KmT, Kilometer-long mooring of high-resolution Temperature measurements results overview

Abstract

The global oceans show extensive bottom topography above which intensive turbulent mixing is generated by breaking internal waves. Growing evidence suggests that the mixing is sufficient to maintain the ocean’s stable vertical density stratification, thereby preventing the deep-ocean from becoming a stagnant pool of cold water. Observational details of the extent of turbulent mixing away from topography are still scarce however. In this paper, results are presented from 760 high-resolution temperature sensors that were moored between 8 and 1146.5 m above a 2380-m deep sloping seafloor of Mount Josephine NE-Atlantic for 4 months. The local seafloor-slope is supercritical for semidiurnal internal tides under average stratification. The purpose of the > 1-km-long densely instrumented mooring is to provide insight in the variability of coherent scales, and in the connection between seamount-slope and mixing-effects up to 7-km horizontally into the ocean-interior. Largest four-month mean turbulence values are found near the seafloor, decreasing to half an order of magnitude lower values at 500 m above, and remaining steady-high further up. Local increases of mean turbulence values are observed in bands of 100–200 m thickness. Larger internal wave breaking occurs during baroclinic spring tide, which also affects internal waves and turbulent overturning in the interior. Spectrally, a turbulence inertial subrange dominates part of the internal wave band continuum near the seafloor. Coupling between interior- and near-seafloor-mixing is not only via previously suggested isopycnal transport of mixed waters, but also via strong internal wave interactions. Seamount-flow contributes to absolute vorticity so that blue-shifted near-inertial motions interact with internal tides.