Description: Drained thermokarst lake basins (DTLBs) are ubiquitous landforms on Arctic tundra lowland. Their dynamic states are seldom investigated, despite their importance for landscape stability, hydrology, nutrient fluxes, and carbon cycling. Here we report results based on high-resolution Interferometric Synthetic Aperture Radar (InSAR) measurements using space-borne data for a study area located on the North Slope of Alaska near Prudhoe Bay, where we focus on the seasonal thaw settlement within DTLBs, averaged between 2006 and 2010. The majority (14) of the 18 DTLBs in the study area exhibited seasonal thaw settlement of 3–4 cm. However, four of the DTLBs examined exceeded 4 cm of thaw settlement, with one basin experiencing up to 12 cm. Combining the InSAR observations with the in situ active layer thickness measured using ground penetrating radar and mechanical probing, we calculated thaw strain, an index of thaw settlement strength along a transect across the basin that underwent large thaw settlement. We found thaw strains of 10–35% at the basin center, suggesting the seasonal melting of ground ice as a possible mechanism for the large settlement. These findings emphasize the dynamic nature of permafrost landforms, demonstrate the capability of the InSAR technique to remotely monitor surface deformation of individual DTLBs, and illustrate the combination of ground-based and remote sensing observations to estimate thaw strain. Our study highlights the need for better description of the spatial heterogeneity of landscape-scale processes for regional assessment of surface dynamics on Arctic coastal lowlands.

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: Lakes are dominant and diverse landscape features in the Arctic, but conventional land cover classification schemes typically map them as a single uniform class. Here, we present a detailed lake-centric geospatial database for an Arctic watershed in northern Alaska. We developed a GIS dataset consisting of 4362 lakes that provides information on lake morphometry, hydrologic connectivity, surface area dynamics, surrounding terrestrial ecotypes, and other important conditions describing Arctic lakes. Analyzing the geospatial database relative to fish and bird survey data shows relations to lake depth and hydrologic connectivity, which are being used to guide research and aid in the management of aquatic resources in the National Petroleum Reserve in Alaska. Further development of similar geospatial databases is needed to better understand and plan for the impacts of ongoing climate and land-use changes occurring across lake-rich landscapes in the Arctic.

Description: Arctic river deltas are dynamic and rapidly changing permafrost environments in a warming Arctic. Our study presents new data on permafrost carbon and nitrogen stocks from 26 soil permafrost cores collected from the Noatak, Kobuk and Selawik river deltas in Western Alaska. We analyzed 318 samples for total carbon (TC) and total nitrogen (TN). Average landscape-scale carbon storage is 50.1 ± 7.8 kg C (both organic and inorganic) and 2.4 ± 0.3 kg N m-2 (0-200 cm). This totals 67 ± 11 Mt C and 3.3 ± 0.6 Mt N in the first two meters of soil in the Noatak, Kobuk and Selawik deltas combined. Our findings demonstrate that Arctic river deltas are important regions of permafrost soil carbon storage and need to be considered in panarctic permafrost carbon estimations.

Description: Thermokarst lakes are characteristic and dynamic landscape features of ice-rich permafrost environments. Our study of sedimentary records and shoreline expansion of Peatball Lake on the Alaska Arctic Coastal Plain reveals 1,400 years of thermokarst activity. While Peatball Lake likely initiated from a remnant pond of a drained lake basin, the catchment is likewise characterized by mid to late Holocene aged drained basins and remnants of Pleistocene and early Holocene aged uplands. As the lake expanded through lateral permafrost degradation, the sediment source has changed as indicated by internal-lake variability in sediment deposition. Reversed radiocarbon ages show recycling of “old” carbon and degraded organic matter became redeposited in the lake basin resulting in nutrient-poor sublittoral deposits. Our sedimentary records reflect the complexity of depositional environments in thermokarst lakes due to spatio-temporal changes in lake and catchment morphology as well as the impact of thermokarst lake activity on carbon storage of periglacial landscapes.

Description: Eroding permafrost coasts are likely indicators and integrators of changes in the Arctic System as they are susceptible to the combined effects of declining sea ice extent, increases in open water duration, more frequent and impactful storms, sea-level rise, and warming permafrost. However, few observation sites in the Arctic have yet to link decadal-scale erosion rates with changing environmental conditions due to temporal data gaps. This study increases the temporal fidelity of coastal permafrost bluff observations using near-annual high spatial resolution (〈1 m) satellite imagery acquired between 2008–2017 for a 9 km segment of coastline at Drew Point, Beaufort Sea coast, Alaska. Our results show that mean annual erosion for the 2007–2016 decade was 17.2 m yr−1, which is 2.5 times faster than historic rates, indicating that bluff erosion at this site is likely responding to changes in the Arctic System. In spite of a sustained increase in decadal-scale mean annual erosion rates, mean open water season erosion varied from 6.7 m yr−1 in 2010 to more than 22.0 m yr−1 in 2007, 2012, and 2016. This variability provided a range of coastal responses through which we explored the different roles of potential environmental drivers. The lack of significant correlations between mean open water season erosion and the environmental variables compiled in this study indicates that we may not be adequately capturing the environmental forcing factors, that the system is conditioned by long-term transient effects or extreme weather events rather than annual variability, or that other not yet considered factors may be responsible for the increased erosion occurring at Drew Point. Our results highlight an increase in erosion at Drew Point in the 21st century as well as the complexities associated with unraveling the factors responsible for changing coastal permafrost bluffs in the Arctic.