From Fracture to Flow: How Calving Ice Sheets Drive Mélange Behavior and Fjord Ocean Dynamics

The rapid mass loss of the Greenland Ice Sheet (GrIS) has drawn attention to its glacial fjords for two primary reasons: enhanced submarine melting is a plausible trigger of glacier retreat, and the increasing freshwater discharge from the GrIS could influence coastal ecosystems, sea level, and the global climate. For fast-flowing glaciers, calved icebergs, bergy bits, and sea ice form proglacial ice mélange. The mechanical coupling between the ocean and the mélange, particularly during calving seasons, remains poorly understood. Observations show that, following calving events, icebergs within the mélange can move away from the terminus at speeds reaching 1.5 m/s, decaying to 0 m/s within an hour. Such one-hour impulses occur daily to weekly across the GrIS and last for months. Since the calving-induced mélange velocity is greater than the ocean fluctuating velocities from shelf forcing (~0.5 m/s) or the summer mean velocity (~0.04 m/s), the mélange imposes a shear stress on the ocean from the surface down to the mélange keel depth (10 m - 800 m), potentially driving fjord circulation, mixing, and water mass structure. There can be associated feedbacks on the submarine melting and calving of the glacier, plus impacts on the export of freshwater from the fjord.We study this new mechanism driving fjord circulation along the Greenland Ice Sheet: drag exerted by these calving-induced mélange surges on the ocean and its impacts. We use benchmark flume experiments to develop a parameterization of mélange-ocean drag coefficient based on mélange keel depths observed from digital elevation models. To quantify the energy budget of a capsizing iceberg within the coupled glacier–mélange–ocean system, we develop a particle-based model by coupling the discrete element method (DEM) with smoothed particle hydrodynamics (SPH). Building on the capsizing dynamics captured by the DEM–SPH model at the tabular iceberg scale (O(1 km)), we upscale using the MIT General Circulation Model (MITgcm) to investigate the impact of rapid mélange motion on fjord-scale circulation (O(10–100 km)). The resulting changes in ocean mixing, circulation, and water mass structure are expected to enhance glacial submarine melting, reduce mélange buttressing force, facilitate calving, and affect freshwater discharge.