Late Quaternary Organic Carbon Flux and Biomarker in the Laptev Sea and the Adjacent Continental Margin

Kirsten Fahl Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany

Ruediger Stein Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany

Sediment samples from the Laptev Sea taken during the 1993 RV Polarstern expedition ARK IX/4 were investigated for their amount and composition of the organic-carbon fraction. Of major interest is the identification of different processes controlling the organic-carbon deposition (i.e., terrigenous supply vs. surface-water productivity). Long-chain highly unsaturated alkenones derived from coccolithophorides and fatty acids derived from diatoms and dinoflagellates were analysed by means of gaschromatography and mass spectrometry. First results on the distribution of these biomarker in surface sediments indicate that the surface-water productivity signal is well preserved in the sediment data. This is shown by the distribution of the 16:1 (n-7) and the 20:5 (n-3) fatty acids (Fig. 1), indicative for diatoms, and the excellent correlation with the chlorophyll a concentrations in the surface-water masses and the biogenic-opal content and hydrogen indices of the sediments. The high concentration of these unsaturated fatty acids in shallow-water sediments show the recent deposition of the organic material, whereas in deep-sea sediments the concentrations are low. This decreased content is typical for phytoplankton material which is broken down by microorganisms or autoxidation. In general, the alkenone concentrations are very low, suggesting low production rate of coccolithophorides. Long-chain n-alkanes as well as high C/N ratios and low hydrogen indices indicate the importance of (fluvial) supply of terrigenous organic matter.

Further organic-geochemical investigations of sediment cores will give us more detailed informations about the biomarker composition and its change through time. This kind of data will allow reconstructions of paleoproductivity and terrigenous organic-carbon input in relationship to climate change.