Agulhas current meanders facilitate shelf-slope exchange on the Eastern Agulhas Bank

Abstract

Large solitary meanders are arguably the dominant mode of variability in the Agulhas Current. Observational studies have shown that these large meanders are associated with strong upwelling velocities and affect the shelf circulation for over 100 days per year. Here 10-year time series from two ocean general circulation models are used to create a composite picture of the Agulhas Current and its interactions with the shelf circulation in meandering and nonmeandering modes. Both models show good agreement with the size, propagation speed, and frequency of observed meanders. These composite meanders are then used to examine the response of shelf waters to the onset of large meanders, with the use of model output enabling the dynamics at depth to be explored. Results show a composite mean warming of up to 3 degrees C of depth-averaged temperature along the shelf edge associated with an intrusion of the current jet onto the shelf driven by an intensification of the flow along the leading edge of large meanders. However, this intensification of flow results in cooling of bottom waters, driving cold events at the shelf break of <10 degrees C at 100 m. Thus, the intensification of the current jet associated with large meander events appears to drive strong up and downwelling events across the inshore front of the Agulhas Current, facilitating shelf-slope exchange.