The effects of salinity and river runoff on idealized brackish ice-covered lakes

The effects of freshwater river runoff on dynamics of ice-covered brackish lakes have not been adequately studied to date. Compared to freshwater lakes, the circulation patterns in brackish lakes are complicated by non-linear effects of temperature and salinity on density stratification and mixing, and as a result on the ice melt. Quantifying these effects is essential for understanding circulation of large endorheic lakes in cold regions and their ecological and physical characteristics. We present modeling results on circulation caused by river runoff in a typical ice-covered brackish lake obtained with the Regional Ocean Modeling System (ROMS). The lake water salinity was set to 14 practical salinity units (PSU). In the initial state, the water temperature increased linearly from the freezing point at the surface to the temperature of maximum density, at the bottom, both accounting for the water salinity. Mixing of cold freshwater river inflow with the warmer saline waters produces negative buoyancy and downslope flow of dense currents near the river inlets with a secondary geostrophically-balanced circulation throughout the lake. We use the modeling results to quantify the contribution of this circulation mechanism on deep lake circulation and ventilation of the near-bottom waters.