Análise bioestratigráfica e paleoceanográfica com foraminíferos planctônicos do quaternário tardio no Atlântico sul ocidental

Os foraminíferos planctônicos são excelentes ferramentas utilizadas em estudos bioestratigráficos e paleoceanográficos do Cenozoico devido à sua abundância, altas taxas de evolução, distribuição ampla e boa preservação. Além disso, suas carapaças carbonáticas se precipitam em equilíbrio isotópico com a água do mar, registrando as condições paleoceanográficas dos ambientes onde habitaram. Por tais razões, utilizaram-se as associações de foraminíferos planctônicos do testemunho SAT-048A, recuperado do talude médio da porção norte da Bacia de Pelotas para: i) avaliar o potencial de aplicação dos bioecozoneamentos desenvolvidos para as bacias de Santos e Campos, ii) reconstruir as condições oceanográficas de superfície e fundo e, iii) propor um modelo teórico para melhor avaliar os efeitos da dissolução na fragmentação dos foraminíferos planctônicos. Para isto, esta dissertação se baseia em dados inéditos de cunho paleomicrontológico, geoquímico e sedimentológico do testemunho SAT-048A, e dados não publicados do testemunho SIS-188. O artigo i) demonstra a aplicabilidade das bioecozonas da parte mais tardia do Quaternário, porém, se reconhece que antigos limites considerados síncronos, responderam realmente de forma “temporal- progressiva” devido às mudanças no contexto do Oceano Atlântico. O artigo ii) reconstrói as variações na paleoprodutividade e paleotemperaturas da superfície, assim como os fluxos de matéria orgânica ao fundo e seus possíveis efeitos na dissolução das testas dos foraminíferos planctônicos. Além de variações de cunho glacial-interglacial, a influência da insolação foi reconhecida nas bacias de Pelotas e Santos. O artigo iii), baseado na subjetividade que existe em relação à avaliação da fragmentação das testas, explora um novo método que relaciona a área e o perímetro dos restos de testas não completas. É proposta a medida “Intensidade da Fragmentação” e a mesma é avaliada com respeito aos outros indicadores de dissolução. Estudos futuros deverão i) estudar a aplicabilidade e, eventualmente, calibrar os bioecozoneamentos mais profundos no tempo, ii) avaliar a influência das massas d’água do fundo na dissolução das testas dos foraminíferos planctônicos e, iii) testar a efetividade da “Intensidade da Fragmentação” com amostras recentes e fósseis em diversas áreas e contextos sedimentológicos.Planktonic Foraminifera are excellent tools used in Cenozoic biostratigraphic and paleoceanographic studies due to their abundance, high rates of evolution, wide distribution, and good preservation. In addition, their carbonate shells are precipitated in isotopic equilibrium with the sea water, registering the paleoceanographic conditions of the environments where they lived. For these reasons, the planktonic Foraminifera associations of the SAT-048A core were used, recovered from the continental slope of the northern portion of the Pelotas Basin, to: i) evaluate the application potential of the bioecozonations developed for the Santos and Campos basins, ii) reconstruct the oceanographic surface and bottom conditions and, iii) propose a theoretical model to better evaluate the effects of dissolution on the planktonic Foraminifera fragmentation. To accomplish these objectives, this dissertation is based on unpublished paleomicrontological, geochemical and sedimentological data from the core SAT-048A, and unpublished data from the core SIS-188. Article i) demonstrates the applicability of the bioecozones of the latest Quaternary, however, it is recognized that old limits considered synchronous, really responded in a “temporal-progressive” way due to changes in the context of the Atlantic Ocean. Article ii) reconstructs the variations in surface paleoproductivity and paleo-temperatures, as well as the sea floor organic matter fluxes and their possible effects on the dissolution of planktonic Foraminifera tests. In addition to glacial- interglacial variations, the insolation influence was recognized in the Pelotas and Santos basins. Article iii), based on the subjectivity that exists in relation to the tests fragmentation assessment, explores a new method that relates the area and perimeter of the planktonic Foraminifera fragmentation remains. The “Fragmentation Intensity” index is proposed and it is evaluated with respect to the other dissolution indicators. Future studies should i) study the applicability and, eventually, calibrate the bioecozonations deeper in time, ii) evaluate the influence of the bottom water masses in the planktonic Foraminifera tests dissolution, and iii) test the effectiveness of the “Fragmentation Intensity” with recent and fossil samples in different areas and sedimentological contexts

Bioerosion on late Quaternary Planktonic Foraminifera related to paleoproductivity in the western South Atlantic

Planktonic Foraminifera are widely used in paleoceanographic reconstructions, although studies of their trophic interactions are still rare, especially those focusing on predation. Drilling holes are the most frequent traces of bioerosion in foraminifer tests, but environmental factors that control bioerosion are not yet understood. To determine if paleoceanographic variables are associated with bioerosion rates in late Quaternary planktonic foraminifers of the western South Atlantic, geochemical and assemblage analyses were made on a 46 kyr record from a piston core. An age model was constructed based on 10 AMS 14C dates. To reconstruct the paleoproductivity, δ13C, benthic/planktonic foraminifer and the relative abundances of Globigerina bulloides and Globigerinoides ruber (high and low productivity, respectively) were used. Bioeroded tests were counted and found in 21 of the 25 identified species, with frequencies ranging from 8.84% to 16.7%. Bioerosion was different in two groups identified by cluster analysis, with a higher intensity during glacial times, showing a strong correlation with paleoceanographic fluctuations. Paleoproductivity estimates and bioerosion rates show a significant correlation, suggesting that bioerosion is more frequent in eutrophic environments and more inhibited in oligotrophic conditions. However, even with a strong correlation between bioerosion and productivity, there is also a negative correlation with sea surface temperature in the study area. Since conditions that promote higher productivity are accompanied by a decrease in surface temperature, the precise distinction between the influence of both variables is hampered. Further research will allow us to explore the potential of planktonic foraminiferal bioerosion as a tool in paleoceanographic studies

Bioerosion on late Quaternary Planktonic Foraminifera related to paleoproductivity in the western South Atlantic

Planktonic Foraminifera are widely used in paleoceanographic reconstructions, although studies of their trophic interactions are still rare, especially those focusing on predation. Drilling holes are the most frequent traces of bioerosion in foraminifer tests, but environmental factors that control bioerosion are not yet understood. To determine if paleoceanographic variables are associated with bioerosion rates in late Quaternary planktonic foraminifers of the western South Atlantic, geochemical and assemblage analyses were made on a 46 kyr record from a piston core. An age model was constructed based on 10 AMS 14C dates. To reconstruct the paleoproductivity, δ13C, benthic/planktonic foraminifer and the relative abundances of Globigerina bulloides and Globigerinoides ruber (high and low productivity, respectively) were used. Bioeroded tests were counted and found in 21 of the 25 identified species, with frequencies ranging from 8.84% to 16.7%. Bioerosion was different in two groups identified by cluster analysis, with a higher intensity during glacial times, showing a strong correlation with paleoceanographic fluctuations. Paleoproductivity estimates and bioerosion rates show a significant correlation, suggesting that bioerosion is more frequent in eutrophic environments and more inhibited in oligotrophic conditions. However, even with a strong correlation between bioerosion and productivity, there is also a negative correlation with sea surface temperature in the study area. Since conditions that promote higher productivity are accompanied by a decrease in surface temperature, the precise distinction between the influence of both variables is hampered. Further research will allow us to explore the potential of planktonic foraminiferal bioerosion as a tool in paleoceanographic studies

Time-spatial boundaries of bioecozonations (planktonic foraminifera) in the latest Quaternary: a case study from the western South Atlantic

Planktonic foraminifera assemblages accurately record climate fluctuations that occurred during the Quaternary. These assemblage variations (frequently abundance changes) are widely used to establish bioecozones. Since climate variations are neither synchronous nor spatially homogenous, this paper assesses the application of the bioecozonations from the south Brazilian continental margin to its understudied southern extreme. To accomplish this purpose, census counts were made on core SAT-048A, retrieved from the continental slope of the southern extreme, and were compared to published records from the south Brazilian continental margin. According to the age model, the sediment core SAT-048A spans the last 42 kyr. The last reappearance of the Globorotalia menardii complex is dated for the first time in the Pelotas Basin at 8.5 ka, marking the biochronologic limit of bioecozones Y/Z. The last disappearance of Pulleniatina spp., marker of the sub-bioecozones Y2/Y1, is dated at 25.7 ka, showing an asynchronous characteristic already reported for the Caribbean and Equatorial Atlantic, meanwhile, its last reappearance, that marks the Y1B/Y1A limit, is dated at 15.5 ka, agreeing with previous studies. The Pleistocene/Holocene boundary can be recognized based on the Last Abundance Peak of the Globorotalia truncatulinoides dextral morphotype (GtdLAP), also recognized in other cores of the south Brazilian continental margin