CHARACTERISTICS OF SEDIMENTS IN THE SOUTHERN SOUTH CHINA SEA DURING LAST 500 kA AND THEIR PALEOENVIRONMENTAL SIGNIFICANCESl

Study of sediment samples from the southern South China Sea core MD05-2897 (08°49.53' N,111°26.51' E,water depth 1 658 m,core-length 30.98 m)indicates that the core covers a complete sequence of MIS1-12 with the age of about 500 ka at the core bottom. The carbonate content curve runs mostly parallel to the benthic foraminiferal δ¹⁸O curve, showing that the higher values of CaCO₃ content correspond to the lower δ¹⁸O values. The CaCO₃ cycle in this area is mainly influenced by terrigenous dilution, displaying the "type of Atlantic Ocean". Both the appearance of CaCO₃ peaks and content change are found earlier than oxygen isotope during deglacial periods, indicating the effect of "Carbonate Pump" on CO₂ and temperature in the lower latitude sea area. The content curve of terrigenous clasts (grain-size 3~5 μm) is parallel to the oxygen isotope curve and mainly controlled by sea level change, which can be used as an indirect index for sea-level changing. The sediments with grain-size of 1.5~2.5 μm are mainly suspended in water and transported by river, and their content is influenced by the Asia Summer Monsoon and precipitation, so it might reflect the change of the summer monsoon intensity. By the spectrum analysis, the 0.1 Ma eccentricity, 40 ka obliquity, 20 ka precession and 10 ka semi-precession cycles are all recognized in the monsoon records of marine sediments in the southern South China Sea, showing the high response of the tropic sea area climate changes to the orbital cycle.