Late‐summer pack ice in the Canadian archipelago: Thickness observations from a ship in transit

Abstract

A digital video camera was used to photograph ice blocks turned on edge by the passage of the icebreaker CCGS Des Groseilliers operating in the Canadian High Arctic in August 2002. Ice thickness was derived from photogrammetry to an accuracy of about 10%, with a possible negative bias of about 3%. Further (presumably negative) bias related to route selection is unknown. The average thickness of blocks measured during half‐hour intervals of observation varied between 0.35 and 0.70 m; the higher values are likely indicative of second‐year ice. The greatest thickness of any single block was less than 2 m. Histograms of thickness were nearly symmetric and approximately Gaussian. There is evidence to indicate that the scarcity of ridged ice reflects the ice conditions of the area and is not an artefact of the method. Based on ancillary wintertime data, the pack ice in open waters of the north‐eastern Archipelago thawed at about 0.02 m d–1 in the summer of 2002, about three times less rapidly than ice near the shore. Whereas coastal ice had vanished five weeks prior to our voyage, pack ice in Norwegian Bay, though thin, persisted until the end of September and became second‐year ice. The difference is likely a consequence of the different microclimate near land, particularly with respect to the time of onset of the thaw season.