C13B-0268 1340h
The Interaction Between Trends and Periodical Components in Air and Soil Temperature Time-Series Over the Asian Territory of Russia
We used Singular Spectrum Analysis (SSA) to detect trend and periodic components (rhythms) in annual and seasonal time series of surface air temperature (SAT) and of soil temperature (ST) at depths of 40, 160, and 320 cm, for the northern (to the north of the 60th latitude) and southern (to the south of the 60th latitude) parts of Western Siberian Plain, western and eastern parts of Central Siberian Plateau, Transbaikalia, and the territory located to the east of Lena River. We analyzed SAT data from 1902 to 1995 and ST data from 1960 to 1990. SSA-detected trends in the annual ST time series generally track trends detected in the annual SAT time series. They show a statistically significant increase in annual ST down to 320 cm for the Central Siberian Plateau, Transbaikalia, and south of Western Siberian Plain. The least soil warming between 1960 and 1990 is observed for the territory east of the Lena River. SSA-detected rhythms in the annual SAT and ST time series are coincident for the north of West Siberia Plain (7.7 years) and the western Central Siberian Plateau and Transbaikalia (2.7 years), and they are close but not coincident for eastern Central Siberian Plateau (4.7 and 4.3 years for SAT and ST, respectively). No coincident rhythms were found for the south of West Siberia Plain and territory located to the east of Lena River.For the majority of the study regions, winter, spring, and autumn ST tracked the 2- to 3-year periodic components of the corresponding SAT time series. Although summer ST over the Central Siberian Plateau and Transbaikalia coincides with the 5- to 7-year rhythms in the corresponding SAT, rhythms reconstructed in the annual ST time series are mainly coincident with those in the winter ST time series. Only winter ST over the western Central Siberian Plateau tracked the 9.8-year rhythms in the corresponding SAT time series. Trend and periodic components in the summer ST time series manifested themselves in annual ST time series only for the West Siberian Plain. This work was support by the North Atlantic Treaty Organization under a Grant awarded in 2003 (DGE-0312143), as well as NSF grants OPP-0229766 and OPP-0352910
C13B-0269 1340h
Mapping the Distribution of Seasonally Frozen Ground in the Northern Hemisphere
Seasonal freezing and thawing processes of soils have a great impact on surface energy balance, hydrological cycle, carbon exchange, and serious natural hazard at high latitudes. Areal extent of seasonally frozen ground is greater than any other major cryospheric components (such as seasonal snow cover, sea ice, permafrost, ice sheets, and glaciers). However, study on seasonally frozen ground has received little attention. We will give a brief review on study of seasonally frozen ground in the past decades. We will map annual distribution of seasonally frozen ground using annual freezing index of air temperature. Based on annual freezing index, we will estimate the potential maximum freezing depth at each grid pixel and areal extent of seasonally frozen ground in the Northern Hemisphere. We will further investigate inter-annual/inter-decadal variability of areal extent of seasonally frozen ground in the Northern Hemisphere. Annual freezing index of air temperature will be calculated based on daily ERA-40 reanalysis data. Over the contiguous United States, annual freezing index will also be calculated based on gridded daily air temperature using ground-based measurements. Comparison of the results from two data sets will be conducted to evaluate the accuracy of the ERA-40 reanalysis data over the contiguous United States and its applicability in the Northern Hemisphere.
C13B-0270 1340h
Monitoring Climate Variability and Change in Northern Alaska: Updates to the U.S. Geological Survey (USGS) Climate and Permafrost Monitoring Network
Observations of long-term climate and surficial geological processes are sparse in most of the Arctic, despite the fact that this region is highly sensitive to climate change. Instrumental networks that monitor the interplay of climatic variability and geological/cryospheric processes are a necessity for documenting and understanding climate change. Improvements to the spatial coverage and temporal scale of Arctic climate data are in progress. The USGS, in collaboration with The Bureau of Land Management (BLM) and The Fish and Wildlife Service (FWS) currently maintains two types of monitoring networks in northern Alaska: (1) A 15 site network of continuously operating active-layer and climate monitoring stations, and (2) a 21 element array of deep bore-holes in which the thermal state of deep permafrost is monitored. Here, we focus on the USGS Alaska Active Layer and Climate Monitoring Network (AK-CLIM). These 15 stations are deployed in longitudinal transects that span Alaska north of the Brooks Range, (11 in The National Petroleum Reserve Alaska, (NPRA), and 4 in The Arctic National Wildlife Refuge (ANWR)). An informative overview and update of the USGS AK-CLIM network is presented, including insight to current data, processing and analysis software, and plans for data telemetry. Data collection began in 1998 and parameters currently measured include air temperature, soil temperatures (5-120 cm), snow depth, incoming and reflected short-wave radiation, soil moisture (15 cm), wind speed and direction. Custom processing and analysis software has been written that calculates additional parameters such as active layer thaw depth, thawing-degree-days, albedo, cloudiness, and duration of seasonal snow cover. Data from selected AK-CLIM stations are now temporally sufficient to begin identifying trends, anomalies, and inter-annual variability in the climate of northern Alaska.
C13B-0271 1340h
The influence of long-term changes in snow cover on the ground thermal regime: Implications for borehole climatology
In the past decades it has been widely recognized that geothermal data can provide complimentary information to the meteorological records of past long-term ground surface temperature (GST) trends. The inversion methods used to retrieve the climatic signal from subsurface temperatures assume a direct coupling between the surface air temperature (SAT) and GST. Because snow cover insulates the ground in the winter, systematic and persistent variations of snow cover could alter the air-ground temperature coupling and complicate the reconstruction of GST histories. We used a one-dimensional, finite differences heat transfer model with phase changes to carry out a series of synthetic simulations to examine the effect of long-term variations of the snow-cover thickness and of the snow-cover duration. Results indicate that long-term changes in snow cover can have a significant effect on ground temperatures. For seasonal frost cases, we find that GST can change by 1.5 K if the snow-cover thickness is increased by 1cm/year over a period of 200 years. A change in the snow-cover duration of 1day/decade for a period of 200 years can potentially alter the GST by 0.5 K. In areas of permafrost with similar variations in snow-cover thickness and duration, the ground surface temperatures can change much more. We find that critical depths of snow thickness are about 70 cm and 130 cm for the seasonal frost and permafrost cases respectively. Increasing the snow-cover thickness beyond these values has no significant effect on the GST. Our model suggests that for a constant annual SAT the Canadian regional snow trends of the last 50 years (www.socc.ca) would induce GST decreases of 0.5 K and 0.7 K in eastern and western Canada respectively for cases with seasonal frost and permafrost. This cooling is mainly due to a decrease in snow cover. In parts of Atlantic Canada and Nunavut, where snow trends have increased in the last 50 years, GST are warmer by 0.1K and 0.4 K respectively. If we include western and eastern Canada SAT trends in the above experiment, results show that the GST decreases by 0.5 K even though the SAT increased by 0.5 K during the past 50 years. In parts of Atlantic Canada, although the air temperature decreased by 0.4 K in the past 50 years, our model shows a GST increase of 0.2 K under the influence of an increasing snow cover. Our results suggest that changes in snow cover alone can alter the temperature of the ground. Lower or higher GST are likely a coupled response to the variation in snow cover and to changes in SAT. Early snow melt may be a significant contributor to the warming of the permafrost area. Although long-term snow cover data are few in Canada, century-long trends do not appear significant. However, the trends of the last 50 years could potentially create subsurface transients and should be considered in the reconstruction of past climatic changes from geothermal data.
C13B-0272 1340h
Climatic Impacts of Snow Depth Anomalies over Frozen Ground
Frozen ground may be overlain by snow cover of varying thickness, or in the case of seasonally frozen ground may be at times snow-free. Anomalous snow cover is known to suppress local surface temperatures, and it is commonly presumed that the higher (lower) albedo associated with the presence (absence) of snow is primarily responsible for this response. In this study, numerical general-circulation model experiments are performed to investigate the atmospheric response to snow presence vs. snow depth anomalies, and the relevant surface thermodynamic processes involved. Results indicate that snow depth anomalies and associated insulative properties of the snowpack (e.g., thermal conductivity and latent heat flux) suppress local temperatures to an extent comparable to the snow presence / albedo mechanism. Furthermore, we find that realistic, continental-scale snow presence and snow depth anomalies acting in conjunction can not only suppress local temperatures, but can also produce a hemispheric-scale climate system response. The specific influence of snow depth anomalies on local and regional climate adds new insight to our understanding of the climatic impacts of changes in frozen ground, especially in permafrost regions where snow depth anomalies are more likely than snow presence anomalies.
C13B-0273 1340h
Temperature Inversions and Permafrost Distribution in a Mountain Valley: Preliminary Results From Wolf Creek, Yukon Territory, Canada
The BTS (Basal Temperature of Snow) method to predict permafrost probability in mountain basins uses elevation as an easily available and spatially distributed independent variable. The elevation coefficient in the BTS regression model is, in effect, a substitute for ground temperature lapse rates. Previous work in Wolf Creek ($60\deg$8'N $135\deg$W), a mountain basin near Whitehorse, has shown that the model breaks down in a mid-elevation valley (1250 m asl) where actual permafrost probability is roughly twice that predicted by the model (60% vs. 20-30%). The existence of a double tree-line at the site suggested that air temperature inversions might be the cause of this inaccuracy (Lewkowicz and Ednie, 2004). This paper reports on a first year (08/2003-08/2004) of hourly air and ground temperature data collected along an altitudinal transect within the valley in upper Wolf Creek. Measurements were made at sites located 4, 8, 22, 82 and 162 m above the valley floor. Air temperature inversions between the lowest and highest measurement points occurred 42% of the time and in all months, but were most frequent and intense in winter ($>$60% of December and January) and least frequent in September ($<$25% of time). They generally developed after sunset and reached a maximum amplitude before sunrise. Only 11 inversions that lasted through more than one day occurred during the year, and only from October to February. The longest continuous duration was 145 h while the greatest inversion magnitude measured over the 160 m transect was $19\deg$C. Ground surface temperatures are more difficult to interpret because of differences in soils and vegetation cover along the transect and the effects of seasonal snow cover. In many cases, however, air temperature inversions are not duplicated in the ground temperature record. Nevertheless, the annual altitudinal ground temperature gradient is much lower than would be expected from a standard atmospheric lapse rate, suggesting that the inversions do have an important impact on permafrost distribution at this site. More generally, therefore, it appears probable that any reduction in inversion frequency resulting from a more vigorous atmospheric circulation in the context of future climate change, would have a significant effect on permafrost distribution in mountain basins.
C13B-0274 1340h
Preliminary field investigations and findings of thermokarst evolution and sediment transport in a sub-arctic watershed
The rapid thermokarst development in the Caribou Poker Creeks Research Watershed is a relatively new feature in this predominantly discontinuous permafrost region. The thermokarst was initiated by permafrost degradation and precipitated primarily by the rain event that occurred in July 2003. Initial results of a field study on the thermokarst evolution and sediment transport are presented here. The rapid morphologic changes have been observed by comparing topographical surveys carried out during two consecutive summer seasons. Groundwater flow from ground ice thaw coupled with summer precipitation has led to an enormous amount of sediment being transported from the upstream end of the thermokarst to a considerable distance downstream of the site. However, liquid discharge measurements at the input and downstream locations show a loss in the discharge, suggesting a complex network for the transport of water and sediment within the active layer. Preliminary data on suspended sediment concentration indicate that higher sediment transport occurs during and after rainfall events with infilling of the thermokarst by sedimentation to a depth of 18 inches in the downstream reaches. The high sediment transport is a clear indication that erosion of the area is an active and ongoing process. It shows the extreme sensitivity of permafrost to climate induced surface modifications.
C13B-0275 1340h
Influence Of Clear-cutting On Thermal and hydrological Regime In The Active Layer Near Yakutsk, Eastern Siberia
Thermal and hydrological conditions in the active layer were investigated simultaneously at a mature larch forest (control site) and a cutover, which experienced clear-cutting in November 2000 during the thawing periods from 2001 to 2003, near Yakutsk, Eastern Siberia. The two sites were located about 100m apart and the cutover was formerly a part of the control larch forest site. The aims were to clarify the characteristics of heat and water budget in the active layer, and to assess the influence of clear-cutting on permafrost and active layer conditions, based on field observations at both intact and clear-cut forest. Clear-cutting enhanced ground thawing and the difference in the active layer thickness between the forest and the cutover (1-year) was 14cm. The soil water content drastically decreased at the forest, while that at the cutover was retained in during the first thawing season after clear-cutting. Marked changes in the active layer conditions were limited only to the first thawing season. The difference in the maximum thaw depth did not expand significantly in the second thawing season despite the increased ground heat flux at the cutover site. Thermal and hydrological analyses of the active layer revealed that the storage of latent heat was a predominant component in the energy balance in the active layer. Thus, the soil moisture condition, especially spring ice content in the active layer, plays an important role in controlling the energy balance of the active layer. Further increases in the maximum thaw depth at the cutover site were inhibited by the thermal inertial effect of the larger amount of ice in the second spring after disturbance.
C13B-0276 1340h
Soils, Permafrost, Fires and Climate Change Impacts
One of the main soil forming factors is climate and in a world that is facing a changing climate in what many refer to as the Antropocene Era humans have gone from having no significant impact on the climate to an era where they may be one of the major drivers. Many of the Global Climate Models (GCMs) suggest the greatest change in temperature will occur at the high latitudes and this is expected to have a major impact on the soils and the permafrost within these regions. This summer Alaska had more fires than in recent history resulting in the largest number of acres ever burned. With regards to soils the hottest fires were on sandy soils where the organic layer was the driest. As the climate warms the organic layer even on areas with permafrost close to the surface will dry more and the intensity of fires will increase in larger and larger areas. Fire has always been part of the natural ecosystem in Alaska but more intensive fires over larger areas may well have a negative impact on the soils and the underlying permafrost. The organic layer is the insulation that helps maintain the permafrost. Once there is a burn the active layer goes deeper. In an area burned in June 2004 and sampled in August 2004 the difference in the active layer was very evident, in the burned area the active layer was about 70 cm and in an adjacent unburned area the active layer was only about 30 cm. Soils (Pedosphere) are where the Cryosphere meets the other spheres, they are the area that will be immediately susceptible to change and changes to the soils will have a major impact on the Cryosphere.
C13B-0277 1340h
Potential Impacts of Increased Thermokarst Activity on Aquatic Ecosystems in Arctic Landscapes
Recent observations suggest that thermokarst formation has increased in the area near the Toolik Lake Field Station in the foothills region of the Brooks Range on the North Slope of Arctic Alaska. This area has been the subject of continuous observation and research since the early 1970's and few thermokarsts had been observed here until the last few years. In August 2003 a thermokarst formed catastrophically on a slope in the headwaters of the Toolik River after an intense rainfall in the area. The mode of failure was unusual. The area lies in a region with silt-rich deposits which apparently also contain extensive ice wedges. Prior to the hillslope failure, a large ($\sim$ 0.75 m x 2 m) tunnel formed $\sim$1 m below the surface, extending at least 50 to 100 m down slope. The initial failure occurred when the roof of this tunnel collapsed. Subsequently, peat and soil continued to erode from the site leading to a displacement of $\sim$4000 m $^{3}$ of sediment by August 2004. Macronutrients (in particular NH $_{4}$ and PO $_{4}$) and suspended sediments in the water draining the thermokarst have increased by 1 to 2 orders of magnitude. The impacts of this thermokarst formation on aquatic ecosystems are uncertain. On the one hand, our previous research has shown that even minor increases in nutrient loading (especially PO $_{4}$) stimulate primary and secondary production in these streams. However, the massive increase in sediment loading could smother benthic communities and negate the positive impacts of increased nutrient delivery. We have calculated that the mass of sediment mobilized by this individual failure is sufficient cover a 20 to 40 km length of the river with sediment to a thickness of 0.5 cm. During the 2004 field season we noted at least 2 new thermokarsts with failure modes similar to the one observed in 2003 along with numerous slip failures. Although the terrestrial area impacted by these thermokarsts is limited, the aquatic habitat altered by these failures is extensive. It is likely that warming in the Arctic foothills region will lead to additional and perhaps accelerated thermokarst formation which may have considerable impacts on aquatic ecosystem over wide areas and at least decadal time scales.
http://cc.usu.edu/~gooseff/arctic_proj.html
C13B-0278 1340h
The North Slope of Alaska and Tourism: Potential Impacts on the Arctic National Wildlife Refuge (ANWR)
The hydrocarbon industry of Alaska is currently the leading producer of revenue for the Alaskan state economy. Second only to hydrocarbons is the tourism industry. Tourism has been a viable industry since the 1890's when cruises touted the beauty of glaciers and icebergs along the Alaskan coastline. This industry has seen a steady growth for the past few decades throughout the state. The North Slope of Alaska, particularly Prudhoe Bay and the National Petroleum Reserve, has long been associated with hydrocarbon development and today displays a landscape dotted with gravel drill pads, gas and oil pipelines and housing for the oil workers. While tourism is not usually considered hand in hand with the hydrocarbon industry, it has mimicked the development of hydrocarbons almost since the beginning. Today one not only sees the effects of the oil industry on the North Slope, but also the tourist industry as planes unload dozens of tourists, or tour buses and private vehicles arrive daily via the Dalton Highway. In Deadhorse, hotels that once only housed the oil workers now welcome the tourist, offering tours of the oil fields and adjacent areas and have become jumping off sites for wilderness trips. Tourism will create jobs as well as revenue. However, at present, there are few restrictions or guidelines in place that will deal with the potential impacts of increased tourism. Because of this there are many concerns about the possible impacts tourism and the infrastructure development will have on the North Slope. To list several concerns: (1) What are the impacts of increased tourism and the infrastructure development? (2) What will the impacts be on the Arctic National Wildlife Refuge (ANWR), which sits a mere 60 miles to the east of Deadhorse? (3) Will hydrocarbon development in ANWR and the associated infrastructure exacerbate potential impact by encouraging greater use of the Refuge by tourists? (4) Will tourism itself have a negative impact on this fragile environment? Safeguarding the fragile environment of ANWR and for that matter all of the North Slope for future generations will require that all types of environmental impacts are carefully considered. The majority of this region is underlain by permafrost and is at risk because of possible global warming coupled with infrastructure development, tourism and potential hydrocarbon development.
C13B-0279 1340h
Time lapse imaging of thaw-bulb development beneath arctic streams using ground-penetrating radar
We are investigating the responses of arctic tundra stream geomorphology, hyporheic zone hydrology, and biogeochemical cycling to climate change. Field results from summer, 2003, demonstrate that GPR is an effective tool for imaging the depth to sub-stream permafrost. The results presented here are the next step in the use of ground-penetrating radar (GPR) data for measuring sub-stream thaw over the summer season. We acquired a series of GPR profiles at seven sites from May - September, 2004, using 100, 200, and 400 MHz antennas. We selected sites with the objective of including stream reaches spanning a range of geomorphologic conditions in rivers and streams on Alaska's North Slope. Generally the streams can be placed into two categories: 1) as low-energy water flow with organic material lining the streambeds (peat streams) or 2) as high-energy water flow with cobble to gravel material lining the streambeds (alluvial streams). We acquired data using a pulsed radar system with high-power transmitter. Early in the field season we used the 400 and 200 MHz antennas to maximize resolution potential, then gradually shifted to the lower frequency 100 MHz antennas later in the season to increase depth of penetration. We placed the radar antennas in the bottom of a small rubber boat, then pulled the boat across the bank and through the stream while triggering at a constant interval via a string odometer system. Depth to permafrost was verified by pressing a metal probe through the active layer to the point of refusal. In addition, we recorded temperature data using thermocouples placed at varying substream depths along two of the seven GPR profiles. We used the temperature profiles to constrain and verify the GPR interpretation. At several sites we obtained excellent results and have produced images of thaw-bulb growth through the summer season in both alluvial and peat stream morphologies.
C13B-0280 1340h
Active Layer Thermal Response to Stream Water Temperatures
The hyporheic zone is comprised of sediments below and adjacent to a stream through which stream water flows in and out. In polar regions, the shape, dimensions, physical and chemical characteristics of this zone are affected by the seasonal freezing and thawing of the active layer. One factor that may influence the active layer temperature regime is stream water temperature, both its absolute value and cyclic variations in its value. Many of the glacial meltwater streams in Taylor Valley in the McMurdo Dry Valleys of Antarctica, exhibit daily temperature patterns with lows of 0 or $1\deg$C and highs of 10 or, on occasion, $15\deg$C. Because the viscosity of water decreases significantly with increasing temperature, these daily maxima may increase infiltration and the exchange of water and heat between the stream and the hyporheic zone. To investigate the influence of stream water temperature and flow paths on the active layer temperature regime and vice versa, two conservative tracer injection experiments were conducted. Both took place in the same 200-meter reach, which was instrumented with temperature and conductivity probes. Both also took place at the same time of day during which the stream reaches its temperature maximum. However, in one experiment snow from a nearby patch was added to the stream to suppress the temperature maximum by 3$\deg$C from 10 to $7\deg$C. The temperature data show that the snow addition slowed the rate of hyporheic zone warming and suppressed temperature increases in the hyporheic zone by 1-3$\deg$C when compared with the non-perturbation experiment. The electrical conductivity data indicate that during the snow addition experiment, the stream neither gained nor lost water while during the non-perturbation experiment, the stream lost water. These results suggest that the stream water cooling decreased infiltration and heat transfer into the hyporheic zone.
C13B-0281 1340h
The Nines Creek Ice and Rock Avalanche: an Example of the Impact of Climate Change on Catastrophic Geomorphic Processes in the Kluane Ranges, Yukon Territory, Canada
Detailed field investigations of an exceptionally large ice and rock avalanche deposit were undertaken to characterise the cause, behaviour, and impacts of the failure. Distinguishing features of the deposit include a general paucity of matrix material, a high concentration of large boulders along the periphery and at the toe of the deposit, and virtually ubiquitous perched clasts and boulders. The failure had an exceptionally long runout distance (H/L= 0.31), transporting several boulders larger than 50 m3 a distance of up to 1.8 km. The largest intact boulder at the toe of the fan was 250 m3. Plough marks made by boulders and large ice blocks that have since melted are traceable for nearly 40 m in aerial photographs. Arcuate push ridges, developed in the terminal zone, show evidence of both shearing and folding of the pre-existing soil. Calving of a hanging glacier initiated the avalanche. A portion of the glacier detached and dropped down a 200 m high near-vertical basalt cliff, entraining massive blocks of bedrock in the process. Below the cliff, the ice fragments and rock debris travelled 1100 m over a valley glacier to a 165 m wide constriction in the valley bottom. The mass then travelled up to 600 m further, spreading out over the low-angled glacier fore-field with an average slope of 10 degrees. The deposit covers an area totalling 0.4 km2. The event was likely seismically triggered by a M 5.2 earthquake that occurred in June 1995, during the same week as the failure. Repeated aerial photography of the site, however, indicates that glacial recession and thinning had taken place for at least five decades prior to the failure and is likely an important pre-condition for the initial ice collapse. The results of this study distinguish the deposit from other types of debris accumulations, and highlight a rarely documented climate change related glacier hazard with potential to damage infrastructure in the northern Cordillera.
C13B-0282 1340h
A coupled thermo-mechanical model of the differential frost heave
Research investigates cryoturbation processes in the Arctic tundra, and mechanisms that cause differential frost heave in the active layer. The project explores the influence of seasonal freeze/thaw cycles on the dynamics of frost boils north of the Alaska's Brook Range. The main question to be addressed is, "How changes in surface conditions such as vegetation, snow cover and climate affect the seasonal dynamics of water and heat within frost-boil systems?" A coupled thermo-mechanical model of the frost boil phenomena based on principles of thermodynamic equilibrium and continuum mechanics will be presented. The soil is treated as a heterogeneous fully saturated mixture of ice, water and soil particles, which obeys laws of elasticity for slow deformations in a porous media. The pore water migration towards the freezing zone and its consequent freezing are the main driving forces of the soil deformation. The model includes the heat and mass conservation laws, continuity equation, the Claiperon equation, and an empirical formula, which relates unfrozen water content to temperature. The basic system of equations is reduced to a computationally convenient set of coupled equations for temperature, liquid water pressure, porosity, and the velocity of soil particles in a three-dimensional domain with an assumption of cylindrical symmetry. A finite element method and an implicit scheme in time are utilized to construct a non-linear system of equations, which are solved iteratively.
http://www.gi.alaska.edu/snowice/Permafrost-lab/
C13B-0283 1340h
Preliminary Hyperspectral Land Cover Classification of the Alaskan Arctic Coastal Plain- Application to Landscape Chronologies and the Thaw-Lake Geomorphic Cycle
Georeferenced ground- and helicopter-acquired spectral libraries have been assembled for a variety of vegetation and other land cover types related to drained thaw lake basins on the Arctic Coastal Plain of Alaska between Barrow and Atqasuk. Challenging illumination conditions and resulting low signal-to-noise ratios in the short wave infrared (SWIR) portion of the spectrum have persuaded us to focus our efforts on the visible and near infrared (VNIR) parts of the spectrum. Preliminary supervised classifications of atmospherically corrected VNIR hyperspectral Hyperion imagery from the EO-1 satellite with ground- and helicopter-acquired training spectra show generally good agreement with ground truth observations of vegetation with some exceptions. The supervised classifications of Hyperion imagery are particularly useful in the search for recently drained thaw lake basins, and for some key vegetation types usually associated with specific age-related stages in basin vegetation succession. Comparison of ground- and helicopter-acquired training spectra illustrate significant differences associated with spatial scaling issues and the need for hyperspectral spectral resolution. For example, some of the oldest geomorphic surfaces have some of the highest helicopter-acquired Normalized Difference Vegetation Index (NDVI) values due to absorption of red wavelengths by water in well-developed ice-wedge troughs despite relatively modest near infrared (NIR) reflectance values. Helicopter-borne NDVI measurements of these older surfaces are similar to those of recently drained thaw-lake basins. However, map view outlines of the older and irregular high NDVI surfaces are quite different from those of the younger high NDVI surfaces, which are usually similar to recently drained thaw lakes. These observations suggest that the most effective methods for tundra land cover classification with regard to the thaw lake geomorphic cycle will probably be hybrid methods that combine hyperspectral and textural classifications at relatively high (sub-5-meter) spatial resolutions.
C13B-0284 1340h
Paleoecological Studies From Peatlands on the Arctic Coastal Plain of Alaska
The dominant landscape process on the Arctic Coastal Plain of northern Alaska is the formation and drainage of thaw lakes. Lakes and associated drained thaw-lake basins account for approximately 75% of the modern surface expression of the Outer Coastal Plain. Drained thaw-lake basins are wet depositional environments well suited for accumulation preservation of organic carbon and pollen in peat deposits. However, the paleoclimatic record is limited to the period since lake drainage and subsequent revegetation, and the primary signal records local plant succession. In contrast, uplands represent regions that have escaped the effects of thaw lake processes. Analyses of records from these sites demonstrate the response of vegetation to both regional and local change, and can be used to reconstruct temporal patterns of carbon sequestration during the Holocene. Regional geomorphic processes operate across several spatial and temporal scales, modifying local expression of the vegetation and altering rates of carbon and nutrient cycling. Local vegetation succession, soil development, and cryogenic processes may not be directly linked to climatic change, but the regional patterns of edaphic and geomorphic processes in varied settings can lead to an integrated understanding of past climatic influences. This research demonstrates that sensitive records of past landscape change on the Arctic Coastal Plain are obtainable, and that we can differentiate between local landscape processes and climate change effects.
http://www.geography.uc.edu/~kenhinke/dtlb/
C13B-0285 1340h
Peatland Carbon Accumulation in West Siberia Over the Last 2,000 Years
The peatlands of the West Siberia Lowland (WSL) are of global significance owing to the massive carbon (C) stocks they hold (70 Pg C) and their location at the focus of both observed and predicted Arctic warming. Greater understanding of the potential warm-climate sensitivity of northern peatlands using paleoecological approaches is limited by past large shifts in hydrology and plant communities, as well as large temperature and moisture changes over the course of the Holocene (today's peatlands and climate are different than their mid-early Holocene counterparts). Therefore, we investigated the last 2,000 years to identify baseline peat C accumulation rates and behavior more relevant to the modern WSL. We identified the 2,000-year-old level in 21 peat cores from across the WSL (57-68\deg N) via successive $^{14}$C-AMS radiocarbon age determinations of specific plant fragments. Peat organic C content at 2-10 cm resolution in each core was calculated from ash-free bulk density and a mean C content of peat organic matter (52%). Over the last 2,000 years, 11 northern WSL cores (north of 63\deg N) accumulated 12-58 cm peat (7-33 kg C m$^{-2}$, or 5-32% total C per core) and 10 southern WSL cores (south of 63\deg N) accumulated 63-258 cm peat (23-56 kg C m$^{-2}$, or 14-70% total C per core). Mean net C accumulation, incorporating slow decomposition losses (0.00002 yr$^{-1}$), in southern WSL cores was about twice that of northern WSL. We calculated the apparent rate of Holocene C accumulation for each core using 21 $^{14}$C-AMS radiocarbon ages of basal bulk peat. Long-term Holocene apparent rates show no relationship with apparent rates over the last 2,000 years. More than half the cores show slower recent rates, including some southern cores. Overall, these results show that net atmospheric C sequestration in WSL over the last two millennia has been spatially disproportionate: sequestration has slowed substantially from mid-early Holocene rates in the north, and shows significantly stronger C sink with decreasing latitude in the south. Our findings suggest that concentrating on C accumulation trends over recent millennia is the best paleoecological approach to identify the spatial nature of modern long-term terrestrial C sinks.
C13B-0286 1340h
Saalian to Holocene Paleoenvironmental History Documented in Permafrost Sequences of Arctic Siberia (New Siberian Archipelago, Bolshoy Lyakhovsky Island)
Permafrost sequences exposed at the coast of the southernmost New Siberian Island are studied multidisciplinary by a Russian-German team using cryolithology, sedimentology, geochronology, geochemistry of ground ice, and bioindicators. The oldest horizon contains remains of a periglacial reworked Palaeogene weathering crust as proved by the occurrence of weathering products like kaolinite and montmorillonite. Separate epigenetic ice wedges and the absence of bio-indicators also characterize this horizon. Saalian climate fluctuations are documented in two sedimentological units formed c. 200-120 ky ago. The lower unit (c. 200-170 ky) is very ice-rich and contains large ice wedges. Cryolithologically it is similar to the Late Pleistocene deposits of the so-called Ice Complex. The lower part of this unit contains pollen assemblages of sparse grass-sedge vegetation and reflects stadial environment. The upper part of this ice-rich unit is characterized by pollen spectra of dense grass-dominated tundra reflecting interstadial conditions. This Saalian Ice Complex deposits were eroded and covered by a younger Saalian unit (c. 170-120 ky). Well-sorted fine-grained sand contains less ground ice and pollen spectra of sparse grass-sedge dominated vegetation assigned to a Late Saalian Stadial. The accumulation of these loess-like floodplain and lake deposits, and the formation of ice wedge polygon systems took place under extremely cold and dry conditions. The following unit, assigned to the Eemian Interglacial, contains large ice wedge casts with many paleoecological evidences of interglacial environment. Humid and warm conditions resulted in thawing of ice wedge systems and the formation of ice wedge casts and thermokarst lakes. Subsequently, the permafrost sequences were locally eroded down to the old Ice Complex deposits. Lacustrine and loess-like floodplain deposits with ice wedge polygon systems were accumulated again during the Early Weichselian stadial (c. 100-50 ky) under extremely cold and dry conditions. They consist of fine-grained, well-sorted sands with rare grass and sedge pollen. These deposits turn gradually into an about 20 m thick ice-rich Late Weichselian Ice Complex horizon, dated 50-28 ky BP and containing the pollen spectra of typical mammoth tundra-steppe associations. The Ice Complex contains big ice wedge polygon systems. It represents a swampy, poorly drained habitat, which existed under extreme continental climate. Whereas peaty deposits of the Middle Weichselian Interstadial (c. 40-30 ky BP) occur regularly, Late Weichselian Stadial sequences were not found. The Ice Complex deposits appear to be eroded during that time and covered by Late Glacial/Holocene deposits afterwards. Active thermokarst processes during the Late Pleistocene/Holocene transition (c. 12-10 ky BP) resulted in the formation of large thermokarst depressions. New ice wedge polygon systems were formed during the Late Holocene climate deterioration. The Late Pleistocene/Holocene transition, including the Aller\o d warming and Younger Dryas cooling events, is preserved within lacustrine thermokarst deposits in a thermokarst depression flanking the Late Weichselian Ice Complex sequences.