Estimating excess ground ice in Arctic tundra landscapes by a statistical analysis of drained thermokarst lake basins - A comparison between research sites in Alaska.


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Moritz.Langer [ at ] awi.de

Abstract

Excess ice is determining the sensibility of permafrost landscapes in a warming climate. As excess ice thaws several morphodynamical processes can occur, which can change the Arctic landscape significantly. Up until now, the excess ice content is only known for small areas of the Arctic, but not Arctic wide. Mappings that cover large areas are mostly based on classifications of the land surface and are therefore not very precise. The limited amount of data about excess ice affects the precision of the modelling of the degradation of Permafrost, because it affects the sensitivity of permafrost landscapes including all biogeochemical and geophysical processes. To estimate the amount of excess ice in a landscape, differences in altitude formed by thermoerosion processes were analyzed. Height differences are formed by melting excess ice in the ground, causing subsidence. It is presumed that the content of excess ice around the thermoerosion structures is about as thick as the subsidence of the structure itself. Some factors, like erosion, slope and others, must be kept in mind when interpreting the results. The research question of the thesis is: Is it possible to make a rough estimation of the excess ice content of permafrost soil in tundra landscapes by an analysis of a digital elevation model (DEM)? The Barrow Peninsula and the Seward Peninsula, both located in Alaska, U. S., are the two research sites of this work, characterized by current thermokarst lakes and former ones, which are nowadays Drained Thermokarst Lake Basins (DTLBs). For the analysis of the basin height in comparison to the surrounding area, the Arctic DEM is used as main data resource together with data of the DTLBs. ArcGIS and R were used to calculate the height of the lakes and DTLBs and to statistically analyze the results. Various height differences and elevation distribution patterns for the two research sites were found out without a significantly related distribution pattern with the age or general elevation of the DTLBs. The discussion includes the importance of the distribution pattern of the elevation data for the interpretation of the excess ice and which other factors must be considered in the interpretation, like the age of the DTLB, the landscape type and soil and permafrost properties. Problems occurred, e.g. regarding the comparability between the research sites because of the age classes and due overlapping of buffers. Furthermore, ideas of an improvement of the method are proposed. The result includes the mean difference of the buffer height minus the basins height, but several other factors need to be included, such as the active layer thickness, the permafrost depth and more. Therefore, the named difference can not be equalized to the excess ice volume.



Item Type
Thesis (Master)
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Primary Division
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Peer revision
Not peer-reviewed
Publication Status
Published
Eprint ID
51207
Cite as
Schramm, L. (2019): Estimating excess ground ice in Arctic tundra landscapes by a statistical analysis of drained thermokarst lake basins - A comparison between research sites in Alaska. , Master thesis, Institute of Geography, Catholic University of Eichstätt - Ingolstadt.


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