Felipe Antonio de L Toledo

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

Relationship between isotopic composition (Δ18O and Δ13C) and plaktonic foraminifera test size in core tops from the Brazilian Continental Margin

O tamanho de testa dos foraminiferos e uma importante fonte de variabilidade isotopica (δ18O e δ13C) em amostras de sedimento marinho comprometendo as interpretacoes paloeceanograficas. No presente estudo, avaliou-se a relacao entre o sinal isotopico medido em diferentes fracoes de tamanho de testa das especies planctonicas, Globigerinoides ruber (branca) e Globorotalia truncatulinoides (dextral) em amostras de topo de dois testemunhos localizados na Margem Continental Brasileira. Os valores de δ18O foram utilizados para estimar a profundidade de calcificacao de cada fracao de tamanho. Os desequilibrios nos valores de δ13C para cada fracao de tamanho foram estimados. Os valores de δ18O em G. ruber (branca) nao apresentaram tendencia com o tamanho sugerindo que calcifica dentro de um mesmo intervalo de profundidade (c.a. 100 m) durante a ontogenia. Os valores de δ18O em G. truncatulinoides (dextral) apresentaram aumento com o tamanho refletindo a migracao ontogenica em aguas da termoclina (250-400 m). Os valores e desequilibrios de δ13C aumentaram com o tamanho nas duas especies indicando o efeito da variacao nas taxas fisiologicas durante a ontogenia. Em G. ruber (white) os valores de δ13C dos maiores tamanhos (300µm e >355µm) refletem melhor os valores de δ13CDIC indicando que sao mais apropriados para utilizar nas reconstrucoes paleoceanograficas.

Stable isotope/test size relationship in Cibicidoides wuellerstorfi

C) measurements in foraminifera tests are widely used for paleoceanographic interpretations (WEFER et al., 1999; ROHLING; COOKE, 1999). This is attained since during calcification foraminifera registered in their tests the stable isotope signature and environmental conditions of seawater of their local of calcification in a somehow predictable way (ROHLING; COOKE, 1999). Foraminifera test size is an important source of stable isotope variability found in sediment samples. Some of this variability is associated to foraminifera physiological effects (e.g., symbiotic photosynthesis, respiration and calcification) which can vary along ontogeny and affect stable isotope measurements in foraminifera tests (ZEEBE et al., 1999). Regional environmental variables can also affect simultaneously both stable isotope values and foraminifera test size resulting in another source of test size/stable isotope variability (DEUSER et al., 1981). Although it is especially important in planktonic foraminifera (RAVELO; FAIRBANKS, 1995), some studies have found test size/stable isotope variation in benthic foraminifera (CORLISS et al., 2002). This test size/stable isotope variability can result in offsets from predicted values having important implications when choosing test size fractions for paleoceanographic interpretations (OPPO; FAIRBANKS, 1989). Cibicidoides wuellerstorfi is an epibenthic foraminifera species of great importance in stable isotopic paleoceanographic studies (MACKENSEN; LICARI, 2003). Nevertheless its paleoceanographic importance no stable isotope ( δ