Flow of bottom water in the Somali Basin

Repeat CTD surveys by the R.R.S. Charles Darwin in the Somali Basin at the height of subsequent northeast and southwest monsoons show only small differences in the circulation of the bottom water. About 4 × 10⁶ m⁶ s^-1 moves north along the continental rise of Africa below a zero-velocity surface at the potential isotherm 1.2°C in a deep western-boundary current near 3°S. Cross-equatorial sections suggest that this flow turns eastward near the equator. North of the equator a large mass of cold water is found in the interior, east of the Chain Ridge. The presence of this feature reinforces the evidence that the deep western-boundary current observed south of the equator turns east at the equator and feeds the interior circulation in the northern part of the basin from the equator, and not from the boundary. The deep circulation observed in the Somali Basin is roughly consistent with a flat-bottom uniform upwelling Stommel-Arons calculation with realistic basin geometry, source location and uniform upwelling. However, the model results indicate that the boundary current crosses the equator, whereas the observational analysis suggests that it turns eastward there.