Field Observations of the Bering Sea Ice Edge Properties during March 1979

Abstract

During March 1979 field observations in the Bering Sea show that because of the interaction of winds and ocean swell with the ice, the ice edge divides into three distinct zones. First, adjacent to the open ocean is an ?edge" zone, 1?15 km in width, which consists of heavily rafted and ridged floes with thicknesses of 1?5 m and measuring 10?20 m on a side. Second is a ?transition? zone measuring ?5 km in width, which consists of rectangular ice floes with thicknesses of ?0.5 m and measuring 20?40 m on a side. Third is the ?interior? zone, which extends over hundreds of kilometers and consists of very large, relatively flat floes with thicknesses of ?0.3 m. In the edge zone the incident swell causes the floes to fracture, raft and form pressure ridges, resulting in small thick floes. In the transition zone the swell amplitude is reduced to the point that the floes fracture in a rectangular pattern with very little rafting or ridging taking place. In the interior zone the swell amplitude is further reduced such that the waves propagate without fracturing the ice, so that the floes have horizontal dimensions of kilometers. Because of this ice distribution, when strong winds blow off the ice, bands of ice floes form at the ice edge. The reason bands form is that the edge zone ice has a large aerodynamic drag due to the heavy rafting and ridging, so that this ice moves downwind ahead of the rest of the pack. Once this ice moves away from the pack, the combination of aerodynamic drag plus the absorption of wind wave and swell energy leads to the band formation. We observed that these bands, which are on the order of 1 km wide and 10 km in length, move south into warmer water until they melt.