Thermokarst Activity Research Articles

Carbon stock estimation and changes associated with thermokarst activity, forest disturbance, and land use changes in Eastern Siberia

This study was conducted to evaluate the change in total soil carbon [TSC = litter carbon (LIC) + soil organic carbon (SOC) + soil carbonate carbon (SCC)] associated with recent thermokarst activity and forest disturbance induced by the climate change and land use change in the permafrost-affected soils of Eastern Siberia. TSC stock from 80 sites in three types of the ecosystem: forests, arable land, and thermokarst were analyzed. The SOC content was positively correlated with root C density in all ecosystems. In the forest and arable land ecosystems, soil texture strongly affected SOC content, but water content was the main factor in SOC accumulation in the thermokarst ecosystem. Although the composition ratio of TSC stock significantly differed among the ecosystem, SOC was the main component of the TSC in all ecosystems. SOC and TSC stocks in thermokarst ecosystem (137.1 ± 125.5 Mg SOC ha−1 30 cm−1 and 150.5 ± 123.9 Mg TSC ha−1 30 cm−1) were significantly higher than those in the forest (28.3 ± 13.5 Mg SOC ha−1 30 cm−1 and 51.4 ± 20.9 Mg TSC ha−1 30 cm−1) and arable land ecosystem (41.9 ± 16.9 Mg SOC ha−1 30 cm−1 and 54.6 ± 23.1 Mg TSC ha−1 30 cm−1), suggesting that thermokarst formation accumulates C. In the thermokarst ecosystem, significantly higher SOC stock was observed in moderately-wet and wet grassland than dry grassland suggesting that flooding increases C by suppressing organic matter decomposition. Among the forest ecosystem, forest disturbance significantly altered the C balance. Forest fire did not change the SOC and SCC stock but significantly burned the LIC stock at an average rate of 51.7 ± 65.0% of the LIC. Water damage to the forest significantly increased the SOC stock by increasing the water content, but 58.5 ± 62.4% of the LIC stock was dismissed. Forest cultivation significantly reduced TSC stock at an average rate of 37.3 ± 47.2% by mineralization of the LIC. On the other hands, abandonment of arable land significantly restored TSC stock at an average rate of 92.4 ± 83.5% by increasing C input. This study revealed that redistribution of the C stock has been occurred under the climate change and human activity.

Minor contribution of small thaw ponds to the pools of carbon and methane in the inland waters of the permafrost-affected part of the Western Siberian Lowland

Despite the potential importance of small (< 1000 m2) thaw ponds and thermokarst lakes in greenhouse gas (GHG) emissions from inland waters of high latitude and boreal regions, these features have not been fully inventoried and the volume of GHG and carbon in thermokarst lakes remains poorly constrained. This is especially true for the vast Western Siberia Lowland (WSL) which is subject to strong thermokarst activity. We assessed the number of thermokarst lakes and their size distribution for the permafrost-affected WSL territory based on a combination of medium-resolution Landsat-8 images and high-resolution Kanopus-V scenes on 78 test sites across the WSL in a wide range of lake sizes (from 20 to 2 × 108 m2). The results were in fair agreement with other published data for world lakes including those in circum-polar regions. Based on available measurements of CH4, CO2, and dissolved organic carbon (DOC) in thermokarst lakes and thaw ponds of the permafrost-affected part of the WSL, we found an inverse relationship between lake size and concentration, with concentrations of GHGs and DOC being highest in small thaw ponds. However, since these small ponds represent only a tiny fraction of the landscape (i.e. ~1.5% of the total lake area), their contribution to the total pool of GHG and DOC in inland lentic water of the permafrost-affected part of the WSL is less than 2%. As such, despite high concentrations of DOC and GHG in small ponds, their role in overall C storage can be negated. Ongoing lake drainage due to climate warming and permafrost thaw in the WSL may lead to a decrease in GHG emission potential from inland waters and DOC release from lakes to rivers.

Accelerating Thermokarst Transforms Ice‐Cored Terrain Triggering a Downstream Cascade to the Ocean

AbstractRecent climate warming has activated the melt‐out of relict massive ice in permafrost‐preserved moraines throughout the western Canadian Arctic. This ice that has persisted since the last glaciation, buried beneath as little as 1 m of overburden, is now undergoing accelerated permafrost degradation and thermokarst. Here we document recent and intensifying thermokarst activity on eastern Banks Island that has increased the fluvial transport of sediments and solutes to the ocean. Isotopic evidence demonstrates that a major contribution to discharge is melt of relict ground ice, resulting in a significant hydrological input from thermokarst augmenting summer runoff. Accelerated thermokarst is transforming the landscape and the summer hydrological regime and altering the timing of terrestrial to marine and lacustrine transfers over significant areas of the western Canadian Arctic. The intensity of the landscape changes demonstrates that regions of cold, continuous permafrost are undergoing irreversible alteration, unprecedented since deglaciation (~13 cal kyr B.P.).

Differences in behavior and distribution of permafrost‐related lakes in Central Yakutia and their response to climatic drivers

AbstractThe Central Yakutian permafrost landscape is rapidly being modified by land use and global warming, but small‐scale thermokarst process variability and hydrological conditions are poorly understood. We analyze lake‐area changes and thaw subsidence of young thermokarst lakes on ice‐complex deposits (yedoma lakes) in comparison to residual lakes in alas basins during the last 70 years for a local study site and we record regional lake size and distribution on different ice‐rich permafrost terraces using satellite and historical airborne imagery. Statistical analysis of climatic and ground‐temperature data identified driving factors of yedoma‐ and alas‐lake changes. Overall, lake area is larger today than in 1944 but alas‐lake levels have oscillated greatly over 70 years, with a mean alas‐lake‐radius change rate of 1.6 ± 3.0 m/yr. Anthropogenic disturbance and forest degradation initiated, and climate forced rapid, continuous yedoma‐lake growth. The mean yedoma lake‐radius change rate equals 1.2 ± 1.0 m/yr over the whole observation period. Mean thaw subsidence below yedoma lakes is 6.2 ± 1.4 cm/yr. Multiple regression analysis suggests that winter precipitation, winter temperature, and active‐layer properties are primary controllers of area changes in both lake types; summer weather and permafrost conditions additionally influence yedoma‐lake growth rates. The main controlling factors of alas‐lake changes are unclear due to larger catchment areas and subsurface hydrological conditions. Increasing thermokarst activity is currently linked to older terraces with higher ground‐ice contents, but thermokarst activity will likely stay high and wet conditions will persist within the near future in Central Yakutian alas basins.

Acceleration of thaw slump activity in glaciated landscapes of the Western Canadian Arctic

Climate change is increasing the frequency and intensity of thermokarst, but the influences of regional climate and physiography remain poorly understood. Retrogressive thaw slumping is one of the most dynamic forms of thermokarst and affects many areas of glaciated terrain across northwestern Canada. In this study, we used airphotos and satellite imagery to investigate the influence of climate and landscape factors on thaw slump dynamics. We assessed slump size, density, and growth rates in four regions of ice-rich terrain with contrasting climate and physiographic conditions: the Jesse Moraine, the Tuktoyaktuk Coastlands, the Bluenose Moraine, and the Peel Plateau. Observed increases in: (1) the area impacted by slumps (+2 to +407%), (2) average slump sizes (+0.31 to +1.82 ha), and (3) slump growth rates (+169 to +465 m2 yr−1) showed that thermokarst activity is rapidly accelerating in ice-rich morainal landscapes in the western Canadian Arctic, where slumping has become a dominant driver of geomorphic change. Differences in slump characteristics among regions indicate that slump development is strongly influenced by topography, ground ice conditions, and Quaternary history. Observed increases in slump activity occurred in conjunction with increases in air temperature and precipitation, but variation in slump activity among the four regions suggests that increased precipitation has been an important driver of change. Our observation that the most rapid intensification of slump activity occurred in the coldest environment (the Jesse Moraine on Banks Island) indicates that ice-cored landscapes in cold permafrost environments are highly vulnerable to climate change.

Detection and spatiotemporal analysis of methane ebullition on thermokarst lake ice using high-resolution optical aerial imagery

Abstract. Thermokarst lakes are important emitters of methane, a potent greenhouse gas. However, accurate estimation of methane flux from thermokarst lakes is difficult due to their remoteness and observational challenges associated with the heterogeneous nature of ebullition. We used high-resolution (9–11 cm) snow-free aerial images of an interior Alaskan thermokarst lake acquired 2 and 4 days following freeze-up in 2011 and 2012, respectively, to detect and characterize methane ebullition seeps and to estimate whole-lake ebullition. Bubbles impeded by the lake ice sheet form distinct white patches as a function of bubbling when lake ice grows downward and around them, trapping the gas in the ice. Our aerial imagery thus captured a snapshot of bubbles trapped in lake ice during the ebullition events that occurred before the image acquisition. Image analysis showed that low-flux A- and B-type seeps are associated with low brightness patches and are statistically distinct from high-flux C-type and hotspot seeps associated with high brightness patches. Mean whole-lake ebullition based on optical image analysis in combination with bubble-trap flux measurements was estimated to be 174 ± 28 and 216 ± 33 mL gas m−2 d−1 for the years 2011 and 2012, respectively. A large number of seeps demonstrated spatiotemporal stability over our 2-year study period. A strong inverse exponential relationship (R2 &gt; = 0.79) was found between the percent of the surface area of lake ice covered with bubble patches and distance from the active thermokarst lake margin. Even though the narrow timing of optical image acquisition is a critical factor, with respect to both atmospheric pressure changes and snow/no-snow conditions during early lake freeze-up, our study shows that optical remote sensing is a powerful tool to map ebullition seeps on lake ice, to identify their relative strength of ebullition, and to assess their spatiotemporal variability.

Spatio-Temporal Variation in High-Centre Polygons and Ice-Wedge Melt Ponds, Tuktoyaktuk Coastlands, Northwest Territories

High-centred polygonal terrain is a widespread feature of Arctic landscapes that is sensitive to increasing ground temperatures because of its high ground-ice content. Understanding spatial variation in the distribution and sensitivity of high-centred polygonal terrain is important for predicting landscape change. In the Tuktoyaktuk Coastlands, Northwest Territories, Canada, mean annual ground temperatures in permafrost have increased between 1 and 2°C over the last 40 years and high-centred polygonal terrain comprises about 10 per cent of the terrestrial landscape. To investigate factors affecting the distribution and potential degradation of ice wedges, we mapped high-centred polygonal terrain and ice-wedge melt ponds, and documented ice wedge related thermokarst at anthropogenic disturbances using 2004 aerial photographs. Historical melt pond distribution was assessed using 1972 aerial photographs. The density of polygonal terrain (up to 37%) was significantly higher in the northern than the southern part of the study area, where more abundant lacustrine sediments and lower ground temperatures have favoured ice-wedge development. Larger proportional melt pond area (0.68%), increases in pond area (up to 3.74%) and a higher frequency of major thermokarst activity following anthropogenic surface disturbance (54%) suggest that high-centred polygonal terrain in the northern part of the study area is more susceptible to degradation than in the southern part. Copyright © 2016 John Wiley & Sons, Ltd.

Remote sensing measurements of thermokarst subsidence using InSAR

AbstractThawing of ice‐rich permafrost followed by surface subsidence results in irregular, depressed landforms known as thermokarst. Many remote sensing studies have identified thermokarst landforms and mapped their changes. However, the intrinsic dynamic thermokarst process of surface subsidence remains a challenge to quantify and is seldom examined using remote sensing methods. In this study we used spaceborne interferometric synthetic aperture radar (InSAR) data to map surface subsidence trends at a thermokarst landform located near Deadhorse on the North Slope of Alaska. A pipeline access road constructed in the 1970s triggered the thawing of the permafrost, causing subsequent expansion of the thermokarst landform. Using Phased Array type L band Synthetic Aperture Radar images acquired by the Advanced Land Observing Satellite‐1, our InSAR analysis reveals localized thermokarst subsidence of 2–8 cm/yr between 2006 and 2010, equivalent to an ice volume loss of about 1.2 × 107 m3/yr. Comparisons between InSAR subsidence trends and lidar microtopography suggest a characteristic time of 8 years of thermokarst development. We also quantitatively explain the difficulty, uncertainties, and possible biases in separating thermokarst‐induced, irreversible subsidence from cyclic seasonal deformation. Our study illustrates that InSAR is an effective tool for mapping and studying active thermokarst processes and quantifying ice loss.

Mid‐Wisconsin to Holocene Permafrost and Landscape Dynamics based on a Drained Lake Basin Core from the Northern Seward Peninsula, Northwest Alaska

AbstractPermafrost‐related processes drive regional landscape dynamics in the Arctic terrestrial system. A better understanding of past periods indicative of permafrost degradation and aggradation is important for predicting the future response of Arctic landscapes to climate change. Here, we used a multi‐proxy approach to analyse a ~ 4 m long sediment core from a drained thermokarst lake basin on the northern Seward Peninsula in western Arctic Alaska (USA). Sedimentological, biogeochemical, geochronological, micropalaeontological (ostracoda, testate amoebae) and tephra analyses were used to determine the long‐term environmental Early‐Wisconsin to Holocene history preserved in our core for central Beringia. Yedoma accumulation dominated throughout the Early to Late‐Wisconsin but was interrupted by wetland formation from 44.5 to 41.5 ka BP. The latter was terminated by the deposition of 1 m of volcanic tephra, most likely originating from the South Killeak Maar eruption at about 42 ka BP. Yedoma deposition continued until 22.5 ka BP and was followed by a depositional hiatus in the sediment core between 22.5 and 0.23 ka BP. We interpret this hiatus as due to intense thermokarst activity in the areas surrounding the site, which served as a sediment source during the Late‐Wisconsin to Holocene climate transition. The lake forming the modern basin on the upland initiated around 0.23 ka BP and drained catastrophically in spring 2005. The present study emphasises that Arctic lake systems and periglacial landscapes are highly dynamic and that permafrost formation as well as degradation in central Beringia was controlled by regional to global climate patterns as well as by local disturbances. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity

Abstract. High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback. Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrams of carbon (Pg-C) (68% range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40% of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest CH4 emission rates of about 50 Tg-CH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03–0.14 °C (68% ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 °C (68% range) to simulated global mean surface air temperatures in the year 2300.

Thawing of massive ground ice in mega slumps drives increases in stream sediment and solute flux across a range of watershed scales

AbstractIce‐cored permafrost landscapes are highly sensitive to disturbance and have the potential to undergo dramatic geomorphic transformations in response to climate change. The acceleration of thermokarst activity in the lower Mackenzie and Peel River watersheds of northwestern Canada has led to the development of large permafrost thaw slumps and caused major impacts to fluvial systems. Individual “mega slumps” have thawed up to 106 m3of ice‐rich permafrost. The widespread development of these large thaw slumps (up to 40 ha area with headwalls of up to 25 m height) and associated debris flows drive distinct patterns of stream sediment and solute flux that are evident across a range of watershed scales. Suspended sediment and solute concentrations in impacted streams were several orders of magnitude greater than in unaffected streams. In summer, slump impacted streams displayed diurnal fluctuations in water levels and solute and sediment flux driven entirely by ground‐ice thaw. Turbidity in these streams varied diurnally by up to an order of magnitude and followed the patterns of net radiation and ground‐ice ablation in mega slumps. These diurnal patterns were discernible at the 103 km2 catchment scale, and regional disturbance inventories indicate that hundreds of watersheds are already influenced by slumping. The broad scale impacts of accelerated slumping are indicated by a significant increase in solute concentrations in the Peel River (70,000 km2). These observations illustrate the nature and magnitude of hydrogeomorphic changes that can be expected as glaciogenic landscapes underlain by massive ice adjust to a rapidly changing climate.

Thermokarst Processes and Depositional Events in a Tundra Lake, Northeastern Siberia

ABSTRACTThe relationships between thermokarst activity, limnogeological processes and climate change in the Siberian Arctic are not well understood. The objective of this paper is to identify the factors controlling the patterns of deposition, using grain size distribution, organic content, elemental composition and mineralogical composition of a 137‐cm long sediment core with a maximum age of ~ 10.9 cal. kyr BP from Lake El'gene‐Kyuele in the tundra of northeastern Siberia. Eight fine sand layers are attributed to depositional events associated with thaw slump activity acting upon orthogonally oriented patterns of ice‐wedge networks in the ice‐rich permafrost on the NW margin of the lake catchment. Sr/Rb ratios, which correspond to the total feldspar and illite content, serve as high‐resolution grain size proxies. The Br content relates to the total organic carbon content, and the Fe/Mn ratio reflects the degree of oxidisation. Our results indicate a relationship between repeated phases of fine sand input and retrogressive thaw slumping dependent on hydroclimate variability and orthogonally oriented ice‐wedge networks within the catchment. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Surface exposure to sunlight stimulates CO2release from permafrost soil carbon in the Arctic

Recent climate change has increased arctic soil temperatures and thawed large areas of permafrost, allowing for microbial respiration of previously frozen C. Furthermore, soil destabilization from melting ice has caused an increase in thermokarst failures that expose buried C and release dissolved organic C (DOC) to surface waters. Once exposed, the fate of this C is unknown but will depend on its reactivity to sunlight and microbial attack, and the light available at the surface. In this study we manipulated water released from areas of thermokarst activity to show that newly exposed DOC is >40% more susceptible to microbial conversion to CO(2) when exposed to UV light than when kept dark. When integrated over the water column of receiving rivers, this susceptibility translates to the light-stimulated bacterial activity being on average from 11% to 40% of the total areal activity in turbid versus DOC-colored rivers, respectively. The range of DOC lability to microbes seems to depend on prior light exposure, implying that sunlight may act as an amplification factor in the conversion of frozen C stores to C gases in the atmosphere.

Using Geospatial Techniques to Analyze Landscape Factors Controlling Ionic Composition of Arctic Lakes, Toolik Lake Region, Alaska

The impacts of climate change on landscapes in arctic Alaska are evident in terms of permafrost melting, frequent thermokarst activity, and the occurrence of more broadleaf vegetation. These changes may alter natural biogeochemical cycles of ions along with major nutrients and affect ionic compositions of lakes, as they are connected with the landscapes. However, the nature of the connectivity between lakes and landscapes in this region is not yet explored. The authors propose that geospatial analysis of landscape properties along with observed lake ion concentrations will enable an understanding of the currently existing landscape controls over ion inputs into the lakes. For the watersheds of 41 lakes in the Arctic Foothills region of Alaska, spatial properties of natural vegetation communities expressed in terms of percentage, shape complexity, and patch density metrics were derived using satellite data. Regression analyses were performed for concentration of ions as well as conductivity in lake water where the spatial metrics along with lake physical properties, lake order, and glacial till age categories were used as predicting variables in the regression. Landscape metrics for major land covers i.e., Percentage of Moist Acidic Tundra (MAT) and Moist Non-acidic Tundra (MNT) were the major predicting variables for concentration of several ions.

Variation in the moisture regime of northeastern interior Alaska and possible linkages to the Aleutian Low: inferences from a late-Holocene δ18O record

Analyses of oxygen and carbon isotopes in bulk carbonate and Chara-stem encrustations, X-ray diffraction, and sediment composition from Keche Lake offer new information on climatic change over the past ~3,400 years in northeastern interior Alaska. The δ18O and δD values of water samples from the lake and its inlet streams suggest that evaporation plays an important role in determining the isotopic composition of Keche Lake water at present. However, evaporative enrichment does not appear to be a major driver of the pronounced fluctuations in the bulk-carbonate δ18O record on the basis of comparison with Chara-δ18O values. The δ18O values of bulk carbonate in the Keche Lake sediments vary by up to 10 ‰ over the past 3,400 years, with maximum values of −12 ‰ around 3,400 cal BP and between 2,100 and 1,500 cal BP. High δ18O peaks are associated with sediments dominated by quartz, feldspar, and clay minerals suggesting the influence of detrital carbonate. Multi-millennial patterns of δ18O variation at Keche Lake appear to be linked with changes in watershed and sediment-depositional processes, which may be driven by varying moisture abundance associated with the position of the Aleutian Low (AL). The increasing trend of carbonate δ18O from 3,400 to ~2,100 cal BP probably reflects the increasing importance of a westerly AL, and the high frequency of δ18O spikes ~2,100–1,500 cal BP may have resulted from the prevalence of a westerly AL position. Predominance of a westerly AL likely increased snowfall and winter temperature in the region. Such conditions would have promoted soil erosion and thermokarst activity during spring snowmelt, resulting in episodic large influxes of detrital carbonate to Keche Lake and elevating bulk-carbonate δ18O. Over the past 1,500 years, bulk-carbonate δ18O remained relatively high at Keche Lake but variation was much less pronounced than before. A broad δ18O peak centered ~400 cal BP may be related to enhanced winter moisture during the Little Ice Age, although our chronology is inadequate for a rigorous assessment of this interpretation. This study contributes a new δ18O record and offers additional information on past moisture-regime shifts associated with changing atmospheric-circulation patterns.

Eastern Beringia and beyond: Late Wisconsinan and Holocene landscape dynamics along the Yukon Coastal Plain, Canada

Terrestrial permafrost archives along the Yukon Coastal Plain (northwest Canada) have recorded landscape development and environmental change since the Late Wisconsinan at the interface of unglaciated Beringia (i.e. Komakuk Beach) and the northwestern limit of the Laurentide Ice Sheet (i.e. Herschel Island). The objective of this paper is to compare the late glacial and Holocene landscape development on both sides of the former ice margin based on permafrost sequences and ground ice. Analyses at these sites involved a multi-proxy approach including: sedimentology, cryostratigraphy, palaeoecology of ostracods, stable water isotopes in ground ice, hydrochemistry, and AMS radiocarbon and infrared stimulated luminescence (IRSL) dating. AMS and IRSL age determinations yielded full glacial ages at Komakuk Beach that is the northeastern limit of ice-free Beringia. Herschel Island to the east marks the Late Wisconsinan limit of the northwest Laurentide Ice Sheet and is composed of ice-thrust sediments containing plant detritus as young as 16.2calkaBP that might provide a maximum age on ice arrival. Late Wisconsinan ice wedges with sediment-rich fillings on Herschel Island are depleted in heavy oxygen isotopes (mean δ18O of −29.1‰); this, together with low d-excess values, indicates colder-than-modern winter temperatures and probably reduced snow depths. Grain-size distribution and fossil ostracod assemblages indicate that deglaciation of the Herschel Island ice-thrust moraine was accompanied by alluvial, proluvial, and eolian sedimentation on the adjacent unglaciated Yukon Coastal Plain until ~11calkaBP during a period of low glacio-eustatic sea level. The late glacial–Holocene transition was marked by higher-than-modern summer temperatures leading to permafrost degradation that began no later than 11.2calkaBP and caused a regional thaw unconformity. Cryostructures and ice wedges were truncated while organic matter was incorporated and soluble ions were leached in the thaw zone. Thermokarst activity led to the formation of ice-wedge casts and deposition of thermokarst lake sediments. These were subsequently covered by rapidly accumulating peat during the early Holocene Thermal Maximum. A rising permafrost table, reduced peat accumulation, and extensive ice-wedge growth resulted from climate cooling starting in the middle Holocene until the late 20th century. The reconstruction of palaeolandscape dynamics on the Yukon Coastal Plain and the eastern Beringian edge contributes to unraveling the linkages between ice sheet, ocean, and permafrost that have existed since the Late Wisconsinan.

Late glacial and holocene landscapes of central Beringia

New palynological and sedimentological data from St. Lawrence Island present a rare view into late-glacial and Holocene environments of the central Bering Land Bridge. The late glaciation was a time of dynamic landscape changes in south-central Beringia, with active thermokarst processes, including the formation and drainage of thaw lakes. The presence of such a wet, unstable substrate, if widespread, probably would have had an adverse impact on food sources and mobility for many of the large mammal populations. The establishment of Betula shrub tundra on the island suggests late-glacial summers that were warmer than present, consistent with regional paleoclimatic interpretations. However, the increasing proximity to the Bering Sea, as postglacial sea levels rose, modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of Beringia at this time. The mid- to late Holocene is marked by more stable land surfaces and development of Sphagnum and Cyperaceae peat deposits. The accumulation of organic deposits, decline of shrub Betula, and decrease in thermokarst disturbance suggest that conditions were cooler than the previous. A recent decline in peat accumulation at the study sites may relate to local geomorphology, but similar decreases have been noted for other arctic regions.

Tracking hydrological responses of a thermokarst lake in the Old Crow Flats (Yukon Territory, Canada) to recent climate variability using aerial photographs and paleolimnological methods

AbstractRecent studies using remote sensing analysis of lake‐rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming. However, images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice‐free season duration. Here, we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the Old Crow Flats (OCF), Canada, and to identify their causes. Images show that the water level in lake OCF 48 declined markedly sometime between 1972 and 2001. In a sediment core from OCF 48, complacent stratigraphic profiles of several physical, geochemical, and biological parameters from ∼1874–1967 indicate hydro‐limnological conditions were relatively stable. From ∼1967–1989, declines in organic matter content, organic carbon isotope values, and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment, and subsequent decline in aquatic productivity, caused by increased thermo‐erosion of shoreline soils. Lake expansion was likely caused by increased summer rainfall, as recorded by increased cellulose‐inferred lake‐water oxygen isotope compositions. Stratigraphic trends defining the lake expansion phase terminated at ∼1989, which likely marks the year when the lake drained. Above‐average precipitation during the previous year probably raised the lake level and promoted further thermo‐erosion of the shoreline soils that caused the lake to drain. These are meteorological conditions that have led to other recent lake‐drainage events in the OCF. Thus, the decline in lake level, evident in the aerial photograph from 2001, is unlikely to have been caused by evaporation, but rather is a remnant of a drainage event that took place more than a decade earlier. After drainage, the lake began to refill, and most paleolimnological parameters approach levels that are similar to those during the stable phase. These findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Coastal erosion dynamics on the permafrost-dominated Bykovsky Peninsula, north Siberia, 1951–2006

This study investigates the rate of erosion during the 1951-2006 period on the Bykovsky Peninsula, located north-east of the harbour town of Tiksi, north Siberia. Its coastline, which is characterized by the presence of ice-rich sediment (Ice Complex) and the vicinity of the Lena River Delta, retreated at a mean rate of 0.59 m/yr between 1951 and 2006. Rates ranged from 434 m of erosion to 92 m of accretion during these 56 years and exhibited large variability (?=45.4). Ninety-seven percent of the rates observed were less than 2 m/yr and 81.6% were less than 1 m/yr. No significant trend in erosion could be recorded despite the study of five temporal subperiods within 1951-2006. Erosion modes and rates actually appear to be strongly dependant on the nature of the backshore material, erosion being stronger along low-lying coastal stretches affected by past or current thermokarst activity. The juxtaposition of wind records monitored at the town of Tiksi and erosion records yielded no significant relationship despite strong record amplitude for both data sets. We explain this poor relationship by the only rough incorporation of sea-ice cover in our storm extraction algorithm, the use of land-based wind records vs. offshore winds, the proximity of the Peninsula to the Lena River Delta freshwater and sediment plume and the local topographical constraints on wave development.Keywords: coastal erosion, permafrost, Arctic, climate change, Russia(Published: 15 September 2011)Citation: Polar Research 2011, 30, 7341, DOI: 10.3402/polar.v30i0.7341

Climate Change in the Arctic – Permafrost, Thermokarst, and Why They Matter to the Non‐Arctic World

AbstractThermokarst terrain develops when some forms of permafrost – or so‐called frozen ground – thaw and the soil subsides under its own mass. The processes that create thermokarst terrain alter the Arctic landscape substantially. The formation of thermokarst terrain is a natural phenomenon that increases or decreases as the climate warms or cools. There is now strong evidence that permafrost has been warming for several decades and that the rate of thermokarst formation has accelerated in many parts of the Arctic. Based on predictions of future climate in Arctic regions, a substantial portion of the permafrost that exists today will disappear in the next 50–100 years. The increase in thermokarst activity observed recently is likely to be an early indicator of permafrost retreat. Taken individually a particular thermokarst feature is perhaps merely an interesting oddity. However, taking a longer temporal and larger spatial perspective, it is reasonable to conclude that thermokarst formation has important impacts on the hydrology, geomorphology, biogeochemistry and ecology of the Arctic landscape. If the rate of thermokarst formation increases as expected, then it is possible that important aspects of the structure and function of the Arctic landscape will change rapidly as well. It is of particular concern that permafrost contains more total carbon than is currently in circulation in the modern atmosphere. New experimental evidence suggests that when permafrost thaws, the carbon it contains will become available for microbial processing and much of the carbon may end up as carbon dioxide or methane in the atmosphere. It is important that we understand these interacting process to better understand how climate change will affect the Arctic environment as well as the global climate, in the future.