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In July 2005, several scientists from the Mackenzie GEWEX (Global Energy and Water Cycle Experiment) Study, known as MAGS, met with aboriginal people in Deline on the shore of Great Bear Lake to exchange information on climate and water in the region. Topics discussed pertained directly to the northern environment, and they included climate variability and change, wind, lightning, lake ice, lake level, and streamflow. The traditional knowledge shared by the residents is a rich source of local expertise about the landscape and climate systems of the Deline area, while the scientific knowledge provided by MAGS presents a scientific basis for many observed climate and water phenomena, particularly on a broad regional scale. Through cordial and open discussions, the meeting facilitated the sharing of traditional knowledge and scientific results. The meeting enhanced the potential for traditional knowledge to help direct and validate scientific investigations and for scientific knowledge to be used in conjunction with traditional knowledge to guide community decision making.

Spaceborne synthetic aperture radar (SAR) images and numerical ice growth modelling were used to determine maximum water depth and water availability in two areas of the North Slope in northwestern Alaska. SAR images obtained between September 1991 and May 1992 were used to identify when and how many lakes froze completely to the bottom, and how many lakes did not freeze completely to the bottom. At Barrow, on the coast, 60% of the lakes froze completely to the bottom in mid-January alone, and by the end of winter 77% of the lakes were completely frozen. In contrast, 100 km to the south in the 'B' Lakes region, only 23% of the lakes froze completely, and there was no sudden freezing of many lakes as occurred at Barrow. A physically based, numerical model was used to simulate ice growth on the lakes. The simulated maximum ice thickness is 2.2 m. Consequently, any lake where some part of the ice cover does not freeze to the bottom has some water more than 2.2 m deep. For those lakes where the ice cover had frozen completely at some time in the winter, the simulated ice growth curve provides the ice thickness at the time each lake had frozen completely to the bottom and thus the lake's maximum water depth. At Barrow, 60% of the lakes are between 1.4 and 1.5 m deep, and 23% are more than 2.2 m deep. At the 'B' Lakes, 77% of the lakes are more than 2.2 m deep. Thus, there is a considerable contrast in lake depth and water availability between the Barrow and the 'B' Lakes regions. This method is simple to implement, and the relatively inexpensive SAR data have good spatial and temporal coverage. This method could be used to determine lake depth and water availability on the entire North Slope and in other polar and subpolar areas where shallow lakes are common. Key words: Synthetic Aperture Radar, Alaskan North Slope, lake ice, lake depth, water availability.

Historically, in Canada, popular and professional interest in river and lake ice were high. In this century, however, there has been a noticeable lack of "formal" interest. In addition, much of the popular and engineering interest in lake and river ice failed to be translated into the development of glaciology. Canadians, who have ignored "home-grown" science and local knowledge in favour of European scientific publications, have failed to recognize the important contribution to glaciology made by Tyrrell and Dumble.

In October 1982 we observed the consequences of migrating barren-ground (Rangifer tarandus groenlandicus) encountering lake ice too thin to bear their weight. The observations were made on a portion of taiga winter range of the Beverly caribou herd during autumn migration in the Northwest Territories. We observed caribou hesitating to cross ice that had no snow cover and also saw caribou breaking through ice. Bulls had greater difficulty extricating themselves from the ice water than did relatively light-bodied cows and young individuals. We necropsied one bull that we found dead after it had broken through the ice and remained in the water for more than 20 hours. The bull had died apparently from stress and hypothermia and had heavily traumatized areas on its forelegs and sternum from struggling to break the ice. We could not evaluate the overall extent of injuries and mortalities to caribou from their encounters with thin ice, although we observed signs that at least hundreds had broken through the ice on different lakes. Key words: behaviour, injuries, barren-ground caribou, Rangifer tarandus groenlandicus , thin ice, autumn migration, Northwest Territories