Intrusion of the Antarctic Intermediate Waters inshore of the Agulhas Current along the Southeast Coast of South Africa: perspectives from GLORYS-12v1 model
Issufo Halo*, Tarron Lamont
Department of Forestry, Fisheries and the Environment
6 Queen road Rondebosch, E44 Edingight Cape Town, Western Cape, South Africa Pincode: +27 Mobile: 794270556 E-mail: email@example.com
The Agulhas Current (AC) is one of the most intense Western Boundary Currents in the worlds ocean. It flows adjacent to the east coast of South Africa, in a southwestward direction, with peak propagation speeds way above 1.5 m.s^-1. The current carries about 70 Sv (1 Sv=10^6m^3s^-1), in the upper 2000 m below the sea-surface, and transports warmer and more saline tropical Indian Ocean waters into the South Atlantic. It is thus an important route for the inter-ocean exchange that feeds the upper branch of the Meridional overturning Circulation which plays a strong role in controlling the regional and global climate system. While earlier studies have described distinct differences in water masses inshore of the AC compared to further offshore, more recent in situ hydrographic observations have revealed the presence of the Antarctic Intermediate Waters (AAIW) along the inshore edge of the AC. This raises an important fundamental question: Given the robust nature of the AC, associated with its intensity and vertical extension through the water column, what could possibly drive the intrusion of the AAIW along the inshore edge of the AC, and over the shallow continental shelf on the southeast coast of South Africa? We explored this question using the output from an eddy resolving Global Oceans Physical Reanalysis (GLORYS 12V1) model, vested with assimilation capabilities, simulated on c-grid, with a spatial lateral resolution of 1/12^o ~ 8 km, and 50 vertical layers discretized on a z-coordinate system. The performance of the model has been satisfactorily assessed against satellite altimetry observations, and high resolution hydrographic data collected as part of the DFFE and ACEP Phakisa Ocean Cruises Initiative on the southeast coast of South Africa, in January/February and July/August of 2017. Our preliminary results suggest that the intrusion of the AAIW along the inshore edge of the AC is mainly driven by the dynamics of mesoscale eddy activity. On one hand, through the lateral advection of intermediate waters, and on the other hand, through upwelling process within the eddies, especially the cyclonic eddies.