Regime Shift in Annual Nitrate Concentration in the Upper Southern Chukchi Borderland Responded to the Westward Shift of the Beaufort Gyre
Bibliographic record
Abstract
Abstract Recent strengthening and westward movement of the Beaufort Gyre (BG), along with the rapid retreat of Arctic sea ice creates a new hotspot for investigating ecosystem responses to environmental changes over the Chukchi Borderland. As an important basis for primary production, nutrient variation and its controls in this hotspot region require to be preliminarily clarified. Using a hindcast simulation of a coupled ocean‐sea ice‐biogeochemical model (NAPA‐BGC) covering 1998–2015, this study suggests a regime shift in annual nitrate concentration in the upper southern Chukchi Borderland with the lower concentration since 2009. The relative contributions of biological and physical processes to annual nitrate variation are quantified via budget estimates. The results show a less temporally variable contribution of biological processes to nitrate variation, while the role of advection shifting from a nitrate source to a nitrate sink since 2009. This suggests physical processes mainly determine the nitrate transition in the upper southern Chukchi Borderland. Driven by the westward shift of the BG, the westward and southward expansion of the upper oligotrophic Canada Basin water narrows the pathway of nitrate‐rich shelf water flowing over the Chukchi Borderland. Meanwhile, the enhanced anticyclonic velocity at the marginal BG leads to an increased westward nitrate flux across the Chukchi Borderland and decreased nitrate supply to the north. Consequently, higher nitrate concentration exists in a narrow region to the south of 75°N, whereas the remaining areas have lower nitrate concentration, contributing to the overall reduction in annual averaged nitrate concentration since 2009 in the southern Chukchi Borderland.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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 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".