Prevalence of strong bottom currents in the greater Agulhas system

Deep current meter data and output from two high-resolution global ocean circulation models are used to determine the prevalence and location of strong bottom currents in the greater Agulhas Current system. The two models and current meter data are remarkably consistent, showing that benthic storms, with bottom currents greater than 0.2 m s^-1, occur throughout the Agulhas retroflection region south of Africa more than 20% of the time. Furthermore, beneath the mean Agulhas Current core and the retroflection front, bottom currents exceed 0.2 m s^-1 more than 50% of the time, while away from strong surface currents, bottom currents rarely exceed 0.2 m s^-1. Implications for sediment transport are discussed and the results are compared to atmospheric storms. Benthic storms of this strength (0.2 m s^-1) are comparable to a 9 m s^-1 (Beaufort 5) windstorm, but scaling shows that benthic storms may be less effective at lifting and transporting sediment than dust storms. Key Points Strong bottom currents are prevalent beneath surface currents in the greater Agulhas systemSurface currents can affect formation of contouritesNoncohesive sediment is lifted more easily by dust storms than by benthic storms