LATE QUATERNARY PALEOCEANOGRAPHY OF THE SOUTH-CHINA-SEA - SURFACE CIRCULATION AND CARBONATE CYCLES

Paleoceanographic information from 34 sediment cores is summarized to investigate the glacial-interglacial variations in sea surface circulation and late Quaternary carbonate cycles in the South China Sea. Judging from the distribution pattern of deposition rates, the enormous terrigenous supply by rivers is responsible for the high rate of hemipelagic sedimentation which was even higher during glacial periods. Paleotemperature maps based on Transfer Function temperature estimates have revealed a E-W gradient of SST for glacial summer and a S-N gradient for glacial winter, and this agrees well with the clockwise surface circulation in summer and counterclockwise in winter during glacials, as shown by a preliminary computer modelling. The high-resolution paleotemperature curves of core V36-3 from the northern slope show an abrupt cooling event which may belong to the Younger Dryas. Carbonate percentage in sediments and preservation of foraminifers and pteropods are used to study the carbonate cycles in the marginal sea. It turns out that two mechanisms are functioning there. Being a basin with large drainage areas, vast amount of river-borne terrigenous input dilutes carbonate, and its intensification during glacial decreases the glacial %CaCO3; being a basin connected with the Pacific, the fluctuations of lysocline, CCD and ACD in the SCS are related to those in the Pacific Ocean, and dissolution is strengthened at interglacial. Thus, above the present CCD the dilution factor predominates and the ''Atlantic cycles'' are produced; below the present CCD the dissolution factor prevails, resulting in the ''Pacific'' pattern of carbonate cycles.