Building and calibrating models for the chemical and thermal evolution of the oceanic lithosphere: implications for ocean chemistry

了解地质时期海水成分的变化对于了解地球系统的长期演变和控制长期气候变化的过程至关重要。科学界目前的主要重点是了解亚空中化学风化和河流化学，以了解从大陆进入海洋的输入及其对海洋化学的影响-这无疑是重要的。然而，目前海洋岩石圈和海洋之间的化学交换的不确定性远远大于现代河流化学通量。这在很大程度上是由于两个因素，即海洋地壳难以进入和海水与海洋地壳之间化学交换的不均匀性。我在这里提出的研究计划将开始以完全定量的方式解决这个问题，通过建立一个在海洋热液系统中运行的过程模型，并根据有助于约束这些过程的多样但稀疏的观测结果对其进行“校准”。这些观察结果包括：（一）从海底回收的岩石的成分;（二）从海底排出的流体的成分;（三）通过地震实验等远程测定的上洋壳的物理特性;（四）通过海底损失的热量。这项工作的结果将为了解过去海洋化学变化的起源提供基础。结合过去对海水成分的独立估计，这些模型将使我们能够确定古代河流输入海洋的成分。只有通过更好地量化这些过程，才能充分理解对气候的长期控制。

Understanding the variation in the composition of seawater over geological time is central to understanding the long-term evolution of the Earth system and the processes that control long-term climate change. The principal emphasis of the scientific community is currently focused on understanding sub-aerial chemical weathering and river chemistry to understand the inputs into the ocean from the continents and their impact on ocean chemistry - this is undoubtedly important to do. However, there is currently far more uncertainty in the chemical exchange between the oceanic lithosphere and oceans than there is in the modern riverine chemical fluxes. This is largely due to two factors, the inaccessibility of the ocean crust and the heterogeneity of chemical exchange between seawater and the oceanic crust. The research program I propose here will start to address this in a fully quantitative manner through building a model of the processes that operate in oceanic hydrothermal systems and 'calibrating' it against the diverse, but sparse, observations that help to constrain these processes. These observations include: (i) the composition of rocks recovered from the seafloor; (ii) the compositions of fluids venting from the seafloor; (iii) the physical properties of the upper oceanic crust determined remotely, for example by seismic experiments; and (iv) the amount of heat that is being lost through the ocean floor. The results of this work will provide the foundation for understanding the origin of past changes in ocean chemistry. In combination with independent estimates of the composition of seawater in the past these models will allow us to determine the composition of the ancient river input into the ocean. Only through better quantifying these processes can the long-term controls on climate be fully understood.