Development and Application of Geochemical and Isotopic Tracers to Investigate Environmental Processes

人类活动正在日益改变气候和环境，我们必须提高预测能力，以决定最佳社会对策，减轻其负面影响。其中最令人关切的是大气中二氧化碳的增加，导致全球变暖和海洋酸化，以及可能进一步影响气候和海洋生态系统服务演变的多重反馈。海洋在过去的大气CO2和气候变化中发挥了关键作用，今天它是人为CO2的主要汇。影响大气中二氧化碳的主要海洋过程是海洋生态系统产生的有机物的循环和下沉通量，这两者都控制着碳向深海的固存以及与大气接触的地表水的化学性质。因此，要预测未来环境和气候变化的轨迹，就需要详细记录这些过程对过去气候变化的反应及其在现代海洋中的量化。实现这种预测能力的一个办法是利用多种地球化学示踪剂的固有综合能力，这些示踪剂要么记录在海洋档案中，提供关于海洋过程与过去气候变异性有关的变化的信息，要么印在水柱中，提供关于现代海洋过程的信息。目前正在开发一系列广泛的地球化学示踪剂，以便在多替代、交叉核对的背景下提供关于多种海洋过程的信息。本提案采用了这一总体办法，并以过去五年取得的成果为基础。它结合了沉积物和水柱研究（1）天然放射性同位素（230 Th，234 Th，231 Pa）来限制海洋和深水循环中的粒子沉降通量;（2）钕同位素，它追踪海洋水团，并提供大陆带入海洋的矿物部分溶解所产生的必需元素的海洋输入信息（3）铬同位素，它提供了关于边界交换、碳固存以及现代和过去海洋氧化还原状态的补充信息。

Human activities are increasingly altering climate and the environment and we must improve our predictive capabilities to decide on optimal societal responses to mitigate their negative impacts. Foremost among these concerns is the rise in atmospheric CO2, resulting in global warming and ocean acidification, and multiple feedbacks that can further affect the evolution of climate and marine ecosystem services. The ocean has played a key role in past changes in atmospheric CO2 and climate, and today it is a major sink for anthropogenic CO2. The main oceanic processes that affect atmospheric CO2 are circulation and the sinking flux of organic matter produced by marine ecosystems, which both control the sequestration of carbon to the deep sea and the chemistry of surface water in contact with the atmosphere. Predicting the trajectory of future environmental and climate changes thus requires a detailed documentation of the evolution of these processes in response to past climate changes and their quantification in the modern ocean. One approach towards achieving such predictive capability is to use the inherent integrative power of multiple geochemical tracers, which are either recorded in marine archives and provide information on changes in oceanic processes in relation to past climate variability, or which are imprinted in the water column and provides information on modern oceanic processes. A wide array of geochemical tracers is being developed to provide information on multiple oceanic processes in a multi-proxy, cross-checking context. The present proposal applies this general approach and builds on results obtained in the past five years. It combines sediment and water column study of (1) natural radioisotopes (230Th, 234Th, 231Pa) to constrain particle sinking flux in the ocean and deep water circulation, (2) neodymium isotopes which trace oceanic water masses and provide information on oceanic input of essential elements from partial dissolution of minerals brought to the sea from continents (a process recently coined as “Boundary Exchange”), and (3) chromium isotopes , which provide complementary information on boundary exchange, carbon sequestration, and the redox state of modern and past oceans.