Agulhas leakage increasing trend: its relation to regime shift in the western boundary of the Tropical Atlantic

Abstract

The Agulhas System is a complex dynamical structure characterized by the intrusion of Indian Ocean waters into the South Atlantic Ocean by means of filaments and rings shed from the Agulhas Current retroflection. This influx of warmer and saltier Indian Ocean waters into the Atlantic –Agulhas leakage – is now recognized to play an important role in the global thermohaline circulation. Due to the absence of an adequate observing system, studies of the Agulhas system have relied on outputs of ocean models, which revealed a recent increase in the Agulhas leakage. Here we present the results of a 1/12° simulation with the Hybrid Coordinate Ocean Model (HYCOM), which also show an augmentation in Agulhas leakage. This increase in the leakage ought to have an impact on the meridional oceanic volume and heat transports in the Atlantic Ocean. Significant linear trends found in the integrated transport at 20 ºS, 15 ºS, and 5 ºS correlate well with Agulhas leakage. The augmented transport seems to be related to an increase in the latent heat flux observed along the NE Brazil coastline since 2003. Our study shows that the precipitation in the Brazilian coast has been increasing since 2005, with the same regime shift observed for the latent heat flux and the volume transport. This strongly suggests that the increase of the Agulhas transport affects the western boundary system of the Tropical Atlantic Ocean, which is directly related to the increase in the precipitation and latent heat flux along the western coast