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

人类活动日益改变气候和环境，我们必须提高预测能力，以决定最佳的社会应对措施，以减轻其负面影响。这些担忧中最重要的是大气中二氧化碳的上升，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。海洋在过去大气二氧化碳和气候的变化中发挥了关键作用，如今它是人为二氧化碳的主要汇。影响大气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，它们既控制着深海的碳封存，也控制着与大气接触的地表水的化学性质。因此，预测未来环境和气候变化的轨迹需要详细记录这些过程的演变，以应对过去的气候变化及其在现代海洋中的量化。实现这种预测能力的一种方法是利用多种地球化学示踪剂固有的综合能力，这些示踪剂要么记录在海洋档案中，提供与过去气候变化相关的海洋过程变化的信息，要么印在水柱中，提供有关现代海洋过程的信息。人们正在开发一系列地球化学示踪剂，以在多代理、交叉检查的背景下提供有关多种海洋过程的信息。本提案应用了这一一般方法，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（230Th、234Th、231Pa），以限制海洋和深水循环中的粒子下沉通量；(2) 钕同位素，可追踪海洋水团并提供从大陆带入海洋的矿物部分溶解所产生的基本元素的海洋输入信息（最近被称为“边界交换”的过程）；以及 (3) 铬同位素，提供有关边界交换、碳封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.