Anomalous Upstream Retroflection in the Agulhas Current

The Agulhas current, the major western boundary current of the Southern Hemisphere, plays a crucial role in the water mass balance of the world oceans by controlling the transfer of thermocline water from the Indian to the Atlantic ocean systems. The main mechanism for such transfer is through the shedding of large rings of warm water at the Agulhas retroflection south of Africa. On the basis of satellite imagery and drifter tracks, anomalous reversals of the current are observed to occur far upstream of its characteristic retroflection location. The observations agree with results of an inertial jet model of the current. These anomalous reversals probably cause abrupt and major changes in the fluxes south of Africa and thus in the rate of ring shedding. This unusual flow bimodality in a major component of the global ocean heat transport system could have important climatic implications.