Ultra-low rare earth element content in accreted ice from sub-glacial Lake Vostok, Antarctica

This paper reports the first rare earth element (REE) concentrations in accreted ice refrozen from sub-glacial Lake Vostok (East Antarctica). REE were determined in various sections of the Vostok ice core in order to geochemically characterize its impurities. Samples were obtained from accreted ice and, for comparison, from the upper glacier ice of atmospheric origin (undisturbed, disturbed and glacial flour ice). REE concentrations ranged between 0.8–56 pg g 1 for Ce and 0.0035– 0.24 pg g 1 for Lu in glacier ice, and between <0.1–24 pg g 1 for Ce and <0.0004–0.02 pg g 1 for Lu in accreted ice. Interestingly, the REE concentrations in the upper accreted ice (AC1; characterized by visible aggregates containing a mixture of very fine terrigenous particles) and in the deeper accreted ice (AC2; characterized by transparent ice) are lower than those in fresh water and seawater, respectively. We suggest that such ultra-low concentrations are unlikely to be representative of the real REE content in Lake Vostok, but instead may reflect phase exclusion processes occurring at the ice/water interface during refreezing. In particular, the uneven spatial distribution (on the order of a few cm) and the large range of REE concentrations observed in AC1 are consistent with the occurrence/absence of the aggregates in adjacent ice, and point to the presence of solid-phase concentration/exclusion processes occurring within separate pockets of frazil ice during AC1 formation. Interestingly, if the LREE enrichment found in AC1 was not produced by chemical fractionation occurring in Lake Vostok water, this may reflect a contribution of bedrock material, possibly in combination with aeolian dust released into the lake by melting of the glacier ice. Collectively, this valuable information provides new insight into the accreted ice formation processes, the bedrock geology of East Antarctica as well as the water chemistry and circulation of Lake Vostok. Published by Elsevier Ltd. 0016-7037/$ see front matter Published by Elsevier Ltd. doi:10.1016/j.gca.2009.05.050 * Corresponding author. Address: School of Earth Sciences and Byrd Polar Research Center, The Ohio State University, Columbus, OH 43210, USA. Fax: +1 614 2924697. E-mail address: [email protected] (P. Gabrielli). 1 Present address: The Royal Museum for Central Africa, Geology Department, 3080 Tervuren, Belgium.