Features of Late Pleistocene massive ice formation in the central Yamal Peninsula based on isotopic signature (18O, 2H) of ice

On Yamal Peninsula massive ice is widespread cryogenic object, lying close to the surface in different sediments, often in a combination with ice wedges. This study is dedicated to tabular massive ground ice exposed in the outcrop of the thermocirque of the third sea terrace in the Central Yamal Peninsula to establish the mechanism of ice formation and the source of water based on the isotopic signature of ice. The tabular massive ground ice body was opened with visual thickness of 2.5 m and a length of 300 m. It had formed from 43 to 37 cal ka BP according to 14C AMS-data. A white ice body was found under the visible lower boundary of the studied tabular massive ground ice. Tabular massive ground ice yielded values of δ18О from −19.9 to −23.1‰ and δ2H from −151.8 to −164.7‰, with variations in deuterium excess from 6.5 to 20.4‰ (average dexc = 13‰). The δ18О and δ2H values of white ice vary from −17.5 to −22.5‰, and from −132.6 to −165.3‰ respectively. The δ2H-δ18О relationship for white ice indicating the injection of water and its freezing in a closed system condition. The study shows that the tabular massive ground ice is an intra-ground ice formed under sub-aquatic conditions from lake water. During syngenetic accumulation of segregated massive ice unstable freezing took place, widespread feature of cold regions, which led to intrusion of water under pressure and form injection ice