Valdenir Veronese Furtado

The Southern Brazilian shelf: general characteristics, quaternary evolution and sediment distribution

S to 22 S the Southern Brazilian shelf constitutes the only part of the Brazilian shelf with a subtropical to temperate environment. The studies on the different geological aspects of the area began in the 1960´s and have recently been reassessed after studies related to the determination of the Economic Exclusive Zone. In terms of morphology, the Southern Brazilian shelf may be divided into three sectors, the Sao Paulo Bight, the Florianopolis-Mostardas Sector and the Rio Grande Cone, characterized by conspicuous differences in terms of geological determining factors, bathymetry, declivities and the presence of canyons and channels. Despite the existence of hundreds of radiocarbon datings the sea level changes curve of southern Brazil during the Last Glacial Cycle is still a matter of debate. A recent controversy on the Middle and late Holocene sea level changes curve raised the question of the amplitude of the oscillations which occurred in the period. Also, a few but relatively consistent radiocarbon datings suggest the occurrence of a high sea level during Isotope Stage 3. In terms of sedimentary cover the Southern Brazilian shelf exhibits a very strong hydrodynamic control, both latitudinal and bathymetrical. The sector southward from 25

Topographic registers of paleo-valleys on the southeastern Brazilian continental shelf

The evolution of paleo-incised-valleys in the Sao Paulo State region of the southeastern Brazilian continental shelf is presented in this study in relation to the post Last Glacial Maximum (LGM) sea-level rises based on the submarine topography modeled by a detailed Digital Elevation Model and evidences noted in high resolution seismic profiles. The hypothesis that has guided this study is that the set of paleo-valley characteristics (i.e. the fluvial parameters of modern coastal drainage systems, the topographical shape and dimensions of the valleys and of the subsurface channels) may indicate aspects of the relation between the influence of the fluvial and the eustatic variation regime in geomorphological-stratigraphic registers. Models described in the literature sustain the view that faster marine transgressions tend to increase erosion in estuaries, which may explain the lack of registers of paleo-drainage both in topography and the sub-surface in areas with wider shelves. On the other hand, on narrower shelves, with a higher slope angle, the transgression process can preserve, or even enhance, the incised valley registers during shoreface retreat. In the area studied, we observed that the dimensions and form of the continental shelf varies from the northern to the southern part of the area, affecting aspects of the geomorphological registers of the submerged incised valleys.

Dinâmica de sedimentação das feições de assoreamento da região lagunar Cananéia-Iguape, Estado de São Paulo

O complexo lagunar de Cananeia e Iguape apresenta tendencias ao assoreamento em seus canais lagunares (Kutner, 1962). Estas tendencias podem ser visualizadas atraves de modificacoes nos canais ocasionadas pelo crescimento de feicoes sedimentares, como pequenas ilhas e esporoes. Para a avaliacao das modificacoes sofridas por essas feicoes, com o tempo, foram usados dois conjuntos de fotografias aereas, um obtido em 1962 e outro em 1973, alem da carta nautica n. 1708 da DHN e observacoes de campo. O trabalho procura evidenciar o crescimento dessas feicoes no mar de Cananeia, mar de Cubatao e mar Pequeno, esquematizando provaveis estagios de evolucao e associando o sentido de crescimento das feicoes a dinâmica local.

Coastal water exchange rate studies at the southeastern Brazilian margin using Ra isotopes as tracers

Abstract The Sao Paulo Bight is the arc-shaped part of the southeastern Brazilian margin extending from 23°S to 28°S. To assess the cross-shelf Ra distributions in Sao Paulo Bight, four shore-perpendicular profiles were collected up to 100 km offshore from 23 to 26 February 2003 (summer). All samples studied here were taken in the selected area between latitudes 23°15′S and 25°50′S and longitudes 44°W and 46°W, in order to estimate coastal mixing rates and groundwater discharge fluxes. The activity concentrations of 223 Ra in surface seawater varied from 0.002 to 0.4 mBq L −1 , 224 Ra in excess from 0.02 to 2.5 mBq L −1 , 226 Ra from 1.2 to 1.8 mBq L −1 and 228 Ra from 0.4 to 4.4 mBq L −1 . The 223 Ra/ 224 Ra and 228 Ra/ 226 Ra activity ratios observed in seawater samples ranged from 0.03 to 2.6 and from 0.3 to 2.4, respectively. These results seem to indicate that Ra isotopes from 232 Th series prevail in a major number of samples, when compared with Ra isotopes from 238 U and 235 U series. Considering the results obtained in the summer 2003, shore-perpendicular profiles of 223 Ra and 224 Ra in surface waters along the coast were modeled to yield eddy diffusion coefficients.

An integrated GIS for sedimentological and geomorphological analysis of a lagoon environment. Barra de Cananéia inlet region, (Southeastern Brazil)

The aim of this work is to use GIS integration data to characterize sedimentary processes in a SubTropical lagoon environment. The study area was the Cananéia Inlet estuary in the southeastern section of the Cananéia Lagoon Estuarine System (CLES), state of São Paulo, Brazil (25°03′S/47°53′W). The area is formed by the confluence of two estuarine channels forming a bay-shaped water body locally called “Trapandé Bay”. The region is surrounded by one of the most preserved tracts of Atlantic Rain Forest in Southwestern Brazil and presents well-developed mangroves and marshes. In this study a methodology was developed using integrated a GIS database based on bottom sediment parameters, geomorphological data, remote sensing images, Hidrodynamical Modeling data and geophysical parameters. The sediment grain size parameters and the bottom morphology of the lagoon were also used to develop models of net sediment transport pathways. It was possible to observe that the sediment transport vectors based on the grain size model had a good correlation with the transport model based on the bottom topography features and Hydrodynamic model, especially in areas with stronger energetic conditions, with a minor contribution of finer sediments. This relation is somewhat less evident near shallower banks and depositional features. In these regions the organic matter contents in the sediments was a good complementary tool for inferring the hydrodynamic and depositional conditions (i.e. primary productivity, sedimentation rates, sources, oxi-reduction rates).

Evolução temporal e espacial da desembocadura lagunar de Cananéia (SP)

Shoreline changes of the Cananeia-Iguape lagoonal system (Sao Paulo State) have been reconstructed in detail through interpretation of aerial photographs since the 1950s. The most important changes are the recession of the northern and the advancement of the eastern side of the sandy segment of Cardoso Island, headed to the ocean, and the erosion of the lagoonal margin in the southern section of Comprida Island. The geomorphologic evolution of the southcoast of Sao Paulo shows to be closely related to the coastal hydrodynamic mechanisms induced by the atmospheric circulation of this part of the South American continent The interaction of these phenomena is fundamental not only to the mobility of sandy sediments, that obstruct or change the displacement of the channels that lead to the lagoonal area, but also for the erosive and depositional processes that affect the ocean side of Cardoso and Cananeia islands.

Utilização da análise dos componentes principais na caracterização dos sedimentos de superfície de fundo da Baía da Ilha Grande (RJ)

The Principal Component Analysis was applied to three sets of data, generated from the results of grain size analysis of 153 surface sediment samples of Ilha Grande Bay, Rio de Janeiro. State. The results show the advantages of the method in the interpretation of the different textural facies of the sediments of the area, in comparison to the classification methods of Shepard (1954) and Folk & Ward (1957). The results show also that the grain size frequencies are the best set of data for the application of the analysis.

Distribuição da matéria orgânica nos sedimentos marinhos costeiros e nos solos hidromórficos da orla litorânea do Estado de São Paulo

The organic matter content in the fine-fraction of 200 marine sediments samples and in 50 whole continental samplel along the Estado de Sao Paulo coast, between Cananeia and Ubatuba, show a close relation between organic content and depositional environment. Samples were collected in coastal plains lagoon-estuarine mangroves and inner continental shelf environments representative of that coastal region.

Levels of Pu-238 and Pu-239+240 in marine sediment samples from south coast of Brazil

O plutonio no meio ambiente e um elemento altamente toxico e dentre os diversos isotopos deste elemento destacam-se o Pu-238, o Pu-239 e o Pu-240, com meias-vidas de 87,5, 24.000 e 6500 anos, respectivamente. No decaimento radioativo liberam particulas alfa e embora esta nao seja uma fonte de irradiacao externa para os seres vivos, internamente e potencialmente perigosa. Nos seres humanos, o maior perigo e a incorporacao pelos pulmoes de particulas contendo o plutonio (UNEP, 1984). Quimicamente, o plutonio e um elemento altamente interessante, seu comportamento esta relacionado aos varios estados de oxidacao que possui, de +3 a +6, que podem ocorrer naturalmente no meio ambiente, dos quais a forma +4 e predominante. Os sedimentos acumulam a maior fracao do plutonio liberado em areas costeiras. A natureza deste radionuclideo nos sedimentos influencia uma maior interacao deste elemento com o meio e a biota presente (Keller, 1988, Mitchell et al., 1995; Strezov et al. 1996). Os dois isotopos mais importantes do plutonio, Pu-239 e Pu-240 sao emissores de particulas alfa com probabilidade de emissao da ordem de 73% e energia de emissao de 5,16 MeV e 5,17 MeV, respectivamente (IAEA, 1986; Bland & Truffy, 1992). Com estas energias proximas e com a baixa resolucao dos equipamentos de deteccao, mede-se a atividade do Pu-239 junto a atividade do Pu-240, na determinacao deste elemento em amostras ambientais. Este trabalho apresenta os resultados obtidos dos niveis de Pu-238 e Pu-239+240 em sedimento marinho da costa sul brasileira. A importância deste trabalho esta no fato de que nao existem, ate o momento, estudos destes radionuclideos na costa brasileira. Todavia, este levantamento e de extrema importância dentro de um contexto ambiental, salientando-se que: • o Brasil possui dois reatores nucleares de potencia em operacao, na regiao de Angra dos Reis, localizado na costa sudeste brasileira; • nao existem dados dos niveis de Pu-238 e Pu-239+240 na costa brasileira; • e necessario o levantamento dos teores de radionuclideos no litoral brasileiro afim de se conhecer o background regional e assim poder detecta r qualque alteraca o n meio, evidenciando uma contaminacao ambiental.

Níveis de Pu-238 e Pu- 239+240 em amostras de sedimento marinho da costa sul do Brasil

O plutônio no meio ambiente é um elemento altamente tóxico e dentre os diversos isótopos deste elemento destacam-se o Pu-238, o Pu-239 e o Pu240, com meias-vidas de 87,5, 24.000 e 6500 anos, respectivamente. No decaimento radioativo liberam partículas alfa e embora esta não seja uma fonte de irradiação externa para os seres vivos, internamente é potencialmente perigosa. Nos seres humanos, o maior perigo é a incorporação pelos pulmões de partículas contendo o plutônio (UNEP, 1984). Quimicamente, o plutônio é um elemento altamente interessante, seu comportamento está relacionado aos vários estados de oxidação que possui, de +3 a +6, que podem ocorrer naturalmente no meio ambiente, dos quais a forma +4 é predominante. Os sedimentos acumulam a maior fração do plutônio liberado em áreas costeiras. A natureza deste radionuclídeo nos sedimentos influencia uma maior interação deste elemento com o meio e a biota presente (Keller, 1988, Mitchell et al., 1995; Strezov et al. 1996). Os dois isótopos mais importantes do plutônio, Pu-239 e Pu-240 são emissores de partículas alfa com probabilidade de emissão da ordem de 73% e energia de emissão de 5,16 MeV e 5,17 MeV, respectivamente (IAEA, 1986; Bland & Truffy, 1992). Com estas energias próximas e com a baixa resolução dos equipamentos de detecção, medese a atividade do Pu-239 junto a atividade do Pu-240, na determinação deste elemento em amostras ambientais. Este trabalho apresenta os resultados obtidos dos níveis de Pu-238 e Pu-239+240 em sedimento marinho da costa sul brasileira. A importância deste trabalho está no fato de que não existem, até o momento, estudos destes radionuclídeos na costa brasileira. Todavia, este levantamento é de extrema importância dentro de um contexto ambiental, salientando-se que: