Thermokarst and land-ocean interactions, Laptev sea region, Russia

Ice complexes (ICs) formed during the Late Pleistocene regression (marine isotope stages 5–3) on the drained Laptev Sea shelf and coastal lowlands. These 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 (alasses) were formed 11–11.5 to 9.5–8.5 ka BP when the shoreline position lay on isobaths −60 to −45 m. Lakes and alasses became traps for sediments formed 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 submarine pingos. As a result of the marine transgression, thermokarst lakes and alasses were transformed into lagoons, particularly on the shallow part of the shelf (between isobath −20 m and the current shoreline). On the Bykovsky Peninsula and in the vast area east of the Yana River Delta, this process still occurs today. The creation of lagoons led to the formation of indented coastlines, an increased shore length subject to thermoerosion, and an acceleration of the shelf's submergence, especially after 7.5 ka BP.