Comparison of the isotopic composition (δ18O, δ2 H) of snowfall and snow cover in Moscow in the winter of 2023/24

Abstract

The aim of the study was to estimate the agreement between the isotope composition of snow cover and precipitation in Moscow during the winter season of 2023/24 characterized by a particularly deep snow cover. We sampled selected layers in snow cover on the campus of the Lomonosov Moscow State University (MSU). All precipitation falling from late November 2023 to late February 2024 at the Moscow State University weather station was sampled. Stable oxygen and hydrogen isotope (δ18О and δ2 Н) composition was analyzed in snow and precipitation samples, and the deuterium excess (dexc) has been calculated. It has been found that equations of δ2 H–δ18O ratio in precipitation and snow cover are similar. In February, the snow column showed an expansion of the range of δ18O and δ2 H values, as well as a general trend of increasing of δ18O values by 1.2–0.6‰ and a decrease in dexc values compared with December–January precipitation. This is most likely due to the aging processes of the snow cover, such as the formation of ice crusts and horizons of loose snow in the lower layers of the snow thickness. In March, the isotopic contrast of the snow column was less pronounced, and during the period of active snowmelt in late March, the range of variations in δ18O and δ2 H values was minimal. It has been shown that, in general, during the winter period of 2023/24 in Moscow, the isotopic characteristics of the snow cover were in good agreement with the weighted average isotopic data for all precipitation fallen during the observational period. That happened mostly due to the conditions of the winter period (predominance of snow precipitation, rare short thaws). Under these conditions partial melting resulted in the formation of ice crusts in the snow cover, but prevented the loss of meltwater.