Thermo-erosion of permafrost coasts in East Siberia

Frank.Guenther [ at ]


Permafrost coasts in the East Siberian Arctic are susceptible to a variety of changing environmental drivers all of which currently point to increasing coastal erosion rates and mass fluxes of sediment and carbon to the shallow arctic shelf seas. In the Laptev Sea region, along more than 1000km of coastline, steep cliffs delimit marshy coastal tundra lowlands that are underlain by continuous permafrost and composed of syncryogenetic continental Late Pleistocene ice-rich permafrost sequences of Ice Complex type. Due to the ubiquitious ground ice, thermo-abrasion and thermodenudation are two major destructive geomorphic processes that act under the strong seasonality of hydrometeorological conditions of a subpolar climate. Varying intensities of cliff bottom and top retreat lead to diverse coastal erosion regimes that have different impacts on coastal land loss and associated mass fluxes. The overarching goal of this thesis is to gain insights into the relationship of both processes as the main driving forces of coastal thermo-erosion. Particular emphasis was put on stereophotogrammetric digital terrain modelling and subsequent ortho-rectification of high resolution optical satellite imagery in order to enable accurate coastline position change measurements over multidecadal to seasonal time scales. A geomorphometric index that accounts for spatially and temporally dynamic thermo-erosion rates was proposed and applied to four large coastline segments across the Laptev Sea. Observations of coastline retreat over time were compared with regional permafrost degradation structures in order to account for endogeneous factors such as ground ice content and topographical constraints on coastal erosion development. Calculation of the seasonal duration available for thermo-abrasion, expressed as sea ice free open water period, and for thermo-denudation, based on thawing degree days, showed a recent increase in the duration of both seasons. As seasons lengthen and permafrost warms, thermo-abrasion and thermo-denudation are increasingly coupled, increasing the effective mass flux resulting from erosion. Over the recent short-term period, the coast has eroded at annual rates almost twice as rapid as the historical mean. Results suggest that higher rates were accompanied by a higher frequency of the thermo-erosion cycle that turned out to connect thermo-abrasion and denudation predominantly on the thermal component.

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Günther, F. (2013): Thermo-erosion of permafrost coasts in East Siberia , PhD thesis, Universität Potsdam.

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