Tongji University, China

Planktonic foraminifer records from 228 samples from ODP Site 1146, located on the northern continental slope of the South China Sea, were used to study variations in upper water temperatures, including sea surface temperature (SST) and subsurface temperature (SSBT). The planktonic foraminiferal transfer function (FP-12E) and sum of the abundance of G. menardii and P. obliquiloculata were used as proxies of sea surface and subsurface temperature, respectively. Results show that SST and SSBT decreased gradually since 1.5 Ma BP, and distinct changes took place during 0.86-0.94 Ma and 0.64-0.68 Ma at ODP Site 1146. Differing from the results of Site 1146, Core 17957, collected by the Sonne 95 cruise in the southern South China Sea in 1994, found that SST and SSBT increased gradually since 1.5 Ma, and significant changes took place during 1.23-1.3 Ma and 0.64-0.68 Ma. The locations of Cores 1146 and 17957 were mainly controlled by the East Asian winter monsoon and West Pacific Warm Pool, respectively. Therefore, variations in upper water temperatures in the two cores indicate the East Asian winter monsoon and the West Pacific Warm Pool have strengthened since 1.5 Ma, especially after 0.68 Ma.