Internal Waves and Mixing Over the Southwest Indian Ridge

Tamara Beitzel Barriquand, Humboldt State University, Oceanography, Arcata, CA, United States and Jennifer A MacKinnon, Scripps Institution of Oceanography, La Jolla, CA, United States
Internal waves over areas of rough topography can lead to heightened mixing, often assumed to be due to the breaking internal tide. One region of rough topography with particularly elevated estimated mixing was the area above the Southwest Indian Ridge, with heightened estimated mixing extending all the way to the surface. Due to its location above a corrugated mid-ocean ridge, the heightened estimated mixing was assumed to be due to the internal tide. To pinpoint the source of this elevated mixing, two moorings were deployed in 2500 meters of water on the north and south ends of the western side of the Atlantis II Fracture Zone in the center of the ridge from December 2007 - January 2008 as part of the Southwest Indian Ridge Mixing Project (SWIRM). Each mooring was equipped with two McLane Moored Profilers, one in the top, and one in the bottom half of the water column, yielding time series throughout the water column. While the M2 internal tide is in fact the dominant signal in the overall velocity power spectra, the dominant signal in the finescale shear spectra is not the internal tide, but rather the inertial signal. This indicates that the mixing in the region is therefore controlled by the near-inertial processes, and not, in fact, by the internal tide.