How Ice Composition Controls Radiatively Driven Convection Under Lake Ice

Abstract Light transmission through the ice cover of lakes can heat near‐surface waters and result in radiatively driven convection (RDC), a prominent source of under‐ice water motion in spring. We investigate the impact of ice composition on the under‐ice water column using fully resolved two‐dimensional numerical simulations of the water that account for light attenuation by both ice and water. Increasing the amount of opaque white ice (relative to that of transparent black ice) decreases thermal forcing of the water and delays Rayleigh‐Taylor instabilities and convective mixing. Other key environmental factors include the attenuation length scale of light and initial stratification of the water column. We determine whether and when (a) the water column first becomes unstable and (b) RDC is initiated. Notably, RDC is delayed by a period of growth of a gravitationally unstable layer. These findings have implications for the cycling of nutrients and gases, and wider ecosystem dynamics.