Transformation processes of submarine permafrost at the northern Siberian continental margin since the last glaciation
Major parts of the continental periphery of the Arctic Ocean is comprised of terrestrial permafrost. Empirical data as well as modeling experiments show that the stability of this particular cryosphere is under immense pressure due to global warming. However, during Quaternary times this frozen landscape was repeatedly changed due to fluctuations in both temperature and sea-level which particularly affected the wide and shallow North-Siberian shelves. As western part of the Beringian landmass this region was subaerially exposed during the last glacial maximum when global sea level was lowest. During the ensuing deglacial time sea-level rose gradually changing a terrestrial permafrost landscape into a shallow, marine shelf environment. Various geochemical, micropaleontological, palynological, and sedimentological data obtained from both conventional gravity cores and drill cores reveal the strong influence of this transformation process on the shelf environment. The sediments from just below the Holocene sediment package drilled on the outer shelf confirm the existence of permanently frozen, ice-bearing terrestrial sediments underneath. However, geochemical evidence of the ice and the porewaters indicate that the frozen sediments were altered by re-freezing processes during and after the global sea-level rise which followed upon the last glacial period. This assumption is further corroborated by high-resolution acoustic data, emphasizing the overall fragility of the natural state of submarine permafrost in the Arctic.