Simulation of pancake-ice dynamics in a wave field

Abstract From many field observations, it has become well known that pancake ice is ubiquitous in a wave-dominated sea. These strikingly uniform circular floes are consistently found in the Antarctic seas during the ice-formation season. Their presence has also been reported in the Bering Sea, the Greenland Sea and in polynyas and leads within pack ice. In one estimate made by P. Wadhams (personal communication, 1991) the areal coverage of pancake ice in the Southern Ocean marginal ice zone is around 6 × 106 km2. Pancake ice forms through a combination of thermodynamic growth and mechanical thickening, caused by rafting of floes that is driven by wave motion This complex growth process is much faster than pure thermodynamic growth and hence may be the main factor responsible for ice-edge advance in marginal ice zones. In this paper we simulate wave/ice-floe dynamics by combining a new three-dimensional discrete element model with wave hydrodynamics. In one set of simulations we calculate ice-drift speed as a function of wave amplitude and ice collisional dynamics. In a second set of simulations we place a non-reflecting vertical barrier meant to simulate the fast-ice edge. The simulation results show the rate of increase of the ice impact force on the barrier, and the accompanying thickening of the rafted region in front of the barrier, as a function of wave amplitude. Results from this study will help quantify the formation process for pancake-ice covers in a wave field.