Summary
There is much speculation over the role of frazil ice in both ocean cavities under ice shelves and in the adjacent ocean where Ice Shelf Water (ISW) plumes are found. Traditionally three-dimensional ocean circulation models have ignored this slurry of small, thin, disk-shaped crystals only millimetres in diameter, instead considering only direct heat and freshwater exchange with the overlying ice shelf or sea ice. However, there has been an increase in the volume of evidence indicating that when ISW plumes become supercooled, clouds of frazil ice crystals form in the water column to reduce the level of supercooling, rather than direct surficial freezing occurring at the ice shelf or sea ice base. Although frazil ice formation and transport have been previously modelled, most studies have been limited to either two-dimensional mixed layer models of the ocean under sea ice, or simple “plume” type models of sub-ice shelf ocean circulation. After reviewing the existing literature we have developed a systematic framework to represent more directly the nature of crystal-crystal collision processes and their role in crystal break-up and aggregation, and in secondary nuclei formation. To help understand the dynamics of the frazil ice model we present results from two ocean models in which the frazil ice model is embedded. The first is a simple one-dimensional ocean model forced by observed conditions in McMurdo Sound, Antarctica. The second has the frazil ice model embedded in a commonly used sub-ice shelf ocean circulation model, which is then applied to a simple ice shelf-ocean model domain.