南沙海区晚上新世海水上层结构变化

LATE PLIOCENE CHANGES OF UPPER OCEAN STRUCTURE IN THE SOUTHERN SOUTH CHINA SEA

对南沙海区水深 2 772m的ODP114 3站 10 0～ 15 0m井段共 10 1块沉积样品进行了浮游有孔虫分析 ,结果表明 ,从 3 2 7Ma到 2 5 5Ma该区表层海水温度逐步降低 ,温跃层逐步加深 ,推测是晚上新世北半球冰盖形成过程中 ,东亚季风相应加强的结果。与此同时 ,南沙与南海北部的温跃层深度差值不断加大 ,可能是西太平洋暖池最终形成或加强的表现。 3 2Ma前后 ,表层海水温度和海水温跃层深度都发生了急剧变化 。

Planktonic foraminifera from Ocean Drilling Program Site 1143, southern South China Sea, was analyzed in order to reconstruct the changes of upper ocean structure during the late Pliocene(3.6～2.1 Ma). The gradual decline of the Globigerinoides sacculifer / Globigerinoides ruber ratios from 3.27 Ma to 2.55 Ma indicates a successive decrease of sea surface temperature. The correspondence between the sea surface temperature and benthic (δ^(18)O) records suggests that the cooling was probably caused by the strengthening of the East Asian winter monsoon, which in turn is associated with the progressive intensification of the Northern Hemisphere glaciation. At the same time, the stepwise increase of the relative abundance of mixed-layer species in the planktonic foraminiferal assemblage suggests a deepening of the thermocline. A comparison with the records from the northern South China Sea, has revealed a significant increase of the southern-northern gradient of the thermocline depth, implying the final formation or further development of the “Western Pacific Warm Pool”. The rapid decrease of SST and the thermocline depth at Site 1143 during about 3.2 Ma, suggest some causal relationship between the Northern Hemisphere glaciation and the “Western Pacific Warm Pool”.