Observations of radiatively driven convection in a deep lake

Observations of radiatively driven convection in deep, ice-free Lake Superior from a set of moorings and an autonomous glider are used to characterize the spatial and temporal scales of the phenomenon. The moored observations show that instability builds at the surface on scales of hours, water near the bottom of the lake begins warming roughly 6 h after sunup, and the water column homogenizes a few hours after sundown. Glider observations suggest the existence of distinct convective chimneys, which carry warmed water to depth with horizontal scales on the order of tens of meters. Patches of photoquenched phytoplankton coincide with patches of anomalously warm water, providing a secondary tracer of water recently in the euphotic zone, and provide insight into the vertical development of convective chimneys. An analysis of the abundance of convective chimneys is used to estimate the lateral scale of convective cells, which appears to be on the order of 50 m.