Effect of salt exclusion from lake ice on seasonal circulation

We describe the circulation of Tailings Lake, located 220 km north of Yellowknife, Northwest Territories, Canada. From Jul 2004 to Sep 2007, temperature and conductivity profiles were collected together with data from three moored temperature chains and a meteorological station. The salt content of the lake was elevated ( salinity 1 g L-1) relative to surrounding natural waters (similar to 0.1 g L-1). Winter ice cover included 60-80 cm of transparent black ice, which excluded up to 99% of the salt from the water as the ice formed. During winter, the salt excluded from the ice was mixed throughout the water column under the ice. In spring, ice melt and snow runoff resulted in a freshwater cap; the density contrast between this fresh epilimnion and the more saline hypolimnion was sufficient to inhibit spring turnover. In summer, the epilimnion was deepened by storms, mixing anoxic water from the hypolimnion into the surface layer. Because spring turnover was suppressed, oxygen replenishment of the hypolimnion occurred only in fall. Although Tailings Lake has been subject to numerous anthropogenic changes, similar effects can be expected in other natural and manmade water bodies with elevated salinity and significant ice cover.