南海北部1144站中更新世浮游有孔虫的千年尺度古气候记录

A Millennial Scale Mid-Pleistocene Paleoclimate Record of Planktonic Foraminifera from the Northern South China Sea Site 1144

南海北部ODP1144站中更新世气候转型时期的浮游有孔虫在千年尺度上以高频率变化为主要特征．冰期旋回主要周期在0．9Ma由41ka转变为100ka，浮游有孔虫组合也随冰期旋回出现大量的冷水种．据转换函数得出的表层水降温高达10℃发生在0．9～0．6Ma间的转型过渡期，跨越MIS22、20、18、16四大冰期．同时，温跃层深度呈阶梯式变浅，在MIS20上升至65m左右．所以，南海北部上层水体环境在中更新世气候转型期出现比末次冰期更重的δ^18O值，温跃层变浅，深水种含量降低或消失，突出了边缘海区南北气候梯度反差和冬季风在冰期增强的讯号．南海南北部的环境差异与东西太平洋的差异，共同表明低纬过程在气候变化中的重要性．

Planktonic foraminifera results from ODP Site 1144 in the northern South China Sea indicate that the Mid-Pleistocene climate transition is characterized by high-frequency changes on the millennial scale. In pace with glacial-interglacial cycles after the dominant glacial cyclicity shifted from 41 ka to 100 ka over the ～0. 9 Ma, sudden increases in the abundance of cool-water planktonic foraminifera species became more evident. The SST variations estimated from transfer function show large decreases of up to 10℃ 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 at MIS20. Therefore, during the Mid-Pleistocene climate transition, the upper ocean water environment in the nouthern South China Sea was marked by δ^18O values heavier than the last glacial maximum, a shoaled thermocline, and significant decrease to 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 the 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 process in climate change.