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In ice-covered lakes, penetrative radiation warms fluid beneath a diffusive boundary layer, thereby increasing its density and providing energy for convection in a diurnally active, deepening mixed layer. Shallow regions are differentially heated to warmer temperatures, driving turbulent gravity currents that transport warm water downslope and into the basin interior.We examine the energetics of these processes, focusing on the rate at which penetrative radiation supplies energy that is available to drive fluid motion. Using numerical simulations that resolve convective plumes, gravity currents, and the secondary instabilities leading to entrainment, we show that advective fluxes due to differential heating contribute to the evolution of the mixed layer in waterbodies with significant shallow areas. A heat balance is used to assess the relative importance of differential heating to the one-dimensional effects of radiative heating and diffusive cooling at the ice-water interface in lakes of varying morphologies.

Lakes and other confined water bodies are not exposed to tides, and their wind forcing is usually much weaker compared to ocean basins and estuaries. Hence, convective processes are often the dominant drivers for shaping mixing and stratification structures in inland waters. Due to the diverse environments of lakes—defined by local morphological, geochemical, and meteorological conditions, among others—a fascinating variety of convective processes can develop with remarkably unique signatures. Whereas the classical cooling-induced and shear-induced convections are well-known phenomena due to their dominant roles in ocean basins, other convective processes are specific to lakes and often overlooked, for example, sidearm, under-ice, and double-diffusive convection or thermobaric instability and bioconvection. Additionally, the peculiar properties of the density function at low salinities/temperatures leave distinctive traces. In this review, we present these various processes and connect observations with theories and model results.

In stratified natural waters, convective processes tend to form nearly homogeneous mixed layers. However, shear‐driven turbulence generated by large‐scale background flow often rapidly smooths them through mixing with the stratified surroundings. Here we studied the effect of background turbulence on convectively driven mixed layers for the case of bioconvection in Lake Cadagno, Switzerland. Along with microstructure measurements, a diffusive‐shape model for the mixed layers allowed us to define (i) mixed layer thickness and (ii) diffusive transition length. Further microstructure analysis was performed allowing estimation of convective turbulence in the mixed layer and shear‐driven turbulence quantified by eddy diffusion in their surroundings. Based upon these results, we propose a Péclet number scaling that relates mixed layer shape to the opposing effects of convection and diffusion. We further validate this quantitative approach by applying it to two other distinct convective systems representative of double‐diffusive convection and radiatively driven under‐ice convection.