SIMULATED RESPONSE OF A PERENNIALLY ICE-COVERED LAKE IN ANTARCTICA TO A LARGE-SCALE FLOOD EVENT USING CE-QUAL-W2

Perennially ice-covered, meromictic lakes provide a unique opportunity to study fundamental lake physics in the absence of wind-driven turnover and the response of nutrient distribution and extremophile productivity to sub-ice currents. The distribution of such lakes is presently limited to Polar regions and is being further reduced by climate change as evidenced by the recent loss of perennial ice from several lakes on northern Ellesmere Island, Canada. These lakes may provide an important terrestrial analogue for lakes which once existed on Mars which were most likely ice-covered and may have provided a refuge for life. This study provides two numerical simulations generated using the 2-D model CE-QUAL-W2 of the physical limnology of Lake Hoare, a perennially ice-covered lake in the McMurdo Dry Valleys of Antarctica. Lake Hoare is a 4 km long, 1 km wide, 34 m deep, meromictic, closed-basin lake impounded by the Canada Glacier which contains the lowest concentrations of dissolved solids found in regional lakes. Consequently, it exhibits weak vertical stability which may allow for greater sub-ice mixing than occurs within neighboring lakes with higher salinity. The first simulation reproduces conditions observed during the 2012-13 field season, a non-flood year during which an acoustic Doppler current profiler recorded sub-ice currents and seiching, a conductivity-temperature-depth probe defined thermal and salinity profiles over the season, a tracer experiment illustrated the distribution of stream input along the lake shoreline, and a digital camera captured downward currents and rotation within ice holes during spring freshet. This evidence of internal circulation allowed us to calibrate our model to match field conditions. The second simulation represents a hypothetical ten-fold increase in 2012-13 inputs analogous to a flood event which occurred in the region during the 2001-02 field season. Simulated results illustrate the response of sub-ice currents and thermal profiles to changes in input from stream discharge and glacial runoff, and indicate the advective transport of nutrients as a function of internal currents. With future development, this model has the potential to simulate the broader impacts of climate change on physical, chemical, and biological conditions within Lake Hoare.