西菲律宾海26万年来古生产力变化的颗石藻证据

Variations of primary productivity in the western Philippine Sea in the past 260000 years:evidence from coccolith

  • 摘要: 基于国际海洋古全球变化研究项目(IMAGES)在西菲律宾海本哈姆海台获取的高质量柱状沉积物岩芯MD06-3047(17°00.44′N、124°47.93′E),利用颗石藻下透光带属种Florisphaera profunda的相对丰度以及初级生产力转换函数,恢复了260 ka以来西菲律宾海上部水体营养跃层以及初级生产力的变化历史。发现该区域26万年以来初级生产力冰期-间冰期变化特征较不明显,冰期生产力平均值略高于间冰期。通过与前人已发表的指示东亚冬季风强弱的伊利石/蒙脱石记录和热带太平洋纬向表层海水温度梯度记录的对比,提出MIS 8期以来,热带西菲律宾海古生产力变化的主要受控因素在MIS 5a左右发生明显转变。在MIS 8后期至MIS 5a之间,初级生产力受到长期类ENSO过程的影响较为显著,当热带东西太平洋海水表层温度梯度较小的时期,认为热带太平洋处于类El Niño状态,此时西菲律宾海营养跃层相对较浅,生产力较高,反之则相反。而在MIS 5末期至末次冰消期时段,生产力受东亚冬季风的影响相对于长期ENSO过程更强,可能掩盖了后者的古生产力信号。冰期东亚冬季风加强,一方面,可以引起上部水体混合加强,增加下部营养物质向上的输送,另一方面大量风尘物质的输入可以刺激颗石藻的生长;反之在冰消期,水体混合较弱,风尘输入显著减少,生产力也随之降低。

     

    Abstract: Primary productivity data of the Core MD06-3047 (17°00.44′N, 124°47.93′E, 2510m water depth) from the International Marine Global Change Study Program (IMAGES) is presented in this paper. The core is taken from the Benham Rise of West Philippine Sea. Coccolith records revealed considerable glacial-interglacial changes of paleoproductivity in the west Philippine Sea over the past 260 ka. The recently published research data of the core made this study possible to reveal the forcing mechanisms of the glacial-interglacial variations in primary productivity. During the period of 260~80 ka, the abundance of F. profunda and primary productivity shows a similar variation trend with the tropical eastern-western Pacific sea surface temperature gradient (ΔSST). The lower ΔSST in the glacial intervals indicate that tropical Pacific was suffered a long term El Niño-like condition, which produced relatively shallow thermocline/nutricline and high primary productivity in the western Pacific. On the contrary, the higher ΔSST in the interglacial intervals indicates a La Niña-like state in the tropical Pacific, which deepened the thermocline/nutricline and suppressed the primary productivity. From the late MIS5 to the last deglacial, we attribute the high values of productivity in the glacial interval and low values in the interglacial intervals to the Eastern Asian winter monsoon, due to the similar trend between illite/smectite ratio and primary productivity in the core MD06-3047.

     

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