A field study of grounded ice features and associated seabed gouging in the Canadian Beaufort Sea

Abstract

During the late summer of 1983, the southern Canadian Beaufort Sea was invaded by vast areas of thick sea ice features called hummock fields. Thousands of these features drifted into shallow water (10–27m water depth), became grounded and remained in place throughout the following winter. During the grounding event, it was assumed that the deeper ice ridge keels would have gouged the seabed. In April 1984, eight features with gouging potential were visited and investigated from the ice surface. Conditions allowed for measurement by sonar of the geometry of seabed gouges at two locations, named M1 and M2, as well as the geometry of the ice keels that caused the gouges. Volume and mass of the ice features were estimated from stereo air photography gathered earlier in the winter, from which elevation profiles were obtained. On-site elevation profiles confirmed elevations. The hummock field at site M1, estimated at 277,000tonnes, produced a gouge 2m in depth and a front mound about 3m high ahead of its keel. This feature had also been uplifted 2m at its leading edge. The deepest gouge was 3.5m, caused by hummock field M2, with an estimated mass of 1.16milliontonnes, which fragmented during the grounding process. A seabed gouging survey conducted in August 1984, in open water conditions, confirmed gouge depth at M2. Data on seabed soils were obtained at the M2 site one year later, in September 1985, as part of a geotechnical field survey. These cases of seabed gouging by massive sea ice features are unique in that they were found and documented with the ice features that made them still in place. All gouge, ice and soils data relevant to these two events are summarized herein, as a full-scale data set intended to increase understanding of seabed gouging and allow validation of models.