南海北部氧同位素3期时上部海水结构的变化*

南海北部海水物理化学性质不但受东亚季风的影响,还受到珠江陆源输入的影响。文章根据对南海北部ODP 1144站浮游有孔虫属种组合变化和氧同位素分析,以及浮游有孔虫表层海水温度转换函数的研究结果表明:南海北部MIS 3期的表层海水温度在H2~H6事件时明显降低,并在H4~H5(45.66~38.77kaB.P.) 期间,表层海水冬季温度变化频繁,且幅度较大。35~29kaB.P. ,浮游有孔虫暖水种含量减少,浮游有孔虫氧同位素值增重,同时高生产力属种Neogloboquadrina dutertrei的含量增加,说明冬季风在该阶段强化。此外,52~46kaB.P.期间,N.dutertrei含量增加,浮游有孔虫氧同位素较低,表层海水温度没有明显的变化,所以此时南海北部的高生产力可能与珠江陆源输入的增加有关,指示东亚夏季风的加强。

VARIATIONS OF UPPER WATER STRUCTURE IN MIS 3 FROM THE NORTHERN SOUTH CHINA SEA

Marine Isotope Stage 3(MIS 3, 60~25kaB.P.) is an interstadial in the last glaciation. It has drawn attention of many paleoclimatologists and marine geologists by its unstable climate change which is characterized by millennial-to-submillennial-scale variations, such as Heinrich events and Dansgaard-Oeschger events. The Ocean Drilling Program(ODP) Leg 184 Site 1144(20°3.18'N, 117°25.14'E; water depth=2037m) is located at the northern slope of South China Sea, yielding hemipelagic sediments with a very high-sedimentation-rate. One of its main objectives is to reconstruct the history of the East Asian Monsoon on orbital to sub-Milankovitch timescales. However, the upper water structure of the South China Sea is affected not only by the East Asian Monsoon, but also by the fluvial runoff of the Pearl River. In this work, sediments between 22.84~72.32m, deposited during about 63.63~21.51kaB.P. from ODP Site 1144 were analyzed to clarify the influence of the Pearl River. Abundance of planktonic foraminifera which is related with sea surface temperature(SST) and oxygen isotopic of a planktonic foraminiferal species, Globigerinoides ruber, were both used to study the upper water structure variation at the millennial- to submillennial-scale in the MIS 3. SST estimated by planktonic foraminiferal transfer function(FP-12E) shows that SST decreased at 23kaB.P. ,30~28kaB.P. ,39kaB.P. ,46kaB.P. ,52~51kaB.P. and 60kaB.P. , which is corresponding with Heinrich 2~6 events, respectively, and the winter SST changed frequently and greatly during 46~39kaB.P. Abandances of warm water species of planktonic foraminifera, Globigerinoides sacculifer and Pulleniatina obliquiloculata, were lower than 10 ％ in the MIS 3, especially during 35~29kaB.P. , but that of high productivity species Neogloboquadrina dutertrei and the value of oxygen isotope increased during 35~29kaB.P. ,which indicates that East Asian winter Monsoon was strengthened during that period. During 52~46kaB.P. , abundance of N.dutertrei increased and oxygen isotope kept relatively high, but SST didnt show evident change, which might be affected by increased fluvial runoff of the Pearl River resulted by strengthened East Asian summer Monsoon.In addition, the results of spectrum analysis of SST of the ODP Site 1144 show that there is 1700a cycles for both of summer and winter SST, and 690a, 1000a, 1700a, 2710a and 6480a, and 970a, 1310a, 1700a, 2592a and 4320a cycles for winter and summer, respectively.