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Mechanisms for Enhanced Turbulence in the Drake Passage Region of the Southern Ocean

Sophia Merrifield, Ph.D., 2016
Louis St. Laurent and Breck Owens, Co-advisors

The Southern Ocean is one of the most energetic regions of the world ocean due to intense winds and storms, strong currents interacting with steep topography, and enhanced mesoscale activity. Consequently, the Southern Ocean is believed to be a hotspot for enhanced oceanic mixing.  This thesis studies the processes that support mixing in the surface boundary layer and at intermediate depths in the Drake Passage region.  Biases between direct measurements and previous indirect estimates of mixing rates are discussed in the context of the internal wave environment and enhanced thermohaline finestructure. The dissipation rate of thermal variance is enhanced in the upper 1000m, with the highest values found in northern Drake Passage where water mass variability is the most pronounced. Double diffusive processes and turbulence both contribute to buoyancy flux, elevating the effective mixing efficiency above the canonical value of 0.2 in the upper 1km. Despite the prevalence of energetic wind events, turbulence driven by downward propagating near-inertial wave shear is weak below the mixed layer. The results of this study inform large-scale modeling efforts through parameterizations of mixing processes in the highly undersampled Southern Ocean.