Isotopic constraints on alkalinity, dissolved organic carbon, and atmospheric carbon dioxide fluxes in the Mississippi River
Bibliographic record
Abstract
We examined carbon cycling in the Mississippi River using stable isotopes of inorganic carbon and dissolved oxygen. Eighteen sites were sampled along the river and its tributaries over 1 year. We estimate using a conservative approach that the flux of CO2 to the atmosphere (1 × 1013 g C yr−1) approximately equaled the flux of alkalinity to the Gulf of Mexico (9.7 × 1012 g C yr−1) and greatly exceeded the flux of dissolved organic carbon (1.5 × 1012 g C yr−1). Though only a first‐order estimate, our work shows that the atmospheric flux of CO2 is significant and should not be ignored when examining the carbon budget of the Mississippi River. As expected, because of the large area covered by the Mississippi watershed, the isotopic composition of dissolved inorganic carbon, δ13CDIC, varied widely. In the Ohio and upper and lower Mississippi basins, δ13CDIC indicates that the source of inorganic carbon in the rivers is primarily from carbonate dissolution by soil CO2. Dissolved inorganic carbon in the Missouri River was enriched in 13C, and the isotopic composition of dissolved oxygen in this river suggests that this results from an excess of aquatic photosynthesis over respiration.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".