Abstract

Over the last 30 years, limnology has become a mature field with most of the energy flux paths now well established and incorporated into 3D models. The energy from the wind and the sun enters a lake via the free surface, the river inflow may form overflows, intrusions or underflows and the selectivity of a withdrawal flow depends strongly on the thermal stratification in the lake. The talk is structured to follow the energy flux from the wind, to surface waves and surface layer turbulence, to basin scale barotropic lake seiching and internal waves, to high frequency free internal waves and free gyres, to the benthic boundary layer to finally the intermittent turbulence field in the water column; this is generated by non linear wave breaking,  Kelvin Hemholz billowing and Holmboe shear instabilities, depending on the relative placement of the shear and density field gradients. Inflows and outflow dynamics is then briefly reviewed. Next, I show how this symphony of motions adds to sustain a weak vertical mass flux and a horizontal dispersion; the latter being critically dependent on the topology of the horizontal residual circulation and the presence of unsteady stagnation points. I will conclude with an illustration of how the full complexity of these motions can be captured with a 3D model that also beautifully illustrates the competitive nature of the various components of the motion in determining the net mixing in a lake and I show how this competition is a strong function of the lake and stratification properties.