大型硅藻通过独特的勃发方式将巨量的有机碳输出到大洋深部，对大气pCO2升高和全球变暖产生负反馈，从而在全球气候变化和大洋碳循环中扮演重要角色。然而，大型硅藻自身的勃发机制及其对大洋碳循环的作用机制悬而未决，营养物循环是个关键环节。本项目以东菲律宾海LGM沉积的两个硅藻席岩芯为材料，利用提取的纯净大型硅藻Ethmodiscus rex的硅、氮、铁和锌同位素等替代指标确定E. rex勃发所需营养物硅酸、硝酸盐、Fe和Zn的来源，重建E. rex对这四种营养物的利用程度，探索Fe受限或富集在大型硅藻勃发中的作用，恢复LGM东菲律宾海的营养物状态。在此基础上，将营养物循环信息与E. rex勃发的主流模式对比，完善大型硅藻的勃发机制；将营养物循环特征与E. rex勃发时的生产力、表层海水pCO2等碳循环参数关联，揭示营养物循环在大型硅藻勃发碳循环中的作用，为检验气候变化驱动机制的假说提供科学依据。

Giant diatoms act as a negative feedback to atmospheric pCO2 rise and global warming by unique form of blooms to transfer massive organic carbon to deep ocean, thus playing an important role in global climate change and ocean carbon cycle. However, the blooming mechanism of giant diatoms themselves and their forcing mechanism on ocean carbon cycle are still not well resolved, therein the nutrient cycle is one of the most key issues. Here, the silicon, nitrogen, iron and zinc isotopic, and other elemental proxies of cleaned giant diatom Ethmodiscus rex extracted from two sediment cores containing laminated diatom mats in the eastern Philippine Sea (EPS) during the Last Glacial Maximum (LGM) are used to trace the source and utilization of nutrients silicic acid, nitrate, Fe and Zn for E. rex blooms, exploit the significance of Fe limitation or repletion in the blooms of giant diatom, and consequently reconstruct the nutrient status in the EPS during the LGM. And then the blooming mechanism of giant diatoms is further revised by the comparison of the nutrient cycle with the relevant information in the popular models for E. rex blooms. Finally, the potential role of nutrient cycle in the carbon cycle during giant diatom blooms is revealed by the linking of nutrient cycle characteristics to carbon cycle parameters such as productivity and surface EPS pCO2. This project will provide new scientific basis for testing the hypotheses regarding the forcing of climate change.