STABLE CARBON ISOTOPE ANALYSIS OF LAKE CORE SEDIMENTS AND LIPID BIOMARKERS AS A PROXY FOR LATE PLEISTOCENE CARBON CYCLING AT ELIKCHAN LAKE, NE SIBERIA

High resolution pollen records from Elikchan Lake, northeastern Siberia, indicate that significant and rapid (1-2 ka) fluctuations in Pinus and Poaceae pollen deposition occurred between 30 and 60 ka. These fluctuations may be associated with rapid climatic shifts documented in the North Atlantic. This study represents an investigation of the organic geochemistry of the Elikchan Lake core sediments and is part of a multi-institutional, international collaboration to create a multi-proxy record of environmental change in northeastern Siberia during the Late Pleistocene. In this project, the organic geochemistry of a newly acquired sediment core from Elikchan Lake is explored to better understand aquatic and terrestrial organic matter deposition during the last ~70 ka.

A 9.9 m core was retrieved from a water depth of 5.5 m, in May, 2004. At Bates College, the percent organic carbon (%OC), carbon/nitrogen (C/N) and d¹³C values were determined for the decalcified, homogenized core sediments every 30 cm. The C/N ratios range between 7.1 and 14.3. These values are consistent with organic matter that is dominated by algal production (C/N <10) and organic matter representing a mix of aquatic and terrestrial sources (C/N between 10 and 20). Between 990 and 300 cm, the carbon isotope values of the bulk sediment fluctuate between -28 and -32‰. In the upper 300 cm of the core, the isotopic values are significantly more depleted with values as low as -37‰.

Higher plant leaf wax lipid biomarkers (i.e., n-fatty acids with even C#>22, n-alkanes with odd C#>21, b-Sitosterol, Campesterol, Stigmasterol) and algal biomarkers (i.e., Brassicasterol, Dinosterol) were quantified and analyzed for carbon isotope composition in an effort to better constrain the meaning of these bulk isotope values. Higher plant leaf wax lipids were abundant throughout the core, whereas aquatic sterols were not present and terrestrial sterols were present only in trace amounts. Compound specific isotope data on these various biomarkers in this study will provide more detailed information on the source of organic matter in the bulk sediments.