Mixing and Diapycnal Advection in the Ocean
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
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In the stratified ocean, vertical motions arise from both adiabatic and diabatic mechanisms. Diapycnal advection is the vertical component of flow across an isopycnal surface which occurs when mixing produces a divergent flux of buoyancy. Buoyancy forcing of the lateral flow by vortex stretching occurs when diapycnal advection rates vary with depth. Microstructure observations of enhanced turbulence above rough topography are presented. These data allow us to distinguish the influence of diabatic forcing on the circulation. Estimates of diapycnal advection are used to quantify the diabatic flow, and the role of diapycnal advection as a mechanism of vortex stretching on the circulation is assessed. The divergence of diapycnal mass flux is found to be a significant forcing mechanism for the circulation occurring above fracture zone topography. Moreover, both the direction and magnitude of diapycnal advection are dependent on the efficiency of turbulence at generating a buoyancy flux. Depth variations of diapycnal advection suggest the mixing efficiency is reduced in weakly stratified abyssal canyons.
- Physical and Dynamic Oceanography