Causes of Uncertainties in Paleoclimatic Reconstructions Based on the Oxygen Isotope Composition of Glacier Ice on Elbrus (Western Plateau)

The isotope signature of glacial ice in the Western Elbrus Plateau (the Caucasus) has been studied based on five ice cores obtained in different years. It has been shown that the isotopic parameters of ice are associated with the processes of accumulation and wind scouring of snow. Three ice cores were obtained in 2013 (C-1, C-2, and C-3), one in 2017 (C-4), and one more in 2018 (C-5). Core sampling has been performed with a resolution of 5 cm. An isotopic analysis has been carried out at the CERL laboratory (AARI) using a Picarro L2130-i isotope analyzer, and the accuracy is 0.06‰ for δ¹⁸О and 0.30‰ for δ²Н. The δ¹⁸О and δ²Н values of the ice of the Western Plateau generally vary from −5 to −30‰ and from −18.7 to −225.8‰, respectively, with well-defined seasonality. A comparison of the isotope record for all cores has shown that the differences in accumulation for individual seasons reach 0.3 m.w.e., and differences in accumulation for individual seasons averaged over 5 years is approximately 0.2 m.w.e. The absolute differences in the average seasonal δ¹⁸O values associated with wind scouring and spatial redistribution of snow (sedimentation noise) averaged over 5 years have reached 1.38‰. The irregularity of amount of precipitation within the season and errors in core dating have been an additional contribution to nonclimate variance (definition noise). The absolute difference in the average seasonal δ¹⁸О values associated with this type of noise averaged over 5 years is 1.7‰. Thus, the total uncertainty for two different types of noise can be estimated at 2.2‰, which is ~20% of the annual seasonal amplitude of δ¹⁸O values of the glacier ice in the Western Plateau (the average difference between the δ¹⁸O values of warm and cold seasons is ~10–11‰). One problem of linking the isotope record to the annual temperature record at the weather station has been solved by using ammonium concentrations for dating the C-1 ice core and calculating the “ideal” annual variation of δ¹⁸O values by a cosine function of the annual amplitude. Using the ammonium ion ( \({\text{NH}}_{4}^{ + }\) ) concentration, each annual layer in the C-1 ice core has been divided into two parts associated to snow deposition in winter and in summer. It has also shown δ¹⁸O values associated to change of seasons. The calculation of the cosine function has shown the simplified δ¹⁸O values for each month of a particular year, due to which the δ¹⁸O values of the season boundaries in the ice core have been related to the calendar months. This assimilation has made it possible to compare the obtained average seasonal δ¹⁸О values from the core with instrumental observations at the Klukhorskiy Pass meteorological station. The δ¹⁸O values of winter seasons have had a weak relation with surface temperatures due to both wind erosion and the high interannual variability of snow accumulation. At the same time, the average δ¹⁸O values of the warm seasons have been significantly positive correlated with surface temperature (r = 0.7, p = 0.1), so ice core δ¹⁸O records can be used as a temperature proxy of the warm period.