Evidence for seafloor-intensified mixing by surface-generated equatorial waves

Abstract

Little is known about mixing in the abyssal equatorial oceans in spite of its inferred importance for upwelling dense water. Here we present full-depth microstructure turbulence profiles obtained in the equatorial Pacific that show evidence for intense wind-generated abyssal mixing. Mixing was intensified over the bottom 700 m where the diffusivity reached 10-3 m2 s-1, of similar intensity to mixing driven by tidal flow over rough topography. However, here the mixing was found over smooth topography. We suggest that the intense mixing could have been driven by surface-generated equatorial waves through two possible mechanisms: (1) near-bottom wave trapping as a result of the horizontal component of the Earth's rotation and (2) inertial instability. The generation of lee waves over smooth topography at low latitudes and their subsequent breaking is another viable mechanism for the mixing.