Radiolarian responses to paleoceanographic events of the southern South China Sea during the Pleistocene

A quantitative radiolarian study at Core 17957-2 from the South China Sea (SCS) allows reconstructing two paleoceanographic events occurring during the last 1500 ka. Based on the abundance variations of siliceous microfossils (radiolarian, diatom and sponge spicule), the definitions of the productivity and thermocline indexes (DAR, diatom accumulation rate, and TSR, thermocline surface radiolarian indexes) as indicators for productivity and thermocline changes as well as changes in the species composition two distinct changes at ∼900 ka and ∼600 ka could be detected being related to the multiple transition phenomena of the mid-Pleistocene revolution (MPR). ange in the species composition at ∼900 ka indicated by an increase in subtropical radiolarians and a decrease in tropical radiolarians exhibits a lowering of the sea surface temperatures in the SCS that can be related to a southward shift of the North Equatorial Current induced by variations in the northern trade wind system. Increasing subsurface and intermediate species, and DAR and TSR indexes at 700–600 ka may reflect higher sea surface productivity and shallowing thermocline caused by stronger upwelling and nutrient supply. mparison of the radiolarian signal recovered from Core 17957-2 with the magnetic susceptibility signal obtained from the Chinese Loess Plateau reveals the close connection of the climatic transitions at 700–600 ka in the southern SCS to strengthening of the East Asian summer monsoon circulation. ectral analyses indicate that ice mass fluctuations (oxygen isotope record) have clear ∼100-ka eccentricity-dominated and processional signals after the MPR, but with a more significant obliquity-related response before the MPR. The surface productivity (e.g. DAR) and thermocline depth (e.g. TSR index) show the ∼100-ka dominant cyclicity before the MPR. The ∼32-ka significant regional cyclicity for the last 1500 ka responds to the surface productivity (e.g. DAR) and thermocline depth (e.g. TSR index) signals.