Core 17954 is located in the modern summer upwelling area in western South China Sea, its sediments recorded the variations of upwelling generated by East Asia Summer Monsoon (EASM) during MIS 3. 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 δ 18o of planktonic foraminifera Globigerinoides ruber (white s.s.). Results show that in Core 17954, the δ 18O record of G.ruber has sig- nificant millennium fluctuations as the δ 18O records from NGRIP icecore and Hulu Cave stalagmites, this indicates that the cli- mate 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.
Quantitative analysis of benthic foraminifera from ODP Site 1146 in the northern South China Sea (SCS) shows that abundance of Bulimina alazanensis, sometimes up to about 90%, decreased gradually since 3.2 Ma, especially at 2.1 Ma. Abundance of other benthic foraminiferal species, Globobulimina sub-globosa and Cibicidoides wuellerstorfi, increased after 2.1 Ma. Comparison with changes in oxygen and carbon isotopes of planktonic and benthic foraminifera shows that high abundance values of B. alazanensis corresponded with lower values of oxygen isotope, but for carbon isotope, high values of the species were consistent with heavier carbon isotope of benthic foraminifera and lighter carbon isotope of planktonic foraminifera, respectively, and vice versa. Considering factors such as uplift of Bashi Strait, expansion of the North Hemisphere Glaciation, strengthening of East Asian winter mon-soon and variations in oxygen and carbon isotope of foraminifera, changes of B. alazanensis in ODP Site 1146 suggest that the source of deep water masses of the northern South China Sea changed from the warm Pacific deep water with high oxygen content to Pacific Intermediate water with low oxygen content at 2.1 Ma. In addition, the strengthened East Asian winter monsoon resulted in increased pri-mary productivity, high nutrient and suboxic bottom water. Variations in species of B. alazanensis seemed to be unable to tolerate environmental stress induced by deep water masses and productivity changes.
