ALBERT

Description: Ground-ice rich terrain in the East Siberian coastal lowlands is being destabilized by continuing permafrost degradation. This degradation includes not only warming of cold permafrost, but also its thawing with consequences for local hydrology, ecosystems, biogeochemical cycling, and sometimes communities. However, thaw-associated mobilization of soil organic carbon and associated release of methane or carbon dioxide as well as relative sea level rise due to terrain subsidence of vast coastal hinterlands has potential regional to global impacts. Regarding land surface elevation of ground-ice-rich terrain, questions remain over whether the absolute surface level returns back to its initial state after a complete annual thaw-freeze cycle or if irreversible loss of ground ice occurred due to active layer deepening, leading to subsidence. Within drained thaw lake basins or areas of current thermokarst activity on yedoma uplands, seasonal thaw-freeze mechanisms proceed simultaneously with long-term geomorphic processes of land surface lowering. Now there are initial indications that ground ice in permafrost is thawing in response to rising temperatures in the Arctic, however, still only few observations of widespread and irreversible thaw subsidence exist. Permanent subsidence depends on topographic gradients enabling effective removal of ground ice melt water. Readjustment of drainage systems due to a landward advancing coastline or thermokarst lake expansion or partial drainage is likely to facilitate thaw subsidence in the coastal hinterland and calls for a more comprehensive consideration. In this study, we placed our observations in the context of an alas-yedoma thermokarst landscape that has already undergone considerable permafrost degradation in the past. Our work aims at finding commonalities and differences of change or no change on uplands, slopes, and thaw depressions on the landscape scale using multi-temporal DEMs from historical aerial photographies and modern very high resolution satellite imagery such as WorldView and GeoEye. In summer 2014 we established several long-term survey grids with geodetic benchmarks on Sobo-Sise island in the eastern Lena Delta and on the Bykovsky Peninsula in North Siberia. Initial ground-based measurements were used to create and evaluate multiple digital elevation models (DEMs) produced with satellite image stereophotogrammetry. The datasets will be used to identify inter-annual trends. Annual repeat ground measurements starting in 2015, relying on our small grid of fiber glass pipes anchored in the permafrost down to 2m depth, will provide information on spatio-temporal variations of local elevation changes in polygonal tundra.