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 foraminíferos é uma importante fonte de variabilidade isotópica (δ18O e δ13C) em amostras de sedimento marinho comprometendo as interpretações paloeceanograficas. No presente estudo, avaliou-se a relação entre o sinal isotópico medido em diferentes frações de tamanho de testa das espécies planctônicas, 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 calcificação de cada fração de tamanho. Os desequilíbrios nos valores de δ13C para cada fração de tamanho foram estimados. Os valores de δ18O em G. ruber (branca) não apresentaram tendência 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 migração ontogênica em águas da termoclina (250-400 m). Os valores e desequilíbrios de δ13C aumentaram com o tamanho nas duas espécies indicando o efeito da variação nas taxas fisiológicas durante a ontogenia. Em G. ruber (white) os valores de δ13C dos maiores tamanhos (300µm e >;355µm) refletem melhor os valores de δ13C DIC indicando que são mais apropriados para utilizar nas reconstruções paleoceanograficas.Stable oxygen (δ18O) and carbon (δ13C) isotopic signature registered in fossil planktonic foraminifera tests are widely used to reconstruct ancient oceanographic conditions. Test size is a major source of stable isotope variability in planktonic foraminifera found in sediment samples and thus can compromise paleoceanographic interpretations. Test size/stable isotope (δ18O and δ13C) relationships were evaluated in two planktonic foraminifer species (Globigerinoides ruber (white) and Globorotalia truncatulinoides (right)) in two core tops from the Brazilian Continental Margin. δ18 Omeasurements were used to predict the depth of calcification of each test size fraction. δ13C offsets for each test size fraction were then estimated. No systematic δ18O changes with size were observed in G. ruber (white) suggesting a similar calcification depth range (c.a. 100 m) during ontogeny. For G. truncatulinoides (right) δ18O values increased with size indicating ontogenetic migration along thermocline waters (250-400 m). δ13C measurements and δ13C offsets increased with size for both species reflecting well known physiological induced ontogenetic-related variability. In G. ruber (white) the largest test size fractions (300µm and >;355µm) more closely reflect δ13C DIC indicating they are best suited for paleoceanographic studies

O Quaternário no Escudo Sul-Rio-Grandense: um Paleoambiente Lacustre em Encruzilhada do Sul, RS.

Quaternary lacustrine deposits were identified and studied for the first time in a 1.2 m core test (PED-92/T-15) on the Precambrian Shield of Rio Grande do Sul at Encruzilhada do Sul. The area of the deposit is about one kilometer square. Sedimentologic and micropaleontologic study identified the following sequence: sand (base) → non laminated, silty black clay → slightly sandy/silty black clay → silty black clay with organic matter and some pebbles. Diatoms of the Order Pennales are the dominant microfossils. The sedimentary sequence shows that an initial shallow, sandy lake eutrophied and became filled with organic-rich clays

Climatically induced changes in late Quaternary bathyal ostracod assemblages of the Camamu Basin, Brazil

Bathybic ostracods (i.e., bathyal and abyssal assemblages) are important indicators of temperature and productivity changes of Cenozoic marine ecosystems. The present work presents the first study on Quaternary ostracods of the Camamu Basin, off the state of Bahia, northeastern Brazilian continental margin. The analysis of 59 samples from the piston-core CMU 14 (14°24’S, 38°49’W; 965 m water depth), revealed rich and abundant assemblages. The 14C accelerator mass spectrometry (AMS) dating indicates that the studied interval covers the last 108 kyr, corresponding to the oxygen stable isotope stages (MIS) 5 to 1. Comparison with data from previous publications allowed discernment of three groups of ostracod species in CMU 14: Pandemic Group of species registered in more than one oceanic basin; Atlantic/Mediterranean Group of species restricted to the Atlantic Ocean and Mediterranean; and Brazilian Group of species restricted to the Brazilian continental margin). Four new species are herein proposed: Cytherella pindoramensis sp. nov., Ambocythere amadoi sp. nov., Pseudobosquetina pucketti sp. nov., and Bythoceratina bonaterrae sp. nov. Ostracod occurrences reveal the influence of glacial/interglacial cycles on assemblages composition. Interglacial stages 5 and 1 in the Camamu Basin are characterized by the association Bythocypris affinis–Cytherella pindoramensis sp. nov.– Cytheropteron perlaria–Bradleya dictyon; glacial stages (i.e., 2 to 4) register decreased diversity, possibly due to lower oceanic productivity

Biogenic composition of calcium carbonate over the past 140,000 years: clues from a marine core in the Santos Basin

This study aimed to investigate the biogenic composition of calcium carbonate (CaCO 3) in pelagic sediments in the Santos Basin over the past 140,000 years. The content and composition of CaCO 3 in different sediment fractions were evaluated, including the bulk sample, coarse fraction (foraminifera), medium fraction (juvenile foraminifera and fragments), and fine fraction (nannofossils), to determine the contribution of each fraction to the carbonated sediment composition. We found that variations in CaCO 3 levels were closely linked to glacial and interglacial periods, with higher values during interglacial periods and lower values during glacial periods. The main factor controlling the variation in CaCO 3 was dissolution, which was mainly linked to the influx of more corrosive southern water masses. Fluctuations in CaCO 3 levels were influenced by variations in productivity and dilution caused by terrigenous sediments. Nevertheless, it is noteworthy that both processes held a relatively minor impact compared to dissolution. Productivity primarily contributed to increased dissolution rates. During periods of low sea levels, dilution by terrigenous sediments became significant (similarly, the influence of the La Plata River plume was notable). However, due to the limited presence of riverine supply in the study area, which contributes directly to major dilution influences, fluctuations in terrigenous materials were considered of lesser magnitude than those caused by dissolution. The nannofossils were found to be the largest contributor to the total CaCO 3 composition, as they were the fraction least affected by the dissolution process. Overall, our results provide insights into the factors influencing CaCO 3 accumulation in marine sediments and can be used as a tool to determine changes between climatic cycles over time

Evaluation of two genera of benthic foraminifera for down-core paleotemperature studies in the western south atlantic

In this study we have compared the oxygen isotopic composition of two genera of benthic foraminifera (Uvigerinaand Cibicidoides) from core-top samples with modern oxygen isotopic composition of seawater (d18O). Based on a new relationship between d18O and salinity for the mid-latitude western South Atlantic, we estimated the isotopic composition of equilibrium calcite (d18Oeq) using two different equations: (1) O'Neil et al. (1969), modified by McCorkle et al. (1997) and (2) Kim & O'Neil (1997). When using (1), the small difference between d18Oeq and d18O of Uvigerina suggests that this genus precipitates its shell close to equilibrium with ambient seawater. The d18OCibicidoides data are 0.82 ‰ lower than the predicted (equilibrium) oxygen isotopic composition. Conversely, using (2) the Cibicidoides d18O data show excellent agreement with the oxygen isotopic composition predicted from d18O and water temperature while Uvigerina d18O data are 0.69 ‰ higher than predicted oxygen isotope equilibrium values. Based on the evidences presented here and on the results from previous studies we suggest using the genus Cibicidoides and applying Kim & O'Neil's (1997) equation for down-core paleotemperature investigations. In the absence of enough Cibicidoides specimens we suggest using Uvigerina d18O data and applying a correction factor of -0.69 ‰.Neste estudo, compara-se a composição de isótopos de oxigênio de dois gêneros de foraminíferos bentônicos (Uvigerina e Cibicidoides) de amostras de topo de testemunho com a composição isotópica moderna da água do mar (d18O). Baseados em uma nova relação entre d18O e salinidade para a latitude média do Atlântico Sul ocidental, estimou-se a composição isotópica da calcita em equilíbrio (d18Oeq) a partir de duas equações diferentes: (1) O'Neil et al. (1969), modificada por McCorkle et al. (1997) e (2) Kim & O'Neil (1997). Utilizando (1), a pequena diferença entre d18Oeq e d18O de Uvigerina sugere que este gênero precipita as suas testas próximo ao equilíbrio com a água. Já os dados de d18O de Cibicidoides são 0,82 ‰ menores que a composição isotópica prevista. Ao contrário, utilizando (2) os dados de d18O de Cibicidoides mostram uma concordância excelente com a composição isotópica esperada, enquanto que os dados de d18O de Uvigerina são 0,69 ‰ maiores que os valores de equilíbrio previstos. A partir das evidências apresentadas neste trabalho e em estudos prévios sugerimos a utilização do gênero Cibicidoides e a aplicação da equação de Kim & O'Neil (1997) para pesquisas de paleotemperatura. Na ausência de suficientes espécimens de Cibicidoides sugerimos a utilização de d18O deUvigerina aplicando um fator de correção de -0,69 ‰

Boletín del Servicio Meteorológico Español: Año XXXIX Número 283 - 1931 Octubre 10

Foram analisados os ostracodes recuperados de 15 perfurações realizadas em duas áreas adjacentes, o município de Imaruí e a região do Rio D’uma, ambas no Estado de Santa Catarina, sul do Brasil. Dentre as 12 espécies identificadas apenas três foram deixadas em nomenclatura aberta. O estudo da estrutura populacional, realizado em cada amostra, permitiu a diferenciação entre fauna alóctone vs. autóctone. As espécies mixohalinas Cyprideis multidentata Hartmann e C. salebrosa Bold são os fósseis autóctones mais abundantes nos testemunhos investigados. A análise tafonômica e as evidências sedimentológicas indicaram um paleoambiente tipicamente lagunar ao longo das 15 perfurações. Tanto a microfauna quanto os dados advindos da geologia sugerem que as espécies marinhas foram transportadas para o ambiente lagunar, retrabalhadas juntamente com a fauna mixohalina e depositadas ao longo da borda da laguna.Late Quaternary ostracodes collected from 15 cores in two adjacent localities, Imaruí and D’Una River, both in Santa Catarina State, southern Brazil, were analyzed. Among the 12 identified species, only three are left in open nomenclature. The population age-structure was studied in order to distinguish between allochthonous vs. autochthonous ostracodes in each sample. Two typically mixohaline species, Cyprideis multidentata Hartmann and C. salebrosa Bold, are the most abundant autochthonous fossils in the cores. The taphonomic analysis and the sedimentological evidences allow the inference of a permanent lagoonal palaeoenvironment in the 15 cores. Micropalaeontological and geological data suggest that the marine species were transported into the lagoonal palaeoenvironment, reworked with the autochthonous mixohaline fauna and deposited along the lagoonal border

FORAMINIFERAL RECORD OF CHANGES IN SUMMER MONSOON PRECIPITATION AT THE SOUTHEASTERN BRAZILIAN CONTINENTAL MARGIN SINCE THE LAST GLACIAL MAXIMUM

Changes in the oxygen isotopic composition of the planktonic foraminifer Globigerinoides ruber and in the foraminifera faunal composition in a core retrieved from the southeastern Brazilian continental margin were used to infer past changes in the hydrological balance and monsoon precipitation in the western South Atlantic since the Last Glacial Maximum (LGM). The results suggest a first-order orbital (precessional) control on the South American Monsoon precipitation. This agrees with previous studies based on continental proxies except for LGM estimates provided by pollen records. The causes for this disagreement are discussed.FAPESP (Fundacao de Amparo a Pesquisa do Estado de Sao Paulo)[04/02819-8]CNPq (Conselho Nacional de Desenvolvimento Cientifico e Tecnologico)[141577/2005-3

Quaternary Calcareous Nannofossils from Campos Basin, Brazil - Systematic and Primary Diagenesis

The analyses of five piston cores (SG91-09/PC-01, SG91-14/PC-04, SG91-14/PC-06, SG91-14/PC08 e SG91- 14/PC09) sampled on Campos Basin - RJ, Brazil, permitted the systematic studies in Quaternary calcareous nannofossils and the description of the primary diagenesis effects on this microfossils using optical microscope and scanning electron microscope. The observation of “in situ” dissolution and reprecipitation of calcium carbonate recorded limitate the systematic studies of calcareous nannofossils and show the importance to use both optical and scaning microscope