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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]

The rates of isopycnal stirring and water mass transport by mesoscale eddies, and of diapycnal mixing by small‐scale turbulence, across the Brazil‐Malvinas Confluence (BMC) are assessed from a set of microstructure and hydrographic measurements in the Argentine Basin. This assessment is founded on a theoretical framework that applies a triple decomposition to the temperature variance equation and assumes eddies to transfer potential vorticity downgradient. The BMC is found to host widespread intense isopycnal stirring at rates of O(103–104 m2 s−1), and generally weak diapycnal mixing at rates of O(10−6–10−5 m2 s−1). Despite such disparity, both diapycnal mixing and isopycnal stirring play roles of comparable importance in determining regional water mass properties within surface and mode waters. In deeper layers, isopycnal stirring prevails. Eddies are further diagnosed to effect an important cross‐BMC transport, at rates of O(1 m2 s−1). When scaled by the along‐stream extent of the BMC, these rates integrate to volume transports that may be as large as O(10 Sverdrups). This suggests that cross‐BMC transfers of waters are substantially effected by eddy‐induced flows. Plain Language Summary: Turbulent mixing plays an important role in large‐scale oceanic processes such as water mass modification, distribution of salinity and temperature properties, and the global overturning circulation. These mixing processes are the direct consequence of different physical phenomena, including mixing across density surfaces (i.e., diapycnal) by small‐scale turbulence and stirring along density surfaces (i.e., isopycnal) by mesoscale eddies. Here, we assess the strength of diapycal mixing and isopycnal stirring across the Brazil‐Malvinas Confluence (BMC). Our results suggest that both processes are key to determine regional water mass properties in the BMC. We find that mixing across density surfaces and stirring along density surfaces are both important in upper layers, while stirring is prevalent in deeper waters. Finally, we estimate the importance of eddies in the exchange of subtropical and subantarctic waters across the BMC, and thus in the Southern Ocean overturning circulation. We find that eddy‐induced flows contribute substantially to the cross‐BMC transfer of water masses. Key Points: We assess the rates of diapycnal mixing and isopycnal stirring and water mass transports by mesoscale eddies in the Brazil‐Malvinas ConfluenceIsopycnal stirring by eddies dominates water mass transformations across the BMC, especially below 500 mEddy‐indiced flows substantially contribute to the transfer of waters across the Brazil‐Malvinas Confluence [ABSTRACT FROM AUTHOR]

Twenty‐five years of high‐resolution (1/12°) ocean reanalysis are used to examine the Confluence of the Malvinas Current (MC) with the Brazil Current (BC) from synoptic to interannual time scales. The model transports of the MC (38.0 Sv ± 7.4 Sv 57 at 41°S) and the BC (23.0 Sv ± 11 Sv at 36°S) agree with observations. The model shows the branching of the MC near the Confluence with an offshore branch returning south and an inner branch sinking below the BC and managing to continue northward along the continental slope. Northward velocities associated with the subsurface inner branch peak at 40 cm/s at 36°S at 700‐m depth. The model documents the migrations of the Subantarctic (SAF) and Subtropical Fronts (STF) at the Confluence. The SAF and STF positions vary over a large range at synoptic (800 km) and interannual scale (300 and 200 km, respectively) compared to the rather small seasonal migrations of the STF (150 km) and SAF (50 km). While trends in the MC are small over the 25 years of the reanalysis, the BC becomes more intense (12.5 cm/s), saltier (0.37 psu), and warmer (2.5°C) in the upper 1,000 m. These trends are accompanied with a southward displacement of the STF and the SAF of 150 and 50 km. Plain Language Summary: The Brazil‐Malvinas Confluence is a highly dynamic region. Reproducing the circulation at the Confluence is a stringent test for operational models. Mercator Ocean high‐resolution (1/12°) ocean systems show remarkable performance in this region. We took advantage of 25 years of ocean reanalysis to examine variations in the Malvinas Current at 41°S, in the Brazil Current at 36°S, and in their confluence. The Malvinas Current branches at the Confluence: one branch veers offshore while the inner part subducts and flows north along the slope. At the Confluence, the Subantarctic and Subtropical Fronts show large synoptic (800 km) and interannual migrations (300 km) compared to rather small seasonal changes (<150 km). Key Points: Twenty‐five years of Mercator Ocean reanalysis are examined at the Brazil Malvinas Confluence from synoptic to interannual time scalesThe Malvinas Current branches at the Confluence: the outer part veers offshore, the inner part subducts, and flows north along the slopeThe migrations of the Subtropical and Subantarctic Fronts are large (small) at the synoptic and interannual (seasonal) time scales [ABSTRACT FROM AUTHOR]

The Brazil‐Malvinas Confluence arises from the frontal encountering of the subtropical Brazil Current and subantarctic Malvinas Current. It displays a complex regional circulation that is accompanied by mesoscale features and thermohaline intrusions. Here we combine altimetry and cruise data to describe the circulation pattern in the upper 2,000 m at two spatial scales encircling the frontal system. The major regional features appear south of the confluence latitude at 39–40°S: (a) a relatively weak Malvinas Current near 41°S, 56°W (28.3 ± 1.4 Sv), followed by its cyclonic retroflection; (b) an intense subtropical anticyclone (59.3 ± 10.7 Sv) that replaces the Brazil Current overshoot; and (c) a very intense subantarctic inflow (78.9 ± 13.7 Sv) near 53°W that is maintained through both an upstream (near 42°S) earlier diversion of the Malvinas Current and the cyclonic recirculation of the flow exiting east along the confluence. North of the confluence, the Brazil Current provides a net input of 30.8 ± 12.0 Sv (29.1 ± 8.3 Sv along the slope). The southern inflow splits nearly equal between barotropic and baroclinic contributions while the entire northern flow is essentially baroclinic. These northern and southern inputs add to an eastward along‐front transport of 109.7 ± 15.1 Sv, with significant contribution of highly oxygenated, relatively fresh Subantarctic Mode and Antarctic Intermediate Waters (58.7 ± 5.6 Sv). The regional circulation experiences substantial temporal variability, with southern waters flowing into the Brazil‐Malvinas Confluence through along‐slope and interior pathways and partly recirculating within the subtropical South Atlantic gyre. Plain Language Summary: The Brazil Malvinas Confluence is an intense frontal system, the meeting point of the southward Brazil Current, which transports subtropical relatively warm, salty, and poorly oxygenated waters, and the Malvinas Current, carrying subantarctic relatively fresh, cold, and highly oxygenated waters. Here we examine the conditions in the confluence at the time of the TIC‐MOC cruise, paying special attention to their previous evolution. South of the confluence (39–40°S), the circulation is characterized by a relatively weak along‐slope Malvinas Current and an interior intense dipole while north of the confluence the main current is the along‐slope Brazil Current; the southern and northern inputs conduce to a very intense eastward along‐front South Atlantic Current. We find that the conditions at the confluence are forced by both the impinging boundary currents and the interior ocean conditions. Further, the confluence is a site where subantarctic waters flow underneath the subtropical layers and recirculate south after experiencing substantial transformations in the subtropical gyre. We may conclude that the confluence acts both as a barrier and a blender of subtropical and subantarctic waters, of especial relevance in the meridional transport of heat and other properties. Key Points: We apply an inverse model to determine barotropic, baroclinic, and total volume transports at two different spatial scales encircling the Brazil‐Malvinas ConfluenceBoth cruise and model data show a weak along‐slope Malvinas Current at 41°S (28 Sv) and a much more intense northward interior branch (79 Sv) into the confluenceThe confluence holds substantial cross‐frontal exchange, including the subduction of subantarctic layers and their diapycnal mixing with subtropical waters [ABSTRACT FROM AUTHOR]

Abstract: It has been suggested that the Subtropical Shelf Front (STSF) could be a preferential site for the detrainment of Subantarctic Shelf Water (SASW) and related planktonic shelf species onto the open SW Atlantic Ocean. The offshore detrainment of SASW and planktonic shelf species might be an exportation mechanism, affecting the population abundances of fishing resources in Argentina, Uruguay, and Southern Brazil. In this study, we characterize for the first time the 3‐D structure of the STSF and the main routes of offshore export of SASW from the Patagonian shelf during austral summer (summer and early fall) and winter (winter and early spring) by using numerical hydrodynamical model results and Lagrangian tracking simulations of neutrally buoyant floats. The transport of SASW toward the open ocean is ~1 Sv (1 Sv = 106 m3/s) during summer and ~0.8 Sv during winter. SASW are exported offshore mainly near the Brazil‐Malvinas Confluence region during both seasons. The STSF appears to act as an important retention mechanism for the plankton over the inner and middle shelf mainly during late summer and early fall. Our findings could explain the life cycle of distinct fish species that are distributed in the region, as well as the population abundance variability of such species. [ABSTRACT FROM AUTHOR]