Anomalous convective dynamics of cold waters due to temperature-dependent material properties

Convection in water has been studied extensively under the Boussinesq approximation, usually entailing constant material properties. However, to what extent is this approximation valid? This question arises when looking at cold freshwaters whose temperatures are around those for the maximum density, i.e., 4°C. While dynamic viscosity and thermal conductivity change monotonically across the latter temperature, density changes a little and in a nonmonotonic way. Although temperature-dependent material properties are expected to influence convective dynamics in cold systems, it is unclear whether the effects are significant. We numerically investigate the effects of temperature-dependent material properties in two different configurations: Horizontal convection and vertical convection, inspired by ice-covered lakes and proglacial lakes, respectively. We find that the temperature-dependent material properties alter the convective dynamics significantly under specific forcing conditions, leading to anomalous behaviors in heat and mass transport of the systems. These findings highlight the potential for misinterpreting the fluid dynamics of cold waters under the classical Boussinesq approximation.