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

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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.