OXYGEN ISOTOPE RECORDS OF CALCAREOUS NANNOFOSSILS SINCE MIS 6 FROM THE MARGINAL AREA OF WEST PACIFIC
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摘要: 对西太平洋边缘不同纬度带的WP7、Ph05-5和Z14-6 3个柱状岩心进行了超微化石氧同位素分析。结果表明,MIS 6期以来这3个岩心中超微化石δ18O值都呈现明显的冰期-间冰期旋回变化特征,冰期δ18O平均值重于间冰期(Z14-6岩心倒数第二次冰期旋回除外),这与冰期时表层海水温度低于间冰期相对应。MIS 6-1期超微化石δ18O平均值从WP7岩心到Ph05-5岩心再到Z14-6岩心依次变重,对应于3个岩心所在海区位置年平均SST依次降低。同一岩心样品中浮游有孔虫温跃层种Neogloboquadrina dutertrei δ18O平均值重于超微化石δ18O平均值,这与超微化石和浮游有孔虫N.dutertrei δ18O值各自所代表的不同水层温度特征相吻合。MIS 6期以来从WP7岩心到Ph05-5岩心再到Z14-6岩心,超微化石与浮游有孔虫N.dutertrei δ18O平均值之间的差值越来越小,这与3个岩心所在位置上部水体扰动越来越强对应。WP7和Ph05-5两个岩心中超微化石和浮游有孔虫N.dutertrei氧同位素差值与超微化石下透光带属种Florisphaera profunda百分含量变化特征共同表明MIS 6期以来西太平洋暖池核心区和西菲律宾海黑潮源区的温跃层间冰期比冰期深。Abstract: Three piston cores, WP7, Ph05-5 and Z14-6,recovered from the marginal area of the West Pacific were analyzed for their δ18O variations of calcareous nannofossils. The nannofossil δ18O values of all the three cores showed apparent glacial-interglacial cycles. The δ18O values were generally lower during interglacials than glacials since MIS 6,corresponding to lower sea surface temperatures (SST) during glacial stage,except for the penultimate glacial cycle in core Z14-6. The average δ18O values of MIS 6-1 show an increasing trend from core WP7 to Ph05-5 and Z14-6, that is explained by the gradually decreasing SST at these locations. At a single location, however,the average δ18O values of planktonic foraminifera Neogloboquadrina dutertrei were higher than those of nannofossils, reflecting different water temperatures at their living water depth. These differences show a decreasing trend from core WP7 to Ph05-5, and Z14-6,that can be explained by increased disturbance in upper water. The δ18O difference between nannofossils and N. dutertrei, as well as the downcore variations in the percentage of Florisphaera profunda in core WP7 and Ph05-5 implies that the thermocline of the coring regions of Western Pacific Warm Pool and the Western Philippine Sea was deeper during interglacials than that in glacials since MIS 6.
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