Modeling the formation and evolution of oriented fractures in sea ice

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Abstract
While sea-ice drift tends to be a relatively coherent field moving largely in response to spatially averaged wind, strain-rate observations show relative ice motion to be much more of a chaotic field with deformation occurring along narrow intersection strikes between effectively rigid plates. This relative motion also has considerable energy at high frequencies which are not coherent with the wind forcing. Plastic rheologies for a strongly interactive medium are inherently able to predict such fractures. To investigate this phenomenon, this paper presents a basic anisotropic theory for multiple-oriented weaknesses. When coupled with short-term evolution equations for ice strength, this model is found to yield strong zones of failure over the Arctic basin, with relatively rigid motion in between. These failure lines typically occur along geostrophic wind contours. These zones are also found to be created with appropriate "Coulombic" isotropic rheologies. When combined with a previously developed inertial embedding procedure for the oceanic boundary layer, the resulting deformation field tends to fluctuate with considerable power near the inertial period even though the wind field is constant. The mechanisms necessary for obtaining such oriented features are discussed.