Effects Of Topography And Buoyant Plumes Near-bottom Currents Over A Mid-ocean Ridge

A three-year program of current meter moorings, CTDs and tethered acoustic Doppler profiler observations in the vicinity of Endeavour Ridge (48'N, 129'37) has revealed marked alteration of the near-bottom flow by topography and hydrothermal venting. Particularly well defined changes in the current speed and frequency content occur within the near-inertial frequency band. Alteration of the flow structure is also seen in the high-frequency internal wave band, in the diurnal tidal band and in the "weather band" centered around periods of 4 to 6 days. Near-bottom motions in the inertial and internal wave bands appear to be amplified by reflection from the seafloor. There is also strong indirect evidence that these motions are attenuated through interaction with the plume-induced current shear at depths of 150 to 200 m above the bottom. Bottom amplified sub-inertial motions are linked to topographically trapped baroclinic planetary waves propagating in the along-ridge direction.