| Summary: | ABSTRACT FINAL ID: PP41C-1792 Changes in paleoceanographic conditions on Shirshov Ridge, Western Bering Sea, are inferred over the last two glacial cycles from the high-resolution study of planktic and benthic foraminiferal assemblages and IRD from the upper and lower parts of an 18m-long piston core SO201-2-85KL (57°30.30'N, 170°24.79'E, water depth 968 m). Here we present evidence of pronounced glacial-interglacial and millennial-scale variations in surface biological productivity, bottom-water ventilation and ice rafting. Along with strong dominance of siliceous microfossils during MIS 1 and MIS 5.5, the interglacial sediments contain diverse benthic foraminiferal assemblages whereas planktic foraminifers are scarce due to selective dissolution. In contrast, the glacials are characterized by strong terrigenous input, including the IRD transported by sea ice and icebergs, and by moderate productivity with the seasonal pulses indicated by the high content of benthic opportunistic species Alabaminella weddellensis. Factor analyses of the benthic fauna clearly show a remarkable difference between glacial assemblages and interglacial fauna which is strongly dominated by Bolivina seminuda and Bulimina tenuata. These species are known to favor rather stable high-productivity conditions with enhanced supply of organic matter to the sediments and decreased oxygen content. Reduced ventilation during the interglacials is also evidenced by high values of the dysoxic benthic group whereas the oxic group is the most abundant during the last glacial. Low-diversity planktic foraminiferal assemblages dominated by the polar species Neogloboquadrina pachyderma sin. indicating a generally cold surface-water layer characterize both glacial-interglacial cycles. However, the intervals with high relative abundance of Globigerina bulloides point to an increase in surface bioproductivity on a millennial scale. In particular, these increases occur at the glacial terminations and are compatible with spikes in planktic and benthic ...
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