Internal-Wave-Driven Turbulence and the Meridional Overturning Circulation

Internal-wave-driven turbulent dissipation rates ε and diapycnal diffusivities K are inferred globally from roughly 30,000 hydrographic casts in the WOCE/CLIMOD database using a finescale parameterization based on internal-wave vertical strain (N² ‒ <N²>)//<N²>. Globally averaged dissipation rates are 4.3 ± 1.0 mW m^–2 (1.5 ± 0.4 TW), consistent with internal-wave power sources from tides and wind. Basin-averages are largest in the North Pacific and smallest in the South Atlantic. Vertically-integrated dissipation rates vary by several orders of magnitude horizontally with elevated values over rough topography but the dependence on bottom forcing is weaker than that of subgridscale parameterizations based on linear internal tide theory that are used in OGCMs. Average diffusivities are (0.3-0.4) × 10^–4 m² s^–1, independent of depth, that is, ε = KN²/γ scales as N². Diffusivities approach or exceed 10^–4 m² s^–1 poleward of 50º in the Indian and Atlantic Oceans. The longitudinal pattern in the Southern Ocean resembles that of inertial wind forcing. Diapycnal vertical velocities w* inferred from the mixing are 0.2-0.4 cm day^–1 below 1000-m depth, corresponding to global upwelling transports of 4 Sv below 3000-m depth, mostly from the south hemisphere, and 11 Sv above 2000 m.