Modelling the reorientation of sea-ice faults as the wind changes direction

A discrete-element model of sea ice is used to study how a 900 change in wind direction alters the pattern of faults generated through mechanical failure of the ice. The sea-ice domain is 400 km in size and consists of polygonal floes obtained through a Voronoi tessellation. Initially the floes are frozen together through viscous-elastic joints that can break under sufficient compressive, tensile and shear deformation. A constant wind-stress gradient is applied until the initially frozen ice pack is broken into roughly diamond-shaped aggregates, with crack angles determined by wing-crack formation. Then partial refreezing of the cracks delineating the aggregates is modelled through reduction of their length by a particular fraction, the ice pack deformation is neglected and the wind stress is rotated by 90 degrees. New cracks form, delineating aggregates with a different orientation. Our results show the new crack orientation depends on the refrozen fraction of the initial faults: as this fraction increases, the new cracks gradually rotate to the new wind direction, reaching 90 degrees for fully refrozen faults. Such reorientation is determined by a competition between new cracks forming at a preferential angle determined by the wing-crack theory and at old cracks oriented at a less favourable angle but having higher stresses due to shorter contacts across the joints.

Details