Cruise data sets, satellite remote sensing observations, and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the southwest of Madagascar: the Southwest MAdagascar Coastal Current (SMACC). The SMACC is a relatively shallow (<300 m) and narrow (<100 km wide) warm and salty coastal surface current, which flows along the south western coast of Madagascar toward the south, opposite to the dominant winds. The warm water surface signature of the SMACC extends from 22°S (upstream) to 26.4°S (downstream). The SMACC exhibits a seasonal variability: more intense in summer and reduced in winter. The average volume transport of its core is about 1.3 Sv with a mean summer maximum of 2.1 Sv. It is forced by a strong cyclonic wind stress curl associated with the bending of the trade winds along the southern tip of Madagascar. The SMACC directly influences the coastal upwelling regions south of Madagascar. Its existence is likely to influence local fisheries and larval transport patterns, as well as the connectivity with the Agulhas Current, affecting the returning branch of the global overturning circulation.

Plain Language Summary

A new coastal current: the Southwest MAdagascar Coastal Current (SMACC) has been uncovered. This coastal current flows along the southwestern coast of Madagascar toward the south. The SMACC is a relatively shallow (<300 m) and narrow (<100 km wide) warm and salty surface current, which is more intense in summer and reduced in winter. The Southwest MAdagascar Coastal Current has a downstream impact on the upwelling system at the south of Madagascar which is a physical process inducing local fertilization. As such, the Southwest MAdagascar Coastal Current has key implications for studies about the greater Agulhas Current system, remote connections between oceanographic systems, biophysical coupling in upwelling systems, fisheries management, local livelihoods, and so forth. The uncovering of the SMACC has significant implications for the improved broader understanding of ocean systems around the world.