North Atlantic temperature change across the Eocene-Oligocene Transition
Bibliographic record
Abstract
The Eocene–Oligocene transition (~34 Ma), is marked by the rapid development of a semi-permanent Antarctic ice-sheet, as indicated by ice-rafted debris. Proxy reconstructions indicate a drop in atmospheric CO₂ and global cooling. How these changes affected sea surface temperatures in the North Atlantic and ocean water stratification remains poorly constrained. In this study, we apply clumped-isotope thermometry to well-preserved planktic foraminifera, that are associated with mixed-layer and thermocline dwelling depths from the drift sediments at IODP Site 1411, Newfoundland, across four intervals bracketing the EOT. The mixed-layer dwelling foraminifera record a cooling of 2.2 ± 2.4 °C (mean ± 95% CI) across the EOT. While the cooling amplitude is similar to previous SST reconstructions, absolute temperatures (Eocene 20.0 ± 2.7 °C, Oligocene 18.0 ± 2.1 °C) appear colder than what is expected for this location based on previously reconstructed SSTs for the northernmost Atlantic. We discuss seasonal bias, recording depth, and appropriate consideration of paleolatitudes, all of which complicate the comparison between SST reconstructions and model output. Thermocline dwelling foraminifera record a larger cooling across the EOT (Eocene 19.0 ± 3.4 °C, Oligocene 14.0 ± 3.1 °C, cooling of 5.2 ± 3.2 °C), than foraminifera from the mixed layer, consistent with an increase in ocean stratification which may be related to the onset or intensification of the Atlantic meridional overturning circulation.
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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".