The geologic history of marine dissolved organic carbon from iron oxides
- Nir Galili
- Stefano M. Bernasconi
- Alon Nissan
- Uria Alcolombri
- Giorgia Aquila
- Marcella Di Bella
- Thomas M. Blattmann
- Negar Haghipour
- Francesco Italiano
- Madalina Jaggi
- Ifat Kaplan-Ashiri
- Kang Soo Lee
- Maxwell A. Lechte
- Cara Magnabosco
- Susannah M. Porter
- Maxim Rudmin
- Robert G. M. Spencer
- Roman Stocker
- Zhe Wang
- Stephan Wohlwend
- Jordon D. Hemingway
2025-08-13
Dissolved organic carbon (DOC) is the largest reduced carbon reservoir in modern oceans 1,2 . Its dynamics regulate marine communities and atmospheric CO 2 levels 3,4 , whereas 13 C compositions track ecosystem structure and autotrophic metabolism 5 . However, the geologic history of marine DOC remains largely unconstrained 6,7 , 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, single-celled organisms combined with severely hypoxic deep oceans, followed by larger, more complex organisms and little change in ocean oxygenation and finally continued organism growth and a transition to fully oxygenated oceans 8,9 . Furthermore, modern DOC is 13 C-enriched relative to the Proterozoic, possibly because of changing autotrophic carbon-isotope fractionation driven by biological innovation. Our findings reflect connections between the carbon cycle, ocean oxygenation and the evolution of complex life.