Dipole-induced Central Water extrusions south of Abrolhos Bank (Brazil, 20.5oS)

Abstract

In this work, we describe a mechanism by which South Atlantic Central Water is upwelled to shelf-break levels, subsequently mixed with the Tropical Water in the upper portion of the water column, and advected oceanward as a plume, reaching a distance of more than 250 km from the shelf break. This process is due to the coupling of two quasi-stationary Brazil Current (BC) mesoscale features: the anticyclonic Abrolhos Eddy (AE) and the cyclonic Vitoria Eddy (VE), located north and south of the Vitoria-Trindade Ridge (~20.5oS) respectively. As they pair around a topographic feature known as Besnard Bank, they form an eddy dipole with a ~2 Sv velocity-intensified BC channeled between the two eddies. During an AE-VE dipole event the BC acquires a cross-isobath direction, which causes horizontal divergence near the shelf break. Therefore, in this scenario, the BC turns into a jet that ejects a nutrient-rich central water mix toward the deep ocean. Considering that we can track the nutrient-rich tongue of water by its higher chlorophyll-a signature, it may be relevant in the understanding of the pelagial biota ecology of the surroundings.