FORMATION AND EVOLUTION OF THE WESTERN PACIFIC WARM POOL RECORDED BY MICROFOSSILS
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摘要: 通过对南海大洋钻探ODP第184航次的ODP1143站和ODP1146站以及中德合作"太阳号"95航次的南沙海区17957-2柱状样中微体化石进行定量分析,提取了近18MaB.P.以来南海上部海水垂向结构的变化.结果发现11.5～10.6MaB.P.之间和3.6～3.3MaB.P.以来南海温跃层深度的南北梯度明显增大,指示了西太平洋暖池雏形的开始和现代暖池的最终形成,且分别对应于印度尼西亚海道和巴拿马地峡的关闭.此后,南沙海区的温跃层深度自约0.9MaB.P.逐渐变浅,至约0.15MaB.P.又再变深,反映了西太平洋暖池的减弱和再次加强.因而,晚新生代西太平洋暖池的形成和演化呈现阶段性.Abstract: Based on the quantitative analysis of microfossils from Sites 1143 and 1146 of the Ocean Drilling Program (ODP) Leg 184 and Core 17957 2 of Sino German joint expedition "Sonne" Cruise 95, the variations in upper water structure during the last 18Ma was reconstructed. It has been found that before about 11.5Ma B.P. the changes in relative abundance of planktonic foraminiferal deep dwelling species, which is associated with shallow depth of thermocline (DOT), display similar trend in the southern and northern South China Sea (SCS), indicating that the western Pacific warm pool(WPWP) did not exist at that time. During the period of 11.5～10 6MaB.P., the south north gradient of the DOT in the SCS occurred for the first time, representing the beginning of the WPWP possibly in response to the close of the Indonesian Seaway. However, the south north gradient of the DOT in the SCS disappeared between 10.6Ma B.P. and 3.6Ma B.P., implying that the WPWP was remarkably weakened or extremely unstable. Since 3.6～3.3MaB.P., the relative abundance of planktonic foraminiferal deep dwelling species displayed an opposite trend in the northern and southern SCS, with high values in the north and low ones in the south, indicating that the DOT shoaled in the north and deepened in the south in the SCS. This means that the south north gradient of the DOT in the SCS conspicuously increased, representing the final formation of the modern WPWP. It is speculated that the emergence of the Isthmus of Panama between the Atlantic and the Pacific could result in shoaled DOT in the eastern Pacific and deepened DOT in the western Pacific, and hence intensified the WPWP. After the WPWP formed, it has still experienced remarkable changes. The DOT of the Nansha area gradually decreased since about 0.9Ma B.P., reached a minimum at about 0.15Ma B.P. and then began to deepen again, reflecting that the WPWP weakened since about 0.9Ma B.P. but strengthened again after about 0.15Ma B.P. Therefore, the formation and evolution of the WPWP clearly displayed stepwise stages during late Cenozoic, providing us the background data for studying the role of the WPWP in the changes of the Earth climate environment.
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Key words:
- western Pacific warm pool /
- South China Sea /
- Ocean Drilling Program /
- microfossils /
- thermocline
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