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Evolution of thermokarst lakes and alasses in the ice-rich permafrost of the Lena River Delta

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Morgenstern, A. , Günther, F. , Ulrich, M. , Fedorova, I. , Rudaya, N. , Boike, J. and Schirrmeister, L. (2012): Evolution of thermokarst lakes and alasses in the ice-rich permafrost of the Lena River Delta , Russian-German cooperation in the scientific exploration of northern Eurasia and the adjacent Arctic ocean. Leopoldina Symposium in cooperation with St. Petersburg State University and the Russian Academy of Sciences, St. Petersburg, 10 September 2012 - 12 September 2012 .
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Abstract:

Thermokarst lakes and basins are ubiquitous landforms in arctic lowlands. Current research has a particular focus on thermokarst processes in ice-rich permafrost deposits in Siberia and the North American Arctic, because these deposits are highly vulnerable to degradation under a warming climate. Their high content of excess ice accounts for their high thawing potential, and the large amount of carbon, which has been stored in these deposits for several thousand years, has a high potential for the release of greenhouse gases. Here, we give a summary of two previous studies on thermokarst lakes and thermokarst basins (alasses) in ice-rich permafrost deposits (Ice Complex) of the Lena River Delta. One study reconstructed the Holocene evolution of one particular alas on Kurungnakh Island in the south central Lena Delta until present using field investigations, remote sensing, GIS, and sediment analyses [1]. The other study investigated different thermokarst stages within the whole Ice Complex extent of the Lena Delta using remote sensing and geoinformation methods to derive information on the potential of future thermokarst evolution in the study area [2]. The results confirm a widespread thermokarst development since the transition from Pleistocene to Holocene with the formation of large and deep thermokarst lakes, which thawed much of the underlying Ice Complex deposits. Most of these large thermokarst lakes drained partly or completely during the Holocene, thereby leading to a much higher coverage of the study area with alasses (20,0%) than with thermokarst lakes (5,2%) at present. Subsequent thermokarst lake development has been restricted and will be restricted in the future. In alasses, residual and secondary thermokarst lakes can change in their spatial extent depending on hydrological and relief conditions, but are not likely to reach the size of the initial lakes and to substantially rework the adjacent Ice Complex deposits. On Yedoma uplands, the development and growth of primary thermokarst lakes is limited by shrinking distances to already existing alasses, delta channels, and other topographic lows that foster lake drainage.

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