Thermokarst and land-ocean interactions, Laptev Sea Region, Russia

Ice complexes (ICs) formed during the Late Pleistocene regression (marine i sotope stages 5-3) on the drained Laptev Sea shelf and coastal lowlands. Th ese sediments can be several dozen metres thick (up to 40-60 m). Over wide areas the lower boundary of the ICs is situated below current sea level. At about 13 ka BP thermokarst processes began to destroy the ICs, both on the shelf and on the coastal lowlands. Thermokarst lakes and depressions (alas ses) were formed 11-11.5 to 9.5-8.5 ka BP when the shoreline position lay o n isobaths -60 to -45 m. Lakes and alasses became traps for sediments forme d via IC decay. Thermokarst processes began before submergence of the shelf in seawater at subzero temperatures. These temperatures created conditions conducive to the repeated freezing of lake taliks and the formation of sub marine pingos. As a result of the marine transgression, thermokarst lakes a nd alasses were transformed into lagoons, particularly on the shallow part of the shelf (between isobath -20 m and the current shoreline). On the Byko vsky Peninsula and in the vast area east of the Yana River Delta, this proc ess still occurs today. The creation of lagoons led to the formation of ind ented coastlines, an increased shore length subject to thermoerosion, and a n acceleration of the shelf's submergence, especially after 7.5 ka BP. Copy right (C) 2000 John Wiley & Sons, Ltd.