Abstract: The authors analyzed oxygen and carbon isotope of planktonic foraminifera from surface sediments and plankton tow samples collected from southern South China Sea (SCS) in spring 2002, and discussed their relationship with marine environmental parameters and depositional process. Their results show that Globigerinoides ruber and G. sacculifer have almost the same average δ18O values in the spring tow samples, which are obviously lighter than those in the surface sediments. In the surface sediments, however, the average δ18O value of G. ruber is apparently lighter than that of G. sacculifer, which may be related to gametogenesis calcification of G. sacculifer and seasonal difference of the two species. The average δ18O value of Pulleniatina obliquiloculata is apparently heavier than that of G. ruber and G. sacculifer in both the surface sediments and the upper water, suggesting a large intra-species δ18O gap between the three species. The average δ18O value of P. obliquiloculata in the upper water in spring is about 0.7‰ lighter than that in the surface sediments, possibly due to the winter flourish of P. obliquiloculata that prefers the low temperature of winter water. The average δ13C values of the three species show a similar trend in both the sediments and the upper water, namely, the heaviest for G. sacculifer, the lightest for P. obliquiloculata, and G. rubber in the middle. The difference of δ13C values between the three species may be mainly caused by vital effect. The regional variations of δ18O values of G. ruber and G. sacculifer in the surface sediments show a similar trend, with heavy values in the northwest and gradually lightening to the southeast of the studied area, all accords with the trend of yearly-averaged sea-surface temperature of gradually increasing from northwest to southeast. Both the δ18O and δ13C of P. obliquiloculata show heavier values in the upwelling stations of the studied area. The relationship of δ13C of P. obliquiloculata with nutrient level of the upper-water mass in southern SCS is contrary to that in northern SCS, which needs to be confirmed by future studies.

Key words: southern South China Sea')">southern South China Sea, planktonic foraminifera, plankton tow, oxygen and carbon isotope, upwelling