Grounding-line retreat of Milne Glacier, Ellesmere Island, Canada over 1966–2023 from satellite, airborne, and ground radar data
Bibliographic record
Abstract
Milne Glacier is a marine-terminating glacier located on the northern coast of Ellesmere Island in the Canadian High Arctic, a region that has experienced extensive ice-mass loss over the last two decades. Milne Glacier flows into Milne Fiord where it transitions from grounded to floating at its grounding line. The glacier rests on a retrograde slope and is therefore potentially vulnerable to marine ice-sheet instability where enhanced basal melt and grounding-line retreat can trigger further deterioration of the glacier. Glacier changes that occur in the ice flexure zone, which spans from the hinge line, the inland limit of tidal flexure, past the grounding line to the landward limit of hydrostatic equilibrium, are critical for glacier dynamics. In this study, we quantify changes in the Milne Glacier grounding-line position from 1966 to 2023 using satellite, airborne, and ground radar observations. Double difference interferometric analysis of Synthetic Aperture Radar (DDInSAR) images acquired between 1992 and 2023 from European Remote Sensing (ERS-1/2) satellites, Sentinel-1 A/B, and RADARSAT Constellation Mission (RCM) was performed to delineate a timeseries of the hinge line. We used these hinge lines to quantify changes in the grounding-line position as their migration rates are directly correlated. RCM-derived results had the highest spatial resolution (10 m) and the best coherence between 4-day repeat acquisitions, which provided the most continuous and detailed hinge-line delineation across the glacier. We also used airborne and ground-based ice penetrating radar (IPR) data collected between 2014 and 2023 to calculate the normalized bed reflection (NBRP) and internal reflection power (NIRP) coefficients to distinguish between basal returns associated with water versus bed and assess signal attenuation within the ice column. Spatial patterns in NBRP and NIRP coefficients allowed us to reliably separate the floating and grounded parts of Milne Glacier. This alternate way of delineating the grounding line was in good agreement with our satellite-based DDInSAR results. Analysis of historical airborne radar surveys in 1966 and 1981 in conjunction with our more recent NBRP/NIRP analysis revealed a ∼3.1 km retreat (or ∼55 m yr −1 ) of the grounding line along the glacier centerline over the past 57 years. DDInSAR analysis provided additional details on this shift across the Milne Glacier. ERS and RCM images acquired in 3 and 4-day repeat cycles, respectively, revealed variability in hinge-line positions. This information allowed us to estimate the landward and seaward bounds, associated with the short-term hinge-line migration, that were used to quantify the grounding-line retreat over years. The grounding line retreat was highly asymmetric with the grounding-line retreating at over twice the average rate near the western margin (124 m yr −1 ) than at the center (53 m yr −1 ) of the glacier between 2011 and 2023. The calculated average retreat rates of grounding line showed a close association with changes in the ocean temperatures and subglacial discharge. Our study demonstrated that satellite-based monitoring of the hinge line at high spatiotemporal resolution is crucial to better assess the grounding line short-term positional variability and reliably quantify its long-term retreat. Airborne and ground-based radar observations can provide additional in-situ information to explain changes in the grounding line that affect glacier dynamics and viability. • The Milne Glacier grounding line retreated ∼3 km over the last 57 years. • The grounding line retreat was more pronounced on the western side of the glacier. • RCM provided the most detailed spatiotemporal information on hinge line variability. • Ground radar transects delineated grounded and floating glacier sections. • Satellite, airborne, and ground radar-derived grounding line positions agreed well.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".