14076092 Abbott, B. W. (University of Alaska, Fairbanks, Department of Biology and Wildlife, Fairbanks, AK); Jones, J.; Schuur, E. A.; Bowden, W. B.; Chapin, F. S., III; Epstein, H. E.; Flannigan, M.; Harms, T.; Hollingsworth, T. N.; Mack, M. C.; Natali, S.; Rocha, A. V.; Tank, S. E.; Turetsky, M. R.; Vonk, J. and Wickland, K. Can increased biomass offset carbon release from permafrost region soils, streams, and wildfire; an expert elicitation? [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-08, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
As the permafrost region warms, up to 288 Pg carbon (CO2 equivalent) may be released from soil by the end of the century, and up to 616 Pg by 2300. This soil carbon can be released to the atmosphere directly via mineralization or wildfire, or enter aquatic ecosystems as dissolved or particulate organic or inorganic carbon. Some models predict an increase in Arctic and boreal living biomass in response to extended growing season, enhanced nutrient cycling, and CO2 fertilization, but we have a poor understanding of how the production of new biomass will compare with loss of carbon from permafrost thaw. We administered surveys to permafrost region experts to assess current understanding of the magnitude and timing of biomass accumulation, hydrologic carbon flux, and wildfire carbon losses. Surveys addressed three time periods (present to 2040, 2100, and 2300) and four warming scenarios based on IPCC representative concentration pathways. Estimates of change in biomass and fire losses were provided individually for the boreal forest and arctic tundra. Experts estimated changes in carbon delivery to freshwater ecosystems as well as delivery to the ocean, including carbon release due to coastal erosion, fluxes infrequently captured in high-latitude models. Initial expert estimates indicated that while tundra biomass would increase substantially, total permafrost region biomass would decrease by the end of the century due to boreal forest drying and browning, followed by a modest increase by 2300 due to vegetation community shifts. Changes in aquatic systems could release an additional 2.7 Pg carbon by 2100 and 7.3 Pg by 2300. Modified wildfire regime could cause the release of an additional 13.6 Pg carbon by 2100 and 51.7 Pg by 2300. Current expert understanding therefore suggests that carbon gains in high-latitude biomass will be orders of magnitude smaller than carbon loss from permafrost soils and that hydrologic and wildfire pathways of carbon loss will likely accelerate carbon mobilization from permafrost region ecosystems.
14076167 Abbott, R. E. (Sandia National Laboratories, Albuquerque, NM). Seismic spatial autocorrelation as a technique to track changes in the permafrost active layer [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0661, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
We present preliminary results from an effort to continuously track freezing and thawing of the permafrost active layer using a small-aperture seismic array. The 7-element array of three-component posthole seismometers is installed on permafrost at Poker Flat Research Range, near Fairbanks, Alaska. The array is configured in two three-station circles with 75 and 25 meter radii that share a common center station. This configuration is designed to resolve omnidirectional, high-frequency seismic microtremor (i.e. ambient noise). Microtremor is continuously monitored and the data are processed using the spatial autocorrelation (SPAC) method. The resulting SPAC coefficients are then inverted for shear-wave velocity structure versus depth. Thawed active-layer soils have a much slower seismic velocity than frozen soils, allowing us to track the depth and intensity of thawing. Persistent monitoring on a permanent array would allow for a way to investigate year-to-year changes without costly site visits. Results from the seismic array will compared to, and correlated with, other measurement techniques, such as physical probing and remote sensing methods. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
14076132 Alexander, Heather D. (University of Texas at Brownsville, Brownsville, TX); Davydov, S.; Zimov, N. and Mack, M. C. High severity experimental burns in Siberian larch forests increase permafrost thaw and larch tree regeneration [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33E-0528, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Global change models predict increased fire activity in boreal forests as climate warms and dries. We hypothesized that fire-driven decreases in soil organic layer (SOL) depth will (1) increase permafrost thaw by reducing the insulating capacity of the SOL and (2) improve seedbed conditions for tree regeneration. Over time, these changes will lead to altered patterns of above- and belowground carbon (C) accumulation. To test these hypotheses, we conducted plot-level experimental burns in July 2012 in a low-density, mature larch stand near the Northeast Science Station in Cherskii, Siberia. Dried fuels of naturally occurring vegetation were added to plots to achieve four burn severity treatments based on residual SOL depths: control, low (>8 cm), moderate (5-8 cm), and high severity (2-5 cm). Pre-fire and during two growing seasons post-fire, we measured thaw depth, soil moisture, and soil temperature to determine severity effects on permafrost thaw. We also sowed larch seeds in fall 2012 and quantified germination rates the following growing season. By 1 wk post-fire, thaw depth was 15-25 cm deeper in plots burned at high severity (55 cm) compared to other treatments (30-40 cm). These differences in thaw depth with burn severity were maintained during the subsequent growing season and were associated with increased soil temperature and moisture. Larch regeneration was 10´ higher on severely burned plots than those unburned. Our findings highlight the potential for increased fire severity to degrade permafrost and alter successional dynamics and patterns of C accumulation.
14076131 Becker, Michael S. (McGill University, Geography, Montreal, QC, Canada) and Pollard, Wayne H. A case study of High Arctic anthropogenic disturbance to polar desert permafrost and ecosystems [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33D-0517, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
One of the indirect impacts of climate change on Arctic ecosystems is the expected increase of industrial development in high latitudes. The scale of terrestrial impacts cannot be known ahead of time, particularly due to a lack of long-term impact studies in this region. With one of the slowest community recovery rates of any ecosystem, the high Artic biome will be under a considerable threat that is exacerbated by a high susceptibility to change in the permafrost thermal balance. One such area that provides a suitable location for study is an old airstrip near Eureka, Ellesmere Island, Nunavut (80.0175°N, 85.7340°W). While primarily used as an ice-runway for winter transport, the airstrip endured a yearly summer removal of vegetation that continued from 1947 until its abandonment in 1951. Since then, significant vegetative and geomorphic differences between disturbed and undisturbed areas have been noted in the literature throughout the decades (Bruggemann, 1953; Beschel, 1963; Couture and Pollard, 2007), but no system wide assessment of both the ecosystem and near-surface permafrost has been conducted. Key to our study is that the greatest apparent geomorphic and vegetative changes have occurred and persisted in areas where underlying ice-wedges have been disturbed. This suggests that the colonizing communities rapidly filled new available thermokarst niches and have produced an alternative ice-wedge stable state than the surrounding polar desert. We hypothesize that disturbed areas will currently have greater depths of thaw (deeper active layers) and degraded ice-wedges, with decreased vegetation diversity but higher abundance due to a changed hydrological balance. To test this a comprehensive set of near-surface active layer and ecosystem measurements were conducted. Permafrost dynamics were characterized using probing and high-frequency Ground Penetrating Radar (500 MHz) to map the near-surface details of ice-wedges and active layer. Vegetation was measured using quadrat sampling for species richness and abundance. Soil measures consisted of temperature at depth, moisture content, and bioavailable nutrients, all augmented with hourly microclimate data. NMDS ordination was performed as an exploratory analysis of clustering between disturbed/undisturbed microsite differences. Further statistical analysis showed that disturbed polygon tops have an active layer 30% deeper than other microsites (p<.001) despite having no greater vegetation cover than undisturbed polygon tops. Conversely, disturbed troughs show no difference in active layer, but their soils have double the water content of other microsites (p<.001), likely accounting for a significantly greater, but less-diverse, biomass that may be buffering the active layer from further development. Our results suggest that a disturbance to the thermal regime of high Arctic ice-wedge polygon systems results in long-lasting and significant effects on the polar desert landscape. Understanding how the polar desert responds to disturbance after 60 years of 'recovery' will provide useful information for applying conceptual thermal models of landscape disturbance in the high Arctic, as well as information to governments and industries hoping to plan and minimize their impacts.
14076086 Bowden, W. B. (University of Vermont, Burlington, VT). Impacts of upland thermal erosional features on the vulnerability of carbon and nutrient fluxes from permafrost on the North Slope, Alaska, USA [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Recent reports have concluded that substantial amounts of carbon and other nutrients are currently stored in organic matter in shallow permafrost (upper 3m) in the arctic region. This organic matter is known to be labile and there is currently intense interest to determine the portion of this presently frozen organic matter that is likely to thaw in the future and to determine its fate. The best available estimates are that most of this shallow permafrost could thaw in the next 100 years. But there is still considerable uncertainty about the fates for carbon and nutrients that might be liberated as this organic matter thaws. The short-term manifestations of permafrost thaw are varied. There may be little to no obvious physical change, subtle to dramatic subsidence of the soil surface, or catastrophic failures of entire hillslopes. These latter manifestations are collectively referred to as thermokarst terrain and have been the subject of a large integrated study called the Arctic System Science Thermokarst Project (ARCSS/TK). In this project we focused on the physical, chemical, biological, and hydrological characteristics of several forms of thermo-erosional features (TEFs) that are common on the North Slope of Alaska (USA) and elsewhere in the arctic. The TEFs included glacial thaw slumps, retrogressive thaw slumps, gully erosion thermokarsts, and active layer displacement slides. These TEFs represent an extreme end of the continuum of permafrost thaw dynamics. However, recent evidence suggests that these features have become more numerous in our study area as well as elsewhere in upland arctic landscapes. In the ARCSS/TK project we followed the dynamics of nearly two dozen different TEFs in the vicinity of the Toolik Field Station (68° 38' N, 149° 36' W). We studied 6 of these TEFs in sufficient detail to be able to construct crude budgets for the amounts of materials translocated within the disturbance sites versus the amounts exported from the sites by hydrological processes and net exchange with the atmosphere. Translocation within a site is important because the disturbance process opens new niches that allow different biological communities (from microbes to vegetation) to flourish for different periods of time. However, at a regional to global scale, translocation does not result in a loss of carbon or nutrients from the local site. Net export in water or to the atmosphere is required to generate local-scale losses that might then sum to a significant regional-scale loss. At all of the sites we examine intensively, our data suggests that the local, translocation fluxes were larger than the summed export fluxes, at least in the short term (5 years). However, given the number of TEFs that we have identified in our region, the small individual flux estimates may still sum to a significant regional loss term. This rate of loss is highly dependent on the rate at which TEFs "turnover"; i.e., become active and then become dormant. Our understanding of these dynamics is highly uncertain. However, through the ARCSS/TK project we have begun to put some bounds on this uncertainty and on the potential loss rates.
14076117 Cory, R. M. (University of Michigan, Earth and Environmental Sciences, Ann Arbor, MI); Page, Sarah E.; Kling, G. W.; Sander, Michael; Harrold, Katie H. and McNeill, Kristopher. The role of iron and reactive oxygen in the degradation of dissolved organic matter draining permafrost soils [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B32C-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
As the permafrost boundary deepens from climate warming it will create conditions for redox reactions between soil-derived dissolved organic matter (DOM) and iron where those conditions did not previously exist. These new conditions will facilitate the transformation of DOM, and the overarching question is whether the pathway to CO2 released to the atmosphere or the export of DOM to coastal oceans will be favored. Our findings suggest that in either dark soils or sunlit surface waters, the presence of iron promotes the degradation of DOM to CO2. Evidence in support of iron-mediated oxidation of DOM to CO2 includes (1) strong positive correlations between iron and formation of hydroxyl radical (·OH), a highly reactive oxygen species implicated in DOM mineralization, (2) complete oxidation of DOM in the presence of high iron concentrations, and (3) loss of permafrost-derived DOM and iron from a thermokarst-impacted lake over time. For example, iron and DOM-rich soils or surface waters had the highest dark or photochemical ·OH formation respectively, both consistent with a dark or light Fenton source of ·OH and subsequent oxidation of DOM by ·OH. Photo-oxidation of DOM to CO2 was favored over partial photo-oxidation in surface waters characterized by high DOM and dissolved iron concentrations, consistent with photochemical reactions mediated by iron. Changes in DOM quality and quantity over time in a lake receiving permafrost carbon via a landslide (thermokarst slump) were also consistent with iron-mediated photodegradation of DOM. Given differences in DOM degradation across tundra ecosystems varying in iron, along with the abundance of water-logged soils supplying reduced iron to soil water or shallow streams, preliminary calculations at the landscape scale indicate that iron-mediated mineralization of DOM in soils and surface waters may be at least as important to carbon cycling as is bacterial respiration of DOM in the water column of streams and lakes. Thus, in the dark or the light, iron-mediated degradation of DOM may be critical to understanding the fate of C released from thawing arctic soils.
14076088 de Baets, S. L. (University of Exeter, Geography, Exeter, United Kingdom); Lewis, R.; van de Weg, M. J.; Quine, T. A.; Shaver, G. R. and Hartley, I. P. Fire, temperature and nutrient responses on the C balance of Arctic tundra soils from surface, mineral horizons and permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Models predict substantial release of carbon (C) from thawing permafrost as the climate warms. Therefore, determining how the decomposition of the organic matter stored in near surface permafrost is controlled represents a key research priority. Important questions remain regarding how readily decomposable the organic matter may be, as well as the extent to which microbial activity is limited by the low temperatures, the rate of new labile C inputs, and/or nitrogen (N) availability. Accurate model predictions require that these questions are addressed.Disturbances, including fire, which is becoming increasingly common in the tundra biome, may promote rates of permafrost thaw. In 2007, the Anaktuvuk River fire burned over 1,000 km2 of tundra on the North Slope of the Brooks Range, Alaska, USA, doubling the cumulative area burned in this region over the past 50 years. This fire enhanced active layer thickness by removing insulating plant biomass and exposing surfaces with low albedo. In this study we investigated how temperature, N and labile C additions affected rates of CO2 production over a one-year incubation of samples collected from different depths (topsoil, mineral horizons and near-surface permafrost) in burnt and unburnt sites within the Anaktuvik river catchment. The results show that respiration rates did not decline substantially during the 1-year incubation, indicating there were relatively large amounts of readily decomposable C present. However, decomposition rates per gram of C did decline with depth, especially in the burnt sites where some of the surface soil may have been lost. This indicates that the C present in the near surface permafrost may be less labile than C nearer the soil surface. In addition, respiration rates in the deeper horizons were more temperature sensitive, potentially reflecting the lower lability of the C present. Against expectations, N addition inhibited respiration in the deeper layers, especially at low temperatures. Labile C additions promoted the decomposition of soil organic matter in the deep soil samples, but not in the surface samples, with the positive priming effect being lost following N addition. This study indicates that there is the potential for considerable loss of C following the thaw of near-surface permafrost in Alaskan tussock tundra, although the C present may be slightly less readily decomposable than C stored nearer the surface. The decomposition of near-surface permafrost C was shown to be highly temperature sensitive and thus accurately simulating the soil thermal regime post-thaw is likely to be important in predicting rates of C release. In addition, root colonisation of previously frozen horizons may stimulate decomposition if labile C inputs increase. On the other hand, the inhibition of activity by N addition suggests that the positive feedback associated with reduced microbial N limitation in a warming Arctic may not be ubiquitous.
14076205 Etzelmuller, B. (University of Oslo, Oslo, Norway); Westermann, S.; Berntsen, T.; Dunse, T.; Gisnas, K.; Hagen, J.; Kristjansson, J. E.; Isaksen, K.; Schuler, D. V.; Schuler, T.; Stordal, F. and Aas, K. S. CRYOMET; concept and results for bridging models between the atmosphere and the terrestrial cryosphere (glacier and permafrost) [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C44B-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Predictions of the future climate are generally based on atmospheric models operating on coarse spatial scales. The impact of a changing climate on most elements of the cryosphere, however, becomes manifest on much smaller scales, which complicates sound predictions on glacier and permafrost development. CryoMET is a collaborative project between atmospheric modeling, glacier and permafrost research groups, seeking to bridge the scale gap between coarsely-resolved Earth System Models and the process and impact scales on the ground. This is done especially for snow-related variables, as (1) snow is a crucial factor both for the thermal regime of permafrost and the mass balance on glaciers, and (2) the snow depth and properties can vary considerably on small scales, which a.o. lead to distinctly different soil temperatures in permafrost areas on distances of tens of meters. To address this problem we use WRF to downscale atmospheric variables to an "interface scale" of 1 km to 3 km resolution, where these variables are constant to a good approximation. In a second step, we employ probabilistic downscaling of the average snow water equivalent at the "interface scale" (as delivered by WRF) using snow redistribution models. With probability density functions of snow depth, the distribution of environmental parameters affected by snow, e.g. of permafrost temperatures, are inferred for each grid cell at the interface scale. We present here results from Svalbard and southern Norway, demonstrating the capacity of the scheme in delivering the distribution of permafrost-relevant variables.
14076151 Frederick, J. M. (University of California Berkeley, Earth and Planetary Science, Berkeley, CA) and Buffett, B. A. Estimating gas escape through taliks in relict submarine permafrost and methane hydrate deposits under natural climate variation [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33K-0605, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost-associated methane hydrate deposits exist at shallow depths within the sediments of the Arctic continental shelves. This icy carbon reservoir is thought to be a relict of cold glacial periods, when sea levels are much lower, and shelf sediments are exposed to freezing air temperatures. During interglacials, rising sea levels flood the shelf, bringing dramatic warming to the permafrost and gas hydrate bearing sediments. Degradation of this shallow-water reservoir has the potential to release large quantities of methane gas directly to the atmosphere. Although relict permafrost-associated gas hydrate deposits likely make up only a small fraction of the global hydrate inventory, they have received a disproportionate amount of attention recently because of their susceptibility to climate change. This study is motivated by several recent field studies which report elevated methane levels in Arctic coastal waters. While these observations are consistent with methane release as a result of decomposing submarine permafrost and gas hydrates, the source of gas cannot easily be distinguished from other possibilities, including the escape of deep thermogenic gas through permeable pathways such as faults, or microbial activity on thawing organic matter within the shelf sediments. In this study, we investigate the response of relict Arctic submarine permafrost and permafrost-associated gas hydrate deposits to warming with a two-dimensional, finite-volume model for two-phase flow of pore fluid and methane gas within Arctic shelf sediments. We track the evolution of temperature, salinity, and pressure fields with prescribed boundary conditions, and account for latent heat of water ice and methane hydrate formation during growth/decay of permafrost or methane hydrate. The permeability structure of the sediments is coupled to changes in permafrost. We assess the role of taliks (unfrozen portions of continuous permafrost) as a pathway for methane gas escape and make predictions of gas flux to the water column as a result of relict permafrost-associated gas hydrate dissociation due to natural climate variations. Several hydrate saturation values (20%, 50%, 80% pore volume within hydrate layers) and talik widths (0.5 km, 1.0 km, 1.5 km, 2.0 km) are explored for model parameters representative of the 20 m isobath at the North American Beaufort and East Siberian Arctic Seas (ESAS). Preliminary results estimate the maximum present-day gas flux at the North American Beaufort is 0.229 kg/yr/m2 (average 0.005 kg/yr/m2), which produces a methane concentration of 75 nM in the overlying water column for a representative ocean current of 4 cm/s. For the ESAS, preliminary results estimate the maximum present-day gas flux is 0.277 kg/yr/m2 (average 0.030 kg/yr/m2), which produces a methane concentration of 452 nM in the overlying water column. A desired outcome of this study is to provide a framework for discussion on the potential magnitude of methane release that might be attributed to relict permafrost-associated hydrate deposits in regions where the submarine permafrost has been compromised.
14076148 Genet, H. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); McGuire, A. D.; Johnstone, Jill F.; Breen, A. L.; Euskirchen, E. S.; Mack, M. C.; Melvin, April M.; Rupp, T. S.; Schuur, E. A. and Yuan, F. Modeling post-fire vegetation succession and its effect on permafrost vulnerability and carbon balance [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33I-0585, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Wildfires are one of the main disturbances in high latitude ecosystems and have important consequences for the large stocks of carbon stored in permafrost soils. Fire affects carbon balance directly by burning vegetation and surface organic material and indirectly by influencing post-fire vegetation composition and soil thermal and hydrological regimes. Recent developments of ecosystem models allow a better representation of the effects of fire on organic soil dynamics and the soil environment, but there is a need to better integrate post-fire vegetation succession in these models. Post-fire vegetation regeneration is sensitive to fire consumption of soil organic layer horizons, where high severity burning promotes the establishment of deciduous broadleaf trees. In comparison to conifers, deciduous forests are less flammable, more productive, have higher nutrient turnover, and deeper permafrost. However, deciduous forests generally store less soil carbon than conifer forests. Therefore, the fire-induced shifts in vegetation composition have consequences for ecosystem carbon balance. In this study, we present the development of an ecosystem model that integrates post-fire succession with changes in the structure and function of organic soil horizons to better represent the relationship between fire severity and vegetation succession across the landscape. The model is then used to assess changes in the carbon balance at a 1 km resolution, in response to changing fire regime across the landscape in Interior Alaska.
14076089 Goswami, S. (Oak Ridge National Laboratory, Climate Change Science Institute and Environmental Sciences Division, Oak Ridge, TN); Hayes, D. J.; Grosse, G.; Sloan, V. L.; Liebig, J. A.; Norby, R. J. and Wullschleger, S. D. Spectral characterization of disturbance gradients in permafrost landscapes using ground-based remote sensing and satellite imagery; initial results from the central Seward Peninsula, Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-05, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Climate warming and associated permafrost thaw accelerate soil microbial decomposition of the frozen carbon pool, creating a positive feedback to climate. Thawing of ice-rich permafrost drives thermokarst processes characterized by irregular surfaces of marshy hollows and small hummocks across the Arctic landscape. To better understand thermokarst dynamics on various scales, it is important to study local to regional variables that drive permafrost conditions and its degradation, such as hydrology, geomorphology, vegetation, and climate. Remote sensing can take an important role in upscaling of thermokarst inventories to large scales. Spectral characterization of thermokarst landforms will be crucial for image interpretation, classification, and scaling. Developing abilities to characterize the dependence of thermokarst processes on various environmental factors as well as being able to quantify these processes across scales will help us to better understand their feedback to the pan-Arctic carbon dynamics with reduced uncertainties. Multi-scale remote sensing and ecosystem models can potentially help us to develop our ability to characterize and model these processes over multiple spatial and temporal scales across the pan-Arctic. As a first step towards developing inventories of thermokarst processes and associated ecosystem variables, we conducted reconnaissance field surveys along thermokarst landform gradients on the central Seward Peninsula, AK during late June of 2013. The field data collected include ground-based spectral library, digital photographs, survey-grade land surface elevations and meso-scale topography, and detailed vegetation characterization along multiple 50m long transects covering three thaw lake basins of different ages and their surrounding transitional slopes and undisturbed uplands. Our initial results show that these different landscape units have distinct spectral signatures indicating that satellite remote sensing data could potentially identify these features across large areas. Analysis of historical aerial imageries and satellite data for the 1950-2012 period also indicated that the partially ice-rich permafrost landscape of our study region has experienced substantial change over the recent decades, as indicated by active thermal erosion gullies, new thermokarst pond formation, and recently drained lakes.
14076096 Grosse, G. (University of Alaska Fairbanks, Geophysical Institute, Fairbanks, AK); Romanovsky, V. E.; Arp, C. D. and Jones, B. M. Rapid disturbances in Arctic permafrost regions [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31H-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost thaw is often perceived as a slow process dominated by press disturbances such as gradual active layer thickening. However, various pulse disturbances such as thermokarst formation can substantially increase the rate of permafrost thaw and result in rapid landscape change on sub-decadal to decadal time scales. Other disturbances associated with permafrost thaw are even more dynamic and unfold on sub-annual timescales, such as catastrophic thermokarst lake drainage. The diversity of processes results in complex feedbacks with soil carbon pools, biogeochemical cycles, hydrology, and flora and fauna, and requires a differentiated approach when quantifying how these ecosystem components are affected, how vulnerable they are to rapid change, and what regional to global scale impacts result. Here we show quantitative measurements for three examples of rapid pulse disturbances in permafrost regions as observed with remote sensing data time series: The formation of a mega thaw slump (>50 ha) in syngenetic permafrost in Siberia, the formation of new thermokarst ponds in ice-rich permafrost regions in Alaska and Siberia, and the drainage of thermokarst lakes along a gradient of permafrost extent in Western Alaska. The surprising setting and unabated growth of the mega thaw slump during the last 40 years indicates that limited information on panarctic ground ice distribution, abundance, and vulnerability remains a key gap for reliable projections of thermokarst and thermo-erosion impacts, and that the natural limits on the growth and size of thaw slumps are still poorly understood. Observed thermokarst pond formation and expansion in our study regions was closely tied to ice-rich permafrost terrain, such as syngenetic Yedoma uplands, but was also found in old drained thermokarst lake basins with epigenetic permafrost and shallow drained thermokarst lake basins whose ground ice had not been depleted by the prior lake phase. The very different substrates in which new ponds have been forming indicate a broad range of possible biogeochemical feedbacks that require further study. Finally, thermokarst lake drainage observed in regions of continuous permafrost shows that local permafrost degradation, such as thermo-erosional gully formation, may increase permafrost extent in a region, in particular by new permafrost aggradation in freshly exposed, refreezing lake basin sediments. Thermokarst lake drainage across all types of permafrost extent increases habitat diversity, is important for regional biogeochemical cycling, and results in carbon sequestration. While all three disturbance types differ in spatial scale and current abundance, they also point at specific vulnerabilities of permafrost landscapes that are tied to local factors such as ground ice, highlight critical knowledge gaps for predictive ecosystem and biogeochemical models, and indicate the potential for rapid, substantial, and surprising changes in a future warmer Arctic.
14076168 Harada, K. (Miyagi University, Sendai, Japan); Narita, K.; Saito, K.; Iwahana, G.; Sawada, Y. and Fukuda, M. Detection of surface and subsurface conditions in permafrost area after wildfire by using satellite images, Seward Peninsula, Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0662, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
In 1971 and 2002, large tundra fires burned a wide area that is underlain by discontinuous permafrost near the Kougarok River on the Seward Peninsula in western Alaska. Both fires destroyed the vegetation and altered the ground surface thermal conditions. The objective of this study is to understand the characteristics of the post-fire variations in the distribution and condition of the permafrost and of the changes attributed to the wildfire in the thermal and water conditions in the active layer. Especially, we tried to detect thaw depth, surface and subsurface conditions by using satellite images. Summer field observations were conducted at both burned and unburned sites in the area beginning in 2005. The average thaw depth at the burned sites in 2012 was 30% deeper than the depths at the unburned sites. The differences in thaw depth have decreased over time. Boring surveys up to a depth of 2 m conducted in 2012 confirm the presence of massive ice at both sites, which implies the possibility of thermokarst development caused by the thawing of the permafrost after wildfires. The visible satellite image for the burned site detected white-colored areas, corresponding to Clamagrostis canadensis growing areas, surrounded by green-colored areas. The thaw depth at the white-colored areas was deeper by 60% than at the surrounding burned areas. The surface roughness values were also high at these white-colored areas. There was a significant difference in the normalized difference vegetation index (NDVI) between the white-colored areas and the other areas. Thus, satellite images of areas after wildfires may help detect low NDVI areas that have a deeper thaw depth with the possibility of thermokarst development.
14076152 Heslop, J. (University of Alaska Fairbanks, Water and Environmental Research Center, Faibanks, AK); Walter Anthony, K. M.; Sepulveda-Jauregui, A. and Martinez-Cruz, K. Methane production potentials in a thermokarst lake and its underlying permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33K-0606, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Thermokarst lakes, formed in permafrost-thaw depressions, are known sources of atmospheric methane (CH4) and carbon dioxide (CO2) but the location of gas production in a thermokarst-lake environment is not well constrained. This study compares CH4 and CO2 production potentials of samples collected from various depths along a 5-m deep lake sediment core and an adjacent 40-m deep undisturbed permafrost profile, allowing for direct determination as to where CH4 and CO2 are originating within an active thermokarst-lake landscape. Vault Lake and Vault Creek Permafrost Tunnel are located approximately 40 km north of Fairbanks, Alaska in a region characterized by yedoma permafrost. The Vault Lake sediment core, collected in the center of a ~4000 m2 lake, captured the surface lake sediments, talik (thaw bulb), and the permafrost actively thawing beneath the lake for comparison to parallel permafrost soil samples from the Vault Creek Permafrost Tunnel. Samples were analyzed for bulk density, ice and water content, organic and inorganic carbon content, C:N ratios, and water-soluble organic C. Initial soil organic matter (SOM) composition was characterized using Fourier transform infrared (FTIR) spectroscopy and pyrolysis-gas chromatography/mass spectrometry (py-GC/MS). CH4 and CO2 production potentials and their stable carbon isotope values from 21 depths along the lake core and 17 depths along the permafrost tunnel were measured in anaerobic laboratory incubations. We incubated samples at four temperatures (0 C, 3 C, 10 C and 25 C) to test the potential response of methanogenesis to increasing temperature in scenarios of future climate warming. Preliminary results suggest methanogenesis is highest in the top 1 m of the Vault Lake core and at the base of the talik, which is the permafrost thaw front beneath the lake.
14076121 Jansson, J. R. (Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA); Tas, N.; Wu, Y.; Ulrich, C.; Kneafsey, T. J.; Torn, M. S.; Hubbard, S. S.; Chakraborty, R.; Graham, D. E. and Wullschleger, S. D. Metagenomics reveals microbial community composition and function with depth in Arctic permafrost cores [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B32C-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The Arctic is one of the most climatically sensitive regions on Earth and current surveys show that permafrost degradation is widespread in arctic soils. Biogeochemical feedbacks of permafrost thaw are expected to be dominated by the release of currently stored carbon back into the atmosphere as CO2 and CH4. Understanding the dynamics of C release from permafrost requires assessment of microbial functions from different soil compartments. To this end, as part of the Next Generation Ecosystem Experiment in the Arctic, we collected two replicate permafrost cores (1 m and 3 m deep) from a transitional polygon near Barrow, AK. At this location, permafrost starts from 0.5 m in depth and is characterized by variable ice content and higher pH than surface soils. Prior to sectioning, the cores were CT-scanned to determine the physical heterogeneity throughout the cores. In addition to detailed geochemical characterization, we used Illumina MiSeq technology to sequence 16SrRNA genes throughout the depths of the cores at 1 cm intervals. Selected depths were also chosen for metagenome sequencing of total DNA (including phylogenetic and functional genes) using the Illumina HiSeq platform. The 16S rRNA gene sequence data revealed that the microbial community composition and diversity changed dramatically with depth. The microbial diversity decreased sharply below the first few centimeters of the permafrost and then gradually increased in deeper layers. Based on the metagenome sequence data, the permafrost microbial communities were found to contain members with a large metabolic potential for carbon processing, including pathways for fermentation and methanogenesis. The surface active layers had more representatives of Verrucomicrobia (potential methane oxidizers) whereas the deep permafrost layers were dominated by several different species of Actinobacteria. The latter are known to have a diverse metabolic capability and are able to adapt to stress by entering a dormant yet viable state. In addition, several isolates were obtained from different depths throughout the cores, including methanogens from some of the deeper layers. Together these data present a new view of potential geochemical cycles carried out by microorganisms in permafrost and reveal how community members and functions are distributed with depth.
14076169 Lebedev, V. (Lomonosov Moscow State University, Department of Materials Science, Moscow, Russian Federation); Loranty, M. M.; Kholodov, A. L. and Spektor, V. Applicability of resistivity surveys for examination of heterogeneity in continuous permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0663, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Electrotomography and resistivity measurements are modern visualisation methods, applicable for non-destructive underground surveys. This method is based on differences in resistivity of frozen and thawed soil, fresh and saline water, ice and mineral phases. In permafrost regions it can be applied to understand heterogeneity in the active layer and to search for ice-rich bodies. These factors are strongly connected with permafrost thaw and related processes. By using a large number of electrodes we can obtain pseudo cross-sections, where top layers of data points contain resistivity, measured from neighbor electrodes and bottom layers -- from electrodes with higher distances between each other. Obtained cross-section can be compared with another methods of probing, like acoustic methods and permafrost coring. We conducted resistivity surveys of continuous permafrost in Kolyma River basin in Northeastern Siberia. Measurements were made at several sites, including experimentally burned plots, near permafrost coring sites and at yedoma deposits exposure at Dyvanny Yar cliff. We changed the spacing between electrodes to measure resistivity from different depths. For measurements of active layer depth (~ 0.5-1.5m) we used 0.3-0.5m spacing and compared obtained results with direct probing of thaw layer. We found a relationship between measured and real depth. For deeper surveys (up to 10m depth) we used larger spacing -- 2-3m between electrodes. Comparison of resistivity cross-sections with permafrost core data and visual observation at Dyvanny Yar show possibility of finding ice wedge positions and agreement between average resistivity of bottom layers and ice content in the permafrost at a similar depth. Resistivity measurements in continuous permafrost are challenging but our results suggest that the method could be useful for examination of thawing changes.
14076100 Leifer, Ira (University of California, Santa Barbara, Santa Barbara, CA); Shakhova, N. E.; Semiletov, Igor P.; Yurganov, L. and Stubbs, C. Implications of a warming Arctic-methane emissions from submerged permafrost underlying the rapidly warming East Siberian Arctic Sea [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31I-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Methane (CH4) release from thawing Arctic permafrost is one of the few carbon-climate mechanisms that could change dramatically, forecast climate change in the near term. Submerged Arctic permafrost, such as underlies the vast East Siberian Arctic Sea (ESAS), is at particular risk due to rapidly warming oceans transferring heat to these deposits. Based on multibeam sonar surveys spanning thousands of kilometers, extensive methane bubble emissions across the ESAS have been documented. These bubble emissions are ubiquitous and in shallow water (<50 m) depositing a fraction of the escaping gas into the water column with the rest directly escaping to the air. Multibeam sonar data was analyzed to estimate ebullition fluxes for the ESAS and compared well with a mass balance estimate based on "storm ventilation" mass budget measurements. Maps of the spatial distribution of ebullition emissions correlated with warm riverine input, suggesting a new positive feedback system between warming climate and methane emissions. These inputs are mirrored in satellite methane column data.
14076090 Persson, A. (Lund University, Department of Physical Geography and Ecosystem Sciences, Lund, Sweden); Hasan, A. and Harder, S. Modelling active layer changes in permafrost peatlands with a topographic wetness index [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The release of methane (CH4) and other greenhouse gases from thawing permafrost has been documented in several studies. The processes behind the formation of e.g. CH4 are closely related to ground temperature and hydrology both in the thawed parts and in the permafrost zone of northern wetlands. In permafrost peatlands the thawing and freezing of the ground add to the emissions of the thawed period. The active layer thickness (ALT) and the site specific wetness are therefore important for any attempt to quantify the emissions from these peatlands. A pilot study with a modified Kudryavtsev's approach model where the ALT changes were based on a topographic wetness index (TWI) resulted in an ALT-map which show the spatial patterns of the ALT changes. In this study, a more extensive test of the model has been conducted, including active layer measurements and water level measurements over three seasons. The TWI is calculated in a high resolution, LIDAR derived, digital elevation model (DEM) for a 1.6 km2 permafrost mire complex in northern Sweden. The SSW measurements are spatially distributed around all the wetland types in the mire from surrounding fen, collapsed palsa to permafrost underlain palsa mire. Water levels are recorded bi-hourly in 40 wells. The ALT is measured from May to October at the well sites and at an additional 105 sites. The average ALT change for the palsa mire is estimated to +46 cm with a predicted change of the mean annual air temperature of +1 C. From the model and field data of ALT we can conclude that the permafrost in this mire is going to thaw out rapidly with the predicted temperature changes at high latitudes. The model sensitivity tests against field data show that the model and the use of topographic data of the mire is a tool that creates a valuable tool for the temporal ALT pattern changes.
14076150 Portnov, Alexey (University of Tromso, Tromso, Norway); Mienert, Jurgen and Cherkashov, G. A. Offshore permafrost decay and massive seabed methane escape in water depths >20 m at the south Kara Sea shelf [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33K-0604, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
We study the West-Yamal Shelf in the Kara Sea, offshore Western Russia. We present new high-resolution seismic data (2-16 kHz) and gas geochemical data from 2012 cruises. In high-resolution seismic data, we found extensive acoustic anomalies in the water column, which we interpreted to be gas (bubble) flares rising from the seafloor. These anomalies were widespread throughout the study area, but seemed to be limited to water depths >20 meters below sea level (mbsl). One seepage site in ~6 m water depth released gas that reached almost to the sea surface. The hydroacoustic anomalies are limited by the 20 m isobaths, and it may be controlled by the extension of permafrost that is still present below the seafloor at these depths providing an impermeable layer through which gas and other fluids cannot migrate. We detected acoustically transparent zones in sediments in the upper 2-5 meters below seafloor (mbsf). We interpret these acoustic anomalies to record the presence of free gas. Deeper seismic data show that acoustic anomalies in sediments near the seafloor are connected to gas chimneys that extend to depths >2000 mbsf. This suggests that gas is migrating from deeper hydrocarbon reservoirs and therefore it has very likely a thermogenic origin. In addition to the more widespread and disperse acoustically transparent zones, we discovered two prominent transparent mounds that are 1.5-2 km in diameter and that are elevated 10-15 meters above the seafloor. These features bear striking resemblance to the pingo-like features (PLF) that have been studied on the Beaufort Shelf (e.g. Shearer et al., 1971; Paull et al., 2007), and Pechora Sea (Rokos, 2009). Tentative results of numerical modelling estimate the thickness of permafrost, which was during the last sea level regression 170-300 meters thick. Based on the model of permafrost melting we state, that continuous sub-seabed permafrost may extend to water depths of ~20 m offshore creating a seal through which gas cannot migrate. Discontinuous and local permafrost areas may exist further offshore in up to 115 m water depth. This study provides one of the key examples of an Arctic marine shelf where seafloor gas release is widespread and where permafrost degradation is an ongoing process. These initial results provided targets for drilling and data acquisition in the summer of 2013 and for future research cruises in the Kara Sea. A better understanding of hydrocarbon seepage at the seafloor is important for assessing both the natural release of gas to the atmosphere and the hydrocarbon potential for new exploration regions like the Kara Sea.
14076139 Sather, K. L. (St. Olaf College, Northfield, MN); Connolly, C. T.; Mann, Paul J. and Schade, J. D. Stream sediment flux responses to varied permafrost carbon composition in the Siberian Arctic [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0558, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic systems are warming at a faster rate than lower latitudes, which is leading to significant changes in soil dynamics including deeper seasonal thaw and permafrost degradation. Deeper thaw may cause previously unprocessed and potentially more bioavailable organic carbon to be released for transport to stream networks. Arctic streams receiving this material may act as avenues for carbon export and/or processors of this material. The role that stream beds play in microbial processing of terrigenous material is poorly understood. Stream microbial response to newly thawed organic matter is important in predicting the fate of ancient carbon. Our study focused on microbial activity, measured as CO2 and CH4 flux, from stream sediments in response to inputs of carbon from ancient permafrost and modern soil horizons. To simulate the responses of stream sediment microbial communities, we incubated three distinct benthic sediment types from a small stream in the Kolyma River watershed (Siberia) with leachates from either active layer or yedoma permafrost soils that varied in carbon composition. Flux of CO2 differed strongly between sediment types, with highest respiration rates measured in sediments taken from a tussock grass dominated wetland, intermediate rates were seen in sediments underlying a pool in the stream channel, and low rates in rocky sediments from a small riffle. CH4 was only produced in grass wetland sediments. The initial rate of CH4 production was highest in the incubations receiving permafrost leachate, suggesting that input of labile carbon from thawing permafrost may increase the contribution of stream sediment processes to greenhouse gas production from high latitude streams.
14076146 Sato, Hisashi (Nagoya University, Graduate School of Environmental Studies, Aichi, Japan); Iwahana, G. and Ohta, Takeshi. The role of organic soil layer on the fate of Siberian larch forest and near-surface permafrost under changing climate; a simulation study [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33I-0583, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Siberian larch forest is the largest coniferous forest region in the world. In this vast region, larch often forms nearly pure stands, regenerated by recurrent fire. This region is characterized by a short and dry growing season; the annual mean precipitation for Yakutsk was only about 240 mm. To maintain forest ecosystem under such small precipitation, underlying permafrost and seasonal soil freezing-thawing-cycle have been supposed to play important roles; (1) frozen ground inhibits percolation of soil water into deep soil layers, and (2) excess soil water at the end of growing season can be carried over until the next growing season as ice, and larch trees can use the melt water. As a proof for this explanation, geographical distribution of Siberian larch region highly coincides with continuous and discontinuous permafrost zone. Recent observations and simulation studies suggests that existences of larch forest and permafrost in subsurface layer are co-dependent; permafrost maintains the larch forest by enhancing water use efficiency of trees, while larch forest maintains permafrost by inhibiting solar radiation and preventing heat exchanges between soil and atmosphere. Owing to such complexity and absence of enough ecosystem data available, current-generation Earth System Models significantly diverse in their prediction of structure and key ecosystem functions in Siberian larch forest under changing climate. Such uncertainty should in turn expand uncertainty over predictions of climate, because Siberian larch forest should have major role in the global carbon balance with its huge area and vast potential carbon pool within the biomass and soil, and changes in boreal forest albedo can have a considerable effect on Northern Hemisphere climate. In this study, we developed an integrated ecosystem model, which treats interactions between plant-dynamics and freeze-thaw cycles. This integrated model contains a dynamic global vegetation model SEIB-DGVM, which simulates plant and carbon dynamics. It also contains a one-dimensional land surface model NOAH 2.7.1, which simulates soil moisture (both liquid and frozen), soil temperature, snowpack depth and density, canopy water content, and the energy and water fluxes. This integrated model quantitatively reconstructs post-fire development of forest structure (i.e. LAI and biomass) and organic soil layer, which dampens heat exchanges between soil and atmosphere. With the post-fire development of LAI and the soil organic layer, the integrated model also quantitatively reconstructs changes in seasonal maximum of active layer depth. The integrated model is then driven by the IPCC A1B scenario of rising atmospheric CO2, and by climate changes during the twenty-first century resulting from the change in CO2. This simulation suggests that forecasted global warming would causes decay of Siberian larch ecosystem, but such responses could be delayed by "memory effect" of the soil organic layer for hundreds of years.
14076147 Sonnentag, Oliver (Université de Montréal, Geography, Montreal, QC, Canada); Helbig, Manuel; Detto, M.; Wischnewski, Karoline; Chasmer, Laura; Marsh, P. and Quinton, W. L. Establishment of a meso-network of eddy covariance towers to quantify carbon, water and heat fluxes along a permafrost and climate gradient in the Taiga plains, Northwest Territories, Canada [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33I-0584, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Recent research suggests an increase in active-layer depth in the continuous permafrost zone and degradation of the sporadic and discontinuous permafrost zones into seasonally frozen ground. Increasing active-layer depth and continued permafrost degradation will have far-reaching consequences for northern ecosystems with net feedbacks of unknown magnitude and direction to the climate system by altered regional hydrology and topography, vegetation composition and structure, land surface properties, and carbon dioxide (CO2) and methane (CH4) sink-source strengths. Several important questions are currently unanswered: 1) What is the net effect of permafrost thawing-induced biophysical and biogeochemical feedbacks to the climate system? 2) How do these two different types of feedback differ between the sporadic, discontinuous and continuous permafrost zones? 3) Is the decrease (increase) in net CO2 (CH4) exchange measured over mostly tundra sites in the continuous permafrost zone generalizable to forested landscapes in the sporadic, discontinuous and continuous permafrost zones? To address these questions we initiated a meso-network of eddy covariance towers to quantify carbon (CO2, CH4), water and heat fluxes along a permafrost and climate gradient in the Taiga Plains, Northwest Territories, Canada including the following four sites from south to north (Fort Simpson-Norman Wells-Inuvik): Scotty Creek (boreal forest-peatland landscape with sporadic/discontinuous permafrost; fully operational since May 2013), Norman Wells (boreal forest with discontinuous/continuous permafrost; to be established in 2014), Havikpak Creek (boreal forest with continuous permafrost; partly operational since April 2013) and Trail Valley Creek (tundra with continuous permafrost; partly operational since April 2013). At all sites the eddy covariance measurements are or will be complemented by repeated surveys of surface and frost table topography and vegetation, by land cover-type specific fluxes of CO2 and CH4 measured with a static chamber technique, and by remote sensing-based footprint analysis. With this contribution, we report on the current status of meso-network development and present results from the first growing season of eddy covariance measurements at Scotty Creek, Trail Valley Creek and Havikpak Creek. Net CO2 uptake started earlier and was more pronounced at the forested Havikpak site compared to the tundra site (Trail Valley Creek), which experienced similar air temperatures but later snow melt than Havikpak. Overall, Scotty Creek experienced the strongest net CO2 uptake but also the highest nighttime respiration. At the same time, meteorological conditions at Scotty Creek are markedly different with higher air temperatures and earlier snowmelt than at the two northern sites.
14076097 Thornton, P. E. (Oak Ridge National Laboratory, Oak Ridge, TN); Kumar, Jitendra; Painter, S. L.; Bisht, G.; Hammond, G. E.; Mills, R. T. and Tang, G. A multi-scale approach to representing tundra permafrost dynamics in a coupled climate system model [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31H-05, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Current generation Earth system models do not resolve the microtopographic features and sub-surface structural complexity of ice-wedge polygonal tundra in the Arctic. The high carbon density of permafrost soils in many polygonal tundra systems raises concern about the potential for strong positive feedbacks under conditions of radiatively-forced climate warming. The thermal and hydrologic responses of these systems to warming are thought to depend in part on existing drainage patterns and how those patterns might change as the active layer thickens, while the balance of net carbon flux occurring as carbon dioxide versus methane depends on biological, thermal, and hydrologic state. By explicitly representing microtopographic variability and sub-surface dynamics in a fine-scale model, informed by intensive site-scale measurements and laboratory experimentation, we are able to generate semi-empirical parameterizations that capture the mean behavior of energy, water, and carbon fluxes at scales amenable to application in an Earth system model. We demonstrate an example of this multi-scale approach merging observations and modeling for polygonal tundra near Barrow, Alaska, as a component of the Next Generation Ecosystem Experiment (NGEE) Arctic project.
14076087 van Huissteden, K. J. (Vrije Universiteit Amsterdam, Earth Sciences, Amsterdam, Netherlands); Gallagher, A.; Budishchev, A.; van Kester, B. and Belelli-Marchesini, L. Rapid thaw pond formation in northeast Siberia transfers permafrost carbon to the atmosphere [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The formation of small ponds by shallow thawing of ice-rich permafrost may represent an immediate reaction of permafrost soils to climate change, contrasting with thaw lakes which take a longer development and may be inherited from the past. We studied thaw ponds in arctic tundra on ice-rich continuous permafrost in the Indigirka lowlands of Northeast Siberia, an area that has experienced modest warming. Dominating landforms are thaw lakes, drained lake basins, thaw lakes and remnants of Pleistocene ice complex deposits ('yedoma'). With increasing age, the soils in drained lake basin accumulate more ice in ice wedges and mineral palsas. Thaw ponds in the area result from melting of ice wedges (ice wedge ponds, IWP) or from degradation of mineral palsas (palsa thaw ponds, PP). The PP's have a diameter of a few meters, a depth up to 0.5 m and may be intermittently dry. The IWP's are deeper, and have an elongate ditch-like shape. IWP and PP can be discriminated from ice wedge polygon centre ponds (PCP) which show a regular polygonal pattern and do not show die-back of dry tundra vegetation by paludification as in IWP and PP. PP's show more rapid vegetation succession than the IP's, leading to the (partial) recovery of vegetation. Most of the PP's appear to have formed spontaneously. However, pond formation was also induced by accidental or experimental disturbance of the tundra vegetation cover. Comparison of a Keyhole satellite image from 1977 with a GeoEye image from 2010 shows that the number of PP's increased significantly. This indicates a 2.9 ± 0.9 times increase in the number of ponds in 33 years. The ponds are significant sources of CH4 and CO2, derived from decomposition of dead vegetation and soil organic matter. Averaged CO2 fluxes measured with static chambers amount for PP's +106±29 mg CO2 m-2 hr-1, for PCP ponds -77±30 mg CO2 m-2 hr-1, for dry palsa surface with Betula nana -180±22 mg CO2 m-2 hr-1. When PP's re-vegetate, a sedge vegetation develops, with an uptake flux of -224±42 mg CO2 m-2 hr-1. CH4 fluxes for the same areas are 3.60±1.2 mg CH4 m-2 hr-1 (PP), 3.69±0.56 mg CH4 m-2 hr-1 (PCP), -0.38±0.15 mg CH4 m-2 hr-1 (dry palsa), 3.97±0.25 mg CH4 m-2 hr-1 (re-vegetated pond). IWP's show the highest CH4 fluxes, 4.42±3.60 mg CH4 m-2 hr-1. The thaw ponds therefore transfer areas of dry tundra vegetation with CO2 and CH4 uptake to areas of strong emission of both greenhouse gases. Upon vegetation regrowth, high CH4 emissions remain but this is balanced by strong CO2 uptake. The speed of re-vegetation process is likely in the order of several years to decades. By contrast to ponds, thaw lakes in the same area show minor expansion. Our data suggest that a drastic increase in the number of small thaw ponds, rather than thaw lake expansion, represents a fast response of ice-rich permafrost soils to climate change and may contribute significantly to the increase of greenhouse gas emissions and carbon from permafrost soils. Moreover, the creation of similar ponds by anthropogenic vegetation disturbance suggests that increase of human activity in permafrost areas aggravates greenhouse gas emissions from permafrost soils.
14076119 Waldrop, M. P. (U. S. Geological Survey, Menlo Park, CA); Blazewicz, S.; Jones, Miriam; McFarland, J. W.; Harden, J. W.; Euskirchen, E. S.; Turetsky, M. R.; Hultman, Jenni and Jansson, J. R. Microbial communities of the deep unfrozen; do microbes in taliks increase permafrost carbon vulnerability? [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B32C-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The vast frozen terrain of northern latitude ecosystems is typically thought of as being nearly biologically inert for the winter period. Yet deep within the frozen ground of northern latitude soils reside microbial communities that can remain active during the winter months. As we have shown previously, microbial communities may remain active in permafrost soils just below the freezing point of water. Though perhaps more importantly, microbial communities persist in unfrozen areas of water, soil, and sediment beneath water bodies the entire year. Microbial activity in taliks may have significant impacts on biogeochemical cycling in northern latitude ecosystems because their activity is not limited by the winter months. Here we present compositional and functional data, including long term incubation data, for microbial communities within permafrost landscapes, in permafrost and taliks, and the implications of these activities on permafrost carbon decomposition and the flux of CO2 and CH4. Our experiment was conducted at the Alaska Peatland Experiment (APEX) within the Bonanza Creek LTER in interior Alaska. Our site consists of a black spruce forest on permafrost that has degraded into thermokarst bogs at various times over the last five hundred years. We assume the parent substrate of the deep (1-1.5 m) thermokarst peat was similar to the nearby forest soil and permafrost C before thaw. At this site, flux tower and autochamber data show that the thermokarst bog is a sink of CO2, but a significant source of CH4. Yet this does not tell the whole story as these data do not fully capture microbial activity within the deep unfrozen talik layer. There is published evidence that within thermokarst bogs, relatively rapid decomposition of old forest floor material may be occurring. There are several possible mechanisms for this pattern; one possible mechanism for accelerated decomposition is the overwintering activities of microbial communities in taliks of thermokarst soils. To test this idea, we conducted anaerobic incubations of deep (1 m) bog soils at two different temperatures to determine microbial temperature response functions. We also measured soil profile CO2 and CH4 concentrations and functional gene assays of the deep bog microbial community. Incubation data in combination with overwinter temperature profiles show that the talik has high potential rates of CO2 and CH4 production compared to the mass of C from forest floor and permafrost C to 1 m depth. Results highlight the potential importance of taliks affecting the vulnerability of permafrost carbon to decomposition and reduction to methane.
14076166 Walvoord, M. A. (U. S. Geological Survey, National Research Program, Denver, CO); Jepsen, S. M.; Voss, C. I.; Minsley, B. J. and Rover, J. Linkages between changes in lake extent and the distribution of permafrost, Yukon Flats basin, interior Alaska, USA [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0660, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Approximately one in 10 lakes in the Yukon Flats basin of interior Alaska has undergone substantial change in surface area over the last 30 years. Although permafrost degradation is a likely cause, its role is not clear, making future predictions of lake evolution difficult. Our hypothesis is that changes in lake surface area and permafrost distribution are causally related via changes in either vertical groundwater flow through open taliks, or lateral groundwater flow over a deepening permafrost table. This hypothesis is tested by: (i) evaluating the proportion of lakes overlying frozen and unfrozen sediment (gravel overlying silt), inferred from resistivity profiles from an airborne electromagnetic survey, that show statistically significant trends in surface area (1979-2009); and (ii) using the results of the above statistical analysis to guide hydrological and thermal modeling of lake mass response to deepening of the permafrost table and development of open taliks. The thermodynamic phase of sublacustrine gravel (i.e., frozen or unfrozen) is found to be associated more strongly with lake surface area change than the phase of the deeper silt (p < 0.01 vs. 0.55 based on chi-squared tests). Moreover, lakes overlying unfrozen gravel are 3.2 times more likely to show a significant trend in surface area than those overlying frozen gravel. These findings may indicate that thermal changes in the shallow, gravel-rich permafrost have more influence on lake evolution than thermal changes in the deeper silt. Hydrological and thermal modeling will be presented along with the the statistical analysis outlined above.
14080981 Ford, Derek C. (McMaster University, School of Geography and Earth Sciences, Hamilton, ON, Canada). Karst development in the glaciated and permafrost regions of the Northwest Territories, Canada [abstr.]: in Proceedings of the 16th international congress of Speleology (Filippi, Michal, editor; et al.), Proceedings of the International Congress of Speleology, 16, Vol. 3, p. 54, 2013. Meeting: 16th international congress of Speleology, July 21-28, 2013, Brno, Czech Republic.
14076120 Chakraborty, R. (Lawrence Berkeley National Laboratories, Berkeley, CA); Pettenato, A.; Tas, N.; Hubbard, S. S. and Jansson, J. R. Metabolic and growth characteristics of novel diverse microbes isolated from deep cores collected at the Next Generation Ecosystem Experiment (NGEE)-Arctic site in Barrow, Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0561, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The Arctic is characterized by vast amounts of carbon stored in permafrost and is an important focal point for the study of climate change as increasing temperature may accelerate microbially mediated release of Carbon stored in permafrost into the atmosphere as CO2 and CH4. Yet surprisingly, very little is known about the vulnerability of permafrost and response of microorganisms in the permafrost to their changing environment. This deficiency is largely due to the difficulty in study of largely uncultivated and unknown permafrost microbes. As part of the U.S. Department of Energy (DOE) Next Generation Ecosystem Experiment (NGEE) in the Arctic, we collected permafrost cores in an effort to isolate resident microbes. The cores were from the Barrow Environmental Observatory (BEO), located at the northern most location on the Alaskan Arctic Coastal Plain near Barrow, AK, and up to 3m in depth. In this location, permafrost starts from 0.5 m in depth and is characterized by variable water content and higher pH than surface soils. Enrichments for heterotrophic bacteria were initiated at 4°C and 1°C in the dark in several different media types, under both aerobic and anaerobic conditions. Positive enrichments were identified by an increase in optical density and cell counts after incubation period ranging from two to four weeks. After serial transfers into fresh media, individual colonies were obtained on agar surface. Several strains were isolated that include Firmicutes such as Bacillus, Clostridium, Sporosarcina, and Paenibacillus species and Iron-reducing Betaproteobacteria such as Rhodoferax species. In addition, methanogenic enrichments continue to grow and produce methane gas at 2°C. In this study, we present the characterization, carbon substrate utilization, pH, temperature and osmotic tolerance, as well as the effect of increasing climate change parameters on the growth rate and respiratory gas production from these permafrost isolates.
14076138 Connolly, C. T. (Holy Cross College, Worcester, MA); Sather, K. L.; Ludwig, S.; Schade, J. D.; Sobczak, W. V. and Mann, Paul J. Organic matter biolability and enzyme activities within stream benthic sediments in northeastern Siberia [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0557, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Predicted climate warming and permafrost thaw in northeastern Siberia is expected to alter hydrologic flow paths, changing the quantity and quality of organic matter (OM) supplied to streams. With deeper flow paths, higher contributions of OM sourced from permafrost soils may be exported. This material can be relatively biolabile and has been shown to stimulate microbial production of enzymes crucial for the degradation of carbon in stream waters. Permafrost derived OM that has a different composition than active layer OM may generate hot-spots for microbial activity, and CO2 and CH4 emissions in areas entering stream benthic sediments; however, our understanding of how OM composition influences enzyme activities, and how this affects carbon degradation in these areas remains rudimentary. Here we show that ancient OM residing in Yedoma permafrost (ice rich deposits formed during the late Pleistocene) and modern OM found in a typical Arctic watershed differ in their composition and biolability. Furthermore, we demonstrate that microbes within stream sediments receiving different OM sources (ancient/modern) express different specific enzymes, which is likely affecting OM reactivity and is consistent with a shift in nutrient and organic carbon availability. We also show that differences in stream sediment type from a tussock grass dominated wetland and a stagnant pool in the stream channel may also affect enzyme activity rates. A better understanding of the impact of terrestrial carbon inputs on OM degradation in stream sediments will improve our understanding of potential feedbacks between permafrost and climate change.
14076208 Cuntz, M. (Helmholtz Centre for Environmental Research, Department Computational Hydrosystems, Leipzig, Germany) and Haverd, V. Physically accurate soil freeze-thaw processes in a global land surface scheme [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C44B-07, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Transfer of energy and moisture in frozen soil, and hence the active layer depth, are strongly influenced by the soil freezing curve which specifies liquid moisture content as a function of temperature. However, the curve is typically not represented in global land surface models, with less physically-based approximations being used instead. In this work, we develop a physically accurate model of soil freeze-thaw processes, suitable for use in a global land surface scheme. We incorporated soil freeze-thaw processes into an existing detailed model for the transfer of heat, liquid water and water vapor in soils, including isotope diagnostics - Soil-Litter-Iso (SLI, Haverd & Cuntz 2010), which has been used successfully for water and carbon balances of the Australian continent (Haverd et al. 2013). A unique feature of SLI is that fluxes of energy and moisture are coupled using a single system of linear equations. The extension to include freeze-thaw processes and snow maintains this elegant coupling, requiring only coefficients in the linear equations to be modified. No impedance factor for hydraulic conductivity is needed because of the formulation by matric flux potential rather than pressure head. Iterations are avoided which results in the same computational speed as without freezing. The extended model is evaluated extensively in stand-alone mode (against theoretical predictions, lab experiments and field data) and as part of the CABLE global land surface scheme. SLI accurately solves the classical Stefan problem of a homogeneous medium undergoing a phase change. The model also accurately reproduces the freezing front, which is observed in laboratory experiments (Hansson et al. 2004). SLI was further tested against observations at a permafrost site in Tibet (Weismuller et al. 2011). It reproduces seasonal thawing and freezing of the active layer to within 3 K of the observed soil temperature and to within 10% of the observed volumetric liquid soil moisture. Model-data fusion suggests that model performance is improved when the relatively high thermal conductivity of the ice phase is accounted for. However, the permafrost site is very gravelly so that the model equations for thermal conductivity are at the edge of applicability. The freezing-soil formulation is tested in the presence of snow, using measurements at an orchard site in Idaho. The model reproduces well observed snow-water equivalents and soil temperatures. However, it is highly sensitive to snow emissivity and maximum liquid content of the snow, leading both to modified refreezing of melted water. It is possible that the model would benefit from 1-2 more snow layers to permit simulation of density and temperature gradients in the snow-pack. SLI was run globally on 1´1 degree grid as the soil part of the land surface scheme CABLE. We could therefore demonstrate that this detailed and physically-realistic formulation is fast enough to be a feasible alternative to the much simpler default soil-scheme in CABLE.
14076170 Dafflon, B. (Lawrence Berkeley National Laboratory, Berkeley, CA); Hubbard, S. S.; Ulrich, C.; Peterson, J. E.; Wu, Y.; Wainwright, H. M.; Gangodagamage, C.; Kholodov, A. L. and Kneafsey, T. J. Quantifying Arctic terrestrial environment behaviors using geophysical, point-scale and remote sensing data [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0664, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Improvement in parameterizing Arctic process-rich terrestrial models to simulate feedbacks to a changing climate requires advances in estimating the spatiotemporal variations in active layer and permafrost properties - in sufficiently high resolution yet over modeling-relevant scales. As part of the DOE Next-Generation Ecosystem Experiments (NGEE-Arctic), we are developing advanced strategies for imaging the subsurface and for investigating land and subsurface co-variability and dynamics. Our studies include acquisition and integration of various measurements, including point-based, surface-based geophysical, and remote sensing datasets These data have been collected during a series of campaigns at the NGEE Barrow, AK site along transects that traverse a range of hydrological and geomorphological conditions, including low- to high- centered polygons and drained thaw lake basins. In this study, we describe the use of galvanic-coupled electrical resistance tomography (ERT), capacitively-coupled resistivity (CCR) , permafrost cores, above-ground orthophotography, and digital elevation model (DEM) to (1) explore complementary nature and trade-offs between characterization resolution, spatial extent and accuracy of different datasets; (2) develop inversion approaches to quantify permafrost characteristics (such as ice content, ice wedge frequency, and presence of unfrozen deep layer) and (3) identify correspondences between permafrost and land surface properties (such as water inundation, topography, and vegetation). In terms of methods, we developed a 1D-based direct search approach to estimate electrical conductivity distribution while allowing exploration of multiple solutions and prior information in a flexible way. Application of the method to the Barrow datasets reveals the relative information content of each dataset for characterizing permafrost properties, which shows features variability from below one meter length scales to large trends over more than a kilometer. Further, we used Pole- and Kite-based low-altitude aerial photography with inferred DEM, as well as DEM from LiDAR dataset, to quantify land-surface properties and their co-variability with the subsurface properties. Comparison of the above- and below-ground characterization information indicate that while some permafrost characteristics correspond with changes in hydrogeomorphological expressions, others features show more complex linkages with landscape properties. Overall, our results indicate that remote sensing data, point-scale measurements and surface geophysical measurements enable the identification of regional zones having similar relations between subsurface and land surface properties. Identification of such zonation and associated permafrost-land surface properties can be used to guide investigations of carbon cycling processes and for model parameterization.
14076165 Godin, E. (University of Montreal, Geography, Montreal, QC, Canada) and Fortier, D. Physical modeling and monitoring of the process of thermal-erosion of an ice-wedge during a partially-controlled field experiment (Bylot Island, NU, Canada) [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C43A-0659, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Syngenetic ice-wedges polygons are widespread periglacial features of the Arctic. On Bylot Island, Nunavut, Canada, numerous thermo-erosion gullies up to several 100's m in length developed in polygonal wetlands during the last decades. These gullies contributed to drainage of these wetlands and changed dramatically local ecological conditions. Concentrated and repeated snowmelt surface runoff infiltrated frost cracks, where convective heat transfer between flowing water and ice initiated piping in ice wedges leading to the rapid development of tunnels and gullies in the permafrost (Fortier D. et al., 2007). We conducted field experiments to quantify the convection process and speed of ice wedges ablation. The experiments were accomplished between the 23/06/2013 and the 05/07/2013 over A; an exposed sub-horizontal ice-wedge surface and B; a tunnel in an ice-wedge crack. The ice was instrumented with graduated sticks to calculate the ice ablation following the flow of a defined amount of water. A fixed quantity of water obtained from a nearby waterfall was diverted over the ice through a PVC pipe. Water temperature Wt (K), quantity Wq (L s-1 or m3 s-1), ice ablation rate Iar (m s-1) and convective heat transfer coefficient a (W m-2 K) were obtained during the 5 experiments. The objective of this paper is to quantify the heat transfer process from field measurements from an ice wedge under ablation and to compare with coefficients from previous researches and in the literature. For each experiment with the ice-surface scenario, water temperature varied between 280 K and 284 K. Discharge varied between 0.0001 and 0.0003 m3 s-1. Ablation rate varied between 1.8 * 10-5 and 0.0004 m s-1. Heat transfer coefficient varied between 706 and 11 655 W m-2 K and between 54 and 4802 W of heat was transferred to ice. For each experiment with the tunnel scenario, water temperature was 284 K ± 1 K. Discharge was 0.0002 m3 s-1. Ablation rate varied between 0.0001 and 0.0003 m s-1. Heat transfer coefficient varied between 2644 and 7934 W m-2 K and between 1791 and 5374 W of heat was transferred to ice. Water temperature exiting the tunnel was less than 279 K. Both contexts of experimentation are occurring frequently during gully development. A small input of water over exposed massive-ice can erode significant volume of ice-wedges ice, thermally and mechanically. Empiric determination of the heat transfer coefficient using the parameters measured in the field will provide a better understanding of water temperature and discharge relative importance in the thermo-erosion of ice.
14076075 Goetz, S. J. (Woods Hole Research Center, Falmouth, MA); Coe, M. T. and Brando, P. M. Vulnerability of Arctic and tropical carbon to changing climate [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B11K-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The future trajectory of the global climate system depends, in part, on what happens to the earth's major pools of organic carbon. The largest and most vulnerable pools are stored in tropical forests and the organic soils of boreal and arctic biomes. The fate of the organic carbon stored in tropical and boreal ecosystems will depend on how plants respond to both average climate change (e.g. mean change in temperature and precipitation) and the associated changes to extreme weather events (e.g. droughts). In the arctic there is evidence a biome shift is taking place, with warmer drier climate leading to forest productivity changes, increased tree mortality and unprecedented fire events that alter the composition of successional pathways. In the tundra regions the warmer climate has led to increases in woody vegetation, total landscape biomass, and altered albedo and net radiation. Warming in the arctic also has the potential to release ancient organic carbon to the atmosphere via permafrost thaw. In contrast, large areas of the moist tropical forests are being altered by land-use practices and increasingly severe weather. People are clearing, thinning, and changing the composition of forests. Severe, episodic droughts are superimposed upon these land-use activities, thereby increasing forest susceptibility and mortality to escaped management fires. The deforestation and forest degradation have led to significant direct transfer of carbon from aboveground biomass pools to the atmosphere. We report on use of field measurements, satellite observations, and numerical models to quantify historical and potential future changes in arctic-boreal and tropical terrestrial productivity as a function of natural and human-induced land cover and climate disturbances. We contend that both arctic-boreal and tropical biomes are strongly influenced by the same fundamental biophysical processes controlling carbon exchange. These include changes in productivity, tree mortality, the frequency and severity of disturbance, it's implications for post-disturbance vegetation structure and function, and the influence of climate. We argue that drought, expressed as extended vapor pressure deficits, plays a critical role in driving these interacting processes in each of these biomes.
14076071 Graham, D. E. (Oak Ridge National Laboratory, Oak Ridge, TN); Roy Chowdhury, T.; Herndon, E.; Chourey, K.; Ladd, M.; Tas, N.; Jansson, J. R.; Elias, D. A.; Hettich, R. L.; Phelps, T. J.; Gu, B.; Liang, L. and Wullschleger, S. D. Biogeochemical controls on microbial CO2 and CH4 production in interstitial area polygon soils from the Barrow Environmental Observatory [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B11J-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Organic matter buried in Arctic soils and permafrost will become accessible to increased microbial degradation as the ground warms due to climate change. The rates of organic matter degradation and the proportion of CH4 and CO2 greenhouse gasses released in a potential warming feedback cycle depend on the microbial response to warming, organic carbon structure and availability, the pore-water pH, and available electron acceptors. To adapt and improve the representation of these Arctic subsurface processes in land models for the NGEE Arctic project, we examined soil organic matter transformations from elevated and subsided areas of low- and high-centered polygons from interstitial tundra on the Barrow Environmental Observatory (Barrow, AK). Significant amounts of iron(II) in organic and mineral soils of the active layer and groundwater indicate anoxic conditions in most soil horizons. Unamended, anoxic incubations of soils at -2, +4 or +8 °C produced both CH4 and CO2, with different response curves. CO2 formed rapidly while CH4 production lagged. Rates of formation for both CH4 and CO2 were substantially higher in microcosms containing active layer O horizon (38-43% total carbon) compared to B horizon (17-18% carbon) samples. The ratio of CO2 to CH4 produced decreased with increasing temperature. A constant Q10 relationship is not adequate to explain temperature effects from -2 to +8 °C. Measurements of ionic species dissolved in soil porewater from frozen cores, humic-rich surface water, or groundwater indicated low levels of nitrate and sulfate, constraining the role of these alternative electron acceptors in anaerobic respiration. The surface water pH (4.4) was significantly lower than groundwater (5.8 to 6.3). Organic acid degradation and Fe(III) reduction increased the pH in soil water during some incubations. Substantial differences in other ionic species confirm that surface and groundwater do not mix rapidly in the field. Biomass extracted from frozen mineral soil samples or thawed microcosms was analyzed for relative protein abundance using metaproteomics, and numerous peptide spectra were matched to an Arctic genomic and metagenomic database. Signature proteins from acetoclastic methanogens were identified in frozen permafrost and active-layer samples. After microcosm incubations, however, methanogenic proteins were found only in active-layer samples, consistent with headspace gas analyses. Therefore, soil thawing and warming caused increases in microbial biomass and significant changes in microbial composition that determine the composition of greenhouse gas product mixtures. Differential microbial growth and migration through the thawing soil column may be key to changes in microbial population size and activity during prolonged thaw seasons. Methanogenesis and microbial growth account for most electron transfer from soil organic matter in O horizon samples, but iron reduction and microbial growth account for most electron transfer in the B horizon.
14076207 Grenier, C. F. (Université de Versailles Saint-Quentin-en-Yvelines, Versailles, France); Roux, N.; Costard, F. and Pessel, M. INTERFROST; a benchmark of thermo-hydraulic codes for cold regions hydrology [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C44B-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Large focus was put recently on the impact of climate changes in boreal regions due to the large temperature amplitudes expected. Large portions of these regions, corresponding to permafrost areas, are covered by water bodies (lakes, rivers) with very specific evolution and water budget. These water bodies generate taliks (unfrozen zones below) that may play a key role in the context of climate change. Recent studies and modeling exercises showed that a fully coupled 2D or 3D Thermo-Hydraulic (TH) approach is a minimal requirement to model and understand the evolution of the river and lake - soil continuum in a changing climate (e.g. Mc Kenzie et al., 2007; Bense et al 2009, Rowland et al 2011; Painter 2011; Grenier et al 2012; Painter et al 2012 and others from the 2012 special issue Hydrogeology Journal: "Hydrogeology of cold regions"). However, 3D studies are still scarce while numerical approaches can only be validated against analytical solutions for the purely thermal equation with conduction and phase change (e.g. Neumann, Lunardini). When it comes to the coupled TH system (coupling two highly non-linear equations), the only possible approach is to compare different codes on provided test cases and/or to have controlled experiments for validation. We propose here to initiate a benchmark exercise, detail some of its planned test cases (phase I) and invite other research groups to join. This initial phase of the benchmark will consist of some test cases inspired by existing literature (e.g. Mc Kenzie et al., 2007) as well as new ones. Some experimental cases in cold room will complement the validation approach. In view of a Phase II, the project is open as well to other test cases reflecting a numerical or a process oriented interest or answering a more general concern among the cold region community. A further purpose of the benchmark exercise is to propel discussions for the optimization of codes and numerical approaches in order to develop validated and optimized simulation tools allowing in the end for 3D realistic applications. A web site hosted by LSCE is under construction (wiki.lsce.ipsl.fr/interfrost/) to allow easy interaction or downloading. Future prospects will be envisioned including organization of specific meetings or conference sessions. This will provide the opportunity to propel networking among researchers, discuss the content of further phases of the benchmark (increase model or parameter complexity) and discuss strategies for project funding. Please consider joining the benchmark.
14076143 Gu, B. (Oak Ridge National Laboratory, Oak Ridge, TN); Herndon, E.; Graham, D. E.; Phelps, T. J.; Wullschleger, S. D. and Liang, L. Geochemical characterization of Arctic tundra and implications for organic matter degradation [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0565, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Tundra soils are uniquely cold terrestrial environments that face irrevocable change under warming climate conditions. Specifically, many tundra soils store large quantities of organic carbon that may rapidly degrade with increasing temperature, releasing C into drainage systems or to the atmosphere as greenhouse gases (CH4, CO2). In order to predict rates of C release from tundra soils, it is necessary to quantify how biogeochemical factors such as pore water chemistry, terminal electron acceptor availability, and mineral adsorption regulate rates and pathways of soil organic carbon (SOC) degradation. In this study, we examine spatial and seasonal patterns of aqueous geochemistry and SOC characteristics from across an area of tundra landscape in the Arctic. We aim to identify factors that increase or decrease rates of SOC degradation, including: 1) the composition of organic substrates, 2) abundance of terminal electron acceptors, 3) vertical transport and spatial variability of both organic and inorganic compounds, and 4) adsorption to mineral surfaces. Soil and water samples were obtained from the Barrow Environmental Observatory (BEO) in northern Alaska as part of the Next Generation Ecosystem Experiment (NGEE) Arctic project. Tundra at the BEO is characterized by permafrost below ~60 cm and polygonal features that induce topographic gradients of water saturation. Soils are organic-rich and store large amounts of slowly decomposing plant material. Chemical and physical extractions were used to obtain operationally-defined pools of SOC to evaluate their mineral associations. Water samples collected in early and late summers were analyzed for pH, electrical conductivity, and dissolved concentrations of anions, cations, organic carbon, inorganic carbon, and ferrous iron, as well as dissolved and soil gases (CH4 and CO2). We observe a steep pH gradient, with acidic pH in surface waters and near neutral pH in pore waters >20 cm below the surface. Dissolved organic carbon and Fe are dominant ionic species in both surface waters and soil pore waters. Fe(II) increases with depth in the soil, from which we infer that Fe(III) reduction may serve as a primary metabolism, driving organic respiration in oxygen-limited areas. Additionally, dissolved concentrations of Fe(II)/Fe(III), CH4, and CO2 vary with soil moisture, indicating that geochemical differences induced by water saturation may dictate microbial products of organic matter degradation. We continue to analyze chemical characteristics of dissolved and particulate organic carbon to evaluate C substrates and mobility. Freeze-dried soil extracts are being processed to determine relative ages of different C fractions in the soil and obtain information on rates of decomposition. We discuss potential implications of these findings in understanding sources, rates, and geochemical controls of C fluxes from tundra soils, which form the basis for a computational modeling framework in predicting feedbacks to warming climate.
14076141 Han, Peter Daniel (SUNY College of Environmental Science and Forestry, Syracuse, NY); Schade, J. D.; Mann, Paul J.; Natali, S. and Zimov, N. Linking composition of extractable carbon from active layer soils with thaw depth [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0562, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
As the climate warms and active layers deepen, subsurface waters will receive increased periods of time to penetrate and leach deeper soil horizons. Carbon and nutrients previously locked in these frozen soils will become increasingly available for processing and transport, potentially altering the flux of organic matter from subsurface sources. We examined differences in soil and water carbon and nitrogen content between sites with deep and shallow thaw depths to help gain an understanding of the implications of deepening active layers on the chemical composition of subsurface waters in arctic ecosystems. We collected soil samples from six sites along a small stream in the Kolyma River watershed in Eastern Siberia that drains a subwatershed underlain by permafrost soils dating back to the Pleistocene. Three sites were classified as "deep" 33 to 40 cm and three "shallow" 55 to 63 cm. Soil samples were collected from the top and bottom of the mineral layer, as well as from frozen soil at a depth of one meter. We measured gravimetric water content and carbon content (as loss on ignition). Water extractions were conducted to measure solubility and to assess the relative lability of the extractable dissolved organic carbon (DOC) pool for all three sets. Although water content was much greater in the frozen samples under shallow relative to deeper sites, there was no significant difference in the raw percent carbon content between deep and shallow sites. However, in water extractions, higher DOC concentrations were found in frozen samples under the shallow sites than the deep. Furthermore, during a five-day incubation, DOC concentrations from samples under shallow sites declined by 19%, more than double that of the 8% loss observed under deeply thawed sites. These results suggest that in the recent future a new wave of highly labile DOC will enter the watershed through subsurface water. Indeed, this pulse of available, nutrients has the potential to change the character of these small streams, and on a large scale, the warming arctic environment. through subsurface water. Indeed, this pulse of available nutrients has the potential to change the character of these small streams, and on a larger scale, the warming arctic environment.
14076069 Harden, J. W. (U. S. Geological Survey, Menlo Park, CA); Lawrence, C. R.; Schulz, M. S.; Heckman, K. A.; Maher, K. and Marin-Spiotta, E. Deep soil carbon and vulnerabilities to anthropogenic change [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B11J-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Soil organic carbon, including its form and turnover, influences and is influenced by soil development processes, yet our understanding of rates and mechanisms that control C fate are inversely proportional to depth. Surface and shallow C are reasonably captured by databases, models, and experimental studies. Deep C, by contrast, remains as a large uncertainty with regard to both current stock and future susceptibility to climate and land use changes. Soil development occurs over all timescales as a result of many physical, biological, hydrological, and biogeochemical processes, all of which are inexorably linked to biology and the cycling of organic carbon. Here we explore basic principles of soil formation and C cycling in order to identify useful proxies for explaining the depth distributions of C storage and turnover. Geochemical weathering, secondary mineral distribution, leaching, plant production, and temperature are compared to C stocks and soil radiocarbon as a tool for assessing turnover. In general B horizons, which represent zones of secondary mineral accumulation, retain organic C in direct proportion to surface area, indicating the key role of organomineral bonding in C storage of deep mineral soils. Meanwhile turnover of soil C is inversely proportional to depth and rooting activity, indicating that hydrology, biotic and abiotic mixing, and erosion/sedimentation play key roles as well. C storage in peats and organic rich soils of permafrost landscapes is associated more with water storage than with mineral surface area, indicating the fundamental importance of water/oxygen depletion/fire interactions in these soils. Implications: Changes in climate and associated changes in vegetation may most dramatically impact the turnover of deep C through changes in flowpaths and rooting depths, but may impact net C storage less profoundly owing to compensating effects of primary production. By contrast, given the depth dependencies of C turnover, disturbance such as land use change, erosion/sedimentation, or urbanization are likely to impact both storage and turnover of deep soil C according to the type magnitude, depth, and duration of disturbance.
14076144 Liang, Chao (Argonne National Laboratory, Biosciences Division, Argonne, IL); Steffens, M.; Jastrow, J. D.; Zhang, X.; Antonopoulos, D. A. and Kogel-Knabner, I. Decoupled connection between soil microbial community and organic geochemical composition; a case study in the Arctic tundra, North Slope of Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0566, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Two-way feedback interactions persist between the soil microbiology and the carbon (C) geochemistry through C substrate-uptake preference and microbial utilization/transformation. Therefore, an understanding of how those continuously iterative processes influence soil microbial community and geochemical composition of soil organic matter is essential. However, finding direct correlations between the both has remained a challenge and been little explored. Here we show an unequivocal evidence that the forces structuring the soil microbial community and the organic geochemical composition of tundra soils differ. We determined soil microbial community and soil organic C (SOC) composition by four molecular-level techniques, i.e. DNA pyrosequencing and phospholipids fatty acid (PLFA) biomarkers for microbial analysis and solid-state 13C NMR spectroscopy and neutral sugars for SOC characterization for active-layer and permafrost. By independently summarizing explanatory structures of the relative abundance of microbial groups and soil C forms (using ordination and cluster analysis), we found that microbial community and the SOC chemistry were each consistently characterized by the two distinct measurement approaches. These methods identified distinct pattern differences between soil horizons (permafrost layer versus active organic layer) in both microbial community and the SOC. We used correlations to build the hypothesis about "decoupled connection between microbiology and SOC geochemistry", particularly of their non-linearity in tundra soils, and then to assess how the C decomposition rate constants (at 4°C) relate to those structural patterns. We demonstrate that the controls on soil microbial community structure are fundamentally different from those on substrate C composition within tundra soils, thus enriching our understanding of C biogeochemical cycling and associated microbial behaviors.
14076118 Lipson, D. (San Diego State University, San Diego, CA); Miller, K. and Lai, Chun-Ta. Methane suppression; the impacts of Fe(III) and humic acids on net methane flux from Arctic tundra wetlands in Alaska and Finland [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B32C-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic soils contain large reservoirs of carbon (C) that are vulnerable to loss from climatic warming. However the potential global impacts of this C depend on whether it is lost primarily in the form of methane (CH4) or carbon dioxide (CO2), two gases with very different greenhouse warming potentials. In anaerobic environments, the relative production of CH4 vs. CO2 may be controlled by the presence of alternative terminal electron acceptors, which allow more thermodynamically favorable anaerobic respiratory pathways to dominate over methanogenesis. This work investigated how the addition of terminal electron acceptors, ferric iron (Fe(III)) and humic acids, affected net CH4 fluxes from high-latitude wetland ecosystems. We conducted two manipulative field experiments in Barrow, Alaska (71°N) and Finnish Lapland (69°N). The ecosystem in Barrow was known from previous studies to be rich in Fe(III) and to harbor a microbial community that is dominated by Fe(III)--and humic acid-reducing microorganisms. The role of these alternative electron acceptors had not previously been studied at the Finnish site. CH4 and CO2 fluxes were measured using a portable trace gas analyzer from experimental plots, before and after amendments with Fe(III) (in the chelated form, ferric nitrilotriacetic acid), humic acids, or water as a control. Both in the ecosystem with permafrost and naturally high levels of soil Fe (Barrow, AK) and in the ecosystem with no permafrost and naturally low levels of soil Fe (Petsikko, Finland), the addition of the alternative electron acceptors Fe(III) and humic acids significantly reduced net CH4 flux. CO2 fluxes were not significantly altered by the treatments. The reduction in CH4 flux persisted for at least several weeks post-treatment. There was no significant difference between the reduction caused by humic acids versus that from Fe(III). These results show that the suppression of CH4 flux by Fe(III) and humic acids is a widespread phenomenon that could significantly alter the future release of greenhouse gases from high latitude wetland ecosystems, depending on how the availability of these alternative electron acceptors changes due to processes such as increased thaw depth, altered deposition patterns and climate-induced changes in soil organic matter quality and quantity.
14076103 Miller, Charles E. (California Institute of Technology, Jet Propulsion Laboratory, Pasadena, CA); Miller, John B.; Chang, Rachel Y.; Sweeney, Colm; Karion, Anna; Wofsy, S. C.; Henderson, J.; Eluszkiewicz, J.; Mountain, M. and Oechel, W. C. CARVE measurements of atmospheric methane concentrations and emissions in Arctic and boreal Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31I-05, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) is a NASA Earth Ventures (EV-1) investigation designed to quantify correlations between atmospheric and surface state variables for the Alaskan terrestrial ecosystems through intensive seasonal aircraft campaigns, ground-based observations, and analysis sustained over a 5-year mission. CARVE bridges critical gaps in our knowledge and understanding of Arctic ecosystems, linkages between the Arctic hydrologic and terrestrial carbon cycles, and the feedbacks from fires and thawing permafrost. We present CARVE airborne measurements of spatial and temporal patterns in atmospheric CH4 concentrations and estimated surface-atmosphere emissions for Arctic and Boreal Alaska. Continuous in situ CH4, CO2 and CO data are supplemented by periodic whole air flask samples from which 13CH4 and non-methane hydrocarbons are used to assess the relative contributions of wetlands, fossil fuel combustion, and oil and gas production to the observed CH4 signals. The CARVE project has also initiated monthly 14CH4 sampling at Barrow, AK (BRW) and the CARVE Tower in Fox, AK (CRV) to evaluate seasonal changes in the fraction of old carbon being mobilized via methanogenesis.
14076064 Moreaux, V. (San Diego State University, San DIiego, CA); Oechel, W. C.; Losacco, S.; McEwing, R.; Murphy, P. and Zona, D. CO2 and CH4 fluxes along a latitudinal transect in northern Alaska using eddy covariance technique in challenging conditions; first results of a long term experiment in the Arctic tundra [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B11H-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Being one of the most sensitive regions on earth, the Arctic is likely to be one of the most affected by global change. Physical changes (drying, snow cover, active layer depth, permafrost thawing, etc.) could create feedbacks in the release of greenhouse gas to the atmosphere. Correlated to the significant increase in air temperature, changes in trace gas balance have already been reported (Oechel et al. 1998). Carbon (C) is currently trapped as organic matter in the permafrost that underlies much of the Arctic. C represents about 30-50% of the global belowground organic carbon pool (Tarnocai et al.2009, Zona et al. 2012). Stored organic matter can form the substrate for significant release of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Ubiquitous arctic wetlands are additional sources of CH4 and CO2 to the atmosphere (Melton et al. 2013). CO2 is important because of the magnitude of its fluxes, and CH4 is of interest since its global warming potential is 23 times higher than the CO2 over a 100-year time horizon. CH4 is produced by the decomposition of dead plant material in anaerobic soils, especially in tundra ponds. Methane release is mostly influenced by temperature, water table, and active layer depth. The spatial and temporal variability results in very large uncertainties of current CH4 fluxes from the Arctic. The sporadic studies available create a generally inadequate baseline from which to determine a change in emissions from this critical and sensitive environment. Here we initiate a large scale, continuously monitored, study of CO2 and CH4 budgets from tundra ecosystems across a latitudinal gradient of more than 400 km. Our main questions for this study are: (i) does the release of CO2 and CH4 from biological and geothermal processes exceed the sink of greenhouse gases from active vegetation and surface organisms? (ii) How does this balance behave over latitudinal and environmental gradients? The observations presented are the result of the first year of a new long-term study that includes the results of the upgrading of 5 sites in Northern Alaska across a latitudinal transect (Barrow, Atqasuk, and Ivotuk) and across a moisture gradient (Barrow) in the Arctic. These sites are equipped with different eddy covariance systems to follow CO2 and CH4 fluxes, combined with a full data set of meteorological and soil measurements. The study summarizes a full analysis of energy balance, CO2 and CH4 fluxes correlated to changes in meteorological and soil conditions on the 5 sites of the transect. Based on the results available, CH4 fluxes averaged approximatively 8 mgC m-2 d-1 in the north (Barrow) to 13 mgC m-2 d-1 in the south (Ivotuk). In between these two sites, a daily value of about 20 mgC m-2 d-1 in the wetter, vegetated drained lake basin was observed. Surprisingly, from our preliminary data investigation, the southernmost and warmer site (Ivotuk) did not present the highest CH4 emission, which instead was the highest in the 200 km north site (Atqasuk) with a mean daily value of 25 mgC m-2 d-1. The importance of fall season CH4 emissions will also be presented and their importance relative to summertime emissions.
14076091 Rawlins, M. A. (University of Massachusetts, Amherst, Department of Geosciences, Amherst, MA). Changes in the carbon cycle of northern Eurasia simulated by process models [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B12D-07, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Pronounced warming across the northern high latitudes is impacting water and carbon cycles and raising concern over possible feedbacks to global climate. Recent model studied point toward a weakening of the terrestrial land carbon sink across the northern high latitudes, one notable manifestation of a warming Arctic. We explore links between regional climate and the carbon cycle using data from models participating in the Vulnerability of Permafrost Carbon Research Coordination Network (RCN). The domain of interest is the drainage basin within the Northern Eurasia Earth Science Partnership Initiative (NEESPI) region. Model outputs examined include gross primary production (GPP), heterotrophic respiration (RH), net ecosystem exchange (NEE), and total soil carbon storage. Mean flux budgets and their changes over the period 1960-2009 are calculated from the model estimates for the entire NEESPI region and for each major land cover category within the region. Use of an independent model, which captures well the spatial pattern in soil freeze/thaw dynamics, indicates that the reduction in permafrost extent over the NEESPI basin was 4-6% over recent decades. Modeled influences of permafrost thaw on the region's water and carbon cycles are evaluated in the context of recent measurements. Estimates of the flux of CO2 due to fire are also examined in order to better understand how these disturbances are altering regional carbon sink/source dynamics.
14076098 Romanovsky, V. E. (University of Alaska Fairbanks, Fairbanks, AK); Cable, W.; Walker, D. A.; Yoshikawa, K. and Marchenko, S. S. Last decade of changes in ground temperature and active layer thickness in the High Canadian Arctic and in Barrow [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31H-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The impact of climate warming on permafrost and the potential of climate feedbacks resulting from permafrost thawing have recently received a great deal of attention. Most of the permafrost observatories in the Northern Hemisphere show substantial warming of permafrost since circa 1980-1990. The magnitude of warming has varied with location, but was typically from 0.5 to 2°C. Permafrost is already thawing within the southern part of the permafrost domain. However, recent observations documented propagation of this process northward into the continuous permafrost zone. The close proximity of the exceptionally icy soil horizons to the ground surface, which is typical for the arctic tundra biome, makes tundra surfaces extremely sensitive to the natural and human-made changes that may resulted in development of processes such as thermokarst, thermal erosion, and retrogressive thaw slumps that strongly affect the stability of ecosystems and infrastructure. In 2003-2005, three Ecological Permafrost Observatories where established in the High Canadian Arctic (Green Cabin on the Banks Island, Mould Bay on the Prince Patrick Island, and Isachsen on the Ellef Ringnes Island) as a part of the University of Alaska Fairbanks NSF funded Biocomplexity Project. These observatories represent the northern part of the North American Arctic Transect (NAAT) established as a result of this project. The climatic and ground temperature data collected at these observatories show a general warming trend similar to what has been observed at the other locations in the North American Arctic. An important result of this resent warming is a significant increase in the active layer thickness (ALT) during the last decade. For example, ALT at the Isachsen observatory increased from 0.4-0.42 m in 2005 to 0.54 m in 2012. The maximum ALT of 0.58 m was recorded in 2008. In a shallow excavation across an ice wedge at the Isachsen site, we estimated that the top of the ice wedge ice was located at 42-45 cm from the ground surface in 2005. Increase in the active layer beyond this depth triggered the melting of the upper part of the ice wedges and widespread ground settlement at this location. In our presentation we will report on the observed changes in local topography in relation to changes in ground temperature and ALT at all three mentioned sites. In 2001, a Permafrost Observatory was also established within the Barrow Environmental Observatory in Barrow, Alaska under the auspices of the International Arctic Research Center of the University of Alaska Fairbanks. Since 2001, permafrost temperature at this depth increased by 0.5°C. Most of this increase happened after 2005. A site-specific numerical model for the Barrow permafrost temperature regime was developed in the GI Permafrost Lab. The daily air temperatures and snow cover thickness during the entire period of measurements (1924-2013) at the Barrow meteorological station were used as input data. Analysis of the resulting time series will be used in this presentation to reveal the effect of changes in air temperature and in snow depth on permafrost temperature and on the active layer thickness. This will help to put our decade-long observations along NAAT into a longer time perspective.
14076099 Stackhouse, B. T. (Princeton University, Geosciences, Princeton, NJ); Vishnivetskaya, T. A.; Layton, A.; Bennett, P.; Mykytczuk, N.; Lau, C. M.; Whyte, Lyle and Onstott, Tullis C. CO2, CH4, and DOC flux during long term thaw of High Arctic tundra [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31H-08, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic regions are expected to experience temperature increases of >4°C by the end of this century. This warming is projected to cause a drastic reduction in the extent of permafrost at high northern latitudes, affecting an estimated 1000 Pg of SOC in the top 3 m. Determining the effects of this temperature change on CO2 and CH4 emissions is critical for defining source constraints to global climate models. To investigate this problem, 18 cores of 1 m length were collected in late spring 2011 before the thawing of the seasonal active layer from an ice-wedge polygon near the McGill Arctic Research Station (MARS) on Axel Heiberg Island, Nunavut, Canada (N79°24, W90°45). Cores were collected from acidic soil (pH 5.5) with low SOC (~1%), summertime active layer depth between 40-70 cm (2010-2013), and sparse vegetation consisting primarily of small shrubs and sedges. Cores were progressively thawed from the surface over the course of 14 weeks to a final temperature of 4.5°C and held at that temperature for 15 months under the following conditions: in situ water saturation conditions versus fully water saturated conditions using artificial rain fall, surface light versus no surface light, cores from the polygon edge, and control cores with a permafrost table maintained at 70 cm depth. Core headspaces were measured weekly for CO2, CH4, H2, CO, and O2 flux during the 18 month thaw experiment. After ~20 weeks of thawing maximum, CO2 flux for the polygon edge and dark treatment cores were 3.0±0.7 and 1.7±0.4 mmol CO2 m-2 hr-1, respectively. The CO2 flux for the control, saturated, and in situ saturation cores reached maximums of 0.6±0.2, 0.9±0.5, and 0.9±0.1 mmol CO2 m-2 hr-1, respectively. Field measurements of CO2 flux from an adjacent polygon during the mid-summer of 2011 to 2013 ranged from 0.3 to 3.7 mmol CO2 m-2 hr-1. Cores from all treatments except water saturated were found to consistently oxidize CH4 at ~atmospheric concentrations (2 ppmv) with a maximum rate of -196±12 (dark) nmol CH4 m-2 hr-1. Saturated cores occasionally acted as slight CH4 sources (17±17 nmol CH4 m-2 hr-1) but were generally found to still behave as CH4 sinks (maximum rate -93±56 nmol CH4 m-2 hr-1). Dissolved CH4 in the permafrost pore water immediately upon thaw was ~0.5 mM in all treatments, and remained at this concentration in the saturated cores. In in situ water saturation treatments, however, pore water CH4 concentrations decreased from 0.6±0.3 mM to 0.2±0.1 mM over the course of three weeks without release into the core headspace. This is likely due to aerobic methanotrophy, as the concentration of genomic sequences associated with methanotrophic bacteria was found to be 30 times greater in the upper 60 cm than in the permafrost. Sustained concentrations of CH4 in the deeper portion of saturated cores indicated that methanogenesis is occurring at depths near and below the permafrost table. Measurements of in situ DOC were 0.22±0.05 mmol L-1, whereas core DOC values increased to a maximum of >1.7 mmol L-1 (primarily acetate) during the course of the thawing experiment. These findings indicate that in a warming Arctic, even under various hydrological regimes, these soil types will be able to act as a sink of atmospheric CH4, a moderate source of CO2 and a potential source for DOC.
14076142 Tas, N. (Lawrence Berkeley National Laboratory, Berkeley, CA); Wu, Y.; Smith, Lydia J.; Ulrich, C.; Kneafsey, T. J.; Torn, M. S.; Hubbard, S. S.; Wullschleger, S. D. and Jansson, J. R. Integrated metagenomics and field measurements of polygon features at the NGEE-Arctic Barrow site [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B33G-0563, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic soils contain an estimated 12-42% of terrestrial carbon, most of which is sequestered in permafrost. High latitudes have experienced the greatest regional warming in recent decades and observations suggest that permafrost degradation is now commonly observed in the region. With increasing global temperatures, permafrost soils are becoming a potential source of greenhouse gas (GHG) emissions. Because of widespread permafrost thaw much of the soil organic matter may be available for rapid mineralization by microorganisms in the soil. Yet little is known about the vulnerability of permafrost and the potential response of soil microorganisms to availability of new carbon sources. On the Alaskan North Slope the collapse and rise of soil due to formation of ice wedges and permafrost thaw create distinct features called polygons. As part of the U.S. Department of Energy (DOE) Next Generation Ecosystem Experiment (NGEE) in the Arctic, we aimed to determine the distribution of microbial populations across a range of polygon features and to correlate the microbial data to GHG flux data. To determine the microbial community distribution and metabolic potential, we collected seasonally thawed active layer soil samples along two polygon transects (Site 0 and AB), including high-centered, transitional and low-centered polygons. Illumina HiSeq technology was used to sequence 16SrRNA genes and metagenomes from these active layer soils. The sequence data was correlated to GHG flux measurements and to environmental data from the site, including geophysical and geochemical soil characteristics. Both the microbial communities and the flux measurements varied along the polygon transect. Each polygon had a distinct microbial community structure; however, these microbial communities shared many metabolic capabilities. For example, many genes involved in degradation of chitin could be found all three polygons. Functional genes involved in methanogenesis and CH4-flux measurements were higher in low centered and wetter polygons than high centered drier polygons. On the edges of polygons the microbial community compositions and flux data were indicative of CO2 production. The metagenome sequence data suggested that nitrate was utilized as a nitrogen source, but not lost through denitrification. The long-term goal is to use information gleaned from datasets to better inform climate models.
14076101 Laurila, Tuomas J. (Finnish Meteorological Institute, Climate Change Research, Helsinki, Finland); Aurela, Mika; Hatakka, Juha; Aalto, Tuula; Lohila, Annalea; Asmi, Eija; Kondratyev, V.; Ivakhov, V.; Reshetnikov, Alexander; Makshtas, A. P.; Dlugokencky, E. J. and Uttal, Taneil. Observations of atmospheric methane concentrations and sources at two supersites Tiksi, northern Siberia and Pallas-Sodankyla, northern Finland [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract B31I-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Arctic and Boreal regions are important in the global methane budget mainly because emissions are large from the extensive wetlands. Recently the potential for increased emissions from methane hydrates under sediments at the bottom of the Arctic Ocean has been recognized. Resource exploitation in the Arctic is expanding and includes gas and oil drilling. Together with climate warming, we may expect changes in methane emissions from high northern latitudes. The main tools to probe the effect of this development on atmospheric methane are atmospheric methane observations and local emission measurements by micrometeorological and chamber methods. To better understand emissions at small and large scales, so called supersites have been introduced. At these sites, both atmospheric concentrations and emissions from representative ecosystems, together with suite of other environmental information, are measured continuously. We are running two of these supersites: Pallas-Sodankyla in northern Finland and Tiksi in Siberia on the coast of the Laptev Sea. In spite of the fact that both sites are north of the Arctic Circle, environmental conditions differ very much. In northern Scandinavia, climate is relatively marine, and wetland methane emissions are active throughout the year. In continental Tiksi the active layer is 30-80 cm and methane emissions cease during the coldest months when soil temperature is close to -20°C. Air mass advection is either from continental Siberia or from the Siberian seas. Forest and tundra fires are relatively common. At Pallas, advection is from the forested boreal and industrialized areas of Europe or the Norwegian or Barents Sea. In this presentation, we show seasonal variations of atmospheric methane concentrations at World Meteorological Organization-Global Atmosphere Watch sites: Pallas-Sodankyla and Tiksi. Source areas have been analyzed by trajectories. The main sources of methane in Tiksi were wetlands and the Laptev Sea, which is oversaturated regarding methane. Concentrations and their variability were high in June-October due to terrestrial and marine emissions. Sea ice restricts marine emissions very much. Interesting periods were when the sea froze in October and when the ice melted in early July. Seasonal pattern of tundra methane emissions will be presented including growing season onset in June-July, high season in August and late season emission rates extending to winter. These will be compared to emission rates at typical northern boreal fens of the Pallas-Sodankyla site. It is expected that the Tiksi and Pallas-Sodankyla site will form the foundation for further pan-Arctic comparisons between the observatories in the IASOA consortium (www.iasoa.org).
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