Turbulent exchange characteristics in the hypolimnion layer of Lake Ontario

Flow regime and turbulence characteristics in a hypolimnion of Lake Ontario are determined using time series current measurements from a vertical string of moored current meters and a bottom mounted Acoustic Doppler Current Profiler (ADCP). The diffusion and turbulent structures of the water column are parameterised in terms of horizontal exchange coefficients for momentum (K-x and K-y) during these deployments. The analysis suggests that the structure of the turbulent fluctuations is isotropic. The kinetic energy and horizontal exchange coefficients decrease with depth. The mean flow at all moorings appears to be strongly correlated with the zonal surface wind stress. Fifteen to twenty metres above the bottom, the flow is marked by an increase in kinetic energy, turbulence intensities, and eddy viscosity coefficients. Strong episodic wind impulse decreases horizontal exchange coefficients through the water column but probably enhances the vertical mixing due to increase in current shear. It is suggested that the associated current-induced sediment resuspension may contribute to the establishment and maintenance of a Nepheloid layer in Lake Ontario.