Variations in Ice Discharge and a Frontal Ablation Estimate of Marine-Terminating Glaciers Throughout Alaska from 2015-2021

Marine-terminating glaciers are major contributors to sea-level rise, yet their frontal ablation—the combined loss from ice discharge and terminus retreat—remains poorly constrained. This study presents a monthly time series of ice discharge for 40 marine-terminating glaciers in Alaska from 2015 to 2021, derived from Sentinel-1 velocity data, and reconstructed ice thickness information. Frontal ablation was calculated as the sum of ice discharge and terminus mass loss, from manually delineated terminus positions. The mean annual ice discharge was 11.81 ± 5.35 Gt a⁻¹, dominated by Hubbard, Columbia and Yahtse glaciers, which together accounted for ~70% of Alaska’s total ice discharge. Terminus retreat contributed an additional 1.30 ± 0.07 Gt a⁻¹, resulting in a total frontal ablation of 13.11 ± 5.35 Gt a⁻¹. Most glaciers exhibited late-summer velocity minima likely indicating seasonal changes in subglacial drainage efficiency, while interannual variability corresponded with El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) phases. These findings confirm that Alaska’s marine-terminating glaciers currently lose relatively little mass through frontal retreat compared to their regional mass balance, suggesting that most glaciers have passed their phase of rapid retreat. The presented analysis also provides fundamental information for refining sea-level rise projections.