Latitude-dependent finescale turbulent shear generations in the Pacific tropical-extratropical upper ocean.

Turbulent mixing, which is critically important for the equilibrium of ocean circulation, is controlled by finescale turbulent shear (S2) of oceanic flows through shear instability. Although the relationship between S2 and mixing is well understood, the latitude-dependent generation processes of S2 remain poorly known due to the lack of geographically extensive, long-term finescale velocity measurements. Here, using one-year ADCP data from 17 moorings along 143°E, we first show that the upper-ocean S2 and its resultant mixing rate have a W-shaped latitudinal distribution in the tropical-extratropical northwest Pacific with peaks at 0-2°N, 12-14°N, and 20-22°N, respectively. Further analyses reveal that these S2 peaks are caused by vertically-sheared equatorial currents, parametric subharmonic instability of diurnal tide, and anticyclonic eddy's inertial chimney effect, respectively. As climate model simulations are sensitive to the mixing parameterizations, our findings highlight the need to incorporate the latitude-dependent generation mechanisms of S2 to improve climate models' prediction capabilities.