OXYGEN ISOTOPE COMPOSITION OF DIATOMS FROM SEDIMENTS OF LAKE KOTOKEL (Buryatia)
S.S. Kostrova1, H. Meyer2, P.E. Tarasov3, E.V. Bezrukova1,4, B. Chapligin2, A. Kossler3, L.A. Pavlova1, M.I. Kuzmin1
1Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
2Alfred Wegener Institute for Polar and Marine Research, Research Unit Potsdam, Bdg. A43, Telegrafenberg, Potsdam, 14473, Germany
3Institute of Geological Sciences, Freie Universitaet Berlin, Bdg. D, Malteserstrasse 74-100, 12249, Germany
4Institute of Archeology and Ethnography, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Lavrentieva 17, Novosibirsk, 630090, Russia
Keywords: Isotope analysis, lacustrine sediments, biogenic silica, climate changes, hydrologic variation, southern Siberia
Abstract
This is a summary of new oxygen isotope record of diatoms from Lake Kotokel sediments, with implications for responses of the lake system and its environment to global change over the past 46 kyr. Fossil diatoms in all samples are free from visible contamination signatures and contain no more than 2.5 % Al2O3, which ensures reliable reconstructions. The δ18O values in diatoms vary between +23.7 and +31.2‰ over the record. The results mark mainly diatom assemblages of summer blooming periods, except for the time span between 36 and 32 kyr, when the isotopic signal records a shift from summer to spring blooming conditions. Possible water temperature changes only partly explain the changes in the isotopic record. The observed isotopic patterns are produced mainly by isotope changes in lake water in response to variations in air temperature, hydrology, and atmospheric circulation in the region. During Marine Isotope Stage (MIS) 2 (Last Glacial maximum), high δ18Odiatom resulted from rapid evaporation and low fluvial inputs. The high δ18Odiatom values of about +29 to +30 ‰ during the first half of MIS 1 (Holocene interglacial) suggest an increased share of summer rainfalls associated with southern/southeastern air transport. The δ18Odiatom decrease to +24 ‰ during the second half of MIS 1 is due to the overall hemispheric cooling and increased moisture supply to the area by the Atlantic air masses. The record of Lake Kotokel sediments provides an example of complex interplay among several climatic/environmental controls of δ18Odiatom during the Late Pleistocene and the Holocene.
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