Investigation of a deep ice core from the Elbrus western plateau, the Caucasus, Russia

Abstract. A 182 m ice core was recovered from a borehole drilled into bedrock on the western plateau of Mt. Elbrus (43°20´53.9'' N, 42°25´36.0'' E; 5115 m a.s.l.) in the Caucasus, Russia, in 2009. This is the first ice core in the region that represents a paleoclimate record that is practically undisturbed by seasonal melting. Relatively high snow accumulation rates at the drilling site enabled the analysis of the intraseasonal variability in climate proxies. Borehole temperatures ranged from −17 °C at 10 m depth to −2.4 °C at 182 m. A detailed radio-echo sounding survey showed that the glacier thickness ranged from 45 m near the marginal zone of the plateau up to 255 m at the glacier center. The ice core has been analyzed for stable isotopes (δ¹⁸O and δD), major ions (K⁺, Na⁺, Ca²⁺, Mg²⁺, NH₄⁺, SO₄^2-, NO₃^-, Cl^-, F^-), succinic acid (HOOCCH₂COOH), and tritium content. The mean annual net accumulation rate of 1455 mm w.e. for the last 140 years was estimated from distinct annual oscillations of δ¹⁸O, δD, succinic acid, and NH₄⁺. Annual layer counting also helped date the ice core, agreeing with the absolute markers of the tritium 1963 bomb horizon located at the core depth of 50.7 m w.e. and the sulfate peak of the Katmai eruption (1912) at 87.7 m w.e. According to mathematical modeling results, the ice age at the maximum glacier depth is predicted to be ~ 660 years BP. The 2009 borehole is located downstream from this point, resulting in an estimated basal ice age of less than 350–400 years BP at the drilling site. The glaciological and initial chemical analyses from the Elbrus ice core help reconstruct the atmospheric history of the European region.