Red Sea Intermediate Water in the source regions of the Agulhas Current

Red Sea Intermediate Water (RSIW) has been shown to move down the Agulhas Current as distinct lenses. It has been assumed that this intermittency is the result of variable input. To clarify and quantify the nature of RSIW contributions from the source regions of the Agulhas Current observations at 15 hydrographic sections were examined using a multi-parameter analysis. In the northern Mozambique Channel RSIW is found to be layer-like, but with patches of distinctly different contributions. In the southern part of the channel the layer-like distribution disappears with RSIW mostly confined within anticyclonic and cyclonic eddies exhibiting varying maximum contributions ranging from 15–20% to 25–30% purity. Net transports across the channel ranged from −0.45 to −0.7 Sv. At the southern tip of Madagascar RSIW contributions exhibited similar purity variability ranging from 10–15% to 15–20%. The net southward transport of RSIW in the East Madagascar Current displayed an even greater variability due to changes in the flux of the undercurrent ranging from negligible to −0.3 Sv. Indications therefore were that the transport of RSIW to the Agulhas Current occurs in both cyclones and anti-cyclones through the Mozambique Channel whilst from the East Madagascar Current it is mostly confined to anti-cyclones. This variability in the inflow was also reflected in the northern part of the Agulhas Current proper. The maximum contributions of RSIW range here from 10–15% to 20–25% purity and net transports from −0.75 to −1.39 Sv off Durban. As it was east of Madagascar RSIW was mostly confined to the slope.