Publication Date:
2014-07-06
Description:
The intensity of thermo-erosion in the coastal zone of the Laptev Sea region mirrors the strong seasonality of exogenous hydro-meteorological conditions, mainly the presence or absence of sea ice and large temperature amplitudes. Permafrost, and in particular the widespread presence of syngenetic ground ice, both above and below sea level, constitute endogenous local conditions that make this coastline highly susceptible to currently observed warming and the associated extension of the open water season on the East Siberian arctic shelf. Although the general magnitude of erosion dynamics along Ice Complex coasts has been investigated, substantial information about local, regional, seasonal, and inter-annual variations still remain unknown. Monitoring capabilities could be increased by using the large areal coverage of historical records, accompanied by new acquisitions of contemporary high and very high resolution remote sensing data. Based on topographic reference measurements during field campaigns, we derived digital elevation models for subsequent orthorectification, in order to enable consistent distance and area measurements.
A distinction was made between two related processes that work together, but with temporal and quantitative differences. Cliff top erosion (thermo-denudation) and cliff bottom erosion (thermo-abrasion) have different impacts on the volume of land loss and subsequent mass displacements. For a geographically broad baseline of well-distributed key areas, a proportional relationship of both processes on a multi-decadal long-term scale was observed, at site-specific average rates of -1.8 to -3.4 m/yr on Muostakh Island off the coast of Tiksi and along the continental coast of the Dmitriy Laptev Strait, respectively. However, short-term observations over the recent past revealed not only that erosion rates were 1.6 times more rapid on average, but also responded differently in terms of thermo-denudation and abrasion towards environmental forcings. This response was evaluated using the Normalized Difference Thermo-erosion Index (NDTI), whose value domain differentiates either marine or atmospherically driven erosion regimes, and may additionally indicate near-surface ground ice conditions. Seasonal observations on Muostakh, where the most rapid long-term rates of -9.6 m a-1 have been measured, revealed the existence of a thermo-erosional cycle, during which rates of either thermo-denudation or abrasion are overtaken by the respective opposite process. The frequency of this recurring pattern is also likely to have increased, at least since 2005, when the summer sea ice free period in the southern central Laptev Sea was above average and the sum of positive daily average surface air temperatures in Tiksi reached new all-time maxima. This is necessarily accompanied by larger short-term fluctuations of NDTI, causing coastal cliff morphologies to change more often, resulting in more effective volumetric erosion.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Conference
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notRev
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