Ice ridging and ice drift in southern Gulf of St Lawrence, Canada, during winter storms

Abstract

During February and March 2004, satellite-tracked ice beacons and helicopter-borne sensors collected ice-drift and ice-thickness data from the southern Gulf of St Lawrence, Canada, to study the region's ice-thickness evolution and ice-drift behavior in response to winter storms. Three northeasterly storms passed through the area during the observation period, pushing the pack ice against the north shore of Prince Edward Island. The resulting severe ice deformation caused major changes in the ice-thickness distribution of two pack-ice areas tracked by ice beacons that survived the storms. The ice drift ranged from 1.4% to 2.9% of the wind speed during free ice-drift conditions, decreasing to 0% when the pack ice compacted against the shoreline. Most of the thinner ice deformed first, increasing the mean ice thickness over 6-8 km line sections around the beacons from 0.6 and 0.3 m before the storms to 1.9 and 2.0 m after the storms. The ice-thickness increases can be accounted for by the reduced pack-ice area due to ice ridging. Over the next 4 weeks, deformation continued and the mean ice thickness around the beacons increased to 2.8 m, well in excess of the maximum undeformed possible ice growth of 65 cm. Ice charts captured the ice thickness of undeformed and composite ice floes but did not capture the ice volume in ice-rubble fields.