Chlorofluorocarbon constraints on North Atlantic ventilation
Bibliographic record
Abstract
The North Atlantic Ocean vigorously ventilates the ocean interior. Thermocline and deep water masses are exposed to atmospheric contact there and are sequestered in two principal classes: Subtropical Mode Water (STMW: 26.5 {le} {sigma}{thetas} {le} 26.8) and Subpolar Mode Water (SPMW: 26.9 {le} {sigma}{thetas} {le} 27.8). These ventilation rates and pathways are uncertain, and a powerful way to estimate them is to monitor the penetration of chlorofluorocarbon (CFC) tracers. Here, a CFC dataset of over 44 000 observations, taken between 1982 and 1998, is combined with a non-eddy-resolving ( resolution) general circulation model of the North Atlantic Ocean. The CFC data are assimilated with the model by optimizing the uncertain air{ndash}sea CFC flux. The assimilated CFC fields are then systematically compared with the observations to identify the best fit and hence the most realistic ventilation. Three GCM experiments are performed this way to find the dependence on model thickness diffusivity. Each GCM solution is close to being statistically consistent with the CFC observations and likely sources of error. Lower diffusivity gives the best match to data although some systematic bias in sequestering tropospheric CFC remains. Lower diffusivity, around 150 m2 s{ndash}1, permits a stronger circulation with a more realistic North Atlantic Current. For this experiment, the subduction rate is around 16 Sv (Sv {equiv} 106 m3 s{ndash}1) in the subtropics and eastern subpolar Atlantic (26.35 {le} {sigma}{thetas} {le} 27.13) averaged over 1975{ndash}95. Around 26 Sv is formed in the Labrador and Irminger Seas (27.58 {le} {sigma}{thetas} {le} 27.8). Only about 40{percnt} of the CFC carried into the subpolar interior by this flux remained there in 1998, however. The rest was returned to the subpolar mixed layer after an average period of 6{ndash}8 yr. In contrast, 70{percnt} of the CFC subducted into the subtropical interior remained there in 1998
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".