Moored observations of mesoscale features in the Cape Basin: Characteristics and local impacts on water mass distributions

Abstract

Abstract. The eastern side of the SAMBA array (South Atlantic Meridional overturning circulation Basin-wide Array) along the latitude 34.5°S is used to assess the nonlinear, mesoscale dynamics of the Cape Basin. This array presently consists of current meter moorings and CPIES (bottom mounted Inverted Echo Sounders with pressure sensor and current meter) deployed across the continental slope. These data, available from September 2014 to December 2015, combined with satellite altimetry allow us to investigate the characteristics and the impact of these mesoscale structures on local water masses distribution and cross-validate the different data sets. We demonstrate that the upper slope moorings are affected by cyclonic eddies generated at the South Benguela upwelling front, while the deeper slope moorings are affected by the more complex dynamics of the Cape Basin involving Agulhas Rings and cyclonic eddies. This complex dynamics induces strong intra-seasonal upper-ocean velocity variations and water masses exchanges across the shelf and the open ocean, but also across the subantarctic and subtropical waters. Under four case studies, the full-water column hydrographic properties of each mesoscale feature has been evaluated. Our analyses show that exchange of water masses happens through the advection of water by mesoscale eddies but also via wide water mass intrusions engendered by the existence of intense dipoles. The high spatial and temporal scales resolved by the moorings allows us to define the substantial role of these mesoscale features over the full-water column. Future investigations with longer time series at these existing sites will lead to a better understanding of the eastern boundary current variability, and ultimately improve our understanding of the strength and