15万年以来热带西太平洋颗石藻碳酸钙输出通量演变及其影响因素

The continual increase of carbon dioxide fraction is considered to be the main contributor to the global temperature increase known as global warming. Global carbon cycle has become one of the hot topics in climate change research for decades. As the most prominent air-sea exchange region, the western Pacicfic Ocean is influenced by the East Asian, Walker circulation and Hadley circulation. Due to the features of low seasurface productivity and deep ocean dissolution on the western Pacific Ocean, the research related to global carbon ocean in the late Quaternary was few. Coccolithophores are phytoplankton that live in the upper layers of the world's oceans. The creatures use calcium carbonate, the material that makes up chalk and seashells, to build tiny plates on their exterior. Coccolithophores are responsible for a large part of modern oceanic carbonate production. By measuring the single coccolith mass of different species, the coccolith mass export fluxes can be derived. This will give powerful support for the discussion of mechanism for western pacific carbonate cycles, and also be helpful for assessing the influnces to coccolith by atmosphere pCO2 variaion. In this project, coccolith assembalgess, coccolith absolute abundance, single coccolith mass of each species and carbonate content of bulk sediment will be analyzed for the core MD06-3052, which located in the Kuroshio Source region, belong to the western Pacific. Using these proxies, we could reconstruct variation of the primary production and coccolith carbonate flux in the past 150ka. Combining with the existing data of environments such as temperature, salinity and carbonate parameters in this sediment core, the role of tropical pacific in the global carbon cycle will be estimated.

在全球变暖及大气CO2浓度不断增高的背景下，全球碳循环研究是古海洋学研究的热点问题。热带西太平洋作为季风环流、沃克环流以及哈德莱环流的辐聚带，是全球海-气交换最显著的区域。然而，由于表层海水生产力低以及深部海水溶解作用强等客观因素，目前对热带西太平洋碳循环研究相对较少。颗石藻在热带西太平洋广泛分布，作为重要的海洋初级生产力，是海洋沉积物中碳酸钙组份的重要来源。通过测量不同种属单个颗石重量，不仅能够计算出颗石碳酸钙的输出通量，为探索太平洋型碳酸盐旋回机制提供依据，还可以评估地质时期颗石对大气CO2变动的响应。本项目选取位于西太平洋黑潮源区的MD06-3052岩心，全面分析其颗石群落组成、绝对丰度、各种属单个颗石的重量、以及全样碳酸盐含量。进而恢复15万年以来热带西太平洋初级生产力演化特征以及其颗石输出通量变化。结合本岩心已发表的温度、盐度、碳酸盐等环境参数，探讨热带海区在全球碳循环中的作用。

全球碳循环时古海洋学研究的热点问题，热带太平洋海域是全球海气交换最显著的区域。因而在本海域进行过去全球碳循环的研究重要意义。颗石藻作为海洋初级生产者，在热带西太平洋广泛分布，且是海洋沉积物中碳酸钙组分的重要来源。本项目以位于西太暖池附近的巴布亚湾的两个沉积物柱状岩心MD49和MD50为主要研究对象，综合使用年代学、钙质超微化石定量制片技术、Syraco自动鉴定系统等实验手段，重建了150ka以来颗石藻群落组成的演变过程、营养跃层深度变化过程、古初级生产力演变过程以及颗石藻碳酸钙输出通量演变过程等。并通过颗石藻群落组成以及不同种属颗石藻碳酸钙在不同地质时期的变化趋势，评估颗石藻不同种属在大洋碳循环中的贡献。初步发现，上层水体古初级生产力与大洋沉积物中的颗石藻化石丰度之间并不是简单的正相关对应关系。通过对位于西菲律宾海的MD06-3047岩心，以Fp%推算初级生产力水平变化，发现MIS8-MIS5a时期，热带太平洋处于类El Nino状态。而在MIS5末期至末次冰消期时段，生产力受东亚冬季风的影响相对强于长期ENSO过程，可能掩盖了后者的生产力信号。冰期东亚冬季风加强，引起上层水体混合家具，并带来大量陆源风尘输入。