Mean State AMOC Affects AMOC Weakening through Subsurface Warming in the Labrador Sea
Bibliographic record
Abstract
Abstract While most models agree that the Atlantic meridional overturning circulation (AMOC) becomes weaker under greenhouse gas emission and is likely to weaken over the twenty-first century, they disagree on the projected magnitudes of AMOC weakening. In this work, CMIP6 models with stronger climatological AMOC are shown to project stronger AMOC weakening in both 1% ramping CO 2 and abrupt CO 2 quadrupling simulations. A physical interpretation of this result is developed. For models with stronger mean state AMOC, stratification in the upper Labrador Sea is weaker, allowing for stronger mixing of the surface buoyancy flux. In response to CO 2 increase, surface warming is mixed to the deeper Labrador Sea in models with stronger upper-ocean mixing. This subsurface warming and corresponding density decrease drives AMOC weakening through advection from the Labrador Sea to the subtropics via the deep western boundary current. Time series analysis shows that most CMIP6 models agree that the decrease in subsurface Labrador Sea density leads AMOC weakening in the subtropics by several years. Also, idealized experiments conducted in an ocean-only model show that the subsurface warming over 500–1500 m in the Labrador Sea leads to stronger AMOC weakening several years later, while the warming that is too shallow (<500 m) or too deep (>1500 m) in the Labrador Sea causes little AMOC weakening. These results suggest that a better representation of mean state AMOC is necessary for narrowing the intermodel uncertainty of AMOC weakening to greenhouse gas emission and its corresponding impacts on future warming projections.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".