Estimates of diapycnal mixing in the abyssal ocean.

Profiles of diapycnal eddy diffusivity to a maximum depth of 4000 meters were derived from ocean velocity and temperature microstructure data obtained in conjunction with separate experiments in the Northeast Pacific and Northeast Atlantic oceans. These profiles indicate that in the ocean interior where the internal wave field is at background intensity, the diapycnal eddy diffusivity is small (on the order of 0.1 x 10(-4) meters squared per second) and independent of depth, in apparent contradiction with large-scale budget studies. Enhanced dissipation is observed in regions of elevated internal wave energy, particularly near steeply sloping boundaries (where the eddy diffusivity estimates exceed 1 x 10(-4) meters squared per second). These results suggest that basin-averaged mixing rates may be dominated by processes occurring near the ocean boundaries.