VARIATIONS AND CONTROL FACTORS OF PERCENT CONTENT OF LOWER-PHOTIC CALCAREOUS NANNOFOSSIL SPECIES-FLORISPHAERA PROFUNDA IN THE MIDDLE OF OKINAWA TROUGH SINCE MIS 6

Core Z14-6 (27°07'N,127°27'E, and water depth 739 m) retrieved from the central Okinawa Trough was selected for planktonic foraminifera and calcareous nannofossil study. On the comparison with SPECMAP δ¹⁸O the stratigraphy of Z14-6 was established. By contrast with data of three adjacent cores, the variations and control factors of percent content of Florisphaera profunda in this region during the last 150 ka BP were discussed. Results showed that the variations of percent content of F. profunda since MIS 6 were characterized by glacial-interglacial cycles. During the last glacial cycle, percent content of F. profunda was lower in glacial period than that in interglacial period, while which was the reverse situation during the penultimate glacial cycle. The main control factor of percent content of F. profunda in core Z14-6 is the strengthening changes of Kuroshio Current. The percent content of F. profunda began to decrease since the end of MIS 5e during the penultimate glacial cycle, based on which we presume that the main current of Kuroshio should weaken or migrate eastward and the coastal water ran into Okinawa Trough.