Massive ice (MI) bodies exposed in floodplain and terraces at 7 sites have been studied from 1985 to 2020. In recent research stable oxygen and hydrogen isotope composition of massive ice bodies on the extreme North-Eastern Chukotka (near Lavrentiya settlement and Koolen' lake) have been studied in detail. It was concluded that studied massive ice bodies have intrasedimental origin and most likely are dated back to the Late Pleistocene age. Mean δ18O values range from –18.5 ‰ to –15 ‰ whereas mean δ2H values range from –146‰ to –128 ‰ that is higher than expected for the Late Pleistocene ice bodies in this region, which most likely resulted from isotopic fractionation during freezing of water-saturated sediments in a closed system when forming ice isotopically enriched compared with initial water. The analysis of co-isotope ratios for massive ice shows that initial water is mainly of meteoric origin (precipitation, water of lakes and taliks).

For stable isotope analysis, ice was sampled both vertically and horizontally from the ice beds, depending on the outcrop accessibility. Isotope oxygen in MI sampled in 1985-1987 was measured using a G-50 device in the isotope geology laboratory at the Institute of Geology, Tallinn, Estonia (Prof. R. Vaykmäe) and in the isotope hydrology laboratory at the Institute of Water Problems of Russian Academy of Science (Dr. A. Esikov). Control measurements were taken in both laboratories. The massive beds sampled during field studies in 2016-2020 were analyzed in the stable isotope laboratory of the Geography Faculty at Lomonosov Moscow State University (Prof. Yu. Vasil'chuk and Dr. N. Budantseva) using a Finnigan Delta-V Plus mass spectrometer applying equilibration techniques. International water standards (SMOW, GRESP, and SLAP) were used for calibration. Analytical precision was ±0.4‰ for δ18O and ±1‰ for δ2H. All values are presented in δ-notation in per mille (‰) relative to the Vienna Standard Mean Ocean Water (VSMOW).