The Global Meridional Overturning Circulation (MOC) of the oceans is driven by the formation of deep water at the poles, water which upwells to the surface from all ocean basins in the southern ocean under the action of both surface wind forcing and abyssal turbulence. In the Atlantic sector the shallower North Atlantic Deep Water (NADW) driven cell appears to be primarily adiabatic, while the deeper Antarctic Bottom Water (AABW) driven cell requires the influence of stratified turbulence to effect the vertical flux of mass that enables this deep water to return to the surface. This abyssal turbulence is strongly related to the dissipation of the internal tide raised in the oceans by the flow of the barotropic tide over bottom topography. Direct numerical simulations of stratified turbulence are enabling the construction of parameterizations of its influence in the oceans. One product of such analysis has been development of a deeper understanding of the efficiency with which stratified turbulence mixes the density field.