Search

The Argentine Continental Shelf and its shelf break are among the most productive marine areas in the world, sustaining a high biodiversity and biomass of seabirds. The at-sea distribution of these species is greatly affected by biological and physical variability. Most prior studies about assemblages of seabirds in the study area are restricted to waters south of 40°S during the austral summer. This study aims to describe and analyze the seabird assemblages associated with the Brazil–Malvinas Confluence area off the coast of northern Patagonia, Argentina during the austral winter, and the effect environmental variability exerts on species richness and abundance in pelagic areas. Data were collected during an oceanographic survey performed between May and June 2022, in continental shelf and oceanic waters (37−41°S, 53−58°W). A total of 968 individuals belonging to 21 species were observed with the Black-browed albatross, the White-chinned petrel, and the Atlantic petrel being the most abundant and frequent species recorded. The highest seabird abundances and species richness were recorded along the continental shelf and shelf break (38º00'−38º30'S). Wind direction, wind intensity, cloudiness, and atmospheric pressure had significant effects on seabird abundance and richness. The study area is of particular interest for the extraction of both living and non-renewable resources; thus, the information provided by this study can contribute to better administration of fisheries, as well as to the creation of management plans for the exploitation of non-renewable resources. [ABSTRACT FROM AUTHOR]

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 Brazil–Malvinas Confluence (BMC) is one of the most complex oceanic areas in the Earth's oceans and the prediction of high frequency structures tends to fail. The authors studied the BMC using Multiscale Ultrahigh Resolution (MUR) imagery for the Sea Surface Temperature (SST) to address why the predictions are not as good as expected. The studies were carried out by means of two approaches. The first approach is the non-linear fitting of a harmonic model keeping the frequencies as parameters pixel by pixel. The second approach is from fractal geometry. The three first q-order Rényi dimensions were computed. At the same time, an inverse fractal interpolation was carried out to compute the contraction factor. Both of them are related to the chaotic behavior of nature. This work has three relevant contributions. The correlation between the harmonic models and the SST data is quite poor in general, implying the low harmonicity, and low harmonic predictability, of the pixel-by-pixel time series. It is verified that the quasi-annual and quasi-semiannual waves have periods of about 420 and 210 days, respectively. The second one is the confirmation of the high complexity of the BMC area because the three Rényi dimensions are equal. This has the strong finding of the monofractality of the dynamic of the SST in the BMC. Finally, the contraction factor, one of the parameters of the fractal interpolation, is relatively high, implying the presence of highly complex internal structures in the SST temporal evolution. [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]

The Brazil–Malvinas Confluence (BMC) is one of the most complex oceanic areas in the Earth’s oceans and the prediction of high frequency structures tends to fail. The authors studied the BMC using Multiscale Ultrahigh Resolution (MUR) imagery for the Sea Surface Temperature (SST) to address why the predictions are not as good as expected. The studies were carried out by means of two approaches. The first approach is the non-linear fitting of a harmonic model keeping the frequencies as parameters pixel by pixel. The second approach is from fractal geometry. The three first q-order Rényi dimensions were computed. At the same time, an inverse fractal interpolation was carried out to compute the contraction factor. Both of them are related to the chaotic behavior of nature. This work has three relevant contributions. The correlation between the harmonic models and the SST data is quite poor in general, implying the low harmonicity, and low harmonic predictability, of the pixel-by-pixel time series. It is verified that the quasi-annual and quasi-semiannual waves have periods of about 420 and 210 days, respectively. The second one is the confirmation of the high complexity of the BMC area because the three Rényi dimensions are equal. This has the strong finding of the monofractality of the dynamic of the SST in the BMC. Finally, the contraction factor, one of the parameters of the fractal interpolation, is relatively high, implying the presence of highly complex internal structures in the SST temporal evolution.

The variability and drivers of the cross-shelf exchanges between the Southwestern Atlantic shelf and the open ocean from 30 to 40°S are analyzed using a high-resolution ocean model reanalysis at daily resolution. The model's performance was first evaluated using altimetry data, and independent mooring and hydrographic data collected in the study area. Model transports are in overall good agreement with all other estimates. The record-mean (1993–2018) cross-shore transport is offshore, 2.09 ± 1.60 Sv. 73% of the shelf-open ocean exchange occurs in the vicinity of Brazil-Malvinas Confluence (~38°S) and 20% near 32°S. This outflow is mostly contributed by northward alongshore transport through 40°S (63%) and the remaining by southward transport through 30°S (37%). The cross-shore flow presents weak seasonal variations, with a maximum in austral summer, and high variability at subannual and weekly time scales. The latter is mainly associated with abrupt wind changes generated by synoptic atmospheric systems. Alongshore wind variations set up sea-level changes in the inner shelf which in turn drive large anomalies in the associated geostrophic alongshore flow. The difference in inner shelf sea-level anomalies at 30 and 40°S is a good indicator of cross-shelf exchange at seasonal and shorter time scales. Episodes of extreme offshore transport that reach up to 9.45 Sv and last about 2 days are driven by convergence of these alongshore flows over the shelf. Large exports of shelf waters lead to freshening of the upper open ocean as revealed by in-situ and satellite observations. In contrast, onshore extreme events drive open ocean water intrusions of up to 6.53 Sv and last

Planktonic foraminifera census data have been widely used to reconstruct changes in ocean ecosystems as well as ocean chemistry and circulation through calibration functions. Here we analyse new core‐top census data from 22 sites in the western South Atlantic, improving the geographical coverage and spatial resolution of the environmental gradients from the region covered by the Brazil–Malvinas Confluence (˜38°S–53°W). We combine them with previous data to provide an up‐to‐date compilation of the western South Atlantic planktonic foraminifera–calibration data set. We study the relationship between the assemblages present in the core‐top samples and the most dynamic environmental variables from the region to establish the environmental variable(s) more resolved by the assemblages. Therefore, we develop and assess a new calibration function using the data set and testing several statistical models at different water depths. Our results reveal that the distribution and abundance of the species in the Brazil–Malvinas Confluence region mainly reflect the influence of two environmental variables: the mixed layer temperature and mixed layer depth (57% of total variance). The most precise reconstructions were obtained when using sub‐surface temperatures between 40 and 50 m water depth. The application of the calibration function to a Holocene sediment core at ˜37°S–53°W revealed mean annual sub‐surface temperature reconstructions between 8°C and 11°C, confirming the northward displacement of the Brazil–Malvinas Confluence during the onset of the Holocene and suggesting a major influence of the Malvinas Current during the entire Holocene at the studied site. [ABSTRACT FROM AUTHOR]

This dataset, gathered during the RETRO-BMC cruise, reports multiple-scale measurements at the Confluence of the Brazil and Malvinas Currents. The cruise was carried out between 8 and 28 April 2017 onboard R/V Hespérides, departing from Ushuaia and arriving to Santos. Along its track, the vessel recorded near-surface temperature and salinity, as well as the horizontal flow from 20 m down to about 800 m. A total of 33 hydrographic stations were completed in a region off the Patagonian Shelf, within 41.2°S–35.9°S and out to 53.0°W. At each station, a multiparametric probe and velocity sensors were deployed inside the frame of a rosette used to collect water samples at selected depths; these samples were later used for several water analyses, including inorganic nutrient concentrations. Microstructure measurements were carried out in 11 of these hydrographic stations. In addition, two high-resolution three-dimensional surveys were conducted with an instrumented undulating vehicle between 40.6°S–39.0°S and 55.6°W–53.8°W. Lastly, eight high-frequency vertical profilers were deployed in the region and five position-transmitting drifters were launched. These data allow the description of the Confluence from the regional scale to the microscale, and provide a view of the variability of the frontal region on time scales from days to weeks.

Turbulent air–sea heat fluxes were computed from in situ high‐frequency micrometeorological data during two research cruises performed in the southwestern Atlantic Ocean (SWAO) occurring in June 2012 and October 2014. Two different and dynamical areas were covered by the cruises: the Brazil‐Malvinas Confluence (BMC) and the Southern Brazilian Continental Shelf (SBCS). The eddy covariance (EC) method was used to estimate the air–sea sensible‐ and latent‐heat fluxes. This article compares these novel high‐frequency estimates of heat fluxes with bulk parametrizations made at the same location and time from independent measurements taken on board the ships. When comparing the EC and bulk‐estimated time series of sensible‐heat fluxes, we found a good agreement both in their magnitude and variability, with small bias (generally <20 W·m−2) between the datasets from the two study areas in the SWAO. However, the EC and bulk latent‐heat flux comparisons show large biases ranging from 75 W·m−2 to 100 W·m−2 in the SBCS and BMC, respectively. These biases were always associated with short‐term, high‐frequency environmental perturbations occurring either in the atmosphere or in the ocean with the majority related to strong wind burst events and large air–sea temperature gradients. The short period changes in atmospheric conditions were mostly related to the passage of transient synoptic systems over the two study areas. The large air–sea temperature gradients were mostly linked to the surface characteristics of the BMC and SBCS regions, where sharp oceanographic fronts are located. Our results are able to contribute to improving weather and climate simulations of the mid‐ to high latitudes of South America, a region largely influenced by the sea‐surface temperature patterns of the SWAO in combination with the frequent propagation of transient atmospheric systems. [ABSTRACT FROM AUTHOR]

Ocean frontal systems may act both as barriers and mixers between different water masses, the latter thanks to very energetic structures with relatively short temporal and spatial scales. Here, we explore the high‐frequency temperature variability in the Brazil‐Malvinas Confluence through the joint analysis of novel high‐resolution SeaSoar measurements and sea surface temperature imagery. Surface spatiotemporal correlation scales range between 1.5 and 6 days and between 20 and 50 km, with the shortest scales along the shelf‐break path of the Brazil Current and over the confluence and the longest ones along the Malvinas Current. The spatial scales display minima along the front, at the surface because of the presence of brackish shelf waters and at the subsurface due to both mesoscale and submesoscale thermohaline intrusions. The smallest cross‐frontal vertical correlations, in the 5‐ to 10‐m range, are associated with submesoscale processes. Overall, temperature variability is enhanced at depth in the frontal system. Plain Language Summary: The analysis of correlation scales may be used to recognize the spatial and temporal coherence of ocean properties, which allows identifying the main forcing mechanisms and dynamic processes in a certain oceanic region. This is of special relevance in frontal systems, which may possibly appear as barriers between different water masses but, because of enhanced activity with relatively short temporal and spatial scales, may also behave as water mixers. Here, we use high‐resolution satellite imagery and in situ novel measurements to examine the temporal and spatial temperature correlation scales in the Southwest Atlantic Ocean; our focus is on the Brazil‐Malvinas Confluence, a very intense open‐ocean frontal system that has extraordinary importance in the global overturning circulation. Our results show that indeed the frontal system is the locus of high‐frequency small‐scale processes, which likely act as an efficient mechanism for the down‐gradient transfer of properties. Further, these processes are smaller and faster at the subsurface (down to at least 200 m) than at the sea surface. Our results emphasize the necessity of understanding and monitoring these subsurface processes if we are to properly represent those regional processes that bear global implications. [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 (BMC) is one of the most dynamical regions of the global ocean. Its variability is dominated by the mesoscale, mainly expressed by the presence of meanders and eddies, which are understood to be local regulators of air-sea interaction processes. The objective of this work is to study the local modulation of air-sea interaction variables by the presence of either a warm (ED1) and a cold core (ED2) eddy, present in the BMC, during September to November 2013. The translation and lifespans of both eddies were determined using satellite-derived sea level anomaly (SLA) data. Time series of satellite-derived surface wind data, as well as these and other meteorological variables, retrieved from ERA5 reanalysis at the eddies’ successive positions in time, allowed us to investigate the temporal modulation of the lower atmosphere by the eddies’ presence along their translation and lifespan. The reanalysis data indicate a mean increase of 78% in sensible and 55% in latent heat fluxes along the warm eddy trajectory in comparison to the surrounding ocean of the study region. Over the cold core eddy, on the other hand, we noticed a mean reduction of 49% and 25% in sensible and latent heat fluxes, respectively, compared to the adjacent ocean. Additionally, a field campaign observed both eddies and the lower atmosphere from ship-borne observations before, during and after crossing both eddies in the study region during October 2013. The presence of the eddies was imprinted on several surface meteorological variables depending on the sea surface temperature (SST) in the eddy cores. In situ oceanographic and meteorological data, together with high frequency micrometeorological data, were also used here to demonstrate that the local, rather than the large scale forcing of the eddies on the atmosphere above, is, as expected, the principal driver of air-sea interaction when transient atmospheric systems are stable (not actively varying) in the study region. We also make use of the in situ data to show the differences (biases) between bulk heat flux estimates (used on atmospheric reanalysis products) and eddy covariance measurements (taken as “sea truth”) of both sensible and latent heat fluxes. The findings demonstrate the importance of short-term changes (minutes to hours) in both the atmosphere and the ocean in contributing to these biases. We conclude by emphasizing the importance of the mesoscale oceanographic structures in the BMC on impacting local air-sea heat fluxes and the marine atmospheric boundary layer stability, especially under large scale, high-pressure atmospheric conditions.

In recent decades, southern elephant seals (SES) have become a species of particular importance in ocean data acquisition. The scientific community has taken advantage of technological advances coupled with suitable SES biological traits to record numerous variables in challenging environments and to study interactions between SES and oceanographic features. In the context of big dataset acquisition, there is a growing need for methodological tools to analyze and extract key data features while integrating their complexity. Although much attention has been paid to study elephant seal foraging strategies, the continuity of their surrounding three-dimensional environments is seldom integrated. Knowledge gaps persist in understanding habitat use by SES, while the representativeness of a predator-based approach to understanding ecosystem structuring is still questioned. In this study, we explore SES habitat use by using a functional data analysis approach (FDA) to describe the foraging environment of five female elephant seals feeding in the Southwestern Atlantic Ocean. Functional principal component analysis followed by model-based clustering were applied to temperature and salinity (TS) profiles from Mercator model outputs to discriminate waters sharing similar thermohaline structures. Secondly, in situ TS profiles recorded by the SES were employed to determine the habitat visited within the range of potential environments identified from the model data. Four Functional Oceanographic Domains (FOD) were identified in the Brazil-Malvinas Confluence, all visited, in varying proportion, by four of the five females studied. We found that the females favored areas where all the FODs converge and mix, generating thermal fronts and eddies. Prey-capture attempts increased in such areas. Our results are in accordance with previous findings, suggesting that (sub-)mesoscale features act as biological hotspots. This study highlights the potential of coupling FDA with model-based clustering for describing complex environments with minimal loss of information. As well as contributing to better understanding of elephant seal habitat use and foraging strategies, this approach opens up a wide range of applications in oceanography and ecology. • Functional data analysis coupled with clustering can identify oceanographic domains. • A functional oceanographic domain possesses similar vertical thermohaline features. • Coupling model data with elephant seal profiles allows to characterize habitats use. • The studied elephant seals tend to visit all oceanic domains in varying proportion. • Prey captures of elephant seals increase with high probabilities of changing domains. [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]

Copyright of Anuario do Instituto de Geociencias is the property of Universidade Federal do Rio de Janeiro, Instituto de Geociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The oceanographic dynamics on the continental shelf off southeastern South America are primarily controlled by the southward-flowing warm Brazil Current, converging with the northward-directed cold Malvinas (Falkland) Current, and interacting with the continental discharge of the Plata River. The seasonally reversing regional wind field together with the seasonal cycle of riverine discharge, determines which of these three components provides the dominant forcing. The Uruguayan shelf is thus located in a transitional zone that extends from the region influenced by the Brazil-Malvinas Confluence (BMC) in the open ocean to the Subtropical Shelf Front (STSF) on the continental shelf. Understanding how the resulting oceanic seasonal variability responded to different climatic boundary conditions may shed light on its future behavior. This study presents the first reconstruction of mid-deglacial seasonal hydrographic variability on the continental shelf off southeastern South America in seasonal resolution based on stable oxygen and carbon isotopes (δ18O, δ13C) from a thick-walled shell of a long-living bivalve. The mid-deglacial (14.3 cal ka BP; Bølling-Allerød interstadial) Retrotapes exalbidus bivalve shows a mean δ18O of 3.27 ± 0.42‰ (2.50 ± 0.42‰ when corrected for changes in global ice volume) and a seasonal δ18O amplitude of 1.69‰ for raw isotopic excursions. Moreover, the δ13C exhibits abrupt negative peaks coincident with more negative δ18O values that indicate seasons of elevated freshwater discharge. Finally, the growth rate of the bivalve suggests that the specimen was closer to the metabolically optimum than modern individual of this species from southern South America. Combining biogeographic and ecologic information with these isotopic data, the results point to colder waters and a slightly lower mid-deglacial seasonal amplitude in temperature compared with modern conditions at this shelf site. Because of the northward-displaced Plata River mouth during deglacial times, negative δ13C peaks are expected to reflect an influence of non-point freshwater sources in the form of small fluvial distributaries along the paleo-coast. Most of this signal may, however, be driven by seasonal metabolic effects associated with low ambient water temperatures related to a shallow-water environment located closer to the respective paleo-coastline due to the low sea level at those times. • This study offers the first high-res reconstruction of seasonal oceanic variability off southeastern South America (SESA) during mid-deglacial. • We analyzed a 6-yr 18O and 13C isotope record of a long-living bivalve. • Reconstructing ocean water parameters without species-specific paleo-temperature equations is challenging. • Our data suggests colder waters and more variable variable nearshore salinity during Bølling-Allerød interstadialCoincident and abrupt negative peaks in δ18O and δ13C suggest freshwater discharge pulses. [ABSTRACT FROM AUTHOR]

This article presents the results of a summer survey of marine mammal occurrence at the Brazil-Malvinas Confluence in the Argentine Sea shelf break. A total of 61 marine mammal sightings were recorded. The most frequent species recorded were South American fur seals (Arctocephalus australis; 75.4%; 78-4670 m), followed by sperm whales (Physeter macrocephalus; 8.2%; 478-2825m), sei whales (Balaenoptera borealis; 4.9%; 1513-4674 m) and long-finned pilot whales (Globicephala melas; 3.3%; 1119-1534m), with a small number of unidentified cetaceans (4.9%; 87-2248 m). This new information about marine mammal species in the Brazil-Malvinas Confluence updates knowledge of their distribution in this highly productive area. [ABSTRACT FROM AUTHOR]

In the present study, the distribution and abundance of microphytoplankton were assessed in the southwestern Atlantic Ocean from subtropical to polar waters (34°-62°S) in two austral springs with contrasting hydrographic conditions. Vertical profiles of open-ocean (ca. 54°W) samples (≥ 18 L filtered water) were performed in 20 stations (0-100 m) in 1994 and in 17 stations (0-50 m) in 1995. The latitudinal patterns of microphytoplankton groups, chlorophyll a, and diatom and silicoflagellate species were analyzed and compared with our previous study carried out in spring 1993 (30°-61°S). In the three springs, 197 diatom species, 173 of which showed mean relative density lower than 1 %, were identified. A consistent diatom biogeographic pattern emerged in the three consecutive springs, defining the Transitional (corresponding to the Brazil-Malvinas Current Confluence), Subantarctic and Antarctic Zones; and the Subantarctic and Polar Fronts, as their boundaries. This zonation reflects persistent features of this hydrographically heterogeneous region. The Polar Front was a weaker biogeographic boundary for diatom species than the Subantarctic Front. Interannual changes in diatoms (mainly in species richness, dominant species and degree of dominance of species with different ecological affinities) were detected. The Transitional Zone, which is one of the most hydrographically variable regions of the world ocean, showed the highest changes in the diatom assemblage, reflecting a colder spring in 1995 and a warmer spring in 1994 than normal (1993). These changes agreed with differences reported for 1993-1995 in large-scale hydrographic conditions, including a widespread diversity decrease in 1995 due to a weaker influence of subtropical waters. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) anomaly events in the Brazil-Malvinas Confluence (BMC) were investigated through wavelet analysis and numerical modeling. Wavelet analysis was applied to recognize the main spectral signals of SST anomaly events in the BMC and in the Drake Passage as a first attempt to link middle and high latitudes. The numerical modeling approach was used to clarify the local oceanic dynamics that drive these anomalies. Wavelet analysis pointed to the 8-12-year band as the most energetic band representing remote forcing between high to middle latitudes. Other frequencies observed in the BMC wavelet analysis indicate that part of its variability could also be forced by low-latitude events, such as El Niño. Numerical experiments carried out for the years of 1964 and 1992 (cold and warm El Niño-Southern Oscillation (ENSO) phases) revealed two distinct behaviors that produced negative and positive sea surface temperature anomalies on the BMC region. The first behavior is caused by northward cold flow, Río de la Plata runoff, and upwelling processes. The second behavior is driven by a southward excursion of the Brazil Current (BC) front, alterations in Río de la Plata discharge rates, and most likely by air-sea interactions. Both episodes are characterized by uncoupled behavior between the surface and deeper layers. [ABSTRACT FROM AUTHOR]

Abstract: The hydrology of the Southwestern Atlantic margin is dominated by the confluence of water masses with contrasting thermohaline properties, generating a frontal zone that extends from the Brazil-Malvinas Confluence zone (BMC) in the open ocean to the Subtropical Shelf Front (STSF) on the continental shelf. However, the hydrodynamics of the transition between these hydrographic features is still not fully understood. High-resolution morphological (multibeam) and hydrological (CTD) data were integrated with sedimentological data (textural and productivity proxies) in order to develop a sound framework to understand surface sedimentation of the slope extension of the STSF (subsurface, outer shelf and upper slope) and of the BMC (intermediate level, middle slope) on the Uruguayan continental margin (34° to 36°S). Since the detailed morphology of the study area is presented for the first time, related geological processes are briefly discussed. On the outer shelf and upper slope, and north of the STSF, the current direction of erosive mound scarps indicates the dominance of the southward-flowing Brazil Current (BC). This suggests a northernmost boundary for the distribution of the STSF. A strong flux of the BC favored by a steeper slope as well as by the occurrence of canyons incised on the upper slope is evidenced by the occurrence of coarser sediments and low values of productivity proxies, but also by the presence of deep sea coral reefs. Southwards, the effect of a less energetic Malvinas Current (MC) and the highly productive STSF is indicated by the deposition of fine sediments with high organic matter content, as well as by the absence of deep sea coral reefs. This depositional scenario is enhanced by a smooth slope and the occurrence of canyons incised deeper in the middle slope. Off-shelf sediment transport along the STSF is inferred by the similar texture registered between the outer shelf and shallow upper slope, the occurrence of biogenic shelly reworked sands and gravel, and by the observed decrease in grain size with depth. Glacial iceberg transport northwards and/or gravity processes are suggested by the occurrence of igneous/metamorphic gravel in lag deposits on the upper slope. On the middle slope, the northernmost influence of the erosive Antarctic Intermediate Water is evidenced by the vanishing of morphologic contouritic structures. This is also imprinted in a pronounced northward fining in grain size. This contribution increase our understanding of this highly dynamic and complex area, providing the first detailed analysis of the regional sediment patterns and oceanographic and morphological controls on surface sedimentation. [Copyright &y& Elsevier]

The Brazil-Malvinas Confluence (BMC) region constitutes one of the most important ocean features in the South Atlantic Ocean basin. Understanding the BMC upper ocean temperature variability could represent one of the key factors to understanding its connection to local and global ocean circulation. Some important local and remote ocean processes are related to the annual and interannual variability of its thermal/salt front position. This paper investigates the upper ocean variability in the BMC region under the influence of an El Niño/Southern Oscillation-type wind stress field using an oceanic general circulation model (Modular Ocean Model version 4.0). The results revealed the occurrence of positive anomalies, with values ranging from 0.5ºC to 1.0ºC (centered at 40.5ºS and 55.0ºW), near the BMC region associated with upper ocean velocity anomalies during the peak of the ocean kinetic energy phase. This mechanism was a response of a volume transport balance between the Brazil Current (BC) and the Malvinas Current (MC), the latter being accelerated by the Antarctic Circumpolar Current (ACC). The occurrence of positive anomalies was always associated with an enhanced BC meridional surface volume transport, together with a decrease of the ACC zonal volume transport, vertically integrated across the Drake Passage, and a correspondent decrease in the upper layer MC volume transport. It was possible to see negative upper layer temperature anomaly predominance just before the peak ocean kinetic energy month and positive anomaly predominance immediately following this month. The occurrence of upper layer temperature anomalies in the BMC region was not restricted to just the peak ocean kinetic energy month since they occurred throughout the perturbed experiment integration time.

This study uses nine years of daily 9-km Pathfinder AVHRR/NOAA Sea Surface Temperature (SST) images to estimate the SST temporal variability of the southwestern Atlantic Ocean on time-scales ranging from sub-seasonal to inter-annual. First, we evaluated the annual and semi-annual deterministic signals in the total variability of the SST fields using a least-squares fit. We then removed the annual and semi-annual components from the original data and used a low-pass filter to estimate the contribution of the inter-annual component of total variability. Finally, the inter-annual signal was removed and the variance associated to the remaining residuals was calculated to address the intra-annual component. The annual signal was found to dominate over the area with a coefficient of determination higher than 85%, with amplitudes ranging from 1° to 13°C. The largest amplitudes were found on the continental shelf, with the highest values near the La Plata River estuary as a consequence of the river runoff. The semi-annual signal was significant near the Brazil/Malvinas Confluence (BMC), due to mesoscale activity with same periods. The Southern Annular Mode (SAM) appeared to be related to the high values of semi-annual amplitudes found close to 50º S, 65º W. The results for the oceanic area north of BMC showed that the region between 24°S and 32°S had semi-annual amplitudes close to 1.5°C. We suggested that this high amplitude was related to the South Atlantic Convergence Zone. The domain, as a whole, experienced weak inter-annual variations, except in the vicinity of the BMC where higher values (~1.2º C) were found. The Argentine shelf and the South Brazil Bight also presented significant inter-annual variability related to the inter-annual variations in the La Plata river discharge forced by ENSO events. The region close to the BMC and the South Atlantic Current were associated with high intra-annual variances due to intense mesoscale activity normally observed in these areas. Low intra-annual variance found in the Zapiola Drift was related to the anticyclone flow in this region which tended to isolate the circulation in the center of the drift. This gyre was forced by the meso-scale events of the BMC and the Antarctic Circumpolar Current that appeared as high values of intra-annual variance around the Zapiola Drift. The higher resolution SST data set, the longer time series and the larger domain permitted to identify new and important oceanographic features and to extend the results already reported in the southwestern Atlantic.

The South Atlantic (SA) circulation plays an important role in the oceanic teleconnections from the Indian, Pacific and Southern oceans to the North Atlantic, with inter-hemispheric exchanges of heat and salt. Here, we show that the large-scale features of the SA circulation are projected to change significantly under ‘business as usual’ greenhouse gas increases. Based on 19 models from the Coupled Model Intercomparison Project phase 5 there is a projected weakening in the upper ocean interior transport (1000 m), mainly related to a decrease in the North Atlantic deep water transport. Between 30° and 40°S, there is a consistent projected intensification in the Brazil current strength of about 40% (30%–58% interquartile range) primarily compensated by an intensification of the upper interior circulation across the Indo-Atlantic basin. The Brazil–Malvinas confluence is projected to shift southwards, driven by a weakening of the Malvinas current. Such a change could have important implications for the distribution of marine species in the southwestern SA in the future.

Abstract: Bottom currents and their margin-shaping character became a central aspect in the research field of sediment dynamics and paleoceanography during the last decades due to their potential to form large contourite depositional systems (CDS), consisting of both erosive and depositional features. A major CDS at the northern Argentine continental margin was studied off the Rio de la Plata River by means of seismo- and hydro-acoustic methods including conventional and high-resolution seismic, parametric echosounder and single and swath bathymetry. Additionally, hydrographic data were considered allowing jointly interpretation of morphosedimentary features and the oceanographic framework, which is dominated by the presence of the dynamic and highly variable Brazil–Malvinas Confluence. We focus on three regional contouritic terraces identified on the slope in the vicinity of the Mar del Plata Canyon. The shallowest one, the La Plata Terrace (∼500m), is located at the Brazil Current/Antarctic Intermediate Water interface characterized by its deep and distinct thermocline. In ∼1200m water depth the Ewing Terrace correlates with the Antarctic Intermediate Water/Upper Circumpolar Deep Water interface. At the foot of the slope in ∼3500m the Necochea Terrace marks the transition between Lower Circumpolar Deep Water and Antarctic Bottom Water during glacial times. Based on these correlations, a comprehensive conceptual model is proposed, in which the onset and evolution of contourite terraces is controlled by short- and long-term variations of water mass interfaces. We suggest that the terrace genesis is strongly connected to the turbulent current pattern typical for water mass interfaces. Furthermore, the erosive processes necessary for terrace formation are probably enhanced due to internal waves, which are generated along strong density gradients typical for water mass interfaces. The terraces widen through time due to locally focused, partly helical currents along the steep landward slopes and more tabular conditions seaward along the terrace surface. Considering this scheme of contourite terrace development, lateral variations of the morphosedimentary features off northern Argentina can be used to derive the evolution of the Brazil–Malvinas Confluence on geological time scales. We propose that the Brazil–Malvinas Confluence in modern times is located close to its southernmost position in the Quaternary, while its center was shifted northward during cold periods. [Copyright &y& Elsevier]

Abstract: Surface currents and sediment distribution of the SE South American upper continental margin are under the influence of the South American Monsoon System (SAMS) and the Southern Westerly Wind Belt (SWWB). Both climatic systems determine the meridional position of the Subtropical Shelf Front (STSF) and probably also of the Brazil–Malvinas Confluence (BMC). We reconstruct the changing impact of the SAMS and the SWWB on sediment composition at the upper Rio Grande Cone off southern Brazil during the last 14cal kyr BP combining sedimentological, geochemical, micropaleontological and rock magnetic proxies of marine sediment core GeoB 6211-2. Sharp reciprocal changes in ferri- and paramagnetic mineral content and prominent grain-size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments. Our interpretations support the assumption that the SAMS over SE South America was weaker than today during most of the Late Glacial and entire Early Holocene, while the SWWB was contracted to more southern latitudes, resembling modern austral summer-like conditions. In consequence, the STSF and the BMC were driven to more southern positions than today's, favoring the deposition of Fe-rich but weakly magnetic La Plata River silts at the Rio Grande Cone. During the Mid Holocene, the northern boundary of the SWWB migrated northward, while the STSF reached its northernmost position of the last 14cal kyr BP and the BMC most likely arrived at its modern position. This shift enabled the transport of Antarctic diatoms and more strongly magnetic Argentinean shelf sands to the Rio Grande Cone, while sediment contributions from the La Plata River became less important. During the Late Holocene, the modern El Niño Southern Oscillation set in and the SAMS and the austral tradewinds intensified, causing a southward shift of the STSF to its modern position. This reinforced a significant deposition of La Plata River silts at the Rio Grande Cone. These higher magnetic silts with intermediate Fe contents mirror the modern more humid terrestrial climatic conditions over SE South America. [Copyright &y& Elsevier]

Abstract: Large sedimentary deposits consisting of several major contourite drifts were studied by means of high-resolution multichannel seismic data at the middle slope along the Northern Argentina Continental Margin to determine their evolutionary stages as well as to identify and assess the possible impact of Northern Source Deep Water (NSDW) on the slope architecture. The imaged contouritic sediments allow decoding on the regional paleo-oceanographic setting of the last 32Ma. Earliest contouritic sedimentation can be observed close to the Eocene/Oligocene boundary based on an aggradational stacking pattern with a complex and wavy seismic facies, pointing toward a hydrodynamically turbulent flow pattern. This facies is most likely related to the opening of the Drake Passage associated with global cooling and a strengthening of surface, intermediate and deep ocean currents in the Southern Ocean. During the Middle Miocene plastered drift sequences with an aggradational reflection pattern were deposited. Their depositional style indicates weak, non-turbulent current conditions, which are interpreted to be related to a vertical shift of water mass interfaces caused by the first formation of NSDW during the Mid-Miocene climatic optimum. On top, the formation of plastered drift sequences led to the modern extent of the Ewing Terrace, which was probably controlled by the continuous strengthening and thickening of NSDW until the final closure of the Central American Seaway (CAS). During the Pliocene and Quaternary, after the complete closure of the CAS and under the influence of the full force of the NSDW, mounded plastered drift sequences are built upon the Ewing Terrace generating the modern slope morphology. Therefore, we suggest that deep-water production in the northern hemisphere plays a significant role by controlling the shape of the continental slopes in the southwestern South Atlantic since the Middle Miocene. [Copyright &y& Elsevier]

This study investigates the relationships between the spring phytoplankton community and environmental factors in the Brazil-Malvinas confluence region. Phytoplankton community composition was determined by the high performance liquid chromatography/CHEMTAX approach, complemented with microscopic examination. Abiotic factors included temperature, salinity, dissolved inorganic macronutrients (ammonium, nitrite, nitrate, phosphate and silicate), water column stability and upper mixed layer depth (UMLD). These environmental variables were reasonably informative to explain the variability of the phytoplankton communities (44% of variation explained). Cluster and canonical correspondence analyses allowed discrimination of four zones (coastal, Sub-Antarctic, tropical and intermediate zones), also identifiable in the T–S diagrams and in the nutrient spatial distribution patterns. The presence of nutrient-rich Sub-Antarctic waters was a major oceanographic feature, associated with diatoms and dinoflagellates. However, in the Sub-Antarctic zone, biomass was particularly low, probably as a result of grazing pressure, as suggested by chemical and biological indicators. In contrast, in oligotrophic tropical waters, phytoplankton was mainly composed by small nanoflagellates and cyanobacteria. A large intermediate zone was also dominated by nanoflagellates, mainly Phaeocystis antarctica, probably favored by strong water column stability. The coastal zone exhibited fairly similar conditions to those in the intermediate zone, but with deeper UMLD, a favorable condition for diatom growth. These results emphasize the importance of the properties of water masses and also biological processes such as grazing in structuring phytoplankton communities in the region. [ABSTRACT FROM AUTHOR]

Abstract: We explored the potential to use the stable isotopic compositions of planktonic foraminifera as a proxy for the position of the Brazil-Malvinas Confluence (BMC) in the Argentine Basin. For this purpose, we measured the oxygen and carbon isotopic compositions of Globigerinoides ruber (pink and white varieties measured separately), Globigerinoides trilobus, Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides (left- and right-coiling forms measured separately) from a latitudinal transect of 56 surface sediment samples from the continental slope off Brazil, Uruguay and Argentina between 20 and 48°S. Lowest oxygen isotopes values were found in G. ruber (pink), followed by G. ruber (white) and G. trilobus reflecting the highly stratified near surface water conditions north of the BMC. Globigerina bulloides was present mainly south of the BMC and records subsurface conditions supporting earlier plankton tow studies. Globorotalia inflata and G. truncatulinoides (left and right) were both available over the whole transect and calcify in the depth level with the steepest temperature change across the BMC. Accordingly, the δ 18O of these species depict a sharp gradient of 2‰ at the confluence with remarkably stable values north and south of the BMC. Our data show that the oxygen isotopic composition of G. inflata and G. truncatulinoides (left and right) are the most reliable indicators for the present position of the BMC and can therefore be used to define the past migration of the front if appropriate cores are available. [Copyright &y& Elsevier]

Abstract: Recent studies have revealed that lateral transport and focusing of particles strongly influences the depositional patterns of organic matter in marine sediments. Transport can occur in the water column prior to initial deposition or following sediment re-suspension. In both cases, fine-grained particles and organic-rich aggregates are more susceptible to lateral transport than coarse-grained particles (e.g., foraminiferal tests) because of the slower sinking velocities of the former. This may lead to spatial and, in the case of redistribution of re-suspended sediments, temporal decoupling of organic matter from coarser sediment constituents. Prior studies from the Argentine Basin have yielded evidence that suspended particles are displaced significant distances (100–1000km) northward and downslope by strong surface and/or bottom currents. These transport processes result in anomalously cold alkenone-derived sea-surface temperature (SST) estimates (up to 6°C colder than measured SST) and in the presence of frustules of Antarctic diatom species in surface sediments from this area. Here we examine advective transport processes through combined measurements of compound-specific radiocarbon ages of marine phytoplankton-derived biomarkers (alkenones) from core tops and excess 230Th (230Thxs)-derived focusing factors for late Holocene sediments from the Argentine Basin. On the continental slope, we observe 230Thxs-based focusing factors of 1.4–3.2 at sites where alkenone-based SST estimates were 4–6°C colder than measured values. In contrast, alkenone radiocarbon data suggest coeval deposition of marine biomarkers and planktic foraminifera, as alkenones in core tops were younger than, or similar in age to, foraminifera. We therefore infer that the transport processes leading to the lateral displacement of these sediment components are rapid, and hence probably occur in the upper water column (<1500m). [Copyright &y& Elsevier]

Abstract: Community structure and diversity patterns of planktonic copepods were investigated for the Southwestern Atlantic Ocean between 34 and 41°S. Our objectives were (1) to define copepod assemblages, (2) to accurately identify their association to different water masses/hydrodynamic regimes, (3) to characterize the assemblages in terms of their community structure, and (4) to test if frontal boundaries between water masses separate copepod assemblages. Biogeographic patterns were investigated using multivariate analysis (cluster and ANOSIM analyses). Biodiversity patterns were examined using different univariate indexes (point species richness and taxonomic distinctness). Five regions of similar copepod assemblages were defined for our study area each one corresponding to different environments (freshwater, estuarine, continental shelf, Malvinas and Brazil current assemblages). These assemblages have major community structure differences. In spite of the complex oceanographic scenario of our study area, that can lead us to expect a pattern of copepod communities with diffuse boundaries, we found a strong spatial correspondence between these limits and the presence of permanent frontal structures. [Copyright &y& Elsevier]

Abstract: A warm core eddy was detected south of the Brazil–Malvinas (Falkland) Confluence (BMC) region in satellite images of the southwestern Atlantic Ocean in late 2002. The structure was also sampled by in situ instruments deployed by a ship in 2 days of November 2002. An analysis of satellite data was performed to account for the lifecycle, dimension, surface temperature, surface chlorophyll concentration, surface height anomaly and displacement of the eddy since it was detached from the Brazil Current in September 2002. Satellite data were derived from several sources such as the AMSR-E, MODIS and radar altimeter. The structure lasted 64 days at south of the Brazil–Malvinas Confluence region later being re-assimilated by the Brazil Current return flow. In situ data collected during 2 days showed that the eddy was about 150 m deep, 5.5 °C warmer and 1 practical salinity unit saltier than adjacent waters. The salt anomaly associated to the eddy was estimated as 1.37×1012 kg while its heat content was 4.24×1018 J. These are typical estimates for eddies present at the BMC region. Sea surface temperature (SST), chlorophyll concentration, and sea surface height anomaly time series were analyzed for the eddy''s center along its trajectory path throughout its lifetime. Mean translational velocities for the eddy during its lifetime were computed from visual interpretation and by using an adaptation of the Maximum Cross-Correlation (MCC) method on AMSR-E SST images. The overall deviation between the two methods was 26%. This suggests that the MCC method has a potential to be applied in monitoring programs to automatically account for the translational velocities of eddies in the BMC region. [Copyright &y& Elsevier]

Abstract: Diversity and structure of epipelagic copepod communities were investigated using 70 zooplankton samples collected from the top 50 m of the Brazil–Malvinas Confluence area between 35° and 55°S. Biogeographic patterns were investigated using multivariate analysis. Biodiversity patterns were examined using different univariate indexes. Representatives of 35 species of copepods from 23 genera and 13 families were found. Two zones were delimited based on their copepod composition, one in the subtropical waters of the Brazil current, and the other in the subantarctic waters of the Malvinas current. Both environments displayed contrasting patterns of biodiversity depending upon which element is measured (regional species richness as well as mean point species richness were significantly higher in the subtropical group of stations, whereas taxonomic distinctness was significantly higher in the subantarctic community). Based on these contrasting results, we suggest the use of both kind of indexes when defining priority areas for conservation. [Copyright &y& Elsevier]