Paired terrestrial cosmogenic nuclides support the mapping of relict polythermal terrains under the Keewatin Ice Divide, central mainland Nunavut, Canada
Bibliographic record
Abstract
Understanding basal thermal regimes of paleo-ice sheets is fundamental to provide constraints on ice sheet dynamics and geometry, subglacial hydrology and sediment fluxes, landscape evolution, and long-term climate responses. While various methods have characterized glacial terrains from a range of subglacial conditions, the relationship between landsystem mapping and terrestrial cosmogenic nuclides (TCNs) remains largely unexplored. Here, we investigate a continuum of relict polythermal landsystems and surrounding warm-based terrains mapped in areas formerly covered by the Keewatin Ice Divide by utilizing paired 10 Be and 26 Al cosmogenic nuclide analyses on bedrock, boulder, and till samples in the eastern Keewatin region of Nunavut, northern Canada. Exposure ages in low-elevation warm-based landscapes cluster at 8.2 ± 0.6 ka and align with the timing of deglaciation (7.7 ± 1 ka) indicating relatively high (deep) glacial erosion under dominantly warm-based conditions. Moderate nuclide abundances and apparent mean ages of 23.5 ± 4.6 ka (surface tills) and 21.8 ± 2.1 ka (bedrock trimlines at marine limit) in relict intermediate landsystems extending across the ice divide migration zone above 200 m elevation reflect moderate erosion during transient cold-based and warm-based conditions. High nuclide abundances and apparent mean 10 Be ages of 53.7 ± 4.6 ka (bedrock and boulder) in relict cold-based landsystems, predominant where the ice divide was anchored in the uplands above 400 m elevation, are consistent with low erosion and persistent cold-based conditions partially preserving surfaces weathered prior to the last glaciation. The apparent exposure ages in the relict terrains, significantly exceeding expected deglacial ages, and the relatively long periods of burial derived from 26 Al/ 10 Be ratios, indicate widespread TCN inheritance and reflect differential erosion under polythermal basal ice regimes as inferred from landsystem mapping. Our findings emphasize the importance of geomorphological mapping and landsystem analysis to inform the TCN sampling plan and highlight the need for caution in interpreting exposure ages within predominantly warm-based glacial landscapes in a core region of the Laurentide Ice Sheet where relict weathered terrains are recognized. • Surface exposure dating in eastern Keewatin agrees with mapped polythermal terrains. • Exposure ages exceed deglacial ages and 26 Al/ 10 Be ratios indicate inheritance. • Cosmogenic isotopes reflect variable glacial erosion under the Keewatin Ice Divide. • Exposure ages in warm-based landscapes align with the timing of deglaciation.
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".