Abstract

Turbulent mixing in oceanic western boundary currents plays a potentially important role in the global tracer circulation, biogeochemical cycles, mode water formation, and the energetics of the general circulation. Yet, the physics that lead to turbulence in the thermocline of western boundary currents are not well understood, either theoretically or empirically. Recent (2007 and 2012) observations in the winter Gulf Stream reveal coherent downward propagating near-inertial internal waves and enhanced turbulence localized to the upper thermocline of the front. The inferred average diapycnal diffusivity (~10 ^m2/s) is an order of magnitude larger than both the canonical average diffusivity in the ocean thermocline and the maximum average diffusivity observed in the Gulf Stream thermocline during several previous experiments in other seasons.

Consideration of how the physics of near-inertial internal waves are modified by the strongly baroclinic Gulf Stream gives insight into how and why the upper thermocline of the Gulf Stream might be a hotspot for near-inertial wave activity and diapycnal mixing during winter, as observed. However, comparisons between theory, numerical simulations, and observations also reveal new questions for future research.