南海西南部海区近200ka来的动力环境与东亚古季风

DYNAMICAL ENVIRONMENT IN SOUTHWESTERN SOUTH CHINA SEA AND ITS RELATION TO EAST ASIAN PALEOMONSOON SINCE 200ka B.P.

包括南海在内的热带海洋是东亚夏季风的发源地,分析其动力环境特征的演变历史,可提供东亚古季风活动的海洋证据。对取自该海区的NS93 5柱状样做了详细的粒度分析,结合氧同位素地层结果、微体古生物观察统计和CaCO3测试资料,尝试采用高精度的粒度分析作为替代性指标,讨论近200ka以来的水动力及古生产力变化特征。结果认为,自末次盛冰期以来该海区的海洋动力环境发生了明显的变化,而在此之前则变化不显著,在倒数第2次冰期中由于夏季风作用致该局部区域上升流发育和海面温度偏高。古生产力变化规律一般是:在冰期较高,并呈稳定或上升趋势;在间冰期较低,出现下降现象。近200ka来的特殊情况出现于全新世早期,古生产力达到最高值。通过与黄土高原及其它地区的古季风环境对比,发现东亚古季风区内在全新世和末次盛冰期的遥相关较好,而在倒数第2次冰期中存在明显差别,说明在冬季风和夏季风的相互作用下,产生了特定时期内典型季风区的局部海洋区域性特征。

As located in the tropic west Pacific area, the southern South China Sea is a cradle of East Asian summer monsoon. It is significant for providing marine evidance of east Asian paleomonsoon activity to analyse the evolutional history of dynamical environment in this sea area. Based on the detailed analysis on the grain size of core NS935 from southwestern South China Sea and its oxygen isotopic stratigraphy, and on the observation of microfossil composition and CaCO3 content, the changing features of dynamical environment and paleoproductivity since 200ka were discussed mainly by using high resolution grainsize as the proxies in this paper. It is concluded that the marine dynamical environment changed little before the Last Maximum Glacial (LMG) but changed obviously since the LMG. It also illustrated the existence of summer paleomonsoon in the second last glacial period in this sea area, which had caused the upwelling activity and a relative higher temperature of surface water. In generally, the paleoproductivity was higher and showed a stable or rising tendency in the glacial period, and lower and declined in the interglacial period. The special situation of paleoproductivity variation during the last 200ka appeared in the early Holecene, when its value reached the highest. Comparing the East Asian paleomonsoon environment in this region with that in the loess plateau and other regions, we found that there was a better teleconnection during Holocene and LMG, but a distinct difference in the second last glacial epoch, which showed a regional feature of typical monsoon area under the interaction of winter monsoon and summer monsoon in a special period.