Northern Hemisphere ice sheets during the M2 Pliocene glacial
Bibliographic record
Abstract
The large glacial period that immediately precedes the mid-Pliocene Warm Period (mPWP) is a ~0.6‰ benthic oxygen isotope shift at 3.3Ma, known as M2. The excursion is roughly equivalent to 60m of sea level drop or 40msle (metres sea level equivalent) more ice than today. However, there is significant uncertainty in both these values and the potential locations of any large volumes of ice. Previous modelling studies have either used Last Glacial Cycle analogues for the M2 ice sheets or failed to reproduce the large Northern Hemisphere ice sheets implied by global ice volume proxies. Here we present new climate and ice sheet models simulating the M2 glacial period, by lowering Pliocene atmospheric carbon dioxide concentrations and selecting specific Pliocene orbital forcing. These climates are sufficiently cold to produce ice sheets in North America and northern Europe within our modelling framework. The largest components of these ice masses are centred over regions with significant landscape differences between Pliocene and present day, including the Hudson Bay, Canadian Archipelago and Barents Sea. This suggests that the M2 glacial may have had very different initiation locations to the most recent glacial cycles and that Pliocene palaeogeographic changes may be key to understanding the M2 glacial.
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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 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".