The oceanic carbon cycle is fundamentally important for regulating the Earth system because, in sediments and seawater, the balance between the degradation and preservation of organic carbon (OC) exerts a first order control on atmospheric CO2 and O2. These gases have mediated global climate, planetary oxidation and Earth’s habitability through geologic time, while increasing CO2 levels now present a major climate threat. In sediments, OC is preserved over millions of years, while in seawater, a dissolved form of recalcitrant OC has been recently recognised as critical to OC storage over anthropogenic timescales. Both sedimentary and seawater OC are derived from living organisms, and should therefore be easily degraded. Their persistence in the oceans is therefore one of the most enduring paradoxes in marine biogeochemistry. MINORG will quantify the role of minerals in the preservation of OC for the first time, by combining cutting-edge molecular-level techniques with the first ever comprehensive and fully integrated experimental and modelling campaign, to determine in unprecedented detail the exact mechanisms responsible for the interaction of OC with minerals, and its subsequent degradation and preservation behaviour. This project will make a major contribution to our quantitative understanding of the oceanic carbon cycle, and so to predicting and mitigating current and future climate change.