Seagrass communities are composed of numerous organisms that depend on water-column nutrients for metabolic processes. The rate at which these organisms remove a nutrient from the water column can be controlled by physical factors such as hydrodynamic regime or by biological factors such as speed of enzyme reactions. The impact of hydrodynamic regime on rates of nutrient uptake for seagrass (Thalassia testudinum) communities and for organisms that comprise the community (seagrass, epiphytes, phytoplankton, and microphytobenthos) was quantified in a series of field flume experiments employing the use of 15N-labeled ammonium and nitrate. Rates of ammonium uptake for the entire community and for seagrass leaves and epiphytes were significantly dependent on bulk velocity, bottom shear stress, and the rate of turbulent energy dissipation. Relationships between uptake rates and these parameters were consistent with mass-transfer theory and suggest that the effect of water flow on ammonium uptake is the same for the benthos as a whole and for the organisms that form the canopy. In addition, epiphytes on the surface of T. testudinum leaves were shown to depress leaf uptake by an amount proportional to the area of the leaf covered by epiphytes. Water flow influenced rates of nitrate uptake for the community and the epiphytes; however, uptake rates were depressed relative to those for ammonium suggesting that uptake of nitrate was also affected by biological factors such as enzyme activity. Epiphytes reduced uptake of nitrate by the leaves; however, the amount of reduction was not proportional to the extent of epiphyte cover, which provided further evidence that nitrate uptake by T. testudinum leaves was biologically limited. As an additional component of the research, hydrodynamic regime of a mixed seagrass and coral community in Florida Bay was characterized using an acoustic Doppler velocimeter. Hydrodynamic parameters estimated from velocity data were used in mass-transfer equations to predict nutrient uptake by the benthos over a range of water velocity. Measured rates of uptake from field flume experiments conducted in the same community confirmed that hydrodynamic data could be used to accurately predict nutrient transport to the benthos under natural flow conditions.

Due to Earth’s efficient crustal recycling through plate tectonics, the remaining physical record of Earth’s first two billion years consists of mineral fragments and heavily metamorphosed rocks in isolated Archean cratons. Characterization of Earth’s earliest tectonic processes requires investigation of all available records; the mineral garnet has been largely overlooked. The major element chemistry and samarium-neodymium (Sm-Nd) isotope ratios preserved in fragmented detrital garnet and Archean metamorphic garnet record the timing and conditions of early tectonic events. This work presents detailed methodology for a new detrital garnet geochronometer unlocking age information from previously undateable detrital garnet surviving recycling in sediment, sedimentary rocks, and metasedimentary rocks. The new method’s utility is demonstrated by dating garnet from a Scottish sedimentary rock and nineteen individual garnet grains from a tributary to the French Broad River in the southern Appalachians. In the southern Appalachians, garnet and existing monazite ages overlap (though the mean garnet age is slightly younger) to record the most recent metamorphic event and both are younger than inherited zircon ages. Proof-of-concept testing demonstrating protocol development for blank-correction and routine analysis of samples smaller than 1 ng advances small Sm-Nd analysis. Additionally, this work applies existing Sm-Nd garnet geochronology methods to search for garnet older than 2.5 Ga and provide age constraints on the complicated metamorphic histories of two Archean cratons. A search for detrital garnet in a sample from the Jack Hills metasedimentary belt of Western Australia hosting the Earth’s oldest known terrestrial materials (ca. 4.3 Ga) failed to produce garnet. Instead, two samples collected ~4 km south of the Jack Hills belt in the Narryer Terrane were dated to confirm Narryer regional metamorphism at ca. 2.6 Ga. The Acasta gneiss of northern Canada, arguably Earth’s oldest known cohesive rock outcrop (ca. 4.0 Ga), produced one of the Earth’s oldest known garnet ages. Garnet ages of ca. 2.95 Ga constrain the timing of Archean metamorphism and the data also indicate potential for preservation of even older garnet. Finally, a compilation of published garnet ages in the literature is presented to summarize the community’s progress in the search for Earth’s oldest garnet. / 2017-12-06T00:00:00Z

Baile Herculane, located in southwestern Romania, is a unique city that exploits its thermal waters. The geology consists of a granitic basement covered by 200 meters of limestone, marl, and flysch deposits. Extreme faulting carries heat ascending from the mantle, which intercepts percolating meteoric waters. Local springs have high concentrations of dissolved sulfide gas (H2S) and dissolved sulfate (SO4²-).These dissolved species indicate the progression of sulfate reduction in the aquifer. Water samples were collected in polyethylene syringes to prevent oxidation of sulfide. Then, sulfide and sulfate were quantitatively reacted for stable isotope analysis. Total sulfur isotopic composition was calculated to determine the source of the dissolved sulfur. The source of the sulfur is a sulfate of marine origin (𝛅34S≅20%0), which I found to come from impurities in the limestone since the Cerna Valley does not possess marine evaporites. The limestones of the Cerna Valley are host to a number of caves, which possess relatively large deposits of sulfates and exotic morphologic features that suggest speleogenesis by sulfuric acid. 𝛅34S of the sulfates relates to sulfide isotopic values from the springs, showing that the dissolved sulfide (upon oxidation) forms sulfuric acid s that reacts with limestone to produce sulfate minerals. A wide range of cave sulfate 𝛅34S values exist indicating that isotopic values of these deposits depend on several factors such as sulfur source, extent of sulfate reduction, and completeness of sulfide oxidation. This also implies that a single, narrow range of sulfur isotopic values does not represent sulfuric acid speleogenesis.

Early research into the stable hydrogen isotopic compositions (δD) of petroleum involved bulk deuterium/hydrogen (D/H) measurements which, while providing some useful information, had to contend with the analysis of complex mixtures of hydrocarbons, and alteration resulting from the rapid exchange of nitrogen-, oxygen- and sulphur-bound hydrogen. The use of gas chromatography-isotope ratio mass spectrometry (GC-irMS) overcomes these problems by allowing the analysis of individual compounds containing only the most isotopically conservative aliphatic carbon-bound (C-bound) hydrogen. This project investigates the geochemical utility and reliability of compound-specific δD values, with the aim to better understand and exploit this analytical capability. To demonstrate the source diagnostic potential of compound-specific δD values, normal and branched alkanes extracted from series of immature bog-head coals (torbanites) were analysed. The torbanites contain immature organic matter predominantly from a single, freshwater algal source, i.e. Botryococcus braunii (B. braunii). The δD values of n-alkanes reflect the climate regime at the time of deposition of the torbanites, and vary mainly in response to the δD values of the source meteoric waters in their depositional environments. n-Alkanes from torbanites deposited at high latitude in a glacial climate are depleted in D by up to 70% relative to those from a torbanite deposited at low latitude under a tropical climate regime. Torbanites deposited in a mid-latitude region under cool-temperate conditions contain n-alkanes with δD values falling in between those of n-alkanes from tropical and glacial torbanites. / The δD values of the n-alkanes also reflect their multiple source inputs. For example, a saw-toothed profile of n-alkane δD values in Australian torbanites is attributed to a dual-source system: a predominant B. braunii input, with a minor terrestrial plant input to odd-carbon-numbered n-alkanes in the range n-C20 [subscript] to n-C29 [subscript]. The δD values of n-alkanes and isoprenoids (pristane and phytane) differ significantly in two Permian torbanites from Australia, thought to be reflective of the offset between the δD values of their precursors in extant organisms. The torbanite data indicate that a biological δD signal has been preserved for at least 260–280 million years, extending the utility of δD values for palaeoclimate studies. To elucidate the effect of sedimentary processes on the δD values of petroleum hydrocarbons, three sedimentary sequences have been studied. These comprise one from the Perth Basin (Western Australia) and two from the Vulcan Sub-basin (northern Australia) covering a wide range of maturities, i.e. 0.53–1.6% vitrinite reflectance (Ro). The δD values of n-alkanes extracted from immature-early mature sediments (marine shales/siltstones and mudstones) are consistent with that expected of marine-derived n-alkyl lipids. The hydrocarbons become enriched in D with increasing maturity. The large (ca. 115%) biologically-derived offset between the δD values of n-alkanes and acyclic isoprenoids from immature sediments gradually decreases with increasing maturity, as the isoprenoids become enriched in D more rapidly than the n-alkanes. The D-enrichment in isoprenoids correlates strongly with Ro and traditional molecular maturity parameters. / This suggests that H/D exchange during maturation occurs via a mechanism involving carbocation-like intermediates, which proceeds more rapidly with compounds containing tertiary carbon centres. Significant epimerisation of pristane and phytane coincides with their D-enrichment, suggesting that hydrogen exchange occurs at their tertiary carbons. A mechanism is proposed which can account for both H/D exchange and the epimerisation of pristane and phytane in the sedimentary environment. Pristane and phytane extracted from a post-mature sediment from the Paqualin-1 sequence are significantly enriched in D (ca. 40%) relative to the n-alkanes, indicating that D-enrichment persists at very high maturity, and is more pronounced for the regular isoprenoids than the n-alkanes. This supports the notion that H/D exchange causes the observed shift in δD values, rather than free-radical hydrogen transfer. The differences between the δD values of pristane and phytane show opposite trends in the Perth Basin and Vulcan Sub-basin sediments. In the Perth Basin, phytane is enriched in D relative to pristane, likely due to a dominant algal source. In the Vulcan Sub-basin, pristane is enriched in D relative to phytane, and thus is attributed to a lower relative input of algal organic matter. The variance of the δD values of pristane and phytane is generally consistent throughout the maturity range and provides evidence that pristane and phytane exchange hydrogen at similar rates. δD analysis of crude oils and condensates reservoired in the Perth Basin and Vulcan Sub-basin has been carried out to evaluate potential applications in oil-source correlation. / The n-alkanes from crude oils and condensates are often more enriched in D than n-alkanes extracted from their supposed source rocks, and the oils also show relatively small differences between the δD values of n-alkanes and isoprenoids. These results suggest significant H/D exchange has occurred, implying that the liquids were generated from mature source rocks. A Perth Basin crude oil (Gage Roads-1) thought to be derived from a lacustrine/terrestrial source contains hydrocarbons that are significantly depleted in D relative to Perth Basin oils derived from a marine source, attributed to variability in the isotopic composition of marine and terrestrial source waters. δD values of n-alkanes from Vulcan Sub-basin crude oils and condensates are largely consistent with their prior classification into two groups: Group A, having a marine source affinity; and Group B, having a terrigenous source affinity. Some oils and condensates are suggested to be mixtures of Group A and Group B hydrocarbons, or Group A hydrocarbons and other as yet unknown sources. An exception is a former Group A oil (Tenacious-1) containing n-alkanes that are enriched in D relative to those from other Group A oils and condensates, attributed to mixing with another source of more mature hydrocarbons. The n-alkane δD profile appears to be indicative of source and sedimentary processes. One Perth Basin crude oil (Dongara-14) contains lower-molecular-weight n-alkanes that are depleted in D relative to higher-molecular-weight n-alkanes, attributed to a mixed marine/terrestrial source. / Group A crude oils and condensates from the Vulcan Sub-basin display a ‘bowl-shaped’ profile of n-alkane δD values. An upward inflection in the n-alkane δD profile from n-C11 [subscript] to n-C15 [subscript] is suggested to represent the addition of D-enriched lower-molecular-weight n-alkanes from a more mature wet gas/condensate to an initial charge of lower maturity oil. Ultimately, this project has demonstrated that the δD values of individual petroleum hydrocarbons can be used to elucidate the nature of source organic matter and depositional environments. The preservation potential of lipid δD values is greater than previously thought, although it is clear that H/D exchange accompanying maturation can have a significant effect on the δD values of certain hydrocarbons. Thus, great care must be taken when interpreting δD values of individual hydrocarbons, particularly those derived from sediments of high thermal maturity.

Stable isotope probing (SIP) is an established technique that can be applied to identify the metabolically active micro-organisms within a microbial population. The SIP method utilises an isotopically-labelled substrate and PCR techniques to discern the members of a microbial community that incorporate the isotope into their DNA or RNA. The current literature gap around using 15N isotopes with RNA-SIP offers real potential and advantages for targeting and identifying active members from mixed communities involved in global biogeochemical nitrogen cycling. This study specifically investigated whether nitrogen based compounds can be used as substrates in RNA-SIP methodologies and whether they can in turn be used to probe mixed community environments known to be actively fixing nitrogen. The nitrogen-limited systems targeted represented an ideal opportunity to assess the suitability of 15N-RNA-SIP approaches due to their known high nitrogen fixation rates. Identifying these nitrogen-fixing bacteria could provide a better representation analysis of the community, leading to an improved prediction on how to manage and optimise the treatment performance of target waste systems and to exploit the unique bioconversion properties of these types of organisms. Initially, the project undertook methodological proof of concept by using a soluble nitrogen source, 15NH4Cl, to label the RNA of Novosphingobium nitrogenifigens and a mixed microbial community. Successful separation of the 14N- (control) and 15N-RNA was achieved for both pure and mixed communities using isopycnic caesium trifluoroacetate (CsTFA) gradients in an ultracentrifuge. The usefulness of this technique to identify active diazotrophs in real environmental samples was tested using a nitrogen-fixing community from a pulp and paper wastewater treatment system. After growing the mixed culture with 15N2 as the sole nitrogen source, the labelled RNA was extracted and fractionated using isopycnic centrifugation in CsTFA gradients. The community composition of the active nitrogen-fixing community in the 15N2 enriched fraction was analysed by establishing a 16S rRNA gene clone library containing over 200 members. These were analysed by comparison with published sequences and by phylogenetic analysis. It was found that the more isotopic label substrate incorporated, the further the buoyant density (BD) separation between 15N- and 14N-RNA. Novosphingobium nitrogenifigens gave an average BD shift of 0.03 + 0.004 g ml-1 (95.0 atom % 15N) with 15NH4Cl. For mixed communities the average BD shift was 0.02 + 0.004 g ml-1 (80.0 atom % 15N) with 15NH4Cl and 0.013 + 0.002 g ml-1 (32.6 atom % 15N) when using 15N2. Clone library analysis of 16S rRNA genes present in the enriched 15N-RNA fraction of the mixed community was shown to consist of a diverse population of bacteria as indicated by a Shannon Weaver index value of gt;2.8. Three dominant genera (Aeromonas, Pseudomonas and Bacillus) were identified by comparison with published sequences and phylogenetic analysis. Many other groups not known as archetypal nitrogen-fixing bacteria were also identified, demonstrating that 15N2-RNA-SIP provides a useful tool for the identification of important and previously unknown contributors to nitrogen fixation in a range of environments. Overall, this project has established that nitrogen based RNA-SIP is a powerful tool that can be used successfully and reproducibly with both pure and complex mixed microbial communities to study active diazotrophs in environmental samples.

Les microorganismes extrêmophiles jouent un rôle déterminant dans le cycle du fer (oxydation et précipitation) dans les drainages miniers acides. Les phases minérales formées peuvent piéger efficacement des éléments toxiques tels que l'arsenic. L'objectif de ce travail est de mieux comprendre le rôle de l'activité bactérienne dans les processus d'atténuation naturelle des concentrations en Fe et As dans les DMA. Pour cela, différents marqueurs potentiels de l'activité bactérienne ont été étudiés (changement de spéciation, formation de biominéraux, fractionnement isotopique). L'approche de terrain a été combinée à des expériences de laboratoire. Des variations journalières et annuelles des concentrations en fer et arsenic ont été mises en évidence dans le DMA du Reigous, attribuées respectivement à des facteurs physico-chimiques et hydrologiques. La tooéléite, un oxyhydroxysulfate de Fe(III) et As(III), est présente dans les concrétions bactériennes tout au long de l'année. L'influence des facteurs biotiques (identité des souches bactériennes d'Acidithiobacillus ferrooxidans et concentration cellulaire) sur la formation de ce minéral a été étudiée en laboratoire. L'évolution de la composition isotopique du fer dans l'eau et les solides, mesurée au cours de ces expériences d'incubation et in situ (Reigous et Rio Tinto) montre un enrichissement systématique en isotopes lourds dans les solides par rapport à l'eau de départ quelle que soit la spéciation du fer initiale. Bien que l'activité bactérienne intervienne dans l'oxydation et la précipitation du fer dans ces systèmes, les fractionnements observés sont des fractionnements d'équilibre dominés par des processus abiotiques.

L'objectif de cette thèse était de déterminer dans quelle mesure l'équilibre en apports énergétiques et azotés dans la ration de ruminants en croissance (agneaux) pouvait avoir un impact sur l'efficacité d'utilisation de l'azote et en particulier des acides aminés (AA) chez ces animaux. Ce travail s'est particulièrement intéressé à l'utilisation des AA au niveau de l'aire splanchnique (tube digestif et foie) qui est utilisatrice importante d'AA et entre en compétition avec les muscles pour l'utilisation de ces AA. Les résultats montrent qu'une baisse des apports azotés seuls dans la ration relativement aux recommandations alimentaires ne se traduit pas nécessairement par une baisse de croissance, ce qui implique donc une meilleure efficacité d'utilisation de l'azote alimentaire. Ceci s'explique en partie par une diminution du prélèvement hépatique des AA (diminution du catabolisme des AA) et une meilleure efficacité d'utilisation des AA au niveau hépatique. A l'inverse, dans le cas d'une baisse des apports alimentaires en énergie seule dans le régime, la baisse de croissance et de rétention azotée est immédiate, associée à un catabolisme des AA et une uréogenèse intense chez les animaux. Ainsi, les recommandations en terme d'apports azotés chez les ruminants en croissance mériteraient d'être réévalués chez les ruminants afin de maximiser l'efficacité d'utilisation de l'azote dans la ration et limiter les rejets azotés dans l'environnement. A l'inverse, les recommandations énergétiques ne doivent pas être diminuées sous peine de pénaliser la croissance et l'accrétion protéique des animaux.

L'interaction entre la température des océans et la teneur isotopique des précipitations antarctiques est étudiée à l'aide d'un modèle de circulation générale atmosphérique, en distinguant différentes sources des précipitations. La contribution de ces sources est estimée pour des conditions climatiques modernes et glaciaires, il y a 21000 ans. Les variations entre ces climats résultent du refroidissement de l'océan et du renforcement du gradient méridien de température. Différentes reconstructions des températures tropicales glaciaires, mal connues, montrent leur forte influence sur la contribution des sources. Pour les latitudes polaires, la teneur isotopique des précipitations issues de chaque source est reliée à la température de la source et à sa distance au lieu de précipitation. Contrairement à l'idée développée par Boyle (1997), un refroidissement glaciaire généralisé des sources n'est pas susceptible de biaiser l'interprétation classique des isotopes en paléotempérature, car il est compensé dans nos simulations par une plus forte contribution des sources chaudes. La distribution de l'oxygène 18 dans l'océan est simulée à l'aide d'un modèle de circulation générale océanique, en prescrivant des flux isotopiques issus du modèle atmosphérique. Ces mêmes flux servent à simuler une 'salinité' passive, cohérente avec l'oxygène 18. Les différentes caractéristiques ainsi que la corrélation spatiale entre ces 2 traceurs, salinité et isotope, sont correctement reproduites. La modélisation permet d'étudier la sensibilité de leur relation aux flux de surface, et notamment à l'écoulement continental. L'effet du mélange océanique horizontal est apprécié par comparaison avec un modèle en boite. L'impact des conditions (température et humidité) et de la teneur isotopique de la surface océanique sur l'excès en deutérium des précipitations antarctiques est aussi évalué.

L'île de la Martinique a connu l'histoire volcanique la plus complète de l'arc des Petites Antilles, de 25 Ma à l'actuel. L'hétérogénéité chimique et isotopique des laves de l'île est très importante non seulement par rapport aux autres îles de l'arc mais aussi par rapport aux autres arcs intra-océaniques. L'objectif de ces travaux est d'expliquer la variabilité géochimique des laves de la Martinique et de caractériser les processus de genèse des produits volcaniques émis sur l'île. Pour cela, nous avons effectué une étude géochimique approfondie (éléments majeurs, éléments traces, rapports isotopiques du Pb, Sr, Nd et Hf) sur des échantillons de laves représentatifs de toute l'histoire volcanique de la Martinique. Grâce à une collaboration avec Aurélie Germa et Xavier Quidelleur de l'université Orsay - Paris XI, l'étude géochimique a été couplée à une datation des laves par méthode K-Ar. Les laves martiniquaises forment des droites et hyperboles de mélanges entre pôles appauvris mantelliques et pôle enrichis crustaux. Il apparaît que deux mélanges distincts sont visibles, un premier mélange est formé par les laves « anciennes » (entre 25 et 7 Ma) et un deuxième mélange est formé par les laves « récentes » (entre 5 Ma et l'actuel). Les pôles mantelliques et les pôles crustaux impliqués dans les sources des magmas ne sont pas les mêmes avant et après 6 Ma. Ce changement de source est probablement lié au passage de la ride asismique qui a décalé la moitié nord de l'arc des Petites Antilles. L'origine de la signature crustale des laves martiniquaises est testée en comparant un modèle de mélange à la source entre des sédiments de la plaque plongeante et le coin mantellique et un modèle d'assimilation de la croûte de l'arc par les magmas mantelliques ascendants. Le modèle d'assimilation intra-crustale ne peut pas reproduire les tendances décrites par les laves alors que le modèle de mélange à la source le fait parfaitement. La comparaison entre les pôles crustaux impliqués dans les mélanges et les sédiments entrants dans la subduction indique qu'il n'y a pas de fractionnement entre le Pb, le Sr, le Nd et l'Hf ce qui implique que les sédiments sont probablement ajoutés à la source par fusion partielle et non par déshydratation. Le rapport La/Yb des laves martiniquaises apparait comme un proxy de la proportion de sédiments dans la source des magmas et non du taux de fusion partielle ou de la nature de la phase alumineuse du manteau bien que la fusion, de l'ordre de 10%, ait lieu dans la zone de stabilité du grenat. Le gradient géographique du rapport La/Yb au sein de l'île traduit donc un gradient géographique de la proportion de sédiments, et montre que la proportion de sédiments dans la source augmente avec l'éloignement à la fosse.

There is an intense interest in the availability of radioactive isotopes that could be developed into nuclear batteries. Promethium-147 is one of the isotopes of interest for use in nuclear batteries as well as in other compact low power applications. Pm-147 is a pure beta (β-) emitter with a half-life of 2.62 years. For this research, Pm-147 was produced from enriched Nd-146 via the neutron capture method in the Hydraulic Tube facility of HFIR at the Oak Ridge National Laboratory. Radioisotopic impurities produced via the neutron capture method have significant effects on its potential final use for nuclear battery applications. This research provides information on the co-production levels of the radioisotopic impurities in the samples containing Pm-147 and their effects on the required shielding. Gamma spectroscopy analysis served as the primary method in the evaluation of the impurities. Previous research had identified the presence of these impurities but it had not studied them in detail.