Radiatively Driven Convection in Ice Covered Lakes: Impact of Ice Composition

In spring, an increase in the amount of light transmission through the ice cover of lakes can heat near-surface waters, overcome inverse stratification and result in Radiatively Driven Convection (RDC), a major source of under-ice water motion. Since the ice cover is a key control parameter, we investigate the impact of ice composition on the under-ice water column using two-dimensional numerical simulations in a framework that models flow and light attenuation, by both ice and water, with no melting to isolate the effect of composition. We find that increasing the amount of opaque white ice (relative to that of transparent black ice) decreases thermal forcing of the water column which delays the formation of Rayleigh-Taylor instabilities and subsequently the convective mixed layer. Other key environmental factors include the attenuation length of light, and initial stratification, of the water column. We also determine whether and when the water column first becomes unstable and if RDC is initiated. Notably, RDC is delayed by a period of growth of a gravitationally unstable layer.