Effects of variability in the Agulhas Leakage on the western boundary systems of the South and tropical Atlantic Ocean

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 at the Agulhas Current retroflection. This influx of warmer and saltier Indian Ocean waters into the Atlantic - the Agulhas leakage - is now recognized to play an important role in the global thermohaline circulation and climate. Studies have shown that the variability of the Agulhas leakage can be associated with the onset and terminations of glacial periods. This work is an investigation of the implications of changes in the Agulhas leakage on the South Atlantic Ocean. To this end, outputs of a numerical experiment with the Hybrid Coordinate Ocean Model (HYCOM), with 1/12-degree resolution and 22-isopycnal layers, are analyzed for the period 1970-2010. Results show an increase in the leakage and in integrated transports across the South and tropical Atlantic. Significant linear trends are found in the transport at 20ºS, 15ºS, and 5ºS. These trends correlate well with decadal fluctuations of the Agulhas leakage. It is also found that it takes 6 to 8 years for anomalies in the Agulhas volume transport to arrive at the tropical Atlantic region. This seems to be related to an increase in the latent heat flux observed along the NE Brazil coastline since 2003, with impacts on near-coastal processes