Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate

Waterhouse, AF, MacKinnon JA, Nash JD, Alford MH, Kunze E, Simmons HL, Polzin KL, St Laurent LC, Sun OM, Pinkel R, Talley LD, Whalen CB, Huussen TN, Carter GS, Fer I, Waterman S, Naveira Garabato AC, Sanford TB, Lee CM.  2014.  Global patterns of diapycnal mixing from measurements of the turbulent dissipation rate. Journal of Physical Oceanography. 44(7):1854–1872.


We present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to (ii) shipboard observations of upper ocean shear and (iii) strain as measured by profiling floats, and (iv) shear and strain from full-depth LADCP/CTD profiles. Vertical profiles of the turbulent dissipation rate are bottom-enhanced over rough topography and abrupt, isolated ridges. The geography of depth-integrated dissipation rate shows spatial variability related to internal-wave generation, suggesting one direct energy pathway to turbulence. The global-average diapycnal diffusivity below 1000-m depth is O(10-4 m2 s-1) and above 1000-m depth O(10-5 m2 s-1). The compiled microstructure observations sample a wide range of internal-wave power inputs and topographic roughness, providing a data set with which to estimate a representative global-average dissipation rate and diffusivity. However, there is strong regional variability in the ratio between local internal-wave generation and local dissipation. In some regions, the depth-integrated dissipation rate is comparable to the estimated power input into the local internal wave field. In a few cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources. However, at most locations, the total power lost through turbulent dissipation is less than input into the local internal wave field. This suggests dissipation elsewhere, such as continental margins.