University of Adelaide, Australia

Planktonic Foraminifera from ODP Site 1144 in the northern South China Sea indicate that the Middle Pleistocene climate transition is characterized by high-frequency changes on a millennial scale. On pace with glacial-interglacial cycles after the dominant glacial cyclicity shifted from 41 ka to 100 ka over the last 0.9 Ma, sudden increases in the abundance of cool-water planktonic foraminiferal species became more evident. SST variations estimated by the transfer function show large decreases of up to 10 degrees C during the four major glacial periods of MIS22, 20, 18 and 16 between 0.9-0.6 Ma. Cooler conditions in glacial times also caused the thermocline depth to shoal in steps to a minimum of about 65 m during MIS20. Therefore, during the Middle Pleistocene climate transition, the upper ocean water environment in the northern South China Sea was marked by delta (super 18) O values heavier than at the last glacial maximum, a shoaled thermocline, and a significant decrease to an almost complete absence of several deep-water planktonic foraminiferal species, amplifying the paleoclimatic signals of SST contrasts between the northern and southern South China Sea and a strengthened winter monsoon on a millennial scale. Together with the E-W equatorial Pacific record, the N-S contrasts in the South China Sea demonstrate the significance of low latitude processes in climate change.