Resumo em Inglês:

Abstract The Santos Basin in eastern Brazil is adjacent to the largest human populations in the southwestern Atlantic Ocean, with several potential threats to marine vertebrates. In this study, we provided a systematic bibliographic review and integrated unpublished primary datasets to provide an overview on species, research topics and gaps, and threats to seabirds in the Santos Basin. Bibliographical sources were used for species recorded within the limits of the basin, while species census data were obtained through research and monitoring projects. We analyzed 156 studies from 1914 to 2021. An increase in the number of publications was observed from the 2000s onward (> 80%), with the state of Santa Catarina showing the highest number of publications (56%) on seabirds. Notes and Records (27%), Population and Community Structure (22%), and Fishing (11%) were the main subjects studied. Among the 76 seabird species reported in the Santos Basin (~2/3 of the species reported in Brazil), Procellariiformes was the most prevalent order (51%), including 14 species listed as threatened, either globally or nationally. Resident (28%) and long-distance migratory species, such as visitors from the Southern (39%) and Northern (17%) Hemispheres and Europe (12%), were widely recorded in the region, as well as vagrant species. The inclusion of different data sources allowed broadening the geographic cover used by species to consider both coastal (predominating in previous studies) and offshore areas. The association of seabird distribution with oceanographic and meteorological features should be addressed in future studies, as should studies on the impact of fishing and pollution on a range of common species.

Resumo em Inglês:

Abstract Activities related to the marine exploration of oil and gas reservoirs tend to cause a concentration of natural radionuclides in related materials. As such, knowledge regarding the distribution of radionuclides in sedimentary basins with current oil operations is essential for modeling radiological hazards and possible risks of site contamination. This study investigated the distribution of 226Ra and 228Ra, radioisotopes from the 232U and 232Th decay chains in bottom sediment of the Santos basin. Sediment samples were collected from sites in a sampling grid based on depth contours and were analyzed through high-resolution gamma spectrometry. A distribution model of the spatial variation of these isotopes, the frst of its kind for the Basin, supported the interpretation of similar tendencies in their distribution. From studying the spatial trends of the mean levels of the isotopes with descriptive statistics and variance analysis, latitudinal and bathymetric diferences in the content of radionuclides emerged. These diferences are probably derived from the distinct sources of these elements, as 226Ra originates in the deep ocean from the decay of parent 230Th and from the patterns of sedimentation driven by open ocean circulation, while 228Ra is supplied by terrigenous materials transported by the northward-fowing Brazilian Coastal Current.

Resumo em Inglês:

ABSTRACT The ocean bottom morphology, depth, sediment grain size, sediment sorting, carbonate content, and water depth are used to compose seafloor maps as support for biological studies. Sediments are reworked by waves and currents and accumulate according to the hydrodynamic level on the continental shelf. In contrast, sediments are accumulated by pelagic settling, mass wasting, turbidity flows, and boundary currents on the slope. Sea level oscillations during the Quaternary also played an important role in modifying the shelf seabed's morphology and sedimentary mosaic composition. The work addresses these topics in the Santos Basin based on extensive bathymetric data, shallow seismic records, and stratified bottom sediment samples in water depths ranging from 25 to 2,400m, as part of The Santos Basin Regional Environmental Characterization Project (PCR-BS). The main objective is to provide broad background information on the sedimentology and morphology of Santos Basin, focusing on the continental shelf. The morphology, sediment supply, shelf orientation, and ocean climate imprint the Santos Basin's characteristics. The Northern shelf sector is the most dynamic because of the narrow shelf, steep gradient, and East-West shoreline orientation, providing conditions for storm waves to approach and mobilize sediment in the ocean bottom shallow than 50 m water depth. The Southern sector of the shelf is much broader than the Northern sector; it displays a gentler gradient, and its orientation is Northeast-Southwest; therefore, less subject to storm waves than the Northern sector.

Resumo em Inglês:

Abstract The organic matter (OM) of surface sediments (0–2 cm) from the Santos Basin was characterized by employing elemental (C, N, P), isotopic (δ 13C and δ 15N), biochemical (total carbohydrates, proteins, and lipids), and pigment (chlorophyll-a and phaeopigments) proxies, as part of the Santos Project – The Santos Basin Regional Environmental Characterization (PCR-BS) – coordinated by PETROBRAS. Samples were collected in a regional scale throughout the entire basin, including 11 isobaths from eight cross-margin transects ranging from 25 to 2,400 m water depths, and 12 additional samples obtained from the São Paulo Plateau. The aims of this study were two-fold, namely, to identify the major oceanographic and depositional processes driving OM transport and accumulation and to provide information on OM origin and availability to benthic secondary producers. The multiple employed proxies and the use of machine learning allowed to categorize distinct OM accumulation provinces displaying two major regional features: shallow sediments (< 50-m isobaths) are OM-poor (TOC < 2.0 mg g -1) but the available amount is readily hydrolysable, and mid-shelf deposits (75-m and 100-m isobaths) throughout the entire basin present muddy and OM-rich sediments (TOC ranging from 7.0 to 14.0 mg g-1) seemingly available to heterotrophs. Similarly, relatively OM-rich deposits are found at depths ranging from 700 to 1,300-m isobaths throughout the basin, but their composition and nutritional value (as suggested by biochemical indicators) are not related to mid-shelf deposits. The general overview of OM accumulation and composition provided herein validated the selected organic geochemical proxies for benthic ecology studies at the shelf and deep ocean sectors of the studied region.

Resumo em Inglês:

Abstract Primary production is essential in shaping biogeochemical cycles and microbial and ecosystem dynamics. The distribution of chemosynthetic rates in pelagic zones and their participation in the carbon cycle, especially when compared to photosynthetic rates in the Southwestern Atlantic Ocean, are poorly constrained. This study aimed to measure pelagic photo- and chemosynthetic productivity and to analyze their spatial distribution and abiotic drivers. Samples for photosynthesis experiments collected at the surface and deep chlorophyll maximum (DCM) were incubated with 14C-bicarbonate at eight light levels, simulating in situ conditions. Samples for chemosynthesis experiments were collected throughout the water column, from the surface, DCM, 250 m, 900 m, 1,200 m, and 2,300 m, and were incubated in the dark. Rates were analyzed using statistical tests to verify spatial differences between groups of samples and generalized linear models to identify correlations with environmental variables (temperature, salinity, density, mixed layer depth, dissolved oxygen, nitrite, nitrate, silicate, phosphate, turbidity, CDOM, and phycoerythrin and chlorophyll-a concentrations). Moreover, both processes were integrated from the surface to the DCM and compared at the same stations to determine the relative contribution in the epipelagic zone. The photosynthetic and chemosynthetic rates were, on average, 3.00 ± 3.26 mg C m-3 h-1 and 0.97 ± 1.22 mg C m-3 h-1, respectively. In most stations, chemosynthesis represented an average of 10.2% of total primary productivity, but surpassed photosynthesis in three experiments (reaching 63.4 – 78.8%). Photosynthesis displayed a clear offshore-onshore gradient, along with correlated CDOM concentrations, indicating an autochthonous production of the latter. Chemosynthesis, on the other hand, exhibited high variability and lack of prediction by studied environmental variables, with isolated points of substantially higher activity.

Resumo em Inglês:

Abstract This study aimed to characterize the spatial distribution and composition of living Benthic Foraminifera (BF) and to comprehend how environmental conditions (e.g., organic matter) can affect communities of these protozoa in the northern and southern sectors of the Santos Basin (SB), in the continental slope and São Paulo Plateau. In this context, 23 stations (65 samples including replicates at each station) were collected between 400 and 2,400 m water depth. Multivariate analyses revealed that the ecological structure of the community changes mainly along the bathymetric gradients. Stations located between 400 and 700 m, both in northern and southern sectors, are characterized by the presence of indicator species of high intensity of currents, such as Globocassidulina subglobosa and Trifarina bradyi. These stations are also mainly marked by the occurrence of Epistominella exigua, a phytodetritivore species. The stations at 1,000 and 1,300 m depth, in both sectors, are characterized by high accumulation of organic matter in the sediments, which favors the development of agglutinated foraminifera species, such as those of the genus Reophax. Finally, the lower slope and the São Paulo Plateau, in both sectors, are oligotrophic regions, with pulses of labile organic carbon, probably low current velocities and the presence of Alabaminella weddellensis. The quantity and quality of food, which are closely related to hydro-sedimentary dynamics and bentho-pelagic coupling in the slope and São Paulo Plateau, are the main factors that influence the distribution of living BF assemblages in the SB.

Resumo em Inglês:

Abstract This study aims model the distribution of meiofauna indicators in relation to environmental variables from the Santos Basin continental margin, SE Brazil, using machine learning techniques, to provide baseline information and foster future monitoring programs. A total of 100 sampling stations were distributed in eight transects and 11 isobaths (25 to 2,400 m) perpendicular to the coast. In each station, three replicates were sampled for meiofauna and 38 environmental parameters. A total of 28 meiofauna taxa were found, with a mean richness varying from 3 to 15 taxa per station. Meiofauna mean density varied between 55 and 2,001 ind. 10 cm-2. Density of meiofauna and its most frequent taxa (Nematoda, Copepoda, Kinorhyncha, and Polychaeta), and taxa richness were used as descriptors for the models. Meiofauna and nematode density showed the highest training and testing accuracies, with R² values above 0.74. Based on the distribution of meiofauna descriptors and their responses to environmental conditions, we suggest a mosaic of six benthic zones. The La Plata Plume zone and the Cabo Frio Upwelling zone are two of the most diverse and productive zones in the continental shelf, wich are separated by the less productive Central Continental Shelf zone. A fourth zone, with very low meiofauna densities, corresponds to the carbonated sediments of the shelf-break. The Upper and Mid-Slope is a narrow zone along the entire basin, with intermediate densities and small amounts of high-quality organic carbon. The largest, impoverished zone, the Lower Slope and Plateau comprises the deepest areas and the São Paulo Plateau. The study showed that, although some zones can be recognized by most meiofauna descriptors, others are better characterized by specific ones, implying that meiofauna indicators should be monitored concomitantly. We recommend the optimization of sampling design based on our model to reduce costs and increase our understanding of the system.

Resumo em Inglês:

Abstract Continental margins usually have a high degree of environmental heterogeneity, which, in turn, promotes high benthic biodiversity. The South-Southeast regions concentrate the most well-mapped areas of the Brazilian continental margin regarding seafloor geomorphology and physical oceanography. However, the structure of the soft-sediment benthic fauna of the continental slope is still unknown. Characterization and understanding of the Brazilian continental slope biota are imperative since human activities are increasing in the last decades, especially after the discovery of the pre-salt reservoir in Santos Basin. In this study, we aimed to establish a baseline of the spatial distribution of the benthic macrofaunal communities regarding their latitudinal and bathymetric patterns in the Santos Basin to support future environmental monitoring activities in the region. As part of the Santos Project – The Santos Basin Regional Environmental Characterization (PCR-BS) – coordinated by CENPES/PETROBRAS, a benthic oceanographic cruise was carried out in 2019. Sediment samples were collected using a GOMEX-type box corer in 47 stations distributed in eight transects (400– 2,400 m depth range). In total, 12 additional stations (1,300–2,200 m) were defined to cover an area where oil and gas are exploited. Our results showed that macrofaunal assemblages of the Santos Basin present strong depth zonation related to changes in organic matter input, as well as to temperature, carbonate, and grain size. At local scale, the northern sector stood out for having a higher abundance of macrofauna in the upper slope (400 m) and it probably reflects the oceanographic processes and the organic enrichment caused by the upwelling events that occur at Cabo Frio region. The zonation pattern and the dominance of some polychaete, peracarid crustacean, and bivalve families were similar to other SE Brazilian continental margins.

Resumo em Inglês:

Abstract The extensive coverage of 3-D seismic data on the Santos Basin deep water offered an integrated vision of the local physiography and medium- to small-scale geomorphological features, which enhances the understanding of its constructive/deconstructive natural processes and their interrelations. The Santos Basin is a divergent marginal basin composed of three main physiographic provinces: its continental shelf, continental slope, and the São Paulo Plateau, whose dimensions, orientation, gradients, and relief interact with oceanographic, biological, and geological processes. This study geologically contextualized environmental data related to the Regional Environmental Characterization Project of the Santos Basin (hereinafter referred to as PCR-BS), especially regarding the regional physiographical architecture and deep-water geomorphological provinces as a background for the benthic communities and the distribution of several of its geochemical parameters. The integrated analysis of 3-D seismic and multibeam bathymetric data and its derivatives (gradient and edge maps) — calibrated by 108 piston cores — aimed to evaluate its seafloor physiographic features and geological processes. Edge detection seismic attributes enhance gradient contrast, which, in turn, can map innumerous medium- to small-scale geomorphic features (features solved in maps at a 1:1,000,000 scale or larger), such as canyons, channels, ravines, pockmark units, pockmark fields, lineaments, carbonate and coral mounds, salt-related features (crests, minibasins, and crestal grabens), scars and rugous relief associated with mass-transport deposits, and bottom current-related features (depressions and furrows). The slope and the gently dipping plateau (São Paulo Plateau) that follow it eastward show four geomorphological domains based on their direction, profile, average gradient, shelf break isobath, distribution of its medium-small scale geomorphic features, and the presence or absence of evaporites at subsurface. The central-northern São Paulo Plateau contains salt-related topographic elevations (salt diapirs and walls) and depressions (minibasins) that give a rough aspect to the seafloor relief.

Resumo em Inglês:

Abstract This work describes the circulation over the continental slope and the São Paulo Plateau in the Santos Basin during the SANSED winter 2019 survey. The cruise consisted of four legs in the period between June, 11 and August, 03 2019. The observed circulation is dominated by the Atlantic southwestern boundary current regime and remotely-generated anticyclones and cyclones. The former is composed by the Brazil Current, the Intermediate Western Boundary Current and their mesoscale meanders; the latter are 300km vortical rings with origin in the eastern side of the South Atlantic Basin. A Lagrangian scheme applied over satellite altimeter maps indicate that the origin of these rings is primarily the Cape Basin of South Africa. The interaction between the boundary currents, their cyclonic meanders, and the anticyclonic rings is complex, and varies widely. During the SANSED winter 2019 survey period, three anticyclones interacted with the Brazil Current, instabilizing it, forming dipoles with the current cyclonic meanders, leading to their downstream propagation. Ancienter cyclonic eddies within Santos Basin may interfere with the propagation of the large anticyclones further south. In addition, the continuous arrival of remotely-originated anticyclones, the larger portion over the São Paulo Plateau presented a tendency of counter-clockwise circulation during the whole cruise period.

Resumo em Inglês:

Abstract This study describes the hydrography and water masses of the Santos Basin Continental Shelf (SBCS) during two hydrographic campaigns (SANAGU, SANSED) in 2019. Coastal Water (CW) is the dominant water mass in the southern portion of the SBCS, with relatively low salinity values (S<35.5 g kg–1), and satellite data show that local precipitation and river discharge could not account for the low salinity observed during the cruises in the southern region of the domain. The low salinity observed is explained by the transport from the south influenced by Subtropical Shelf Water (STSW), which was influenced by the La Plata River discharge. In the northern region of the SBCS, the South Atlantic Central Water (SACW) dominates the bottom layers of the water column, with the wind playing a major role in the uplift of this water mass, as evidenced by a wind impulse analysis. In this part of the shelf, Tropical Water (TW) was the second water mass in volume and occupied the surface layers and offshore the shelf. CW is restricted to a thin surface layer, which reaches distances of a few kilometers from the coast. Our analysis show the differences in the hydrographic structure of the SBCS and suggests that the SBCS can be divided in two regions with distinct characteristics: 1) the area southwest of São Sebastião, where the hydrographic parameters were modulated by the presence of the Subtropical Shelf Water (STSW); 2) the area northeast of São Sebastião, where the uplifting of SACW was the dominant process.

Resumo em Inglês:

Abstract Integrating intricate environmental data within a unified analytical framework for extensive conservation and monitoring initiatives encounters several challenges. These challenges encompass defining a conceptual model outlining cause-and-effect relationships, addressing dissimilarities in data source quantity and information content, grappling with missing or noisy data, fine-tuning model optimization, achieving accurate predictions, and tackling the issue of imbalanced observations across factors. In the context of the Santos project, dedicated to comprehending the spatio-temporal dynamics of benthic, pelagic, and physical systems for the facilitation of conservation and monitoring programs, the application of machine learning’s random forest (RF) technique for modeling univariate data offers notable advantages. This approach adeptly handles non-linearity, covariation, and interactive effects among predictors. For modeling multivariate data sets, a hybrid strategy combining a self-organizing map (SOM) and RF is harnessed to effectively tackle the challenges. Addressing missing values, the bagging imputation technique demonstrated superior performance compared to other methods. Both machine learning techniques discussed herein exhibit resilience against the impact of noisy data, yet the identification of noisy data remains feasible based on model outputs. In scenarios of imbalanced data sets, we investigate the correlation between the RF model’s overall statistics and those of individual classes. The joint interpretation of these statistics aids in comprehending model limitations and facilitates discussions on the environmental mechanisms shaping observed patterns. We propose two analytical workflows that not only enable the exploration and enhancement of model accuracy but also facilitate the investigation of potential cause-and-effect relationships inherent in the data. Furthermore, these workflows lay the foundation for implementing long-term learning algorithms, a pivotal increment for monitoring initiatives. Notably, these workflows, alongside the discussed analytical challenges, can be seamlessly implemented within iMESc, an open-source application.

Resumo em Inglês:

Abstract The Santos Basin (SB) is the main petroliferous basin in the Brazilian continental margin and one of the most studied marine areas in Brazil. However, historical data suggest that new efforts should be carried out to acquire quantitative biological data, especially in the deep sea, to establish the baseline of essential ocean variables in different ecosystems for future monitoring programs. The Brazilian energy company Petrobras planned and executed 24 oceanographic cruises over a period of 2 years to assess the benthic (SANSED cruise) and pelagic (SANAGU cruise) systems of the SB (356 days at sea in 2019 and 2021/2022). These efforts were part of the Santos Project, which comprised a comprehensive environmental study aimed at investigating benthic and pelagic variables to characterize ecology, biogeochemistry, thermohaline properties of water masses, and ocean circulation patterns, geomorphology, and sedimentology, as well as organic and inorganic chemistry. Here we present the detailed sampling designs and the field methods employed on board, during the SB scientific cruises. All sampling protocols were based on standardized approaches. For the benthos analyses, triplicate sediment samples were performed using a GOMEX-type box corer (0.25 m²) or a large modified Van Veen grab (0.75 m²) at 100 stations ranging from 25 to 2400 m depth. At each station, 25 geochemical and physico-chemical parameters were analyzed in addition to micro-, meio-, and macrofauna and living foraminifera samples. For the pelagic system, 60 stations were selected to investigate the plankton community, ranging in size from pico- to macroplankton, through vertical, horizontal, and oblique net hauls (20, 200, and 500 μm mesh size), as well as 25 biogeochemical parameters collected with an aid of a CTD-rosette sampler. Part of this scientific information also serves the Regional Environmental Characterization Project (PCR-BS) in support of Petrobras’ Santos Basin drilling licensing process led by the Brazilian Environmental Agency – IBAMA. This project contributes to the sustainable development of the SB, in line with the guidelines of the United Nations Decade of Ocean Science for Sustainable Development.