Anomalous North Atlantic Oceanography And Overturning During The Last 250 Years
Bibliographic record
Abstract
ATLAS work package 1 presentation at ATLAS 3rd General Assembly. The circulation of the Atlantic Ocean plays an essential role in climate and ecosystems through its redistribution of heat, nutrients and mixing, and its influence on the carbon cycle. However, short observational datasets preclude a longer-term perspective on the modern state and variability of key features, such as Labrador Sea convection, the Atlantic Meridional Overturning Circulation (AMOC) and gyre variability. Here, we provide several lines of paleoceanographic evidence that circulation in the North Atlantic has been anomalous since 1750-1850, including weakened Labrador Sea deep convection, weakened Iceland-Scotland overflows and weakened AMOC, a northerly shift in the position of the Gulf Stream and a warming and reduction of frontal activity in the Iceland Basin. The reconstructions suggest that transitions began around the end of the LIA, with some differences in timing between regions, and have continued over the past 150-250 years. We suggest that enhanced freshwater fluxes from the Arctic and Nordic Seas towards the end of the LIA, sourced from melting glaciers and sea-ice, weakened Labrador Sea convection and the AMOC. The lack of a subsequent recovery may result from hysteresis or anthropogenic warming and freshening of the North Atlantic. Our results highlight that recent decadal variability in the North Atlantic has occurred during an atypical background state. Future work should aim to constrain the role of internal climate variability versus early anthropogenic forcing in the changes described here.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.004 | 0.008 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.017 | 0.005 |
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".