Spreading velocities and dilution of North Atlantic Deep Water in the tropical Atlantic based on CFC time series
Bibliographic record
Abstract
Repeated observations of CFC‐11 and CFC‐12 in the western tropical Atlantic over the period from 1990 to 2002 are used to fit parameters of the age spectra for several North Atlantic Deep Water components: the upper Labrador Sea water (ULSW), the Labrador Sea water (LSW), and the lower North Atlantic Deep Water (LNADW). The most robust results are the mean spreading velocities, u , from the formation region in the Labrador Sea and the Denmark Strait, of 1.5 ± 0.3 cm/s for the two LSW water masses and 2.0 ± 0.2 cm/s for LNADW, respectively. These values are equivalent to an age of about 15–22 years for all three components at 16°N and 21–31 years at the equator at 35°W. The results are compatible with simpler tracer methods, as CFC ratios or “effective” ages. The fractions, f , of the “young” component (i.e., the fraction of the water mass ventilated in the last 50 years), turned out to be quite small, ranging from 25% to less than 5%. The downstream decrease of f indicates mixing of young NADW with CFC‐poor older NADW vintages and/or mixing with other CFC‐free water masses from the Southern Hemisphere. The lowest fractions were found in the LNADW, with a sharp downstream decrease from the equator at 35°W to 10°S, probably caused by the bifurcation into a zonal flow along 2°S and a southward flow along the Brazilian coast. Unlike the small uncertainties estimated for the inferred velocities, isopycnal diffusivities, κ, range from 100 to 10000 m 2 /s. The temporal evolution of f in the LSW shows a maximum, propagating from 7°N in 1996, downstream to 5°S in the Deep Western Boundary Current, and along 2°S to 23°W. We interpret this signal as the arrival of the intensely ventilated LSW formed in 1972–1976. Decreasing fractions of the ULSW and LSW south of the equator between 2000 and 2002 are presumably caused by local dynamics.
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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 | 0.000 | 0.000 |
| 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 | 0.001 |
| 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".