Early Maastrichtian carbon cycle perturbation and cooling event: Implications from the South Atlantic Ocean
Bibliographic record
Abstract
Published stable isotope records in marine carbonate are characterized by a positive δ18O excursion associated with a negative δ13C shift during the early Maastrichtian. However, the cause and even the precise timing of these excursions remain uncertain. We have generated high‐resolution foraminiferal stable isotope and gray‐scale records for the latest Campanian to early Maastrichtian (∼73–68 Ma) at two Ocean Drilling Program sites, 525 (Walvis Ridge) and 690 (Weddell Sea). We demonstrate that the negative δ13C excursion is decoupled from the δ18O increase with a lag of about 600 ka. Our δ13C records (both planktic and benthic) show an amplitude for the negative excursion of 0.7‰ that falls between about 72.1 and 70.7 Ma. Our planktic δ18O records indicate an overall increase of 1.2‰ from 73 to 68 Ma at Site 690, whereas at Site 525 they record a slightly smaller increase (∼1‰) that peaks around 70.1 Ma with decreasing values thereafter. Our benthic δ18O data indicate an increase of ∼1.5‰ at Site 525 and ∼0.7‰ at Site 690 between about 71.4 and 69.9 Ma. Benthic δ18O values show different baseline values at the two sites before and after the excursion, but the larger increase at Site 525 means that the values attained at the peak of the excursion are similar at the two sites. We interpret this observation in terms of water mass changes. The excursion is interpreted to reflect a cooling of bottom waters in response to the strengthening contribution of intermediate‐ to deep‐water production in the high southern latitudes rather than increased ice volume. The associated carbon cycle perturbations that we observe are interpreted to reflect a weakening of surface water stratification and increased productivity, as supported by our gray value data.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".