ClimaTea Lecture

Speaker: Alex Robel

Title: "The Direct Influence of Sea Ice on Ice Sheets through Granular Iceberg Melange".

Abstract: The recent acceleration in mass loss at many glaciers in Greenland and Antarctica has been accompanied by rapid breakup of iceberg melange, a dense aggregation of icebergs and sea ice floating at glacier termini. Observations suggest that melange suppresses calving through the direct application of back force on the glacier. Unfortunately, current ice flow models are not capable of simulating melange to test this speculation. I simulate melange as a granular material with cohesive elastic bond formation and breaking using a specially-adapted version of the Discrete-Element bonded-particle Sea Ice model (DESIgn), a toolbox of LAMMPS-LIGGGHTS, an open-source discrete element method simulator. Icebergs are simulated as semi-rigid cylinders floating in seawater and sea ice is simulated as compressible elastic plates that form between proximate icebergs and break upon exceedance of material strength or length thresholds.

Simulations show that melange laden with thick sea ice can exert sufficient back force on the glacier terminus to shut down calving and thinning of sea ice reduces this back force, increasing the likelihood of calving. Calving events initiate jamming waves within melange and cause the fracture of the sea-ice matrix that bonds melange, increasing the likelihood of subsequent calving events. I discuss the comparison between simulations and observations of melange, the benefits and shortcomings of using a discrete element approach and the potential for melange coupling to ice sheet flow models.