Observations of the flow in the Mozambique Channel

During a recent research cruise to investigate the nature and continuity of the Mozambique Current, we observed that the flow in the Mozambique Channel is dominated by a train of large anticyclonic eddies (diameters>300 km) that reach to the channel bottom and propagate southward. At a frequency of 4 per year they cause a net poleward transport of about 15 Sv (1 Sv=106 m3/s). In the deep sea, a Mozambique Undercurrent flows equatorward along the continental slope. Using a lowered acoustic Doppler current profiler maximum observed velocities are about 0.2 m/s around 2400 m with another current core around 1000 m. It carries about 5 Sv of intermediate (AAIW) and deep waters (NADW) of Atlantic origin into the Channel. Subsequently, the equatorward flowing AAIW is largely entrained by the eddies and, while mixing with intermediate water from the North Indian Ocean in the eddy core, returned to the Agulhas Retroflection region.