Bottom-up controls on ocean chemistry

Determining the geochemical controls on the chemistry of the oceans is fundamentally important for understanding the modern and ancient Earth system. Concentrations of micronutrient metals in the modern oceans control photosynthesis and thus modern climate, whilst concentrations and isotopic compositions of these micronutrients recorded in ocean sediments can reflect contemporaneous ocean chemistry at the time of sediment deposition and can thus shed light on micronutrient cycling in the ancient oceans and the links between ocean chemistry and the evolution of Earth’s atmosphere and biosphere. Currently the controls on ocean chemistry are typically considered within a top-down framework, in which metals are sourced largely from rivers and recycled within the water column. Assuming a top-down ocean however, it is difficult to explain recently observed elevated micronutrient concentrations in deep waters and benthic fluxes are now well-established for iron. A bottom-up ocean implies that processes within sediments and at the interface between sediments and seawater are key in controlling ocean chemistry, yet these processes are poorly understood. This project will constrain the sediment processes that control the cycling of micronutrient metals, particularly focusing on metal retention or release from sediments during diagenesis, and will use this new understanding to investigate how release of micronutrients from sediments impacts seawater chemistry in the modern and ancient oceans, and thus the biogeochemical evolution of the Earth system over time.