) lakes formed in icy, organic-rich yedoma permafrost soils were 6-fold higher than from non-yedoma lakes near Toolik Field Station and the rest of Alaska. Total CH4 emission was correlated with soil carbon stocks adjacent to lakes, concentrations of phosphate and total nitrogen in lake water, Secchi depth and lake area, with yedoma lakes having higher carbon stocks and nutrient concentrations, shallower Secchi depth, and smaller lake areas. Our findings suggest that permafrost type plays important roles in determining CH4 emissions from lakes by both supplying organic matter to methanogenesis directly from thawing permafrost and by enhancing nutrient availability to primary production, which can also fuel decomposition and methanogenesis.
15095640 Watts, Jennifer D. (University of Montana, Numerical Terradynamic Simulation Group (NTSG), Missoula, MT); Kimball, John S. and Bartsch, A. Satellite microwave detection of boreal-Arctic wetland inundation changes and their impact on regional methane emission estimates [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B54F-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Surface water inundation strongly regulates land-atmosphere energy and carbon exchange in northern environments. However, the dynamic nature of inundation in boreal-Arctic landscapes, and the impact of changing surface water extent on wetland methane (CH4) emissions, is not well understood. We examine recent (2003-2011) changes and spatiotemporal variability in surface inundation across high latitude wetland regions (>45°N) using passive microwave remote sensing retrievals of fractional open water extent (Fw) derived from Advanced Microwave Scanning Radiometer for EOS (AMSR-E) 18.7 and 23.8 GHz brightness temperatures. The daily Fw retrievals are sensitive to sub-grid scale (~25-km resolution) open water area (e.g. lakes and emergent vegetation), and are insensitive to solar illumination and atmosphere contamination effects. We also explore the potential implications of surface Fw variability on high latitude methane emissions using a remote sensing data driven model sensitivity analysis. Our results show widespread surface wetting across the Arctic continuous permafrost zone, which increased model simulated high latitude methane emissions by 0.56 Tg CH4 yr-1 relative to the 2003-2011 mean. This increase was largely offset (-0.38 Tg CH4 yr-1) by drying in boreal Alaska, Canada and western Eurasia. We also find that accounting for dynamic Fw variability in model simulations may significantly lower regional methane emission budgets. These findings accentuate the need for frequent satellite remote sensing driven Fw monitoring across the high latitude systems, to better assess regional sensitivities to climate change. An extended Fw record using AMSR2 data and enhanced (3-9 km) resolution L-band active/passive microwave retrievals from the NASA Soil Moisture Active Passive mission, are expected to improve understanding of regional surface water trends and variability, and reduce uncertainty in boreal-Arctic wetland emission estimates.
15092487 Winterfeld, Maria (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany); Goni, M. A.; Just, Janna; Hefter, Jens; Han, P. and Mollenhauer, G. Characterization of terrestrial organic matter transported through the Lena River Delta (NE Siberia) to its adjacent nearshore zone using lignin phenols, d13C and D14C [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B11J-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Lena River in central Siberia is one of the major pathways translocating terrestrial organic matter (OMterr) from its southernmost reaches near Lake Baikal to the coastal zone of the Laptev Sea and the Arctic Ocean. Permafrost soils from its vast catchment area store huge amounts of pre-aged OM, which is expected to be remobilized due to climate warming. To characterize the composition and vegetation sources of OM discharged by the Lena River, we analyzed the lignin phenol and carbon isotopic composition (d13C and D14C) in total suspended matter (TSM) from surface waters collected in spring and summer, surface sediments from the Buor Khaya Bay along with soils from the Lena Delta. A simple linear mixing model based on the lignin phenol distributions indicates OM in TSM samples from the delta and Buor Khaya Bay surface sediments contains comparable contributions from gymnosperm sources, which are primarily from the taiga forests south of the delta, and angiosperm material typical for tundra vegetation. Considering the small area covered by tundra (~12% of total catchment), the input of tundra-derived OM input is substantial and likely to increase in a warming Arctic. Radiocarbon compositions (D14C) of bulk OM in TSM samples varied from -55 to -391 ppm, i.e. 14C ages of 395 to 3920 yrs BP. Using d13C compositions to estimate the fraction of phytoplankton-derived OM and assuming that this material has a modern 14C signature, we inferred the D14C compositions of OMterr in TSM exported by the Lena River to range between -190 and -700 ppm. Such variability in the ages of OMTERR (i.e. 1640 to 9720 14C yrs BP) reflects the heterogeneous composition and residence time of OM in the Lena River catchment soils (Holocene to Pleistocene ages). Lignin phenol and D14C compositions of surface sediments from the adjacent Buor Khaya Bay suggest that OMTERR deposited there is older and more degraded than materials present in river particles and catchment soils. Stronger diagenetic alteration in Lena Delta TSM and marine sediments relative to soils may reflect degradation of more labile components during permafrost thawing and transport. Despite the high natural heterogeneity in catchment soils, the lignin biomarker compositions and radiocarbon ages of OMTERR exported by the Lena River reflect catchment characteristics such as vegetation and soil type.
15095601 Wylie, B. K. (U. S. Geological Surcey, Earth Resources Observation & Science (EROS), Sioux Falls, SD); Pastick, N.; Jorgenson, T.; Nield, Shawn and Johnson, Kristofer D. Quantifying the distribution and landscape controls of peatlands and organic layer thickness within Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B51H-0111, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The northern circumpolar region is estimated to contain 50% of the global belowground carbon pool and is experiencing climate change at rates higher than anywhere else globally. Surface organic horizons associated with these immense carbon pools are important to ecosystem functioning in terms of soil moisture and temperature regulations, permafrost degradation, successional trajectories, and soil respiration levels. However, fire-induced changes to surface organics and their distribution are poorly understood, especially on landscape scales. These ambiguities make future predictions uncertain for these significant carbon pools, which have the potential for significant feedbacks to global warming. Moreover, given the significant impacts and increasing severity and amount of fires in boreal systems, the spatial quantification of post-fire surface organic thickness is important for ecosystem model calibrations and comparisons, and can improve future projections of vegetation types and albedo, carbon stocks and fluxes, and future thaw depths. Here we present the results of pioneering studies that quantified the distribution and controls of peatlands and soil organic layer thickness in Alaska through the use of statistical models, field data, spatial analyses, and remote sensing (Landsat). Our empirical modeling approach enabled us to produce medium-resolution (30-m pixels) maps of peatlands and organic layer thickness throughout Alaska, which is important for land management practices and enhances the understanding of the risk and feedbacks associated with fires and climate feedbacks.
15092535 Zhang, X. (University of Florida, Ft Walton Beach, FL); Bianchi, T. S. and Allison, M. A. Historical reconstruction of organic carbon inputs to sediments in the Colville River delta, Alaska; the application of biomarker proxies [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13E-0242, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic permafrost represents about 50% of the total belowground global carbon pool, and thus the fate of this pool, as it thaws in the wake of global warming, warrants close attention. Large-river delta-front estuaries (LDEs) have been shown to be important recorders of natural and human-induced changes in watersheds, as they are critical zones for the exchange of organic carbon between the continents and the ocean. The Colville River is the largest North American Arctic River with a continuous permafrost watershed. Simpson's Lagoon, an eastward distal component of the Colville River Delta is an excellent location for historical reconstruction work since it is an area well protected from intense ice grounding and has minimal bioturbation. Sediment cores were collected from the mouth of the river and the lagoon in August of 2010, and analyzed for bulk organic carbon and nitrogen proxies, biomarkers (including lignin phenols, fatty acids), and compound-specific 13C isotope analysis (CSIA) of fatty acids. Downcore sediment data from CSIA of short-chain fatty acids (C14-C18) to the delta over the past ca. 50 years were found to be more depleted and had a wider isotopic range (-17.0~-33.2 ppm) than long-chain fatty acids (C22-C30, -30.3~-36.8 ppm). This possibly reflects alterations of inputs of freshwater flow to the delta which could have resulted in isotopic changes that caused corresponding changes in marine versus freshwater phytoplankton inputs. Downcore short-chain saturated and monounsaturated fatty acid profiles reflected differences in the abundance of bacteria and post-depositional decay of algal inputs across different regions of the delta. Ongoing analyses will also focus on compound-specific radiocarbon analyses (CSRA) of fatty acids and lignin phenols to better understand the changes of organic inputs from terrestrially-derived organic-rich horizons in surface soils vs. old deep permafrost-derived organic horizons.
15092517 Zlamal, Jaime E. (San Diego State University, San Diego, CA); Raab, T. K. and Lipson, D. Biological chlorine cycling in arctic peat soils [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B13A-0167, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soils of the Arctic tundra near Barrow, Alaska are waterlogged and anoxic throughout most of the profile due to underlying permafrost. Microbial communities in these soils are adapted for the dominant anaerobic conditions and are capable of a surprising diversity of metabolic pathways. Anaerobic respiration in this environment warrants further study, particularly in the realm of electron cycling involving chlorine, which preliminary data suggest may play an important role in arctic anaerobic soil respiration. For decades, Cl was rarely studied outside of the context of solvent-contaminated sites due to the widely held belief that it is an inert element. However, Cl has increasingly become recognized as a metabolic player in microbial communities and soil cycling processes. Organic chlorinated compounds (Clorg) can be made by various organisms and used metabolically by others, such as serving as electron acceptors for microbes performing organohalide respiration. Sequencing our arctic soil samples has uncovered multiple genera of microorganisms capable of participating in many Cl-cycling processes including organohalide respiration, chlorinated hydrocarbon degradation, and perchlorate reduction. Metagenomic analysis of these soils has revealed genes for key enzymes of Cl-related metabolic processes such as dehalogenases and haloperoxidases, and close matches to genomes of known organohalide respiring microorganisms from the Dehalococcoides, Dechloromonas, Carboxydothermus, and Anaeromyxobacter genera. A TOX-100 Chlorine Analyzer was used to quantify total Cl in arctic soils, and these data were examined further to separate levels of inorganic Cl compounds and Clorg. Levels of Clorg increased with soil organic matter content, although total Cl levels lack this trend. X-ray Absorption Near Edge Structure (XANES) was used to provide information on the structure of Clorg in arctic soils, showing great diversity with Cl bound to both aromatic and alkyl groups. Incubations were conducted in the laboratory providing arctic soils with Clorg, and measurements taken to assess rates of organohalide respiration show an increase in chloride production due to microbial activity. Investigating these soils with diverse techniques affirms the importance of Cl-cycling in a pristine arctic tundra ecosystem.
15103009 Côté, Jean and Allard, Michel, chairpersons. GeoQuébec 2015; Challenges from North to South; conference program; abstracts--GeoQuébec 2015; Des défis du Nord au Sud; programme de la conférence; résumés: Canadian Geotechnical Society, Canada, Canadian National Committee for the International Permafrost Association, 246 p., (English, French), 2015. Meeting: GeoQuébec 2015; 68th Canadian geotechnical conference and the 7th Canadian permafrost conference, Sept. 20-23, 2015, Quebec City, QC, Canada. Individual abstracts are not cited separately.
URL: http://www.geoquebec2015.ca/documents/58/files/PROG_GeoQc2015_web_vF_compressed. ...
15095604 Du, Jinyang (University of Montana, Numerical Terradynamic Simulation Group, Missoula, MT); Kimball, John S. and Moghaddam, Mahta. Soil active layer freeze/thaw detection using combined L- and P-band radar remote sensing [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B51H-0120, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Monitoring of soil active layer freeze-thaw (FT) dynamics is critical for studying high-latitude ecosystem and environmental changes. We evaluated the potential of inferring FT state dynamics within a tundra soil profile using combined L- and P-band radar remote sensing and forward radiative transfer modeling of backscatter characteristics. A first-order two-layer soil scattering model (FTSS) was developed in this study to analyze soil multi-layer scattering effects. The FTSS was evaluated against other sophisticated modeling approaches and showed comparable performance. The FTSS was then applied to analyzing L- and P-band microwave responses to layered soil. We find that soil volume scattering is rather weak for the two frequencies for frozen or dry soil with mean particle size below 10 mm diameter. Dielectric contrast between adjacent soil layers can contribute to total backscatter at both L- and P-band with more significant impact on P-band than L-band signals depending on the depth of soil profile. Combined L- and P-band radar data are shown to have greater utility than single channel observations in detecting soil FT dynamics and dielectric profile inhomogeneity. Further analysis using available airborne synthetic aperture radar (SAR) data and in-situ measurements also confirm that soil profile heterogeneity can be effectively detected using combined L- and P-band radar backscatter data. This study demonstrates the potential of lower frequency SARs from airborne missions, including UAV-SAR and AirMOSS, for Arctic and alpine assessment of soil active layer properties.
15095645 Harp, Dylan R. (Los Alamos National Laboratory, Los Alamos, NM); Atchley, Adam L.; Coon, E.; Painter, S. L.; Wilson, C. J.; Romanovsky, V. E. and Liljedahl, A. K. Effects of soil property uncertainty on projected active layer thickness [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract C11C-0382, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Uncertainty in future climate is often assumed to contribute the largest uncertainty to active layer thickness (ALT) projections. However, the impact of soil property uncertainty on these projections may be significant. In this research, we evaluate the contribution of soil property uncertainty on ALT projections at the Barrow Environmental Observatory, Alaska. The effect of variations in porosity, thermal conductivity, saturation, and water retention properties of peat and mineral soil are evaluated. The micro-topography of ice wedge polygons present at the site is included in the analysis using three 1D column models to represent polygon center, rim and trough features. The Arctic Terrestrial Simulator (ATS) is used to model multiphase thermal and hydrological processes in the subsurface. We apply the Null-Space Monte Carlo (NSMC) algorithm to identify an ensemble of soil property combinations that produce simulated temperature profiles that are consistent with temperature measurements available from the site. ALT is simulated for the ensemble of soil property combinations for four climate scenarios. The uncertainty in ALT due to soil properties within and across climate scenarios is evaluated. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.
|
