Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-07-27T16:16:01Z No. of bitstreams: 1 MAIA 2016.pdf: 4239749 bytes, checksum: 3670e8f040c7e0ba5e1a4bba302867d4 (MD5) / Made available in DSpace on 2016-07-27T16:16:01Z (GMT). No. of bitstreams: 1 MAIA 2016.pdf: 4239749 bytes, checksum: 3670e8f040c7e0ba5e1a4bba302867d4 (MD5) / Conselho Nacional de DesenvolvimentO Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências - Geoquímica. Niterói, RJ / O sistema de circulação oceânica desempenha um importante papel na regulação e manutenção do clima no planeta. Uma vez que o Atlântico Equatorial representa o ponto de conexão entre o Atlântico Sul e Norte, estudos paleoceanográficos nesta área podem contribuir para o entendimento dos processos e fatores envolvidos nas variações climáticas ao longo do tempo geológico, principalmente durante o Quaternário. Dentro desse contexto, o presente estudo visou descrever elementos representativos da paleoprodutividade do Atlântico Equatorial Oeste no Pleistoceno tardio, por meio da análise de dados sedimentológicos e geoquímicos do testemunho sedimentar MD09-3243CQ coletado no talude da margem continental do nordeste do Brasil. A partir desse testemunho, foi recuperado o período entre 33.700 e 10.150 anos cal A.P., o qual foi dividido em seis fases principais, de acordo com a análise de agrupamento das frações granulométricas representativas do testemunho. As fases apresentaram características distintas em função de mudanças das condições paleoambientais, paleoceanográficas e da paleoprodutividade. O cenário do último glacial (Fase V), caracterizado pela alta produtividade carbonática e baixa produtividade orgânica (COT = 0,40 ± 0,12%; NT = 0,05 ± 0,01%; derivados de clorofila = 0,06 ± 0,04 SPDU; teor de carbonato = 51,04 ± 6,39%), foi gradualmente substituído por ambiente com certa influência terrígena em virtude do clima mais seco e maior erosão, como sugerido pela razão C/N e δ13C, que proporcionou o aumento da produtividade fitoplanctônica, e, assim, das concentrações de COT (0,90 ± 0,25%), NT (0,09 ±0,02%) e derivados de clorofila (0,12 ± 0,07 SPDU) durante o Último Máximo Glacial (Fase IV). No H1, por outro lado, foi observada uma redução abrupta das concentrações destas variáveis e da razão C/N, concomitante com o aumento do teor de carbonato, δ13C e δ15N, indicando uma produtividade estritamente marinha, com maior remineralização da matéria orgânica. Essas alterações na paleoprodutividade estão relacionadas ao enfraquecimento da AMOC e aumento da temperatura no Atlântico Equatorial durante o H1, que resultaram em um ambiente mais oligotrófico e com maior precipitação de carbonatos. O YD (Fase II) apresentou uma tendência oposta ao H1 e semelhante ao LGM. O tardiglacial (final da Fase II e Fase I), por sua vez, apresentou uma redução do COT, NT e derivados de clorofila de 1,21 ± 0,24%, 0,11 ± 0,02% e 0,27 ± 0,08 SPDU para 0,83 ± 0,06%, 0,08 ± 0,01% e 0,15 ± 0,05 SPDU, respectivamente, acompanhado de uma ligeira diminuição do C/N (de 10,98 ± 1,05 para 10,47 ± 0,59) e valores menos negativos de δ13C (-21,92 ± 1,26‰ para -20,31 ± 0,25‰). De uma forma geral, a relação entre a razão C/N e δ13C sugeriu a presença de matéria orgânica predominantemente marinha ao longo do testemunho, com alguns períodos com tendências terrígenas. A taxa de sedimentação foi relativamente baixa 0,013 ± 0,051 cm.ano-1, apresentando maiores valores nos primeiros 100 cm. Os resultados mostram que a paleoprodutividade nessa região foi influenciada pelas alternâncias de inputs terrestres e produção de carbonatos ao longo do Pleistoceno tardio / The ocean circulation system plays an important role in climate on Earth. Once the Equatorial Atlantic is the connection point between the South and North Atlantic, paleoceanographic studies in this area can contribute to the understanding of the processes and factors involved in climate variations over geological time, especially during the Quaternary. Within this context, The present study aimed to describe representative elements of the western equatorial Atlantic paleoproductivity during the Last Glacial through the sedimentological and geochemical analysis of sedimentary MD09-3243CQ core collected in the slope of the continental margin of northeastern Brazil. It was recovered the period between 33,700 and 10,150 years B.P., which was divided into six main phases, according to the cluster analysis of representative size fractions. Stages had different characteristics due to changes of paleoenvironmental conditions, paleoceanographic and paleoproductivity. The Last Glacial scenario (Phase V), characterized by high productivity and low carbonate marine primary productivity (TOC = 0.40 ± 0.12%; TN = 0.05 ± 0.01%, derived from chlorophyll = 0.06 0.04 ± SPDU; carbonate = 51.04 ± 6.39%) was gradually replaced by environmental influenced by terrigenous material because the drier climate and greater erosion, as suggested by the C/N ratio and δ13C that provided increased phytoplankton productivity, and thus the concentrations of TOC (0.90 ± 0.25%), TN (0.09 ± 0.02%) and derivatives of chlorophyll (0.12 ± 0.07 SPDU) during the Last Glacial Maximum (Phase IV). During H1, on the other hand, an abrupt reduction of the concentrations of these variables and the C/N ratio, concomitant with the increase in carbonate content, δ13C and δ15N was observed, indicating a strictly marine productivity with increased remineralization of organic matter. These changes in paleoproductivity are related to the weakening of AMOC and increase of temperature in the Equatorial Atlantic during H1, which resulted in a more oligotrophic environment and greater precipitation carbonates. The YD (Phase II) had an opposite trend to H1 and was similar to LGM. The Late Glacial (end of Phase II and Phase I), in turn, showed a reduction in TOC, TN and derivatives of chlorophyll 1.21 ± 0.24%, 0.11 ± 0.02%, and 0.27 ± 0.08 SPDU, to 0.83 ± 0.06%, 0.08 ± 0.01% and 0.15 ± 0.05 SPDU, respectively, accompanied by a slight decrease in the C/N (10.98 ± 1.05 to 10.47 ± 0.59) and less negative values of δ13C (-21.92 ± 1.26 ‰ to -20.31 ± 0.25 ‰). In general, the relation between the C/N ratio and δ13C suggested organic matter predominantly marine with some periods with terrigenous trends. The sedimentation rate was relatively low, 0.013 ± 0.051 cm.year-1, with higher values in the first 100 cm. The results show that paleoproductivity in the studied region was influenced by the alternation of terrigenous input and carbonate production during the Late Pleistocene

SYRACO est un SYstème de Reconnaissance Automatisée des COccolithes, développé à son origine par Luc Beaufort et Denis Dollfus à partir de 1995 et plus récemment avec Yves Gally. L'utilité d'un tel système est de permettre aux spécialistes un gain de temps majeur dans l'acquisition et le traitement des données. Dans ce travail, le système a été amélioré techniquement et sa reconnaissance a été étendue aux nannofossiles calcaires du Cénozoïque. Ce système fait le tri entre les nannofossiles et les non-nannofossiles avec une efficacité respectivement estimée à 75% et 90 %. Il s'appuie sur une nouvelle base d'images de référence d'espèces datant de l'Eocène Supérieur aux espèces vivantes, ce qui représente des centaines d'espèces avec une forte variabilité morphologique. Il permet de réaliser une classification en 39 morphogroupes par la combinaison de réseaux de neurones artificiels avec des modèles statistiques. Les résultats sont présentés sous forme de comptages automatisés, de données morphométriques (taille, masse...) et de mosaïques d'images. Il peut ainsi être utilisé pour des analyses biostratigraphiques et paléocéanographiques. / SYRACO is an automated recognition system of coccoliths, originally developed since 1995 by Luc Beaufort and Denis Dollfus, and more recently with the help of Yves Gally. The main purpose of this system is for specialists to save time in the acquisition and treatment of data. By this recent work, the system has been technically improved and its ability of recognition has been extended to calcareous nannofossils of the Cenozoic Era. It sorts nannofossils and non-nannofossils with a reliability respectively estimated to 75% and 90%. It is based on a new reference images database of species from the Upper Eocene up to living species. This represents hundreds of species with a high morphological variability. It leads to the establishment of a classification arranged in 39 morphogroups, combining artificial neural networks to statistical models. The results are presented as automated counting, morphometrical data (size, mass...) and mosaics of images. Those results can be valuable in biostratigraphical and paleoceanographical analyses.

Ce travail avait pour but de reconstituer l'évolution de la température et du δ¹⁸O des eaux de surface et des eaux de la thermocline dans la Warmpool indo-pacifique (IPWP) en combinant la thermométrie Mg / Ca et la mesure des isotopes stables de l'oxygène sur des foraminifères planctoniques de surface et de sub-surface prélevés dans des carottes de sédiments situées dans l'océan Indien tropical oriental. Ce travail a permis de ré-évaluer les effets des différentes méthodes de nettoyage et de la dissolution in situ sur la thermométrie Mg/Ca des foraminifères planctoniques, mettant en évidence la nécessité de corrections différentes suivant les espèces. L’évolution de l’IPWP au cours des 270 000 dernières années a été reconstituée. Les résultats indiquent que le δ¹⁸O des eaux de surface reflètent principalement l'advection latérale plutôt que l'historique des précipitations régionales, et suggèrent que l'hydrologie de surface IPWP est contrôlée par la migration latitudinale de la zone de convergence intertropicale aux échelles de temps orbitales mais aussi en réponse aux événements climatiques abrupts de l'hémisphère nord (eg. événements de Heinrich). Les variations de salinité de surface sont étroitement corrélées aux changements d’export vers l’Atlantique au niveau du Courant des Aiguilles (Sud de l’Afrique). Puis, les changements dans le transport des eaux de la thermocline issues de l’ITF vers l'océan Indien ont été étudiés. Les résultats montrent que le transport était plus faible pendant les glaciations (ie. MIS 6 et 4-2) que pendant les périodes interglaciaires (ie. MIS 7, MIS 5 et Holocène) et exerçaient une influence significative sur les changements de la température de la thermocline dans l'Océan Indien. / This work aimed at reconstructing the late Quaternary evolution of surface and thermocline temperature and ocean surface water δ¹⁸O in the Indo-Pacific Warm Pool by combining Mg/Ca-thermometry and stable oxygen isotope analyses on surface and thermocline-dwelling planktonic foraminifers retrieved from sediment cores in the eastern tropical Indian Ocean. This study allowed to re-evaluate the effects of different cleaning methods and in-situ dissolution on the Mg-thermometry of planktonic foraminifers, evidencing the need for species-dependent corrections. Then, the IPWP evolution over the last 270,000 years has been explored. Results indicate that surface water δ¹⁸O chiefly reflects lateral advection rather than local precipitation history, and suggest that surface IPWP hydrology is controlled by the latitudinal migration of the Intertropical Convergence Zone at orbital timescale as well as during abrupt northern hemisphere climatic events (i.e. Heinrich events). Ocean surface salinity in the IPWP and Agulhas leakage region varied synchronously, implying their teleconnection through oceanic and atmospheric circulation. Moreover, changes in the transport of thermocline water to the Indian Ocean by the Indonesian Throughflow (ITF) have been reconstructed. Results show that thermocline water transport was weaker during glacials (i.e. MIS 6 and 4-2) than during interglacials (MIS 7, MIS 5 and Holocene), and exerted significant influence on Indian Ocean TWT change.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (p. 221-236). / This thesis focuses on ocean circulation and atmospheric forcing in the Atlantic Ocean at the Last Glacial Maximum (LGM, 18-21 thousand years before present). Relative to the pre-industrial climate, LGM atmospheric CO₂ concentrations were about 90 ppm lower, ice sheets were much more extensive, and many regions experienced significantly colder temperatures. In this thesis a novel approach to dynamical reconstruction is applied to make estimates of LGM Atlantic Ocean state that are consistent with these proxy records and with known ocean dynamics. Ocean dynamics are described with the MIT General Circulation Model in an Atlantic configuration extending from 35°S to 75°N at 1° resolution. Six LGM proxy types are used to constrain the model: four compilations of near sea surface temperatures from the MARGO project, as well as benthic isotope records of [delta]¹⁸O and [delta]¹³C compiled by Marchal and Curry; 629 individual proxy records are used. To improve the fit of the model to the data, a least-squares fit is computed using an algorithm based on the model adjoint (the Lagrange multiplier methodology). The adjoint is used to compute improvements to uncertain initial and boundary conditions (the control variables). As compared to previous model-data syntheses of LGM ocean state, this thesis uses a significantly more realistic model of oceanic physics, and is the first to incorporate such a large number and diversity of proxy records. A major finding is that it is possible to find an ocean state that is consistent with all six LGM proxy compilations and with known ocean dynamics, given reasonable uncertainty estimates. Only relatively modest shifts from modern atmospheric forcing are required to fit the LGM data. The estimates presented herein succesfully reproduce regional shifts in conditions at the LGM that have been inferred from proxy records, but which have not been captured in the best available LGM coupled model simulations. In addition, LGM benthic [delta]¹⁸O and [delta]¹³C records are shown to be consistent with a shallow but robust Atlantic meridional overturning cell, although other circulations cannot be excluded. / by Holly Janine Dail. / Ph.D.

No description available.

O objetivo do presente estudo é avaliar o uso associado dos proxies ?18O e Mg/Ca obtidos em testas de foraminíferos. Para alcançar tal objetivo foram realizadas análises de ?18O e Elemento/Ca em amostras de foraminíferos planctônicos (G. ruber e G. sacculifer) e bentônicos (Cibicidoides spp., C. corpulentus, Uvigerina spp. e H. elegans) de dois testemunhos do Atlântico Sul. Os resultados demonstraram que apesar dos proxies ?18O e Mg/Ca apresentarem perfis distintos em relação às espécies os mesmos se correlacionam de forma apropriada, sendo possível estimar a temperatura e os sinais de ?18OSW e ?18OLocal a partir dos mesmos. A partir dos dados de temperatura estimados com base em Mg/Ca foi possível identificar uma anomalia negativa das águas superficias entre o LGM e o HL de -1,5 ± 0,2 °C, enquanto que nas águas profundas observou-se uma anomali positiva de 1,7 ± 0,4 °C para o mesmo período. Os dados de ?18OSW estimados com base nos dados de temperatura e ?18O indicaram uma oscilação de 1,0 ± 0,1 ? e 2,0 ± 0,2 ? para as espécies planctônicas e bentônicas durante o LGM e o HL. Segundo o valor esperado para a variação do volume de gelo (~1,2 ?) há uma oscilação muito baixa da salinidade nas águas superficias da região de estudo, em contraste com uma oscilação bem marcada da salinidade nas águas de fundo. As estimativas de ?18OLocal indicaram uma oscilação entre o LGM e o HL muito pequena da salinidade (~0,1 ?) nas águas superficiais, com uma oscilação maior nas águas de fundo (1,0 ± 0,3 ?). O aumento da salinidade das águas de fundo durante o LGM corrobora a anomalia positiva da temperatura observada neste estudo, visto que, para a ocorrência da mesma, é necessário que a densidade das águas de fundo seja suficiente para manter a estratificação da coluna de água. / The goal of this study is to evaluate the associated use of the proxies ?18O and Mg/Ca, both analyzed in foraminifera tests. ?18O and trace metals analyses were performed in order to achieve this purpose on samples of planktonic (G. ruber and G. sacculifer) and benthic (Cibicidoides spp., C. corpulentus, Uvigerina spp. and H. elegans) species of foraminifera from two cores from South Atlantic. Despite of the fact that the proxies used on this study present distinct fits within the species they correlate very well, being possible to estimate the values of temperature, ?18OSW and ?18OLocal. Based on the temperature estimated by Mg/Ca it was possible to identify a negative anomaly of -1,5 ± 0,2 °C between the LGM and HL, meanwhile a positive anomaly of 1,7 ± 0,4 °C was observed in the deep waters for the same period. The ?18OSW data estimated by temperature and ?18O indicate an oscilation of 1,0 ± 0,1 ? and 2,0 ± 0,2 ? for planktonic and benthic species between the LGM and the HL. Based on the literature value for the ice volume signal (~1,2 ?) the superficial waters of the study area indicated a very low salinity oscilation, opposite to the high salinity oscillation in the deep waters. The ?18OLocal estimatives exhibited a very weak salinity oscillation between LGM and HL in the superficial waters (~0,1 ?), providing a much more strong oscilation in the deep waters (1,0 ± 0,3 ?). The salinity increase during the LGM in the deep waters establish the validity of the positive temperature anomaly observed in this study, since the density of the deep water needs to be adequate to maintain the water column stratification.

O objetivo do presente estudo é avaliar o uso associado dos proxies ?18O e Mg/Ca obtidos em testas de foraminíferos. Para alcançar tal objetivo foram realizadas análises de ?18O e Elemento/Ca em amostras de foraminíferos planctônicos (G. ruber e G. sacculifer) e bentônicos (Cibicidoides spp., C. corpulentus, Uvigerina spp. e H. elegans) de dois testemunhos do Atlântico Sul. Os resultados demonstraram que apesar dos proxies ?18O e Mg/Ca apresentarem perfis distintos em relação às espécies os mesmos se correlacionam de forma apropriada, sendo possível estimar a temperatura e os sinais de ?18OSW e ?18OLocal a partir dos mesmos. A partir dos dados de temperatura estimados com base em Mg/Ca foi possível identificar uma anomalia negativa das águas superficias entre o LGM e o HL de -1,5 ± 0,2 °C, enquanto que nas águas profundas observou-se uma anomali positiva de 1,7 ± 0,4 °C para o mesmo período. Os dados de ?18OSW estimados com base nos dados de temperatura e ?18O indicaram uma oscilação de 1,0 ± 0,1 ? e 2,0 ± 0,2 ? para as espécies planctônicas e bentônicas durante o LGM e o HL. Segundo o valor esperado para a variação do volume de gelo (~1,2 ?) há uma oscilação muito baixa da salinidade nas águas superficias da região de estudo, em contraste com uma oscilação bem marcada da salinidade nas águas de fundo. As estimativas de ?18OLocal indicaram uma oscilação entre o LGM e o HL muito pequena da salinidade (~0,1 ?) nas águas superficiais, com uma oscilação maior nas águas de fundo (1,0 ± 0,3 ?). O aumento da salinidade das águas de fundo durante o LGM corrobora a anomalia positiva da temperatura observada neste estudo, visto que, para a ocorrência da mesma, é necessário que a densidade das águas de fundo seja suficiente para manter a estratificação da coluna de água. / The goal of this study is to evaluate the associated use of the proxies ?18O and Mg/Ca, both analyzed in foraminifera tests. ?18O and trace metals analyses were performed in order to achieve this purpose on samples of planktonic (G. ruber and G. sacculifer) and benthic (Cibicidoides spp., C. corpulentus, Uvigerina spp. and H. elegans) species of foraminifera from two cores from South Atlantic. Despite of the fact that the proxies used on this study present distinct fits within the species they correlate very well, being possible to estimate the values of temperature, ?18OSW and ?18OLocal. Based on the temperature estimated by Mg/Ca it was possible to identify a negative anomaly of -1,5 ± 0,2 °C between the LGM and HL, meanwhile a positive anomaly of 1,7 ± 0,4 °C was observed in the deep waters for the same period. The ?18OSW data estimated by temperature and ?18O indicate an oscilation of 1,0 ± 0,1 ? and 2,0 ± 0,2 ? for planktonic and benthic species between the LGM and the HL. Based on the literature value for the ice volume signal (~1,2 ?) the superficial waters of the study area indicated a very low salinity oscilation, opposite to the high salinity oscillation in the deep waters. The ?18OLocal estimatives exhibited a very weak salinity oscillation between LGM and HL in the superficial waters (~0,1 ?), providing a much more strong oscilation in the deep waters (1,0 ± 0,3 ?). The salinity increase during the LGM in the deep waters establish the validity of the positive temperature anomaly observed in this study, since the density of the deep water needs to be adequate to maintain the water column stratification.