L’injection de CO2 dans un réservoir géologique n’a rien d’un processus anodin : les impacts sur la roche hôte peuvent menacer l’intégrité du stockage suite à des modifications des propriétés pétrophysiques. Nous proposons ainsi d’envisager l’utilisation des isotopes stables du chlore comme indicateurs des processus physicochimiques générés par une injection de CO2. L’ion chlorure Cl- est en effet un élément conservatif et ubiquiste dans les eaux des réservoirs, et le rapport δ37Cl est connu pour être modifié par divers processus (diffusion, filtration ionique, précipitation de sel, changements de phase). La méthodologie adoptée a consisté à investiguer les effets de ces différents processus sur le signal isotopique du Cl en conditions P-T d’un réservoir de stockage. Des expériences en autoclaves ont montré que le Cl était solubilisé dans le CO2sc, mais en quantités suffisamment faibles pour ne pas impacter le signal isotopique dans les saumures si fractionnement isotopique il y a. Des expériences de migration d’une saumure réactive par advection (banc de percolation ICARE1, Université de Montpellier) et par diffusion (cellule développée à IFPEN) ont également été réalisées. Aucune évolution de δ37Cl n’a été mesurée au cours de la percolation (transport advectif conservatif) et les effets de la diffusion restent à évaluer et à mettre en relation avec les évolutions de porosité et perméabilité des roches. Les expériences de séchage et de précipitation de sel en milieu poreux ont montré que les concentrations en Cl et les valeurs de δ37Cl permettaient de caractériser les processus de transport en jeu. Ces résultats expérimentaux ont permis d’identifier des processus capables de modifier les abondances isotopiques de Cl et indiquent l’intérêt des isotopes pour le monitoring de site de stockage de CO2 / CO2 injection in a reservoir leads to physicochemical processes which can have harmful consequences on the reservoir integrity due to porosity and permeability alteration. In this work, we propose to test the possibility that stable chlorine isotopes could be used as a geochemical tool to assess these effects. Indeed, chloride is a conservative and a major component of reservoir brines, and it is already known that several processes can modify the ratio of its two stable isotopes δ37Cl (diffusion, ionic filtration, salt precipitation or phase change). To test this possibility, several types of experiments were performed to investigate the effects generated by a CO2 injection on Cl-isotopes. Autoclave experiments have shown that Cl can be solubilized in CO2SC, but the amounts would be too low to modify the isotopic signal of brines in case of any fractionation process. Reactive brine migration experiments by advection (ICARE1 percolation apparatus in Montpellier University) and diffusion (diffusion cell developed at IFPEN) were also conducted. No δ37Cl was observed during percolation (conservative advective transport) and the effects of diffusion remain to be investigated with regard to the evolution of rock porosity and permeability. Drying and salt precipitation experiments on porous media have shown that Cl concentrations and δ37Cl values can give information about transport processes during water evaporation. These experimental results allowed us to identify the processes capable of modifying the δ37Cl signal, and that Cl-isotopes can be of use for the monitoring of CO2 storage site

abstract: Natural variations in 238U/235U of marine carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ~7.5 and ~ 8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ~ 8.5, with heavier U in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007+0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ~7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3 (aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2, [Ca], or [Mg] concentrations. In general, these effects are likely to be small (<0.13 ‰), but are nevertheless potentially significant because of the small natural range of variation of 238U/235U. / Dissertation/Thesis / Masters Thesis Chemistry 2015

abstract: Variations of 238U/235U in sedimentary carbonate rocks are being explored as a tool for reconstructing oceanic anoxia through time. However, the fidelity of this novel paleoredox proxy relies on characterization of uranium isotope geochemistry via laboratory experimental studies and field work in modern analog environmental settings. This dissertation systematically examines the fidelity of 238U/235U in sedimentary carbonate rocks as a paleoredox proxy focusing on the following issues: (1) U isotope fractionation during U incorporation into primary abiotic and biogenic calcium carbonates; (2) diagenetic effects on U isotope fractionation in modern shallow-water carbonate sediments; (3) the effects of anoxic depositional environments on 238U/235U in carbonate sediments. Variable and positive shifts of 238U/235U were observed during U uptake by primary abiotic and biotic calcium carbonates, carbonate diagenesis, and anoxic deposition of carbonates. Previous CaCO3 coprecipitation experiments demonstrated a small but measurable U isotope fractionation of ~0.10 ‰ during U(VI) incorporation into abiotic calcium carbonates, with 238U preferentially incorporated into the precipitates (Chen et al., 2016). The magnitude of U isotope fractionation depended on aqueous U speciation, which is controlled by water chemistry, including pH, ionic strength, carbonate, and Ca2+ and Mg2+ concentrations. Based on this speciation-dependent isotope fractionation model, the estimated U isotope fractionation in abiotic calcium carbonates induced by secular changes in seawater chemistry through the Phanerozoic was predicted to be 0.11–0.23 ‰. A smaller and variable U isotope fractionation (0–0.09 ‰) was observed in primary biogenic calcium carbonates, which fractionated U isotopes in the same direction as abiotic calcium carbonates. Early diagenesis of modern shallow-water carbonate sediments from the Bahamas shifted δ238U values to be 0.270.14 ‰ (1 SD) higher than contemporaneous seawater. Also, carbonate sediments deposited under anoxic conditions in a redox-stratified lake—Fayetteville Green Lake, New York, USA— exhibited elevated δ238U values by 0.160.12 ‰ (1 SD) relative to surface water carbonates with significant enrichments in U. The significant U isotope fractionation observed in these studies suggests the need to correct for the U isotopic offset between carbonate sediments and coeval seawater when using δ238U variations in ancient carbonate rocks to reconstruct changes in ocean anoxia. The U isotope fractionation in abiotic and biogenic primary carbonate precipitates, during carbonate diagenesis, and under anoxic depositional environments provide a preliminary guideline to calibrate 238U/235U in sedimentary carbonate rocks as a paleoredox proxy. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2018

No description available.

Formaldehyde emissions from non-structural wood composites are regulated and the regulation target is urea-formaldehyde (UF) resin. UF resins are hydrolytically unstable and constantly emit formaldehyde as a function of temperature and relative humidity. When heated, wood also generates formaldehyde, but this was of little concern until 2010 when formaldehyde regulations became much more demanding. This regulation motivated the industry to account for all formaldehyde sources, synthetic as from resin, and biogenic as from wood. This effort represents first steps towards quantifying biogenic and synthetic contributions to formaldehyde emissions in non-structural wood composites. It is possible to distinguish the 13C/12C isotope ratio of UF resins from the isotope ratio of plant biomass. Conditions during and after composite hot-pressing promote reactions that generate formaldehyde from wood and UF resin, and the kinetic isotope effect continuously lowers the product isotope ratios as a function of yield. If such isotope fractionation did not occur, it would be a simple matter to quantify contributions of wood and UF resin to formaldehyde emissions using static isotope ratios. Isotope fractionation, therefore, complicates the requirements for distinguishing biogenic and synthetic formaldehyde in wood composite emissions. Those requirements are 1) establish the reference carbon isotope ratios in wood and in UF resin (just the formaldehyde portion of UF), and 2) estimate the kinetic isotope effects in formaldehyde generation by wood and cured UF resin. The latter requirement fixes a range for the respective isotope ratios; the numerical ranges enable a simple model of the average isotope ratio for a mixture of biogenic and synthetic formaldehyde in wood composite emissions. Finally, the measured isotope ratio of captured emissions would be compared to the model. This work did not achieve all aspects of the requirements mentioned, but a solid foundation was established for future completion of the ultimate goals. In reference to requirement 1, the carbon isotope ratio of experimental Pinus taeda wood was accurately measured (including some isolated fractions) using isotope ratio mass spectroscopy (IRMS). IRMS of UF resin first requires removal of urea carbons- UF resin was subjected to acid hydrolysis and capture of the resin formaldehyde into aqueous ammonium hydroxide. This provided a nearly quantitative conversion (negligible isotope fractionation) of resin formaldehyde into hexamine for IRMS. Using this hexamine method, the formaldehyde carbon isotope ratios of two industrial UF resins were accurately measured, demonstrating basic feasibility for the project goal. Estimating the kinetic isotope effect (Requirement 2) required creation of a thermochemical reactor, where wood or cured UF resin was heated under N2 flow such that the emitted formaldehyde was easily captured. In this case, conversion of captured formaldehyde into hexamine was abandoned in favor of silica gel cartridges loaded with sodium bisulfite. Isolation and IRMS of the formaldehyde-bisulfite adduct were effective and considered easily transferable to industrial settings. This system was employed to measure fractionation in cured resin as a function of relative humidity, and in Pinus taeda wood as a function of relative humidity, temperature, and time. More information about isotope fractionation is required; but most notable was the fractionation behavior in wood where evidence was found for multiple formaldehyde generating reactions. Overall, this work established feasibility for the goals and laid the foundation for future efforts. / Master of Science / Home-interior products like cabinetry are often produced with wood composites adhesively bonded with urea-formaldehyde (UF) resin. UF resins are low cost and highly effective, but their chemical nature results in formaldehyde emission from the composite. High emissions are avoided, and the federal government has regulated and steadily reduced allowable emissions since 1985. The industry continuously improved UF technologies to meet regulations, as in 2010 when the most demanding regulations were implemented. At that time, many people were unaware that wood also generates formaldehyde; this occurs at very low levels but heating during composite manufacture causes a temporary burst of natural formaldehyde. Some wood types produce unusually high formaldehyde levels, making regulation compliance more difficult. This situation, and the desire to raise public awareness, created a major industrial goal: determine how much formaldehyde emission originates from the resin and how much originates from the wood. These formaldehyde sources can be distinguished by measuring the carbon isotope ratio, 13C/12C. This ratio changes and varies due to the kinetic isotope effect. Slight differences in 13C and 12C reactivity reveal the source as either petrochemical (synthetic formaldehyde) or plant-based (biogenic formaldehyde). This work demonstrates that achieving the industry goal is entirely feasible, and it provides the analytical foundation. The technical strategy is: 1) establish reference isotope ratios in wood and in UF resin, and 2) from the corresponding wood composite, capture formaldehyde emissions, measure the isotope ratio, and simply calculate the percentage contributions from the reference sources. However, a complication exists. When the reference sources generate formaldehyde, the respective isotope ratios change systematically in a process called isotope fractionation (another term for the kinetic isotope effect). Consequently, this effort developed methods to measure fractionation when cured UF resin and wood separately generate formaldehyde, with greater emphasis on wood. Isotope fractionation in wood revealed multiple fractionation mechanisms. This complexity presents intriguing possibilities for new perspectives on formaldehyde emission from wood and cured UF resin. In summary, this work demonstrated how source contributions to formaldehyde emissions can be determined; it established effective methods required to refine and perfect the approach, and it revealed that isotope fractionation could serve as an entirely novel tool in the materials science of wood composites.

The global marine distributions of Cd and phosphate are closely correlated, which has led to Cd being considered as a marine micronutrient. Recent developments in Cd stable isotope mass spectrometry have revealed that Cd uptake by phytoplankton causes isotopic fractionation in the open ocean and in culture. The explanation for this nutrient-like behaviour is unknown as there is only one identified biochemical function for Cd, an unusual Cd/Zn carbonic anhydrase (CdCA1). This thesis investigates why Cd appears to act as an algal nutrient by performing subcellular analyses of microorganisms genetically-modified to express the CdCA1 gene. It was found that CdCA1 was not a significant contributor to whole-cell Cd isotope compositions. Instead, a large proportion of the internalized Cd is sequestered into cell membranes with a similar direction and magnitude of Cd isotopic fractionation as seen in surface seawater. This observation is explained if Cd is mistakenly imported with other divalent metals and subsequently managed by binding within the cell to avoid toxicity. This result implies that surface seawater Cd isotope compositions, if captured by an appropriate archive, may be invaluable for reconstructions of past marine productivity. The role of environmental factors in modulating the inorganic partitioning of Cd isotopes into calcite was investigated through a series of laboratory analogue experiments. In seawater, the light isotopes of Cd are always preferred in calcite. The magnitude of fractionation showed no response to temperature, ambient [Mg], or precipitation rate. To further identify suitable palaeaoceanographic archives, the Cd isotopic composition of a suite of modern deep-sea corals were investigated. It was found that the Cd/Ca and Cd isotope composition of coralline calcium carbonate followed the predicted trend for closed-system Rayleigh fractionation in the calcifying space. The lack of isotopic offsets between some corals and seawater will simplify the application of Cd isotopes in deep-sea corals -- and potentially other marine calcifying organisms that vacuolize seawater prior to calcium carbonate precipitation -- to palaeoceanography.

Master of Science / Department of Geology / Matthew E. Brueseke / Mid-Miocene epithermal Au-Ag ores of the northern Great Basin USA are related to magmatism associated with the inception of the Yellowstone hotspot. The geochemical chemical connection between these ores and spatially and temporally related volcanism is not well understood, but has been suggested (Kamenov, 2007; Saunders et al., 2015). These Cu- and Pb- isotope studies show that the ore and associated gangue minerals have different sources of Pb, which supports evidence that the metal(loids) originate from a deep magmatic source (Saunders et al., 2008). Cu isotopes as a tool for exploring linkages between ore deposits and related volcanic rocks is a new and evolving field. A suite of mid-Miocene Northern Great Basin (NGB) and Snake River Plain (SRP) volcanic rocks was analyzed by aquaregia leach for their δ⁶⁵Cu compositions. These samples have all been previously characterized and include basalts, trachybasalt, basaltic andesites, and basaltic trachyandesites that are representative of regional flood basalt magmatism and younger basalt eruptions in central Idaho. Included are rocks from the Santa Rosa-Calico volcanic field, NV (e.g., Buckskin-National district); Owyhee Mountains, ID (Silver City District); Midas, NV region, near Jarbidge, NV; and a locality proximal to Steens Mountain, OR. Also included are two Pleistocene basalts from the central Snake River plain unequivocally related to the Yellowstone hotspot volcanism (McKinney Basalt and Basalt of Flat Top Butte), and one Eocene basalt from the Owyhee Mountains that is related to pre-hotspot arc volcanism. International rock standards ranging from ultramafic to intermediate were also analyzed in this study for comparison. Our new δ⁶⁵Cu data greatly expands the range of known Cu isotopic compositions for basalts, with values ranging from -0.84‰ to +2.61‰. These values overlap with the δ⁶⁵Cu of regional ores, further suggesting a link between the source(s) of the ores and the NGB rocks. The range of δ⁶⁵Cu values also overlaps with mantle rock values, suggesting that the Cu isotopic composition may be a signature derived from the mantle source. Fractionation mechanisms that cause such a broad range in Cu isotopes are still unclear but liquid-vapor transitions and mantle metasomatism are being explored. Furthermore, δ⁶⁵Cu values of international rock standards reported in this study did not agree with previously reported data (Archer and Vance, 2004; Bigalke et al., 2010; Moeller et al., 2012; Liu et al., 2014, 2015) suggesting that aquaregia leach may not be a preferable technique when analyzing volcanic rocks.

The global silicon (Si) cycle is of fundamental importance for the global carbon cycle. Diatom growth in the oceans is a major sequestration pathway for carbon on a global scale (often referred to as the biological pump). Patterns of diatoms preserved in marine sediment records can reveal both natural and anthropogenic driven environmental change, which can be used to understand silicon dynamics and climate change. Si isotopes have been shown to have great potential in order to understand the Si cycle by revealing both past and present patterns of dissolved Si (DSi) utilization, primarily when diatoms form their siliceous frustules (noted as biogenic silica, BSi). However, studies using Si isotopes are still scarce and only a few studies exist where stable Si isotopes are used to investigate the biogeochemical Si cycle in aquatic systems. Therefore, this thesis focuses on developing analytical methods for studying BSi and DSi and also provides tools to understand the observed Si isotope distribution, which may help to understand impacts of climate change and human perturbations on marine ecosystems. The Baltic Sea, one of the biggest estuarine systems in the world, was chosen as the study site. BSi samples from a sediment core in Bothnian Bay, the most northern tip of the Baltic Sea, and diatom samples from the Oder River, draining into the southern Baltic Sea were measured and reported in Paper II and III, after establishing a method for Si isotope measurements (Paper I). Si isotope fractionation during diatom production and dissolution was also investigated in a laboratory-controlled experiment (Paper IV) to validate the observations from the field. The major result is that Si isotope signatures in BSi can be used as an historical archive for diatom growth and also related to changes in climate variables. There is isotopic evidence that the Si cycle has been significantly altered in the Baltic Sea catchment by human activities. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>

No description available.

Underlying all applications of sulfur isotope analyses is our understanding of isotope systematics. This dissertation tests some fundamental assumptions and assertions, drawn from equilibrium theory and a diverse body of empirical work on biochemical kinetics, as applied to the multiple sulfur isotope systematics of microbial sulfate reduction. I take a reductionist approach, both in the questions addressed and experimental approaches employed. This allows for a mechanistic, physically consistent interpretation of geological and biological sulfur isotope records. The goal of my work here is to allow interpreters a more biologically, chemically and physically parsimonious framework to decipher the signals coded in modern and ancient sulfur isotope records. / Earth and Planetary Sciences