Abrupt changes of radiolarian fauna at 600 and 120 ka B. P. in the southern South China Sea and their paleoceanographic implications

Abrupt changes in radiolarian composition are discovered over the last 600 and 120 ka B.P.based on quantitative analyses of radiolarians in Core 17957-2 of the southern South China Sea.The distinct changes at 600 ka B.P.could correspond to the onset of the 100 ka cycle during the glacial and interglacial periods.This abrupt change in the 100 ka cyclicity at 600 ka B.P.occurred also in the magnetic susceptibility signal that is obtained from loess and plaeosol sequences of the China Loess Plateau.The larger amplitude and stronger cyclicity in the susceptibility signal after 600 ka B.P. reflect the prominent change in the intensity of the monsoon,induced by an enhancement of the monsoon circulation.Stronger seasonality during the glacial period in the South China Sea,resulted from strengthening of winter monsoon,might lead to the changes in the radiolarian composition at 600 and 120 ka B.P.It can be suggested that only species adapted to a broader temperature range might have been able to live in this environment.Therefore,the abrupt changes in radiolarian composition at 600 and 120 ka B.P.could be attributed to the stronger SST differences between summer and winter that were caused by the striking change in the intensity of the monsoon circulation.