Evidence of Synoptic Cross-shelf Pathways of Mid-depth Salinity Maximum Intrusions in the South Brazil Bight

Cross-shelf exchanges play a crucial role in distributing heat, salt, pollutants, and biogeochemical properties between the continental shelf and the open ocean. Among the processes shaping these exchanges, the intrusion of salty and warm waters (mid-depth Salinity Maximum, S max ) remains poorly understood in the South Brazil Bight (SBB). Here, we present observational evidence of S max intrusions in the Northeast SBB (NE-SBB) from independent measurements between February and March 2022. The dataset identified the Cabo Frio Eddy (CFE) as the main mechanism driving a cross-shelf pathway to the shelf break, with advection further enhanced by interaction with an Agulhas Ring. Backward Lagrangian analysis confirmed this pathway and traced the origin of S max to northeastern locations outside the NE-SBB. It also suggested an additional southwestward along-shelf pathway, resembling the non-meandering Brazil Current, directly advecting S max from their source region. In both cases, once S max reached the shelf break, Burger number (Bu) analysis revealed an onshore counterflow at mid-depths (Bu >1), driven by wind-induced circulation and reinforced by mesoscale dynamics. These findings highlight the role of the CFE in connecting offshore waters to the shelf and emphasize the importance of remote intrusions in shaping the thermodynamics and biogeochemistry of the SBB.