Internal Waves and Mixing above the South-West Indian Ridge

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The southwest Indian Ridge (SWIR) is a slow spreading jagged ridge that extends 7700 kilometers along the edge of the Antarctic and African plates. The SWIR is one of the largest areas that experiences open ocean energy loss due to barotropic tides and the generation of internal waves. Several major branches of sub-surface currents in the Western Indian Ocean flow over the SWIR and are subject to turbulent mixing which may have a significant effect on the circulation of all of the water masses that pass through this region. Recent evidence suggests that increased turbulent mixing due to internal waves exists along the entire length of the SWIR, however, scientists need a better understanding of the dynamical processes that produce elevated turbulence to determine the actual source of this turbulent influence. Oceanographers from Scripps Institute of Oceanography propose two probable origins for small vertical-scale internal waves along the SWIR, topographically scattering low-mode near-inertial waves that propagate from the Southern Ocean, and locally generated internal tides produced by barotropic tidal flow over rough bathymetry. The investigators of this project propose to study the magnitude, spatial structure, and causes of elevated mixing above the SWIR utilizing a collection of innovative instrumentation. Through the use of a series of numerical modeling experiments and a combination of shipboard Doppler sonar, a rapid profiling CTD, and McLane moored profilers, the principle investigators will obtain a high resolution time series of internal waves and mixing in several locations over the SWIR. This work is expected to make a significant contribution to understanding diapycnal mixing in the Indian Ocean basin and shed new light on the fundamental dynamics governing mixing in locations of rough topography worldwide, an important and relatively little studied topic physical oceanography. In addition to the primary scientific contributions, the proposed work will provide funding to support the development of two early-career scientists as well as education and training for graduate students to participate in both field work and data analysis.