The geologic history of marine dissolved organic carbon from iron oxides

Dissolved organic carbon (DOC) is the largest reduced carbon reservoir in modern oceans1,2. Its dynamics regulate marine communities and atmospheric CO2 levels3,4, whereas 13C compositions track ecosystem structure and autotrophic metabolism5. However, the geologic history of marine DOC remains largely unconstrained6,7, limiting our ability to mechanistically reconstruct coupled ecological and biogeochemical evolution. Here we develop and validate a direct proxy for past DOC signatures using co-precipitated organic carbon in iron ooids. We apply this to 26 marine iron ooid-containing formations deposited over the past 1,650 million years to generate a data-based reconstruction of marine DOC signals since the Palaeoproterozoic. Our predicted DOC concentrations were near modern levels in the Palaeoproterozoic, then decreased by 90−99% in the Neoproterozoic before sharply rising in the Cambrian. We interpret these dynamics to reflect three distinct states. The occurrence of mostly small, ...