Abstract: Variations in phytoplankton community and primary productivity, terrestrial high-carbon n-alkanes input and vegetation change in their source during the last 9.6 ka B.P. are investigated based on high-resolution biomarker (brassicasterol, dinosterol, nC₃₇-alkenone, nC₃₀-diol) extraction and measurement at Site B2-9 from the northern Bering Sea Slope. The researched results show that surface phytoplankton and primary productivity appeared obviously periodic change from high to low and again to high during the Holocene, which might be controlled by the sea-ice extension on the shelf-break, the nutrient supplement in sea surface and climate change. Diatoms were the greatest contributor to primary productivity, in turn followed by dinoflagellates, coccolithophores and eustigmatophytes, which indicate lower order of magnitude than two formers in the steady phytoplankton community. In the clear competitive relationship between diatoms and dinoflagellates, the former toke the obviously advantage and made the main contribution to organic carbon sinks in the Bering Sea. Furthermore, stepwise total n-alkanes dropped quickly at 7.8 ka B.P., 6.7 ka B.P. and 5.4 ka B.P., respectively, showing four relatively stable stages, which might be controlled by sea-level rise during early Holocene and environmental change of terrestrial vegetation source of surrounding the Bering Sea. The molecular parameters indicate that n-alkanes were originated from terrestrial higher plant with stable vegetation structure, and then woody plant dominated in this kind of combination. Mono-carbon isotopic results denote that the nC₂₇ content was the main carbon peak and dominated in total n-alkanes, which might be related to the prosperous woody plants from vegetation source and their spatial distribution. Higher nC₂₃ content may be mainly derived from the submerged plants which widely distributed along coastal areas in Northern Hemisphere.

Key words: Bering Sea, bio-marker, phytoplankton and primary productivity, high-carbon Alkane input and terrestrial vegetation structure, holocene