The geologic history of marine dissolved organic carbonfrom iron oxides
Bibliographic record
Abstract
Abstract 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 entirely unconstrained⁶,⁷, hindering our ability to mechanistically reconstruct coupled ecological and biogeochemical evolution. To address this, we developed the first direct proxy for past DOC signatures using co-precipitated organic carbon in iron ooids, and we applied this to 26 marine iron ooid-containing formations deposited over the past 1650 million years. Predicted DOC concentrations were near modern levels in the Paleoproterozoic then decreased by 90-99% in the Neoproterozoic before sharply rising in the Cambrian. We interpret these dynamics to reflect three distinct states: (i) small, single-celled organisms combined with severely hypoxic deep oceans; (ii) larger, more complex organisms and little change in oxygenation; (iii) continued organism growth and a transition to fully oxygenated oceans⁸,⁹. Furthermore, modern DOC is significantly ¹³C-enriched relative to the Proterozoic, likely due to changing autotrophic fractionation driven by biological innovation; together with isotopically invariant carbon inputs to Earth's surface¹⁰, this implies increasing relative organic carbon burial through time. Our results reveal new connections between the carbon cycle, ocean oxygenation, and the evolution of complex life.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".