Observing Muostakh Island disappear: Erosion of a ground-ice-rich coast in response to summer warming and sea ice reduction on the East Siberian shelf

Abstract

Observations of coastline retreat using contemporary very high resolution satellite imagery and historical air photos were compared to measurements of open water fractions and summer air temperatures. A systematical analysis of seasonal and interannual variations of thawing induced cliff top retreat (thermo-denudation) and thermally strengthened marine abrasion (thermo-abrasion) was confined to the rapidly eroding arctic island Muostakh in the southern central Laptev 5 Sea, which is composed of ground-ice-rich permafrost deposits of Ice Complex type, susceptible to degradation from the sea side, resulting in land loss. Based on topographic reference measurements during field campaigns, we generated digital elevation models using stereophotogrammetry, in order to block adjust and ortho-rectify 1951 aerial photographies and GeoEye, QuickBird, WorldView-1, and WorldView-2 imagery from 2010 to 2012 for change detection. Using sea ice concentration 10 data from the Special Sensor Microwave Imager (SSM/I) and air temperature time series in Tiksi, we calculated seasonal duration available for thermo-abrasion, expressed as open water days, and for thermo-denudation, based on thawing degree days. Geomorphometric analysis revealed total ground ice content on Muostakh is made up of equal numbers of intrasedimentary and macro ground ice, while its vertical hourglass distribution turned out to provide very favorable local preconditions for 15 acceleration of coastal thermo-erosion and occurence of yedoma terrain subsidence under intensifying environmental forcings, as observed in this study. Our results showed a close interrelationship of mean summer air temperature and coastal thermo-erosion rates, which is in accordance with observations made under permafrost conditions different from East Siberian Ice Complex coasts elsewhere in the Arctic. Seasonality and recent interannual variations of coastline retreat rates showed an in-20 teresting interaction of endogeneous and exogeneous parameters and reflected the cycling nature of coastal thermo-erosion, currently considerably increasing in frequency.