海山结壳高分辨率地球化学记录：上新世以来中北太平洋经向环流演化

The meridional overturning circulation strongly influences CO2 storage in the deep ocean, latitudinal heat transport and air-sea exchange, and hence plays a key role in regulating the global climate. Comparatively little is known about the development of intermediate and deep ocean circulation in the Pacific during the Pliocene-Pleistocene transition, characterized by dramatic global cooling and Northern Hemisphere Glaciation onset. Here we propose to perform in-situ high-resolution elemental and neodymium isotopic analyses on the cobalt-rich ferromanganese crust samples obtained from different water depths of the central Pacific seamount region. We will focus on the variability of geochemistry characteristics on orbital time-scales and its relationship with the global climate change, on the basis of precise age model established using the method of orbital pacing. The redox conditions of the mediate and deep water masses and the past Pacific overturning circulation will be investigated according to the temporal changes of redox condition proxies and neodymium isotope composition. Our study would provide convincing evidences and scientific basis for understanding the reorganization of global meridional overturning circulation during the Pliocene-Pleistocene transition.

大洋经向环流是控制深海CO2储存、经向热量传输和海气交换的重要过程，故而是全球变化的重要内在因素。以全球变冷和北半球冰盖开始形成为特征的上新世—更新世气候转型期是地质历史时期重要的气候变化阶段之一，然而，目前对这一时期太平洋经向环流的变化知之甚少。本项目通过对中太平洋海区的不同水深海山结壳样品开展高分辨率原位主、微量元素、稀土元素和钕同位素分析，基于利用地球轨道周期法建立的高精度年代框架，重点研究富钴结壳元素地球化学特征在轨道时间尺度上的变化，揭示其与全球变化之间的联系，并根据海水氧化还原状态指标和钕同位素的变化探讨上新世以来北太平洋中、深层水团氧化还原环境和经向环流的演化，为进一步理解上新世-更新世气候转型期全球洋流结构的重组提供科学依据。

海山富钴结壳是重建古水团和古大洋环流的理想材料。本研究分别利用LA-ICPMS和LA-MC-ICPMS获取了结壳生长剖面上高分辨率的主微量元素分布和钕同位素分布剖面。逐一探讨了微量元素含量与结壳形成环境以及矿物相之间的联系，认为Ba/Fe可以作为古生产力的指标，232Th是风尘输入通量的指标，且在晚更新世呈现明显的冰期间冰期旋回，稀土元素Ce异常可能由生源物质输入通量、陆源碎屑输入通量和海水的氧化还原状态共同决定。样品中钕同位素的变化与其显微构造对应，可能反映在北半球冰川化过程中南极底流增强，中北太平洋深层水经历了含氧量先下降后上升的特征。该研究明确了结壳中Th含量的气候响应，精细了上—更新世气候转型期间太平洋钕同位素的变化特征，为北半球冰川化的全球响应提供了可靠的科学依据。