Modelling ice-ocean interactions in and around ice shelves

Abstract

Physical processes in Antarctica and the Southern Ocean are of great importance to the global climate system. This thesis considers two such processes, namely ice- ocean interaction in ice shelf basal crevasses and the conditional instability of frazil ice growth. It has been suggested that freezing within basal crevasses can act as a stabilising in uence on ice shelves, preventing their break up. Using Fluidity, a nite element ocean model, it is found that ocean circulation within a crevasse is highly dependent upon the amount of freezing in the crevasse. It is also found that frazil ice formation is responsible for the vast majority of freezing within a crevasse, and that there is a non linear relationship between the amount of supercooling in a crevasse and its freeze rate. The conditional instability of frazil ice growth is a little investigated mechanism of ice growth. Any frazil forming in the water column reduces the bulk density of a parcel of frazil-seawater mixture, causing it to rise. Due to the pressure-decrease in the freezing point, this causes more frazil to form, causing the parcel to accelerate, and so on. Numerical modelling nds that the instability does not operate in the presence of strong strati cation, high thermal driving (warm water), a small initial perturbation, high `background' mixing or the prevalence of large frazil ice crystals. Given a large enough initial perturbation this instability could allow signi cant rates of ice growth even in water that is above the freezing point. The research presented in this thesis forms the material for two peer-reviewed publi- cations; `Modelling ice ocean interactions in ice shelf basal crevasses' (Jordan et al., 2014) and `On the conditional frazil ice instability in seawater' (Jordan et al., 2015)