188 Seafloor-Intensified Mixing by Surface-Generated Equatorial Waves

Thursday, 29 June 2017
Salon A-E (Marriott Portland Downtown Waterfront)
Bertrand Delorme, Stanford University, Stanford, CA

Mixing in the equatorial oceans plays a major role in upwelling dense water and closing the deep branch of the meridional overturning circulation. However, little is known about the mechanisms driving its spatio-temporal variability. Recent observations of small-scale turbulence obtained in the equatorial Pacific show evidence of intense abyssal mixing over smooth topography. It has been hypothesized that the intense mixing could have been driven by surface-generated equatorial waves trapped and amplified near the bottom as a result of the horizontal component of the Coriolis parameter, fh, and weak abyssal stratification. In this work, we test this hypothesis by using the MITgcm, a quasi-hydrostatic, nonlinear numerical model, that allows for non-zero fh. Using the KPP mixing scheme, we show evidence of enhanced mixing near the seafloor after the downward propagation of a mixed planetary-gravity wave generated in the upper ocean. A suite of numerical simulations where the properties of the waves and their medium are varied allow us to provide quantitative estimates of the contribution of this mechanism to mixing in the equatorial ocean and explore its sensitivity to key parameters.
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