The oxygen isotope composition (δ18O) of ice wedges sampled in 2015 - 2017 and 2021 was analyzed in the stable isotope laboratory of the Geography Faculty at Lomonosov Moscow State University (Prof. Yu. Vasil'chuk and Dr. N. Budantseva). International water standards (SMOW, GISP, GRESP, and SLAP) were used for calibration. Analytical precision was ±0.4‰. Oxygen isotope compositions of ice wedges sampled in 2022 were carried out at the Resource Center X-ray Diffraction Research Methods of the Science Park of St. Petersburg State University (Dr. I. Tokarev). International reference materials (V-SMOW-2, GISP, SLAP, USGS-45, and USGS-46) were used for the calibration. Analytical precision was ±0.02‰.
The sampling was carried out using an axe, after first clearing 5-10 cm of ice from the surface.