Ocean Circulation Kinetic Energy: Reservoirs, Sources, and Sinks

The ocean circulation is a cause and consequence of fluid scale interactions from millimeters to 10,000km. Although the wind field produces a large energy input to the ocean, all but about 10% appears to be dissipated within about 100m of the sea surface, rendering very difficult observations of the energy divergence necessary to maintain the full water column flow. Attention thus shifts to the physically different kinetic energy reservoirs of the circulation, and their maintenance, dissipation, and possible influence on the very small scales representing irreversible molecular mixing. Oceanic kinetic energy is dominated by the geostrophic eddy field, and depending upon the vertical structure (barotropic versus low-mode baroclinic), direct and inverse energy cascades are possible. The pathways towards dissipation of the dominant geostrophic eddy kinetic energy depend crucially on the direction of the cascade, but are difficult to quantify because of serious observational difficulties for wavelengths shorter than about 100200km. At high frequencies, kinetic energy is dominated in the internal wave band by inertial motions (frequencies near the local Coriolis parameter), whose shears appear to be a major source of wave breaking and mixing in the ocean interior.