Thickness of pro-glacial mélange impacts calving dynamics of Greenland glaciers

Iceberg calving is a major contributor to Greenland’s ice mass loss. Proglacial ice mélange is a collection of sea ice and icebergs that is tightly packed in tidewater glacier fjords and can suppress calving by providing resisting stresses called buttressing. Previous observations highlight seasonal change of some Greenland glacier termini, which advance quasi-statically in winter, and retreat by calving in summer. Finite-element models have indicated that the seasonal calving dynamics are related to buttressing from ice mélange. As it remains an ongoing challenge to instrument remote, ice-chocked fjords, there is a lack of detailed measurements of the buttressing stress in ice mélange.

To quantify the mélange buttressing force on the glacier terminus, we develop a continuum theory that reveals the scaling between the buttressing force and the mélange thickness. We also develop a three-dimensional discrete element model (DEM) that simulates a moving terminus pushing against a collection of cubic icebergs with a pow-law size distribution. Varying the mélange thickness, we retrieve corresponding steady-state buttressing forces and validate the proposed scaling law. Our results show that to provide effective buttressing, the averaged mélange thickness at the terminus must be larger than 145 meters. We further validate the thickness threshold by remote sensing data.