Impact of ice mélange thickness on mélange melt rate in Greenland’s glacial fjords

In recent decades, Greenland’s marine-terminating glaciers have retreated and accelerated, contributing significantly to global sea level rise. The presence of an ice mélange, and its associated buttressing force on a glacier terminus, has a significant impact on glacier advance and retreat. The buttressing force is modulated by the thickness of the ice mélange, which in turn is influenced by mélange melt rate, but our understanding of ice mélange melting remains limited. In particular, a quantitative understanding of how the thickness of an ice mélange impacts melt rates is lacking.

Here, we model the melting of ice mélange by the ocean using the ocean model MITgcm to simulate the water flow in the first 15km down-fjord from the calving front, focusing specifically on the relationship between the melt rate and the mélange thickness. Ice mélange is represented in the model by cuboid icebergs that are thermodynamically active, divert the fluid flow and represent a range of sizes to reflect realistic observed iceberg distributions. We find that melt rate generally increases with mélange thickness and is particularly sensitive to mélange thickness at thicknesses below approximately 100 metres. Based on these simulations, we develop a parameterisation for mélange melt rate as a function of subglacial discharge, oceanic thermal forcing and mélange thickness. We then apply this parameterisation around Greenland to the ice mélange at 27 glaciers. We estimate melt rates in the range 0.05 – 0.92 m/d, which is comparable with observational estimates, and extract the dominant factors that control glacier-to-glacier variability in mélange melt. The development of this parameterisation is a key step in advancing our understanding of the dynamics of ice mélange and enabling a representation of ice mélange in larger climate and ice sheet models.