Nonlinear increase in seawater <sup>87</sup> Sr ∕ <sup>86</sup> Sr in the Oligocene to early Miocene and implications for climate-sensitive weathering
Bibliographic record
Abstract
Abstract. The 87Sr / 86Sr of marine carbonates provides a key constraint on the balance of continental weathering and hydrothermal Sr fluxes to the ocean, and the mid-Oligocene to mid-Miocene period features the most rapid rates of increase in the 87Sr / 86Sr of the Cenozoic. Because previous records of the 87Sr / 86Sr increase with time were based on biostratigraphically defined age models in diverse locations, it was difficult to unambiguously distinguish million-year-scale variations in the rate of 87Sr / 86Sr change from variations in sedimentation rate. In this study, we produce the first 87Sr / 86Sr results from an Oligocene to early Miocene site with a precise age-model-derived orbital tuning of high-resolution benthic δ18O at Equatorial Pacific Ocean Drilling Program (ODP) Site 1218. Our new dataset resolves transient decreases in 87Sr / 86Sr, as well as periods of relative stasis. These changes can be directly compared with the high-resolution benthic δ18O at the same site. We find that slowing of the rate of 87Sr / 86Sr increase coincides with the onset of Antarctic ice expansion at the beginning of the mid-Oligocene glacial interval, and a rapid steeping in the 87Sr / 86Sr increase coincides with the benthic δ18O evidence for rapid ice retreat. This pattern may reflect either northward shifts in the Intertropical Convergence Zone precipitation to areas of nonradiogenic bedrock and/or lowered weathering fluxes from highly radiogenic glacial flours on Antarctica. We additionally generate the first 87Sr / 86Sr data from ODP Site 1168 on the Tasman Rise and Integrated Ocean Drilling Program (IODP) Site 1406 of the Newfoundland Margin during the Oligocene to early Miocene to improve the precision of age correlation of these Northern Hemisphere and Southern Hemisphere midlatitude sites and to better estimate the duration of early Miocene hiatus and condensed sedimentation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.000 | 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 teacher head, 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".