Overturning circulation driven by breaking internal waves in the deep ocean

A global estimate of the water-mass transformation by internal wave-driven mixing in the deep ocean is presented. The estimate is based on the energy conversion from tidal and geostrophic motions into internal waves combined with a turbulent mixing parameterization. We show that internal wave-driven mixing in the deep ocean can sustain 20-30Sv of water-mass transformation. One third or more of this transformation is attributed to lee waves generated by geostrophic motions flowing over rough topography, primarily in the Southern Ocean. While these results are uncertain due to many assumptions, poorly constrained parameters and data noise that enter in the calculation, the result that lee wave-driven mixing plays an important role in the abyssal ocean circulation is likely robust. The implication is that lee wave-driven mixing should be represented in ocean and climate models, but currently it is not.