Deep Water Renewal in the Amerasian Basin: Updates from Natural and Anthropogenic Tracers
Bibliographic record
Abstract
The deep waters of the Amerasian Basin in the Arctic Ocean are among the most isolated in the modern Arctic Mediterranean Sea (e.g., Schlosser et al., 1997). In this study, we use a suite of tracers spanning a range of timescales—including CFCs, SF₆, radiocarbon (14C), and the radioactive noble gas argon-39 (39Ar)—to assess the mean age and renewal rates of deep and bottom waters in the Canada and Makarov basins. Measurements from the 2015 U.S. Arctic GEOTRACES expedition (GN01), combined with data from samples collected since 1979, reveal a homogeneous deep layer below ~2500 m depth characterized by limited ventilation and gradual warming, consistent with estimates of geothermal heat fluxes. Apparent tracer ages in this layer average ~450 years, with a standard deviation of about ±40 years. Sparse but detectable CFC maxima in bottom waters observed at several stations suggest episodic inputs of dense, shelf-derived waters, likely resulting from the downslope cascading of brine-enriched plumes. Salinity and oxygen isotope analyses indicate that these inputs originate primarily from the Chukchi Borderland and Beaufort Sea shelf. Time-dependent mass balance calculations show that present-day ¹⁴C and ³⁹Ar concentrations can be explained by radioactive decay since a single deep water renewal event. These results indicate that the most recent basin-wide deep water renewal occurred approximately 450 years ago and constrain present deep ventilation rates to no more than approximately 0.01 Sv.
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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 | 0.003 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.004 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| 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 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".