The East Madagascar Current (EMC) is one of the western boundary currents of the South Indian Ocean. As such, it plays an important role in the climate system by transporting water and heat towards the pole and recirculating to the large-scale Indian Ocean through retroflection modes of its southern extension. Five cruise datasets and remote sensing data from different sensors are used to identify three states of the southern extension of the East Madagascar Current (EMC): early retroflection, canonical retroflection and no retroflection. Retroflections occur 47% of the time. EMC strength regulates the retroflection state, although impinged mesoscale eddies also contribute to retroflection formation. Early retroflection is linked with EMC volume transport. Anticyclonic eddies drifting from the central Indian Ocean to the coast favour early retroflection formation, anticyclonic eddies near the southern tip of Madagascar promote the generation of canonical retroflection, and no retroflection appears to be associated with a lower eddy kinetic energy (EKE). Knowledge of the EMC retroflection state could help predict (1) coastal upwelling south of Madagascar, (2) the southeastern Madagascar phytoplankton bloom, and (3) the formation of the South Indian Ocean Counter Current (SICC).

Plain Language Summary

Using in situ and satellite observations, we show that the East Madagascar Current (EMC), a strong current flowing along the East Coast of Madagascar, often detaches from the coast before the southern tip of the island and goes directly into the Indian Ocean, the so-called EMC retroflection. The EMC retroflection is characterized by three well-defined forms: early retroflection, canonical retroflection, and no retroflection. The EMC Early Retroflection is an unusual abrupt return current straight to the Indian Ocean without reaching the detachment point, while the EMC Canonical Retroflection returns the mass flow in the vicinity of the southern tip of the island. No retroflection is characterized by the straight propagation of the flow towards the Agulhas Current. These three forms of retroflection are due to the strength of the EMC and the contribution of mesoscale eddies arriving from the Indian Ocean. Retroflections have implications for coastal upwelling strength, Southeast Madagascar phytoplankton bloom occurrences, and South Indian Ocean Counter Current (SICC) formation.