Orientador: Alexandre M. da Silva / Banca: Luiz Fernando Charbel / Banca: Cassio José Montagnani Figueira / Resumo: Estudar a qualidade do solo é um instrumento que subsidia o conhecimento sobre as consequencias da mudança da cobertura dos solos, além de mostrar as mudanças do solo e a tomade de decisões no planejamento do desenvolvimento futuro das regiões. Neste trabalho analisou-se a variação regional dos teores de C e N e suas assinaturas insotópicas, bem como de outros elementos na camada superior dos solos do município de Iperó-SP. Amostras deformadas e indeformadas de solos foram coletadas nos primeiros 20 cm superficiais em 29 pontos, considerando as diferentes classes de cobertura da terra. As amostras foram secas, pesadas e peneiradas para análises posteriores em laboratórios específicos. Adicionalmente, mapas digitais de espacialização das informações foram elaborados para dar suporte à interpretação dos dados. O município de Iperó apresenta predominância de pastagens e, diferentemente das outras regiões, um alto índice de vegetação nativa remanescente, devido à presença da FLONA. Os dados de isótopos de C indicam valores médios de -26,46% para a classe Cerrado, -24,62% para a Mata e -17,19% para pastagem. De modo geral, os indicadores de qualidade física e química se apresentaram condizentes com a realidade embora com diferenças discretas entre as diferentes classes de cobertura da terra, não apresentado diferenças significativas / Abstract: Studying the soil quality supports the knowledge of consequences of land cover change, and supportsmaking decision in planning the future development of the regions. In this work the regional variation in the levels of C and N and their isotopic signatures was analyzed, as well as other elements in topsoil from Iperó-SP. Deformed and original soil samples were collected in the first 20 cm in 29 points, considering the different classes of land cover. All samples were georreferenced. Samples were dried, weigted, seived, and delivered for further analysis in specific laboratories. Additionally, digital maps were prepared to support the interpretation of the data. In Iperó there is a high occurrence of pasture and, unike other regions, a high rate of rennant native vegetations, due to the presence of the FLONA. The C isotope data indicate mean values of - 26.46% for class Savannah, -24,62% for Forest and -17.19% for pasture. Values between classes of Savannah and Forest were similar among themselves. In general, the indicators of physical and chemical used are consitent with reality but with subtle different classes of land cover, showing no significant differences / Mestre

Orientador: Luiz Edivaldo Pezzato / Banca: Wilson Massamitu Furuya / Banca: José Fernando Machado Menten / Banca: Carlos Ducatti / Banca: José Roberto Sartori / Resumo: O objetivo deste trabalho foi avaliar a capacidade da tilápia do Nilo em 5 balancear sua dieta, quando fornecidas duas misturas de ingredientes, utilizando os 6 isótopos estáveis de carbono. Foram utilizados 225 juvenis de tilápia (peso: 5,0 ± 0,5 g), 7 distribuídos em cinco tanques. Os indivíduos alocados em um dos tanques eram 8 alimentados com uma mistura de alta proteína (MAP; δ13C = -22,62‰), os alocados em 9 um segundo tanque eram alimentados com uma mistura de baixa proteína (MBP; δ13C = 10 -14,34‰) e os animais dos outros tanques tinham acesso livre a ambas, quatro vezes ao 11 dia. Foram realizadas coletas de músculo, fígado e sangue a cada cinco dias por 86 dias, 12 exceto para o grupo alimentado com MBP (alimentado por 120 dias). As amostras 13 foram analisadas em espectrômetro de massa e as proporções consumidas das misturas 14 foram estimadas a partir do enriquecimento isotópico do carbono (δ13C). O 15 balanceamento realizado indicou redução no consumo relativo de proteína. Contudo, 16 esta relação não apresentou padrão definido em relação ao peso dos indivíduos, ou seja: 17 o balanceamento de proteína e energia para tilápia do Nilo está relacionado 18 principalmente à idade dos animais e não é claro se este processo está relacionado 19 também ao seu peso. As estimativas de consumo de um grupo animais desta espécie por 20 meio dos isótopos estáveis de carbono são semelhantes aos obtidos por outras técnicas, 21 portanto este método permite observação da diversidade deste comportamento no 22 autobalanceamento entre os indivíduos que compõe tal grupo. / Abstract: This study aimed to assess the Nile tilapia ability to balance its own diet, 6 when two ingredient mixes were offered, using carbon stable isotopes. In order to 7 accomplish that, 225 Nile tilapia juveniles (average initial weight 5.0g ± 0.5g) were 8 distributed in five tanks, each containing a group of 45 fish. One group of fish were fed 9 exclusively a high protein mix (HPM; δ13C = -22.62‰), a second one fed only a low 10 protein mix (LPM; δ13C = -14.34‰). The other groups had free access to both mixes 11 (free choice system). The fish from all tanks were fed four times a day. Muscle, liver 12 and blood samples were collected at each five days (from 2 fish/tank/collection) for 86 13 days, except for the fish fed with MBP (fed for a 120 days period). The samples were 14 analyzed in a mass spectrometer and proportions of the mixes consumed were estimated 15 through its carbon isotope enrichment (δ13C). The fish diminished their protein intake 16 along the time. However, consumption did not present a clear pattern in relation to the 17 individual weight, i.e.: protein consumption patterns are mainly related to the age of the 18 individuals and it is not clear if it is also correlated to their weight. The consumption 19 estimative through stable isotopes of carbon did not conflict other studies reported in the 20 literature. Additionally this technique allowed observation of consumption among the 21 individuals from an experimental group 22. / Doutor

Stable isotope composition of bulk leaf water is a useful proxy for geochemical and biological processes and is, thus, appreciated in ecological research and global modelling. The mechanisms determining the abundance of different isotopes in leaf water are not fully understood. The research presented in this thesis aimed to describe variability in leaf water isotopes which occurs under natural conditions and to distinguish which factors generate such variability. For that purpose, field sampling, water extraction, stable isotope analysis and measurements of several additional environmental and physiological characteristics were carried out at one sampling site during three subsequent growing seasons. The results obtained point out that oxygen isotopes rather then hydrogen isotopes have greater potential to be used in higher scale applications. Apart from that, several interesting ecophysiological interpretations of isotopic data have been made.

A utilização de traçadores como os isótopos estáveis de carbono e nitrogênio, é crescente e complementa as técnicas convencionais nos estudos referentes à dieta em animais silvestres. Isso é possível pois o valor isotópico dos itens utilizados na alimentação é refletido nos tecidos. A diferença isotópica resultante chamada de fator de discriminação ou fracionamento, está associada aos processos metabólicos necessários para que ocorra a incorporação de nutrientes. O estudo teve como objetivo medir o tempo de incorporação dos isótopos no plasma e nas células sanguíneas, componentes de \"tecido\" não mortal reamostrável, e determinar o fator de discriminação em cinco espécies de quelônios de água doce: Podocnemis expansa (tartaruga-da-Amazônia), Podocnemis unifilis (tracajá), Phrynops geofroanus (cágado-de-barbicha), Trachemys scripta (tartaruga-de-orelha-vermelha) e Trachemys dorbigni (tigre-d\'água). Os animais foram mantidos em cativeiro e as diferenças isotópicas dos 10 indivíduos adultos de cada espécie, foram medidas a partir da troca de dietas com valores isotópicos distintos. Com a mudança da dieta, o turnover do carbono e nitrogênio foram estimados entre 7 e 185 dias por meio de regressão exponencial não linear, quando os novos fatores de fracionamento foram estimados. O tempo de turnover para as espécies de quelônios variou de 72 a 337 dias para o carbono, e de 29 a 270 dias para o nitrogênio no plasma. Nas células sanguíneas o turnover variou de 3 a 373 dias para o carbono, e de 51 a 216 dias para o nitrogênio. Os fatores de discriminação que eram em média próximos a zero para o carbono, e entre 3-4‰ para o nitrogênio, variaram de 1,01 a 3,28‰ para o 13C e -0,76 a 0,49‰ para o 15N no plasma, e de 1,49 a 3,98‰ para o 13C e 0,99‰ a 4,69 para o 15N nas células sanguíneas, com a diminuição de 3,7‰ e aumento de 6,2‰, respectivamente para carbono e nitrogênio, na nova dieta. A diferença encontrada entre os fatores de discriminação calculados anteriormente a troca da dieta e após a troca, mostraram que provavelmente a incorporação dos isótopos estáveis se dá de forma heterogênea nos tecidos. De acordo com a literatura foi possível analisar que fatores como a memória isotópica, as rotas metabólicas e elementos característicos dos répteis possivelmente estão ligados ao turnover mais lento, diferente dos animais endotérmicos em que esse processo é mais rápido. / The use of tracers such as stable carbon and nitrogen isotopes is crescent and complements the conventional techniques used in the studies referring to the diet in wild animals. This is possible because the isotopic value of the items used in the diet reflects their isotopic values on the tissues. The resulting isotopic difference called the discrimination factor or fractionation is associated with the metabolic processes required for nutrient incorporation to occur. The object of the study was to measure the incorporation time of isotopes into plasma and blood cells, components of re-portable non-lethal \"tissue\", and to determine the discriminant factor of five species of freshwater chelonians: Podocnemis expansa (Amazonia tortoise), Podocnemis unifilis (tracajá), Phrynops geofroanus (geoffroy´s side necked turtle), Trachemys scripta (red-eared slider turtle) and Trachemys dorbigni (d\'orbigny\'s slider). The isotopic differences of 10 adult individuals of each species kept in captivity were measured through shifting diets with different isotopic values. With the diet variation, carbon and nitrogen turnover was estimated between 7 and 185 days by non-linear exponential regression, when the new fractionation factors were estimated. The turnover time for the chelonians species varied from 72 to 337 days for carbon, and from 29 to 270 days for the plasma nitrogen. In blood cells, the turnover ranged from 3 to 373 days for carbon, and from 51 to 216 days for nitrogen. Discrimination factors that were, in average, close to zero for carbon and between 3 and 4‰ for nitrogen ranged from 1.01 to 3.28‰ for 13C and -0.76 to 0.49‰ for 15N in plasma, and from 1.49 to 3.98‰ for 13C and 0.99 to 4.69 for 15N in blood cells, with a decrease of 3.7‰ and an increase of 6.2‰, respectively for carbon and nitrogen in the new diet. The difference found between the discrimination factors calculated before and after the diet shift, showed that stable isotopes incorporation probably occurs in a heterogenous way in tissues. According to the literature it was possible to analyze that factors such as isotopic memory, metabolic routes and reptiles characteristic elements are possibly linked to slower turnover, different from endothermic animals in which this process is faster.

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O delta do rio Tubarão, situado na costa centro-sul catarinense entre os municípios de Tubarão, Jaguaruna e Laguna, constitui raro exemplo de delta lagunar ativo no Brasil. Sua planície deltaica cobre área aproximada de 250km2, onde são encontradas evidências de migração de canais fluviais dadas por séries de truncamentos de antigos distributários, alguns ainda ativos. Dez testemunhos foram obtidos junto aos principais canais distributários do rio Tubarão, a partir dos quais foram realizadas análises de fácies, granulométrica, de minerais pesados, de teor de matéria orgânica e de relações químio-isotópicas, além de datações 14C. Também foram levantados acervos históricos de fotografias aéreas e de dados de prospecção mineral de subsuperfície. Cerca de 5000 anos atrás, na região de seu ápice, próximo ao rio tributário Capivari de Baixo, o delta do rio Tubarão ingressou numa antiga baía lagunar e ramificou-se em sete distributários principais que, desde seus momentos iniciais de migração, foram controlados por avulsões autogênicas rumo a antigas depressões do fundo da bacia receptora. Tais avulsões progradaram o delta inicialmente para SW, depois para ENE, e então para NNE, favorecendo a fragmentação da antiga baía lagunar em uma série de lagos e lagunas menores. Diante deste cenário dinâmico, sambaquis foram erigidos no entorno do sistema lagunar, constituindo importantes registros arqueológicos de interação entre evolução sedimentar e ocupação humana pré-histórica. O resultado das análises granulométricas indicou que a sedimentação deltaica, nas proximidades de encostas de morros, foi misturada com colúvio e/ou depósitos de fluxos gravitacionais, como evidenciado pela presença de intervalos texturalmente muito imaturos em alguns testemunhos. Em relação à análise de minerais pesados, o principal fator de controle nas variações da assembleia em depósitos de delta e de bacia é a proveniência sedimentar. Em termos mediatos, essa proveniência reflete fontes plutônicas e metamórficas (médio a alto grau) do Batólito de Florianópolis (e xenólitos associados) e do Complexo Granito-Gnáissico, e rochas arenáceas alteradas da Bacia do Paraná. Em termos imediatos, depósitos deltaicos destacam-se pela afinidade mineralógica com as areias do rio Tubarão, inferida sobretudo a partir da presença mútua de grãos alterados de cianita e estaurolita, enquanto que depósitos da bacia lagunar destacam-se por sua similaridade mineralógica com areias dos rios tributários Braço do Norte e Capivari de Baixo, neste caso principalmente pela presença de zircão. A matéria orgânica presente nos depósitos do delta e de sua bacia receptora resulta do aporte de fontes terrestres (fornecido pelos rios) e marinhas (trazido via desembocaduras lagunares), fato que é evidenciado pelos resultados de \'delta\'\'POT.13 C\', \'delta\'\'POT.15 N\' e razão \'C IND.ORG\'/\'N IND.TOTAL\'. Particularmente, nos sedimentos da bacia, variações entre diferentes tipos de matéria orgânica têm ocorrido ao longo do Holoceno, as quais são atribuídas tanto ao isolamento físico progressivo do sistema lagunar em relação ao mar aberto como por mudança climática regional (aumento destacado de precipitação). A análise isotópica de oxigênio (\'delta\'\'POT 18 O\') de conchas de moluscos em depósitos da bacia indicou enriquecimento relativo em \'ANTPOT.16 O\' durante o Holoceno. Este resultado, a exemplo daquele dos isótopos de carbono e de nitrogênio dos sedimentos, sugere isolamento gradual das águas lagunares em relação às de mar aberto. / The Tubarão river delta, located on the centre-south coast of Santa Catarina State, among the municipalities of Tubarão, Jaguaruna and Laguna, is rare example of active lagoonal delta in Brazil. Its delta plain covers an area of about 250km2, where there are evidences of migration of fluvial channels in a set of truncations of ancient distributaries, some of these still in activity. Ten cores were acquired adjacent to the main distributary channels of the Tubarão river, from which analyses of facies, grain size, heavy minerals, organic matter, chemistry-isotope ratios, and radiocarbon datings were performed. Also, aerial photographies and data of subsurface mining were surveyed from historical collections. Thereabout 5,000 years ago, in the region of its apex, near Capivari de Baixo tributary river, the Tubarão river delta entered an ancient lagoonal bay and branched seven main distributaries. Since the beginning of its migration, these distributaries were controlled by autogenic avulsions towards ancient depressions in the bottom of the basin. Initially, these avulsions prograded the delta towards SW, afterwards to ENE, and then to NNE, favoring the fragmentation of the ancient lagoonal bay in a set of smaller lakes and lagoons. Faced with this dynamical scenario, shellmounds were erected surrounding the lagoon system, composing important archaeological records of the interaction between sedimentary evolution and prehistoric human occupation. The results of the grain size analysis showed that the deltaic sedimentation, in the vicinity of slopes of hills, was mixed with colluvium and/or gravity flow deposits, that is evidenced by the presence of texturally very immature intervals in some cores. The analysis of heavy minerals, by its turn, showed that the main controlling factor in the variations of its assemblage in deposits of delta and basin is the sedimentary provenance. In terms of mediate sources, this provenance reflects plutonic and metamorphic (medium to high grade) rocks of the Florianópolis batholith (including its xenoliths) and of the Granite-Gneiss Complex, and weathered sedimentary sandstones of the Palaeozoic Paraná basin. Regarding immediate sources, deltaic deposits stand out by its mineralogical affinity with sands of the Tubarão river, mainly by the mutual presence of weathered grains of kyanite and staurolite, whereas deposits of the lagoon have mineralogical similarity with the sands of Braço do Norte and Capivari de Baixo tributary rivers, especially in relation to the presence of zircon. The origin of the organic matter found in the deposits of the delta and in its lagoonal basin is both from sedimentary input of terrestrial sources (provided by rivers) and marine (brought via inlets), fact evidenced by results of \'delta\'\'POT.13 C\', \'delta\'\' POT.15 N\', and \'C IND.ORG\'/\'N IND. TOTAL\' ratio. Particularly, in the sediments of the basin, variations between different types of organic matter have occurred during the Holocene, and are attributed both to the progressive physical isolament of the lagoon system from the open sea, and by local climate change (pronounced augment of precipitation). The isotope analyses of oxygen (\'delta\'\'POT.18 O\') of molluskan shells from the deposits of the basin present relative enrichment in \'ANTPOT.16 O\' during the Holocene. This result, as well as the one from isotope analyses of carbon and nitrogen of sediments, suggests gradual isolation of the lagoonal waters of influence of waters from the open sea.

The different reproductive strategies of males and females underlie differences in behavior that may also lead to differences in nutrient use between the two sexes. We studied sex differences in the utilization of two essential amino acids (EAAs) and one non-essential amino acid (NEAA) by the Carolina sphinx moth (Manduca sexta). On day one post-eclosion from the pupae, adult male moths oxidized greater amounts of larva-derived AAs than females, and more nectar-derived AAs after feeding. After 4 days of starvation, the opposite pattern was observed: adult females oxidized more larva- derived AAs than males. Adult males allocated comparatively small amounts of nectar-derived AAs to their first spermatophore, but this allocation increased substantially in the second and third spermatophores. Males allocated significantly more adult-derived AAs to their flight muscle than females. These outcomes indicate that adult male and female moths employ different strategies for allocation and oxidation of dietary AAs.

The Cassenha Hill copper-gold prospect is situated in the Catabola area, Huambo Province, southwestern Angola. Geologically, the prospect is part of the Angolan Central Eburnean Zone (CEZ) and consists of Paleoproterozoic metasedimentary rock sequences which have been intruded by Eburnean granitoids at ± 2.1 Ga. The prospect itself comprises an area of 180 Km2 and has been intermittently explored since 2005 by Rift Valley Resources (RVR) and its associates. The Cassenha Hill prospect is characterized by the occurrence of partially altered and highly oxidized metasedimentary rocks (meta-mudstone, meta-siltstone, carbonate-rich rock, meta-sandstone, breccia, and quartzite), and altered isolated granitoids. This study represents the first detailed study of the prospect and aims to shed light on the characteristics of the various rock types (i.e., host and barren rocks), their source/provenance, styles of alteration, and the origin and/or type of the fluid responsible for the mineralization. Techniques applied include borehole core logging, petrography, whole-rock geochemistry (XRF and ICP-MS), and stable isotope geochemistry on samples collected on the surface and from exploration boreholes drilled as part of RVR exploration program. Overall, the petrographic and geochemical studies undertaken in the rocks of the Cassenha Hill prospect indicate the following: (1) The rocks are moderately to strongly fractured; (2) The rocks have experienced weak to moderate chemical weathering; (3) The rocks are compositionally immature and originated from felsic provenance; (4) The rocks are sulfur-poor, and lacking in sulfide minerals (5) The rocks are enriched in LREE and LILE elements and depleted in HREE and HFSE elements; (6) The mineralization is associated with chloritization alteration and predominantly occurs within and/or at the edges of quartz/chlorite-rich veins/fractures and is not restricted to any rock type. Two ore stages could be identified, namely, hypogene ore (stage I) consisting of pyrite ± chalcopyrite ± other copper sulfides, and supergene ore (stage II) consisting of malachite ± azurite ± chrysocolla, which represents the prevalent mineralization at the prospect. The δ 18O value of quartz veins range from +12.81 to +13.53‰, while the δD of chlorite minerals range from -51 to -45‰. Therefore, assuming fluid-rock interaction took place at ≈ 350oC, due to the presence of quartz, the fluid had δ 18OH20 values of about +8‰, which are typical of magmatic waters. On the other hand, at a temperature of ≈ 350oC, and with the difference between chlorite and water being -33.5‰, such fluids would have had δDH20 values of about -20‰ (δ 18OH20= -4‰), which are typical of meteoric waters. Although the various mineral phases have yielded different isotopic signatures, this study suggests that water is ultimately of meteoric origin but exchanged with hydrogen-poor magmatic rock, thus maintaining the meteoric signature. The continuous influx of meteoric waters within the fracture system led to the development of copper oxides such as malachite, azurite and chrysocolla, which possibly originated from the insitu oxidation of the hypogene sulfides. This signature, together with other field, petrographic and geochemical observations allows one to, tentatively, suggest that the Cassenha Hill prospect represents an extension of a polymetallic vein-type of porphyry Cu deposit that has been subjected to supergene processes at the weathering profile.

Si la relation entre l’enregistrement géochimique au sein de ces travertins et les paramètres environnementaux semble admise, le détail des processus, notamment cinétique et dégazage, ainsi que leur poids respectifs dans les reconstitutions paléoenvironnementales ne sont clairement établis. Afin de mieux contraindre ces processus, un travail minutieux de reconnaissance des mécanismes de précipitation et d’enregistrement de la signature géochimique a été effectué sur les travertins –récents et fossiles- d’une source carbogazeuse située dans le Massif Central (France). Il couple expériences de laboratoire innovantes et travail sérié sur le terrain.Le taux de dégazage du CO2 dans les sources carbogazeuses est l’un des facteurs principaux conduisant aux conditions de précipitation via la modulation du taux de précipitation de la calcite et par conséquent, sa composition en 18O et 13C. Les tests en laboratoire ont été conduits en deux étapes : (1) caractérisation des mécanismes de dégazage seuls, et (2) des expériences combinant dégazage et précipitation pour mieux appréhender les processus cinétiques lors de la précipitation des travertins. En parallèle, un travail de terrain spécifique par pose de plaques de plexiglas le long de différents écoulement de la source, nous a permis de connaitre la résolution de précipitation des travertins et d’obtenir une meilleure estimation des facteurs de fractionnement.Les tests en laboratoire confirment que, lors d’un dégazage important, i.e. conduisant à la précipitation de travertins, la spéciation des espèces du carbone inorganique dissout (CID) et les flux entre ces espèces sont des paramètres primordiaux à considérer. Le facteur de fractionnementεDIC-CO2(g) qui dépend du pH suit alors une distillation de Rayleigh dans un système cinétique. Les évolutions des espèces carbonées en solution ont ainsi pu être modélisées à l’aide d’une équation de diffusion faisant intervenir les paramètres propres à l’expérience.Les résultats de terrain permettent de démontrer que les variations de conditions de précipitation sont principalement dues aux variations de conditions hydrodynamiques et, secondairement, aux variations de température, ce qui a pu être modélisé à l’aide de l’équation définie par Plummer en 1968 et qui a montré la variabilité des conditions de précipitation in-situ. Dans le cas des expériences de précipitation en laboratoire et par comparaison avec les données de terrain, le facteur de fractionnement εCID-calcite va dépendre des concentrations de chaque espèce de CID mais aussi de la partition du carbone entre phase gaz et phase solide. Pour l’oxygène 18, de 0°C à 10°C, les résultats acquis sur les travertins actuels nous ont permis d’utiliser la droite définie récemment par Coplen (2007) pour lier de façon fiable la température au moment de la précipitation et le facteur de fractionnement. Toutefois, pour des températures plus élevées, le facteur de fractionnement est plus important que ce qu’il devrait et confirmant ainsi la non-représentativité des droites de Coplen pour la détermination de la température de précipitation. Lors des expériences de précipitation la tendance est inverse à celle observée pour les travertins confirmant l’influence de la vitesse de dégazage et de l’indice de saturation sur le fractionnement isotopique. Nous avons également confirmé avec les expérimentations, l’impact de la vitesse de précipitation sur les teneurs isotopiques enregistrées dans les travertins.Ce travail a mis en lumière des mécanismes cinétiques complexes et qui ne sont pas complètement contraints par la seule utilisation des outils isotopiques. L’utilisation du partitionnement des éléments traces est un outil primordial pour appuyer l’étude de ces mécanismes. / The response of continental groundwater systems to recent climate fluctuations can be reconstructed via the continuous measurement of groundwater level, spring flow and climatic chronicles. When any data exist, recent reconstructions of groundwater dynamics may be reached through various recorders of environmental and hydrological conditions such as travertine. Although the relationship between geochemical records in travertine and environmental parameters seems to be accepted, the details of processes and their respective weight in the paleo-information are not clearly established.Rate of CO2 degassing in CO2-rich spring likely influences calcite precipitation rate and the related δ18O and δ13C composition. Isotopic equilibrium is rarely maintained during travertine deposition and the degassing rate is the main controlling factor of the disequilibrium. Due to the lack of knowledge, fractionation processes, either kinetic or equilibrium, occurring between CO2-rich water, gas and travertine required specific pH and temperature-controlled laboratory tests. These tests were conducted on synthetic water at different pH to focus only on the degassing processes. Other tests were conducted on trace elements partitioning during calcite precipitation, to identify the origin of isotopic signature variability, and to constraint the way of recording past conditions.All these tests confirmed that during a degassing leading to travertine precipitation, the speciation of dissolved inorganic carbon species is a major parameter to be tackled since a linear relationship between εDIC-CO2(g) and pH is observed. Indeed, we highlighted that for a high degassing rate, the isotopic equilibrium is not reached because the reaction greater involves light isotopes than heavy ones. There is thus different reaction rate between the species of dissolved inorganic carbon, the reactions occurring faster in the water than the one between water and gas, the latter being controlled by diffusion.

Stable isotope analyses are powerful tools for reconstructing ancient ecologies and ecosystems, as they are independent of morphology and directly reflect dietary ecology. The application of stable isotope analyses, however, is not without limitations, as determination of food web dynamics using these methods often relies on poorly tested assumptions. The guiding thread of this thesis is the testing of foundational cornerstones on which these methods rely, in order to validate the suitability of applying these techniques to different mammalian clades, and to more reliably and confidently interpret the isotopic signals preserved in extinct organisms. The first chapter of this thesis tests the validity of an important assumption behind the interpretation of stable carbon isotope analyses for understanding diet in terrestrial mammalian herbivores: if, as assumed for almost two decades, mammalian bioapatite δ¹³C is enriched by 14‰ relative to dietary δ¹³C. By analyzing new isotopic data from a never before assessed herbivorous group spanning a broad range of body masses—sloths (Xenarthra, Mammalia)— and other mammals with experimentally controlled or observationally known diets, I discovered considerable variation in diet–bioapatite δ¹³C enrichment among mammals. Statistical tests (ordinary least squares, quantile, robust regressions, Akaike information criterion model tests) documented independence from phylogeny, and a previously unrecognized strong and significant correlation of δ¹³C enrichment with body mass for all mammalian herbivores. A single-factor body mass model outperformed all other single-factor or more complex combinatorial models evaluated, including for physiological variables (metabolic rate and body temperature proxies), and indicated that body mass alone predicts δ¹³C enrichment. These analyses, spanning more than 5 orders of magnitude of body sizes, yield a size-dependent prediction of isotopic enrichment across Mammalia and for distinct digestive physiologies, permitting reconstruction of foregut versus hindgut fermentation physiologies for fossils and refined mean annual paleoprecipitation estimates based on δ¹³C of mammalian bioapatite. Second, I sought to evaluate the existing paradigm governing identification of closed canopy rainforests in the fossil record using mammalian δ¹³C data: the presence of mammals with dietary δ¹³C <-31‰, which has only been observed in closed canopy rainforests in Equatorial Africa, the only other tropical ecosystem sampled extensively. This chapter provides a characterization of δ¹³Cbioapatite, δ¹³Chair and δ¹⁵Nhair of a modern mammalian community in western Amazonia, in Peru, to test if the isotopic structure of mammals in this Neotropical ecosystem is similar to those in African tropical rainforests. The results indicate that despite their marked geographical and taxonomic differences, median δ¹³Cdiet values from closed canopy rainforests in Amazonia (-27.4‰) and equatorial Africa (-26.9‰) are not significantly different. Amazonian mammals, however, seem to exploit a narrower spectrum of dietary resources than equatorial African mammals, as depicted by the absence of highly negative δ¹³Cdiet values previously proposed as indicative of rainforests (<-31‰). I hypothesize that differential effects of late Pleistocene extinction may be responsible for the ecological disparities among the two rainforests, by significantly reducing evolutionary time and dietary breadth reflected in the modern Amazonian mammalian community. Finally, the third chapter of this dissertation evaluates assumptions behind δ¹⁵N amino acid compound specific analyses in order to test the controversial hypothesis of carnivory and consumption of proteins of animal origin in fossil sloths. This analytical technique relies on three main assumptions. First, that the offset between the δ¹⁵N of glutamic acid (δ¹⁵NGlx) and phenylalanine (d15NPhe) in the organism under study will increase with increasing trophic level. Second, that the offset between δ¹⁵NGlx and δ¹⁵NPhe at the base of the food chain is relatively constant and has a value of -8.4‰ for C3 ecosystems. Third, that the trophic discrimination factor in all ecosystems (the difference in δ¹⁵NGlx relative to δ¹⁵NPhe with increasing trophic level) is 7.6‰. The results of my experiments conducted on extant xenarthrans (sloths and anteaters) with controlled diets document that only the first assumption holds true. Rather than relying on an equation with constants introducing uncertainties and that are not applicable to organisms feeding on a combination of items of different origin (e.g., C3 + C4 plants), δ¹⁵NGlx and δ¹⁵NPhe values by themselves can accurately reconstruct the trophic position of organisms. Indeed, the results on δ¹⁵NGlx and δ¹⁵NPhe herein obtained for five xenarthran species in controlled feeding experiments, combined with mammalian data available from the literature, show strong and significant correlations between these two AAs and with trophic positions. Both the TP equation and the regression analyses of δ¹⁵NGlx and δ¹⁵NPhe suggest that the Pleistocene fossil ground sloths 𝘔𝘺𝘭𝘰𝘥𝘰𝘯 𝘥𝘢𝘳𝘸𝘪𝘯𝘪𝘪 and 𝘕𝘰𝘵𝘩𝘳𝘰𝘵𝘩𝘦𝘳𝘪𝘰𝘱𝘴 𝘴𝘩𝘢𝘴𝘵𝘦𝘯𝘴𝘪𝘴 were not pure herbivores as commonly presumed, but rather that they were both mixed feeders/omnivores, incorporating items of animal origin in their diets.