"Granular Dynamics of Sea Ice at the Ice Sheet-Ocean Interface"
Mass loss from marine-terminating glaciers in Greenland and Antarctica has recently accelerated, significantly increasing the ice sheet contribution to ongoing sea level rise. In many cases, this increasing mass loss has been accompanied by the breakup of nearby sea ice within mélange, a dense aggregation of icebergs and sea ice floating in front of glaciers. In glacier models, a prescribed mechanical back force applied by mélange on a marine-terminating glacier can prevent iceberg calving and mass loss. However, the physical processes that set the magnitude of this back force within mélange are not well understood. Current continuum glacier models are not capable of simulating the interactions of icebergs and sea ice within mélange and the transition of mélange from a semi-rigid ice flow in cold conditions to a granular aggregation of icebergs in warm conditions. In this talk, I will present a new approach to simulating mélange as a granular material with cohesive elastic bond formation and breaking using a specially-adapted version of an open-source discrete element simulator. Icebergs are simulated as rigid cylinders floating in seawater and sea ice floes are simulated as deformable elastic plates between proximate icebergs. Using these simulations, I show that that mélange laden with thick or dense landfast sea ice can exert sufficient back force on an advancing glacier terminus to shut down calving. Thinning of sea ice reduces the back force of the mélange on the glacier terminus, leading to an increase the rate of iceberg calving. When calving events occur, they initiate jamming waves within the mélange and can cause the fracture of the sea-ice matrix that bonds mélange, increasing the likelihood of subsequent calving events. These jamming waves compare well to observations of mélange variability at a large marine-terminating glacier in Greenland and provide a potential explanation for the rapid transition to vigorous calving that occurs at many glaciers in spring. I discuss the potential for using new continuum approaches from granular flow theory to incorporate mélange dynamics into ice sheet models, and the broader effort to improve our understanding of the physical processes that drive rapid sea level rise. [Background reading]