Description: Lake-rich arctic lowland landscapes are particularly sensitive to changes occurring in both summer and winter climate. In northern Alaska, lakes may account for more than 20% of the land surface cover and thus factor prominently in the arctic system. However, long-term, integrated observations from lake-rich arctic landscapes are relatively sparse. During the past decade, we have developed two new landscape-scale arctic observatories in northern Alaska – the Teshekpuk Lake Observatory (TLO) and the Fish Creek Watershed Observatory (FCWO) to help fill critical data gaps associated with these prominent components of the arctic system. The TLO focuses on the largest arctic lake in Alaska and the ice-rich permafrost terrain between it and the Beaufort Sea coast to the north. The FCWO focuses on a 4,500 sq. km. watershed where lakes occupy 19% of the surface cover. Combined, the TLO and FCWO capture the diverse mosaic of terrain units and aquatic habitats that occur on the Arctic Coastal Plain of northern Alaska including deep dune trough lakes, shallow thermokarst lakes, drained thermokarst lake basins, thermokarst pits, beaded streams, both sand and gravel bedded rivers, rapidly eroding coastlines, and deltaic habitats. The TLO and FCWO are also ideal locations for long-term observations as these landscapes are responding rapidly to climate change and are also subject to land use changes associated with petroleum development. Here we provide an overview of the research infrastructure available at the TLO and FCWO and present data and findings from sensor networks, field studies, remotely sensed image analysis, models, limnological surveys, and paleoecological analyses. Ongoing projects at both observatories include establishment of automated and near-real time data transmission stations, detailed field studies, analysis of remotely sensed datasets to quantify regional landscape changes, climatic and hydrologic modeling, and analysis of paleoecological archives that will help place some of the recent observed changes into a longer-term context. The establishment of the Teshekpuk Lake Observatory and the Fish Creek Watershed Observatory will provide much needed information on the potential future status of these dynamic and sensitive arctic landscapes.

Description: Arctic river deltas are highly dynamic environments at the interface of land to ocean. Arctic deltas are underlain by permafrost deposits, which are highly vulnerable to a warming climate. The amount of soil carbon stored in these deltas and potentially vulnerable to mobilization due to permafrost thaw is poorly known and based on few data only. Previous soil carbon estimates (e.g. Hugelius et al., 2014, Tarnocai et al., 2009) were based on data from three large deltas, and no data is so far available for small (〈 500 km2) Arctic river deltas. In this study, we investigate the soil carbon pools of two small Arctic river deltas entering the Beaufort Sea on the Alaska North Slope, the Ikpikpuk and the Fish Creek river deltas. Our approach couples soil carbon information with remotely sensed data to estimate the total carbon stock in the upper 1 m for these environments. Both river deltas are located within the continuous permafrost zone and are characterized by typical fluvial-deltaic features and processes, such as river channels and islands, floodplains and mudflats, sand dunes, as well as episodic flooding, erosion, and deposition. In addition, permafrost processes are an important factor for thaw, erosion, transport, and accumulation dynamics within these deltas. As a result, features specific to permafrost-dominated deltas are widespread such as thermokarst lakes, drained thaw lake basins and ice wedge polygonal tundra. Under future climate warming projections, Arctic river deltas will be threatened due to thawing permafrost (including melting and settling of ice-rich deposits) and a rising sea level in combination with coastal erosion. To better estimate how much soil carbon may be vulnerable to mobilization under these projected changes and might be released as greenhouse gases, it is necessary to study the total soil carbon storage in Arctic river deltas. This study presents the first carbon storage estimation in surface soils and sediments for two small Arctic deltas, which each cover each an area of about 100 km2. Nine different soil cores between 54 and 215 cm depth, including both, non-permanently and permanently frozen deposits, were collected in April 2014 and July 2015, and were analyzed in the laboratory for total organic carbon (TOC), total carbon (TC), total nitrogen (TN), stable isotopes (δ13C), grain size, and deposit age (14C). The soil C parameters were upscaled to each delta based on landcover classifications derived from Landsat and Spot images in combination with high-resolution digital terrain models (DTM) from airborne LIDAR and IfSAR datasets. The upscaling of the total carbon storage was based on different approaches including the correlation of near surface soil carbon storage with various remotely sensed landcover indices. These indices, such as the Tasseled Cap or NDVI for the year 2014 were derived from linear trend analyses of Landsat data taking into account the full Landsat 5-8 archive from 1985-2014. For comparison, a supervised classification (maximum likelihood) with Landsat 8 and Spot 5 images was established based on training areas derived from field information from two field trips, very high resolution aerial and satellite images, and high resolution surface elevation information. The carbon content was finally upscaled based on mean carbon values for the different land cover classes. The total organic carbon storage for the two deltas ranges between 1.5 and 2 teragrams (Tg) of carbon each for the first meter of soil (excluding all water areas), depending on the upscaling method and dataset used. The results compare favorably (comparing the mean carbon storage values per square meter) with what has been previously estimated for other, larger Arctic river deltas. This study shows that remote sensing is a suitable tool to upscale soil carbon values in remote Arctic river deltas where only few soil data is available. We are further working on extending our approach to other Arctic permafrost-influenced river deltas, such as the large Lena river delta, Siberia, where we and other colleagues have previously collected a substantial amount of soil carbon and landcover ground truth data. Hugelius G, Strauss J, Zubrzycki S, Harden JW, Schuur EAG, Ping C-L, Schirrmeister L, Grosse G, Michaelson GJ, Koven CD, O`Donnell OA, Elberling B, Mishra U, Camill P, Yu Z, Palmtag J, Kuhry P. 2014. Estimated stocks of circumpolar permafrost carbon with quantified uncertainty ranges and identified gaps. Biogeosciences 11: 6573-6593. DOI:10.5194/bg-11-6573-2014 Tarnocai C, Canadell JG, Schuur EAG, Kuhry P, Mazhitova G, Zimov S. 2009. Soil organic carbon pools in the northern circumpolar permafrost region. Global Biogeochemical Cycles 23: GB2023. DOI:10.1029/2008GB003327

Description: Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, d13Corg) and stable water isotopes (d18O, dD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22,800 +/- 280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11,800 cal. a BP (Unit B). At about 9,000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1,060 cal. a BP, including post-drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.

Description: Thermokarst processes characterize a variety of ice-rich permafrost terrains and often lead to lake formation. The long-term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate, vegetation and ground conditions, including the volume of excess ground ice and its distribution. The current lake status of thermokarst-lake landscapes and their future trajectories under climatewarming are better understood in the light of their long-term development. We studied the lake-rich southern marginal upland of the Yukon Flats (northern interior Alaska) using dated lake-sediment cores, observations of river-cut exposures, and remotely-sensed data. The region features thick (up to 40 m)Quaternary deposits (mainly loess) that contain massive ground ice. Two of three studied lakes formed ~11,000–12,000 cal yr BP through inferred thermokarst processes, and fire may have played a role in initiating thermokarst development. From ~9000 cal yr BP, all lakes exhibited steady sedimentation, and pollen stratigraphies are consistentwith regional patterns. The current lake expansion rates are low (0 to b7 cmyr−1 shoreline retreat) compared with other regions (~30 cm yr−1 or more). This thermokarst lake-rich region does not showevidence of extensive landscape lowering by lake drainage, nor of multiple lake generations within a basin. However, LiDAR images reveal linear “corrugations” (N5 m amplitude), deep thermo-erosional gullies, and features resembling lake drainage channels, suggesting that highly dynamic surface processes have previously shaped the landscape. Evidently, widespread early Holocene permafrost degradation and thermokarst lake initiation were followed by lake longevity and landscape stabilization, the latter possibly related to establishment of dense forest cover. Partial or complete drainage of three lakes in 2013 reveals that there is some contemporary landscape dynamism. Holocene landscape evolution in the study area differs from that described from other thermokarst-affected regions; regional responses to future environmental change may be equally individualistic.

Description: The interaction and feedbacks between surface water and permafrost are fundamental processes shaping the surface of continuous permafrost landscapes. Lake-rich regions of Arctic lowlands, such as coastal plains of northern Alaska, Siberia, and Northwest Canada, where shallow thermokarst lakes often cover 20-40% of the land surface are a pronounced example of these permafrost processes. In these same Arctic coastal regions, current rates of near-surface atmospheric warming are extremely high, 0.8 °C / decade for example in Barrow, Alaska, primarily due to reductions in sea ice extent (Wendler et al., 2014). The thermal response of permafrost over recent decades is also rapid, warming approximately 0.6°C / decade for example at Deadhorse, Alaska, yet this permafrost is still very cold, less than -6°C (Romanovsky et al., 2015). The temperature departure created by water in lakes set in permafrost is well recognized and where mean annual bed temperatures (MABT) are above 0 °C, a talik develops (Brewer, 1958). The critical depth of water in lakes where taliks form is generally in excess of maximum ice thickness, which has historically been around 2 m in northern Alaska. Thus, lakes that are shallower than the maximum ice thickness, which are the majority of water bodies in many Arctic coastal lowlands, should maintain sublake permafrost and have a shallow active layer if MABT’s are below freezing. Recent analysis, however, suggests a lake ice thinning trend of 0.15 m / decade for lakes on the Barrow Peninsula, such that the maximum ice thickness has shifted to less than 1.5 m since the early 2000’s. We hypothesized that the surface areas most sensitive to Arctic climate warming are below lakes with depths that are near or just below this critical maximum ice thickness threshold primarily because of changing winter climate and reduced ice growth. This hypothesis was tested using field observations of MABT, ice thickness, and water depth collected from lakes of varying depths and climatic zones on the coastal plain and foothills of northern Alaska. A model was developed to explain variation in lake MABT by partitioning the controlling processes between ice-covered and open-water periods. As expected, variation in air temperature explained a high amount of variation in bed temperature (72%) and this was improved to 80% by including lake depth in this model. Bed temperature during the much longer ice-covered period, however, was controlled by lake depth relative to regional maximum ice thickness, termed the Effective Depth Ratio (EDR). A piecewise linear regression model of EDR explained 96% of the variation in bed temperature with key EDR breaks identified at 0.75 and 1.9. These breaks may be physically meaningful towards understanding the processes linking lake ice to bed temperatures and sublake permafrost thaw. For example if regional lake ice grows to 1.5 m thick, the first break is at lake depth of 1.1 m, which will freeze by mid-winter and may separate lakes with active-layers from lakes with shallow taliks. The second EDR break for the same ice thickness is at a lake depth of 2.9 m, which may represent the depth where winter thermal stratification becomes notable (greater than 1 °C) and possibly indicative of lakes that have well developed taliks that store and release more heat. We then combined these ice-covered and open-water models to evaluate the sensitivity of MABT to varying lake and climate forcing scenarios and hindcast longer-term patterns of lake bed warming. This analysis showed that MABT in shallow lakes were most sensitive to changes in ice thickness, whereas ice thickness had minimal impact on deeper lakes and variation in summer air temperature had a very small impact on MABT across all lake depths. Using this model, forced with Barrow climate data, suggests that shallow lake beds (1-m depth) have warmed substantially over the last 30 years (0.8 °C / decade) and more importantly now have an MABT that exceeds 0 °C. Deeper lake beds (3-m depth), however, are suggested to be warming at a much slower rate (0.3 °C / decade), compared to both air temperature (0.8 °C/ decade) and permafrost (0.6 °C/ decade). This contrasting sensitivity and responses of lake thermal regimes relative to surrounding permafrost thermal regimes paint a dramatic and dynamic picture of an evolving Arctic land surface as climate change progresses. We suggest that the most rapid areas of permafrost degradation in Arctic coastal lowlands are below shallow lakes and this response is driven primarily by changing winter conditions. References: Brewer, M. C. (1958), The thermal regime of an arctic lake, Transactions of the American Geophysical Union, 39, 278-284. Romanovsky, V. E., S. L. Smith, H. H. Christiansen, N. I. Shiklomanov, D. A. Streletskiy, D. S. Drozdov, G. V. Malkova, N. G. Oberman, A. L. Kholodov, and S. S. Marchenko, (2015). The Arctic Terrestrial Permafrost in “State of the Climate in 2014” . Bulletin of the American Meteorological Society, 96, 7, 139-S141, 2015 Wendler, G., B. Moore, and K. Galloway (2014), Strong temperature increase and shrinking sea ice in Arctic Alaska, The Open Atmospheric Science Journal, 8, 7-15.

Description: Ice-rich permafrost that formed in glacial periods of the Quaternary is highly vulnerable to thaw under ongoing climate warming and anthropogenic disturbance. The mega thaw slump near the village of Batagay (Yakutia, Russia) is an outstanding example of permafrost degradation and demonstrates that thermo-erosion processes may occur in unexpected locations, develop very rapidly in particular after disturbances, and leave behind deep rutted badlands. Retrogressive thaw slumps are particularly frequent along riverbanks and coastlines of regions where buried glacier ice or ice-rich glacial till have been mapped. In East Siberia, syngenetic Late Pleistocene Ice Complex (Yedoma) permafrost deposits accumulate volumetric ground ice contents of up to 80-90% % and extend tens of meters below the ground surface. Beyond the Yedoma main distributional range in the coastal lowlands of the Laptev and East Siberian seas, these deposits are also found on slopes of the Verkhoyan Mountain Range and in valleys of surrounding foothills, providing favorable preconditions for rapid thaw development. The Batagay mega slump exposes a profile of 30m thick Yedoma deposits underlain by ice saturated alluvial sand of around 60 m thickness and another very ice-rich layer at the base. We present data from a multi-sensor remote sensing time series investigation of the mega slump in order to assess the planimetric and volumetric dimensions and its decadal and interannual expansion rates. For ortho-rectification purposes and for volumetric analyses, we photogrammetrically derived highly detailed digital elevation models. The height difference between the headwall and the slump outflow is 145 m along a distance of 2300 m, while the maximum slump width is 840 m. Our analysis does not show any signs of stabilization after several decades (since 1980s) of slump growth, with the headwall retreating with observed rates of generally 〉10 m and more recently up to 30m per year. Reconstruction of a paleo-surface revealed that the slump has carved into the rolling topography to a depth of up to 73 m. The current size of the slump is 〉69 ha, while it had thawed 〉25 × 106 m³ of ice-rich permafrost through 2016. The majority of sediment released from the slump episodically dams up the Batagay River, forming a large temporary lake which then empties catastrophically.

Description: Arctic river deltas and ice-rich permafrost regions are highly dynamic environments which will be strongly affected by future climate change. Rapid thaw of permafrost (thermokarst and thermo-erosion) may cause significant mobilization of organic carbon, which is assumed to be stored in large amounts in Arctic river deltas and ice-rich permafrost. This study presents and compares new data on organic carbon storage in thermokarst landforms and Arctic river delta deposits for the first two meters of soils for five different study areas in Alaska and Siberia. The sites include the Ikpikpuk river delta (North Alaska), Fish Creek river delta (North Alaska), Teshekpuk Lake Special Area (North Alaska), Sobo-Sise Island (Lena river delta, Northeast Siberia), and Bykovsky Peninsula (Northeast Siberia). Samples were taken with a SIPRE auger along transects covering the main geomorphological landscape units in the study regions. Our results show a high variability in soil organic carbon storage among the different study sites. The studied profiles in the Teshekpuk Lake Special Area – dominated by drained thermokarst lake basins – contained significantly more carbon than the other areas. The Teshekpuk Lake Special Area contains 44 ± 9 kg C/m2 (0-100 cm, mean value of profiles ± Std dev) compared to 20 ± 7 kg C/m2 kg for Sobo-Sise Island – a Yedoma dominated island intersected by thaw lake basins and 24 ± 6 kg C/m2 for the deltaic dominated areas (Fish Creek and Ikpikpuk). However, especially for the Ikpikpuk river delta, a significant amount of carbon (25 ± 9 kg C/m2) is stored in the second meter of soil (100-200cm). This study shows the importance of including deltaic and thermokarst-affected landscapes as considerable carbon pools, but indicates that these areas are heterogeneous in terms of organic carbon storage and cannot be generalized. As a next step, the site-level carbon stocks will be upscaled to the landscape level using remote sensing-based land cover classifications to calculate the carbon storage potential for Arctic deltas and larger thermokarst regions, to estimate mobilization potentials from thermokarst and thermo-erosion, and to provide input data for future permafrost carbon feedback models.