Water mass transports and pathways in the North Brazil ‐ Equatorial Undercurrent retroflection

Ignasi Vallès‐Casanova, Eugenio Fraile‐Nuez, Marta Martín‐Rey, Erik Sebille, Anna Cabré, Anna Olivé‐Abelló, Josep L. Pelegrí

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The equatorial retroflection of the North Brazil Current (NBC) into the Equatorial Undercurrent (EUC) and its posterior tropical recirculation is a major regulator for the returning limb of the Atlantic Meridional Overturning Circulation. Indeed, most surface and thermocline NBC waters retroflect at the equator all the way into the central and eastern Atlantic Ocean, before they recirculate back through the tropics to the western boundary. Here, we use cruise data in the western equatorial Atlantic during April 2010 and reanalysis time series for the equatorial and tropical waters in both hemispheres in order to explore the recirculation pathways and transport variability. During the 1998–2016 period, the annual-mean EUC transports 15.1 ± 1.3 Sv at 32°W, with 2.8 ± 0.4 Sv from the North Atlantic and 11.4 ± 1.3 Sv from the South Atlantic. At 32°W most of the total EUC transport comes from the western boundary retroflection south of 3°N (7.2 ± 0.9 Sv), a substantial fraction retroflects north of 3°N (5.6 ± 0.4 Sv), and the remaining flow (2.3 Sv) joins through the interior basin. The South Atlantic subtropical waters feed the EUC at all thermocline depths while the North Atlantic and South Atlantic tropical waters do so at the surface and upper-thermocline levels. The EUC transport at 32°W has a pronounced seasonality, with spring and fall maxima and a range of 8.8 Sv. The 18 yr of reanalysis data shows a weak yet significant correlation with an Atlantic Niño index, and also suggests an enhanced contribution from the South Atlantic tropical waters during 2008–2016 as compared with 1997–2007.

Original languageEnglish
Article numbere2021JC018150
Pages (from-to)1-21
JournalJournal of Geophysical Research: Oceans
Volume127
Issue number5
DOIs
Publication statusPublished - May 2022

Keywords

  • Lagrangian transports
  • Tropical Atlantic
  • western boundary current

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