1. Fisheries and Oceans, Canada, Arctic Aquatic Research Division, Winnipeg, Manitoba R3T 2N6 Canada, Department of Environment and Geography, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Canada, Environment Canada, Water Research Directorate, Burlington, Ontario L7R 4A6 Canada, and School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8W 3 V6 Canada