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Western boundary currents (WBCs) have intensified and become more eddying in recent decades due to the spin-up of the ocean gyres, resulting in warmer open ocean temperatures. However, relatively l...

Recent observations report a poleward shift in several of the world’s western boundary current extensions in response to a warming climate. However, the nature and variability of the Agulhas Return Current (ARC) is still relatively unknown, leading to uncertainty in its response to gyre intensification. The objective of this work is to investigate meridional migration and eddy kinetic energy (EKE) trends in the ARC over the past 27 years using satellite-derived altimetry products. A difference is seen between the western and eastern regions of the ARC, the former exhibiting a predominantly equatorward migration and the latter moving predominantly poleward. The ARC is shown to be a region highly influenced by its bathymetry. Additionally, we show that the regional EKE peaks during austral summer months and that there has been a significant rise in summertime EKE levels between 1994–2011.

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°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

International audience; South Indian Ocean eddies (SIDDIES), originating from a high evaporation region in the eastern Indian Ocean, are investigated by tracking individual eddies from satellite data and co-located Argo floats. A subsurface-eddy identification method, based on its steric dynamic height anomaly, is devised to assign Argo profiles to surface eddies (surfSIDDIES) or subsurface eddies (subSIDDIES). These westward-propagating, long-lived features (>3 months) prevail over a preferential latitudinal band, forming a permanent structure linking the eastern to the western Indian Ocean, that we call the 'SIDDIES Corridor'. Key features have been revealed in the mean thermohaline vertical structure of these eddies. Anticyclonic SIDDIES are characterized by positive subsurface salinity anomalies, with subSIDDIES not exhibiting negative surface anomalies, as opposed to surfSIDDIES. Cyclonic subSIDDIES also occur, but their related salinity anomalies are weaker. SubSIDDIES exhibit two cores of different temperature polarities in their surface and subsurface levels. Cyclonic subSIDDIES have their cores at around 150-200 m depth along the 25.4-25.8 kg m-3 potential density layer with anticyclonic subSIDDIES having their cores at 250-300 m along the 26-26.4 kg m-3 density layer. The SIDDIES corridor acts as a zonal pathway for both eddy-types to advect water masses and biogeochemical properties across the basin. This study provides a new insight on heat/salt fluxes, showing that 58% (32%) of the total heat eddy-flux is ascribed to cyclonic (anticyclonic) subSIDDIES, respectively, in the eastern South Indian Ocean. Anticyclonic subSIDDIES have also been found to be the sole high-saline water eddy-conveyor toward the western Indian Ocean.