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LATE QUATERNARY SURFACE PALEOPRODUCTIVITY AND VARIATIONS OF THE EAST ASIAN MONSOON IN THE SOUTH CHINA SEA

Jian Zhimin;Wang Lujiang;M.Kienast(Laboratory of Marine Geology, Tongji University Shanghai 200092)(Institut fur Geowissenschaften, Keil Universitat,Germany)  
Benthic foraminifera in gravity and piston cores from tWo sites of the northern and southern slopes of the South China Sea (SCS) were analyzed to evaluate changes in surface paleoproductivity and hence the variations of the East Asian Monsoon over the last 40 000 years. Our observations suggest that the distribution patterns and accumulation rates of some deep-sea benthic foraminiferal species may be primarily controlled by the organic carbon (Corg) flux tO the seafloor in the SCS. TWo major subgroups of these species serve as proxy to distinguish tWo different ranges of Corg flux ( 2.5 and 3.5gC/ (m2· 103a). When Corg flux increases above 3.5gC/(m2·103a)in the southern SCS during the Last Glacial Maximum (LGW) and in the northern SCS during the early Holocene, a group of detritus feeders such as Bulimina aculeata and Uvigerina peregrina dominates. However, the suspension feeders such as Cibicidoides wuellerstorfi and "opportunistic" species such as Oridosalis umbonatus,Melonis barleeanum and Chilostomella ovoidea gradually become more important than detritus feeders as soon as the Corg flux decreases tO 2.5-3.5gC/(m2. 103a).During the LGM, the high Corg flux and increased abundances and accumulation rates of B. aculeata and U.peregrina in the southern SCS are mainly caused by the enhanced NE winter monsoon-driven upwelling and associated productivity, and panly by the increased input of terrigenous nutrientS as a result of the lowered sea level.However, during the first part of the Holocene, around 10 000aB.P., the remarkably increased abundances and accumulation rates of B. aculeata and Uperegrina especially in the northern part of the SCS, together with the high Corg flux, point tO increased productivity, probably driven by a maximtim intensity in the SW summer monsoon.
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