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2016050367 Dashjamts, Dalai (Mongolian University of Science and Technology, School of Civil Engineering and Architecture, Ulaabaatar, Mongolia); Batsaikhan, Anand and Dugersuren, Enkhbaatar. Permafrost and geotechnical investigations in Nalaikh Depression of Mongolia: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 438-455, illus. incl. 12 tables, 8 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation. Includes appendix.
Mongolia is a land-locked country in Central Asia, located between Russia and China. The country's high altitude results in cold, dry, and harsh climatic conditions with permafrost being widespread through the territory. Although the capital city Ulaanbaatar is situated in an area with discontinuous permafrost, the downtown section has recently seen a disappearance of permafrost due to an underground central heating system. During the last decade, expansion of the suburbs toward the Nalaikh Depression has resulted in construction of a new residential complex (Urgakh Naran), construction materials trading center, cement factory and agricultural products market. In the next 10 years, projects such as a university campus, logistics center, residential complex, railway and highway extensions connecting Russia and China have been planned. Engineering-geological and geotechnical investigations have been conducted for these construction projects. This paper presents some of the results determining the engineering geocryological conditions of Nalaikh district and offers foundation design options.
DOI: 10.3724/SP.J.1226.2015.00438
2016050350 Lutskiy, Svyatoslav Ya. (Moscow State University of Railway Engineering, Federal State-Funded Educational Institution of Higher Vocational Education, Moscow, Russian Federation); Shepitko, Taisia V. and Cherkasov, Alexander M. Technological monitoring of subgrade construction on high-temperature permafrost: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 316-322, illus., 19 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Three stages of complex technological monitoring for the increase of high-temperature-permafrost soil bearing capacity are described. The feasibility of process monitoring to improve the targeted strength properties of subgrade bases on frozen soils is demonstrated. The rationale for the necessity of predictive modeling of freeze-thaw actions during the subgrade construction period is provided.
DOI: 10.3724/SP.J.1226.2015.00316
2016050358 Tian Yahu (Beijing Jiaotong University, School of Civil Engineering, Beijing, China); Shen Yupeng; Yu Wenbing and Fang Jianhong. Monitoring and analysis of ground temperature and deformation within Qinghai-Tibet Highway subgrade in permafrost region: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 370-375, illus., 11 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
In order to study the stability of the Qinghai-Tibet Highway embankment at Chumaerhe in the permafrost region of northwest China, the ground temperature and deformation at different depths were monitored under the left and right shoulders of the embankment where thermosyphons were set up only on the left shoulder. Based on the monitored data, characteristics of ground temperature and deformation of the left and right shoulders are analyzed and discussed. The results show that the start time of freezing or thawing of the seasonal active layer was about one to two months later than that of the embankment body itself. The stability of each shoulder was mainly controlled by the settlement of different soil layers, whereas frost heave of soil had scarcely any effect on the stability of the embankment. For the left shoulder, the settlement was mainly influenced by the seasonal active layer and then by the embankment body itself, due to freeze-thaw cycles which may change the soil properties; however, the permafrost layer remained fairly stable. For the right shoulder, creep of the warm permafrost layer was the main influence factor on its stability, followed by settlement of embankment body itself, and finally settlement of the seasonal active layer. Compared with the deformation of the left shoulder, the permafrost layer under the right shoulder was less stable, which indicates that the thermosyphons had a significantly positive effect on the stability of warm permafrost.
DOI: 10.3724/SP.J.1226.2015.00370
2016050747 Akerstrom, F. S. (University of Cincinnati, Cincinnati, OH); Townsend-Small, A. and Hinkel, K. M. Carbon cycling-climate change feedback of thawing permafrost in arctic Alaskan lakes; monitoring methane emissions [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31C-0562, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Arctic Alaska is being impacted by elevated atmospheric temperatures and one consequence could be intensified emissions of greenhouse gases from Arctic lakes as the underlying permafrost thaws. We measured two pathways for methane release from lakes: diffusion and ebullition. The dissolved CH4 concentration in the lake will be determined by performing a headspace extraction. Ebullition and diffusive flux will be measured using floating gas chambers at the lake surface and be measured on a set time interval. Furthermore, stable isotope measurements will establish the CH4 source as biogenic (d13C-61 ppm) or thermogenic (d13C-41 ppm). Methane is a very potent greenhouse gas compared to carbon dioxide (CO2) with a global warming potential of 34 times CO2 on a one-hundred year time scale. It is important establish the role of CH4 emissions from Arctic lakes as part of the global CH4 budget, due to the large carbon reserves that can become active in the carbon cycle from thawing of the underlying permafrost as lake temperature warms. The measurements will be collected throughout the day for about three weeks in August 2015. The CH4 flux trends will be compared to factors such as time of day, weather conditions, lake temperature, lake depth and size, and concentration of dissolved organic carbon and total nitrogen. The lakes in this study are part of the Circum-Arctic Lakes Observation Network and include 35 lakes on the Arctic Coastal Plain of Alaska. Previous studies have shown that concentrations of CH4 in these lakes ranges from 1-8 micrograms per liter, with diffusive CH4 fluxes between 2 to 500 g CH4 per minute. Measured ebulliative fluxes range from 100 to 5000 g CH4 per minute.
2016050719 Anderson, C. (Pacific Northwest National Laboratory, Biological Sciences Division, Richland, WA); Stegen, J.; Bond-Lamberty, B. P.; Tfaily, M. M.; Huang, M. and Liu, Y. Coupling soil carbon fluxes, soil microbes, and high-resolution carbon profiling in permafrost transitions [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B22D-03, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Microbial communities play a central role in the functioning of natural ecosystems by heavily influencing biogeochemical cycles. Understanding how shifts in the environment are tied to shifts in biogeochemical rates via changes in microbial communities is particularly relevant in high latitude terrestrial systems underlain by permafrost due to vast carbon stocks currently stored within thawing permafrost. There is limited understanding, however, of the interplay among soil-atmosphere CO2 fluxes, microbial communities, and SOM chemical composition. To address this knowledge gap, we leverage the distinct spatial transitions in permafrost-affected soils at the Caribou Poker Creek Research Watershed, a 104 km2 boreal watershed ~50 km north of Fairbanks, AK. We integrate a variety of data to gain new knowledge of the factors that govern observed patterns in the rates of soil CO2 fluxes associated with permafrost to non-permafrost transition zones. We show that nonlinearities in fluxes are influenced by depth to permafrost, tree stand structure, and soil C composition. Further, using 16S sequencing methods we explore microbial community assembly processes and their connection to CO2 flux across spatial scales, and suggest a path to more mechanistically link microbes to large-scale biogeochemical cycles. Lastly, we use the Community Land Model (CLM) to compare Earth System Model predictions of soil C cycling with empirical measurements. Deviations between CLM predictions and field observations of CO2 flux and soil C stocks will provide insight for how the model may be improved through inclusion of additional biotic (e.g., microbial community composition) and abiotic (e.g., organic carbon composition) features, which will be critical to improve the predictive power of climate models in permafrost-affected regions.
2016050773 Buxbaum, T. M. (University of Alaska Fairbanks, Fairbanks, AK); Thoman, R. and Romanovsky, V. E. Achieving the NOAA Arctic action plan; the missing permafrost element-permafrost forecasting listening session results [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0600, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost is ground at or below freezing for at least two consecutive years. It currently occupies 80% of Alaska. Permafrost temperature and active layer thickness (ALT) are key climatic variables for monitoring permafrost conditions. Active layer thickness is the depth that the top layer of ground above the permafrost thaws each summer season and permafrost temperature is the temperature of the frozen permafrost under this active layer. Knowing permafrost conditions is key for those individuals working and living in Alaska and the Arctic. The results of climate models predict vast changes and potential permafrost degradation across Alaska and the Arctic. NOAA is working to implement its 2014 Arctic Action Plan and permafrost forecasting is a missing piece of this plan. The Alaska Center for Climate Assessment and Policy (ACCAP), using our webinar software and our diverse network of statewide stakeholder contacts, hosted a listening session to bring together a select group of key stakeholders. During this listening session the National Weather Service (NWS) and key permafrost researchers explained what is possible in the realm of permafrost forecasting and participants had the opportunity to discuss and share with the group (NWS, researchers, other stakeholders) what is needed for usable permafrost forecasting. This listening session aimed to answer the questions: Is permafrost forecasting needed? If so, what spatial scale is needed by stakeholders? What temporal scales do stakeholders need/want? Are there key times (winter, fall freeze-up, etc.) or locations (North Slope, key oil development areas, etc.) where forecasting would be most applicable and useful? Are there other considerations or priority needs we haven't thought of regarding permafrost forecasting? This presentation will present the results of that listening session.
2016050774 Cassidy, A. E. (University of British Columbia, Geography, Vancouver, BC, Canada); Christen, A. and Henry, G. H. The impacts of permafrost disturbances on vegetation and growing season carbon dioxide exchange in a high arctic tundra ecosystem [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0601, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost disturbances are widespread across the Fosheim Peninsula, Ellesmere Island, Canada, where they take the form of active layer detachment slides and retrogressive thaw slumps. This project analyzes the impacts of these disturbances on ecosystem structure and function. Eddy covariance and static chamber measurements were used during the 2013 growing season to determine net ecosystem exchange (NEE) and ecosystem respiration (ER) from multiple retrogressive thaw slumps located in areas with different vegetation types. Two eddy covariance towers were established at the beginning of the growing season and ran continuously throughout the summer. Flux partitioning based on wind direction allowed us to determine NEE fluxes from disturbed tundra, which were compared with fluxes from surrounding undisturbed tundra. A static chamber system was utilized throughout the season to measure ER from corresponding disturbed and undisturbed tundra. Vegetation composition and environmental variables were determined across multiple disturbances. NEE and ER were separated throughout the season into three periods of analysis based on temperature, precipitation, and vegetation development. Eddy covariance measurements indicate decreases in NEE in disturbed areas. In one site, this decrease shifted the system from a net sink to a net source of carbon over the entire growing season. Vegetation community composition determines the overall impact of disturbance on carbon dioxide fluxes. Seasonal shifts in fluxes are also apparent. Disturbances increased ER in sedge tundra and decreased ER in dwarf shrub communities. Analysis of vegetation indicates a decrease in overall vegetation cover within two active disturbances when compared with undisturbed surrounding areas. This corresponds with differing dominant vegetation types in these zones. We determined the impacts of permafrost disturbances on ecosystem structure and function by quantitatively measuring vegetation composition and carbon dioxide fluxes from disturbed and undisturbed tundra.
2016050785 Celis, G. (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ); Mauritz, M.; Bracho, R. G.; Salmon, V. G.; Webb, E.; Hutchings, J. A.; Natali, S.; Crummer, K. G.; Schuur, E. and Schaedel, C. The tundra is a net source of CO2 measured by autochambers and eddy covariance techniques during five years in a site with permafrost thawing [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0612, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Current and future warming of high latitude tundra ecosystems will play an important role in climate change through feedbacks to the global carbon (C) cycle. Long-term observational and experimental studies are pivotal for detecting and understanding changes in the coming decades. Yet studies of the C feedbacks from observational studies and manipulative experiments made on tundra plant communities often have significantly different conclusions with regards to impacts of warming on the ecosystem. Comparing results from these two study types, however, often involves integrating CO2 flux measurements that were collected on different spatial scales using a variety of methods. The process of data assimilation for landscape level analysis is often complicated by the fact that many projects only utilize one method for measuring CO2 fluxes at a given site. This study compares five years of C dynamics in a moist acidic tundra from control plots in a manipulative warming experiment (CiPEHR--plot-scale) and landscape-level natural permafrost thaw gradient (Gradient--Eddy covariance) observations all within a 1km distance from each other. We found net ecosystem exchange (NEE) to be an annual net source of carbon using both methods (Gradient 12.3-125.6 g CO2-C m-2 and CiPEHR warming manipulation 80.2-175.8 g CO2-C m-2). The differences between sites were biggest in the first three years of observation, and can be explained by lower growing season gross primary production (GPP-first three years) from the manipulation (CiPEHR), and lower ecosystem respiration (Reco) from CiPEHR in the first year only. Suppressed GPP and Reco could be from the impact of experimental setup (chamber soil collars-root damage), which lowered the plant community's capacity to fix C, but recovered within three years. This warrants caution of making generalization of short-term experiments in the tundra and more research is needed evaluating coupling of belowground and aboveground C dynamics.
2016050763 Estop-Aragones, C. (University of Alberta, Edmonton, AB, Canada); Olefeldt, D. and Schuur, E. Synthesizing the use of carbon isotope (14C and 13C) approaches to understand rates and pathways for permafrost C mobilization and mineralization [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0590, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
To better understand the permafrost carbon (C) feedback it is important to synthesize our current knowledge, and knowledge gaps, of how permafrost thaw can cause in situ mineralization or downstream mobilization of aged soil organic carbon (SOC) and the rate of this release. This potential loss of old SOC may occur via gaseous flux of CO2 and CH4 exchanged between soil and the atmosphere and via waterborne flux as DOC, POC (and their subsequent decomposition and release to the atmosphere). Carbon isotope (14C and 13C) approaches have been used to estimate both rates and pathways for permafrost C mobilization and mineralization. Radiocarbon (14C) has been used to estimate the contribution of aged C to overall respiration or waterborne C export. We aim to contrast results from radiocarbon studies, in order to assess differences between ecosystems (contrasting wet and dry ecosystems), thaw histories (active layer deepening or thermokarst landforms), greenhouse gas considered (CO2 and CH4) and seasons. We propose to also contrast methodologies used for assessing the contribution of aged C to overall C balance, and include studies using 13C data. Biological fractionation of 13C during both uptake and decomposition has been taken advantage of both in order to aid the interpretation of 14C data and on its own to assess sources and mineralization pathways. For example, 13C data has been used to differentiate between CH4 production pathways, and the relative contribution of anaerobic CO2 production to overall respiration. Overall, carbon isotope research is proving highly valuable for our understanding of permafrost C dynamics following thaw, and there is a current need to synthesize the available literature.
2016050789 Fiddes, J. (WSL Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland). Large area mountain permafrost simulation at DEM resolution; results from the European Alps and Himalaya [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0616, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
We present a system that is able to simulate land-surface conditions at continental scales while accounting for parameters that vary on order of 10's of meters (e.g., topography or surface cover) by using a statistical subgrid scheme (Fiddes and Gruber 2012). The model chain is driven by output from atmospheric datasets with a simple in-house downscaling scheme which uses only data on atmospheric pressure-levels and a DEM (Fiddes and Gruber 2014). The scheme has been tested in the case of mountain permafrost in the European Alps (Fiddes and Gruber 2015) with good results. However the strength of the scheme is application to remote data-sparse regions. Recently we have applied the scheme to simulate permafrost conditions in the Western Himalaya. This included a simple approach to correct snow mass balance using MODIS products, as input precipitation from atmospheric models may often have bias. The scheme is flexible in choice of atmospheric model input data, numerical surface model and surface data. In this abstract we will (1) present the model chain, (2) show the results of simulating permafrost conditions over large areas using only global datasets as input and (3) give an outlook to simulating future conditions. Fiddes, J., Endrizzi, S., and Gruber, S. 2015: Large-area land surface simulations in heterogeneous terrain driven by global data sets: application to mountain permafrost, The Cryosphere, 9, 411-426, DOI:10.5194/tc-9-411-2015, 2015. URL: http://dx.doi.org/10.5194/tc-9-411-2015, Fiddes, J. & Gruber, S. 2014: TopoSCALE V. 1.0: downscaling gridded climate data in complex terrain, Geoscientific Model Development, 7, 387-405, URL: http://dx.doi.org/10.5194/gmd-7-387-2014, Fiddes, J. & Gruber, S., 2012: TopoSUB: a tool for efficient large area numerical modelling in complex topography at sub-grid scales, Geoscientific Model Development, 5, 1245-1257, URL: http://dx.doi.org/10.5194/gmd-5-1245-2012
2016050790 Graham, D. E. (Oak Ridge National Laboratory, Oak Ridge, TN); Roy Chowdhury, T.; Zheng, J.; Moon, J. W.; Yang, Z.; Gu, B. and Wullschleger, S. D. Temperature effects on microbial CH4 and CO2 production in permafrost-affected soils from the Barrow environmental observatory [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0617, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Warmer Arctic temperatures are increasing the annual soil thaw depth and prolonging the thaw season in Alaskan permafrost zones. This change exposes organic matter buried in the soils and permafrost to microbial degradation and mineralization to form CO2 and CH4. The proportion and fluxes of these greenhouse gases released into the atmosphere control the global feedback on warming. To improve representations of these biogeochemical processes in terrestrial ecosystem models we compared soil properties and microbial activities in core samples of polygonal tundra from the Barrow Environmental Observatory. Measurements of soil water potential through the soil column characterized water binding to the organic and mineral components. This suction combines with temperature to control freezing, gas diffusion and microbial activity. The temperature-dependence of CO2 and CH4 production from anoxic soil incubations at -2, +4 or +8 °C identified a significant lag in methanogenesis relative to CO2 production by anaerobic respiration and fermentation. Changes in the abundance of methanogen signature genes during incubations indicate that microbial population shifts caused by thawing and warmer temperatures drive changes in the mixtures of soil carbon degradation products. Comparisons of samples collected across the microtopographic features of ice-wedge polygons address the impacts of water saturation, iron reduction and organic matter content on CH4 production and oxidation. These combined measurements build process understanding that can be applied across scales to constrain key response factors in models that address Arctic soil warming.
2016050778 Hedgpeth, A. (University of Hawaii at Manoa, Honolulu, HI); Beilman, D. and Crow, S. E. Resilience of Arctic permafrost carbon in Mackenzie River basin; an incubation experiment to observe priming potentials and biodegradability of Arctic permafrost peatlands [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0605, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Arctic permafrost zones cover 25% of the Northern Hemisphere and hold 1672Pg of soil carbon (C) with 277Pg in Arctic permafrost peatlands, which is 1/3 of the CO2 in the atmosphere. This currently protected C is a potential source for increased emissions in a warmer climate. Longer growing seasons resulting in increased plant productivity above and below ground may create new labile C inputs with the potential to affect mineralization of previously stable SOM, known as the priming effect. This study examined the response of soil respiration to labile substrate addition in carbon-rich (42-48 %C) permafrost peatland soils along a N-S transect in the central Mackenzie River basin (69.2-62.6°N). Active layer and near surface soils (surface D14C values > -140.0) were collected from four sites between -10.5 and -5.2 MAT. Soils were spiked with 0.5 mg D-glucose g-1 soil, and incubated at 10°C for 23 days to determine potential, short term (i.e., apparent) priming effects. On average glucose addition increased respiration in all samples. One site showed priming evidence in active layer soils despite one-way ANOVA not illustrating statistically significant differences between control and treated final cumulative CO2. Apparent priming effects were seen in two near surface permafrost samples, however cumulative increases in CO2 were not identified as significant. When all results from all sites and depths were considered, the addition of glucose showed no significant effect on total CO2 production relative to controls (p=0.957), suggesting that these sites may be resilient to increased inputs in that little priming evidence was observed. To test the idea that the soils that showed priming effects are of poorer quality, we conducted an additional incubation experiment to explore the biodegradability of these permafrost peatland soils. Soils from these four sites were inoculated and incubated for 17 days. The two sites with observed priming showed the highest biodegradability; suggesting that, compared to other soils, permafrost peat soils may not be sensitive to the priming effect and respond uniquely to warming and increased litter inputs. Therefore C loss from priming decomposition may be trivial when compared to other C loss mechanisms in Arctic permafrost peatlands.
2016050745 Helbig, M. (Université de Montréal, Montreal, QC, Canada); Wischnewski, K.; Kljun, N.; Chasmer, L.; Quinton, W. L.; Detto, M. and Sonnentag, O. Land cover change in the zone of sporadic permafrost causes shift in landscape-scale turbulent energy fluxes [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31A-0521, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Boreal forests in the sporadic permafrost zone have been shown to decline at the expense of wetlands following permafrost disappearance. These land cover changes cause shifts in ecosystem properties and affect biosphere-atmosphere interactions. The goal of our study is to examine the effects of permafrost disappearance on landscape-scale sensible (H) and latent heat fluxes (LE) and related potential feedbacks on regional air temperatures (Ta) We use a combination of nested eddy covariance flux towers, flux footprint and planetary boundary layer (PBL) dynamic modelling, and MOderate-resolution Imaging Spectroradiometer (MODIS) remote sensing products to resolve spatio-temporal dynamics in H and LE at the landscape scale at Scotty Creek, NWT (61°18' N; 121°18' W) and in radiometric land surface temperatures (LST) at the regional scale across the southern Taiga Plains in the sporadic permafrost zone of northwestern Canada. The heterogeneous landscape comprises boreal forests with permafrost and permafrost-free wetlands. Our results show that H above the heterogeneous landscape was about twice as high as above a nearby treeless, permafrost-free bog. In contrast, landscape-scale LE was only about 50 % of LE over the bog. These differences were primarily driven by higher heat transfer efficiency of the aerodynamically rougher forest and lower albedo of the forest compared to the bog (about 10 % lower during summer and about 40 % lower during late winter). Aerodynamic LST increased with the fraction of forest in the flux footprints. This effect was strongest (r2 = 0.55, slope = 0.06 K per % forest) at the end of winter when contrasts in albedo are largest. Bulk surface conductance increased with the fraction of wetlands in the footprints. On a regional scale, radiometric MODIS LST increased with tree cover during the snow cover period (0.06 K per % tree cover), but decreased during the summer (-0.04 K per % tree cover). Modeling results showed that a shift from the current heterogeneous to a homogeneous bog landscape could lead to a decrease in the maximum PBL height by about 700 m and to a decrease in regional Ta by 1 to 2 K. Our results show clearly that permafrost degradation and forest cover shifts will affect local and regional surface energy balances in the boreal zone and could represent important modifiers of future climates.
2016050780 Hutchings, J. A. (University of Florida, Fort Walton Beach, FL); Schuur, E.; Bianchi, Thomas S. and Bracho, R. G. Biomarkers as indicators of respiration during laboratory incubations of Alaskan Arctic tundra permafrost soils [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0607, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
High latitude permafrost soils are estimated to store 1,330-1,580 Pg C, which account for ca. 40% of global soil C and nearly twice that of atmospheric C. Disproportionate heating of high latitude regions during climate warming potentially results in permafrost thaw and degradation of surficial and previously-frozen soil C. Understanding how newly-thawed soils respond to microbial degradation is essential to predicting C emissions from this region. Laboratory incubations have been a key tool in understanding potential respiration rates from high latitude soils. A recent study found that among the common soil measurements, C:N was the best predictor of C losses. Here, we analyzed Alaskan Arctic tundra soils from before and after a nearly 3-year laboratory incubation. Bulk geochemical values as well as the following biomarkers were measured: lignin, amino acids, n-alkanes, and glycerol dialkyl glycerol tetraethers (GDGT). We found that initial C:N did not predict C losses and no significant change in C:N between initial and final samples. The lignin acid to aldehyde (Ad:Al) degradation index showed the same results with a lack of C loss prediction and no significant change during the experiment. However, we did find that C:N and Ad:Al had a significant negative correlation suggesting behavior consistent with expectations. The failure to predict C losses was likely influenced by a number of factors, including the possibility that biomarkers were tracking a smaller fraction of slower cycling components of soil C. To better interpret these results, we also used a hydroxyproline-based amino acid degradation index and n-alkanes to estimate the contribution Sphagnum mosses to soil samples--known to have slower turnover times than vascular plants. Finally, we applied a GDGT soil temperature proxy to estimate the growing season soil temperatures before each incubation, as well as investigating the effects of incubation temperature on the index's temperature estimate.
2016050791 Jastrow, J. D. (Argonne National Laboratory, Argonne, IL); Burke, V. J.; Vugteveen, T. W.; Fan, Z.; Hofmann, S. M.; Lederhouse, J. S.; Matamala, R.; Michaelson, G. J.; Mishra, U. and Ping, C. L. Bioavailable carbon and the relative degradation state of organic matter in active layer and permafrost soils [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0618, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The decomposability of soil organic carbon (SOC) in permafrost regions is a key uncertainty in efforts to predict carbon release from thawing permafrost and its impacts. The cold and often wet environment is the dominant factor limiting decomposer activity, and soil organic matter is often preserved in a relatively undecomposed and uncomplexed state. Thus, the impacts of soil warming and permafrost thaw are likely to depend at least initially on the genesis and past history of organic matter degradation before its stabilization in permafrost. We compared the bioavailability and relative degradation state of SOC in active layer and permafrost soils from Arctic tundra in Alaska. To assess readily bioavailable SOC, we quantified salt (0.5 M K2SO4) extractable organic matter (SEOM), which correlates well with carbon mineralization rates in short-term soil incubations. To assess the relative degradation state of SOC, we used particle size fractionation to isolate fibric (coarse) from more degraded (fine) particulate organic matter (POM) and separated mineral-associated organic matter into silt- and clay-sized fractions. On average, bulk SOC concentrations in permafrost were lower than in comparable active layer horizons. Although SEOM represented a very small proportion of the bulk SOC, this proportion was greater in permafrost than in comparable active layer soils. A large proportion of bulk SOC was found in POM for all horizons. Even for mineral soils, about 40% of bulk SOC was in POM pools, indicating that organic matter in both active layer and permafrost mineral soils was relatively undecomposed compared to typical temperate soils. Not surprisingly, organic soils had a greater proportion of POM and mineral soils had greater silt- and clay-sized carbon pools, while cryoturbated soils were intermediate. For organic horizons, permafrost organic matter was generally more degraded than in comparable active layer horizons. However, in mineral and cryoturbated horizons, the presence of permafrost appeared to have little effect on SOC distribution among size fractions. Future studies will investigate the utility of using organic matter pools defined by SEOM and particle size to predict the bioavailable pools characterized through more time-consuming long-term incubation studies of permafrost region soils.
2016050761 Kang, S. G. (Korea Polar Research Institute, Incheon, South Korea); Hong, J. K.; Jin, Y. K.; Kim, S.; Kim, Y. G.; Dallimore, Scott; Riedel, M. and Shin, C. Velocity models and images using full waveform inversion and reverse time migration for the offshore permafrost in the Canadian Shelf of Beaufort Sea, Arctic [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0588, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
During Expedition ARA05C (from Aug. 26 to Sept. 19, 2014) on the Korean icebreaker RV ARAON, the multi-channel seismic (MCS) data were acquired on the outer shelf and slope of the Canadian Beaufort Sea to investigate distribution and internal geological structures of the offshore ice-bonded permafrost and gas hydrates, totaling 998 km L-km with 19,962 shots. The MCS data were recorded using a 1500 m long solid-type streamer with 120 channels. Shot and group spacing were 50 m and 12.5 m, respectively. Most MCS survey lines were designed perpendicular and parallel to the strike of the shelf break. Ice-bonded permafrost or ice-bearing sediments are widely distributed under the Beaufort Sea shelf, which have formed during periods of lower sea level when portions of the shelf less than ~100m water depth were an emergent coastal plain exposed to very cold surface. The seismic P-wave velocity is an important geophysical parameter for identifying the distribution of ice-bonded permafrost with high velocity in this area. Recently, full waveform inversion (FWI) and reverse time migration (RTM) are commonly used to delineate detailed seismic velocity information and seismic image of geological structures. FWI is a data fitting procedure based on wave field modeling and numerical analysis to extract quantitative geophysical parameters such as P-, S-wave velocities and density from seismic data. RTM based on 2-way wave equation is a useful technique to construct accurate seismic image with amplitude preserving of field data. In this study, we suggest two-dimensional P-wave velocity model (Figure 1) using the FWI algorithm to delineate the top and bottom boundaries of ice-bonded permafrost in the Canadian shelf of Beaufort Sea. In addition, we construct amplitude preserving migrated seismic image using RTM to interpret the geological history involved with the evolution of permafrost.
2016050772 Kleinen, T. (Max Planck Institute for Meteorology, Hamburg, Germany) and Brovkin, V. Modelling carbon in permafrost soils from preindustrial to the future [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0599, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The carbon release from thawing permafrost soils constitutes one of the large uncertainties in the carbon cycle under future climate change. Analyzing the problem further, this uncertainty results from an uncertainty about the total amount of C that is stored in frozen soils, combined with an uncertainty about the areas where soils might thaw under a particular climate change scenario, as well as an uncertainty about the decomposition product since some of the decomposed C might result the release of CH4 as well as CO2. We use the land surface model JSBACH, part of the Max Planck Institute Earth System Model MPI-ESM, to quantify the release of soil carbon from thawing permafrost soils. We have extended the soil carbon model YASSO by introducing carbon storages in frozen soils, with increasing fractions of C being available to decomposition as permafrost thaws. In order to quantify the amount of carbon released as CH4, as opposed to CO2, we have also implemented a TOPMODEL-based wetland scheme, as well as anaerobic C decomposition and methane transport. We initialize the soil C pools for the preindustrial climate state from the Northern Circumpolar Soil Carbon Database to insure initial C pool sizes close to measurements. We then determine changes in soil C storage in transient model experiments following historical and future climate changes under RCP 8.5. Based on these experiments, we quantify the greenhouse gas release from permafrost C decomposition, determining both CH4 and CO2 emissions.
2016050744 Lee, H. (Uni Research, Bergen, Norway); Swenson, S. C.; Lawrence, D. M. and Slater, A. G. Incorporating excess ground ice in the community land model on projections of permafrost in a warming climate [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B24D-01, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
In permafrost soils, "excess ice", also referred to as ground ice, exists in amounts exceeding soil porosity in forms such as ice lenses and wedges. Here, we incorporate a simple representation of excess ice in the Community Land Model (CLM4.5) to investigate how excess ice affects projected permafrost thaw and associated hydrologic responses. We initialize spatially explicit excess ice obtained from the Circum-Arctic Map of Permafrost and Ground-Ice Conditions. The excess ice in the model acts to slightly reduce projected soil warming by about 0.35°C by 2100 in a high greenhouse gas emissions scenario. The presence of excess ice slows permafrost thaw at a given location with about a 10 year delay in permafrost thaw at 3 m depth at most high excess ice locations. The soil moisture response to excess ice melt is transient and depends largely on the timing of thaw with wetter/saturated soil moisture conditions persisting slightly longer due to delayed post-thaw drainage. Based on the model projections of excess ice melt, we can estimate spatially explicit gridcell mean surface subsidence with values ranging up to 0.5 m by 2100 depending on the initial excess ice content and the extent of melt.
2016050730 Liddicoat, Spencer K. (Met Office Hadley Centre for Climate Science and Services, Exeter, United Kingdom); Wiltshire, A.; Burke, E.; Gedney, N.; Jones, C.; O'Connor, F. M.; Robertson, E. and Zaehle, S. Twenty-first century climate simulated by HadGEM2-ES under RCP8.5 modified to account for the effects of thawing permafrost, wetlands and nitrogen limited vegetation on CO2 and methane concentrations [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B23G-0672, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Emissions of carbon dioxide and methane from thawing permafrost and wetlands, together with reduced uptake of CO2 by vegetation due to nitrogen limitation, are expected to exert a positive feedback of increasing magnitude on the climate system over the coming century. The current generation of Earth System models is unable to simulate interactively these climate-carbon cycle feedbacks. We have used offline methodologies to estimate a range of CO2 and methane emissions from permafrost, methane emissions from wetlands, and reduced sequestration of CO2 by nitrogen-limited vegetation under the high-end representative concentration pathway, RCP8.5. By translating these fluxes into increments to the concentration of each gas we have generated a new range of scenarios, exceeding RCP8.5 by up to 266 ppm of CO2 and 732 ppb of methane by 2100. We have used these new scenarios to force the Hadley Centre Earth System model, HadGEM2-ES, over the 21st century. We found that accounting for these feedbacks leads to additional global mean warming of up to 1.5 °C relative to the standard RCP8.5.
2016050781 Malhotra, A. (McGill University, Department of Geography, Montreal, QC, Canada) and Roulet, N. T. The effect of abrupt permafrost thaw on the water table, vegetation and carbon feedback; results from a sub-arctic peatland [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0608, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Uncertainty in estimating the carbon loss from thawing ice-rich permafrost is attributed, in part, to the abrupt changes in ecosystem structure and function after thaw. In a thawing peat plateau in the discontinuous permafrost zone (Stordalen, Mire, Sweden; ST), we tested for the occurrence of abrupt changes in hydrology and the effects of these changes on the water table and vegetation feedback. Using a chronosequence approach along three transects that capture several transitional thaw stages, we found abrupt hydrological changes following thaw, wherein adjacent areas (1 m apart) had unrelated water table depth (WTD) fluctuations. Despite these abrupt changes, surprisingly, the same Gaussian model of plant abundance explained by WTD could be applied to data from both ST and an undisturbed ombrotrophic peatland (Mer Bleue Bog, Canada; MB). However, the Gaussian model fit was better at MB than at ST. Furthermore, explanatory power of the model at ST decreased with increasing permafrost thaw. While water table and vegetation feedback in a thawing landscape is similar to that of a peatland without transitional land cover types, the vegetation and carbon feedback is complicated by non-linear shifts in the partitioning of gaseous effluxes between CO2 and CH4. These results will be presented along with key implications for modeling carbon loss from thawing landscapes.
2016050787 Manies, K. (U. S. Geological Survey, Menlo Park, CA); Jones, M. and Waldrop, M. P. Using a thermokarst bog chronosequence to examine post-thaw changes in net carbon balance and the interactions between permafrost, vegetation, and carbon [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0614, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Northern forest soils and wetlands have served as carbon (C) sinks for thousands of years. The boreal region contains 50% of the world's soil organic C, with northern peatlands accounting for 30% of that pool. However, climate change in this region, in the form of warming air temperatures, has the potential to release a significant portion of this C due to changes in ecosystem structure and function. In particular, permafrost thaw in low-lying, moderately ice-rich areas results in the formation of collapse-scar bogs, dramatically altering the C cycle. Recent studies have shown that the transition from permafrost plateau to thermokarst bog results in the rapid loss of silvic (forest) peat, followed by a slow accumulation of C in post-thaw bog peat. Results from these studies suggest that this transition may turn these areas from net C sinks to C sources in the decades to centuries following thaw. Here we examine a bog chronosequence located within the Tanana River floodplain of Interior Alaska to determine if this pattern of C loss and gain holds true. Peat cores were taken to mineral soil from a permafrost plateau and three bogs with different ages of thaw (within the last several decades, within the last century, and within the past several centuries). All sites were located within the Bonanza Creek Long-term Ecological Research (LTER) site near Fairbanks, AK. We examined how the complex history of these thermokarst features can affect the C cycle. Macrofossil analysis reveals that most cores contained multiple cycles of permafrost aggradation and degradation, with the permafrost aggradation occurring epigenetically after peat initiated from a floodplain fen. Differences in vegetation communities that form peat, and the respective bulk densities associated with fens, permafrost plateaus, and collapse-scar bogs, resulted in different C accumulation rates. These data will provide insight into the fate of C within thermokarst bogs with complex permafrost histories in Interior AK, ultimately providing a better understanding of past and present controls on the regional C balance.
2016050754 Mu, C. (LZU Lanzhou University, Lanzhou, China). Permafrost carbon loss and chemical changes associated with thaw slumps in the northern Qinghai Tibetan Plateau [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0581, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost thaw causes ground subsidence or thermokarst. Thermokarst terrain on hilly slopes can lead to the formation of thaw slumps, which dramatically alter soil properties and carbon emissions, but little is known regarding the effects of thaw slumps on the biogeochemical processes of soil carbon. In the present study, we measured the soil carbon contents and physiochemical properties in different thaw slump stages (no slump, slumping and slumped) in the upper reach of the Heihe River basin in the northeastern Qinghai Tibetan Plateau (QTP). With these samples, the C mineralization rates were measured using laboratory incubations. Meanwhile, the chemistry changes of organic matter were examined using Fourier transform infrared (FTIR) spectroscopy analyzer before and after the incubation. The results showed that there was a significant decrease in soil carbon and nitrogen stocks in the slumping and slumped stages. The loss of organic carbon and total nitrogen was 29.6 ± 5.9% and 31.1 ± 8.8% in the upper 0-10 cm layer of the slumping soil compared to the no slump soil. The slumped soil had a significantly lower loss of carbon and nitrogen content than the slumping soil (t-test, p < 0.05). The incubation results implied that slumped soil has significantly higher cumulative CO2 production than that of slumping soil (t-test, p < 0.05). In addition, the slumped soil had a higher intensity of hydrocarbons and lignin/phenol backbone composition than that of no slump and slumping soil for the 0-10 cm layer. This study demonstrates that abundant carbon and nitrogen loss occurs during the process of thaw slumps. Slumped soil can accumulate some organic matter, accompanied by substantial changes in its carbon chemical structure and characteristics. These results demonstrate that thaw slump plays an important role in the impact of permafrost thaw on chemical characteristics of organic matter and merits greater attention.
2016050788 Nicolsky, D. (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, V. E.; Panda, S. K.; Marchenko, S. S. and Muskett, R. R. Assessment of the permafrost changes in the 21st century and their impact on infrastructure in the Alaskan Arctic [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0615, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Thawing and freezing of Arctic soils is affected by many factors, with air temperature, vegetation, snow accumulation, and soil moisture among the most significant. Here, we employ the permafrost module of the Alaska Integrated Ecosystem Model (AIEM) and establish several high spatial resolution (1km ´ 1km) and very high resolution (30m ´ 30m) scenarios of changes in permafrost characteristics in the Alaskan Arctic in response to projected climate change. Impact of these changes in permafrost on northern Alaskan ecosystems and infrastructure are assessed and regional maps of the possible impacts are developed. The GIPL-2 numerically simulates soil temperature dynamics and the depth of seasonal freezing and thawing by solving the 1-D non-linear heat equation with phase change. In this model the processes of soil freezing and thawing are occurring in accordance with the volumetric unfrozen water content curve and soil thermal properties. The snow temperature and thickness dynamics are simulated assuming the snow accumulation, compaction and phase change processes. We validate our model simulations by comparing with available active layer, permafrost temperature and snow depth records from existing permafrost observatories operated by USGS and the Geophysical Institute of UAF in the North Slope region. Properties of surface vegetation, soil type, layering and moisture content are up-scaled using the Ecosystems of Northern Alaska map (Jorgenson and Heiner, 2003).
2016050764 Panda, S. K. (University of Alaska Fairbanks, Fairbanks, AK); Romanovsky, V. E.; Marchenko, S. S. and Swanson, D. K. Forecast of permafrost distribution, temperature and active layer thickness for Arctic national parks of Alaska through 2100 [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0591, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Though permafrost distribution, temperature and active layer thickness at high spatial resolution are needed to better model the ecosystem dynamics and biogeochemical processes including emission of greenhouse gases at regional and local scale, no such high-resolution permafrost map products existed for Arctic national parks of Alaska until recently. This was due to the lack of information about ecosystem properties such as soil and vegetation characteristics at high spatial resolution. In recent years, the National Park Service (NPS) has carried out several projects mapping ecotype and soil in the Arctic parks from Landsat satellite data at 28.5 m spatial resolution. We used these detailed ecotype and soil maps along with downscaled climate forcing from the IPCC and Climatic Research Unit, University of East Anglia (UK) to model near-surface permafrost distribution, temperature and active layer thickness at decadal time scale from the present through 2100 at 28.5 m resolution for the five Arctic national parks in Alaska: Gates of the Arctic National Park and Preserve, Noatak National Preserve, Kobuk Valley National Park, Cape Krusenstern National Monument, and Bering Land Bridge National Preserve. Our results suggest the near-surface permafrost distribution, i.e. permafrost immediately below the active layer, will likely decrease from the current 99% of the total park area (five parks combined) to 89% by 2050 and 36% by 2100. The near-surface permafrost will likely continue to exist in the northern half of the Gates of the Arctic and Kobuk Valley parks, and in majority of the Noatak preserves by 2100, though its temperature will be up to 5 °C warmer than the present at certain places. Taliks will likely occupy the ground below the active layer in rest of the park areas. These products fill an essential knowledge and data gap and complement research of other Arctic disciplines such as ecosystem modeling, hydrology and soil biogeochemistry. Also, these products enable the NPS personnel to identify geomorphic units vulnerable to climate change and incorporate that knowledge in making policy decisions about management of park resources and public use.
2016050768 Pastick, N. J. (Stinger Ghaffarian Technologies Sioux Falls, Sioux Falls, SD); Jorgenson, T.; Wylie, B. K.; Minsley, B. J.; Brown, D. N.; Genet, H.; Johnson, K. D.; McGuire, A. D.; Kass, A. and Knight, J. F. Towards a better understanding of the sensitivity of permafrost and soil carbon to climate and disturbance-induced change in Alaska [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0595, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Recent increases in air temperature and disturbance activity have led to amplified rates of permafrost degradation and carbon remobilization across portions of Alaska. Further warming, coupled with increases in disturbance frequency and severity (i.e. wildfire, thermokarst), may exacerbate permafrost thaw and disappearance, which would have a profound effect on high-latitude ecological and socio-economic systems. Here we present research aimed at characterizing the sensitivity of different permafrost landscapes to climate and disturbance-induced change through a compilation of in-situ observations, remote sensing and geophysical data, time series analyses, and spatio-temporal modeling. Our data-driven approach allowed for the development of a quantitative assessment of permafrost's potential response to climate change. This analysis also identified indicators of permafrost's susceptibility to disturbances in Alaska. Initial results suggest that further climate-induced permafrost degradation is most likely to occur in regions characterized by discontinuous permafrost and transition zones between tundra, boreal, and temperate forest ecosystems. Permafrost-affected soils, underlying upland ecosystems, are typically more prone to climate and fire-induced change than lowland ecosystems with relatively thicker organic soil layers. However, field and geophysical data indicate that carbon rich silty lowlands are also prone to deep permafrost thaw (> 5 m) following severe disturbance. Because a substantial amount of frozen soil carbon will become susceptible to decomposition upon permafrost thaw, we combined recently developed permafrost carbon maps and future projections of permafrost distribution to highlight areas that may become potential emission hotspots under warmer temperatures. Despite advances in understanding of the drivers of ecological change, more work is needed to integrate studies that link observations of permafrost dynamics to factors that drive those dynamics.
2016050771 Pegoraro, E. (Northern Arizona University, Flagstaff, AZ); Schuur, E. and Bracho, R. G. Priming-induced changes in permafrost soil organic matter decomposition [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0598, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Warming of tundra ecosystems due to climate change is predicted to thaw permafrost and increase plant biomass and litter input to soil. Additional input of easily decomposable carbon can alter microbial activity by providing a much needed energy source, thereby accelerating soil organic matter decomposition. This phenomenon, known as the priming effect, can increase CO2 flux from soil to the atmosphere. However, the extent to which this mechanism can decrease soil carbon stocks in the Arctic is unknown. This project assessed priming effects on permafrost soil collected from a moist acidic tundra site in Healy, Alaska. We hypothesized that priming would increase microbial activity by providing microbes with a fresh source of carbon, thereby increasing decomposition of old and slowly decomposing carbon. Soil from surface and deep layers were amended with multiple pulses of uniformly 13C labeled glucose and cellulose, and samples were incubated at 15° C to quantify whether labile substrate addition increased carbon mineralization. We quantified the proportion of old carbon mineralization by measuring 14CO2. Data shows that substrate addition resulted in higher respiration rates in amended soils; however, priming was only observed in deep layers, where 30% more soil-derived carbon was respired compared to control samples. This suggests that microbes in deep layers are limited in energy, and the addition of labile carbon increases native soil organic matter decomposition, especially in soil with greater fractions of slowly decomposing carbon. Priming in permafrost could exacerbate the effects of climate change by increasing mineralization rates of carbon accumulated over the long-term in deep layers. Therefore, quantifying priming effect in permafrost soils is imperative to understanding the dynamics of carbon turnover in a warmer world.
2016050766 Plaza, C. (Spanish National Research Council, Institute of Agricultral Sciences, Saragossa, Spain); Schuur, E. and Maestre, F. T. The VULCAN Project; Toward a better understanding of the vulnerability of soil organic matter to climate change in permafrost ecosystems [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0593, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Despite much recent research, high uncertainty persists concerning the extent to which global warming influences the rate of permafrost soil organic matter loss and how this affects the functioning of permafrost ecosystems and the net transfer of C to the atmosphere. This uncertainty continues, at least in part, because the processes that protect soil organic matter from decomposition and stabilize fresh plant-derived organic materials entering the soil are largely unknown. The objective of the VULCAN (VULnerability of soil organic CArboN to climate change in permafrost and dryland ecosystems) project is to gain a deeper insight into these processes, especially at the molecular level, and to explore potential implications in terms of permafrost ecosystem functioning and feedback to climate change. We will capitalize on a globally unique ecosystem warming experiment in Alaska, the C in Permafrost Experimental Heating Research (CiPEHR) project, which is monitoring soil temperature and moisture, thaw depth, water table depth, plant productivity, phenology, and nutrient status, and soil CO2 and CH4 fluxes. Soil samples have been collected from the CiPEHR experiment from strategic depths, depending on thaw depth, and allow us to examine effects related to freeze/thaw, waterlogging, and organic matter relocation along the soil profile. We will use physical fractionation methods to separate soil organic matter pools characterized by different preservation mechanisms of aggregation and mineral interaction. We will determine organic C and total N content, transformation rates, turnovers, ages, and structural composition of soil organic matter fractions by elemental analysis, stable and radioactive isotope techniques, and nuclear magnetic resonance tools. Acknowledgements: This project has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 654132. Web site: URL: http://vulcan.comule.com
2016050750 Romanovsky, V. E. (University of Alaska Fairbanks, Fairbanks, AK); Cable, W.; Kholodov, A. L.; Nicolsky, D.; Marchenko, S. S.; Panda, S. K. and Muskett, R. R. Detecting and forecasting permafrost degradation in a warming climate [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0576, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The timing and rate of permafrost degradation are two of the major factors in determining the increase of carbon emissions from thawing permafrost. These changes in permafrost vary both temporally and spatially and do not happen everywhere at the same time. A good example of this heterogeneity is provided by our permafrost data collection in Alaska. Most of the permafrost observatories in Alaska show substantial warming of permafrost since the 1980s. The magnitude of warming varies with location, but is typically between 0.5 and 2°C. However, this warming is not linear in time and not spatially uniform. A short warmer period in the early 1980s was followed by a relative cooling in the mid-1980s. From the late-1980s to the late-1990s, the permafrost and active layer temperatures were increasing. During the first half of the 2000s, permafrost temperatures were not changing significantly at almost all sites in Alaska, except for the sites in the Brooks Range and in its southern foothills were temperature was still increasing. Interesting dynamics in permafrost temperatures have been observed in Alaska since the mid-2000s until present. While permafrost warming resumed on the North Slope of Alaska with a rate of increase between 0.2 to 0.5°C per decade, permafrost temperatures in the Alaskan Interior began a slight cooling trend that has continued during the first half of the 2010s. Most of these changes can be explained by changes in air temperature and snow cover during the observational period. These observations confirm that the future changes in permafrost temperature, in natural undisturbed conditions, will closely follow the changes in climate and as such can be successfully predicted using numerical models forced by established climate change scenarios. In our presentation, we will provide the results from application of our permafrost change models and discuss what this means in terms of potential organic carbon release and its conversion to the greenhouse gases carbon dioxide and methane.
2016050776 Schaedel, C. (Northern Arizona University, Flagstaff, AZ); Ernakovich, J. G.; Harden, J. W.; Natali, S.; Richter, A.; Schuur, E. and Treat, C. C. Strategizing a comprehensive laboratory protocol to determine the decomposability of soil organic matter in permafrost [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0603, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Soil organic matter decomposition depends on physical, chemical, and biological factors, such as the amount and quality of the organic matter stored, abiotic conditions (such as soil temperature and moisture), microbial community dynamics, and physical protection by soil minerals. Soils store immense amounts of carbon with 1330-1580 Pg of carbon in the permafrost region alone. Increasing temperatures in the Arctic will thaw large amounts of previously frozen organic carbon making it available for decomposition. The rate at which carbon is being released from permafrost soils is crucial for understanding future changes in permafrost carbon storage and carbon flux to the atmosphere. The potential magnitude and form of carbon release (carbon dioxide or methane) from permafrost can be investigated using soil incubation studies. Over the past 20 years, many incubation studies have been published with soils from the permafrost zone and three recent syntheses have summarized current findings from aerobic and anaerobic incubation studies. However, the breadth of the incubation synthesis projects was hampered by incomplete meta-data and the use of different methods. Here, we provide recommendations to improve and standardize future soil incubation studies (which are not limited to permafrost soils) to make individual studies useful for inclusion in syntheses and meta-analyses, which helps to broaden their impact on our understanding of organic matter cycling. Additionally, we identify gaps in the understanding of permafrost carbon decomposability, that, when coupled with emerging knowledge from field observations and experiments, can be implemented in future studies to gain a better overview of the overall decomposability of permafrost carbon.
2016050753 Schaefer, K. M. (University of Colorado, National Snow and Ice Data Center, Boulder, CO); Jafarov, E. E.; Jonassen, R. G.; Yarmey, L. and Streletskiy, D. A. Building a permafrost forecasting system [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0579, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost regions are changing rapidly, with even greater changes and potential infrastructure damage projected in coming decades. The Permafrost Forecasting System (PFS) will supply one-year-ahead, seasonal forecasts of Active Layer Thickness (ALT) and permafrost temperature for the state of Alaska to Federal, state, and local stakeholders. The PFS would consist of satellite and in situ data merged with NOAA seasonal forecasts to drive a permafrost forecast model using data assimilation. Measures of skill based upon existing observation networks such as the Circumpolar Active Layer Monitoring (CALM) program would allow critical tests of utility. Many of the required components exist, but require development and integration to create the end-to-end flow of data and products required for the PFS. Advanced permafrost models realistically simulate permafrost dynamics but lack the assimilation tools to link model, observations and NOAA seasonal forecasts. Here we describe the components of the PFS, the physical and organizational infrastructure to support it, and a basic implementation strategy consistent with available state and Federal resources. Such a system could prove useful in other countries with significant permafrost.
2016050751 Tanski, G. (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany). Rapid permafrost carbon degradation at the land-ocean interface [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0577, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Climate change has a strong impact on permafrost coasts in the Arctic. With increasing air and water temperatures, the ice-rich unlithified permafrost coasts will thaw and erode at a greater pace. Organic carbon that has been stored for thousands of years is mobilized and degrades on its way to the ocean. The objective of this study is to investigate to what extent permafrost carbon degrades after thawing before it enters the ocean in a retrogressive thaw slump. A slump located on Herschel Island (Yukon Territory, Canada) was sampled systematically along transects from the permafrost headwall to the coastline. Concentrations of particulate and dissolved organic carbon (POC and DOC) as well as its stable carbon isotopes (d13C-POC and d13C-DOC) were measured and compared in frozen deposits and in thawed sediments. Ammonium, nitrite and nitrate were also analyzed in order to identify and understand the carbon metabolization mechanisms taking place during slump activity. Our results show that major portions of permafrost carbon are metabolized right after thawing. Ammonium concentrations are highest in areas where thawed permafrost material directly accumulates. We suggest that before entering the nearshore zone permafrost organic carbon and nitrogen is subject to major degradation and metabolization. This makes permafrost coasts and retrogressive thaw slumps degradation hotspots at the land-ocean-interface.
2016050756 Wang, X. (Hiroshima University, Higashi-Hiroshima, Japan); Yokozawa, M.; Toda, M. and Kushida, K. Simulating soil carbon accumulation in an upland black spruce ecosystem of interior Alaska; implications for permafrost carbon dynamics to climate change [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0583, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Boreal terrestrial ecosystems act as a huge reservoir of organic carbon, most of which is mainly stored in both active-layer soils and permafrost. Recently, many observational studies have revealed that ongoing climate warming has promoted changes in fire regime, which stimulates the permafrost thaw in the boreal area. Consequently, the decomposition rate of the organic and mineral soils will increase and a large amount of CO2 will be released into the atmosphere. The sustained CO2- release from the soils may create a positive feedback in relation to carbon cycling between the atmosphere and boreal terrestrial ecosystems. However, there still remains substantial uncertainty for evaluating the mechanisms of the carbon cycle feedbacks over centuries. In the present study, we examined the effect of warming and fire episodes on soil carbon dynamics in an upland black spruce ecosystem in interior Alaska, by using a Physical and Biogeochemical Soil Dynamics Model (PB-SDM) which can simulate the feedback cycle of soil organic carbon accumulation with soil thermal and hydrological dynamics. The result indicates that soil carbon accumulation in the organic layer was strongly dominated by increased temperature. In addition, fire events by which a great number of soil layers burned contributed to decrease in soil carbon accumulation largely in the organic layer. On the other hand, remarkably increased temperature conditions (around 9.6° C by 3000) controlled soil carbon accumulation in the mineral layer and changes in soil decomposition rate accompanying with the shift from frozen to thawed conditions with warming accelerated soil carbon decomposition. It is suggested that future climate warming would result in drastic decrease in the soil carbon stock, largely from the organic layer, whereas the vulnerability of deeper soil carbon to future warming is closely connected to permafrost degradation due to wildfire disturbance.
2016050783 Weiss, N. (Stockholm University, Stockholm, Sweden). Exploring indicators for permafrost SOC lability using simple geochemical techniques [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0610, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Considering the vast amount of Soil Organic Carbon (SOC) stored in permafrost soils, it is of great importance to understand and estimate the potential decomposability of this material under a changing climate. Permafrost field studies from contrasting sites in the Russian arctic have been combined to explore the establishment of a usable indicator for potential decomposability, or lability, of SOC in arctic permafrost soils. In order to work with a multitude of environments and samples, the focus lies on simple techniques in order to provide a quick and useful proxy for past and future permafrost SOC lability assessments, at landscape and regional scale levels. Two individual studies from the Russian arctic have been carried out, analyzed, and are partly published. This poster will present the current state of the synthesis of these studies and the determination of an indicator for the likelihood of greenhouse gas release from thawing permafrost soils.
2016050755 Wilson, E. L. (NASA, Goddard Space Flight Center, Greenbelt, MD) and DiGregorio, A. Characterizing thawing permafrost with the Miniaturized Laser Heterodyne Radiometer (mini-LHR) through column measurements of methane [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0582, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
We present mini-LHR measurements of column CH4 from our preliminary field campaign outside of Fairbanks, AK in June 2015. The mini-LHR is fully automated and works in tandem with the AERONET sun photometer for collection of column CH4 every 15 minutes. As part of a comprehensive array of ground based instruments, measurements made by the mini-LHR will aid in monitoring of changes in atmospheric greenhouse gas emissions and help interpret data collected by space-born instruments. The mini-LHR is a passive variation of typical heterodyne radiometry instruments, using sunlight as the light source for measuring CH4 in the infrared. Collecting through collimation optics mounted on the AERONET tracker, the sunlight is chopped in an optical chopper and mixed with a local oscillator in a fast photoreciever (InGaAs detector). The amplitude of the resultant RF (radio frequency) beat signal directly correlates with the concentration of the column gas being measured. Working in conjunction with ground penetrating radar, covariance flux tower, and high-resolution surface CO2 and CH4 measurements, our column CH4 measurements contribute to a holistic view of the atmospheric evolution and response to permafrost thaw. With the intent to expand our observational network to other North American sites, our column CH4 measurements will be instrumental in showing the effects of permafrost thaw on global CH4 levels, as well as benefiting ongoing efforts in retrospective and predictive simulations of greenhouse gasses.
2016050752 Wilson, E. L. (NASA, Goddard Space Flight Center, Greenbelt, MD); Ott, L. E.; DiGregorio, A.; Duncan, B. N.; Euskirchen, E. S.; Carter, L. M.; Tucker, C. J.; Miller, J. H. H.; Liang, Q.; Elshorbany, Y. F.; Edgar, C.; Melocik, K. A.; Ramanathan, A. K.; Mao, J.; Bailey, D. M.; Adkins, E. M. and Melroy, H. Characterizing thawing permafrost carbon emissions; an integrated pilot study in support of satellite evaluation/design and Earth system modeling capabilities [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0578, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
We present a multi-disciplinary, multi-scaled study to measure methane (CH4) and carbon dioxide (CO2) above thawing permafrost at three sites, each representing a different ecosystem, near Fairbanks, AK. We have designed a unique and comprehensive array of ground experiments at these sites that will record permafrost depth and subsurface structure, meteorological data, and concentrations of key GHGs during seasonal ground thaw of the active layer in the summer. This is the first time that these types of measurements have been combined to provide a holistic view of the evolution of, and the atmospheric response to permafrost thaw. These data will allow us to estimate emission fluxes of carbon from the thawing permafrosts. To estimate a global source of GHG emissions from thawing permafrosts, we will use MODIS and Landsat-8 Operational Land Imager and Thermal Infrared Sensor data to "scale up" the data collected at the three sites on the basis of land surface type information. We refer to this effort as a pilot study as we will collect observations near Fairbanks, AK with the intent to expand our observational network in the future to other sites in North America, which will aid in the monitoring of changes in GHG emissions in the Arctic as well as complement and help interpret data collected by space-borne instruments, such as GOSAT, IASI, and AIRS. Based on the data collected at the three sites and a variety of existing satellite data sets, we will develop a computationally-efficient parameterization of emissions from thawing permafrosts for use in the NASA GEOS-5 Atmospheric General Circulation Model (AGCM), thus benefiting ongoing efforts in the NASA Global Modeling and Assimilation Office (GMAO) to build an Earth System Model which is used for both retrospective and predictive simulations of important GHGs. We will use the AGCM to interpret the data collected by tracking methane and CO2 plumes from various sources that impact the three sites. In addition, we will use data collected from aircraft missions and surface stations to understand the signature ratios of trace gases that give important clues as to the identification of sources (e.g. urban, biomass burning).
2016050759 Yang, Y. (Chinese Academy of Sciences, IB Institute of Botany, Beijing, China); Chen, L.; Qin, S.; Ding, J.; Yang, G. and Li, F. Different determinants of soil carbon decomposition between active and permafrost layers; evidence from alpine permafrost on the Tibetan Plateau [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0586, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The fate of permafrost carbon is of great concern among global change community due to its potential positive feedback to climate warming. However, the determinants of soil carbon decomposition between active layer and permafrost layers remain poorly understood. This incubation study was designed to test the following two hypotheses: 1) low carbon quantity and microbial abundances in permafrost soils limit decomposition rates compared with active layer soils; 2) carbon losses from active layer are more controlled by environmental factors, whereas those from permafrost depth are primarily determined by the microbial condition. We collected five active layer and permafrost soils from alpine grasslands on the Tibetan Plateau and compared the carbon dioxide (CO2) emissions at -5 and 5 °C in a 80-days aerobic incubation. The availability of organic carbon and microbial abundances (fungi, bacteria, and actinomycete) within permafrost soils were significantly lower than active layer soils, which, together with the environmental data supports the reduced cumulative CO2 emissions in permafrost depth. However, the decomposability of SOC from permafrost was similar or even higher than surface soils. The carbon loss not only depended on SOC quantity and microbial abundance, but also nitrogen availability and soil pH. Nevertheless, the controls on carbon emissions between active and permafrost layers were significantly different. Cumulative CO2 emission from active layers was best predicted by soil moisture, and carbon emission from permafrost depths was highly associated with fungal-PLFAs. Taken together, these results demonstrate that different controls on carbon emission between active layer and permafrost soils. These differences highlight the importance of distinguishing permafrost depth in Earth System Models when predicting the responses of deep soil carbon to environmental change.
2016050352 Piotrovich, Aleksey A. (Far Eastern State Transport University, Khabarovsk, Russian Federation) and Zhdanova, Svetlana M. To the issue of stabilization of permafrost soil subgrade: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 329-334, illus. incl. 2 tables, 23 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
This paper summarizes an analysis of consequences of railway subgrade construction and maintenance solutions in northern areas of the Russian Far East. An idea of the natural long-term stabilization of the subgrade-base geotechnical system is presented. Proposals to improve the decision-making of construction and engineering solutions are formulated.
DOI: 10.3724/SP.J.1226.2015.00329
2016050356 Chen Xi (Beijing University, School of Civil Engineering, Beijing, China); Liu Jiankun; Xie Nan and Sun Huijing. Probabilistic analysis of embankment slope stability in frozen ground regions based on random finite element method: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 354-364, illus. incl. 1 table, 26 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Prediction on the coupled thermal-hydraulic fields of embankment and cutting slopes is essential to the assessment on evolution of melting zone and natural permafrost table, which is usually a key factor for permafrost embankment design in frozen ground regions. The prediction may be further complicated due to the inherent uncertainties of material properties. Hence, stochastic analyses should be conducted. Firstly, Karhunen-Loeve expansion is applied to attain the random fields for hydraulic and thermal conductions. Next, the mixed-form modified Richards equation for mass transfer (i.e., mass equation) and the heat transport equation for heat transient flow in a variably saturated frozen soil are combined into one equation with temperature unknown. Furthermore, the finite element formulation for the coupled thermal-hydraulic fields is derived. Based on the random fields, the stochastic finite element analyses on stability of embankment are carried out. Numerical results show that stochastic analyses of embankment stability may provide a more rational picture for the distribution of factors of safety (FOS), which is definitely useful for embankment design in frozen ground regions.
DOI: 10.3724/SP.J.1226.2015.00354
2016050359 Guo Lei (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Laboratory of Frozen Soil Engineering, Gansu, China); Yu Qihao; Li Xiaoning; Wang Xinbin and Yue Yongyu. Refreezing of cast-in-place piles under various engineering conditions: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 376-383, illus. incl. 3 tables, 29 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
In the construction of the Qinghai-Tibet Power Transmission Line (QTPTL), cast-in-place piles (CIPPs) are widely applied in areas with unfavorable geological conditions. The thermal regime around piles in permafrost regions greatly affects the stability of the towers as well as the operation of the QTPTL. The casting of piles will markedly affect the thermal regime of the surrounding permafrost because of the casting temperature and the hydration heat of cement. Based on the typical geological and engineering conditions along the QTPTL, thermal disturbance of a CIPP to surrounding permafrost under different casting seasons, pile depths, and casting temperatures were simulated. The results show that the casting season (summer versus winter) can influence the refreezing process of CIPPs, within the first 6 m of pile depth. Sixty days after being cast, CIPPs greater than 6 m in depth can be frozen regardless of which season they were cast, and the foundation could be refrozen after a cold season. Comparing the refreezing characteristics of CIPPs cast in different seasons also showed that, without considering the ground surface conditions, warm seasons are more suitable for casting piles. With the increase of pile depth, the thermal effect of a CIPP on the surrounding soil mainly expands vertically, while the lateral heat disturbance changes little. Deeper, longer CIPPs have better stability. The casting temperature clearly affects the thermal disturbance, and the radius of the melting circle increases with rising casting temperature. The optimal casting temperature is between 2°C and 9°C.
DOI: 10.3724/SP.J.1226.2015.00376
2016050347 Isakov, Alexander (Siberian State University of Railway Engineering, Department of Survey, Novosibirsk, Russian Federation) and Lavrova, Anna. Accounting for the solar radiation in thermal regime prediction for railway subgrade in cold regions: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 293-299, illus., 12 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
This paper presents a comparative analysis of simulation processes of seasonal freezing-thawing of railway subgrade and permafrost degradation, with and without accounting for solar radiation. Also, the effect of sun screens to reduce the degradation of subgrade permafrost under different climatic conditions is numerically substantiated. And finally, the temperature criterion of the origination of permafrost is illustrated.
DOI: 10.3724/SP.J.1226.2015.00293
2016050364 Tang Aiping (Harbin Institute of Technology, Laboratory of Structures Dynamic Behavior and Control, Heilongjiang, China); Zhao Anping and Wen Aihua. Vibration characteristics of frozen soil under moving track loads: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 414-420, illus. incl. 2 tables, 17 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Vibration due to moving traffic loads is an important factor which induces frozen soil damage; this paper analyzed these vibration characteristics of frozen soil foundation under track loads. Firstly, seismic observation array (SOA) technology was applied to monitor the three dimensional dynamic characteristics of frozen soil under movable track load in a permafrost region and seasonal frozen soil area. Secondly, a numerical simulation for the response of frozen soil under movable track load was performed based on finite element analysis (FEA). The results show that dynamic characteristics of frozen soil in perpendicular and parallel direction of the track are obviously different. In the direction perpendicular to the track, the vertical acceleration amplitude had an abrupt increase in the 9-10 m from the track line. In the direction parallel to the track, the acceleration in vertical and horizontal direction had a quick attenuation compared to the other direction. Lastly, various parameters were analyzed for the purpose of controlling the dynamic response of frozen soil and the vibration attenuation in frozen soil layer.
DOI: 10.3724/SP.J.1226.2015.00414
2016050348 Yu Haolin (Harbin Institute of Technology, School of Civil Engineering, Heilongjiang, China); Na, Xinlei and Yang, Zhaohui Joey. Characterization of frozen soil-cement mixture for berm construction in cold regions: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 300-306, illus. incl. 7 tables, 7 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Lagoon berms in western Alaska are difficult to design and build due to limited resources, high cost of construction and materials, and warm permafrost conditions. This paper explores methods to treat locally available frozen materials and use them for berm construction. The goal is to find an optimized mix ratio for cement and additives that can be effective in increasing the strength and decreasing the thaw settlement of an ice-rich frozen silty soil. Soil of similar type and ice content to the permafrost found at a project site in Eek, Alaska is prepared in a cold room. The frozen soil is pulverized and cement, additives and fibers are added to the samples for enhancing shear strength and controlling thaw settlement. Thaw settlement and direct shear tests are performed to assess strength and settlement characteristics. This paper presents a sample preparation method, data from thaw settlement and direct shear tests, and analyses of the test results and preliminary conclusions.
DOI: 10.3724/SP.J.1226.2015.00300
2016050757 Elder, C. (University of California at Irvine, Irvine, CA); Townsend-Small, A.; Hinkel, K. M.; Xu, X. and Czimczik, C. I. Holocene age methane and carbon dioxide dominate Northern Alaska thaw lake emissions [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0584, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Lakes expanding into ice-rich permafrost can rapidly re-introduce large quantities of ancient organic carbon (C) to the atmosphere as carbon dioxide (CO2) or the more powerful greenhouse gas methane (CH4). Quantifying the sources of greenhouse gas emissions from arctic lakes will reduce large uncertainties in the magnitude and timing of the C-climate feedback from the Arctic, and thus trajectories of climate change. This work provides the first regional assessment of integrated whole-lake radiocarbon (14C) ages of dissolved CH4 and CO2 as a proxy for C emission sources in northern Alaska. We collected water samples from below ice along two 170 km north-south transects on the Arctic Coastal Plain (ACP) of Alaska in April 2012 and 2013. These lakes represent a network monitored by the US-NSF funded project, Circum-Arctic Lakes Observation Network (CALON), URL: http://www.arcticlakes.org/. Dissolved CH4 and CO2 were extracted and analyzed for their 14C content. The presence of winter ice on the surface of lakes obstructs the emission of CH4 and CO2 originating from the perennially thawed sub-lake sediments. The trapped gases are forced to mix, thus measured 14C ages are integrated signatures representing the whole-lake emissions. Dissolved CH4 and CO2 ages do not correlate with latitude, yet seem to be driven by surficial geology. Of nearly 150 14C measurements, below-ice dissolved CH4 is the oldest (around 2145 ± 15 14C YBP) in a lake residing on "peaty, sandy lowland" on the northern ACP near the town of Barrow. Modern CH4 and CO2 dominate emissions from "eolian sandy lowlands" in the interior of the ACP. Across all lakes, dissolved CH4 (avg. 836 14C YBP) is older than dissolved CO2 (avg. 480 14C YBP) by a regional average of ca. 360 14C YBP. Results from this study indicate that decomposing Holocene-age organic material is the primary source of CH4 and CO2 emissions from the Alaskan ACP. This baseline dataset provides the foundation for future regional lake monitoring in the warming arctic climate. Our whole-lake proxy facilitates lake-to-lake comparison and regional up scaling, thereby strengthening quantitative understanding of how environmental drivers (water body size, climate, surficial geology) affect the magnitude and sources of biogenic CH4 and CO2 emissions.
2016050749 Fahnestock, M. F. (University of New Hampshire, Durham, NH); Erickson, L. M.; Wik, M.; DeStasio, J.; Halloran, M.; Setera, J.; Bryce, J. G.; McCalley, C. K.; Crill, Patrick M.; Johnson, J. E. and Varner, R. K. Mercury storage in sub-arctic lake sediments in Stordalen Mire, Abisko Sweden [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31C-0572, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost thaw driven by climate change in northern high latitudes is thought to play a significant role in enhancing the mobilization of previously sequestered peatland mercury (Hg) to the atmosphere and hydrosphere. Though studies have shown sub-arctic lake Hg dynamics are impacted by adjacent permafrost thaw, the magnitude and long-term effects of Hg mobilization in sub-arctic lakes remain poorly constrained. Three lakes from the well-characterized Stordalen Mire in Abisko, Sweden were sampled in order to study intra- and inter-lake variability in total lake sediment Hg. These three lakes were chosen due to their proximity to a thawing permafrost peatland and were characterized for their carbon and mercury dynamics. Coring sites included: (1) 6 cores taken at Villasjon, a shallow lake less than 1.5 meters water depth with a previously established methane (CH4) ebullition gradient; (2) 2 cores from Mellarsta Harrsjon, a stream-fed lake with a maximum water depth < 7 m; and (3) 2 cores from Inre Harrsjon, connected to Mellarsta Harrsjon, with a maximum water depth of <5 m. Radiocarbon ages constrain the formation of the three lakes to ~ 3400 years ago. We found both significant inter- and intra-lake variations in total sediment Hg. Within Villasjon, the cores associated with the lowest CH4 ebullition have markedly lower total Hg relative to the cores located in areas with the highest observed CH4 ebullition. The depth of maximum sediment Hg content also varies across the ebullition gradient such that the cores from areas with high ebullition rates had high total Hg as deep as ~30 cm whereas maximum total sediment Hg in the low ebullition cores was located in the top 5 cm. From the inter-lake perspective, Mellarsta Harrsjon and Inre Harrsjon, which contain overall lower methane ebullition fluxes relative to Villasjon, were found to contain significantly less Hg. If sediment Hg is mobilized during CH4 ebullition then this pathway of Hg mobilization needs further understanding.
2016050770 Fan, Z. (Argonne National Laboratory, Argonne, IL); Matamala, R.; Jastrow, J. D.; Liang, C.; Calderon, F.; Michaelson, G. J.; Ping, C. L.; Mishra, U. and Hofmann, S. M. Characterizing organic matter lability in Alaskan tundra soils using mid-infrared spectroscopy [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0597, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Soils in permafrost regions contain large amounts of soil organic carbon (SOC) that is preserved in a relatively undecomposed state due to cold and often wet conditions, yet the potential lability of these SOC stocks is still largely unknown. Traditional methods of assessing SOC lability (e.g., laboratory incubation studies) are labor intensive and time consuming. Fourier-transform mid-infrared spectroscopy (MidIR) provides a means to quickly estimate SOC quantity and quality based on the wealth of spectral information. In this study, we explored the possibility of linking MidIR spectra with SOC lability in Arctic tundra soils. Soils from four sites on the North Slope of Alaska were used in this study: a wet non-acidic tundra site in the coastal plain (CP), two moist acidic tundra sites between the northern foothills and the coastal plain (HC and SH), and another moist acidic tundra site in the northern foothills (HV). Active-layer organic and mineral soils and upper permafrost soils from the four sites were incubated for 60 days at -1, 1, 4, 8 and 16 °C. Thawed soils were allowed to drain to field capacity. Carbon dioxide (CO2) production was measured throughout the study. The chemical composition (e.g., total organic carbon and nitrogen) and MidIR spectra of soil samples were obtained before and after the incubations. CO2 production varied among soils and temperatures. CO2 production was greatest at 16 °C for CP and SH organic layers and for HC and HV permafrost layers. These trends among soil layers and sites remained similar at all temperatures. We found a good correlation between MidIR and cumulative 60-day CO2 production across different soils and temperatures. Characteristic MidIR bands and band ratios previously identified in the literature were also correlated with total CO2 production. For example, several band ratios (such as the ratio of aliphatics to clay or the ratio of lignin or phenolics to minerals) in the mineral active layer were highly correlated with respired CO2, suggesting such ratios might serve as useful lability indicators. Further investigation of characteristic MidIR bands and band ratios for additional soils and for longer term incubations are needed to fully assess their utility as indicators of the relative degradation state and potential decomposability of permafrost-region soils.
2016050765 Heard, K. (Woods Hole Research Center, Falmouth, MA); Natali, S.; Bunn, A. G.; Loranty, M. M.; Kholodov, A. L.; Schade, J. D.; Berner, L. T.; Spektor, V.; Zimov, N. and Alexander, H. D. Analysis of terrestrial carbon stocks in a small catchment of northeastern Siberia [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0592, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
As arctic terrestrial ecosystems comprise about one-third of the global terrestrial ecosystem carbon total, understanding arctic carbon cycling and the feedback of terrestrial carbon pools to accelerated warming is an issue of global concern. For this research, we examined above- and belowground carbon stocks in a larch-dominated catchment underlain by yedoma and located within the Kolyma River watershed in northeastern Siberia. We quantified carbon stocks in vegetation, active layer, and permafrost, and we assessed the correlation between plant and active layer carbon pools and four environmental correlates--slope, solar insolation, canopy density, and leaf area index--at 20 sites. Carbon in the active layer was approximately four times greater than aboveground carbon pools (972 g C m-2), and belowground carbon to 1 m depth was approximately 18 times greater than aboveground carbon pools. Canopy density and slope had a robust positive association with above-ground carbon pools, and soil moisture was positively related to %C in organic, thawed mineral and permafrost soil. Thaw depth was negatively correlated with moss cover and larch biomass, highlighting the importance of vegetation and surface characteristics on permafrost carbon vulnerability. These data suggest that landscape and ecosystem characteristics affect carbon accumulation and storage, but they also play an important role in stabilizing permafrost carbon pools.
2016050794 Hugelius, G. (Stockholm University, Stockholm, Sweden); Loisel, J.; MacDonald, G. M.; Jackson, R. B.; Treat, C. C.; Turetsky, M. R. and Yu, Z. Consolidating and updating estimates of northern peatland extents and carbon stocks [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31F-07, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Conditions favoring peat accumulation have been particularly prevalent in boreal and subarctic regions. The large pool of organic carbon accumulated in Northern peatlands has been an important component in the global carbon cycle throughout the Holocene. All northern peatlands store an estimated 440 Pg organic carbon while a separate study estimates that permafrost region peatlands store ca. 300 Pg organic carbon. However, the degree of overlap between these studies remains unclear and there are differences in methodologies and definitions which prevent direct harmonization of estimates. Here we address this problems by (1) compiling several different databases of field observation data and by (2) comparing previously estimated northern peatland areal extents to the extents of organic soils estimated from compiled harmonized regional and national soil maps from the northern mid and high latitudes. Organic soils are by definition peatlands with >40 cm of near surface peat. The combined estimated extent of organic soils in these maps is 3.44 million km2. This is very similar to the spatial extents of Northern peatlands derived from various national peat resource inventories as reported by previous studies. Our results show that roughly one third of this organic soil area is in permafrost. Based on newly compiled databases we provide spatially distributed estimates of peatland depth and stocks of peat carbon across different biomes. These analyses reveal significant differences in peat depth and carbon stocks between peatland regions and between non-permafrost and permafrost peatlands.
2016050782 Kohnert, K. (Helmholtz Centre Potsdam GFZ German Research Centre for Geosciences, Potsdam, Germany); Serafimovich, A.; Metzger, S.; Hartmann, J. and Sachs, T. Geogenic sources strongly contribute to the Mackenzie River delta's methane emissions derived from airborne flux data [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0609, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Arctic permafrost-associated wetlands and thawing permafrost emit the greenhouse gas methane (CH4), either as a product of recent microbial activity in the active layer or taliks, or from deeper geogenic sources where pathways through the permafrost exist. Current emission estimates vary strongly between different models and there is still disagreement between bottom-up estimates from local field studies and top-down estimates from atmospheric measurements. We use airborne flux data from two campaigns in the Mackenzie River Delta, Canada, in July 2012 and 2013 to directly quantify permafrost CH4 emissions on the regional scale, to analyze the regional pattern of CH4 fluxes and to estimate the contribution of geogenic emissions to the overall CH4 budget of the delta. CH4 fluxes were calculated with a time-frequency resolved version of the eddy covariance technique, resulting in a gridded 100 m x 100 m resolution flux map within the footprints of the flight tracks. We distinguish geogenic gas seeps from biogenic sources by their strength and show that they contribute strongly to the annual CH4 budget of the delta. Our study provides the first estimate of annual CH4 release from the Mackenzie River delta and the adjacent coastal plain. We show that one percent of the covered area contains the strongest geogenic seeps which contribute disproportionately to the annual emission estimate. Our results show that geogenic CH4 emissions might need more attention, especially in areas where permafrost is vulnerable to thawing sufficiently to create pathways for geogenic gas migration. The presented map can be used as a baseline for future CH4 flux studies in the Mackenzie River delta.
2016050767 Kuhn, M. A. (Wheaton College, Norton, MA); Schade, J. D.; Natali, S. and Spawn, S. Fire effects on methane emissions from a larch forest in northeastern Siberia [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0594, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Understanding how boreal forest fires affect the fate of soil carbon in northern permafrost regions is critical to our understanding of feedbacks from Arctic ecosystems on global climate change. The frequency and intensity of fires have been increasing across the northern boreal and tundra region. Fire makes permafrost vulnerable because it removes the insulating plant and organic layers. The removal of these insulating layers in Siberian larch forests underlain by ice and carbon rich permafrost can lead to ground subsidence and saturate soils. Saturated and anoxic soils are ideal conditions for the production of methane, which is ~30x more effective at trapping heat than carbon dioxide. Most boreal ecosystems are currently considered to be sinks for methane, but not much research has been done to study how fire may affect methane production in these regions. We predict that fires will increase methane production in boreal ecosystems underlain by permafrost due to increases in thaw depth, ice wedge thawing, and ground subsidence. This study focused on a ten-year old burn site composed of mainly larch trees and tussocks located near the bank of the Kolyma River in northeastern Siberia. The ground of the burn site was substantially more subsided and had larger areas of surface water and saturated soils than the nearby unburned forest. We investigated the flux of methane from the surfaces of small ponds that formed over thawing ice wedges and in the subsided depressions. While previous studies have reported low dissolved organic carbon concentrations in streams affected by fire in permafrost regions, we found high DOC concentrations in pondwater (21-27 mg/L). Methane fluxes from ice wedge ponds ranged from 20 to 180 mg CH4 m-2 d-1. These values are comparable to fluxes from other permafrost ecosystems including bogs, wet tundra, and fens that are considered globally significant sources of CH4. Additionally, the burned forest contained some subsided areas that were extreme CH4 hotspots, one of which released between 290 and 950 mg CH4 m-2 d-1. These results show that fires in boreal forests underlain by permafrost may cause substantial changes in topography, leading to increased areas of anoxic environments that promote methanogenesis and increase CH4 emissions, possibly turning Siberian forests from a CH4 sink to a source.
2016050779 Li, H. (University of South Carolina Columbia, Columbia, SC) and Ziolkowski, L. A. Alaskan Arctic soils; relationship between microbial carbon usage and soil composition [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0606, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Carbon stored in Arctic permafrost carbon is sensitive to climate change. Microbes are known to degrade Arctic soil organic carbon (OC) and potentially release vast quantitates of CO2 and CH4. Previously, it has been shown that warming of Arctic soils leads to microbes respiring older carbon. To examine this process, we studied the microbial carbon usage and its relationship to the soil OC composition in active layer soils at five locations along a latitudinal transect on the North Slope of Alaska using the compound specific radiocarbon signatures of the viable microbial community using phospholipid fatty acids (PLFA). Additional geochemical parameters (C/N, 13C, 15N and 14C) of bulk soils were measured. Overall there was a greater change with depth than location. Organic rich surface soils are rich in vegetation and have high PLFA based cell densities, while deeper in the active layer geochemical parameters indicated soil OC was degraded and cell densities decreased. As expected, PLFA indicative of Fungi and Protozoa species dominated in surface soils, methyl-branched PLFAs, indicative of bacterial origin, increased in deeper in the active layer. A group of previously unreported PLFAs, believed to correlate to anaerobic microbes, increased at the transition between the surface and deep microbial communities. Cluster analysis based on individual PLFAs of samples confirmed compositional differences as a function of depth dominated with no site to site differences. Radiocarbon data of soil OC and PLFA show the preferential consumption of younger soil OC by microbes at all sites and older OC being eaten in deep soils. However, in deeper soil, where the C/N ratio suggests lower bioavailability, less soil OC was incorporated into the microbes as indicating by greater differences between bulk and PLFA radiocarbon ages.
2016050784 Palmtag, J. (Stockholm University, Stockholm, Sweden); Hugelius, G. and Kuhry, P. Improved estimates of soil organic carbon storage in the Zackenberg Valley, NE Greenland by combining geomorphology and land cover [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0611, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Recent estimates indicate that soils in the northern circumpolar permafrost region store substantial amounts of soil organic carbon (SOC). These soils have large regional and landscape-level variability depending on topographic, ecoclimatic and edaphic factors. This study improves the existing upscaling product from Zackenberg, NE Greenland on SOC storage by using a combination of geomorphological units and land cover classes. Especially in mountainous regions the same vegetation types show in some cases great differences in their SOC storage depending on their topographical position, which makes their further separation into landform units crucial for better upscaling estimates.
2016050786 Parazoo, N. (California Institute of Technology, NASA, Jet Propulsion Laboratory, Pasadena, CA); Miller, C. E.; Commane, R.; Wofsy, S. C.; Koven, C.; Lawrence, D. M.; Lindaas, J.; Chang, R. Y. W. and Sweeney, C. Detecting patterns of changing carbon uptake in Alaska using sustained in situ and remote sensing CO2 observations [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0613, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The future trajectory of Arctic ecosystems as a carbon sink or source is of global importance due to vast quantities of carbon in permafrost soils. Over the last few years, a sustained set of airborne (NOAA-PFA, NOAA-ACG, and CARVE) and satellite (OCO-2 and GOSAT) atmospheric CO2 mole fraction measurements have provided unprecedented space and time scale sampling density across Alaska, making it possible to study the Arctic carbon cycle in more detail than ever before. Here, we use a synthesis of airborne and satellite CO2 over the 2009-2013 period with simulated concentrations from CLM4.5 and GEOS-Chem to examine the extent to which regional-scale carbon cycle changes in Alaska can be distinguished from interannual variability and long-range transport. We show that observational strategies focused on sustained profile measurements spanning continental interiors provide key insights into magnitude, duration, and variability of Summer sink activity, but that cold season sources are currently poorly resolved due to lack of sustained spatial sampling. Consequently, although future CO2 budgets dominated by enhanced cold season emission sources under climate warming and permafrost thaw scenarios are likely to produce substantial changes to near-surface CO2 gradients and seasonal cycle amplitude, they are unlikely to be detected by current observational strategies. We conclude that airborne and ground-based networks that provide more spatial coverage in year round profiles will help compensate for systematic sampling gaps in NIR passive satellite systems and provide essential constraints for Arctic carbon cycle changes.
2016049167 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.; Dyonisius, M.; Buizert, C.; Schilt, A.; Faïn, Xavier; Mitchell, Logan E.; Bauska, T. K.; Orsi, Anais J. and Weiss, R. F. Ice core measurements of 14CH4 constrain the sources of atmospheric methane increase during abrupt warming events of the last deglaciation [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract A23J-01, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Thawing permafrost and marine methane hydrate destabilization in the Arctic and elsewhere 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, ~14,500 years ago) and Younger Dryas-Preboreal (YD-PB; ~11,600 years ago), 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 a record 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, 14C-depleted 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. All samples from before, during and after the abrupt warming and associated CH4 increase yielded 14CH4 values that are consistent with 14C of atmospheric CO2 at that time, indicating a purely contemporaneous methane source. These measurements rule out the possibility of large CH4 releases to the atmosphere from methane hydrates or old permafrost carbon in response to the large and rapid YD-PB warming. To the extent that the characteristics of the YD-PB warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric methane increases from old carbon sources in the Arctic are unlikely. Instead, our measurements indicate that global wetlands will likely respond to the warming with increased methane emissions. Analysis and interpretation of 14CH4 for the abrupt OD-B transition is in progress and these results will also be presented.
2016050769 Selbmann, A. K. (University of Applied Sciences Mittweida, Mittweida, Germany) and Natali, S. A pan-Arctic survey about the meaning of winter respiration in northern high latitudes [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0596, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
The arctic is warming at twice the rate of the rest of the planet, with the greatest warming occurring during the winter months. Despite the cold temperatures during the winter, microbial activity continues and leads to a release of soil carbon during a critical period when plant uptake has ceased. Due to the warming climate, huge pools of carbon stored in permafrost soils are expected to be released to the atmosphere. To identify the annual carbon balance of arctic ecosystems and potential impacts caused by a rise in temperatures, understanding the magnitude of winter respiration is essential. In order to refine current and future estimates of carbon loss from permafrost ecosystems, we conducted a pan-arctic synthesis of winter respiration from northern high latitude regions. We examined differences in cumulative winter respiration among permafrost zones, biomes, ecosystem types, and effects of measurement method on winter respiration estimates. We also examined effect of air temperature and precipitation (Worldclim database) on rates of winter respiration. The database contained 169 measurement points from 46 study sites located throughout the permafrost zones. We found that 21.6 % of annual respiration is happening during non-growing season, which can shift ecosystems from annual sinks during the growing season to net sources of carbon on an annual basis. Across studies, the average carbon loss during the winter was 66 g CO2-C. There was a strong relationship between mean annual air temperature and winter respiration, and lower respiration in continuous compared to discontinuous permafrost zones and northern areas without permafrost. The present results clarify the contribution of winter respiration to annual carbon balance and show the sensitivity of carbon release to rising temperatures in northern high latitudes. These results suggest that permafrost degradation and increased temperature will lead to a higher release of carbon from the Arctic in wintertime, highlighting the importance of including winter respiration in current and future carbon estimates for the northern region.
2016050748 Stern, J. C. (NASA, Goddard Space Flight Center, Greenbelt, MD); White, J. R.; Pratt, L. M. and Thompson, H. A. Real-time measurements of CH4 and CO2 flux and del13C from a proglacial wetland in southwestern Greenland [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31C-0571, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Arctic permafrost environments represent a large repository of stored carbon that may be mobilized as global temperatures increase, providing a substrate for microbial CH4 production. Proglacial wetlands and lakes are important targets of study to better understand how rapidly changing landscapes affected by climate warming adapt their carbon cycling. Recent advances in portable laser spectrometry have enabled rapid in situ measurements of not only greenhouse gas fluxes, but also del13C compositions of these gases. Here we use a Picarro CH4 and CO2 isotope analyzer to continuously measure CH4 and CO2 flux in situ for comparison to static closed chamber measurements where samples are collected at discrete time intervals and returned to the laboratory for analysis. Real-time, in situ analysis also allowed simple light/dark experiments to be performed on chambers containing different vegetation. In addition, this instrument can be used to measure concentration and del13C of both dissolved CH4 and CO--2 in lake waters when appropriate gas stripped methods are used. We present data for CH4 and CO2 flux and del13C of emitted and dissolved gases from permafrost-affected wetlands and lakes associated with proglacial landscapes in southwestern Greenland near the Russell Glacier.
2016050775 Tang, J. (Lund University, Physical Geography and Ecosystem Science, Lund, Sweden). Diagnosis of processes controlling dissolved organic carbon (DOC) export in a subarctic region by a dynamic ecosystem model [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0602, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost thawing in high latitudes allows more soil organic carbon (SOC) to become hydrologically accessible. This can increase dissolved organic carbon (DOC) exports and carbon release to the atmosphere as CO2 and CH4, with a positive feedback to regional and global climate warming. However, this portion of carbon loss through DOC export is often neglected in ecosystem models. In this paper, we incorporate a set of DOC-related processes (DOC production, mineralization, diffusion, sorption-desorption and leaching) into an Arctic-enabled version of the dynamic ecosystem model LPJ-GUESS (LPJ-GUESS WHyMe) to mechanistically model the DOC export, and to link this flux to other ecosystem processes. The extended LPJ-GUESS WHyMe with these DOC processes is applied to the Stordalen catchment in northern Sweden. The relative importance of different DOC-related processes for mineral and peatland soils for this region have been explored at both monthly and annual scales based on a detailed variance-based Sobol sensitivity analysis. For mineral soils, the annual DOC export is dominated by DOC fluxes in snowmelt seasons and the peak in spring is related to the runoff passing through top organic rich layers. Two processes, DOC sorption-desorption and production, are found to contribute most to the annual variance in DOC export. For peatland soils, the DOC export during snowmelt seasons is constrained by frozen soils and the processes of DOC production and mineralization, determining the magnitudes of DOC desorption in snowmelt seasons as well as DOC sorption in the rest of months, play the most important role in annual variances of DOC export. Generally, the seasonality of DOC fluxes is closely correlated with runoff seasonality in this region. The current implementation has demonstrated that DOC-related processes in the framework of LPJ-GUESS WHyMe are at an appropriate level of complexity to represent the main mechanism of DOC dynamics in soils. The quantified contributions from different processes on DOC export dynamics could be further linked to the climate change, vegetation composition change and permafrost thawing in this region.
2016050760 Touyz, J. (George Washington University, Washington, DC); Apanasovich, T. V.; Streletskiy, D. A. and Shiklomanov, N. I. Spatio-temporal modeling of active layer thickness [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0587, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Arctic regions are experiencing an unprecedented rate of environmental and climate change. The active layer (the uppermost layer of soil between the atmosphere and permafrost that freezes in winter and thaws in summer) is sensitive to both climate and environmental changes and plays an important role in the functioning of Arctic ecosystems, planning, and economic activities. Knowledge about spatio-temporal variability of ALT is crucial for environmental and engineering applications. The objective of this study is to provide the methodology to model and estimate spatio-temporal variation in the active layer thickness (ALT) at several sites located in the Circumpolar region spanning the Alaska North Slope, and to demonstrate its use in spatio-temporal interpolation as well as time-forward prediction. In our data analysis we estimate a parametric trend and examine residuals for the presence of spatial and temporal dependence. We propose models that provide a description of residual space-time variability in ALT. Formulations that take into account interaction among spatial and temporal components are also developed. Moreover, we compare our models to naive models in which residual spatio-temporal and temporal correlations are not considered. The predicted root mean squared and absolute errors are significantly reduced when our approach is employed. While the methodology is developed in the context of ALT, it can also be applied to model and predict other environmental variables which use similar spatio-temporal sampling designs.
2016050792 Wilkman, E. (San Diego State University, San Diego, CA); Oechel, W. C. and Zona, D. Plot-level microtopographical controls on Arctic growing season and fall shoulder season soil CO2 flux [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0619, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Permafrost soils are among the most obvious environments in which current constraints on decomposition are likely to change as a result of climatic alterations, potentially exposing large amounts of previously stored carbon (C) to microbial degradation and emission during the next few decades (Davidson & Janssens, 2006). As a best estimate, the soils of the circumpolar Arctic store over 1,035 ± 150 Pg C in the near surface (0-3 m), approximately twice the amount of C that is currently in the atmosphere (Tarnocai et al., 2009; Hugelius et al., 2014). Currently, however, much of this previously stored carbon is at risk of loss to the atmosphere due to accelerated soil organic matter decomposition in warmer future climates (Dorrepaal et al., 2009; Schuur et al., 2015). Polygonization, a predominant cryogenic process, produces micro-topographical and hydrological heterogeneity, as polygon rims produce lower water tables and drier conditions and low polygon centers produce higher water tables and wetter conditions (Brown et al., 1980). As climate models increasingly suggest that current warming trends in the Arctic (4-8 °C higher annual surface air temperatures) will continue by century's end, C cycling in these northern climes may be further amplified (IPCC, 2013). Much uncertainty remains in regard to the spatial and temporal extent of CO2 emissions from these systems, especially in view of the potential for modifications to C cycling in response to increased warming and deeper summer thawing of the active soil layer (Mastepanov et al., 2013). Therefore, an LI-8100 Automated Soil Flux System (LI-COR Biosciences) was deployed in Barrow, AK, to gather high temporal frequency soil CO2 fluxes from a wet sedge tundra ecosystem. Dark chamber fluxes were gathered from 5 microtopographical habitats (designated flat, high, low, polygon rim, and polygon troughs) to calculate daily average, diurnal, and monthly respiratory fluxes. With the addition of concurrently gathered environmental parameters (thaw depth, water table, soil temperature, and eddy covariance meteorological tower data), the relatively high temporal and microspatial extent of this dataset will allow us to better understand the controls of microtopography and water table height on C cycling in this ecosystem.
2016050758 Yi, Y. (University of Montana, College of Forestry and Conservation, Numerical Terradynamic Simulation Group, Missoula, MT); Kimball, J. S.; Rawlins, M. A.; Moghaddam, M. and Euskirchen, E. S. The role of snow cover in affecting pan-Arctic soil freeze/thaw and carbon dynamics [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0585, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Satellite data records spanning the past 3 decades indicate widespread reductions (~0.8-1.3 days decade-1) in mean annual snow cover and frozen season duration across the pan-Arctic domain, coincident with regional climate warming. How the northern soil carbon pool responds to these changes will have a large impact on projected regional and global climate trends. The objective of this study was to assess how northern soil thermal and carbon dynamics respond to changes in surface snow cover and freeze/thaw (F/T) cycles indicated from satellite observations. We developed a coupled permafrost, hydrology and carbon model framework to investigate the sensitivity of soil organic carbon stocks and soil decomposition to recent climate variations across the pan-Arctic region from 1982 to 2010. The model simulations were also evaluated against satellite observation records on snow cover and F/T processes. Our results indicate that surface warming promotes wide-spread soil thawing and active layer deepening due to strong control of surface air temperature on upper (<0.5 m) soil temperatures during the warm season. Earlier spring snowmelt and shorter seasonal snow cover duration with regional warming will mostly likely enhance soil warming in warmer climate zones (mean annual Tair>-5°C) and promote permafrost degradation in these areas. Our results also show that seasonal snow cover has a large impact on soil temperatures, whereby increases in snow cover promote deeper (>&eq;0.5 m) soil layer warming and soil respiration, while inhibiting soil decomposition from surface (≤&eq;0.2 m) soil layers, especially in colder climate zones (mean annual Tair≤&eq;-10 °C). This non-linear relationship between snow cover and soil decomposition is particularly important in permafrost areas, where a large amount of soil carbon is stored in deep perennial frozen soils that are potentially vulnerable to thawing, with resulting mobilization and accelerated carbon losses from near-term climate change.
2016050424 Al Bashaireh, Amineh B. (College of Wooster, Department of Geology, Wooster, OH); Singer, David M. and Herndon, Elizabeth M. Geochemical analysis of iron and phosphorous in Arctic tundra soils [abstr.]: in Geological Society of America, 2015 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 47(7), p. 543, 2015. Meeting: Geological Society of America, 2015 annual meeting & exposition, Nov. 1-4, 2015, Baltimore, MD.
Arctic temperatures are increasing at double the global average rate, making permafrost prone to thawing that will release previously-frozen soil organic carbon (C) into the atmosphere as the greenhouse gases carbon dioxide and methane. Although increases in net primary productivity may partially mitigate C losses from tundra soils, current Earth systems models may overestimate future C storage in plant biomass because they do not consider nutrient limitations. In this study, we evaluated the potential for iron (Fe) oxyhydroxides to impact phosphorus (P) bioavailability in tundra soils obtained from the Barrow Environmental Observatory on the Arctic Coastal Plain in Alaska. Sequential extractions and synchrotron-source microprobe analyses were used to examine Fe and P associations in organic and mineral soil horizons collected from different topographic features of low-centered and high-centered polygons. We hypothesized that P adsorbs to poorly-crystalline iron (Fe) oxyhydroxides that precipitate during seasonal drying of topographic high features. Iron and P geochemistry differed between organic and mineral horizons and varied as a function of soil saturation. Iron was primarily present as poorly-crystalline oxides in all soils (average 56±6%), consistent with observations that organic and mineral constituents in the soil were coated with Fe(III)-phases. Organic horizons were enriched in poorly-crystalline and crystalline Fe-oxides relative to mineral horizons, while mineral horizons contained a higher proportion of organic-bound Fe and magnetite/ilmenite. Phosphorus was contained primarily in organic matter (91±2%) with an additional 8±2% bound to iron oxides. Consistent with our hypothesis, poorly-crystalline Fe oxides increased as soil saturation decreased; however, P was correlated with crystalline (p<0.05) rather than poorly-crystalline Fe oxides. From these results, we infer that P availability to plants may be limited by incorporation into crystalline mineral structures, either iron oxides (e.g., hematite, goethite) or aluminum oxides dissolved in the crystalline extraction. In order to accurately predict global C budgets under changing climate, it is essential to evaluate geochemically-driven nutrient availability in tundra ecosystems.
2016050643 Stanford, Scott D. (New Jersey Geological and Water Survey, Trenton, NJ). Groundwater seepage, landforms, and landscape evolution in the New Jersey Pine Barrens [abstr.]: in Geological Society of America, 2015 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 47(7), p. 821, 2015. Meeting: Geological Society of America, 2015 annual meeting & exposition, Nov. 1-4, 2015, Baltimore, MD.
The New Jersey Pine Barrens consist of dry uplands and wet lowlands formed on highly permeable Miocene quartz sand. Uplands are 15 to 30 m above valley bottoms and are capped with veneers of fluvial quartz and chert gravel of late Miocene through early Pleistocene age. Lowlands contain broad terraces of quartz sand and gravel, including a middle Pleistocene upper terrace up to 10 m above Holocene wetlands on valley bottoms, and a late Pleistocene lower terrace up to 3 m above the wetlands. There is no upland surface runoff, and few slopes are steeper than 5 degrees. This geology creates a geomorphic system dominated by groundwater seepage. Seepage erosion shaped a landscape framed by four events: 1) a permanent sea-level drop of 50 m in the middle and late Miocene, 2) a second sustained sea-level drop of 20 m in the late Pliocene and early Pleistocene, 3) diversion of the Hudson-Pensauken river during early Pleistocene glaciation, and 4) several periods of permafrost in the middle and late Pleistocene. The sea-level drops led to river incision, which provided relief to drive groundwater flow and initiate seepage erosion. The river diversion led to deepened fluvial and marine erosion on the northeast margin of the Barrens, causing westward divide migration and stream capture. Permafrost, by forming an impermeable layer in the subsurface, acted as an accelerant to seepage erosion, and elevated the position of seepage in the landscape. Seepage today occurs at the base of scarps between terraces and valley-bottom wetlands, and in pediment-floored hollows in headwater areas. Paleoseeps are marked by similar hollows higher in the terrain that are dry today. Seepage erosion causes scarp retreat, starting at incising stream channels and working back into uplands, leaving terraces and pediments capped with a thin sand and gravel veneer. The maximum overall denudation rate from this erosion in the Barrens since 10 Ma is 5 m/my. Accelerated seepage occurs on the low side of asymmetric divides, particularly where aided by clay beds beneath the divide. Long-term baseflow measurements in several asymmetric basins on the Atlantic margin of the Barrens show that gaining basins have double to quadruple the groundwater feed of the losing basins. This additional feed drives divide migration, at a minimum rate of 10 km/my since the early Pleistocene.
2016050349 Efimenko, Vladimir N. (Tomsk State University of Architecture and Building, Tomsk, Russian Federation); Efimenko, Sergey V. and Sukhorukov, Alexey V. Accounting for natural-climatic conditions in the design of roads in western Siberia: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 307-315, illus. incl. 1 table, sketch map, 32 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
The paper proposes a methodological scheme that thoroughly accounts for natural-climatic conditions which can impair the stability and longevity of transport facilities (roadways), to ensure the best possible quality of the initial road design. Factors determining the formation of water-heating mode subgrade soils are allocated, and an information database for mathematical modeling of geocomplexes is shown. Values of strength and deformability of clay soils are calculated within the limits of the defined, homogeneous road districts in Western Siberia to provide the required level of reliability of design solutions.
DOI: 10.3724/SP.J.1226.2015.00307
2016050351 Li Dongqing (Chinese Academy of Sciences, Laboratory of Frozen Soil Engineering, Gansu, China); Huang Xing; Ming Feng; Zhang Yu and Bing Hui. Experimental research on acoustic wave velocity of frozen soils during the uniaxial loading process: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 323-328, illus. incl. 2 tables, 11 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Ultrasonic P-wave tests of frozen silt and frozen sand were conducted during uniaxial loading by using an RSMR-SY5(T) nonmetal ultrasonic test meter to study the velocity characteristics of P-waves. The experimental results indicate that the P-wave velocity is affected by soil materials, temperature, and external loads, so the P-wave velocity is different in frozen silt and frozen sand, but all decrease with an increase of temperature and increase at first and then decrease with strain during the loading process. There is an exponential relationship between uniaxial compressive strength and P-wave velocity, and the correlation between them is very good. The characteristic parameters of acoustic waves can, to some extent, reflect the development of internal cracks in frozen soils during loading.
DOI: 10.3724/SP.J.1226.2015.00323
2016050355 Petriaev, Andrei (Saint Petersburg State Transport University, Construction of Roads Transport Complex Department, St. Petersburg, Russian Federation). Stress states of thawed soil subgrade: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 348-353, illus., 9 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
The article presents the field measurement results of the stress states of roadbed thawed soil subgrade during the passage of trains. The dependences of the vertical and horizontal stresses on the velocity of the rolling stock motion, the axle load, and the distance from the sleeper sole have been obtained.
DOI: 10.3724/SP.J.1226.2015.00348
2016050361 Yao Xiaoliang (Chinese Academy of Sciences, Laboratory of Frozen Soil Engineering, Gansu, China); Liu Mengxin; Yu Fan and Qi Jilin. Evaluation of creep models for frozen soils: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 392-398, illus. incl. 3 tables, 31 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
To model the creep behavior of frozen soils, three creep stages have to be reasonably described (i.e., primary, secondary and tertiary stages). Based on a series of uniaxial creep test results, three creep models were evaluated. It was shown that hypoplastic creep model has high prediction accuracy for both creep strain and strain rate in a wide stress range. The elementary rheological creep model can only be used for creep strains at low stress levels, because of the restraints of its mathematical construction. For the soft soil creep model, the progressive change from the primary to secondary and tertiary stages cannot be captured at high stress levels. Therefore, the elementary rheological and soft soil creep models can only be used for low stress levels without a tertiary stage; while the hypoplastic creep model is applicable at high stress levels with the three creep stages.
DOI: 10.3724/SP.J.1226.2015.00392
2016048834 Turetsky, Merritt R. (University of Guelph, Department of Integrative Biology, Guelph, ON, Canada); Olefeldt, David and McGuire, A. David. Pan-arctic trends in lake and wetland thermokarst; implications for carbon storage and methane fluxes [abstr.]: in Goldschmidt conference abstracts 2015, V.M. Goldschmidt Conference - Program and Abstracts, 25, p. 3187, 2015. Meeting: Goldschmidt conference 2015, Aug. 16-21, 2015, Prague, Czech Republic.
URL: http://goldschmidt.info/2015/uploads/abstracts/finalPDFs/3187.pdf
2016050762 Grant, R. F. (University of Alberta, Edmonton, AB, Canada). Ecosystem CO2 and CH4 exchange in a mixed tundra and a fen within an Arctic landscape; modeled impacts of climate change [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0589, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Climate change will have important effects on arctic productivity and greenhouse gas exchange. These changes were projected by the model ecosys under an SRES A2 scenario over the 21st century for a landscape including an upland tundra and a lowland fen at Daring Lake, NWT. Rising temperatures and precipitation caused increases in active layer depths (ALD) and eventual formation of taliks, particularly in the fen, which were attributed to heat advection from warmer and more intense precipitation and downslope flow. These changes raised net primary productivity from more rapid N mineralization and uptake, driven by more rapid heterotrophic respiration and increasing deciduous vs. evergreen plant functional types. Consequently gains in net ecosystem productivity (NEP) of 29 and 10 g C m-2 y-1 were modeled in the tundra and fen after 90 years. However CH4 emissions modeled from the fen rose sharply from direct effects of increasing soil temperatures and greater ALD on fermenter and methanogenic populations, and from indirect effects of increasing sedge growth which hastened transfer of CH4 through porous roots to the atmosphere. After 90 years, landscape CH4 emissions increased from 1.1 to 5.2 g C m-2 y-1 while landscape NEP increased from 34 to 46 g C m-2 y-1. Positive feedback to radiative forcing from increases in CH4 emissions more than offset negative feedback from increases in NEP. This feedback was largely attributed to rises in CH4 emission caused by heat advection from increasing precipitation, the impacts of which require greater attention in arctic climate change studies.
2016050720 Oh, Y. (Princeton University, Princeton, NJ); Medvigy, D.; Stackhouse, B. T.; Lau, M.; Onstott, T. C.; Jorgensen, C. J.; Elberling, B.; Emmerton, C. A.; Saint Louis, V. L. and Moch, J. An underestimated methane sink in Arctic mineral soils [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B22D-04, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Atmospheric methane has more than doubled since the industrial revolution, yet the sources and sinks are still poorly constrained. Though soil methane oxidation is the largest terrestrial methane sink, it is inadequately represented in current models. We have conducted laboratory analysis of mineral cryosol soils from Axel Heiberg Island in the Canadian high arctic. Microcosm experiments were carried out under varying environmental conditions and used to parameterize methane oxidation models. One-meter long intact soil cores were also obtained from Axel Heiberg Island and analyzed in the laboratory. A controlled core thawing experiment was carried out, and observed methane fluxes were compared to modeled methane fluxes. We find that accurate model simulation of methane fluxes needs to satisfy two requirements:(1) microbial biomass needs to be dynamically simulated, and (2) high-affinity methanotrophs need to be represented. With these 2 features, our model is able to reproduce observed temperature and soil moisture sensitivities of high affinity methanotrophs, which are twice as sensitive to temperature than the low affinity methanotrophs and are active under saturated moisture conditions. The model is also able to accurately reproduce the time rate of change of microbial oxidation of atmospheric methane. Finally, we discuss the remaining biases and uncertainties in the model, and the challenges of extending models from the laboratory scale to the landscape scale.
2016050801 Rosenheim, B. E. (University of South Florida Tampa, College of Marine Science, Saint Petersburg, FL); Vetter, L.; Galy, V.; Plante, A. F.; Mollenhauer, G.; Hemingway, J. D.; Grant, K. E. and Derry, L. A. Thermochemical 14C spectra and carbon turnover time in soils; a (changing?) latitudinal gradient? [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B32C-03, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Organic carbon in soils can take on many chemical forms, cycle through different processes, and have different radiocarbon ages. In fact, measurement of different 14C ages in different chemical pools of soil organic carbon (SOC) has demonstrated that the radiocarbon "age" of SOC is more accurately discussed as the turnover time--a measure of the time it takes for SOC to cycle through a specific pool of carbon. Much has been learned, and is still being learned, about SOC turnover times by measuring ages of discrete reservoirs cycling over a continuum of time scales from minutes to millennia. Coupled measurements of radiocarbon age and thermochemical stability of SOC provide a novel approach to deconvoluting SOC turnover times from all present thermochemical reservoirs. We present results over a latitudinal gradient that relate thermochemical radiocarbon spectra to SOC turnover. From subtropical and temperate latitudes, radiocarbon spectra are nearly constant over the continuum of thermochemical stabilities. Contrast is evident at high latitudes, and where inputs of carbon from lateral transport and/or bedrock are high. In the active layer of soil from Svalbard, radiocarbon spectra span time scales of 102-105 14C y while in soil mineral horizons from Taiwan radiocarbon spectra varied between 4,000 and 13,000 14C y. Thus, as polar regions shrink and temperate/subtropical regions expand, thermochemical radiocarbon spectra provide a potential proxy for changes in SOC turnover time. Much remains to be investigated, however, before linking our observations to latitude. If the relationship holds, incorporation of such data into climate models enable more constraint on scenarios for anthropogenic warming such as the IPCC.
2016050777 Tibbett, E. J. (University of California at Davis, Davis, CA); Ziolkowski, L. A. and Li, H. Latitudinal study of the geochemical and lipid biomarkers in Alaskan Arctic soils [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B31D-0604, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.
Warming of the Arctic has the potential for immense climatic feedbacks due to impacts on microbial respiration affecting soil carbon storage and consumption. The chemical composition of soil carries the signature of the source material and the subsequent processes that it underwent to their point of analysis. Therefore, by reading the molecular messages of the soil, we can glean more information about the fate of Arctic soils. In August 2013, we collected a series of active layer soil cores along a north-south transect from Deadhorse to just south of the Brooks Range to study the carbon accumulation and composition during the Holocene. Previously, this transect was shown to have different accumulation rates during the Holocene (Marion and Oechel, 1993). We applied geochemical parameters (total organic carbon and nitrogen, stable carbon and nitrogen isotopes, radiocarbon of bulk soil organic matter) as well as analyzed the lipid biomarkers (alkanes and other markers of degradation). For most cores along the north-south transect, there was a distinct and expected decrease in carbon, nitrogen and alkane concentration with depth. However, with depth there were systematic trends of a series of compounds typically used as biomarkers of organic matter maturity in the ancient rocks. While it is unlikely that these organic matter maturity compounds reflect ancient organic carbon in Arctic soils, we will discuss the compounds that reflect organic matter maturity further as they may be diagnostic of microbial degradation and/or other soil processes.
2016050353 Kim, Sang Yeob (Korea University, School of Civil, Environmental and Architectural Engineering, Seoul, South Korea) and Lee, Jong Sub. Strength and stiffness variation of frozen soils according to confinement during freezing: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 335-339, illus., 16 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
When water between soil particles is frozen, the strength and stiffness behavior of soils significantly change. Thus, numerous experimental studies in the laboratory have been carried out to characterize the strength and stiffness of frozen soils. The goals of this study are to evaluate the strength characteristics of frozen soils, which underwent confinement in freezing and shearing stages, and to estimate the stiffness variation by shear wave velocity during shear phase. The specimens are prepared in a brass cell by mixing sand and silt with 10% degree of saturation at a relative density of 60%. The applied normal stresses as confining stresses are 5, 10, 25 and 50 kPa. When the temperature of the specimens is lowered up to -5°C, direct shear tests are carried out. Furthermore, shear waves are continuously measured through bender elements during shearing stage for the investigation of stiffness change. Test results show that shear strength and stiffness are significantly affected by the confining stress in freezing and shearing phases. This study suggests that the strength and stiffness of frozen soils may be dependent on the confining stresses applied during freezing and shearing.
DOI: 10.3724/SP.J.1226.2015.00335
2016050368 Li Guoyu (Chinese Academy of Sciences, Laboratory of Frozen Soil Engineering, Gansu, China); Ma Wei; Wang Fei; Mu Yanhu; Mao Yuncheng; Hou Xin and Bing Hui. Processes and mechanisms of multi-collapse of loess roads in seasonally frozen ground regions; a review: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 456-468, illus. incl. 1 table, 23 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of operation. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeated freezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to (1) monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, (2) study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and (3) develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for further study of the weakening mechanisms of similar structural soils.
2016050354 Yuan Chang (Chinese Academy of Sciences, Laboratory of Frozen Soil Engineering, Gansu, China); Niu Fujun; Yu Qihao; Wang Xinbin; Guo Lei and You Yanhui. Numerical analysis of applying special pavements to solve the frost heave diseases of high-speed railway roadbeds in seasonally frozen ground regions: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 340-347, illus. incl. 2 tables, 19 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
The Haerbin-Dalian Passenger Dedicated Line is the first high-speed railway constructed in the seasonally frozen ground regions of northeastern China. Frost heave diseases occurred in the first winter of its operation (between October 2012 and January 2013), and frost heave was observed mainly in the roadbed fills that were considered not susceptible to frost heave. This paper proposes applying two special pavements--black pavement and insulation-black pavement--to improve the thermal regime of the roadbed. Three numerical models of the roadbed temperature field were built based on the field conditions of the Changchun section (D3K692+840 to D3K692+860). The results show that: (1) Compared with cement pavement, black pavement and insulation-black pavement could reduce the freezing index at the roadbed surface by 37% and 64%, respectively, which could influence the maximum frozen depth; (2) the maximum frozen depths under the black pavement and insulation-black pavement were respectively 1.3-1.4 m and 1 m. Compared with cement pavement, they could reduce the maximum frozen depth by 0.4 m and 0.7-0.8 m, respectively, which would reduce the permitted amount of frost heave by 4 mm and 7-8 mm, which would meet the deformation limit established by the Code for Design on Special Subgrade of Railway; (3) the freezing periods of the black pavement and the insulation-black pavement were, respectively, approximately four months and two months. Compared with cement pavement, they could reduce the freezing period by approximately 19 days and 40 days, respectively, and delay the initial freezing time by 9 days and 18 days; and (4) compared with cement pavement, black pavement and black-insulation pavement could reduce the frozen areas of roadbeds in the cold season, which suggests that these two special pavements could provide better thermal stability for roadbeds.
DOI: 10.3724/SP.J.1226.2015.00340
2016050362 Zhussupbekov, Askar (L. N. Gumilyov Eurasian National University, Faculty of Civil Engineering, Astana, Kazakhstan) and Shakhmov, Zhanbolat. Experimental investigations of freezing soils at ground conditions of Astana, Kazakhstan: in 2nd international symposium on Transportation soil engineering in cold regions (TRANSOILCOLD2015); special issue A (Liu Jianjun, editor; et al.), Sciences in Cold and Arid Regions, 7(4), p. 399-406, illus. incl. 2 tables, 28 ref., August 2015. Meeting: 2nd international symposium on Transportation soil engineering in cold regions, TRANSOILCOLD2015, Sept. 24-26, 2015, Novosibinsk, Russian Federation.
Kazakhstan regions is seasonal climatic with transient freezing of soil ground during the winter. Roadbed integrity is important to resist the sustained load transmitted by traffic on the road surface. Freezing of soil ground could significantly influence roadbed integrity in the seasonal freezing climate of Kazakhstan. The proper determination magnitude of frost heave and heaving pressure by the influence of freezing temperatures during the winter season are necessary for design and construction of highways. Thus, experimental tests were conducted on specimens obtained from Astana (Kazakhstan) to determine the freezing pressure and magnitude of frost heaving.
DOI: 10.3724/SP.J.1226.2015.00399
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