CALCAREOUS NANNOFOSSILS AND ITS PALEO-OCEANOGRAPHIC IMPLICATION IN THE XISHA TROUGH SINCE THE LAST DEGLACIAL MAXIMUM

The changes in calcareous nannofossils and composition abundances have been studied for the piston core 27A from the Xisha Trough, South China Sea, and planktonic foraminifera oxygen isotopes and calcium carbonate have also been analyzed. The result shows that the 805 cm-long core contains a depostional history since the marine isotope stage2(MIS2). Sedimentary column of the core can be divided into three parts:660~805 cm interval of the last glacial maximum, 465~660 cm interval of the last deglaciation time and 0~465 cm of post-glacial time in Holocene. The study area was influenced by the continent during the last glacial time, whereas by the open ocean during the postglacial time.The primary productivity was higher in the glacial time and lower in the Holocene converted by Florisphaera profunda content. During the glacial time, the dissolution of calcareous nannofossils was stronger than that in Holocene, with characteristic of "Pacific type" of carbonate cycle, while the carbonate content shows a pattern of "Atlantic type" of cycle.