Drivers of oxygen variability on the Canadian Pacific shelf in the context of emerging hypoxia
Bibliographic record
Abstract
Hypoxia is an increasing concern along the Northeast Pacific continental margin, driven by oxygen (O₂) declines related to a warming climate. Despite a declining North Pacific O₂ inventory, historical observations of hypoxia on the central coast of British Columbia, Canada, were rare before 2020. However, recent observations from Queen Charlotte Sound (QCS)—a 120 km-wide shelf sea supporting an ecologically and economically significant ecosystem—indicate that hypoxia is now an emerging issue in this region. This study synthesizes regional observations from numerous platforms to describe O₂ distributions during 2022 and 2023, identifying persistent shelf-wide hypoxia during summer months, including periods of statistically defined extreme hypoxia. Comparisons with the hydrographic record from 2003–2021 show that O₂ concentrations were lower and hypoxia more common in 2022 and 2023 than in previous years. Long-term deoxygenation trends of approximately 5–10 μmol kg⁻¹ per decade are identified at isopycnals representing QCS deep waters, in addition to seasonal and interannual variability of similar magnitude. On annual and seasonal timescales, upwelling strength, upwelling timing, and O₂ consumption modulate O₂ variability, while the offshore supply of O₂ modulates variability on interannual and decadal timescales. It appears that this low-frequency signal propagates from the Northwestern Pacific via North Pacific Gyre circulation with an 8-year lag. The North Pacific Gyre Oscillation (NPGO) is also identified as a strong driver of O₂ variability through its influence on upwelling. The regional emergence of hypoxia has resulted from progressive O₂ declines rather than a sudden shift, and projections suggest that summer hypoxia will become the norm by 2050 in the absence of regional O₂ recovery.
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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 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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 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".