Stable isotope composition of syngenetic ice wedges, 14C dates of Seyakha yedoma and surrounding sediments, and January air palaeotemperatures for 25-21 cal ka BP in northwestern Siberia

Yedoma exposures in northwestern Siberia, on the eastern coast of the Yamal Peninsula at the Seyakha River mouth have been studied in detail. Yedoma strata with thick ice wedges (over 20 m high) were formed in northwestern Siberia during the Late Pleistocene cryochron (dated to 30-11.7 cal ka BP). Direct dating of ice wedges of the Seyakha yedoma on the Yamal Peninsula allows us to conclude that ice wedges were formed between 29 and 18 cal ka BP, and the termination of yedoma strata accumulation had occurred by 13.5 cal ka BP. The δ18O values in ice wedges formed 25-21 cal ka BP vary from -23 to -25‰ and the reconstructed mean January air temperatures during this period were on average -36°C, that is at least 10°C lower than modern ones. Active accumulation of yedoma sediments with ice wedges on the Yamal, Gydan, and Taimyr Peninsulas proves that vast areas of the western sector of the Siberian Arctic were not covered by the Eurasian ice sheet during the LGM (between 25 and 20 cal ka BP).