Vertical mixing is often regarded as the Achilles' heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. This relative agreement, both in magnitude and spatial structure across ocean basins, suggests that internal tides underpin most of observed dissipation in the ocean interior at the global scale. The proposed parameterization is therefore expected to improve understanding, mapping and modelling of ocean mixing.

Finescale parameterizations are powerful tools for estimating the global distribution of turbulent dissipation rates ε. However, they tend to overestimate ε in the Antarctic Circumpolar Current (ACC) region, where bottom-reaching geostrophic flows accompanying vigorous eddies coexist with energetic internal waves: near-inertial internal waves generated by wind disturbances in the upper ocean and internal lee waves generated by the ACC impinging on the small-scale bottom topography. In this study, we explore the reason for such overestimates by analyzing the datasets from the simultaneous microstructure and finestructure measurements carried out in the ACC region. We find that, at the locations where finescale parameterizations overestimate ε, vertical wavenumber spectra of internal wave energy are distorted from the canonical Garrett-Munk (GM) spectrum by a spectral “hump” at low wavenumbers (~ 0.01 cpm). The existing finescale parameterizations formulated based on the “white” GM spectrum overestimates ε for “red” vertical wavenumber spectra. In the ACC region, such shear (strain) spectra with a hump are mainly located in the upper ocean (at near-bottom). Multivariate correlation analyses between the magnitude of spectral humps and various physical parameters suggests that shear (strain) spectral humps are caused by low-vertical-wavenumber near-inertial wave (internal lee wave) packets superposed on a GM-like internal wave field, and these internal wave packets are generated and amplified by large scale geostrophic shear flows.