PALEOCEANOGRAPHIC VARIATIONS OF THE WESTERN PACIFIC WARM POOL DURING THE MIDDLE PLEISTOCENE CLIMATE TRANSITION
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摘要: 通过对大洋钻探(ODP)第130航次807站A孔上部约25 m样品中所含浮游有孔虫的定量统计和鉴定,结合转换函数及稳定同位素分析,揭示了第四纪近1.6 Ma以来冰期旋回中赤道西太平洋的表层海水温度和温跃层深度的变化,为研究西太平洋暖池的变动提供了重要依据。研究表明,西太平洋暖池冬季表层海水温度在第四纪的冰期旋回中变化幅度超过了5℃,而温跃层深度自1.6 Ma以来有所变浅,进一步论证了西太平洋暖池的不稳定性。通过对暖池区和南海及赤道东太平洋的比较,发现南海南部和暖池的海水在第四纪具有较好的连通性,而南海北部则受季风控制影响较大;同时,赤道东、西太平洋及南海,自1.6 Ma以来温跃层深度都有不同程度的变浅。研究中发现中更新世过渡期(MPT)在许多古海洋学指标中都是一条重要的分界线,以此为界,对0~0.9和0.9~1.6 Ma两个时间段的暖池冬季表层海水温度、表层与次表层种浮游有孔虫氧同位素差值与地球轨道参数ETP分别作交叉频谱分析,结果显示暖池在响应全球气候转型的同时也表现出了低纬特有的热带气候变化的特征。Abstract: The quantitative census of planktonic foraminifera from the upper 25 m of ODP 130 Site 807A, combined with the paleotemperature data estimated by using faunal transfer function and the oxygen isotopic record, reveal the periodical changes of sea surface temperature (SST) and thermocline in the Western Pacific Warm Pool (WPWP) during the last 1.6 Ma. Our results indicate that winter SST varied over~5℃ in the glacial-interglacial cycles and the depth of thermocline (DOT) has shoaled gradually since 1.6 MaBP. Compared with the South China Sea (SCS) and the Eastern Equatorial Pacific SSTs and DOT changes, the sea surface water of the WPWP more closely connected with the southern SCS, while the northern SCS seemed to be mainly controlled by the Asian winter monsoon. Meanwhile, the DOT of the SCS and Western and Eastern Pacific became shallower on different scales for the past 1.6 Ma. It is found that the Middle Pleistocene Climate Transition (MPT) was probably the critical boundary for many paleoceanographic changes. Taking the MPT as a time boundary, a cross-spectral analysis was made between the winter SST,Δδ18O P.obliquiloculata-G.ruber and the Earth Orbital Parameter ETP for two time slices of 0~0.9 and 0.9~1.6 Ma respectively. This result shows that the paleoceanographic changes in the WPWP followed the global climate periodicity transition from 41 to 100 ka and displayed a typical tropical forcing character.
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