Current thermo-erosion dynamics of Ice Complex coasts in the Laptev Sea

Frank.Guenther [ at ]


Thermo-erosion causes 74% of the continental coastline in the Laptev Sea region that consist of unconsolidated permafrost deposits of Ice Complex type to continuously retreat during the short time window of the subarctic summer. Insights into past and future landscape dynamics depend on understanding the spatially and temporally variable intensities of coastal erosion and its interaction with endogenous and exogenous forcing factors. Coastal thermo-erosion includes two related processes that work temporally and quantitatively differently together. Cliff top erosion (thermo-denudation) and cliff bottom erosion (thermo-abrasion) are coupled, since the entire coastal cliff profile is super-saturated with respect to ice, largely due to thick syngenetic ice wedges. These erosion types result in annual land loss of up to 0.5 hectares per kilometer of coastline and mobilize deep permafrost organic carbon, in response to seasonal environmental changes in the Arctic. Thermo-abrasion and denudation vary in intensity according to the seasonal cycle. Thermo-abrasion is only active during the open water season, while thermo-denudation can proceed throughout the summer. In order to systematically analyze these seasonal thermo-erosion dynamics, we use a set of contemporary very high resolution satellite imagery, repeated geodetic surveys in the field and historical aerial photographs. Particular emphasis in our change detection study was put on stereophotogrammetric digital terrain modelling and subsequent ortho-rectification in order to enable accurate coastline position change measurements over multidecadal to seasonal time scales and to provide current and historical quantifications of planimetric land loss and volumetric coastal erosion. Across a variety of study sites well distributed along more than 200 km of the Laptev Sea mainland coast, observed recent erosion rates for the last 1 to 4 years were almost twice as rapid as the long-term mean of around 2 m per year. Based on normalization of diverse seasonal and interannual erosion rates, our findings at Muostakh Island demonstrate that the currently higher intensities of coastal erosion are controlled at least in part by the increasing open water season and summer air temperatures. We found that under current hydrometeorological conditions, as seasons lengthen and permafrost warms, thermo-abrasion and thermo-denudation are increasingly coupled, increasing the effective mass flux resulting from erosion. Our results also suggest that higher rates were accompanied by a higher frequency of the thermo-erosion cycle that causes coastal cliffs to pass various stages of morphological evolution, which in turn have different impacts on eroded volumes and subsequent mass displacement in the coastal zone.

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Conference (Talk)
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International conference "Earth Cryology: XXI Century", 29 Sep 2013 - 03 Oct 2013, Pushchino, Russia.
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Günther, F. , Overduin, P. , Sandakov, A. V. , Grosse, G. , Baranskaya, A. , Opel, T. and Grigoriev, M. N. (2013): Current thermo-erosion dynamics of Ice Complex coasts in the Laptev Sea , International conference "Earth Cryology: XXI Century", Pushchino, Russia, 29 September 2013 - 3 October 2013 .

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