Biogeochemical characteristics of a long-lived anticyclonic eddy in the eastern South Pacific Ocean
Bibliographic record
Abstract
Abstract. Eastern boundary upwelling systems are characterized by high productivity that often leads to subsurface hypoxia on the shelf. Mesoscale eddies are important, frequent, and persistent features of circulation in these regions, transporting physical, chemical and biological properties from shelves to the open ocean. In austral fall of 2011, during the Tara Oceans expedition, a subsurface layer (200–400 m) in which the concentration of oxygen was very low (< 2 μmol kg−1 of O2) was observed in the eastern South Pacific, ~ 900 km offshore (30° S, 81° W). Satellite altimetry combined with CTD observations associated the local oxygen anomaly with an intrathermocline, anticyclonic, mesoscale eddy with a diameter of about 150 km. The eddy contained Equatorial Subsurface Water (ESSW) that at this latitude is normally restricted near the coast. Undersaturation (44 %) of nitrous oxide (N2O) and nitrite accumulation (> 0.5 μM) gave evidence for denitrification in this water mass. Based on satellite altimetry, we tracked the eddy back to its region of formation on the coast of central Chile (36.1° S, 74.6° W). We estimate that the eddy formed in April 2010. Field studies conducted on the Chilean shelf in June 2010 provided approximate information on initial O2 and N2O concentrations of "source water" in the region at the time of eddy formation. Concentrations of both O2 and N2O in the oxygen minimum zone (OMZ) of the offshore eddy were lower than its surroundings or "source water" on the shelf, suggesting that these chemical species were consumed as the eddy moved offshore. Estimates of apparent oxygen utilization rates at the OMZ of the eddy ranged from 0.29 to 44 nmol L−1 d−1 and the rate of N2O consumption was 3.92 nmol L−1 d−1. Our results show that mesoscale eddies in the ESP not only transport physical properties of the ESSW from the coast to the ocean interior, but also export and transform biogeochemical properties, creating suboxic environments in the oligotrophic region of the eastern South Pacific. Suboxic water masses that are advected by eddies act as hotspots for denitrification and loss of fixed nitrogen from the system.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".