Articles | Volume 13, issue 1
Ocean Sci., 13, 175–194, 2017
Ocean Sci., 13, 175–194, 2017

Research article 02 Mar 2017

Research article | 02 Mar 2017

Characteristics and causes of Deep Western Boundary Current transport variability at 34.5° S during 2009–2014

Christopher S. Meinen1, Silvia L. Garzoli2,1, Renellys C. Perez2,1, Edmo Campos3,2, Alberto R. Piola4,5,6, Maria Paz Chidichimo4,5,6, Shenfu Dong1, and Olga T. Sato3 Christopher S. Meinen et al.
  • 1Physical Oceanography Division, Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida, USA
  • 2Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, USA
  • 3Instituto Oceanográfico, University of São Paulo, São Paulo, Brazil
  • 4Departamento Oceanografia, Servicio de Hidrografía Naval, Buenos Aires, Argentina
  • 5Departamento Oceanografia, Universidad de Buenos Aires, Buenos Aires, Argentina
  • 6Instituto Franco-Argentino sobre Estudios de Clima y sus Impactos, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina

Abstract. The Deep Western Boundary Current (DWBC) at 34.5° S in the South Atlantic carries a significant fraction of the cold deep limb of the Meridional Overturning Circulation (MOC), and therefore its variability affects the meridional heat transport and consequently the regional and global climate. Nearly 6 years of observations from a line of pressure-equipped inverted echo sounders (PIESs) have yielded an unprecedented data set for studying the characteristics of the time-varying DWBC volume transport at 34.5° S. Furthermore, the horizontal resolution of the observing array was greatly improved in December 2012 with the addition of two current-and-pressure-equipped inverted echo sounders (CPIESs) at the midpoints of the two westernmost pairs of PIES moorings. Regular hydrographic sections along the PIES/CPIES line confirm the presence of recently ventilated North Atlantic Deep Water carried by the DWBC. The time-mean absolute geostrophic transport integrated within the DWBC layer, defined between 800–4800 dbar and within longitude bounds of 51.5 to 44.5° W, is −15 Sv (1 Sv  =  106 m3 s−1; negative indicates southward flow). The observed peak-to-peak range in volume transport using these integration limits is from −89 to +50 Sv, and the temporal standard deviation is 23 Sv. Testing different vertical integration limits based on time-mean water-mass property levels yields small changes to these values, but no significant alteration to the character of the transport time series. The time-mean southward DWBC flow at this latitude is confined west of 49.5° W, with recirculations dominating the flow further offshore. As with other latitudes where the DWBC has been observed for multiple years, the time variability greatly exceeds the time mean, suggesting the presence of strong coherent vortices and/or Rossby Wave-like signals propagating to the boundary from the interior.

Short summary
This study investigates the variability of the Deep Western Boundary Current at 34.5° S. This current carries a large part of the cold deep limb of the Meridional Overturning Circulation, which is a crucial part of the ocean system and has impacts on global weather patterns. Study of this current in the South Atlantic has been limited in the past, and this new study provides insights into the strength and variability of the current as well as the causes for the observed changes.