The rate of subsea permafrost degradation in the 25 years following coastal erosion at Muostakh Island, Laptev Sea

Submarine permafrost is usually created by the inundation of terrestrial permafrost by seawater. The inundation of permafrost follows coastal erosion or relative sea level rise. Low modern sea level rise rates in Siberia mean that coastal erosion is the main mechanism of formation of submarine permafrost. Coastal sections composed of fine-grained sediments that have high ground-ice contents, such as the long Yedoma coastline of eastern Siberia, are especially vulnerable to mechanical and thermal erosion processes [Romanovskii et al., 2004]. When such frozen soft sediments thaw and/or erode, then the state of the permafrost is determined by the transition from sub-aerial to submarine conditions, and the processes that accompany this transition. These include removal of the upper horizons of material, sediment dynamics along the beach and shore face profile, saltwater diffusion, changing thermal regime and sea ice dynamics. For example, driven by the influence of warm and salty seawater, permafrost begins to thaw once inundated due to thermal and chemical degradation. As a result, submarine permafrost degradation may be rapid near the coast, and shows a spatially variable dependence on this set of processes [Overduin et al., 2007]. Our objectives are to investigate changes in coastal geomorphology in combination with geophysical investigations of submarine permafrost distribution in the near-shore zone (< 10 m water depth), in order to infer which processes dominate permafrost degradation in this highly dynamic coastal setting