Lagrangian observations in the Intermediate Western Boundary Current of the South Atlantic

Type Article
Date 2013-01
Language English
Author(s) Legeais Jean-Francois2, Ollitrault Michel1, Arhan Michel1
Affiliation(s) 1 : IFREMER, Ctr Brest, Lab Phys Oceans, CNRS,IRD,UBO, F-29280 Plouzane, France.
2 : IFREMER, Ctr Brest, Lab Phys Oceans, CNRS,IRD,UBO, F-29280 Plouzane, France.
Source Deep-sea Research Part Ii-topical Studies In Oceanography (0967-0645) (Pergamon-elsevier Science Ltd), 2013-01 , Vol. 85 , P. 109-126
DOI 10.1016/j.dsr2.2012.07.028
WOS© Times Cited 15
Keyword(s) Brazil basin, Intermediate water, Western boundary current
Abstract Subsurface float measurements at 800 m depth carried out from 1994 to 2003 in the Brazil Basin are used to characterise the equatorward Intermediate Western Boundary Current (IWBC) and its connections to the ocean interior. Transversally, the boundary flow is less than 100 km wide, and most intense at 10-20 km from the 800 m isobath. Its average velocities range from similar to 0.1 ms(-1) to 0.3 ms(-1) depending on latitude, with individual daily values as high as 0.7 ms(-1). The flow meridional extent exhibits 3 contrasted domains: (i) from 27 degrees S to the Vitoria-Trindade Ridge at 20 degrees 30'S, the boundary flow intensifies northward along a relatively smooth topography. A counter current adjacent to it on its seaward side feeds it with intermediate water from the northern limb of the subtropical gyre. (ii) At latitudes 20-15 degrees S characterised by a very irregular topography, the IWBC becomes weaker with even no real proof of its presence at 18-15 degrees S. An intense mesoscale variability prevails there, which apparently takes over from the boundary flow to ensure the northward transport of water to 15 degrees S, where the IWBC re-forms. (iii) North of this latitude, the boundary flow increases again to similar to 10 degrees S along smooth isobaths, then decreases when encountering a rougher topography and the zonal jets of the equatorial current system. A counter current present from similar to 5 degrees S to similar to 14 degrees S, partly fed from the boundary flow, contributes to its drainage. The IWBC shows two main input locations, at 27-23 degrees S and 15-12 degrees S in the southern parts of the two latitudinal domains of smooth topography where the northward current increases. Output locations coincide with major capes in the continental slope geometry, at 20 degrees S and 18 degrees S (the southeastern and northeastern corners of the Abrolhos Bank), at 8 degrees S near the Recife Plateau, and at 5 degrees S near Cape Sao Roque.
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