Evaporative fractionation of H<sub>2</sub><sup>18</sup>O in the polar ocean and the invisibility of large changes of ice volume and sea level in the Saalian δ<sup>18</sup>O proxy records
Bibliographic record
Abstract
Abstract. The oxygen isotope ratio, δ18O, as measured in skeletons of oceanic foraminifera, is a proxy for changes in world glacial ice volume and sea level and is of fundamental importance in the study of past climate change. However, in the Late Saalian glaciation the δ18O proxy reflects neither a large increase in glacial ice volume from 155 ka–142 ka nor the subsequent major deglaciation from 142 ka–136.5 ka in which sea level rose from about −140 m to +4 m at the end of the Drenthe sub stage. This deglaciation was caused by a large reduction in the ice sheet moisture supply due to storm path diversion associated with the loss of thermohaline circulation and the capping of the high latitude North Atlantic with melt water that passed through the Mediterranean Sea from the overflow of a giant ice-blocked Siberian lake. The δ18O proxy also fails to record the subsequent ice volume buildup of the Warthe substage in which sea level fell about 80 m. The explanation for the invisibility involves the fractionation and sequestration of large mounts of H218O in the effectively isolated and sea-ice-free polar ocean. The sequestration and subsequent release of polar water, enriched in H218O, distorted the fractionation record in the world ocean and destroyed the accuracy of the δ18O proxy. The proposed physical consequences of the ice-free polar ocean also include a sea-ice-free Labrador Sea and Baffin Bay and an oceanic circulation mode that drove the Drenthe substage glaciation to its maximum extent in Eurasia. The initial cause for the anomalous effects in the δ18O record was the known ice-flow blockage of all the Siberian rivers that discharge into the polar ocean west of the Lena River. Without adequate stratification by inflowing fresh river water, sea ice was unable to freeze on the deep polar ocean and the fractionation and the physical changes in the polar ocean that are proposed here followed.
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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 | 0.000 | 0.000 |
| 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) | 0.003 | 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".