Measuring in situ 26Al and 10Be in Post-Glacial Sand Reveals Limited Erosion by Quebec-Labrador Ice Dome
Bibliographic record
Abstract
There is minimal knowledge of the Laurentide Ice Sheet’s erosive behavior prior to the LastGlacial Maximum because, as the ice sheet advanced, it largely erased evidence of previous glaciations. Seeking to understand the erosivity of the eastern portion of the Laurentide Ice Sheet, the Quebec-Labrador Ice Dome, we sampled sand from deglacial features (eskers and deltas) and from rivers across eastern Canada—a landscape repeatedly overrun by ice. We measured concentrations of 10Be and 26Al in quartz isolated from the sediment and, after considering cosmic-ray exposure during the Holocene, used the data to determine nuclide concentration at the time of deglaciation. The mean 10Be concentration in deglacial sediments (n=11) is 1.87 ±1.39*104 atoms g-1 and 3.31±1.57*104 atoms g-1 in modern sediments (n=10). Corrected for Holocene exposure, we determine that deglacial sediment, at the time it was deposited by the ice sheet, contained between 7.60*103 and 5.58*104 atoms g-1 of 10Be inherited from prior periods of surface and near-surface exposure. 26Al/10Be ratios corrected for Holocene nuclide production range from 3.45(-2.26, + 1.10) to 8.45±4.19 in deglacial samples and 5.64±0.78 to 7.92±0.93 in modern river samples. Our data indicate that glacial erosion in eastern Canada was insufficient to remove cosmogenic nuclides produced during prior periods of exposure. This provides further evidence that the Laurentide Ice Sheet was minimally erosive during the last glacial period, as studies on other portions of the ice sheet also show inherited nuclide concentrations preserved by limited erosion. Most 26Al/10Be ratios for deglacial samples are near the production rate for high latitudes, giving a strong indication that the Quebec-Labrador Ice Dome went through multiple periods of Pleistocene interglacial exposure.
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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 | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".