Sack Lunch Seminar (SLS)

The influence of mesoscale eddies on the deep ocean dynamical processes, including low-frequency flows, internal waves and ocean mixing, are examined using observations from a collection of moored instruments located near the crest of the East Pacific Rise (EPR) between 9 and 10N. First, the subinertial velocities at depth are significantly correlated with geostrophic near-surface currents, which are dominated by westward-propagating mesoscale eddies. It is proposed that the subinertial velocity near the EPR crest is a super-position of velocities associated with eddies propagating westward across the ridge and “topographic flows”. Second, the observations reveal subinertial modulations of internal waves, particularly near-inertial oscillations and internal tides. These subinertial modulations are highly correlated with the subinertial flows in the deep ocean. Third, the deep ocean diapycnal diffusivity, which was estimated with a finescale parameterization model, shows variation on the subinertial time scale. In particular, the measurements imply a significant increase in diapycnal diffusivity near the seafloor during episodes of increased subinertial flow. Fourth, combined with previous numerical and theoretical studies, the observations imply energy transfer near the crest of the EPR from low-frequency flows, including mesoscale eddies, to near-inertial oscillations, turbulence and mixing. Considering the ubiquitousness of mesoscale eddies in the ocean, it is expected that the deep ocean dynamics near other portions of the global mid-ocean ridge system is similarly influenced by mesoscale variability and topographic effects.