Sudden collapse of ice mélange under increasing submarine melt at tidewater glaciers

Rapid ice loss from the Greenland Ice Sheet is responsible for roughly 20% of global sea level rise since 2002. Almost half of this loss is moderated by the presence of ice mélange, which influences glacial calving and melt rates. However, the seasonal to interannual drivers of ice mélange extent and collapse are poorly understood. Observations show a spread of behavior for ice mélange in different Greenland fjords, ranging from seasonal collapse each spring over a few days to perennial persistence. Here we present an explanation of ice mélange seasonality and collapse using a coupled ice mélange-ocean model that incorporates both high-resolution ocean circulation and dynamic granular mélange flow. In multi-year simulations, we reproduce observed seasonal variability of ice mélange and characterize the mechanism of collapse. We parameterize the threshold for ice mélange collapse and compare this to observations from five fjords across Greenland. Our results show that perennial ice mélange, currently present at the majority of the largest glaciers in Greenland, may suddenly collapse when subjected to increased submarine melt, which would drive greater calving, glacier mass loss, and sea level rise. This study models the collapse of ice mélange in glacial fjords in response increasing submarine melt rates. It shows that perennial mélange today is vulnerable to collapse subject to increasing melt, potentially accelerating glacier mass loss.