Mid‐Miocene paleoproductivity in the Atlantic Ocean and implications for the global carbon cycle
Bibliographic record
Abstract
A prominent, middle Miocene (17.5–13.5 Ma) carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13 C depleted organic carbon in marine sediments or enhanced carbon burial in peat/lignite deposits on land. Here we test the hypothesis that the marine δ 13 C record reflects a change in productivity with proxy records from three Atlantic Ocean sites (Deep Sea Drilling Program Site 608 and Ocean Drilling Program Sites 925 and 1265). Our multiproxy approach is based on benthic foraminiferal accumulation rates, elemental ratios (Ba/Al and P/Al), the δ 13 C of bulk sedimentary organic matter, and dissolution indices. We compare these proxies to benthic foraminiferal δ 13 C values measured on the same samples. Our results indicate that marine paleoproductivity in the Atlantic Ocean is not related to the benthic foraminiferal δ 13 C excursion. A numerical box model confirms that marine productivity cannot account for the δ 13 C maximum. The model shows that sequestration of 1.5 × 10 18 mol C in the terrestrial realm over a period of 3 Ma leads to a 0.9‰ δ 13 C increase in the deep ocean, which is near the observed records. Therefore, an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean's carbon pool with 13 C, which is consistent with coeval lignite deposits worldwide. The δ 13 C values of bulk sedimentary organic matter parallel the δ 13 C of dissolved inorganic carbon as reflected by benthic foraminiferal δ 13 C values suggesting no significant change in atmospheric p CO 2 levels over the investigated period.
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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 | 0.001 | 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".