Dolomite highlights glacial to interglacial transitions in Ross Sea deposits investigated in AND-1B core, Antarctica

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Helling, D. , Kuhn, G. , von Eynatten, H. , Vogel, S. W. , Rugi, F. , Castellano, E. , Marino, F. , Udisti, R. and Aghib, F. S. (2008): Dolomite highlights glacial to interglacial transitions in Ross Sea deposits investigated in AND-1B core, Antarctica , AGU Fall Meeting, December 14-19, 2008, San Francisco, USA. .
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The retreats of Antarctica's ice masses during the Plio-Pleistocene were characterized by large-scale environmental changes at the continental margin. Increased melt water got in contact with seawater and build up particular conditions for a huge variety of chemical reactions. The precipitates of these reactions, within the sediment deposits, are reliable tools to reconstruct specific paleoenvironmental changes. Discrete horizons with high dolomite and calcite content (up to ~20 and ~30 % respectively) were detected in the AND-1B core from the ANDRILL McMurdo Sound Project. We measured the split core in the field during the austral summer 2006/2007 with a non-destructive AVAATECH XRF-Core Scanner. On discrete samples chemical analysis were carried out and the mineral composition was examined by X-ray diffraction measurements. At the depth of 162.71, 182.10, 224.59 and 292.15 mbsf these high dolomite values were found within the glacial to interglacial transition zones. Our hypothesis states that calcite and dolomite formation in the transition zones is possible under cold glaciomarine conditions with an increased melt-water runoff and a high amount of dissolved HCO3- in contact with Mg+ and Ca+ rich seawater at the grounding line region or in the sub-ice hydrological system. We also detected horizons containing other carbonates like ankerite (i.e. 143.23, 449.26 mbsf) and low Mg calcite that support this hypothesis. Whether in this environment the dolomite was (I) precipitated in the water column, or (II) in the pore water system where sub-ice freshwater was replaced and overlaid by heavier seawater during glacial to interglacial transitions, is under investigation. Anyhow, most of the dolomite formations in the AND-1B core could be related to shelf ice retreats and (bio?)geochemical processes at or close to the sediment surface.

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