Shelf Water Export at the Brazil-Malvinas Confluence Evidenced From Combined in situ and Satellite Observations

Abstract

The Brazil-Malvinas Confluence (BMC) is the region where opposing and intense western boundary currents meet along the Southwestern Atlantic slope at about 38°S, generating one of the most energetic mesoscale regions of the global ocean. Based on shipborne observations acquired within the Uruguayan Economic Exclusive Zone (EEZ), combined with satellite data and an eddy tracking algorithm, we analyze the cross-shelf exchanges during May 2016, when the BMC was in an anomalous northern position. Two types of shelf water export were observed triggered by mesoscale dynamics: one was the export of shallow Rio de la Plata Plume waters driven off-shelf by the retroflection of the Brazil Current. This export formed a 70 km wide, 20 m deep filament that propagated offshore at 0.3 m s–1, with a transport of 0.42 Sv. It lasted about 10 days before being mixed with ambient Confluence waters by strong winds. An additional type of off-shelf transport consisted of a subsurface layer of Subantarctic Shelf Waters (SASW) about 60 m thick that subducted at the BMC reaching 130 m deep and transporting 0.91 ± 0.91 Sv. We show that geostrophic currents derived from satellite altimetry over the slope can be useful to track this subsurface off-shelf export as they are significantly correlated with absolute velocity measurements at this depth. Argo temperature and salinity profiles show evidence of these two types of shelf water export occurring between the BMC front and the separation of the Brazil Current from the shelf-break, suggesting this is a relatively frequent phenomenon, in agreement with previous observations.

Predicting the Loop Current dynamics combining altimetry and deep flow measurements through the Yucatan Channel

“…Maximum correlation with altimetry was not found in the upper layers where ageostrophic currents are considerable, but below 100 m depth, as observed in other regions (e.g. Manta et al, 2022). As a consequence of the altimetric detection of the Loop Current, a resulting limitation of this analysis is that the potential contribution of the higher frequencies (e.g.…”

Circulation and Cross‐Shelf Exchanges in the Northern Shelf of the Southwestern Atlantic: Dynamics

“…Prior studies have also shown that Brazil Current meanders (da Silveira et al., 2008) and eddies play an important role in cross‐shelf exchange in the northern region of Cape São Tome (22°S) (Calado et al., 2010; Palóczy et al., 2014). In the southern region where the Brazil Current collides with the Malvinas Current, offshore eddies are found to play a key role also in the location of the detrainment of the shelfwater to the deep ocean (Manta et al., 2022). Quantitative estimations of the magnitude of those cross‐shelf exchanges have been entirely based on model simulations (Berden et al., 2022; Combes & Matano, 2014; Matano et al., 2010; Palma et al., 2008; Palma & Matano, 2009).…”