南海晚第四纪表层古生产力与东亚季风变迁

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

根据南海南北陆坡两个站位的柱状样中底栖有孔虫分布，结合有机碳、稳定同位素分析，获得南海近4万年来高分辨率的表层古生产力记录，进而探讨晚第四纪东亚古季风的变迁。研究表明，由于冬季风在本次冰期、夏季风在全新世早期约10000aB．P．急剧增强，分别在南海南北陆坡产生海岸上升流，加上陆源营养物输入增多，使得表层古生产力明显增高、有机碳通量增大至3．5gC／（m2·103a）以上，从而底栖有孔虫群中Buliminaaculeata和Uvigerinaperegrina占绝对优势。

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.