Autumn cooling in the Bay of Bothnia provides an opportunity for studying wind mixing, convection and restratification below the temperature for maximum density. Vertical temperature profiles for a 52 day period are analysed for the case of cooling of brackish sea water around the temperature of maximum density. A mathematical model, which is based on the conservation equations for momentum, heat and salt in their one- dimensional form and with an equation of state which is linear with respect to salinity but quadratic with respect to temperature, is presented. Turbulent exchange coefficients are calculated with a kinetic energy- dissipation model of turbulence.

Due to the fact that both salinity and temperature effect stratification and that buoyancy flux changes signat the temperature for maximum density several processes influence the cooling rate. The mathematical model describes these and the general development of the temperature profiles in a most satisfactory way.