南海北部晚第四纪高分辨率元素比值反映的东亚季风演变

LATE QUATERNARY EAST ASIAN MONSOONAL EVOLUTION RECORDED BY HIGH RESOLUTION ELEMENTAL RATIOS IN THE NORTHERN SOUTH CHINA SEA

选取大洋钻探ODP 184航次在南海北部钻取的1144站(20°3.18′N,117°25.14′E;水深2037m)上部岩芯为研究材料,通过X荧光光谱(XRF)岩芯扫描仪获取晚第四纪100ka以来时间分辨率高达10年的元素记录,并与德国"太阳号"95航次在同一站位获得的17940-2柱状样(20°07.0′N,117°23.0′E;水深1728m)的相关数据(包括底栖有孔虫Uvigerina+Bulimina的丰度、有机碳通量和粘土含量)进行比较,发现Ba/Ti和K/Al比值可以分别反映表层生产力和陆地化学风化的变化,且都具有明显的岁差和半岁差周期,呈现典型的热带气候特征,可能与东亚夏季风的变化有关。特别是,Ba/Ti和K/Al比值还具有类似D/O事件的千年尺度(1.4～2.0ka)周期和与太阳活动相关的百年尺度(约200a和500a)变化周期,且其千年尺度的变化特征在形态上更接近于南极冰芯中的氧同位素记录,反映了低纬海区与南半球高纬区的古气候联系。

The Ocean Drilling Program Site 1144 （20°3. 18＇N, 117°25. 14＇E; Water depth 2037m）from the Northern South China Sea was selected for the measurements on elemental contents in deep-sea sediments of the last 100kaB. P.,by using a nondestructive X-ray fluorescence （XRF）core scanner with an interval of lcm （time resolution ca. 10a）. Compared with the relevant data（benthic foraminifera Uvigerina＋Bulimina abundance, organic carbon flux and clay percentage） from Core 17940-2 （20°07.0＇N, 117°23.0＇E; water depth 1728m） recovered during the German SONNE Cruise 95 at almost the same position, our data demonstrated that the elemental ratios such as Ba/Ti and K/Al could be used to indicate the Late Quaternary changes in surface paleoproductivity and chemical weathering,respectively, and hence to reflect the variations of the East Asian summer monsoon. On the orbital time-scale,the changes of Ba/Ti and K/Al ratios showed remarkable ca. 19.5ka processional and obvious ca. 10.9ka semi-processional cycles, the typical signals of tropical climate changes, indicating the tropical characteristics of the East Asian summer monsoon. On the millennial and centennial scale, the records of Ba/Ti and K/Al ratios showed 1.4 - 2.0ka D/O-like cycles and ca. 200a to 500a cycles related to solar activity. Partieularly, their millennial-scale oscillations were much closer to those in the Antarctic ice core δ18O,but anti-phase to that in the Greenland ice cores. These finds further supported the paleo-climate links between the low latitude oceans and the high latitudes of the southern hemisphere.