South Brazil Bight Research Articles

Unveiling the diversity of thaliaceans (Chordata, thaliacea) from the South Brazilian Bight and Southern Subtropical Shelf (22°-33°S)

Unveiling the diversity of thaliaceans (Chordata, thaliacea) from the South Brazilian Bight and Southern Subtropical Shelf (22°-33°S)

Hydrographic climatology of the South Brazil Bight continental shelf and slope

Hydrographic climatology of the South Brazil Bight continental shelf and slope

Salinity Fronts in the South Atlantic

Monthly climatology data for salinity fronts in the South Atlantic have been created from satellite SMOS sea surface salinity (SSS) measurements taken from 2011–2019, processed at the Barcelona Expert Center of Remote Sensing (BEC), and provided as high-resolution (1/20°) daily SSS data. The SSS fronts have been identified with narrow zones of enhanced horizontal gradient magnitude (GM) of SSS, computed using the Belkin–O’Reilly algorithm (BOA). The SSS gradient fields generated by the BOA have been log-transformed to facilitate feature recognition. The log-transformation of SSS gradients markedly improved the visual contrast of gradient maps, which in turn allowed new features to be revealed and previously known features to be documented with a monthly temporal resolution and a mesoscale (~100 km) spatial resolution. Monthly climatologies were generated and analyzed for large-scale open-ocean SSS fronts and for low-salinity regions maintained by the Rio de la Plata discharge, Magellan Strait outflow, Congo River discharge, and Benguela Upwelling. A 2000 km-long triangular area between Africa and Brazil was found to be filled with regular quasi-meridional mesoscale striations that form a giant ripple field with a 100 km wave length. South of the Tropical Front, within the subtropical high-salinity pool, a trans-ocean quasi-zonal narrow linear belt of meridional SSS maximum (Smax) was documented. The meridional Smax belt shifts north–south seasonally while retaining its well-defined linear morphology, which is suggestive of a yet unidentified mechanism that maintains this feature. The Subtropical Frontal Zone (STFZ) consists of two tenuously connected fronts, western and eastern. The Brazil Current Front (BCF) extends SE between 40 and 45°S to join the subantarctic front (SAF). The STFZ trends NW–SE across the South Atlantic, seemingly merging with the SAF/BCF south of Africa to form a single front between 40 and 45°S. In the SW Atlantic, the Rio de la Plata plume migrates seasonally, expanding northward in winter (June–July) from 39°S into the South Brazilian Bight, up to Cabo Frio (23°S) and beyond. The inner Plata front moves in and out seasonally. Farther south, the Magellan Strait outflow expands northward in winter (June–July) from 53°S up to 39–40°S to nearly join the Plata outflow. In the SE Atlantic, the Congo River plume spreads radially from the river mouth, with the spreading direction varying seasonally. The plume is often bordered from the south by a quasi-zonal front along 6°S. The diluted Congo River water spreads southward seasonally down to the Angola–Benguela Front at 16°S. The Benguela Upwelling is delineated by a meridional front, which extends north alongshore up to 20°S, where the low-salinity Benguela Upwelling water forms a salinity front, which is separate from the thermal Angola–Benguela Front at 16°S. The high-salinity tropical water (“Angola water”) forms a wedge between the low-salinity waters of the Congo River outflow and Benguela Upwelling. This high-salinity wedge is bordered by salinity fronts that migrate north–south seasonally.

Length-weight relationship of 104 demersal fish species from the continental shelf of the South Brazilian Bight captured in bottom trawl shrimp nets

Length-weight relationship of 104 demersal fish species from the continental shelf of the South Brazilian Bight captured in bottom trawl shrimp nets

Bryde’s whales in South Brazil Bight: evidence of low genetic diversity and seasonal habitat use

Bryde’s whales in South Brazil Bight: evidence of low genetic diversity and seasonal habitat use

Bio-optical properties of South Brazil Bight coastal waters and implications for satellite chlorophyll-a concentration retrieval

ABSTRACT Retrieving chlorophyll-a concentration (Chla) from remote-sensing data is especially challenging in coastal regions because of the presence of other co-dominant optically significant constituents (OSCs). In this study, we characterize bio-optical variability at a fixed coastal time series station in the South Brazil Bight (SBB), the ANTARES-Ubatuba site (São Paulo, Brazil) from radiometric measurements and water sample analyses, and evaluate the performance of ocean colour (OC) algorithms for Chla retrieval. In situ Chla and the spectral absorption of phytoplankton (aph), detritus, and coloured dissolved organic matter (CDOM), as well as the above-water remote-sensing reflectance (Rrs) were obtained from 2004 to 2019 at a quasi-monthly sampling frequency. Chla exhibited high variability, with a standard deviation twice as large as the mean (1.0 ± 1.83 mg m−3), and values ranging from 0.18 mg m−3 up to 18.09 mg m−3 during episodic bloom events. CDOM was the dominant OSC contributing to the absorption coefficient at 443 nm all-year round, suggesting the influence of continental sources, even though the station is located at the external limit of the inner shelf (40 m). Two optical water types were defined: one composed mainly of ‘blue’ waters with lower concentrations of the OSCs and another of ‘green’ waters with higher concentrations of OSCs. Despite the CDOM spectral dominance, the empirical OCx performed reasonably well with a positive bias for both in situ (17–25%) and satellite (25–31%) Chla retrievals. The performance was slightly better using the 3-band OC3 algorithm by selecting the best band ratio with lower influence of CDM (CDOM + detritus) absorption (Rrs (490/555)). The main sources of uncertainty were caused by higher CDM proportions and phytoplankton-specific absorption, yielding positive biases on the OC3 retrievals. The results suggest that standard satellite products of Chla can be used (with some caution) to monitor and study the dynamics of the phytoplankton biomass within the region, knowing the expected uncertainties.

An inventory of salty and warm subsurface intrusions in the South Brazil Bight

Subsurface intrusions of salty and warm waters onto the shelf can potentially impact the thermodynamics and biogeochemistry of these relatively shallow water environments. Such thermohaline intrusions are usually associated with double diffusive processes and can enhance the vertical and lateral fluxes. In this work, we characterized subsurface intrusions of Tropical Waters (TW) at the South Brazil Bight (SBB) - a mid-latitude continental shelf, which were detected based on salinity vertical profiles from a historical dataset. We found the intrusions tend to follow the pycnocline and are relatively common year-round, occurring at 27% of the dataset, with a maximum salinity highly correlated with the maximum stratification. Intrusions have different along-shelf characteristics, varying with the shelf width and depth. North of São Sebastião Island (SSI) – at the central portion of the SBB –, intrusions were thicker, saltier, and shallower than the ones found at the south of SSI. These differences could be related to the variations of the Coastal Water (CW) and South Atlantic Central Water (SACW) volume along the shelf and throughout the year. We found that intrusions’ thickness presents an inverse correlation with stratification, resulting in thinner intrusions in more stratified environments. This inverse correlation suggests double-diffusively driven intrusions. We apply the Turner Angle method to investigate whether the environment is susceptible to double diffusive processes. This analysis suggests that thermohaline intrusions in the SBB might not be primarily double diffusive. However, the dominance of different double diffusion processes - diffusive convection (salt fingering) at the upper (lower) layer - suggests that these processes influence intrusion growth, steady-state, and erosion. Nonetheless, the mechanism responsible for the initial density perturbation remains unknown and further studies are needed to explore the relationship between the Brazil Current dynamics and thermohaline warm and salty subsurface intrusions.

Identifying Whitemouth Croaker (Micropogonias furnieri) Populations along the Rio de Janeiro Coast, Brazil, through Microsatellite and Otolith Analyses.

The inshore area of the Southwestern Atlantic between 22 °S and 29 °S (South Brazilian Bight) is a transitional climatic zone, where the tropical and warm temperate provinces mix. In its northern part, i.e., in the coastal waters of Rio de Janeiro, Brazil, local oceanographic conditions, such as upwelling in the north, and great bays with different degrees of anthropogenic influences in the center and south can determine the population structure of several fish stocks. The Whitemouth croaker (Micropogonias furnieri) is one the most heavily exploited fishing resources in this area, but there are still some doubts about its population structure. In this study, through combined analyses using nuclear genetic markers and morphological and geochemical signatures of otoliths, a divergence of individuals between two populations was identified using microsatellites, while a finer spatial structure with three populations (north, center and south, respectively) was found based on otolith shapes and elemental signatures. This regional population structure may have direct implications for rational fisheries management and conservation of the species.

Supplementary materials of the article "On the trophic role of pelagic fishes and fishery landings shifts in the South Brazil Bight"

Supplementary materials of the article "On the trophic role of pelagic fishes and fishery landings shifts in the South Brazil Bight"

Supplementary materials of the article "On the trophic role of pelagic fishes and fishery landings shifts in the South Brazil Bight"

Supplementary materials of the article "On the trophic role of pelagic fishes and fishery landings shifts in the South Brazil Bight"

On the trophic role of pelagic fishes and fishery landings shifts in the South Brazil Bight

Knowledge of the feeding habits of pelagic fishes off the Brazilian coast is scarce, making the analysis of trophic interactions often inaccurate. Here, we investigated the diet and trophic role of 12 pelagic fish species by revisiting samples obtained by the ECOSAR II Program (FURG/IO/IBAMA) between 23°S and 28°40'S, an area also known as South Brazil Bight. In addition, we analyzed their biomass and fisheries landings in order to examine shifts over time. The content of 432 stomachs was analyzed at the lowest taxonomic level possible. The frequencies of occurrence were used to cluster species, revealing three trophic guilds: "Planktivorous Clupeiformes", "Planktivorous Carangiformes", and "Piscivores". Most Carangidae consumed mainly copepods and other small crustaceans, except Selene setapinnis which clustered in the piscivorous guild together with Scombriformes specimens. In terms of biomass, the dominance of Trachurus lathami, Sardinella brasiliensis, and Trichiurus lepturus was evident. The species' trophic levels ranged from 2.98 to 4.5, showing that these fishes occupied intermediate to high trophic position. Comparing fisheries landings in two study periods (1986-2002 and 2003-2019), six species showed a decrease, while three an increase. Correlations between landings of the Brazilian sardine (Sardinella brasiliensis) and other pelagic fishes indicate that when the former's decreases, the catch of alternative species, such as Opisthonema oglinum and Chloroscombrus chrysurus, increases. The intermediate position of small pelagics in the food web may affect the availability of commercial species by controlling the abundance of lower and upper trophic-level organisms. These findings fill essential gaps for ecosystem modeling, suggesting that ecosystembased fisheries management should address multispecies issues of the pelagic realm rather than only singlespecies approaches. Combining past survey data with yield trends provides evidence for both natural and humaninduced ocean changes.

Macronutrients, iron and humic substances summer cycling over the extended continental shelf of the South Brazil Bight

We surveyed macronutrients and dissolved iron (DFe) concentrations and speciation in a transect over the shelf of the South Brazil Bight (SBB) at Santa Marta Grande Cape (SE Brazil) during a coastal downwelling episode. Driven by dominant NE winds, coastal downwelling is a common feature during the austral summer and force after water convergence, with contribution of internal wave breaking at the shelf edge, upwelling of macronutrients into the nutrient-depleted waters of the southbound Brazil Current at ~100 km from the coastline. As a result, we found a plume of high turbidity that reached the euphotic layer, a deepening of the silicate, nitrate, and phosphate isolines over the shelf and a bulging of the nitrate and phosphate isolines over the shelf edge and the slope. Our first measurements of DFe concentration and speciation in the area revealed that against prior findings in other coastal areas, macronutrients, DFe, and iron ligand cycles were disentangled. Higher DFe concentrations were often found at the surface indicating aerial deposition. Secondary DFe maxima over the sediment-water interface and in the upwelled plume indicated DFe fluxes from the sediment and from resuspended instable colloids. Iron ligand concentrations were higher than DFe concentrations in most stations with a clear land-to-ocean gradient. Subtraction of HS iron ligands revealed that except in upwelled water, the bulk of surface ligands was the result of local biological processes. The analysis of the concentrations of Fe-HS complexes showed that the contribution of HS to DFe was dominant in upwelled waters, significant in waters close to the coast, but nearly negligible in the rest of the studied area. We hypothesize that the injection of iron-humic complexes into the euphotic layer during summer upwelling episodes is the key to understanding the persistent high chlorophyll meanders found over the shelf edge of the SBB coast.

The Brazil Current mesoscale eddies: Altimetry-based characterization and tracking

The Brazil Current (BC) has been reported as eddy-dominated, with recurrent formation of eddies and meanders along the margin. In this study, we characterize the variability of mesoscale eddies associated with this western boundary current from its origin site to the southern end of the South Brazil Bight (∼15°S – ∼28°S). We apply an eddy detection method on a 27-year multi-satellite altimetry product. We offer a first quantitative estimate of the eddy dominance along the BC path. On average, there are no major differences in the eddy parameters between cyclones and anticyclones. However, north of the 20∘S, the eddies are larger and slower in swirling speed, whereas the opposite patterns occur with the eddies south of 20∘S. Although there is no notable seasonality in the eddy formation in general, there is a tendency to form cyclones in the vicinity of capes and bights of the southeastern Brazilian shelfbreak. In contrast, there is a scattered horizontal distribution of anticyclone formation for most of the BC domain throughout the seasons. The Vitória, Cape São Tomé and Cape Frio Eddies account for ∼30% of the total cyclones in the analysis. The Vitória Eddy (VE) tends to be more often generated in austral autumn, the season of lowest kinetic energy and volume transport of the BC. The Cape São Tomé Eddy (CSTE) and Cape Frio Eddy (CFE) are more energetic in the seasons of the BC’s highest volume transport (austral spring and summer). Despite most of the eddies being described as quasi-stationary in the current literature, our analysis of the eddy trajectories showed that the VE, CFE and CSTE can detach and migrate off of the mean BC axis. We estimate that ∼30% of the CFE events pinch off and migrate southwestward. The CSTE and CFE presented the highest growth rates (0.08 and 0.07 day−1 , respectively) of the recurrent eddies. These results provide a first robust characterization of the BC mesoscale eddies.

Compact Mesoscale Eddies in the South Brazil Bight

Recent studies suggest that the South Brazil Bight (SBB) hosts strong westward propagating mesoscale eddies. We use 28 years of satellite altimetry data and a new Eddy Atlas to estimate how much of the eddy kinetic energy (EKE) observed in the SBB is accounted for by local eddies, generated in the Brazil Current (BC) region, versus remote eddies generated eastward of the BC region. First, we estimate a BC frontal density to obtain a robust definition of BC region. The BC front is well-defined throughout the SBB, occupying the region between the 200-m and 1000-m isobath, except in eddy hotspots downstream of sharp inflections of the continental slope, where the EKE far exceeds the mean kinetic energy (MKE). Compact, closed-contour mesoscale eddies account for 30–50% of the total EKE observed in the SBB, with local eddies accounting for most of the compact EKE in the BC region, defined as the area within 200 km of the 28-year mean BC front. Remote compact eddies account for less than 10% of the EKE observed in the BC region; compact eddies generated at long distances from the SBB, including eddies generated in the Southeastern Atlantic, contribute an insignificant fraction of EKE in the BC region.

Late Pleistocene to Holocene variations in marine productivity and terrestrial material delivery to the western South Atlantic

Despite the increased number of paleoceanographic studies in the SW Atlantic in recent years, the mechanisms controlling marine productivity and terrestrial material delivery to the South Brazil Bight remain unresolved. Because of its wide continental shelf and abrupt change in coastline orientation, this region is under the influence of several environmental forcings, causing the region to have large variability in primary production. This study investigated terrestrial organic matter (OM) sources and marine OM sources in the South Brazil Bight, as well as the main controls on marine productivity and terrestrial OM export. We analyzed OM geochemical (bulk and molecular) proxies in sediment samples from a core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W, 840-m water depth). The organic proxies were classified into “terrestrial-source” and “marine-source” groups based on a cluster analysis. The two sources presented different stratigraphical profiles, indicating distinct mechanisms governing their delivery. Bulk proxies indicate the predominance of marine OM, although terrestrial input also affected the total OM deposition. The highest marine productivity, observed between 50 and 39 ka BP, was driven by the combined effects of the South Atlantic Central Water upwelling promoted by Brazil Current eddies and fluvial nutrient inputs from the adjacent coast. After the last deglaciation, decreased phytoplankton productivity and increased archaeal productivity suggest a stronger oligotrophic tropical water presence. The highest terrestrial OM accumulation occurred between 30 and 20 ka BP, with its temporal evolution controlled mainly by continental moisture evolution. Sea level fluctuations affected the distance between the coastline and the sampling site. In contrast, continental moisture affected the phytogeography, changing from lowlands covered by grasses and saltmarshes to a landscape dominated by mangroves and the Atlantic Forest. Our results suggest how the OM cycle in the South Brazil Bight may respond to warmer and dryer climate conditions.

Past and Contemporaneous Otolith Fingerprints Reveal Potential Anthropogenic Interferences and Allows Refinement of the Population Structure of Isopisthus parvipinnis in the South Brazil Bight

Simple SummaryOtolith geochemical signatures were important tools used to investigate the population of commercially exploited fish species. Historical and contemporary otolith samples of Isopisthus parvipinnis, Bigtooth corvina, an economically and ecologically important Brazilian fish species, collected in five subareas [São Paulo: North—NSP, Center—CSP and South—SSP; Paraná (PR) and Santa Catarina (SC)] of the shallow waters off the coast of the South Brazil Bight were used in this study. Univariate and multivariate statistical analyses showed spatial differences in otolith chemical composition over the years, suggesting that long-term temporal variability in oceanographic conditions, anthropogenic influence, and climate change on this coastal ecosystem influenced the geochemical signatures. Moreover, these results also confirm that I. parvipinnis is not a single and homogeneous fish stock in this geographic area, supporting the existence of a metapopulation structure scenario and corroborating previous studies that used alternative, complementary phenotypic tags.In this study, otolith geochemical signatures (Element:Ca ratios) were used to investigate the long-term spatial shifts of the population structure of Isopisthus parvipinnis, Bigtooth corvina, an economically and ecologically important Brazilian fish species. Two-hundred and ninety-seven juvenile individuals from historical (1975) and contemporary (2018/2019) samples were collected in five subareas [São Paulo: North—NSP, Center—CSP and South—SSP; Paraná (PR) and Santa Catarina (SC)] of the shallow waters off the coast of the South Brazil Bight were analyzed. The main informative single elements were Co:Ca, Cu:Ca, Li:Ca, Mg:Ca, Mn:Ca, Ni:Ca, Na:Ca, and Rb:Ca. Multivariate analysis showed spatial differences in otolith chemical composition over the years. Samples from 1975 presented an overall low reclassification rate (58%), suggesting the existence of two population units: (1) SP + PR; and (2) SC. However, samples from 2018/2019 discriminated four distinct population units with a good overall reclassification (80%): (1) NSP; (2) CSP; (3) SSP + PR; and (4) SC. This spatial differentiation on the geochemical signatures probably reflects the effects of long-term temporal variability in oceanographic conditions, anthropogenic influence, and climate change on this coastal ecosystem. The data also corroborate and refines the population structure scenario of I. parvipinnis recently described using complementary phenotypic tags.

The effect of Oceanic South Atlantic Convergence Zone episodes on regional SST anomalies: the roles of heat fluxes and upper-ocean dynamics

The South Atlantic Convergence Zone (SACZ) is an atmospheric system occurring in austral summer on the South America continent and sometimes extending over the adjacent South Atlantic. It is characterized by a persistent and very large, northwest-southeast-oriented, cloud band. Its presence over the ocean causes sea surface cooling that some past studies indicated as being produced by a decrease of incoming solar heat flux induced by the extensive cloud cover. Here we investigate ocean–atmosphere interaction processes in the Southwestern Atlantic Ocean (SWA) during SACZ oceanic episodes, as well as the resulting modulations occurring in the oceanic mixed layer and their possible feedbacks on the marine atmospheric boundary layer. Our main interests and novel results are on verifying how the oceanic SACZ acts on dynamic and thermodynamic mechanisms and contributes to the sea surface thermal balance in that region. In our oceanic SACZ episodes simulations we confirm an ocean surface cooling. Model results indicate that surface atmospheric circulation and the presence of an extensive cloud cover band over the SWA promote sea surface cooling via a combined effect of dynamic and thermodynamic mechanisms, which are of the same order of magnitude. The sea surface temperature (SST) decreases in regions underneath oceanic SACZ positions, near Southeast Brazilian coast, in the South Brazil Bight (SBB) and offshore. This cooling is the result of a complex combination of factors caused by the decrease of solar shortwave radiation reaching the sea surface and the reduction of horizontal heat advection in the Brazil Current (BC) region. The weakened southward BC and adjacent offshore region heat advection seems to be associated with the surface atmospheric circulation caused by oceanic SACZ episodes, which rotate the surface wind and strengthen cyclonic oceanic mesoscale eddy. Another singular feature found in this study is the presence of an atmospheric cyclonic vortex Southwest of the SACZ (CVSS), both at the surface and aloft at 850 hPa near 24°S and 45°W. The CVSS induces an SST decrease southwestward from the SACZ position by inducing divergent Ekman transport and consequent offshore upwelling. This shows that the dynamical effects of atmospheric surface circulation associated with the oceanic SACZ are not restricted only to the region underneath the cloud band, but that they extend southwestward where the CVSS presence supports the oceanic SACZ convective activity and concomitantly modifies the ocean dynamics. Therefore, the changes produced in the oceanic dynamics by these SACZ events may be important to many areas of scientific and applied climate research. For example, episodes of oceanic SACZ may influence the pathways of pollutants as well as fish larvae dispersion in the region.

A vertical-mode extrapolation scheme applied to the Brazil Current domain: quasi-synoptic scenarios

The Brazil Current (BC) is a western boundary current, with an average vertical extension of 500 m, which occupies the southwestern margin of Atlantic Ocean. Recently, the South Brazil Bight - SBB (23º S - 28º S) has been intensively explored by the oil and gas industries, which brought a high demand in operational oceanography and ocean state monitoring. In this study we present a new technique based on the vertical dynamic modes of oscillation, to extrapolate velocity profiles in the SBB, with potential applications to data acquired by Vessel Mounted Acoustic Doppler Current Profilers (VMADCP). Using four quasi-synoptic crosssectional velocity data, acquired by Lowered Acoustic Doppler Current Profilers (LADCP), we observed that the mean circulation of this region can be characterized as a 2-dynamical mode system. This mean circulation is mainly dominated at surface by the BC and at intermediate levels by the Intermediate Western Boundary Current (IWBC), which flows northward. Furthermore, observed mesoscale vortical features in the SBB, such as eddies and meanders, are shown to be primarily barotropic-mode dominated. In our extrapolation methodology, the use of an independent set of velocity time series obtained by four moorings has shown to be a valid way for obtaining the relative contribution of each dynamical mode in the velocity field in the SBB. Normalized mean squared errors below 10% and radar diagrams show that the presented methodology was able to reproduce the main dynamic features observed by LADCP transects. Also, with this technique, we extrapolated three VMADCP sections and the results agreed with previous observations.

A first assessment of particle flux over the South Brazil Bight continental slope

The vertical export of particulate organic carbon (POC) is a key component of the oceanic biological pump, which regulates the distribution of elements associated with primary production in the upper euphotic zone. To better understand how oceanic biogeochemical processes will respond in climate change scenarios, it is necessary to comprehend the mechanisms that regulate the magnitude and variations of POC flux among distinct oceanic domains, including the boundaries between continental margins and oceanic basins. This work is a first assessment of particle flux over the South Brazil Bight continental slope, a tropical western boundary system dominated by the Brazil Current. Total mass flux, and specific carbon, nitrogen and biogenic silica fluxes were measured periodically by two sediment traps installed at 450 m deep over the 900 m isobath, and at 750 m deep over the 2000 m isobath, from November 2016 to September 2017. Due to strong contribution of advected particles, high and extremely irregular fluxes were registered at the 900 m isobath site (mean = 1.1 g m-2 d− 1, stand. dev. ± 2.9 g m-2 d-1). The captured material suggests this sediment trap was affected by turbidity flows, which precludes the estimation of the biological pump contribution over this isobath. Over the 2000 m isobath, POC flux (3.7 mg m-2 d-1; ±2.5 mg m-2 d− 1) followed the seasonal pattern of primary production measured by satellite. POC flux was strongly correlated with biogenic silica content (r = 0.79; p < 0.01). This ballast mineral was more efficient than CaCO3 in transferring carbon from the base of the euphotic zone to 750 m. We suggest intra-seasonal variations found in the POC flux over the 2000 m isobath to be related to Brazil Current instabilities. Measurements of δ15N suggest that higher POC flux occurred during subsurface nitrate-based production regimes. A regional exponential export model is proposed, with a mean exponent (b value) of 1.4 (±0.3). Although initial, the results of this work allow us to estimate that 2.2 × 1012 g C is exported annually over the South Brazil Bight continental slope.

Sea surface CO2 fugacity in the southwestern South Atlantic Ocean: An evaluation based on satellite-derived images

The South Atlantic Ocean is historically less sampled than the North Atlantic Ocean. Recent efforts have improved our understanding of the carbonate system variable distribution, mainly on sea surface CO2 fugacity (fCO2). However, these studies have been regionally and temporally restricted. Hence, in this research we developed seasonal algorithms of sea surface fCO2 to investigate the CO2 dynamics along the southwestern South Atlantic Ocean during spring-summer and fall-winter periods. The studied region includes the continental shelf areas of the Abrolhos-Campos Region (an area under the influence of central water upwelling), the South Brazil Bight (a large embayment affected by the mesoscale variability in a westward boundary current), the Southern Brazilian Shelf (a coastal zone influenced by freshwater discharge from continent and water mass entrainment), and offshore waters in the open ocean domain of the southwestern South Atlantic Ocean. Monthly satellite images of sea surface temperature, salinity, and chlorophyll-a, which were concomitantly available from August 2011 to June 2015, were used to reconstruct and evaluate the sea surface fCO2 seasonal field. The predicted fields of sea surface fCO2 enabled an investigation of the main drivers that change this variable over the distinct biogeochemical provinces in the region. As expected, the sea surface temperature was the main driver of seasonal changes in sea surface fCO2, but total dissolved inorganic carbon (DIC) and total alkalinity changes were also relevant, mainly in the biogeochemical provinces under the influence of continental freshwater input or central water upwelling. The latter can play an unpredictable role in CO2 dynamics due to nutrient- and DIC-rich water transport close to the surface. Finally, the use of satellite-derived images is a powerful tool to increase biogeochemical knowledge of relatively undersampled ocean regions, while the development of seasonal sea surface fCO2 algorithms allows a better spatiotemporal comprehension of the CO2 distribution, dynamics, and drivers in the southwestern South Atlantic Ocean – a key region for improving the understanding of the global carbon cycle.