New ice margin chronology for the last deglaciation of the North American Ice Sheet Complex
Bibliographic record
Abstract
The North American Ice Sheet Complex (comprising the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass in the Northern Hemisphere that grew towards and waned after the Last Glacial Maximum. The existing ice margin chronology available for the North American Ice Sheet Complex is based on radiocarbon data only and does not reflect other geochronometric information constraining the last deglaciation, such as cosmogenic exposure- or optically stimulated luminescence ages. Here we present a series of newly produced ice margin isochrones from 25 ka to present, in a time step of 500 years. For each isochron, we draw maximum, best estimate, and minimum ice margin position in an attempt to capture the existing uncertainty. The ice margin isochrones are based on (i) an up-to-date dataset of radiocarbon ages (~5000), (ii) 10Be and 26Al cosmogenic nuclide data that directly date ~80 ice-marginal features over North America, (iii) ~350 optically stimulated luminescence ages dating the deposition of an aeolian cover immediately post-deglaciation, (iv) the ice-sheet scale glacial geomorphology record. Our effort brings the information on the last North American Ice Sheet Complex deglaciation on par with that for the Eurasian Ice Sheets and should serve the broad community of Quaternary research from archaeology to numerical ice sheet modelling.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.001 | 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 | 0.001 |
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".