Relaxation scales and the structure of fractures in the dynamics of sea ice

The mechanics of drift ice under the influence of a fixed boundary (landfast ice) are examined, based on field observations and remote-sensing imagery in the Baltic Sea. The data were collected in the ZIP-97 experiment in the Baltic Sea. The motion of the sea-ice field on the coast is modelled, using analytic methods, and the cases are classified according to the role played by coastal friction. The relaxation of the ice motion showed two time scales: a short time scale (hours) determined by the local wind and a long time scale (days) resulting from the spin-down of large-scale ice massifs. The Coulomb friction results are independent of the spatial scale, while fracture mechanics models include surface area/contact length as an important scaling factor.