南海南部近50万年来沉积物特点及古环境意义

对南海南部MD05-2897孔沉积物的分析显示,该孔涵盖氧同位素1~12期,底界年龄约为50万年。碳酸钙含量曲线形态基本与底栖有孔虫氧同位素曲线平行,即碳酸钙高值对应氧同位素轻值,呈现典型的大西洋型碳酸钙分布模式。碳酸钙含量在冰消期的高值出现及含量变化均领先于氧同位素,证明低纬海区"碳酸钙泵"对大气二氧化碳浓度和温度的作用。粒度分析显示,3~5 μm组分含量曲线的变化与氧同位素曲线基本平行,说明它主要受海平面升降变化控制,可作为海平面变化的间接指标。而1.5~2.5 μm粒级颗粒主要通过河流的悬浮搬运,直接受亚洲夏季风及其所带来降雨的影响,可间接反映夏季风的强弱变化。南海南部深海沉积中的季风记录具有0.1 Ma偏心率周期,40 ka斜率周期,20 ka岁差和10 ka半岁差周期等丰富的频谱,显示出低纬度海区气候变化对轨道周期的良好响应。

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.