Spatial and temporal variability of snow accumulation on the Western plateau of Elbrus (Central Caucasus)

Cold glaciers in the middle latitudes are considered unique archives of environmental and climate change. However, alpine ice cores are difficult to interpret, since dynamic changes can occur over very short distances. Detailed radar survey can be used to assess the effect of ice inflow from areas with different conditions of snow accumulation on the surface compared to the drilling point on the isotopic and chemical record in the glacier core. The results of radar studies on the Western plateau of Elbrus (Central Caucasus), located at an altitude of 5100-5150 m above sea level, are presented. A high-frequency ground-based radar survey was carried out in the summer of 2017 to assess the spatial and temporal changes in snow accumulation in the upper (near the top area) part of Elbrus. The ZOND 12-e GPR (ground-penetrating radar, Radar Systems, Inc.) with 500 and 300 MHz shielded antennas was used. The receiving time window was set to 100 ns (500 MHz antenna) and 470 ns (300 MHz) to obtain reflection in the depth range of about 10 m and 50 m, respectively. The results of the GPR sounding are confirmed by data on the stratigraphy, density and chemical composition of the snow-firn thickness from a shallow (24 m) borehole. The density profile made it possible to identify peaks and corresponding ice crusts of 1-2 cm thick that formed during warm periods. The internal reflections, clearly visible on the radar profiles up to 50 m deep, are of isochronous origin and have been interpreted as the boundaries of annual and seasonal layers. Detailed maps of the distribution of snow accumulation covering the cold and warm seasons of 2015-2017 have been obtained. The average thickness of seasonal snow cover on the plateau during this period was equal to 2.07 m, with minimum and maximum values of 0.2 and 3.9 m, respectively. The average values of the water storage in seasonal horizons range from 754 to 1126 mm WE., while the annual accumulation for the 2015/16 and 2016/17 balance years amounted to 2004 and 1874 mm WE., respectively. The data obtained were used in 2018 to determine the optimal location for deep core drilling and will further serve as the basis for modeling the age of ice on the Western Plateau of Elbrus.