Near-surface western boundary circulation off Northeast Brazil

Type Article
Date 2021-01
Language English
Author(s) Dossa Alina N.1, Costa Da Silva Alex1, Chaigneau Alexis2, 3, 4, Eldin Gérard2, Araujo Moacyr1, 5, Bertrand Arnaud1, 6, 7
Affiliation(s) 1 : Laboratório de Oceanografia Física Estuarina e Costeira, Depto. Oceanografia, UFPE, Recife-PE, Brazil
2 : Laboratoire d’Études en Géophysique et Océanographie Spatiale (LEGOS), Université de Toulouse, CNES, CNRD, IRD, UPS, Toulouse, France
3 : Institut de Recherches Halieutiques et Océanologiques du Bénin (IRHOB), Cotonou, Benin
4 : International Chair in Mathematical Physics and Applications (ICMPA–UNESCO Chair), University of Abomey‐Calavi, Cotonou, Benin
5 : Brazilian Research Network on Global Climate Change, São José dos Campos, SP, Brazil
6 : Institut de Recherche pour le Développement (IRD), MARBEC, Univ Montpellier, CNRS, Ifremer, IRD, Sète, France
7 : Universidade Federal Rural de Pernambuco, Recife, Brazil
Source Progress In Oceanography (0079-6611) (Elsevier BV), 2021-01 , Vol. 190 , P. 102475 (15p.)
DOI 10.1016/j.pocean.2020.102475
WOS© Times Cited 5
Keyword(s) Western Tropical Atlantic, North Brazil Undercurrent, North Brazil Current, Flow-topography interaction, Mesoscale activity, ADCP

In the tropical Atlantic Ocean, the North Brazil Undercurrent (NBUC) and the North Brazil Current (NBC) play important roles as near-surface northward paths for the Atlantic meridional overturning circulation. To investigate the meridional evolution of the near-surface western boundary circulation in that region, two surveys were carried out off Northeast Brazil during austral spring 2015 and fall 2017, periods that we show to be representative of typical conditions for the spring and fall seasons. Using conductivity temperature depth oxygen probe and ship-mounted acoustic Doppler current profiler measurements, altimetry data, and numerical reanalysis products, we examine the spatiotemporal variability of the NBUC, providing a comprehensive view of the circulation, including NBUC-NBC transition and the potential impact of mesoscale eddies. The NBUC originating south of 10°S flows equatorward over the continental slope. NBUC mean velocity, transport and vertical extent of the velocity core were higher in spring 2015 (0.81 m s-1, 15.6 Sv, and >400 m) than in fall 2017 (0.65 m s-1, 11.0 Sv, and ∼300 m). The upper limit of the NBUC velocity core rose slightly from 160 m at 9°S to 105 m depth at 6°S. This pattern is associated with a northward increase in current velocity from 0.7 m s−1 at 9°S to 1 m s−1 at 5°S. The orographic effect shifts the flow from northeastward south of 7.5°S to northwestward north of 7.5°S, following the shoreline. Besides, altimetry data show that this flow can be locally influenced by mesoscale activity. Farther north, at ∼4.8°S, data obtained in fall 2017 show that the central branch of the South Equatorial Current (cSEC) enters into the western boundary system where it coalesces with the NBUC to form the NBC, flowing toward the Caribbean Sea. Finally, the NBUC retroflection does not feed the South Equatorial Undercurrent (SEUC), which, instead originates from retroflections of the cSEC and the equatorial branch of the South Equatorial Current (eSEC).

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