| Résumé | The thickness, strength, salinity and temperature of two, drifting multi-year ice floes in the Beaufort Sea are presented here. Although only two floes were sampled during the two-week voyage on the CCGS Amundsen, the floes characterized a wide spectrum of multi-year ice. Floe B1S1 (74.8°N, 128.3°W) originated from the landfast multi-year hummock field off Prince Patrick Island, 250 km to the northeast. Drill-hole measurements revealed ice thicknesses from 3.6 to 9.3 m, for an average floe thickness of 7.2 m (±1.4 m). The ice was quite warm, saline and weak. The uppermost 3 m of ice had an average temperature of -0.9°C and an average salinity of 1.8‰. The average borehole strength of the 7 m thick ice at the two tested boreholes was 7.3 MPa and 4.5 MPa. A total of 10 controlled ship impacts were conducted with Floe B1S1, during which time the ship penetrated several lengths into the floe. Floe B1S2 (75.0°N, 129.0°W) had drill-hole thicknesses from 5.1 to 15.7 m, and an average thickness of 8.0 m (±2.3 m). The hummocked feature that was tested on this floe was thicker, colder and less saline than the ice tested in Floe B1S1. The uppermost 7 m of the hummock had an average temperature of -2.6°C, an average salinity of 1.0‰ and an average borehole strength of 22.0 MPa. It is not surprising then, that the CCGS Amundsen responded very differently to controlled impacts with Floe B1S2. The first three rams produced just a small imprint in the floe edge; the fourth and final ram caused a crack to propagate by exploiting local weaknesses in the ice. It should not be surprising that the Beaufort Sea pack ice consists of floes with great integrity and relatively weak floes. Different types of floes can, and do, occur in close proximity to one another. Floes that circulate in the Beaufort Gyre for many years become weathered and consolidated. Floes that have been recently deformed, such as Floe B1S1, may be thick, but are not as consolidated. Variable types of ice in the Beaufort Sea were also encountered in August 2009: Barber et al. (2009) noted that the CCGS Amundsen operated in extensively decayed ice on 31 August, yet the CCGS Louis S. St-Laurent encountered a 10 km diameter multi-year floe in the southern Beaufort Sea on 8 August 2009, that the ship spent two hours ramming (B. Molyneux, personal communication from Canadian Ice Service) before it could turn out of the floe. Results from the companion study of the ice impact forces on the CCGS Amundsen when ramming Floe B1S1 and Floe B1S2 will be presented in a separate report. The ice thickness comparison of the drill hole measurements, ice-based electromagnetic (EM) sensor and airborne HEM sensor will be published by University of Manitoba at a later date |
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