Articles | Volume 14, issue 5
Ocean Sci., 14, 923–945, 2018
Ocean Sci., 14, 923–945, 2018

Research article 03 Sep 2018

Research article | 03 Sep 2018

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

Marion Kersalé1,2,3, Tarron Lamont1,4, Sabrina Speich5, Thierry Terre6, Remi Laxenaire5, Mike J. Roberts4,7, Marcel A. van den Berg4, and Isabelle J. Ansorge1 Marion Kersalé et al.
  • 1Marine Research Institute, Department of Oceanography – University of Cape Town, Rondebosch, South Africa
  • 2Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, USA
  • 3NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
  • 4Oceans and Coastal Research, Department of Environmental Affairs, Cape Town, South Africa
  • 5Laboratoire de Météorologie Dynamique, UMR 8539 École Polytechnique, ENS, CNRS, Paris, France
  • 6IFREMER, Univ. Brest, CNRS, IRD, Laboratoire d'Océanographie Physique et Spatiale (LOPS), IUEM, Plouzané, France
  • 7Ocean Science & Marine Food Security, Nelson Mandela University, Port Elizabeth, South Africa

Abstract. The eastern side of the South Atlantic Meridional overturning circulation Basin-wide Array (SAMBA) along 34.5° S is used to assess the nonlinear, mesoscale dynamics of the Cape Basin. This array presently consists of current meter moorings and bottom mounted Current and Pressure recording Inverted Echo Sounders (CPIES) 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 mesoscale dynamics on local water mass distribution and cross-validate the different data sets. We demonstrate that the moorings are affected by the complex dynamics of the Cape Basin involving Agulhas rings, cyclonic eddies and anticyclonic eddies from the Agulhas Bank and the South Benguela upwelling front and filaments. 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. These complex dynamics induce strong intra-seasonal upper-ocean velocity variations and water mass exchanges between the shelf and the open ocean but also across the subantarctic and subtropical waters. This work presents the first independent observations comparison between full-depth moorings and CPIES data sets within the eastern South Atlantic region that gives some evidence of eastern boundary buoyancy anomalies associated with migrating eddies. It also highlights the need to continuously sample the full water depth as inter-basin exchanges occur intermittently and affect the whole water column.