Deglacial 14C reservoir ages of surface waters at the northern boundary of Peruvian coastal upwelling
Bibliographic record
Abstract
To constrain the accurate age of a marine sediment record, the radiocarbon (14C) ages need to be corrected for short-term and small-scale changes in planktic 14C reservoir ages (Rplank). Nevertheless, accurate records of past changes in Rplank are scarce. Here we present a high-resolution record of deglacial 14C ages measured on Globigerina bulloides in sediment core M77/2-59-1 from the northern boundary (~4°S, 997 m) of the Peruvian upwelling zone. The fine structure of jumps and plateau boundaries in the 14C record were tuned to synchronous, thus global structures in the atmospheric 14C record of Lake Suigetsu (Bronk Ramsey et al., 2012) and used as tie points for an age model with semi-millennial resolution, moreover to reconstruct deglacial changes in Rplank from 17 to 11 cal. ka. In our record, Rplank drops from 1250 14C yr prior to 14 cal. ka to ~600 – 450 14C yr until the plateau named Top of Younger Dryas. The drop suggests a major decrease in coastal upwelling, possibly the result of a southward (poleward) expansion of the Intertropical Convergence Zone and related shift in the southeastern trade wind belt during the Bølling-Allerød. Subsequent to 14 cal. ka our Rplank values are roughly similar to values obtained for thermocline waters near the equator from the age difference between 14C ages of wood chunks and 14C of G. ruber (Zhao & Keigwin, 2018). Prior to 14 cal. ka our Rplank are ~800 14C yr higher, which corroborates the presumed latitudinal shift of coastal upwelling. Our 14C ages measured on G. bulloides differ in part from paired 14C ages of Neogloboquadrina dutertrei, indicating their habitat in different water masses prior to 14 cal. ka, in support of the upwelling affinity of G. bulloides. In addition, we used our Rplank values to accurately derive past ventilation ages of intermediate waters near 1000 m depth based on the difference of paired benthic and planktic 14C ages, which is important to constrain centennial to millennial scale changes in circulation influencing the extent of the Peruvian oxygen minimum zone. References: Bronk Ramsey, C., et al., Science, 338, 370–374, 2012. Zhao & Keigwin, Nature communications, 9, 3077, 2018.
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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 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".