Impact of Granular Behaviour of Fragmented Sea Ice on Marginal Ice Zone Dynamics

Abstract

Sea ice retreat and opening of large, previously ice-covered areas of the Arctic Ocean to wind and ocean waves is leading to large changes in the sea ice state. The Arctic sea ice cover is becoming more fragmented and mobile, with large regions of ice cover projected to evolve into a marginal ice zone (MIZ). Fragmented sea ice has different dynamics, necessitating changes in sea ice model rheology. The objective of this study is to improve sea ice dynamics in models for forecasting and climate projections. We introduce granular behaviour in the ice dynamics and assess the impact on sea ice behaviour. For this purpose we have implemented a seamless rheology for MIZ and pack ice in an idealised sea ice and ocean model. The study compares the effect of the combined rheology with that of the standard elastic-viscous-plastic (EVP) rheology. The main effect of granular behaviour in ice rheology is on internal ice pressure. The jostling of the floes causes divergence of the sea ice cover. Sea ice viscosities are only weakly impacted. In idealised simulations the new sea ice rheology results in widening of the MIZ and a more diffuse ice edge in a stand-alone set-up. Oceanic feedbacks counteract and can undo this effect. The resolution of the simulation modifies the effect of the rheology: a rheology that accounts for granular effects offers better convergence of the solution than the standard EVP. In conclusion, granular sea ice rheology affects the sea ice in the MIZ in some cases, but the importance of the effect in general is not clear.