Prefrontal bore mixing

Rainbow Ridge, a 1950 m deep upthrusted ultramafic block along the axis of the Mid-AtlanticRidge, has an active hydrothermal vent system at 2400 m on its western slope. However, within 1 km fromthe vent excessive temperatures are barely measurable, probably due to strong turbulent mixing. This mixingis studied here using a 400 m long high-resolution temperature sensor array moored with a 600 m ranging75 kHz acoustic Doppler current profiler. Rich internal wave turbulence was recorded, characterized by100–200 m upshoots and >200 m large overturning in particular near the end of the warming phase of theup and down moving tide. These highly nonlinear internal waves of tides interacting with buoyancyfrequency waves extend up to 400 m above the sloping bottom of the ridge. While a turbulent “bottomboundary layer” could barely be defined, the more intense turbulence higher up in the water column issuggested to lead to the strong dispersion of the hydrothermal plume