250kaB．P．以来西太平洋暖池中心区--ontong Java海台古生产力演化

PALEOPRODUCTIVITY EVOLUTION IN THE ONTONG JAVA PLATEAU——CENTER OF THE WESTERN PACIFIC WARM POOL DURING THE LAST 250ka

多年平均表层水温超过28℃的“西太平洋暖池”，是全球海平面高度的加热中心和大气三大环流的辐散中心。为评价西太平洋暖池中心区域海洋生物泵的演化特征、规律与机制，本文以位于热带西太平洋暖池核心区——0ntong Java海台的WP7柱状样为材料，通过提取浮游有孔虫δ^18C组成、底栖有孔虫群落和钙质超微化石下透光带属种Florisphaera profunda相对百分含量变化等指标，反演该区250kaB．P．以来的古生产力的演化历史。研究结果表明，250kaB．P．以来西太平洋暖池中心区的古生产力演化与地球轨道变化控制的冰期-间冰期旋回以及岁差控制的太阳辐照率密切相关。在冰期-间冰期尺度上，西太平洋暖池中心区距今250ka以来的生产力变化间冰期明显低于冰期，而且在间冰期阶段生产力相对稳定，冰期波动幅度较大。在冰期或间冰期背景下显著的岁差周期是该区古生产力演化的又一重要特征。而且在岁差波段生物生产力的变化可能领先极地冰体积变化2—4ka左右。热带东西太平洋的古生产力演化在冰期-间冰期变化和岁差尺度上存在ENSO式的变动机制，而且二者互相调谐，产生了似30ka和19ka周期，并出现了“半30ka周期”和半岁差周期。此外，WP7 孔 Neogloboqudrina dutertrei的δ^13C显示在MIS1／2，MIS3／4和MIS 5e／6的冰期向间冰期的过渡期的冰消期阶段存在变轻事件，可能与数千年尺度的大洋环流演化有关。

The western Pacific Warm Pool bounded approximately by the 28℃ surface isotherm is the heating center over the global sea surface and the divergence center of the three major atmosphere circulations. To evaluate the features ,patterns, and possible mechanism on the biological pump evolution of the center of the western Pacific Warm Pool, core WP7 collected from the Ontong Java Plateau is used as research materials. Based on multiproxies, such as planktonic foraminifer N. dutertrei δ^13C, relative abundance of benthic foraminifera infaunal species Uvigerina ＋ Bulimina and paleoproductivities estimated by benthic foraminiferal accumulation rate, and percentage of Florisphaera profunda, a dominated species of the coccolithophore communities of the lower photic zone, the paleoproductivity over the last 250ka has been reconstructed. The results show that variations in the center of the western Pacific Warm Pool are primarily controlled by glacial-interglacial variability and by orbit precession changes. At the glacial-interglacial time scale, glacial productivity was considerablely higher than it was during interglacial stages during the last 250ka in the center of the western Pacific Warm Pool. Moreover, the glacial paleoproductivity variations were dramatic while the interglacial paleoproductivity were relatively stable. The dominance of the Earth＇s precession on the background of the glacial-interglacial state is another main character of paleoproductivity in the study region. Phase analysis indicates that the paleoproductivity records precedes the 8180 records by about 2 - 4ka in the precession band. Long-term ENSO-like forcing patterns could be the main mechanism controlling the paleoproductivity variations on both glacial-interglacial and precessional cycles, which resulted in ＂half-3Oka＂ and half precessional cycles in the center of the western Pacific Warm Pool. Additionally, N. dutertrei δ^13C records in core WP7 reveal a broad 813C minimum event during the transition of the MIS 1/2, MIS 3/4, and MIS 5e/6 respectively, which could be associated with ocean circulation evolution at several millennium scales.