Tracing water masses with <sup>129</sup> I and <sup>236</sup> U in the subpolar North Atlantic along the GEOTRACES GA01 section
Bibliographic record
Abstract
Abstract. The distribution of 129I and 236U in 14 depth profiles and the sea surface along the GEOVIDE section (transect GEOTRACES GA01) the subpolar North Atlantic (SPNA) is presented for spring 2014. This work investigates the use of 129I and 236U as circulation tracers of water masses involved in the North Atlantic Meridional Overturning Circulation. The results show that 129I and 236U were distributed by water masses spanning 129I concentrations, 236U/238U atom ratios and 129I/238U atom ratios of (0.2–256) × 107 at/kg, (40–2350) × 10−12 and 0.5–200, respectively. The highest tracer levels were associated with shallow waters carried by the East Greenland Current (EGC) and the Labrador Current (LC), as well as with the overflow waters ventilating the deep SPNA. The presence of these radionuclides in the SPNA is mainly due to global fallout and varying contributions from nuclear reprocessing plants located near Sellafield, United Kingdom, and La Hague, France (0.1 % to > 5 %). Results show that part of the effluents discharged from Sellafield and La Hague apparently enter the eastern SPNA directly through the Iceland-Scotland passage or the English Channel/Irish Sea, as it is shown by elevated 129I concentrations and 129I/238U ratios in shallow central waters flowing in the West European Basin (WEB). The 236U/238U and 129I/238U ratios help identifying Arctic waters of Atlantic origin (PIW-Atlantic) in the EGC and of Pacific origin (PIW-Pacific) in the LC. PIW-Atlantic (PIW-Pacific) enriched in 129I (in 236U) appear to cascade along the slopes of Greenland and Newfoundland contributing to the overflows in the Irminger and Labrador Seas, respectively. The Iceland-Scotland Overflow Water spreading pathways into the eastern SPNA have been confirmed by the unequivocal transport of reprocessing 129I into the deep WEB. Data of 129I and 236U from 2014 and the 129I time series in the Labrador Sea agrees with the hypothesis that Atlantic Waters (tagged with nuclear reprocessing plant effluents) follow at least two circulation loops from their source region: one short loop through the Nordic Seas into the SPNA of about 8–10 years, and a second, long loop, which adds about 8 years more of recirculation in the Arctic Eurasian Basin.
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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 | 0.001 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".