Nannoplankton of Marine Origin from Great Bear Lake in the Northwest Territories of Canada

Abstract

GREAT Bear Lake is situated on the Arctic Circle at a point where the Pre-Cambrian Shield emerges from the adjoining Cretaceous formations. The present lake surface is 143 m above sea level, and because the maximum depth is 542 m there is a cryptodepression of 309 m. The shape of the lake could be described as amoeboid with five arms joining a central “body”. McTavish Arm, with a mean depth of 102 m, contains the deepest water at a point close to the eastern shore. The total surface area is 31,153 km² and the volume 2,200 km³. Surface temperatures seldom exceed 4° C and, although the bottom temperature remains close to 3.56° C throughout the year, complete turnover does not occur annually¹. The lake is extremely oligotrophic with oxygen saturations up to 112 per cent (14 mg/l.) in the upper 50 m in summer and minimum values very close to saturation (12.6 mg/1.) near the bottom at the end of winter. Total dissolved solids are low: 80 p.p.m. with a specific conductance of 155 µmhos. Ice cover reaches a thickness of 2 m by the end of winter and break-up does not occur until the middle of July; this is followed by an open-water season of 3–4 months, the lake becoming ice-covered during November.