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Ocean Science An interactive open-access journal of the European Geosciences Union
Ocean Sci., 14, 273-283, 2018
https://doi.org/10.5194/os-14-273-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
05 Apr 2018
A study of the variability in the Benguela Current volume transport
Sudip Majumder1 and Claudia Schmid2 1Cooperative Institute for Marine and Atmospheric Studies, University of Miami, Miami, Florida, USA
2Atlantic Oceanographic and Meteorological Laboratory, NOAA, Miami, Florida, USA
Abstract. The Benguela Current forms the eastern limb of the subtropical gyre in the South Atlantic and transports a blend of relatively fresh and cool Atlantic water and relatively warm and salty Indian Ocean water northwestward. Therefore, it plays an important role not only for the local freshwater and heat budgets but for the overall meridional heat and freshwater transport in the South Atlantic. Historically, the Benguela Current region is relatively data sparse, especially with respect to long-term velocity observations. A new three-dimensional data set of the horizontal velocity in the upper 2000 m that covers the years 1993 to 2015 is used to analyze the variability in the Benguela Current. This data set was derived using observations from Argo floats, satellite sea surface height, and wind fields. Since Argo floats do not cover regions shallower than 1000 m, the data set has gaps inshore. The main features of the horizontal circulation observed in this data set are in good agreement with those from earlier studies based on limited observations. Therefore, it can be used for a more detailed study of the flow pattern as well as the variability in the circulation in this region. It is found that the mean meridional transport in the upper 800 m between the continental shelf of Africa and 3° E, decreases from 23 ± 3 Sv (1 Sv  =  106 m3 s−1) at 31° S to 11 ± 3 Sv at 28° S.

In terms of variability, the 23-year long time series at 30 and 35° S reveals phases with large energy densities at periods of 3 to 7 months, which can be attributed to the occurrence of Agulhas rings in this region. The prevalence of Agulhas rings is also behind the fact that the energy density at 35° S at the annual period is smaller than at 30° S because the former latitude is closer to Agulhas Retroflection and therefore more likely to be impacted by the Agulhas rings. In agreement with this, the energy density associated with mesoscale variability at 30° S is weaker than at 35° S. With respect to the forcing, the Sverdrup balance and the observed transport at 30° S exhibit a strong correlation of 0.7. No significant correlation between these parameters is found at 35° S.
Citation: Majumder, S. and Schmid, C.: A study of the variability in the Benguela Current volume transport, Ocean Sci., 14, 273-283, https://doi.org/10.5194/os-14-273-2018, 2018.

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Short summary
A new three-dimensional data set of the horizontal velocity in the upper 2000 m that covers the years 1993 to 2015 is used to analyze the variability of the Benguela Current. This data set was derived using observations from Argo floats, satellite sea surface height, and wind fields. With this new observational data set, we identify the complex flow pattern in this region and provide a detailed analysis of the variability in the volume transport of this current.
A new three-dimensional data set of the horizontal velocity in the upper 2000 m that covers the...
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