Description: Lakes and drained lake basins (DLBs) are dominant landforms across Arctic lowland regions. The long-term dynamics of lake formation and drainage is evident in the abundance of lakes and DLBs covering as much as 80% of the landscape in various regions of Arctic Alaska, Russia, and Canada. Lake drainage can be triggered through different mechanisms such as lake tapping by an adjacent stream, bank overflow or ice wedge degradation. Following drainage, DLBs can become valuable grazing land for caribou and reindeer as well as usable land for infrastructure development due to low ground ice content in recent DLBs. In addition, DLBs can be sites for soil organic carbon accumulation in the form of peat which also play a role for carbon cycling. Comprehensive and accurate mapping of DLB distribution, age and drainage mechanism, will further inform our understanding of their role in permafrost landscape evolution across varying timescales. DLBs differ from the surrounding terrain in vegetation structure and composition, soil moisture, elevation, size and types of ice-wedge polygons and other parameters that make them an identifiable target based on remote sensing data. Here, we present a novel approach to map DLBs in permafrost landscapes with a specific focus on the North Slope of Alaska as well as select areas in Siberia and northwestern Canada. To map DLBs, we combined multispectral satellite imagery (Landsat-8 and Sentinel-2), Synthetic Aperture Radar (SAR) acquisitions (Sentinel-1), and DEM data (ArcticDEM). To cover the entire study area in each region, we included Landsat-8 acquisitions from all available years and Sentinel-2 for 2016 and 2018 to create cloud-free mosaics. The classification combines methodologies from pixel-based and object-based image analysis. To allow for processing of these large datasets that cover more than 200.000 km2, a classification workflow was developed in Google Earth Engine. Preliminary results show good agreement of our classification with previously published data sets for subsets of our North Slope study area. This work marks the first attempt to map DLBs at the pan-Arctic scale. Our results highlight the importance of treating areas of different surficial geology and vegetation communities separately in the classification process to ensure higher classification accuracy.

Description: Arctic river deltas are sensitive polar landscapes at the land-ocean interface. In contrast to lower latitude deltas, Arctic deltas are characterized by low temperatures, a strong seasonality and the presence of permafrost. Seasonal freezing conditions and underlying permafrost hinders runoff for most of the year and leads to typical land forms such as ice wedge polygons, frost mounds and thermokarst lakes. However, compared to other permafrost dominated landscapes, Arctic deltas are more dynamic. The surface morphology is changing constantly due to river ice break up and subsequent spring flooding, coastal and shoreline erosion, thaw slumping, and degradation of ice rich deposits. Deltaic sediments also tend to be highly susceptible to ground-ice aggradation, making them more ice-rich than adjacent nondeltaic landscapes. In addition, Arctic deltas will be severely affected by global climate change through sea level rise, lengthened thaw season, changing river discharge, storm surge flooding and thawing permafrost. We are therefore at risk, to face reactivation of millennia-old soil carbon and nitrogen deposits by the degradation of previously permanently frozen river delta deposits. However, there is a lack of studies on Arctic deltas and only very coarse estimates on Arctic delta carbon and nitrogen stocks exist. Here we present a new data-set of 140 soil cores, including more than 1400 samples from 17 different deltas spread across the Arctic. We combine new and legacy soil core data to estimate for the first time pan-Arctic deltaic carbon and nitrogen stocks and close a knowledge gap for deep permafrost stock estimations. We found that Arctic deltas present a significant pool for organic carbon and nitrogen, thus their change poses risks far beyond the Arctic. Permafrost thaw in such dynamic landscapes will increase nutrient transport from land to ocean with implications on Arctic near-shore zones (e.g. affecting foodwebs and biogeochemical processes) as well as increased greenhouse gas release due to large amounts of carbon and nitrogen becoming available from previously frozen ground. Our study highlights the need to better understand dynamic processes in Arctic deltas, since these vulnerable carbon and nitrogen rich deposits will be severely affected by the effects of global climate change.