Dans cette thèse, je reconstitue la dynamique de la circulation méridienne de retournement de l’Atlantique (AMOC) au cours des changements climatiques rapides de la dernière période glaciaire. Je trouve ainsi que le ralentissement de la cellule supérieure de l’AMOC commence 1420 ± 250 (1σ) années avant le déplacement vers le sud de l’ITCZ associé au « Heinrich Stadial » 2 et 690 ± 180 (1σ) années avant celui associé au « Heinrich Stadial » 4. Mes résultats confirment donc qu’un ralentissement de l’AMOC pourrait être à l’origine des migrations de l’ITCZ associées aux « Heinrich Stadials » et fournissent une première estimation précise du décalage temporel entre ces deux variables climatiques. Sur la base de ces résultats, je propose un mécanisme expliquant les différences entre les « Heinrich Stadials » et les « Dansgaard-Oeschger Stadials ».Je montre que deux cellules de circulation étaient probablement actives dans l’océan Atlantique pendant les périodes chaudes au Groenland (« interstadials ») : une cellule supérieure initiée par l’écoulement au-dessus de 2500 m d’une masse d’eau en provenance du nord et se dirigeant vers le sud, et une cellule inférieure initiée par l’écoulement au-dessous de 4000 m d’une masse d’eau en provenance du sud et se dirigeant vers le nord. Le taux de renouvellement de la masse d’eau profonde de la cellule supérieure était probablement plus faible que celle de la masse d’eau actuellement formée dans les hautes latitudes de l’océan Atlantique Nord. Au début des « Heinrich Stadials », la structure de l’AMOC a significativement changé et des eaux en provenance du sud ont probablement dominé l’océan Atlantique en-dessous de 1300 m de profondeur. / In this thesis, I reconstruct the dynamic of the Atlantic Meridional Overturning Circulation (AMOC) during fast climate changes of the last glacial period. I find that the AMOC upper circulation cell started to slowdown 1420 ± 250 (1σ) and 690 ± 180 (1σ) years before the southward shifts of the Inter Tropical Convergence Zone associated with Heinrich Stadial 2 and Heinrich Stadial 4, respectively. I therefore confirm that an AMOC slowdown could be at the origin of the ITCZ shifts that occured during Heinrich Stadials and provide the first precise estimate of the phasing between these two climate variables. Based on these results I propose a mechanism explaining the difference between Heinrich and Dansgaard-Oeschger stadials.Using modeling results, I show that the Atlantic Ocean circulation during periods of higher Greenland temperatures (interstadials) was markedly different from that of the Holocene. Two overturning cells were likely active in the Atlantic Ocean: an upper overturning circulation cell initiated by northern-sourced deep water flowing southward above ~2500 m depth at the equator, and a lower overturning circulation cell initiated by southern sourced deep water flowing northward below ~4000 m depth at the equator. The overturning rate of the upper overturning cell was likely lower than that of present-day North Atlantic Deep Water. At the onset of Heinrich Stadials, the structure of the AMOC significantly changed, and southern-sourced deep-waters likely dominated the equatorial Atlantic Ocean below 1300 m depth.

Le sujet de ma thèse traite les changements paléoenvironnementaux et paléoclimatiques qui ont affecté les écosystèmes du Moyen Atlas marocain depuis la dernière période glaciaire, centrée autour de 25,000 cal BP. Les trois séquences sédimentaires étudiées dans cette thèse ont été prélevées le long d'un transect Nord-Sud dans le Moyen Atlas. Cette étude est basée sur une approche multi-bioindicateurs intégrant la palynologie, la géochimie élémentaire et la granulométrie afin de comprendre la dynamique des écosystèmes passés et de mettre en évidence les impacts anthropiques sur ces écosystèmes et leurs bassins versants. Les résultats obtenus montrent que durant la dernière période glaciaire et jusqu’au début de l’holocène, une végétation steppique a dominé les paysages du Moyen Atlas en réponse à des conditions climatiques froides et arides. Cependant, des populations de cèdres, de chênes et de pins ont persisté durant la période glaciaire dans des micro-refuges. Bien que le début de l’holocène révèle une expansion des chênes et des pins (principaux composants des écosystèmes forestiers méditerranéens), la steppe (composée d'armoise, de chénopodiacées et de graminées) a persisté jusqu’à 6.5 ka cal BP. Ces écosystèmes tolérant à la sécheresse reflètent un début de l’holocène chaud mais avec une quantité de précipitations annuelles assez réduite pour permettre l'expansion des forêts tel que nous l'observons en Europe et d’autres régions de la Méditerranée. Ce n'est qu'à partir de 6.5 ka cal BP que les forêts de cèdre s’installent aux altitudes des sites étudiés (autour de 1600m) et que des plantes aquatiques prolifèrent dans les marais ou nous avons effectué les sondages. Nous observons ensuite une nette régression du couvert arboré à partir de 4.5 ka cal BP, notamment les chênes décidus, et une expansion des taxons herbacés. Ceci est le résultat d’une tendance vers des conditions plus arides témoignant d'une installation du climat méditerranéen tel que nous le connaissons aujourd'hui. Le début des changements environnementaux liés à l'impact humain, à travers les données palynologiques et géochimiques, n'est enregistré qu’à partir de ca. 1500 cal BP. Les résultats obtenus dans cette thèse sont en accord avec ceux d'autres études paléoenvironnementales menées en Méditerranée autant pour la période glaciaire que pour le début des conditions arides à partir de 5.5 ka cal BP. / This thesis discusses the paleoenvironmental and paleoclimatic changes that have affected the ecosystems of the Moroccan Middle Atlas since the last glacial period, and focuses around 25000 cal BP. The three sedimentary sequences that have been studied in this thesis were taken along a North-South transect in the Middle Atlas. This study is based on a multi-bio-indicators approach, including palynology, geochemical elements and particle size, in order to better understand the dynamic of previous ecosystems and to highlight the human activities on these ecosystems and on their catchment areas.The results obtained show that during the last glacial period, and until the beginning of the Holocene, steppe vegetation was predominant in the Middle Atlas, in reaction to cold and arid climate conditions. However, populations of cedars, oaks and pine trees remained in micro-refugia. Although the beginning of the Holocene reveals an expansion of oaks and pines trees (the main components of Mediterranean forests ecosystems), the steppe (which is composed of Artemisia, Chenopodiaceae and grasses) persisted till 6.5 ka cal BP. These drought-tolerant ecosystems reflect a warm beginning of the Holocene, with an amount of precipitation that was low enough to allow the expansion of forests similar to those we can observe in Europe and other areas of the Mediterranean. It’s only since 6.5 ka cal BP that cedars forests have started to grow at the altitudes of the sites we studied (around 1600m), and that aquatic plants have proliferated in the marshes where we took our samples. We can then observe a sharp decline of tree cover, including deciduous oaks, starting 4.5 ka cal BP and an expansion of herbaceous taxa. These are the consequences of a tendency to conditions that were more arid, attesting the installation of the Mediterranean climate as we know it today. The first environmental changes linked to human impact have only been recorded, through palynology and biochemical data, from ca. 1500 cal BP. The results obtained in this thesis are in line with those obtained in other paleoenvironmental studies conducted in the Mediterranean area, for the glacial period as well as for the beginning of arid conditions starting 5.5 ka cal BP.

The remnant montane forests of southern Lebanon provide habitat to a rich diversity of endemic, rare and threatened plant and animal species. Prior to the intensification of human activity during the mid-Holocene period these forests covered most of the Lebanon and Anti-Lebanon Mountain ranges. What is not known is how the dynamics of these forests changed in response to major shifts in climate. The aim of this DPhil thesis was to document changes in vegetation composition in southern Lebanon during the last glacial period (~112 to 35 ka BP). To achieve this aim, a palynological study was conducted on a sedimentary sequence recovered from Aammiq Wetland located in the Bekaa Valley, Lebanon. Fossil pollen was analysed to reconstruct variability in vegetation composition and abundance. Energy dispersive spectroscopy, magnetic susceptibility and loss-on-ignition were used to reconstruct the geomorphological and hydrological processes acting within the wetland and its watershed. Macro and microcharcoal were analysed to reconstruct local and regional fire histories respectively. A chronology was established for this sequence using a combination of radiocarbon and optically stimulated luminescence dating (OSL) techniques. The results indicate significant variability in the composition and abundance of vegetation through the time interval ~ 112 to ~ 35 ka BP closely aligned in time to global and regional climatic events. Changes in the chemical and physical properties of the sediments indicate significant variability in landscape erosion processes and hydrological conditions in the watershed and within the wetland over the similar interval in time. Peaks in local and regional fire activity were concurrent with periods of precession minima and Dansgaard-Oeschger warming events and had a significant impact on the composition of vegetation within the Aammiq region. These findings provide the first account of environmental change in the southern Bekaa Valley and adjacent slopes of the Lebanon Mountains during the last glacial period.

Registros das razões isotópicas do oxigênio (d18O) e do carbono (d13C), juntamente com as taxas de crescimento de espeleotemas, precisamente datados pelo método U/Th, foram utilizados para reconstituição das variações de pluviosidade dos últimos 93 mil anos A.P. na região da Chapada Diamantina, porção central do Estado da Bahia. A reconstituição paleoclimática foi apoiada por estudo de calibração realizado em duas cavernas da região estudada, através do qual se obteve boa relação entre a assinatura isotópica da chuva e do d18O dos gotejamentos e evidências de condições ambientais propícias para deposição de espeleotemas em equilíbrio isotópico com a água de gotejamento. A interpretação climática dos dados de d18O dos espeleotemas considera também a análise da composição isotópica da água da chuva em face da pluviometria, a partir de dados de estações do IAEA-GNIP no Brasil e de simulações das variações do d18O da chuva através do modelo climático ECHAM-4. Esses dados indicam o fator amount effect, como relação preponderante na discussão de pluviosidade através dos registros de espeleotemas, a qual é caracterizada pela diminuição dos valores de d18O com o aumento do volume de chuvas. A partir dos registros de d18O dos espeleotemas foi possível reconstituir os padrões regionais de pluviosidade segundo o ciclo de insolação, como também identificar eventos de mudança abrupta de pluviosidade em escala milenar ocorridos durante o último período glacial e Holoceno. Em escala orbital, foi observado aumento (diminuição) da paleoprecipitação na Bahia durante fases de baixa (alta) insolação de verão (10ºS). Essa relação é evidente na maior parte do registro baiano com exceção do período entre 40 e 20 ky A.P., quando houve predomínio de clima seco, mesmo em fases de insolação baixa. No entanto, tal é relação inversa a que foi descrita em estudos paleoclimáticos do Sul/Sudeste do Brasil e dos Andes. Além disso, variações de paleopluviosidade da Chapada Diamantina estão em fase com as registradas nos trópicos do Hemisfério Norte, na China e Venezuela. Esses resultados indicam influência direta do sistema de Monções Sul-americana (MSA) sobre o regime de chuvas do Nordeste em longa escala de tempo, a qual é primariamente modulada pela intensidade da insolação de verão. Aumentos abruptos da paleopluviosidade em escala milenar, indicados por baixos valores de d18O e d13C, como pelas altas taxas de crescimento de espeleotemas, ocorreram durante predomínio de condições frias no Atlântico Norte, em períodos de grandes mudanças nas condições oceânicas, e são concomitantes com os eventos Heinrich e Younger Dryas. Já fortes diminuições foram observadas durante alguns eventos Dansgaard-Oeschger e Bølling-Allerød. Ao contrário do que foi observado durante os ciclos orbitais, o impacto no clima da Bahia atribuído a esses eventos é semelhante em todo país e também nos Andes, de acordo com estudo comparativo entre testemunhos marinhos/lacustres e espeleotemas. Esses eventos produz efeito na pluviosidade de regiões (sub)tropicais do Hemisfério Norte, assim como registrados em arquivos paleoclimáticos da China e Venezuela. O mecanismo mais provável para geração desses eventos está relacionado com mudanças na Atlantic Meridional Overturning Circulation (AMOC). Com a AMOC desintensificada durante eventos Heinrich no Hemisfério Norte, existe predomínio de um gradiente da temperatura da superfície do Atlântico tropical que favorece posicionamento da Zona de Convergência Intertropical mais a sul durante os eventos úmidos na Bahia. / Speleothem records of stable oxygen (d18O) and carbon isotope ratios (d13C) and speleothem growth rates, precisely dated by U/Th method, were used to reconstruct past changes in precipitation in the last 93,000 years B.P. from Chapada Diamantina region, Bahia State. The paleoclimatic reconstruction takes into account results from a calibration study performed in two caves in the Chapada Diamantina region. It was found a robust relationship between isotope signature in precipitation and cave drip water and also evidenced adequate environmental conditions for speleothem deposition in isotopic equilibrium with drip water. The interpretation of the speleothem d18O records is based on the relationship between isotope composition of precipitation and rainfall amount from IAEA-GNIP stations in Brazil and also results from climate experiments coupled with d18O in precipitation using ECHAM-4. These data indicate the amount effect as the dominant isotope fractionation factor controlling the d18O variations in meteoric water forming speleothems, which is characterized by a decrease in the d18O values with an increase in rainfall amount. Speleothem d18O records allow reconstructing the regional paleoprecipitation patterns on both orbital and millennial time-scales during last glacial period and Holocene. These records indicate an increase (decrease) in paleoprecipitation over central Bahia during low (high) summer insolation (10ºS) phases. This relationship is evident is most of this new speleothem record, except in the period between 40 and 20 ka B.P., when dry climate conditions predominate in the region even during the low insolation phases. However, this relationship is exactly the contrary of the one reported from southern/southeastern Brazil and Central Andes paleoclimate studies. Furthermore, the precipitation variations in Chapada Diamantina are in phase with records from Northern Hemisphere on orbital time-scales, particularly from China and Venezuela. These results suggest a direct influence of the South American Monsoon System (SAMS) on long-term changes in precipitation over northeastern Brazil, which is primarily controlled by gradual changes in summer insolation. Abrupt wet events are defined on millennial time-scales in the Chapada Diamantina records by low values of d18O e d13C and high speleothem growth rates. They occurred under prevalence of cold conditions in Northern Hemisphere, triggered by major changes in oceanic circulation in Atlantic Ocean, during Heinrich and Younger Dryas (YD) events. On the other hand, abrupt decreases in regional precipitation are coincident with some of the Dansgaard-Oeschger (D-O) e Bølling-Allerød (B-A), which are typical warm events in Northern Hemisphere. However, differently from the isotope-climate relationship established on orbital times, the impact of these millennial events on the precipitation variations of Bahia is similar to what is documented in speleothem, lake and marine records from Brazil and Central Andes and opposite to changes described in China and Venezuela, among many other records from Northern Hemisphere. The climate mechanism behind the origin of these millennial events is associated with changes in the Atlantic Meridional Overturning Circulation (AMOC). The Heinrich events are linked to periods of weaker AMOC and sea surface temperature gradients that favor a mean southern position of Intertropical Convergence Zone, which results in very wet conditions in Bahia.

Registros das razões isotópicas do oxigênio (d18O) e do carbono (d13C), juntamente com as taxas de crescimento de espeleotemas, precisamente datados pelo método U/Th, foram utilizados para reconstituição das variações de pluviosidade dos últimos 93 mil anos A.P. na região da Chapada Diamantina, porção central do Estado da Bahia. A reconstituição paleoclimática foi apoiada por estudo de calibração realizado em duas cavernas da região estudada, através do qual se obteve boa relação entre a assinatura isotópica da chuva e do d18O dos gotejamentos e evidências de condições ambientais propícias para deposição de espeleotemas em equilíbrio isotópico com a água de gotejamento. A interpretação climática dos dados de d18O dos espeleotemas considera também a análise da composição isotópica da água da chuva em face da pluviometria, a partir de dados de estações do IAEA-GNIP no Brasil e de simulações das variações do d18O da chuva através do modelo climático ECHAM-4. Esses dados indicam o fator amount effect, como relação preponderante na discussão de pluviosidade através dos registros de espeleotemas, a qual é caracterizada pela diminuição dos valores de d18O com o aumento do volume de chuvas. A partir dos registros de d18O dos espeleotemas foi possível reconstituir os padrões regionais de pluviosidade segundo o ciclo de insolação, como também identificar eventos de mudança abrupta de pluviosidade em escala milenar ocorridos durante o último período glacial e Holoceno. Em escala orbital, foi observado aumento (diminuição) da paleoprecipitação na Bahia durante fases de baixa (alta) insolação de verão (10ºS). Essa relação é evidente na maior parte do registro baiano com exceção do período entre 40 e 20 ky A.P., quando houve predomínio de clima seco, mesmo em fases de insolação baixa. No entanto, tal é relação inversa a que foi descrita em estudos paleoclimáticos do Sul/Sudeste do Brasil e dos Andes. Além disso, variações de paleopluviosidade da Chapada Diamantina estão em fase com as registradas nos trópicos do Hemisfério Norte, na China e Venezuela. Esses resultados indicam influência direta do sistema de Monções Sul-americana (MSA) sobre o regime de chuvas do Nordeste em longa escala de tempo, a qual é primariamente modulada pela intensidade da insolação de verão. Aumentos abruptos da paleopluviosidade em escala milenar, indicados por baixos valores de d18O e d13C, como pelas altas taxas de crescimento de espeleotemas, ocorreram durante predomínio de condições frias no Atlântico Norte, em períodos de grandes mudanças nas condições oceânicas, e são concomitantes com os eventos Heinrich e Younger Dryas. Já fortes diminuições foram observadas durante alguns eventos Dansgaard-Oeschger e Bølling-Allerød. Ao contrário do que foi observado durante os ciclos orbitais, o impacto no clima da Bahia atribuído a esses eventos é semelhante em todo país e também nos Andes, de acordo com estudo comparativo entre testemunhos marinhos/lacustres e espeleotemas. Esses eventos produz efeito na pluviosidade de regiões (sub)tropicais do Hemisfério Norte, assim como registrados em arquivos paleoclimáticos da China e Venezuela. O mecanismo mais provável para geração desses eventos está relacionado com mudanças na Atlantic Meridional Overturning Circulation (AMOC). Com a AMOC desintensificada durante eventos Heinrich no Hemisfério Norte, existe predomínio de um gradiente da temperatura da superfície do Atlântico tropical que favorece posicionamento da Zona de Convergência Intertropical mais a sul durante os eventos úmidos na Bahia. / Speleothem records of stable oxygen (d18O) and carbon isotope ratios (d13C) and speleothem growth rates, precisely dated by U/Th method, were used to reconstruct past changes in precipitation in the last 93,000 years B.P. from Chapada Diamantina region, Bahia State. The paleoclimatic reconstruction takes into account results from a calibration study performed in two caves in the Chapada Diamantina region. It was found a robust relationship between isotope signature in precipitation and cave drip water and also evidenced adequate environmental conditions for speleothem deposition in isotopic equilibrium with drip water. The interpretation of the speleothem d18O records is based on the relationship between isotope composition of precipitation and rainfall amount from IAEA-GNIP stations in Brazil and also results from climate experiments coupled with d18O in precipitation using ECHAM-4. These data indicate the amount effect as the dominant isotope fractionation factor controlling the d18O variations in meteoric water forming speleothems, which is characterized by a decrease in the d18O values with an increase in rainfall amount. Speleothem d18O records allow reconstructing the regional paleoprecipitation patterns on both orbital and millennial time-scales during last glacial period and Holocene. These records indicate an increase (decrease) in paleoprecipitation over central Bahia during low (high) summer insolation (10ºS) phases. This relationship is evident is most of this new speleothem record, except in the period between 40 and 20 ka B.P., when dry climate conditions predominate in the region even during the low insolation phases. However, this relationship is exactly the contrary of the one reported from southern/southeastern Brazil and Central Andes paleoclimate studies. Furthermore, the precipitation variations in Chapada Diamantina are in phase with records from Northern Hemisphere on orbital time-scales, particularly from China and Venezuela. These results suggest a direct influence of the South American Monsoon System (SAMS) on long-term changes in precipitation over northeastern Brazil, which is primarily controlled by gradual changes in summer insolation. Abrupt wet events are defined on millennial time-scales in the Chapada Diamantina records by low values of d18O e d13C and high speleothem growth rates. They occurred under prevalence of cold conditions in Northern Hemisphere, triggered by major changes in oceanic circulation in Atlantic Ocean, during Heinrich and Younger Dryas (YD) events. On the other hand, abrupt decreases in regional precipitation are coincident with some of the Dansgaard-Oeschger (D-O) e Bølling-Allerød (B-A), which are typical warm events in Northern Hemisphere. However, differently from the isotope-climate relationship established on orbital times, the impact of these millennial events on the precipitation variations of Bahia is similar to what is documented in speleothem, lake and marine records from Brazil and Central Andes and opposite to changes described in China and Venezuela, among many other records from Northern Hemisphere. The climate mechanism behind the origin of these millennial events is associated with changes in the Atlantic Meridional Overturning Circulation (AMOC). The Heinrich events are linked to periods of weaker AMOC and sea surface temperature gradients that favor a mean southern position of Intertropical Convergence Zone, which results in very wet conditions in Bahia.

Afin de mieux comprendre la sensibilité du continent européen aux changements climatiques, le potentiel des tétraéthers de glycérol ramifiés (ou « méthylés »), supports de nouveaux indicateurs de température et du pH des sols, a été étudié dans 2 archives sédimentaires. Ces 2 carottes de sédiments marins prélevées à l’embouchure de grands fleuves (Danube et paléo fleuve Manche) de part et d’autre de l’ancienne calotte glaciaire fennoscandinave, offrent l’opportunité d’obtenir des enregistrements contenant une information intégrée à l’échelle de vastes bassins versants depuis le dernier cycle glaciaire. Des reconstitutions continues des températures glaciaires obtenues à partir de l’analyse des tétraéthers ramifiés dans ces carottes sont présentées. Ces enregistrements sont interprétés avec précaution du fait de la relative méconnaissance des organismes producteurs des tétraéthers ramifiés et leur possible production en milieu aquatique. La haute résolution temporelle des reconstitutions permet toutefois de mieux comprendre la variabilité climatique abrupte de la dernière période glaciaire, de part l’estimation des températures associées aux évènements de Heinrich et cycles de Dansgaard-Oeschger, notamment par une estimation quantitative en Europe centrale-est. De plus, l’apport des tétraéthers à la reconstitution du pH des paléosols de cette partie du continent est étudié. Par ailleurs, une méthode automatisée de purification des échantillons, préalable à l’analyse des tétraéthers par HPLC-MS a été mise au point, afin de faciliter le travail préparatoire et promouvoir l’analyse de paléo séquences à haute résolution temporelle utilisant les tétraéthers. / In order to better understand the sensibility of the European continent to climate changes, the potential of branched tetraether lipids, as bases of temperature and soil pH proxies, has been studied in two sedimentary archives. These two marine sediment cores have been chosen for their location at the mouth of major rivers (Danube and paleo Channel river) on both sides of the ancient Fennoscandian ice sheet. Indeed, they enable to get records containing information integrated at large drainage basin scale, since the last glacial cycle. Thus, continuous temperature reconstructions of the last glacial period in Europe, based on branched tetraethers extracted from these cores, are presented. These records are carefully interpreted, notably because of the uncertainties on the tetraether producers and their likely production in the aquatic environment. The high temporal resolution of the reconstruction however enables insights into the last glacial abrupt climate variability, with temperature estimates of Heinrich events and Dansgaard-Oeschger cycles, and especially, quantitative estimations in central eastern Europe. Moreover, the reconstruction of past soil pH in this part of the continent is investigated. Last, an automated purification method for archaeal and bacterial tetraethers in soils and sediments has been developed in order to contribute to enhancing the time resolution of paleosequences based on tetraether biomarkers.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-04-03T16:44:03Z No. of bitstreams: 1 THIAGO ANDRADE DE SOUSA .pdf: 5768772 bytes, checksum: b3c4e1c52ed521e2c3772627711af6fa (MD5) / Made available in DSpace on 2017-04-03T16:44:03Z (GMT). No. of bitstreams: 1 THIAGO ANDRADE DE SOUSA .pdf: 5768772 bytes, checksum: b3c4e1c52ed521e2c3772627711af6fa (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências- Geoquímica Ambiental. Niterói, RJ / Os sedimentos continentais depositados no fundo oceânico estão condicionados, majoritariamente, a evolução do clima, ao substrato geológico e ao tipo de transporte, sendo o transporte fluvial o de maior magnitude. Uma vez depositado, os sedimentos tornam-se registros do passado e carregam informações sob a forma de assinatura geoquímica. Os Elementos Terras Raras (ETR) apresentam um comportamento coerente ao longo de uma coluna sedimentar tornando-os útil nos estudos de proveniência sedimentar. Razões entre elementos maiores (Fe/Ca, por exemplo) são descritos na literatura como indicadores de reconstrução do aporto terrígeno. A geoquímica dos ETR e elementos maiores são determinados neste trabalho para o entendimento da dinâmica paleoclimática sobre o aporte e proveniência dos sedimentos da margem leste (Bacia de Santos) do Brasil, e as anomalias do Ce e Eu, confrontando técnicas analíticas distintas (ICP-MS e XRF core scanner) nos principais eventos abruptos (Younger Dryas e Heinrich events) ao longo dos últimos 45.000 anos. Igualmente é discutido a proveniência do material sedimentar por meio de razões entre Elementos Terras Raras leve (ETRL) e Elementos Terras Raras pesado (ETRP) comparando possíveis fontes disponíveis na literatura. O padrão de distribuição indica enriquecimento em ETRM sobre ETRL e ETRP em todos os eventos. Isso significa que a proveniência deste material, provavelmente, deve-se a uma única fonte. As concentrações dos ETRL são sempre maiores que ETRM e ETRP. Esse padrão é outro indicativo de fonte única do material sedimentar. O somatório das concentrações dos ETR durante o MIS 2 é sempre maior do que o MIS 1. O comportamento dos ETR durante os eventos Heinrich são bem similares. A média das concentrações dos ETR nestes eventos são superiores aos encontrados no MIS 1 – Interglacial. As análises das razões Fe/Ca e Ti/Ca pelas duas técnicas mostram-se coerentes e indicam maiores durante o MIS 2. Isto é devido ao aumento de chuvas na região (intensificação do SMAS), nível do mar regressivo (plataforma continental exposta) e por efeitos de diluição do carbonato marinho estimulada pela entrada de matéria orgânica. As razões Al/Si e Fe/K apresentam sinais distintos ao longo do testemunho deste estudo. O aumento de Si durante o MIS 2, em relação aos outros períodos, indica que o glacial foi menos úmido que o interglacial. O aumento de K dentro dos eventos Heinrich indica mudança no padrão de intemperismo continental devido aos episódios de chuvas e aumento no intemperismo químico nas bacias de drenagens. A anomalia do Ce é negativa em todos os períodos e indica condições oxidantes no ambiente deposicional ou oriundas de uma porção detrítica continental. A anomalia do Eu é ligeiramente positiva para todos os períodos. Isto é um indicativo de assimilação ou acúmulo de feldspato. Dados de cinco possíveis fontes para a proveniência do material foram extraídos da literatura. Os sedimentos de Cabo Frio apresentam fracionamento entre ETRL e ETRP próximos aos dados deste estudo. Entretanto, para a razão (Eu/Sm) observa-se boa correlação com fontes vindas da Patagônia e do Rio da Prata. Alguns autores apontam a pluma do Rio da Prata na contribuição sedimentar na região da Bacia de Santos. / The continental sediments deposited in the ocean floor are conditioned, mainly, to the evolution of the climate, the geological substrate and the type of transport, being the fluvial transport of the greater magnitude. Once deposited, the sediments become records of the past and carry information in a form of geochemical signature. Rare Earth Elements (REE) present a coercive behavior along a sedimentary column making them useful for studies of sedimentary origin. Ratios for larger elements (Fe/Ca, for example) are indicators of the reconstruction of the terrigenous port. The geochemistry of the ETR and major elements are determined in this work to understand the paleoclimatic dynamics on the contribution and provenance of the sediments of the eastern margin (Santos Basin) of Brazil, and the anomalies of the Ce and Eu, confronting different analytical techniques (ICP- MS and XRF core scanner) in the main abrupt events (Younger Dryas and Heinrich events) over the last 45,000 years. The origin of the sedimentary material is also discussed by means of ratios between Light Rare Earth Elements (LREE) and Heavy Rare Earth Elements (HREE) comparing possible sources available in the literature. The distribution pattern indicates MREE enrichment over LREE and HREE in all events. This means that the origin of this material, probably, is related to a single source. LREE concentrations are always higher than MREE and HREE. This pattern is another indicative of a single source of sedimentary material. The sum of REE concentrations during MIS 2 is always greater than MIS 1. The behavior of REE during Heinrich events is very similar. The mean REE concentrations in these events are higher than those found in MIS 1 - Interglacial. The analyses of Fe/Ca and Ti/Ca ratios are stronger than those observed during the investigation period (MIS) due to the regressive margin level (continental shelf exposed), and the effects of dilution of the marine carbonate stimulated by imput of organic matter. The Al/Si and Fe/K ratios show distinct signals over time during this study. The increase of Si during MIS 2, in relation to the other periods, indicates that the glacial was less humid than the interglacial. The increase of K within the Heinrich events indicates a change in the continental weather pattern due to rainfall episodes and increase in chemical weathering in the drainage basins. The Ce anomaly is negative at all periods and indicates oxidizing conditions in the depositional environment or from a continental detrital portion. The Eu anomaly is slightly positive for all periods. This is an indicative of assimilation or accumulation of feldspar. Data from five possible sources for a sample of the material was extracted from the literature. The Cabo Frio sediments show the fractionation between LREE and HREE. However, for a (Eu / Sm) ratio a good correlation is observed with sources coming from Patagonia and Rio de la Plata. Some authors point out a region of the River Plate and a sedimentary region in the region of the Santos Basin.

Le but de cette étude est de retracer l’évolution de l’hydrologie dans la partie occidentale de l’Océan Pacifique subtropical en utilisant le proxy εNd analysé sur les foraminifères et sur les oxydes de ferromanganèse authigéniques dans les sédiments. Ceux-ci proviennent de carottes sédimentaires prélevées au nord de la Mer de Chine du Sud (MCS). Avant d’utiliser l’εNd dans les sédiments profonds de la MCS, 16 profils d’eau de mer, collectés au nord de la MCS et dans le Mer des Philippines, ont été analysés afin d’établir la distribution d’εNd des masses d’eau dans l’ouest du Pacifique tropical et dans la MCS, qui jusqu’à aujourd’hui n’était pas documentée. Les valeurs d’εNd des masses d’eau profondes et intermédiaires varient de -2,7 à -4,4 et augmentent légèrement avec la profondeur. Dans la mer des Philippines, les valeurs d’εNd de l’eau intermédiaire du Pacifique Nord (North Pacific Intermediate Water, NPIW) atteint -2.7±0.4 à moyenne profondeur (500 à 1400m). En-dessous de de 1800m, l’eau profonde Pacifique (Pacific Deep Water, PDW) est caractérisée par du Nd moins radiogénique (-4.1±0.5), indiquant l’intrusion de masses d’eau australes. Pour la plupart des stations du nord de la MCS, les masses d’eau en-dessous de 1500m (PDW) affichent des valeurs d’εNd homogènes (~ -4.1), similaires à celles de la PDW dans la Mer des Philippines. Les valeurs d'εNd pour l'eau intermédiaire de la mer de Chine du Sud (South China Sea Intermediate Water, SCSIW, 500-1500m) varient entre -3.0 et -3.9 dû au mélange vertical de la NPIW avec la PDW. Les valeurs d'εNd de l'eau de mer dans la MCS (-5.3 à -7.0) affichent des modifications locales dans des zones où l'eau s'écoule au-dessus de systèmes de dépôt sédimentaire. Ceci implique que "l'échange à la marge" avec des sédiments non radiogéniques (autour de -11) peut se produire dans le temps et dans l'espace sans modifier la composition isotopique du Nd de la PDW dans le Nord de la MCS. Dans un second temps, l’εNd extrait des foraminifères planctoniques G. ruber a été étudié sur la carotte MD05-2904, collectée à 2000m de profondeur sur la marge nord-ouest de la MCS. Cette étude a été conduite dans le but de retracer les variations hydrologiques depuis le Dernier Maximum Glaciaire (DMG) dans la partie occidentale du Pacifique Nord subtropical. Les enregistrements d'εNd ainsi obtenus couvrent les derniers 25 000 ans. Ils affichent une large gamme de valeurs de -4±0.2 à -6.7±0.3, suggérant d'importants changements dans la contribution de la NPDW (εNd=-4) et de la UCDW (Upper circumpolar Deep Water, εNd -6 to -8) dans la zone étudiée. Durant la déglaciation, les enregistrements d'εNd indiquent une diminution des excursions négatives de l'εNd impliquant une plus forte proportion de SSW (Southern-sourced Water) entre 17 et 15 ka BP ainsi qu'entre 10 et 8 ka BP. Ces intervalles de temps sont contemporains de l’évènement Heinrich 1 (HS1) et de l’Holocène inférieur. Les shifts négatifs centrés sur le HS1 coïncident avec un phénomène d'upwelling renforcé dans l'océan austral, associé à un déplacement vers le pôle des vents d'ouest. Ceci implique une augmentation de la formation de la SSW qui se propage dans l'Ouest du Pacifique subtropical. L'excursion négative de l'εNd durant l’Holocène inferieur (~10-8 cal ka BP) indique une plus grande proportion de SSW qui pourrait être associée avec une plus forte production de SSW, comme observé récemment dans l'atlantique Sud, et/ou avec une possible réduction de la NPIW. Nos données suggèrent que le schéma de circulation actuel dans la partie occidental du Pacifique subtropical s'est mis en place il y a 4600 ans. / The aim of this study is to reconstruct the evolution of the hydrology of the western subtropical North Pacific Ocean by using εNd proxy analysed on foraminifera and dispersed authigenic ferromanganese oxide precipitates in sediments from deep-sea cores collected in the northern SCS. Before using the εNd proxy on deep sea sediments of the SCS, Nd of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated to establish the εNd distribution of water masses along the tropical western Pacific and the SCS that, until now have not been documented. εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from -2.7 to -4.4 and generally increase slightly with water depth. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach- 2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterized by less radiogenic Nd (-4.1±0.5) indicating the instrusion of southern sourced water masses. For most of the stations in the Northern SCS, water masses below 1500m (PDW) display homogenous εNd values (~ -4.1) similar to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500-1500m) vary from -3.0 to -3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS (~5.3 to -7.0) display local modification in areas where the water lies above sediment drift deposit systems. This implies that “boundary exchange” with unradiogenic sediments (around~11) may occur temporally and spatially and does not modify he Nd isotopic composition of the PDW in the Northern SCS. In a second step, seawater εNd extracted from cleaned planktonic foraminifera G. ruber has been investigated on core MD05-2904, collected at a deph of 2000m on the north-western margin of the SCS. This study was undertaken in order to reconstruct hydrological variations since the LGM in the western subtropical North Pacific. The εNd records obtained from foraminifera spanning the past 25kyr. Display a wide range of values, ranging from -4±0.2 to -6.7±0.3, suggesting important changes in the contribution of the NPDW (εNd=-4) and the UCDW (εNd -6 to -8) in the subtropical western Pacific. During the period of deglaciation, εNd records indicate a relative decrease in the negative excursions of the εNd implying a higher proportion of SSW during the time intervals 17-15 cal kyr BP and 10-8 cal kyr BP; these intervals are coeval with the HS1 and early Holocene. The negative shifts centered on the HS1coincide with an enhanced upwelling in the Southern Ocean, associated with a polewards shift of the southern westerlies, inducing an enhanced formation of the SSW that propagates to the subtropical western Pacific. The negative excursion of the εNd during the Early Holocene (~10-8 cal kyr BP) indicates a higher relative proportion of SSW that could be associate with higher production of the SSW, as has been recently observed in the South Atlantic, and/or with a possible reduction of the NPIW. Our data suggest that the present modern circulation pattern in the western subtropical Pacific Ocean was fully established after 4.6 cal kyr BP.