Agulhas leakage into the Atlantic estimated with subsurface floats and surface drifters
Agulhas leakage into the Atlantic estimated with subsurface floats and surface drifters
Date
2006-12-02
Authors
Richardson, Philip L.
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Abstract
Surface drifters and subsurface floats drifting at depths near 800 m were used to study the
pathways of warm salty Indian Ocean water leaking into the South Atlantic that is a
component of the upper limb of the Atlantic meridional overturning circulation. Four
drifters and 5 floats drifted from the Agulhas Current directly into the Benguela Current.
Others looped for various amounts of time in Agulhas rings and cyclones, which
translated westward into the Atlantic contributing a large part of Indian Ocean leakage.
Agulhas rings translated into the Benguela Current where they slowly decayed. Some
large blob-like Agulhas rings with irregular shapes were found in the southeastern Cape
Basin. Drifter trajectories suggest these rings become more circular with time eventually
evolving into the circular rings observed west of the Walvis Ridge. Agulhas cyclones,
which form on the north side of the Agulhas south of Africa, translated southwestward
(to 6°E) and contributed water to the southern Cape Basin. A new discovery is a
westward extension from the mean Agulhas retroflection measured by westward drifting
floats near 41ºS out to at least 5ºW with some floats as far west as 25ºW. The Agulhas
extension appears to split the South Atlantic Current into two branches and to transport
Agulhas water westward where it is mixed and blended with eastward-flowing water
from the western Atlantic. The blended mixture flows northeastward in the northern
branch of the South Atlantic Current and into the Benguela Current. Agulhas leakage
transport was estimated from drifters and floats to be at least 15 Sv in the upper 1,000 m,
which is equivalent to the transport of the upper layer meridional overturning circulation.
It is suggested that the major component of the upper layer overturning circulation in the
Atlantic is Agulhas leakage.
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Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 54 (2007): 1361-1389, doi:10.1016/j.dsr.2007.04.010.