New Thought on the Agulhas Current

A more complete understanding of the fundamental dynamics of the Agulhas Current Proper is evolving rapidly because of new discoveries. The discovery of the Agulhas Undercurrent (Beal and Bryden, 1997) had a profound effect on the overall estimate of the Agulhas Current transport. Also, the discovery of Schouten et al. (2002) that Mozambique Channel Eddies are responsible for the formation of Natal Pulses, which in turn is significantly related to the Indian-Atlantic Interocean leakage of water masses, had a profound effect on how the Agulhas Current System is now perceived. These new insights, historical hydrographic data, and satellite remote sensed data contributed to the formulation of 3 hypotheses on the fundamental dynamics of the Agulhas Current Proper. Hypothesis one: Directly north of the Delagoa Bight the Mozambique Channel Eddies encounter the most northern extend of the shallow Agulhas Current and interact with the seaward side of this Western Boundary Current to form the Delagoa Pulse, obtaining its required cyclonicity from the Delagoa Bight Lee Eddy. Hypothesis two: Water masses of the Agulhas Undercurrent and Red Sea Water are upwelled within the Delagoa Bight Lee eddy which forms the southward propagating Delagoa Pulse. Hence, parts of the Agulhas Undercurrent are transported back into the Atlantic Ocean via a fast-track (10 to 20 km/day) mechanism, the Delagoa Pulse. Hypothesis three: Delagoa Pulses act as mechanisms for the injection of upwelled Agulhas Undercurrent water masses and Red Sea Water onto the eastern Agulhas Bank, supplying a semi-continuous density flow along the 100 m isobath. This density current originates from the Indian Ocean sector of the Agulhas Bank at the Port Alfred Upwelling Cell, feeds the cold bottom ridge, rounds the Alphard Banks, and enters the Atlantic Ocean sector of the Agulhas Bank. The physical and chemical properties of the density flow coined the Lutjeharms (Indian-Atlantic Interocean secondary leakage) Return Current (Meyer et al., 2002) is still largely unknown.