Variations in Upper Water Structure during MIS3 from the Western South China Sea

Global climate changes of last glacial are characterized by millennium-scale fluctuations in oxygen isotope records. Dansgaard-Oeschger cycle (D-O cycle), which is characterized by alternation of interstadial (IS) and stadial in Greenland ice core[1], and Herinch event (H event), which is an event of sudden iceberg discharge into the North Atlantic, are identified to be the major components in the fluctuations. Core 17954 is located in the modern summer upwelling area in the western South China Sea, its sediments recorded the variations of upwelling generated by East Asia Summer Monsoon(EASM) during MIS3. Based on the strict age model of AMS 14C dating,the paleo-Sea Surface Temperature (SST) and Salinity (SSS) are reconstructed by pairing Mg/Ca-Paleothermometer and δ18O of planktonic foraminifera Globigerinoides ruber (white s.s.). Results show that in Core 17954, the δ18O record of G.ruber has significant millennium fluctuations as the δ18O records from NGRIP icecore and Hulu Cave stalagmites, this indicates that the climate changes of western SCS contains both signals from High Latitude of Northern Hemisphere as well as EASM. In order to get more information on upwelling changes, previous records of thermocline and foraminiferal primary productivity in Core 17954 are collected, restudied and compared. Five distinct shallowing periods of thermocline (referred to as S1~S5) are identified in this study. In S1~S4, SST is lower and productivity is higher, these indicate to an enhanced upwelling and strengthened EASM during these periods. And the lower SSS, caused by increasing precipitation or fresh water input, also prove this standpoint.