Summer fresh layers and winter mixed layers in the western Subpolar Gyre
Bibliographic record
Abstract
The strength of the Atlantic Meridional Overturning Circulation has been tied to deep convection in the subpolar North Atlantic. The depth of convection in winter, and the density of its product, depends on the balance between the water column stratification at the end of summer and the buoyancy removed through cooling in winter. As climate change progresses, ocean stratification is expected to increase as a result of warming and increasing fluxes of freshwater from the Arctic and Greenland, which in turn may weaken convection. Recently, a large freshwater anomaly has been seen to go round the Subpolar Gyre and has been speculated to increase stratification to the point where it inhibited convection in the Irminger Sea in 2019. However, less is known about near surface salinity in other years.Both the extent of the upper ocean summer fresh layer and the winter mixed layers are investigated using Argo profiles and gridded salinity products. Particularly the westernmost basins of the North Atlantic Subpolar Gyre are characterized by a strong seasonal cycle in near surface salinity. Fresh layers of around 50 m depth form over spring and summer and are diluted through mixing with deeper, more saline waters in winter. Larger fresh anomalies are seen in recent years, but Argo profiles show that this upper ocean freshwater can still be mixed over the water column if winter cooling is strong enough. This diminishes the fresh signal in amplitude, while spreading it over a much thicker layer. In the Labrador Sea and south of Greenland this can be seen in mixed layers over 1000 m deep, but even in the Irminger Sea fresh mixed layers down to 800 m were recorded in the winter of 2021-2022. Concomitantly, the western Subpolar Gyre has exhibited a freshening of the upper to intermediate water column that may partly be related to this spreading of freshwater over the water column. Documenting the strength and variability of the near surface summer fresh layer, and the extent to which it can be incorporated into winter mixed layers or not, will help project how deep convection may transition to a less frequent or weaker state in the future.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 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) | 0.002 | 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".