PALEOCEANOGRAPHIC IMPLICATIONS OF RADIOLARIA IN THE SOUTHERN OKINAWA TROUGH OVER THE LAST 20,000 YEARS

Quantitative analyses have been carried out on radiolarians from 65 sa mples of Core 255 in the southern Okinawa Trough. The distribution of taxa and the results of Q-mode factor analysis show that during the la st 20 000 years three radiolarian assemblages could be distinguished w hich can be correlated to high and low productivity levels indicated b y the organic carbon content, radiolarian abundance and ratio of Nasse llaria/Spumellaria in the sediment. The Tetrapyle quadriloba assemblag e of the last glaciation and deglaciation is associated with high prod uctivity whereas the early Holocene Polysolenia spinosa and the middle and late Holocene Carposhaera globosa assemblages correspond to low s urface productivity. Meanwhile, the variations in the ratio of radiola rian fragments indicate higher SiO2 dissolution during the Holocene th an during the last glacial stage.