Dynamic Structure of Eddies of the Brazil‐Malvinas Confluence Zone Revealed by Direct Measurements and Satellite Altimetry.

The goal of this work is to study the dynamical structure of eddies of the Brazil‐Malvinas Confluence zone (BMC eddies) using direct velocity measurements carried out by Shipborne Acoustic Doppler Current Profiler during five oceanographic cruises performed in 2016–2022. In total, in situ data of 13 BMC eddies, including nine anticyclones and four cyclones are available. These data show that the orbital velocity in such eddies can reach 189 cm/s and their vertical structure is highly barotropic. In several eddies, the velocities exceeding 100 cm/s are observed down to a depth of 560 m and at a depth of 800 m they are still higher than 80 cm/s. The spatial structure of velocity and horizontal shear in the eddies is strongly asymmetric, with higher velocities in the southern part near the intense thermohaline BMC front. Altimetry data show qualitative agreement with in situ data, but underestimate the horizontal velocity shear and the maximum velocities at the periphery of the BMC eddies. We also use satellite altimetry and Argo float measurements to study these eddies, and estimate their impact on the thermohaline structure. The analysis shows that the eddies with orbital velocities exceeding 100 cm/s cause intense temperature and salinity anomalies reaching 7–9°C and 1 psu in anticyclones and −4°C and 0.8 psu in cyclones at 100–300 m depth. Plain Language Summary: The Brazil and Malvinas currents are the main circulation patterns in the Southwest Atlantic. They flow along the South America continental slope toward each other and meet around 38°S generating a thermohaline front known as the Brazil‐Malvinas Confluence zone. Further downstream, both currents retroflect and instabilities generate mesoscale eddies. In this study, we combine new velocity measurements and satellite data for the analysis of the velocity structure and distribution of eddies in the Southwest Atlantic. The velocity observations were carried out across 13 eddies and revealed high velocities exceeding 100 cm/s even at depths greater than 500 m. While direct measurements provide accurate velocity structure in several crossed eddies, satellite altimetry covers the entire region, allowing us to estimate the mean statistical parameters of all eddies over a long period in 1993–2020. The results show that the study area is characterized by the strongest eddies in the western part of the South Atlantic with intense orbital velocities (more than 100 cm/s) reaching 600 m depth. The composite analysis of altimetry and Argo float data shows that such eddies cause very strong temperature and salinity anomalies and significantly affect the salt and heat content in the region. Key Points: The dynamic structure of 13 intense eddies in the Brazil‐Malvinas Confluence zone is investigated using direct Shipborne Acoustic Doppler Current Profiler measurementsThe maximum measured orbital velocity reaches 189 cm/s and the velocities exceeding 100 cm/s are observed down to a depth of 560 mSubsurface temperature and salinity anomalies in the intense eddies can reach 9°C and 1 psu [ABSTRACT FROM AUTHOR]