Exchange through the Bab el Mandab

During the last 10 years there have been a number of important developments in the understanding of the exchange flow in the Bab el Mandab. New and improved estimates of the fluxes of mass, heat and salt through the Strait have been made directly from oceanographic measurements and indirectly from air–sea flux data. Hydraulic theory has been applied to explain the seasonal variations in the exchange flow, and in particular the three-layer summer circulation. The effects of wind stress, friction, and seasonal sea-level variability on hydraulic control are addressed in this paper. Analyses of oceanographic data have failed to provide direct evidence of hydraulic control, but they have highlighted the importance of tidal scale variability and differences between real continuously stratified fluids and idealised layer flows often used in hydraulic theory. Other studies have investigated the coupling between the flow in the Strait and the circulation within the Red Sea.