HR: 0800h
AN: PP21B-1375    [Abstracts]
TI: Biomarker investigations of a 250ka old Lake El'gygytgyn sedimentary record - preliminary results
AU: * Hanisch, S
EM: shanisch@awi-bremerhaven.de
AF: Institute for Environmental Geology, Technical University Braunschweig, Pockelsstrasse 3, Braunschweig, D-38106 Germany
AU: * Hanisch, S
EM: shanisch@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, D-27515 Germany
AU: Fahl, K
EM: kfahl@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, D-27515 Germany
AU: Gebhardt, C
EM: cgebhardt@awi-bremerhaven.de
AF: Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, Bremerhaven, D-27515 Germany
AU: Juschus, O
EM: juschus@rz.uni-leipzig.de
AF: University Leipzig, Institute for Geophysics and Geology, Talstrasse 35, Leipzig, D-04103 Germany
AB: Lake El'gygytgyn is a 3.6 Mio year old impact crater lake located in central Chukotka, NE Siberia. In recent times the lake is frozen from about October till June with only a few months of open water during the summer. The sedimentary record of the lake has become a major focus of multi-disciplinary multi-national paleoclimatic research. In 1998 and 2003, two 13m (PG1351) and 16m (LZ1024) long sediment cores, respectively, were recovered from the central part of the lake which comprise the last approx. 250ka BP. Based on previous lithological and biogeochemical studies the sediments of PG1351 can be sub-divided into four different facies units showing cyclic alternations. These units were associated with warm, peak warm, cold and dry, and cold and more moist climates, respectively. We have carried out biomarker analysis on such sediment units of core LZ1024. Our chronology is based on matching a magnetic susceptibility record of this core with that of the previously dated core PG1351. Biomarkers such as n-alkanes, dinosterol, brassicasterol, cholesterol, isoarborinol, campesterol, and sitosterol have been identified and quantified by gas chromatography and gas chromatography/mass spectrometry. High TOC values during cold phases with perennial lake ice coverage indicate that organic matter was less affected by degradation as a result of water body stagnation compared to warm phases with summer melt and complete mixing. Our biomarker results exhibit ratios of long- to short-chain alkanes being high during warm and peak warm phases. This suggests that terrigenous input (including long-chain alkanes derived from land plants) was enhanced and/or autochthonous organisms (synthesizing short-chain alkanes) were less abundant as a result of a mixing water column during the summer period. Consistently, the records of dinosterol and brassicasterol derived from aquatic organisms (dinoflagellates and diatoms) exhibit distinctively higher (3 to 10 times) concentrations during cold phases as compared to warm phases. This suggests a relatively high aquatic productivity and preservation during perennial lake-ice coverage in comparison to phases with water column mixing during arctic summer periods. Our biomarker results suggest that the sediments of Lake El'gygytgyn reflect past aquatic organism assemblages and the composition and sources of terrigenous organic matter input. Both appears to be mostly controlled by seasonal ice cover. Thus, biomarkers can be used to interpret the evolution of Lake El'gygytgyn as a reflection of changes in the arctic climate.
DE: 1055 Organic geochemistry
DE: 1600 GLOBAL CHANGE (New category)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting