A challenge to the Regolith Hypothesis for the MPT from present day sediment distribution and coupled climate-ice-sediment physics
Bibliographic record
Abstract
The mid-Pleistocene Transition (MPT) from 41 kyr to 100 kyr glacial cycles occurred in the absence of a change in orbital forcing. This presents a challenge for the Milankovitch theory of glacial cycles. A change from a low to high friction bed under the North American Ice Complex through the removal of pre-glacial regolith is hypothesized to play a critical role in crossing the threshold to longer and stronger glaciations. However, testing this Regolith Hypothesis requires constraint on currently unknown pre-glacial regolith cover as well as assessing whether glacial sediment processes remove the appropriate amount of regolith to enable glacial system change consistent with the MPT. Pleistocene regolith removal has not yet been simulated for a realistic, 3D North American ice sheet fully considering basal processes. Constraints on pre-glacial bed elevation and sediment thickness are sparse and the bounds are wide.What limits on pre-glacial regolith thickness in North America can be inferred from our current understanding of glacial processes and the present-day distribution of unconsolidated sediment? How does pre-glacial sediment thickness influence the evolution of Pleistocene glacial cycles? We answer these questions with an ensemble of whole-Pleistocene simulations with high-variance parametrizations and range of pre-glacial regolith thicknesses.We use the 3D Glacial Systems Model which incorporates the relevant glacial processes: 3D thermomechanically coupled hybrid SIA/SSA ice physics, fully coupled sediment production and transport, subglacial linked-cavity and tunnel hydrology, isostatic adjustment from dynamic loading and erosion, and climate from a 2D non-linear energy balance model and glacial index. This fully coupled system is driven only by atmospheric CO2 and insolation. The model captures the Pleistocene evolution of North American glaciation: 41 to 100 kyr glacial cycles shift, similar latitudinal extent in the early and late Pleistocene, LGM ice volume, deglacial ice margin chronology, and the broad present-day sediment distribution within the parametric and observational uncertainty. Constrained by large scale reconstructions of present-day surface sediment distribution, regional sediment distribution estimates, and regional bedrock erosion estimates, these results bound the mean pre-glacial sediment thickness.Our results suggest thin (
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".