Tidal flexure reveals effective elasticity in grounding zones on the Ross Ice Shelf

Faye M. Elgart , Brent Minchew, Colin R. Meyer

The grounding zones of Antarctic ice shelves are among the continent’s most dynamic regions, where floating ice shelves buttress grounded upstream ice and tidal forcing drives cyclic flexure at the ice-ocean-bed interface. We use ICESat-2 altimetry and airborne ice-penetrating radar to constrain the effective Young’s modulus E* of ice in the flexure zone at three sites on the Ross Ice Shelf. By modeling ice as an elastic beam of variable thickness, we infer a single effective elastic parameter, E*, that encapsulates the combined flexural response of the ice-bed-ocean system. Our results show considerable spatial variability in E*, with values ranging from ~1–9 GPa across sites, and an average of 3.6 ± 2.5 GPa. This variability reflects intersecting basal, oceanographic, and mechanical processes in the grounding zone, including bed stiffness, subglacial hydrology, and viscoelasticity of ice. Because flexure of bed and ice cannot readily be distinguished in observations, we argue for a bulk interpretation of E* that allows uncertainty to be quantified in terms of a single parameter. These results offer a new method for estimating ice shelf thickness and thickness gradient near the grounding line, independent of the hydrostatic assumption, with implications for basal melt rate estimates and future sea-level rise projections.