Mechanisms for Late 20th and Early 21st Century Decadal AMOC Variability
Bibliographic record
Abstract
Abstract Recent studies using data from the OSNAP observational campaign and from numerical ocean models suggest that the Iceland Basin and the Irminger Sea may be more significant for formation of upper North Atlantic Deep Water than the Labrador Sea. Here, we present a set of hindcast integrations of a global 1/4° NEMO simulation from 1958 until nearly the present day, forced with three standard forcing data sets. We use the surface‐forced stream function, estimated from surface buoyancy fluxes, along with the overturning stream function, similarly defined in potential density space, to investigate the causal link between surface forcing and decadal variability in the strength of the Atlantic meridional overturning circulation (AMOC). We use the stream functions to demonstrate that watermasses in the simulations are transformed to higher densities as they propagate around the subpolar gyre from their formation locations in the north‐east Atlantic and the Irminger Sea, consistent with the picture emerging from observations. The surface heat loss from the Irminger Sea is confirmed to be the dominant mechanism for decadal AMOC variability, with the heat loss anomaly from the Labrador Sea having about half the magnitude. A scalar metric based on the surface‐forced stream function, accumulated in time, is found to be a good predictor of changes in the overturning strength. The AMOC variability is shown to be related to that of the North Atlantic Oscillation (NAO), primarily through the surface heat flux, itself dominated by the air‐sea temperature difference, but also with some local feedback from the SST to the surface fluxes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".