Study On The Turbulent Mixing In The Northwestern Pacific And Southern Ocean Based On A Fine-scale Parameterization Method

Internal wave is ubiquitous in the stratified ocean interior, which controls the transport of mass, momentum, and energy. Turbulent mixing in the ocean interior is generated via internal wave breaking caused by the downscale energy cascade associated with weakly nonlinear wave-wave interaction. Small-scale turbulent diapycnal mixing plays an important role in heat, water mass, dissolved substances (nutrients and pollutants) transportation, as well as the global climate, the thermohaline circulation, the marine environment and ecosystems.The turbulent mixing is generated by internal wave breaking. A volume of studies have revealed that the energy of the internal wave field is furnished primarily by the wind, the tides, and the geostrophic flow interacting with rough topography particularly in the Southern Ocean. The temporal and spatial variation of turbulent diapycnal mixing in the northwestern Pacific is analyzed by employing a fine-scale parameterization method based on 6,756 high-resolution CTD profiles spanning a period of 8 years from the Japan Oceanography Data Center (JODC) and the Kuroshio Extension System Study (KESS). The rate of turbulent mixing in the upper ocean within 300-1800 m depth displays a distinct seasonal cycle, bearing a statistically significant correlation to wind-induced near-inertial energy flux. Enhanced turbulent mixing is also found near the rough seafloor relative to that over smooth topography. Elevated dissipation at surface and bottom is found to be able to penetrate the ocean interior up to 1800 m and 3300 m, respectively, with penetration depths varying with the wind-induced near-inertial energy and topographic roughness. Our study here provides evidence for the important role of near-inertial energy input by the wind and the influence of bottom topography in maintaining mixing in the ocean interior.Diapycnal mixing is an important process to return deep ocean water to the surface, and close meridional overturning circulation (MOC). In the Southern Ocean, the neutral density surface 28 kgm-3 is roughly regarded as the divide surface between two cells of MOC. In the Antarctic Circumpolar Current (ACC) region, we combine Argo profiles from Array for Real-time Geostrophic Oceanography (Argo) and CTD data from DIMES (Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean) to estimate mixing in the interior of ACC based on the fine-scale parameterization method. We find that the mixing rate across the two cells over the entire ACC is (1.13±0.14) ×10-4 m2s-1 which is an order of magnitude greater than that in the open ocean. The intense ocean interior mixing is attributed to the sharp west wind power input from the surface and the interaction of strong ACC deep-reaching flow with rough topography from the bottom in this region. The induced diapycnal transport across 28 kgm-3 amounts to 4.8±0.6 Sv, which is more than half of the rate of cold waters injected to the lower-limber overturning cell. The diapycnal fluxes across the lower-limber MOC in the Southern Ocean control the storage of heat, carbon and nutrients in the abyssal ocean, therefore it is important for studying the global climatic and biochemical changes process.