苏门答腊海区末次间冰期以来的季风上升流活动记录

对苏门答腊海域BAR9432岩芯末次间冰期以来的氧碳同位素、AMS 14 C测年、浮游有孔虫组合及其所反映的古生产力、温盐及温跃层变化的研究结果表明: 研究区132kaB.P.以来气候变化的特点,明显受冰期间冰期海平面波动的影响,在此基础上,还与23ka岁差周期引起的北半球高纬太阳辐射变化密切相关。末次间冰期阶段,海平面较高与全新世接近,陆源营养物质输入量减少,研究站位古生产力低,混合层厚,无上升流活动,看不到印度西南夏季风的影响;末次冰期阶段,海平面下降,陆源物质输入量增加,古生产力较高。 在此基础上,北半球夏季日照率高值阶段,古生产力更高,说明当时西南季风活动强烈,西南季风流输送赤道印度洋高盐度水至苏门答腊沿岸,使研究区盐度升高,8月盐度远高于2月,盐度季节差大; 较微弱的印度季风流与赤道逆流,在澳大利亚东南季风的影响下,可以在研究区形成相对显著的上升流活动,混合层薄,古生产力高,澳大利亚东南季风强化了印度西南季风的影响; 而北半球夏季日照率低时,印度西南季风较弱,上升流活动弱,古生产力低,其中氧同位素3期(MIS 3)中期,印度东北季风增强,近岸地区蒸发强烈,2月盐度升高,盐度季节差减小。

RECORDS OF MONSOON AND UPWELLING IN THE SUMATRA SEA DURING THE LATE PLEISTOCENE

The present paper briefly shows the ways how Earth's orbit affects the low-latitude processes such as the monsoon systems, emphasizing the significant role played by orbital forcing in the global climate system through low-latitudinal response.Core BAR9432(0°24.54'N,97°18.12'E)was retrieved during the 1994 BARAT campaign with the RV Baruna Jaya I from 2760m water depth at the Nias Forearc-Basin,offshore the Western Sumatra in the northeastern Indian Ocean. The core consists of 6.73m of foraminiferal-rich clay and 68 samples were taken.Based on analyses of δ18 O,δ13 C,AMS 14 C ages,planktonic foraminiferal assemblages,and on the sea surface temperature and salinity estimated by the planktonic foraminifera Modern Analog Technique,we reconstructed the paleoceanography records over the past ca.132ka and obtained the following results: Climate variation of the studied region was affected by glacial-interglacial sea-level fluctuation obviously,and followed by the 23ka orbit precession cycle. During the last interglacial period when the sea-level was higher and similar to the Holocene,terrigenous material supply decreased,the paleoproductivity was low in the studied area. The mixed layer was thicker and the coastal upwelling was absent,so there is no evident Indian Southwestern Monsoon over the studied area.The increased terrigenous material induced a high paleoproductivity when sea level was lower during the last glacial.On this basis,the higher paleoproductivity implied that the Southwestern Monsoon was strengthened,when the summer insolation in the northern hemisphere strengthened,and the easterly Southwestern Monsoon Current transported the high salinity water of the Equatorial Indian Ocean to the studied area and increased its salinity. In addition,the salinity was higher in August than that in February,the difference in seasonal salinity between August and February was large. Under the influence of Australian Southeast Monsoon,the weaker Indian Monsoon Current and Equatorial Eddy Current could produce a relative obvious upwelling,which made the mixed layer thin and led to a rise in paleoproductivity.Australian Southeast Monsoon boosted up the influence of Indian Southwestern Monsoon.When the summer insolation in the northern hemisphere decreased,the Indian Southwestern Monsoon became weak,upwelling was restrained and paleoproductivity was low.The Indian Northeastern Monsoon seem to be strengthened in the middle MIS 3 over the studied area.The sea surface salinity increased and the seasonal salinity difference between August and February minished due to the strong evaporation near the shore region.