A test of the Regolith Hypothesis with fully coupled glacial sediment and ice sheet modelling
Bibliographic record
Abstract
A leading contender for explaining the mid-Pleistocene transition (MPT) from small 40 kyr glaciations to large, abruptly terminating 100 kyr ones is a shift to high friction bed under the Northern hemisphere ice sheets – the North American ice sheet in particular. The regolith hypothesis posits that this occurred with the removal of deformable regolith – laying bare higher-friction bedrock under ice sheet core domains. Is the regolith hypothesis consistent with the physics of glacial removal of mechanically weak surface material? Self-consistency of the regolith hypothesis has not been tested for a realistic, 3D North American ice sheet, capturing the transition from soft to hard bedded and 40 to 100 kyr cycles, fully considering basal processes and sediment production. To test self-consistency, we simulate the pace and distribution of regolith removal in a numerical ice sheet model incorporating the relevant glacial processes and their uncertainties. Specifically, the Glacial Systems Model includes: fully coupled sediment production and transport, subglacial hydrology, glacial isostatic adjustment, 3D thermomechanically coupled hybrid ice physics, and internal climate solution from a 2D non-linear energy balance model. The sediment model produces sediment via quarrying and abrasion while transporting material englacially and subglacially. The subglacial hydrology model employs a linked-cavity system with a flux based switch to tunnel drainage, giving dynamic effective pressure needed for realistic sediment and sliding processes. Deflection and rebound of the Earth's surface are calculated for a range of solid Earth visco-elastic rheologies. The coupled system is driven only by prescribed atmospheric CO2 and orbitally derived insolation. Starting from a range of initial sediment distributions and simulating an ensemble of model parameter values, we model the rate and spatial distribution of regolith dispersal and compare this against the inferred range of Pliocene regolith thickness, the present day sediment distribution, and the timing of the MPT. A first order fully coupled representation of ice, climate and sediment interactions captures the transition within parametric and observational uncertainty. The system gives the shift from 40 to 100 kyr glacial cycles while broadly reproducing the present day sediment distribution, inferred early Pleistocene extent, LGM ice volume and deglacial margin locations.
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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 | 0.002 | 0.008 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.003 | 0.002 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".