Nitrogen isotope and productivity variations along the northeast Pacific margin over the last 120 kyr: Surface and subsurface paleoceanography
Bibliographic record
Abstract
Glacial‐interglacial changes in sedimentary δ15N over the last 120 kyr display a remarkably similar pattern in timing and amplitude in core records extending from the denitrification zone in the eastern tropical North Pacific (ETNP), where subsurface denitrification is active, to the Oregon margin, where no denitrification occurs today. Low δ15N values (4–6‰) generally characterize glacial stages 2 and 4, and higher δ15N values (7–10‰) are representative of the Holocene, millennial‐scale periods within stage 3, and stage 5. The inferred synchroneity of δ15N variations along the entire margin implies that the nitrate isotopic signal produced in the oxygen‐poor subsurface waters in the ETNP is rapidly advected northward and recorded at sites far beyond the boundaries of the modern denitrification zone. Similar to δ15N, primary production indicators (percent Corg, Ba/Al, and percent opal) show glacial‐interglacial as well as millennial‐scale variations along the NE Pacific margin, with higher primary production during warm periods. However, the relative phasing between δ15N and paleoproduction tracers within individual records changes latitudinally. Whereas δ15N and primary production vary approximately synchronously in the midlatitudes, production lags δ15N in the ETNP by several kiloyears. This lag calls for a new understanding of the processes driving denitrification in the ETNP. We suggest that oxygen input by the Equatorial Undercurrent as well as local organic matter flux controls denitrification rates in the ETNP. Moreover, the differences in relative timing point to a time‐transgressive development of upwelling‐favorable winds along the NE Pacific margin after the last glaciation, with those in the north developing several kiloyears earlier.
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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".