The Internal-Wave-Driven Meridional Overturning Circulation

The upwelling diapycnal limb of the ocean’s meridional overturning circulation is driven by divergence of diabatic turbulent buoyancy fluxes 〈 w ′ b ′〉 across density surfaces. A global assessment of zonally averaged internal-wave-driven turbulent diapycnal buoyancy fluxes from a strain-based finescale parameterization is used to infer mean diapycnal transports in the interior and near the bottom boundary. Bulk interior diabatic transports dominate above 2500-m depth (buoyancies | B | = gγ n / ρ 0 < 0.267 m s −2 , neutral densities γ n < 27.9 kg m −3 ), upwelling at 10–11 Sv (1 Sv = 10 6 m 3 s −1 ); 2, 5, and 3–4 Sv in the Indian, Pacific, and Atlantic, respectively, but are weak in the abyss. Boundary water-mass transformations peak at 18–25 Sv (4–6, 10–14, and 4–5 Sv in the Indian, Pacific, and Atlantic) near buoyancy | B | ~ 0.268 m s −2 ( γ n ~ 28.1 kg m −3 , 4500-m depth) between bottom and lower deep waters, consistent with published 20–30-Sv global Antarctic Bottom Water (AABW) transport estimates. Interior transports above 2500-m depth fall below inverse estimates, consistent with a more adiabatic ocean interior where diapycnal mixing occurs at Southern Hemisphere high-latitude surface density outcrops.