Diapycnal Diffusivities over the Southwestern Indian Ocean Ridge

The southwestern Indian Ocean (SWIO) Ridge stems from the South Atlantic and extends northeastward to Rodrigues Island. The deep trenches and fracture zones between the Crozet Basin and the Madagascar Basin provide the major passages for the deep and the bottom water to enter the Indian Ocean, which is also part of the meridional overturning circulation (MOC) in the Indian Ocean. More than 70 CTD profiles have been conducted over the SWIO Ridge from 2010 up to now. Besides, a mooring was deployed about 2900 m below the sea surface for almost one year. Three Seaguard current meters, nine Sea-Bird Electronics Temperature-pressure sensor, and one Sea-Bird Electronics Temperature-Conductivity-Pressure Sensor were mounted on the mooring. The diapycnal diffusivity over the SWIO Ridge is estimated with two methods, i.e., the Internal Wave Spectrum Method (GHP) which relies on the energy cascade due to wave interactions, and the Thorpe scale method. Large diffusivities on the order of 10^-2 m² s^-1 are found over the rough ridges. Moreover, the temporal and spatial distributions of diapycnal diffusivities are presented and their physical relations with the fine structure of the bottom topography are analyzed in this study.