A study of the variability in the Benguela Current volume transport
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Published:2018-04-05
Issue:2
Volume:14
Page:273-283
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ISSN:1812-0792
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Container-title:Ocean Science
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language:en
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Short-container-title:Ocean Sci.
Author:
Majumder Sudip, Schmid ClaudiaORCID
Abstract
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.
Funder
Climate Program Office
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
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