Lost world - Late Quaternary environment of periglacial Arctic shelves and coastal lowlands in NE-Siberia.

About 1.6 million square kilometres of subaerial shelf land existed between the modern coast and the sea level lowstand in the region of the modern Laptev, East Siberian and Chuchki Seas during the Last Glacial Maximum. We consider this Great Arctic Plain (GAP) as the northern part of the Late Pleistocene Beringia between Siberia and Alaska. Permafrost is the main feature that characterized this landscape. This shelf landscape was neither glaciated during the Late Pleistocene nor throughout the Late Saalian glacial periods. Most parts of the extensive area were flooded in a relatively short time span of 7 ky during the Early-Middle Holocene. How was this lost world originally characterized and how did it react on the Late Quaternary climate variations? Some answers were found in permafrost sequences on the coastal plains around the Laptev Sea, which represent the frozen remnants of the GAP. Since 1998 joint Russian-German expeditions studied ice-rich permafrost deposits exposed in numerous bluffs along the coast as well as on the New Siberian Archipelago. A variety of palaeoenvironmental records are well preserved there in frozen state. The oldest absolute dated permafrost records go back as far as the Saalian Glacial 200,000 years ago. Russian scientists identified ice wedge casts already in Pliocene deposits 2.5 million years old. Permafrost aggraded especially during glacial periods and was partly degraded during interglacials. Large Siberian rivers e.g. Khatanga, Olenyek, Lena, Yana, Indigirka and Kolyma flowed across the gently inclined, extensive accumulation plain on the subaerial shelves. The Great Arctic Plain was covered by steppe-like vegetation serving as food for numerous herds of mammals from the so-called Mammoth Fauna. Mountain ranges of some 100 m height existed on the New Siberian Islands and the mainland bordering the GAP in the south. These mountains were the main sediment source for the formation of ice-rich permafrost deposits. Although permafrost occurs approximately 300-500 m down below surface in northern Siberia, the thickness of Quaternary ice-rich permafrost deposits amounts 10 to 80 m. The ground ice within sediment and ice wedges amounts 60-80 wt%. Taking into account the large area of the GAP covered by ice-rich permafrost a large amount of ground ice was melted during the Early Holocene. The hydrological regime was complete transformed from regional to more local systems caused by large-scale surface subsidence of 10 to 40 meters and the formation of countless lakes on the Great Arctic Plain. The enormous release of freshwater, TOC, and greenhouse gases due to permafrost degradation in a geological relative short time was never quantified before. The role of the enormous freshwater input from thawing permafrost to the world ocean on global sea level or regional sea ice formation is still not known. Furthermore, the impact of the inundation of 1.6 million square kilometres subaerial shelf land in the East-Eurasian Arctic on marine and atmospheric circulation patterns, and on the large-scale interactions between cryosphere, hydrosphere, and atmosphere is not known until now