Characterisation of the eddy-driven variability inshore of the Agulhas Current using Sea Surface Temperature observations

Abstract

Off the east coast of South Africa, coastal waters inshore of the Agulhas Current are largely affected by oceanic mesoscale turbulence, primarily in the form of meanders such as Natal Pulses and Durban Eddies. This study utilises forty years of modern, high-resolution satellite sea surface temperature (SST) data, offering both improved spatial detail and a longer time series than previous products, to characterise these eddies using an automated meander detection algorithm. Notably, automated detection has never before been applied to Durban Eddies, and Natal Pulses have not been analysed using such a high-resolution, long-term SST dataset. The algorithm successfully estimated the daily position of the inshore edge and core of the Agulhas Current and the “first occurrence” of Agulhas waters for the period of the study —the latter defined as the initial emergence of Agulhas Current waters in a filament or plume associated with Natal Pulses. The analysis reveals that the inshore edge of the Agulhas Current is not subject to seasonal variation but is significantly influenced by the presence of Natal Pulses and Durban Eddies. The first occurrence of Agulhas Current waters was only detected during the passage of Natal Pulses. Results indicate increased variability in regions south of 29.8°S, with Natal Pulses showing an increase in size and surface lifespan in the southern region. Conversely, Durban Eddies exhibit a decrease in size and surface lifespan as they propagate southward. Furthermore, seasonal SST anomalies are generally small, with cold events more frequent; Natal Pulses cause higher variability, while Durban Eddies maintain relative stability