Structure and Propagation of Mesoscale Cyclonic Eddies in the Brazil–Malvinas Confluence

Abstract

We present a comprehensive characterization of 1386 cyclonic eddies generated in the Brazil–Malvinas Confluence (BMC) between 1993 and 2022, using satellite altimetry and the META3.2_DT eddy trajectory atlas. By isolating locally generated cyclones over a record spanning three decades, this study distinguishes between retained and exported eddies and links their fate to geometric, kinematic, energetic, and regional circulation constraints. Eddies were analysed in terms of effective radius, amplitude, swirling speed, mean eddy kinetic energy (EKE), lifespan, propagation direction, seasonal genesis, and final detection location. Most cyclones were last detected within the BMC domain, while only 14% escaped the study area. Escaped eddies had longer mean lifespans and larger net displacements than retained eddies, but export was not determined by lifespan alone. Net displacements were more frequent toward the eastern quadrants, whereas westward displaced eddies were generally more confined near the continental margin. Spatial patterns revealed a persistent corridor of eddy formation along the continental slope, modulated by bathymetric gradients and the seasonal displacement of the BMC front. The strongest mean swirling speeds and EKE values were concentrated within the main Brazil Current and Malvinas Current confluence zone, while larger effective radii were not necessarily collocated with the most energetic cells. Annual mean EKE associated with cyclonic eddies showed a weak but statistically significant positive trend during complete calendar years from 1993 to 2021, without a significant increase in interannual variance. Case studies illustrated contrasting pathways, including prolonged retention within the confluence, temporary offshore displacement followed by return, and export toward the open ocean. Taken together, the results show that locally generated cyclonic eddies in the BMC do not follow a single evolutionary pathway. Their persistence, displacement, and energetic expression emerge from the combined influence of eddy coherence, regional circulation, availability of open ocean pathways, and bathymetric constraints.