Turning the Tide on Antarctic Shear Zones

Outlet glaciers play a crucial role in transporting ice from the interior of the Antarctic Ice Sheet to the coast, where they transition into floating ice shelves at the grounding line. Shear margins, which separate these fast-moving glaciers from relatively stationary ice, are regions of intense lateral shearing that generate side drag—a resistive force that counteracts glacier driving stress and mitigates sea-level rise. The nature of this side drag depends largely on bulk ice stiffness, a property which is poorly understood due to the numerous challenges in accessing and measuring these most dynamic regions. Here, we use the vertical displacement of floating ice under tidal loading as a natural experiment to constrain bulk ice stiffness within shear margins. Using a GAMMA Portable Radar Interferometer (GPRI), we monitored the tidal flexure zone of Priestley Glacier, which flows into the Nansen Ice Shelf, over a full spring-neap tidal cycle in December 2024. Preliminary results suggest shear-zone weakening, supported by in-situ GPS measurements capturing the corresponding horizontal ice dynamics and ApRES observations of internal strain within the bending ice column. These findings enhance our understanding of the mechanisms driving ice discharge and provide critical observational constraints for simulations of ice-sheet dynamics, ultimately refining estimates of Antarctica’s contribution to sea-level rise.