Intra-annual grounding line migration and retreat: insights from high-resolution satellite and in-situ observations over Milne Glacier in the Canadian High Arctic
Bibliographic record
Abstract
Abstract. Changes at the boundary where marine terminating glaciers transition from grounded to floating, known as the grounding line, are critical for glacier stability and ice discharge prediction. We explore changes in the ice flexure zone (FZ), which spans from the inland limit of tidal flexure, known as the hinge line, across the actual grounding line, to where the ice tongue becomes freely floating. FZ movements on Milne Glacier, Nunavut, Canada from 2023 to 2024 were measured at a spatial resolution of 10 m using 4-day RADARSAT Constellation Mission (RCM) repeat acquisitions from four different orbits. The Double Difference Interferometric Synthetic Aperture Radar (DDInSAR) technique was employed to delineate 116 FZ positions, which were then examined with respect to tides, glacier velocity, surface and bed topography. Tides modulated by atmospheric pressure were the major driver of changes in the FZ with the correlation coefficient between DDInSAR and sea surface height displacements ranging from 0.81 to 0.94 for different RCM orbits. The lowest error (<0.1 cm in the SAR line-of-sight) occurred during the ‘stable regime’, when changes in glacier velocity were minimal, with ascending RCM tracks at incidence angles below 30°. During the ‘unstable regime’, the glacier velocity became more variable, and the error increased by up to 4 times. In summer, ice in the FZ flowed ~2.7-fold faster than the grounded section upglacier. We discovered a new ~2.4 km grounding line retreat associated with a pinning point at the eastern margin of the glacier. This rapid change is likely due to water intrusion and subglacial melt near the pinning point and shows how these bed features alter the grounding line short-term migration and its long-term retreat.
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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 | 0.002 |
| 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".