On the Deep Western Boundary Current Separation and Anticyclone Genesis off Northeast Brazil

Author(s)

Vilela-Silva, Felipe ; Silveira, Ilson C. A. ; Napolitano, Dante C. ; Souza-Neto, Pedro W. M. ; Bilo, Tiago C. ; Gangopadhyay, Avijit

• Document type: Journal article
• Source: JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS; v. 128, n. 1, p. 21-pg., 2023-01-01.

Abstract

The Deep Western Boundary Current (DWBC) is the main component of the deep limb of the Atlantic Meridional Overturning Circulation (AMOC). Off northeast Brazil, the DWBC breaks up into southwestward-propagating anticyclones. In this study, we investigate the breakup mechanism with hydrographic observations, eddy-resolving numerical model outputs, and theory. Here, we present a quasi-synoptic map of geostrophic velocities and stream function at the DWBC core level between 2.5 degrees S and 11 degrees S. We observe, in horizontal distributions of velocities, that the DWBC breakup site is linked to a topographic feature of the Brazilian continental margin centered at 8 degrees S: the Pernambuco Plateau (PP). Moreover, both observations and model outputs hint at a possible DWBC separation near the PP preceding anticyclone genesis. We test, with three different theories from the literature, whether or not the DWBC separates at 8 degrees S. The results of the tests converge to indicate that the DWBC undergoes a local and intermittent inertial separation while contouring the PP. Downstream of its separation at the plateau, the DWBC sheds eddies similarly to previously reported laboratory experiments. In addition, a regional analysis of energy transfer shows that barotropic instability significantly contributes to the anticyclones growth between 8 degrees S and 13 degrees S. Analysis of the energy budget and separation of waters related to the AMOC pathways into the basin interior provide a better understanding for later studies about heat fluxes and ventilation in the deep tropical South Atlantic. (AU)

• FAPESP's process: 15/21729-4 - The role of the Vitória-Trindade Ridge in the generation of sub and meso-scale dynamics
• Grantee: Ilson Carlos Almeida da SIlveira
• Support Opportunities: Regular Research Grants
• FAPESP's process: 18/06153-7 - Instability processes in Deep Western Boundary Current along the Pernambuco plateau
• Grantee: Felipe Vilela da Silva
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• FAPESP's process: 20/04315-0 - Circulation dynamics in the bottom limit layer of the Cruzeiro do Sul rift (Rio Grande Rise; 28S, 39°W--35°S, 32°W)
• Grantee: Pedro Walfir Martins e Souza Neto
• Support Opportunities: Scholarships in Brazil - Master