Modelling ocean melt of ice mélange at Greenland’s marine-terminating glaciers

Abstract

Many of Greenland’s marine-terminating glaciers have retreated and accelerated in recent decades, contributing significantly to sea level rise. Increased submarine melting of calving fronts is often cited as the dominant driver of this retreat. However, the presence of ice mélange and its associated buttressing force on a glacier terminus is also thought to significantly impact glacier advance and retreat. The buttressing force depends on the mélange thickness, and thickness will be modulated by ocean melt rate, but our understanding of the melting of ice mélange by the ocean remains limited, and it is not yet known how these melt rates vary across a range of glacial and environmental conditions. Here, we perform high-resolution numerical simulations using MITgcm to model the circulation of ocean waters through an ice mélange close to marine-terminating glaciers and estimate the resultant melt. We find that near-surface waters within the ice mélange always warm due to the upwelling of deep warm waters, driven both by the subglacial discharge plume and by the melt-driven convection at the sides of the icebergs themselves. We explore the sensitivity of mélange melt rate to environmental conditions, finding that melt rate increases sublinearly with subglacial discharge and supralinearly with ocean temperature. In this sense, mélange melt rate appears to respond to environmental forcing in a similar manner to submarine melting of the calving front, and can be parameterised as such. The magnitude of the simulated mélange melt rates ranges from 0.26 to 0.92 m d−1, which is in good agreement with observational estimates. This work is a step towards both a better understanding of ice mélange dynamics and a better parameterisation of its effects on glaciers and the ocean.