Arctic sea ice as a granular material

The authors have previously had success in validating that sea ice behaves as a hardening granular plastic material. They investigated sea-ice kinematics from October 1993 through April 1994 using relative motions from 11 drifting buoys with Global Positioning System (GPS) navigation in a 20-km array centered on the Sea Ice Mechanics Initiative (SIMI) Ice Camp, and compared these motions to synthetic aperture radar (SAR)-derived ice velocities over a 100 by 500 km region in the Beaufort Sea. There is excellent correspondence between the deformation of the buoy array and that from the SAR. SAR has provided information to qualitatively verify the underlying plastic hypothesis for sea-ice behavior on regional scales. Inferred ice dynamics was derived from analysis of the two major northerly wind convergence events of the winter. At moderate forcing, i.e., wind stress multiplied by fetch, the ice appears to fail in shear along sliplines, which occur at an acute angle to each other and to the direction of the wind forcing, characteristic of a plastic material at critical state. With longer fetch the ice appears to fail in compression, perpendicular to the wind direction. There appear to be two sliplines in the northern region, one of which went through the camp location. This shearline was verified by the GPS buoys. There are two east-west trending lines, where the authors infer failure due to compression.