Landfast ice motion observed in the Mackenzie Delta region of the southern Beaufort Sea in the 1972/1973 winter

Abstract

During the winter of 1972/1973 movement was recorded at 11 remote stations deployed on the landfast ice in the MacKenzie Delta region of the southern Beaufort Sea. The measurements were made with a spring-tensioned reel/wire system connecting the ice with the sea bed. Coupling of the devices to a telemetry system allowed readings to be taken hourly from a master control station 160 km away. Stations deployed at water depths of 3 m in locations protected by barrier islands were displaced an average of 4 m in a five-month period. At these stations the major portion of the displacement took place in the first month of the recording stations' deployment in December. Ice sheet thickness at the end of this period was 0.8 m. During January to the end of March the ice sheet remained essentially static. From April until the removal of the stations in late May a gradual movement took place. Calculations show this gradual motion may be attributed to thermal expansion. Other stations deployed outside the barrier islands at water depths up to 20 m recorded displacements between 0.1 and 14 m during April and May 1973. During this period continuous motion of an oscillatory nature was recorded. The amplitude of these motions ranged up to 6 m with periods from 2 to 3 hours to several days. Hourly movement rates of up to 2.4 m/hr were observed. Comparison of movement events recorded at three representative stations separated by distances of 25 km indicates agreement in the time of occurrence for some events. The direction of motion during the majority of movement events is normal to the shore. Over the winter the landfast ice sheet for 50 km along the coast had been displaced towards the shore. It is thought that the oscillatory motion recorded at the outer stations may be the result of varying polar pack-ice pressure at the boundary of the landfast ice coupled with an elastic response of the ice sheet. Variation in motion between stations can be explained by the presence of pressure ridges and cracks.