Brazilian Continental Margin Research Articles

Deciphering the complex history of the cabo frio high – SE brazilian continental margin

Extensive seismic reflection interpretation of the Cabo Frio High allowed better understanding of its proximal and distal structure. Seismic lines helped map the salt base and recognize the primary geological interfaces, unconformities, faults, and volcanic intrusions. The proximal Cabo Frio High is a continental basement uplift extending mainly into the Campos Basin. The Cabo Frio Outer High, which is of volcanic origin, lies between Santos and Campos Basins. This volcanism is concentrated at the crossing of two significant structures: Cruzeiro do Sul Lineament and Rio de Janeiro Fracture Zone. The Cabo Frio High fits an NW-SE fold axis, which is well correlated with distension along NW-SE direction generating a regional E-W sinistral plate movement, mainly related to the ENE-WNW sinistral Rio de Janeiro transfer zones. The accumulated uplift is approximately 4 km, achieved by at least four uplifting pulses. The uplifting starts in the Albian-Santonian, characterized by the elevation of the northeast portion of Cabo Frio High, followed by erosion. The sill and dikes intruded in the Upper Cretaceous, and the uplift of the southwest portion of the Cabo Frio High characterizes the second uplift pulse. Subaerial Eocene volcanos characterize the third uplifting pulse. The uplifting of the Blue Marker horizon (Oligocene) characterizes the last pulse.

CSEM Optimization Using the Correspondence Principle

Traditionally, 3D modeling of marine controlled-source electromagnetic (CSEM) data (in the frequency domain) involves high-memory demand, requiring solving a large linear system for each frequency. To address this problem, we propose to solve Maxwell’s equations in a fictitious dielectric medium with time-domain finite-difference methods, with the support of the correspondence principle. As an advantage of this approach, we highlight the possibility of its implementation for execution with GPU accelerators, in addition to multi-frequency data modeling with a single simulation. Furthermore, we explore using the correspondence principle to the inversion of CSEM data by calculating the gradient of the least-squares objective function employing the adjoint-state method to establish the relationship between adjoint fields in a conductive medium and their counterparts in the fictitious dielectric medium, similar to the approach used in forward modeling. We validate this method through 2D inversions of three synthetic CSEM datasets, computed for a simple model consisting of two resistors in a conductive medium, a model adapted from a CSEM modeling and inversion package, and the last one based on a reference model of turbidite reservoirs on the Brazilian continental margin. We also evaluate the differences between the results of inversions using the steepest descent method and our proposed momentum method, comparing them with the limited-memory BFGS (Broyden–Fletcher–Goldfarb–Shanno) algorithm (L-BFGS-B). In all experiments, we use smoothing by model reparameterization as a strategy for regularizing and stabilizing the iterations throughout the inversions. The results indicate that, although it requires more iterations, our modified momentum method produces the best models, which are consistent with results from the L-BFGS-B algorithm and require less storage per iteration.

The Brazilian Santos basin underwater soundscape monitoring project (PMPAS-BS)

This paper describes the Santos Basin Underwater Soundscape Monitoring Project (PMPAS-BS), a Brazilian ocean soundscape monitoring initiative. The main objective of the project is to quantify and assess hydroacoustic noise of anthropogenic origin in a large sedimentary basin extending from 23° S to 28° S on the southeastern Brazilian continental margin of the South Atlantic Ocean. Noise associated with oil and gas (O&G) exploration and production activities is the primary target, but this oceanic region also has busy shipping lanes for commercial, military, and fishing vessels. The two main hubs of Brazil’s export and import of goods by sea are located in this region: Santos and Rio de Janeiro ports. The project has three measurement components: mobile monitoring based on gliders and drifting acoustic profilers, fixed shallow-water monitoring based on acoustic measurements at coastal stations near shipping lanes associated with exploration and production activities in the Santos Basin, and fixed oceanic monitoring based on deep-water mooring lines equipped with passive autonomous acoustic recorders near production units, shipping lanes, and areas with lower intensity of O&G activities (pristine or reference sites). Numerical modeling of anthropogenic underwater acoustic noise has also been included as a fourth project component. The PMPAS-BS covers an area of more than 251,000 km2 and uses several instruments with different methods and sensors for acoustic measurements. Its results provide current sound levels over a very large region of the western South Atlantic, both in areas more and less affected by anthropogenic activities.

Living benthic foraminifera from Almirante Câmara and Grussaí canyons and adjacent slope areas (Campos Basin, Southwest Atlantic): Response to trophic and hydrodynamic conditions

Living (rose Bengal stained) benthic foraminiferal faunas, grain size, geochemical parameters (total organic matter, chlorophyll-a, pheophytin-a, molecular markers, and vertical flux of particulate organic matter) were investigated in 14 stations in two submarine canyons Almirante Câmara and Grussaí considered mature and immature, respectively, and on the adjacent continental slope, from 400 to 1300 m water depth, in the southwestern Atlantic Ocean. Samples were retrieved during two campaigns, in the austral winter 2008 and the austral summer 2009. The density, richness, and species composition of the benthic foraminiferal fauna decrease with depth in the canyons and along the adjacent slope transects, reflecting the availability and quality of sedimentary organic matter. Both canyons act as traps of labile organic matter, mainly towards the head of the Almirante Câmara canyon, promoting high specimen density, species richness, and the occurrence of species indicative of pulses of phytodetritus (e.g., Bolivina pacifica, Nonionella opima, and Nonionella stella). Towards the deeper regions of Almirante Câmara canyon and in the adjacent slope area, the lower abundance, diversity, and richness reflect more oligotrophic conditions and an adverse environment in terms of easily metabolizable organic matter. This multiproxy study demonstrates that the canyons in the southeastern Brazilian continental margin play an important role in accumulating organic matter.

Cephalopod paralarvae in a tropical Brazilian basin: distribution throughout oceanographic features and water masses

The composition and distribution of cephalopod paralarvae were investigated in the Campos Basin, a tropical area on the southeastern Brazilian continental margin with extensive oil exploration. Zooplankton hauls with a multi-mesh net system were conducted during two seasonal oceanographic cruises in 2009 along eight isobaths (25–3000 m) and vertical sampling in five water mass cores (1–2300 m depth). A total of 825 paralarvae belonging to 11 families and at least 16 genera were captured. The majority had a dorsal mantle length of less than 2.60 mm, with a mean of 1.50 mm. The rainy summer showed higher total densities and number of families compared to the drier winter. Most paralarvae were collected at Surface Water (1 m depth), only four at South Atlantic Central Water (250 m), and two at Antarctic Intermediate Water (800 m). Enoploteuthidae and Ommastrephidae were the most abundant families and were positively associated with temperature, with higher densities during the rainy summer. Loliginidae were collected exclusively in the neritic zone. In the oceanic zone, Cranchiidae, Onychoteuthidae Octopoteuthidae, and Tremoctopodidae were collected at 1 m depth, and Ancistrocheiridae and Thysanoteuthidae at 250 m depth. Density peaks of paralarvae occurred during the summer along the continental shelf break and slope, an area known for frequent upwelling driven by cyclonic meanders of the Brazil Current.

Computational Oil-Slick Hub for Offshore Petroleum Studies

The paper introduces the Oil-Slick Hub (OSH), a computational platform to facilitate the data visualization of a large database of petroleum signatures observed on the surface of the ocean with synthetic aperture radar (SAR) measurements. This Internet platform offers an information search and retrieval system of a database resulting from >20 years of scientific projects that interpreted ~15 thousand offshore mineral oil “slicks”: natural oil “seeps” versus operational oil “spills”. Such a Digital Mega-Collection Database consists of satellite images and oil-slick polygons identified in the Gulf of Mexico (GMex) and the Brazilian Continental Margin (BCM). A series of attributes describing the interpreted slicks are also included, along with technical reports and scientific papers. Two experiments illustrate the use of the OSH to facilitate the selection of data subsets from the mega collection (GMex variables and BCM samples), in which artificial intelligence techniques—machine learning (ML)—classify slicks into seeps or spills. The GMex variable dataset was analyzed with simple linear discriminant analyses (LDAs), and a three-fold accuracy performance pattern was observed: (i) the least accurate subset (~65%) solely used acquisition aspects (e.g., acquisition beam mode, date, and time, satellite name, etc.); (ii) the best results (>90%) were achieved with the inclusion of location attributes (i.e., latitude, longitude, and bathymetry); and (iii) moderate performances (~70%) were reached using only morphological information (e.g., area, perimeter, perimeter to area ratio, etc.). The BCM sample dataset was analyzed with six traditional ML methods, namely naive Bayes (NB), K-nearest neighbors (KNN), decision trees (DT), random forests (RF), support vector machines (SVM), and artificial neural networks (ANN), and the most effective algorithms per sample subsets were: (i) RF (86.8%) for Campos, Santos, and Ceará Basins; (ii) NB (87.2%) for Campos with Santos Basins; (iii) SVM (86.9%) for Campos with Ceará Basins; and (iv) SVM (87.8%) for only Campos Basin. The OSH can assist in different concerns (general public, social, economic, political, ecological, and scientific) related to petroleum exploration and production activities, serving as an important aid in discovering new offshore exploratory frontiers, avoiding legal penalties on oil-seep events, supporting oceanic monitoring systems, and providing valuable information to environmental studies.

Twenty Years of CSEM Exploration in the Brazilian Continental Margin

The controlled source electromagnetic (CSEM) method is frequently used as a risk reduction tool in hydrocarbon exploration. This paper aims to provide a comprehensive historical review of the CSEM method’s twenty-year history in the Brazilian continental margin. Since 2003, we have significantly improved our understanding of CSEM resistivity data across various geological scenarios. This review presents a roadmap of the technical advancements in acquisition design and interpretation techniques. As a result, our understanding of the methodology has broadened from traditional to more general use, such as salt imaging, gas hydrates, geohazard mapping, and reservoir characterization. Finally, we indicate the potential upcoming CSEM applications in new energy resources and carbon capture and storage.

Contrasting thermal histories in the Dom Feliciano Belt triggered by magmatism related to the Paraná-Etendeka LIP and fracture zone proximity

The present-day southern Brazilian continental margin rests on top of the Dom Feliciano Belt (DFB) and adjacent cratons. This belt formed through the collision of the Rio de La Plata, Kalahari, Paranapanema, Congo and Luis Alves paleoplates in the Neoproterozoic. Several low-temperature thermochronology works were executed in the area, although none of them demonstrated how the basement temperature of the entire DFB evolved through time. To this end, this work aims to provide new Apatite Fission Track (AFT) and Apatite (UTh)/He (AHe) ages for samples collected in the Catarinense Shield, in the northern DFB, and to perform inverse modeling in those samples. Besides, the collection of the basement temperature of 128 locations across the entire belt and adjacent cratons provided thermal information to create inverse-distance weighted interpolation maps documenting the progression of the temperature from 360 to 30 Ma. New AFT ages range from 126.6 ± 24.1 to 60.3 ± 6.03 Ma, whereas AHe ages span from 153.0 ± 9.2 to 62.5 ± 3.7 Ma. Mean track lengths are short to medium, suggesting complete thermal annealing of apatite crystals. Apatite single-grain eU concentration range from 4.5 to 96 μg/g and display a sparse correlation with AHe ages. Interpolation maps evidence a contrasting temperature evolution of the northern DFB and bordering cratons relative to the southern segment and surrounding cratons. Near-surface exposure of the basement in the northern segment was possibly much earlier than in the south, followed by partial burial by the sedimentary successions of the Paraná Basin. The emplacement of volcanic rocks of the Paraná-Etendeka Large Igneous Province and associated dyke swarms and alkaline volcanic plugs related to the Florianópolis Fracture Zone raised and sustained higher basement temperatures until 30 Ma, resetting low-temperature thermochronometers in the northern DFB, which was minor to absent in the southern DFB.

Development and Application of Predictive Models to Distinguish Seepage Slicks from Oil Spills on Sea Surfaces Employing SAR Sensors and Artificial Intelligence: Geometric Patterns Recognition under a Transfer Learning Approach

The development and application of predictive models to distinguish seepage slicks from oil spills are challenging, since Synthetic Aperture Radars (SAR) detect these events as dark spots on the sea surface. Traditional Machine Learning (ML) has been used to discriminate the Oil Slick Source (OSS) as natural or anthropic assuming that the samples employed to train and test the models in the source domain (DS) follow the same statistical distribution of unknown samples to be predicted in the target domain (DT). When such assumptions are not held, Transfer Learning (TL) allows the extraction of knowledge from validated models and the prediction of new samples, thus improving performances even in scenarios never seen before. A database with 26 geometric features extracted from 6279 validated oil slicks was used to develop predictive models in the Gulf of Mexico (GoM) and its Mexican portion (GMex). Innovatively, these well-trained models were applied to predict the OSS of unknown events in the GoM, the American (GAm) portion of the GoM, and in the Brazilian continental margin (BR). When the DS and DT domains are similar, the TL and generalization are null, being equivalent to the usual ML. However, when domains are different but statically related, TL outdoes ML (58.91%), attaining 87% of global accuracy when using compatible SAR sensors in the DS and DT domains. Conversely, incompatible SAR sensors produce domains statistically divergent, causing negative transfers and generalizations. From an operational standpoint, the evidenced generalization capacity of these models to recognize geometric patterns across different geographic regions using TL may allow saving time and budget, avoiding the collection of validated and annotated new training samples, as well as the models re-training from scratch. When looking for new exploratory frontiers, automatic prediction is a value-added product that strengthens the knowledge-driven classifications and the decision-making processes. Moreover, the prompt identification of an oil spill can speed up the response actions to clean up and protect sensitive areas against oil pollution.

Benthic biogeographic patterns on the deep Brazilian margin.

The Brazilian continental margin (BCM) extends from the Tropical to the Subtropical Atlantic Ocean, with much of its seafloor within deep waters, supporting rich geomorphological features and under wide productivity gradients. Deep-sea biogeographic boundaries on the BCM have been limited to studies that used water mass and salinity properties of deep-water masses, partly as a result of historical under sampling and a lack of consolidation of available biological and ecological datasets. The aim of this study was to consolidate benthic assemblage datasets and test current oceanographic biogeographical deep-sea boundaries (200-5,000 m) using available faunal distributions. We retrieved over 4,000 benthic data records from open-access databases and used cluster analysis to examine assemblage distributions against the deep-sea biogeographical classification scheme from Watling et al. (2013). Starting from the assumption that vertical and horizontal distribution patterns can vary regionally, we test other schemes incorporating latitudinal and water masses stratification within the Brazilian margin. As expected, the classification scheme based on benthic biodiversity is in overall agreement with the general boundaries proposed by Watling et al. (2013). However, our analysis allowed much refinement in the former boundaries, and here we propose the use of two biogeographic realms, two provinces and seven bathyal ecoregions (200-3,500 m), and three abyssal provinces (>3,500 m) along the BCM. The main driver for these units seems to be latitudinal gradients as well as water mass characteristics such as temperature. Our study provides a significant improvement of benthic biogeographic ranges along the Brazilian continental margin allowing a more detailed recognition of its biodiversity and ecological value, and also supports the needed spatial management for industrial activities occurring in its deep waters.

The genus Bradleya Hornibrook, 1952 (Crustacea: Ostracoda) in South America and adjacent oceanic areas, with description of a new bradleyine genus.

The ostracod genus Bradleya Hornibrook is an important taxon of Cenozoic assemblages, occurring practically in all oceanic regions. The wide distribution both in shallow and deep waters turns Bradleya interesting for studies involving phylogeny and paleoceanography. The present work aims at the study of fossil and recent species in South America and adjacent regions, based on bibliographic review and the restudy of samples from the Brazilian continental margin, the Navidad Formation (lower Miocene) and El Peral Beds (meso-upper Miocene), both cropping out in the Central Chile. The chronostratigraphic, (paleo)bathymetric and (paleo)zoogeographic distribution of the species is reviewed and updated. The bridge composition was studied in all species recorded and revealed to be important taxonomic character. The taxa identified were gathered into three morphological groups: two proposed previously (i.e., the dictyon-group and the arata-group) and a new one in the present work (i.e., the normani-group). The dictyon-group and the arata-group gather deep-sea species, while the normani-group is predominantly neritic, including most of the species of Brazilian margin. Bradleya victorjarai sp. nov. is proposed for the Miocene of Chile, and Bradleya ybate (Bergue et al.) is reassigned to Rigracythere gen. nov. Questionable or misidentified species ascribed to Bradleya are briefly discussed.

Sea-air CO 2 fluxes along the Brazilian continental margin

Sea-air CO 2 fluxes along the Brazilian continental margin

On the Deep Western Boundary Current Separation and Anticyclone Genesis off Northeast Brazil

AbstractThe Deep Western Boundary Current (DWBC) is the main component of the deep limb of the Atlantic Meridional Overturning Circulation (AMOC). Off northeast Brazil, the DWBC breaks up into southwestward‐propagating anticyclones. In this study, we investigate the breakup mechanism with hydrographic observations, eddy‐resolving numerical model outputs, and theory. Here, we present a quasi‐synoptic map of geostrophic velocities and stream function at the DWBC core level between 2.5°S and 11°S. We observe, in horizontal distributions of velocities, that the DWBC breakup site is linked to a topographic feature of the Brazilian continental margin centered at 8°S: the Pernambuco Plateau (PP). Moreover, both observations and model outputs hint at a possible DWBC separation near the PP preceding anticyclone genesis. We test, with three different theories from the literature, whether or not the DWBC separates at 8°S. The results of the tests converge to indicate that the DWBC undergoes a local and intermittent inertial separation while contouring the PP. Downstream of its separation at the plateau, the DWBC sheds eddies similarly to previously reported laboratory experiments. In addition, a regional analysis of energy transfer shows that barotropic instability significantly contributes to the anticyclones growth between 8°S and 13°S. Analysis of the energy budget and separation of waters related to the AMOC pathways into the basin interior provide a better understanding for later studies about heat fluxes and ventilation in the deep tropical South Atlantic.

Regional-residual separation and enhancement methods applied to regional analysis of potential data: Structure of Florianopolis and Rio de Janeiro fracture zones in the western South Atlantic

Topographic, gravimetric and magnetic data has been employed to map regional tectonic elements in the South Atlantic presenting major oceanic tectonic structures which had previously lacked continuity when approaching the continental margin. The creation of such contoured maps has proven that numerical transform methods involving regional/residual separation and derivatives of gravity and magnetics can enhance geophysical signatures and unveil hidden structures, especially in the transition from the continental margins to the oceanic basin. In assessing the tectonic trend of the Florianopolis and Rio de Janeiro fracture zones close to the Brazilian continental margin, the fracture zones change direction from E-W in the oceanic region to NE-SW in the continental margin, probably displaced by the cretaceous hinge line in the northern portion of the Santos Basin. The continental structures associated with possible transcurrent and transfer zones that gave rise to the fracture zones of Rio de Janeiro and Florianopolis, probably played an essential role in the evolution of both the SE margin of the Santos Basin and the African conjugated margin. Analysis demonstrates the magnetic and gravimetric signatures of fracture zones can serve as important constraints for reconstructing continental margins in the rift and post-rift.

Connectivity patterns of Brazilian coral reefs associated with potential variation on thermal stress tolerance

The rising trend in sea surface temperature presents a threat to tropical coral reefs, causing increased mass bleaching and mortality events. Brazilian reefs have been characterized as less susceptible to thermal stress, where the assessment of bleaching events based on temperature anomalies often overpredicts its actual occurrences in comparison with other regions of the global ocean. With coral reefs acclimatized to local environmental conditions, larval connectivity presents a potential role in introducing organisms adapted to different temperature conditions. In the present study, we evaluated the connectivity patterns of Brazilian coral reefs, verifying its potential influence on the variation of thermal stress tolerance supported by these communities. Connectivity was estimated based on 27-year larval dispersion simulations, from 1993 to 2019, among 180 reef sites distributed in seven ecoregions on the Brazilian continental margin. Simulations were performed using a biophysical model coupling ocean currents data and life history traits of Mussismilia hispida, a widespread stony-coral type species and one of the major endemic reef builders in the South Atlantic. The potential influence of larval connectivity on thermal stress tolerance was evaluated considering the probability of connections between each reef site, their respective bleaching thresholds, and the accumulation of sea surface temperature anomalies over 12-week periods. The results indicated that connectivity-influenced bleaching estimations were significantly closer to observations reported in the literature when compared to estimations without connectivity (p-value < 0.05). These findings present an evidence that larval connectivity may display a relevant role in the adaptation of Brazilian corals to changes in seawater temperature, leading to a potential variation of ± 0.3°C in local thermal stress thresholds. Different connectivity patterns assessed during the occurrence of El Niño–Southern Oscillation events were also observed in association with the migrations of the South Equatorial Current bifurcation. These conditions led to the disruption of connections between the Eastern and Northeastern reef sites during El Niño, and between the Northeastern and Amazon reef sites during La Niña. Ultimately, it is expected that those findings may contribute to the management of Brazilian coral reefs regarding changes in dispersal pathways and thermal stress tolerance given future climate change scenarios.

The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin

Recent oceanographic observations have identified significant changes of intermediate water masses characterized by increased temperatures, lowered pH and deoxygenation. In order to improve our understanding as to how these changes may impact deep-sea ecosystems one important strategy is to reconstruct past oceanic conditions. Here we examine the applicability of the scleractinian cold-water coral Solenosmilia variabilis as a marine archive for the reconstructions of past intermediate water mass temperatures by using Lithium (Li)/Magnesium (Mg) ratios. In particular, our study addresses 1) the calibration of Li/Mg ratios against in-situ temperature data, 2) the reconstruction of past intermediate water mass temperatures using scleractinian coral fossil samples from the Brazilian continental margin and 3) the identification of intraspecies variability within the coral microstructure. Results showed that Li/Mg ratios measured in the skeletons of S. variabilis fit into existing Li/Mg-T calibrations of other cold-water scleractinian. Furthermore, the coral microstructure exhibits interspecies variability of Li/Ca and Mg/Ca ratios were also similar to what has been observed in other cold-water scleractinian corals, suggesting a similar biomineralization control on the incorporation of Li and Mg into the skeleton. However, the Li/Mg based temperature reconstruction using fossil samples resulted in unexpectedly high variations >10°C, which might not be solely related to temperature variations of the intermediate water mass over the last 160 ka on the Brazilian continental margin. We speculate that such temperature variability may be caused by vertical movements of the aragonite saturation horizon and the associated seawater pH changes, which in turn influence the incorporation of Li and Mg into the coral skeleton. Based on these results it is recommended that future studies investigating past oceanic conditions need to consider the carbonate system parameters and how they might impact the mechanisms of Li and Mg being incorporated into skeletons of cold-water coral species such as S. variabilis.

S/SE Brazilian continental margin sea surface temperature and productivity changes over the last 50 kyr

Off the S/SE Brazilian continental margin, the Brazil Current (BC) drives important oceanographic processes. Over the Deglacial time interval, this shallow current was influenced by the Atlantic Meridional Overturning Circulation (AMOC) at different timescales resulting in changes in sea surface temperature (SST) and primary productivity. In this work, a 50-kyr record retrieved from the upper slope of Santos Basin (NAP63–1, 24°30′10“ S, 44°11’28” W, 842 m) was utilized to evaluate SST and productivity changes based on planktonic foraminifera abundances and Globigerinoides ruber (albus) Mg/Ca ratios. Our results highlight that during Marine Isotopic Stage 3 (MIS 3), the SW Atlantic was marked by increased variability in SST and productivity related to South Atlantic Central Water upwelling during BC strengthening driven by episodic AMOC interruption events. As the AMOC weakened during MIS 2, the BC strengthened, and surface water productivity increased in the Brazilian margin. Towards MIS 1, SST progressively increased while productivity decreased because of a weaker BC as AMOC resumed its interglacial state. Our findings suggest that the previously observed Holocene antiphase relationship between AMOC and BC has been present since MIS 3.

Mecanismos de fertilização inferidos através do registro de cocolitoforídeos durante o Quaternário Tardio na Margem Continental Sul-Brasileira

Mechanisms of fertilization inferred from the coccolithophorid record during the Late Quaternary in the southern Brazilian Continental Margin. This study aimed to understand which fertilization mechanisms are preponderant over oceanic primary productivity and its relationship with remarkable climatic events of the Late Quaternary in the south of the Brazilian Continental Margin. The investigation was carried out through geochemical and coccolithophorid analyzes in the SIS188 marine core, recovered from the Pelotas Basin slope at 1,514 m water depth. The record shows that productivity was related to insolation (with a predominance of the precession cycle) and atmospheric processes that influence ocean dynamics. During the glacial period (MIS 3 and 2), the highest productivity intervals were associated with the expansion of the upwelling system in the Santa Marta Cape region, driven by the northeast winds. However, the interval of greatest productivity recorded in the core is the initial Holocene, when the upwelling was attenuated. This substantial increase in productivity is attributed to lagging processes resulting from the decrease in sea level that occurred during the Last Glacial Maximum. Keywords: productivity, Pelotas Basin, upwelling, Quaternary, coccolithophorids.

Effects of the seasonality of mesoscale eddies on the planktonic dynamics off eastern Brazil

The South Equatorial Current’s southern branch (SSEC) reaches the Brazilian continental margin through several bands between 30°S and 10°S. As the SSEC 14°S band reaches the Brazilian continental margin, it bifurcates into the poleward-flowing Brazil Current (BC), and the surface portion of the equatorward-flowing North Brazil Undercurrent (NBUC). Some semi-permanent eddies are formed in association with the bifurcation, and their variability is controlled by the seasonality of the SSEC bands. This work aims to investigate the role of the seasonality of these mesoscale eddies on the regional phytoplanktonic dynamics. We analyze chlorophyll-a satellite observations and perform two experiments using a Nutrients–Phytoplankton–Zooplankton (NPZ) model coupled to a 112-layer quasi-geostrophic model. The results show that the phytoplankton annual cycle off eastern Brazil is mainly controlled by the seasonally varying advection of material offshore caused by the mesoscale eddies. Such a mechanism may represent an important source of material to the tropical oligotrophic ocean.

Calcium Carbonate Dissolution Triggered by High Productivity During the Last Glacial–Interglacial Interval in the Deep Western South Atlantic

Studies reconstructing surface paleoproductivity and benthic environmental conditions allow us to measure the effectiveness of the biological pump, an important mechanism in the global climate system. In order to assess surface productivity changes and their effect on the seafloor, we studied the sediment core SAT-048A, spanning 43–5 ka, recovered from the continental slope (1,542 m water depth) of the southernmost Brazilian continental margin, deep western South Atlantic. We assessed the sea surface productivity, the organic matter flux to the seafloor, and calcite dissolution effects, based on micropaleontological (benthic and planktonic foraminifers, ostracods), geochemical (benthic δ13C isotopes), and sedimentological data (carbonate and bulk sand content). Superimposed on the induced changes related to the last glacial–interglacial transition, the reconstruction indicates a significant and positive correlation between the paleoproductivity proxies and the summer insolation. From the reconstructed data, it was possible to identify high (low) surface productivity, high (low) organic matter flux to the seafloor, and high (low) dissolution rates of planktonic Foraminifera tests during the glacial (postglacial). Furthermore, within the glacial, enhanced productivity was associated with higher insolation values, explained by increased northeasterly summer winds that promoted meandering and upwelling of the nutrient-rich South Atlantic Central Water. Statistical analyses support the idea that productivity is the main cause for seafloor calcium carbonate dissolution, as opposed to changes in the Atlantic Meridional Overturning Circulation (at least for the 25–4 ka period). Further efforts must be invested in the comprehension and quantification of the total organic matter and biogenic carbonate burial during time intervals with an enhanced biological pump, aiming to better understand their individual roles.