Three decades of research on the greater Agulhas Current

Abstract

Abstract. The greater Agulhas Current has been shown to be a key link in the global thermohaline circulation and an increased understanding of this current system is therefore of more than just local interest. Knowledge on the Agulhas Current system has in fact increased enormously over the past 30 years. This review covers some aspects of what has been learnt on the northern and the southern parts of the Agulhas Current proper and their influence on the waters and circulation of the adjoining continental shelf. It also discusses the Natal Pulse and new information that has been gained on how it is triggered and what influence it has. It deals with the Agulhas retroflection, the shedding of Agulhas rings and the movement and characteristics of these rings that contributes to the meridional overturning circulation of the global ocean. The Agulhas Return Current forms part of the final outflow of the system and current knowledge on that current is appraised. The sources of the Agulhas Current have been a controversial subject for many years and this dispute continues. This is described and discussed, based on what information has been gained from research over the past three decades. Building on what is currently known, some suggestions are given on the most important remaining knowledge gaps and how these could most efficaciously be filled.

Observed eddy dissipation in the Agulhas Current

“…Once identified, the algorithm calculates different properties of the eddy such as position (longitude and latitude), direction of rotation, amplitude, radii, and circum‐averaged speeds over a 7 day interval. In this study, only eddies passing through the northern sector of the Agulhas Current, defined by Grundlingh [] and Lutjeharms [] to be 28–29.5°S and 31–35°E, were considered (black box in Figure ). Surface current velocities in this region are known to exceed 1.3 ± 0.3 m/s [ Grundlingh , ].…”

Long range transport of a quasi isolated chlorophyll patch by an Agulhas ring

“…Mesoscale eddies play a fundamental role in the transport of material and dynamical quantities over different parts of the World Ocean [ Danabasoglu et al , 1994]. The importance of horizontal eddy transport is manifested at the Agulhas Current system, where Agulhas rings ‐ the largest mesoscale eddies in the world Ocean [ Olson and Evans , 1986] ‐ are key agents in the transfer of warm and salty waters from the Indian Ocean to the South Atlantic [ Lutjeharms , 2007]. Agulhas rings shed intermittently from the Agulhas retroflection south of Africa, have been shown to contribute to approximately 50% of the total heat and mass fluxes across the Aghulas Ridge [ Treguier et al , 2003].…”

A New Seismic Stratigraphy in the Indian‐Atlantic Ocean Gateway Resembles Major Paleo‐Oceanographic Changes of the Last 7 Ma

“…The AP region is characterized by a strong water mass transport at all depth levels (Hernández-Guerra & Talley, 2016;Macdonald, 1993). The surface circulation is dominated by the Agulhas Return Current (Lutjeharms & Ansorge, 2001), which flows eastward over the AP and can reach down to more than 1,500 m (Lutjeharms, 2007). The Agulhas Return Current originates from the Agulhas Retroflection south of Cape Agulhas where the Agulhas Current takes a counterclockwise turn and doubles back on itself ( Figure 1a).…”