Mid-lower bathyal benthic foraminifera of the Campos Basin, southeastern Brazilian margin: biotopes and controlling ecological factors

Abstrac

Inorganic and organic geochemical fingerprinting of sediment sources and ocean circulation on a complex continental margin (São Paulo Bight, Brazil)

In this study, we use inorganic (metal) and organic (bulk and molecular) markers in sediment samples of the south-eastern Brazilian margin to investigate the response of geochemical fingerprints to the complex hydrodynamic processes present in the area. Results indicate the potential of export of terrigenous siliciclastic and organic constituents to the upper slope, even in an area with limited fluvial supply. Metal contents and especially the ln(Ti = Al) and ln(Fe = K) ratios make it possible to recognise the extension of shelf sediments toward the upper slope. Potassium, here expressedas ln(K = Sc) and ln(K = Al) ratios used as proxies of illite–kaolinite variations, proved to be an important parameter, especially because it allowed us to decipher the imprint of the northward flow of the Intermediate Western Boundary Current (IWBC) in comparison to the southward flows of the Brazil Current (BC) and Deep Western Boundary Current (DWBC). Using organic matter analyses, we were able to evaluate the extent of terrestrial contributions to the outer shelf and slope, even without the presence of significant fluvial input. In addition, molecular markers signify a slight increase in the input of C4-derived plants to the slope sediments, transported from distant areas by the main alongshore boundary currents, indicating that the terrestrial fraction of the organic matter deposited on the slope has a distinct origin when compared to shelf sediments

The ITRAX core scanner, a useful tool to distinguish anthropic vs. climatic influences in lagoon of Aveiro (N Portugal)

The main goal of this work is to distinguish anthropic and climatic influences in sediments from the lagoon of Aveiro (Portugal). This study is based on a core (240-cm long) collected in Murtosa Channel. Optical and X-radiographic images and high-resolution elemental profiles were acquired with ITRAX micro-X-ray fluorescence (XRF) core scanner. Samples collected at each ≈3 cm along the core were analysed for grain size and total organic carbon. Furthermore, the fine fraction of selected layers was subjected to geochemical analysis by ICP-MS, after total acid digestion of the sediments, and mineralogical analysis, by XRD techniques. A radiocarbon age was determined by AMS, using molluscs shells collected at a depth of 90 cm. Sediments along the core are composed by fine and medium sand, with several mud layers. Sediments composing the first 100-cm may have been deposited after 1950, as it is indicated by the radiocarbon data, the increasing trend of Zn/Al, Pb/Al and Cu/Al and total concentrations of Zn, Pb, Cu, V, Cr, As and Ni in this interval that therefore might be linked with industrial activities of Chemical Complex of Estarreja. The progressive increase of Si/Al, Cl/Al, Rb/Al, K/Al and Br/Al and reduced Al concentrations, from the base to the top of this core, are interpreted as being related to higher marine influence and greater differences in tidal currents with longer exposition to air of the sediments with the consequent formation of brines favouring minerals precipitation in the area (e.g. anhydrite). These results seem to be a consequence of several works developed over time like: i) dredging to improve the navigation access to the harbour, located in the external sector of the lagoon; ii) the control of the course of some rivers influencing the supply of sediments. The tendency of sea level rise may have also emphasized the gradual increase of marine influence in this area. Fine-grained sections, related to an increase in Al, phyllosilicates, organic matter, pyrite and siderite contents would be attributed to phases of greater supply of fine-sediments during heavy rainfall events by the nearby Antuã river and other streams during negative phases of North Atlantic Oscillation. Higher deposition of organic matter enhanced diagenetic changes with pyrite and siderite formation. In the bottom of the core another record of pollution was unveiled to mining activities at the beginning of 20th century.FCT de Portugal - C/CTE/UI4035/2011CNPq - 401803/2010-

Natural radionuclides distribution in the shelf and upper slope off southeast Brazil

In recent decades, Oceanography has been using a variety of radionuclides as tracers to understand the ocean\ud dynamic processes, handling and disposal of sediments of seabed. In this context, the determination of natural\ud radionuclides distributions (238U, 232Th and 40K) has been carried out with sediments samples from the shelf and\ud upper slope off Southeast Brazil using a gamma spectrometry technique. The samples were sliced into strata of\ud 2 cm, dried, ground and properly packed to be analysed. The concentration of activities was performed in a\ud hyperpure Ge detector with a resolution of 1,9 keV for the peak of 1332,3 keV of 60Co, model GEM50P by\ud EGG&ORTEC. The study area is located between latitudes 28°40'S and 23°00'S and extends from Cabo Frio\ud (RJ) to Cabo de Santa Marta Grande (SC). The activity concentrations varied from 0,6 to 52,8 BqKg-1 for 238U,\ud from 1,6 to 50,9BqKg-1 for 232Th and from 65,4 to 873,3 BqKg-1 for 40K. From these results it is possible to\ud establish a correlation between the depositional area dynamics and the samples size parameter

137Cs Inventory in sedimentary columns from continental shelf of São Paulo State

137Cs is an artificial radioactive isotope produced by 235U fission. This radionuclide has a high fission yield and\ud a half-life of 30 years. It has been detected in the environment since 1945 and its principal contamination source\ud has been nuclear tests in the atmosphere. There are other sources of 137Cs contamination in the environment,\ud such as: release from nuclear and reprocessing plants, radioactive dumping and nuclear accidents (Chernobyl,\ud for example). This paper presents an inventory of 137Cs on the Continental Shelf of São Paulo State, a region\ud located between Cabo de Santa Marta Grande (Santa Catarina state) and Cabo Frio (Rio de Janeiro state). In this\ud area, 9 cores were collected by the Instituto Oceanográfico da Universidade de São Paulo (São Paulo\ud University Institute of Oceanography). The cores were sliced at every 2 cm; sub-samples were lyophilized,\ud grinded and stored in plastic containers. 137Cs was determined by 661 keV photopeak using a gamma\ud spectrometry detector (Ge hyperpure). The analysis was performed by efficiency and background in different\ud counting times. 137Cs concentration activities varied from 0.3 to 3.6 Bq kg-1 with a mean value of 1.2±0.6 Bq\ud kg-1. The inventory of 137Cs in this area was 13±7 Bq m-2. Values obtained are in agreement with the Southern\ud Hemisphere, a region contaminated by atmospheric fallout due to past nuclear explosions

Levantamento dos fatores de enriquecimento do As e metais em \ud sedimentos superficiais do Canal de Bertioga (SP), Brazil

Em virtude do desenvolvimento econômico do litoral paulista, ao longo do século XX, ocorreram modificações no ambiente costeiro proveniente de construções de rodovias, melhorias na estrutura portuária de Santos e implantação do pólo petroquímico de Cubatão. Localizado na porção mais a NE do complexo estuarino da Baixada Santista, o Canal de Bertioga, com aproximadamente 25 km de extensão, faz a ligação entre o oceano e o alto estuário santista. O canal é considerado como uma conexão secundária do oceano ao complexo estuarino de Santos, com sua desembocadura a nordeste localizada próxima a cidade de Bertioga, e a desembocadura oposta próxima ao canal do alto estuário santista. Assim, esse trabalho teve como objetivo fazer um levantamento dos fatores de enriquecimento de As, Cr, Cu, Mn, Ni, Pb e Zn em 147 amostras de sedimentos superficiais coletadas ao longo do Canal. As amostras foram inicialmente liofilizadas, procedendo-se a digestão ácida e determinação dos elementos de interesse por espectrometria de emissão ótica por plasma indutivamente acoplado (ICP-OES). Os resultados obtidos mostraram-se distribuídos dentro de dois padrões, um deles apresentando maiores valores de fator de enriquecimento na desembocadura sul, próximo à região de Guarujá e o outro, na desembocadura norte, o qual sofre grande influência do estuário Santista e das inúmeras fontes ali presente

Buracas: Novel and unusual sinkhole-like features in the Abrolhos Bank

Novel and unusual sinkhole-like features are described for the Abrolhos Bank continental shelf, eastern Brazil, based on geophysical and geological assessments. These unusual structures are large cup-shaped depressions similar to sink/blueholes (10–75 m in diameter, 8–39 m in height), occurring in a consolidated carbonate substrate in the mid and outer shelf. A total of 36 such features, locally named buracas, were found between 41 and 161 km off the coast and between 24 and 65 m depth (the bottom of these features may be as deep as 93 m). The buracas’ walls are mainly composed of encrusting coralline algae. Radiocarbon dating has provided ages of 5400±90 yr Cal BP, 8630±90 yr Cal BP and 39,200±400 yr BP. Besides providing a comprehensive description of these novel structures within the mesophotic zone, the potential mechanisms by which these sinkhole-like structures originated are discussed here, as well as the possible active mechanisms impeding their filling with sediments and biogenic material. We hypothesize that their origin could be related to either typical sinkhole formation during subaerial exposure or to a partially Holocene growth pattern influenced by antecedent morphology and gas/fluid escaping due to organic matter decomposition. The buracas are relevant not only because they comprise outstanding novel features, but also because they are relevant targets for marine conservation, as they enhance productivity and aggregate biomass in a region under growing fishing pressure.Gordon and Betty Moore Foundation, Conservation International’s Marine Management Areas Science Program - 14CNPq PROABROLHOS - 420219/2005-6CNPq Universal - 482001/2009-7FAPERJCNPq/FAPES Sisbiot