A New Thermal Categorization of Ice-covered Lakes

Lakes are traditionally classified based on their thermal regime and trophic status. While this classification adequately captures many lakes, it is not sufficient to understand seasonally ice-covered lakes, the most common lake type on Earth. In this talk, we will describe the thermal stratification and convection underneath the ice, which is driven by the nonlinearity of the equation of state near 4 o C. We will then describe the thermal stratification in 19 highly varying lakes and derive a model that predicts the initial water temperature as a function of wind stress, area, and depth. The results suggest an additional subdivision of seasonally ice-covered lakes to differentiate under-ice stratification. When ice forms in smaller and deeper lakes, inverse stratification will form with a thin buoyant layer of cold water (near 0°C) below the ice, which remains above a deeper 4°C layer. In contrast, the entire water column can cool to ∼0°C in larger and shallower lakes.

Bernie completed an undergraduate degree in McGill University, specializing in mathematics. He then completed a PhD at the University of Toronto under the supervision of Mathew Wells, where he focused on understanding convection in ice-covered lakes, which is the basis of this talk. Bernie is currently a postdoctoral fellow working at the University of Victoria in British Columbia, Canada. He works with glider observations in the Northeast Pacific to understand eddy mixing in the region.