Inverting InSAR Observations to Estimate Basal Melt Rates: A Grounding‑Line Response Function Approach

The grounding line hinge position for the Fimbul Ice Shelf (Antarctic Peninsula) was determined using Synthetic Aperture Radar (SAR) Interferometric data from June 2023 through October 2024. The data were used to determine the hinge position over eight different time intervals (i.e., SAR Pairs) at an average spatial resolution of 20 meters. The Fimbul Ice Shelf area of interest (AOI) was defined as 301,800 – 561,400 meters East (E); 1,997,480 – 2,235,240 meters North (N), and referenced to the EPSG:3031 WGS 84 Antarctic Polar Stereographic Coordinate System. A total of 75% of the detected hinges were verified through the co-location with large vertical displacement gradients. The grounding line hinge positions varied by up to +/−70 kilometers across the AOI and exhibited a temporal variability of 53-140 km during the time spanned by the data collection. Tidal forcing accounted for only 2.6% of the variance in the hinge position data collected. Seasonal variation accounted for 1.0% of the variance. However, basal melt rates derived from Southern Ocean State Estimate (SOSE) ocean temperatures accounted for 30.2% of the variance. The combination of tidal forcing, seasonal ice shelf dynamics, and basal melt rate estimates explained 71.2% of the variability in hinge position data (Adjusted R² = 0.496; Root Mean Squared Error = 21.91 km). Basal melt driven ice shelf thinning represented 44.5% of the relative importance in explaining hinge position variability, while seasonal dynamics represented 38.6%, and tidal flexure represented 16.9%. Therefore, it is estimated that there are additional factors that represent 28.8% of the variance in hinge position variability that may be related to high frequency ocean variability or rheological characteristics of the ice shelf. Therefore, the findings indicate that the grounding line hinge position for the Fimbul Ice Shelf is extremely sensitive to changes in ocean thermal properties. Specifically, each 1 degree Celsius increase in ocean temperature results in a migration of the grounding line hinge position toward the landmass of approximately 2.5 kilometers. These findings have significant implications for understanding how ice shelves will respond to projected increases in Southern Ocean temperatures (approximately 1-2 degrees Celsius) by the year 2100 and subsequently how sea levels will be impacted by these changes.