Abstract
ABSTRACTGarrow Lake (area 418 ha, greatest depth 47 m), Little Cornwallis Island, NWT, Canada, is the northernmost recorded hypersaline meromictic lake, Covered 11 months annually with ice up to 2.4 m thick and internally stratified, its waters at 20 m reach temperatures of 9.1°C from solar heating throughout the year. Salinity varies from less than 0.01% at the surface to over 75% at the bottom. Isostatic uplift isolated the lake from the sea about 3000 BP. Isotope dating indicates that the bottom water has been unmixed for nearly 2500 years. An advancing permafrost wedge appears to have forced brine from pores in rock strata below the watershed into a talik (chimney) in the lake centre. From November 1981 the lake has received approximately 100 tonnes/hr of mine tailings rich in lead and zinc. Dissolved oxygen introduced along with the slurry may be important in reducing anaerobic photosynthetic bacteria. Biotic diversity is low. Only one vertebrate, Myoxocephalus quadricornis (four-horned sculpin), occurs in the lake. The zooplankton consists of only one species, Limnocalanus macruras; phytoplankton includes 51 taxa dominated by flagellates.
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