Dissolved organic carbon dynamics in a changing ocean: an ESM2M-COBALTv2 coupled model analysis
Bibliographic record
Abstract
Dissolved organic carbon (DOC) constitutes a major component of the marine carbon cycle, yet its present contributions to carbon export, and the response to future climate change remain poorly constrained. Using ESM2M-COBALTv2 – GFDL's ocean biogeochemistry model COBALTv2 coupled to the ESM2M Earth System Model – we evaluate present-day DOC distribution and export and project their responses to a high-emission future scenario RCP8.5 to the year 2100. Our model reproduces well the observed large-scale DOC patterns, with highest concentrations (70–80 µmol C kg−1) in subtropical gyres and lower values (40–50 µmol C kg−1) in subpolar and equatorial upwelling regions. Biological DOC production and remineralization rates are highest in nutrient-rich upwelling zones. The net DOC produced is then transported to the stratified oligotrophic gyres where DOC accumulates, thereby forming the observed global DOC distribution. Present-day global DOC export at 100 m is estimated at 1.6 Pg C yr−1, accounting for about 19 % of the total organic carbon (TOC) export modeled at that depth. By 1000 m, DOC export decreases sharply to 0.09 Pg C yr−1, solely because microbial remineralization removes a significant fraction of DOC as it descends deeper into the water column. At 100 m, globally integrated mixing-mediated export is nearly twice that of advection, especially in boundary current regions and subpolar gyres where strong seasonal mixing occurs, whereas advection dominates in subtropical gyres via large-scale subduction of accumulated DOC. At 1000 m, however, advection dominates, particularly in the North Atlantic where deep-water formation facilitates DOC export. Under future warming, intensified stratification and reduced nutrient supply drive a net decline in global DOC production. Nevertheless, upper-ocean DOC concentrations increase slightly, underscoring the continued importance of physical transport in redistributing DOC. The model projects a 6 % reduction in DOC export at 100 m, driven primarily by weakened mixing, and a 25 % reduction in advection-dominated deep export at 1000 m depth.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".