Thesis (Ph. D.)--University of California, San Diego, 1998. / Vita. Includes bibliographical references.

Th. Univ.--Claude Bernard-Lyon 1, 1989. / Résumé en anglais. Bibliogr. p. 155-174.

Th. Univ.--Energétique--Montpellier 2, 1990. / Bibliogr. p. 183-198.

Proefschrift--Utrecht. / Bibliography: p. 54.

Thesis (Ph. D.)--Columbia University, 1935. / Vita. "Most of the material in this dissertation appeared in the Journal of chemical physics, volume 2, no. 11 ... November, 1934." Bibliography: p. 9.

abstract: Historically, uranium has received intense study of its chemical and isotopic properties for use in the nuclear industry, but has been largely ignored by geoscientists despite properties that make it an intriguing target for geochemists and cosmochemists alike. Uranium was long thought to have an invariant 238U/235U ratio in natural samples, making it uninteresting for isotopic work. However, recent advances in mass spectrometry have made it possible to detect slight differences in the 238U/235U ratio, creating many exciting new opportunities for U isotopic research. Using uranium ore samples from diverse depositional settings from around the world, it is shown that the low-temperature redox transition of uranium (U6+ to U4+) causes measurable fractionation of the 238U/235U ratio. Moreover, it is shown experimentally that a coordination change of U can also cause measurable fractionation in the 238U/235U ratio. This improved understanding of the fractionation mechanisms of U allows for the use of the 238U/235U ratio as a paleoredox proxy. The 238U/235U ratios of carbonates deposited spanning the end-Permian extinction horizon provide evidence of pronounced and persistent widespread ocean anoxia at, or immediately preceding, the extinction boundary. Variable 238U/235U ratios correlated with proxies for initial Cm/U in the Solar System's earliest objects demonstrates the existence of 247Cm in the early Solar System. Proof of variable 238U/235U ratios in meteoritic material forces a substantive change in the previously established procedures of Pb-Pb dating, which assumed an invariant 238U/235U ratio. This advancement improves the accuracy of not only the Pb-Pb chronometer that directly utilizes the 238U/235U ratio, but also for short-lived radiometric dating techniques that indirectly use the 238U/235U ratio to calculate ages of Solar System material. / Dissertation/Thesis / Ph.D. Geological Sciences 2011

Understanding the spatial and temporal dynamics occurring in headwater catchments enhances our ability to effectively manage the natural and unnatural inputs from the landscape to the stream. DOC is particularly important in northern peat dominated catchments, where concentrations in rivers have been increasing over recent decades. Due to the significant downstream impacts this increase has on the functioning of aquatic ecosystems and the quality of drinking water, it is vital to understand the tight coupling between the landscape and the stream. This study set out to explore the use of integrating high-frequency DOC data, stable isotopes and modelling as a novel way to increase our understanding of the hydrological and biogeochemical processes that control spatial and temporal DOC dynamics. By deploying in-situ FDOM sensors, across nested catchments, we captured 15 minute DOC dynamics. This yielded insights into seasonal, event and diel temporal variability, along with spatial variability. Results showed the utility of linking these DOC dynamics with stable isotopes and water ages, extracted from a tracer-aided runoff model. This allowed the main runoff generating processes, that transport the DOC from the sources to the stream, to be assessed, and showed the effects of hydrologic connectivity and antecedent conditions on DOC delivery. Incorporating modelling allowed the non-stationary hydrological processes influencing runoff generation, which cannot be easily measured by field techniques, to be evaluated. Overall, the findings of this thesis underline the utility of integrating highfrequency DOC data, stable isotopes and modelling to extract a highly informative dataset that helps produce a more complete symphony of the highly variable dynamics occurring in upland catchments. Such knowledge is crucial in order to effectively evaluate the influence of climate change on the water resources that both nature and humans so heavily depend on.

Tree-rings are natural archives of the climate variation experienced by trees during their life span. Because trees actively discriminate against 13C versus 12C in atmospheric carbon dioxide due to environmental forcing inducing higher assimilation of 12C in optimal conditions for growth, the ratio between these two isotopes represents a record of climate variability occurring at the time of the wood formation. Therefore, the delta13C can be used to reconstruct palaeoclimate from when the trees sampled were living. As the instrumental period from meteorological methods to measure climate is relatively short (last 150 years), the calibration between delta13C time series and climatic data can be used to improve the understanding of climate variability through longer periods. The main objective of this study is to produce a consistent methodology for the reconstruction of climate and environmental forcing on trees from the high resolution delta13C time series over the period 1997-2009 at three study sites in Europe where extensive eddy covariance measurements have been conducted. This atmospheric measurement technique permits a very fine resolution to observe the exchange of gases between the atmosphere and a land surface with additional applications in meteorology. At Hyytiala, dendrometer and microcore measurements were used to test if a methodology can be developed to predict the occurrence of radial growth during years when dendrological data are missing. The modeling of the intra-annual rate of growth is then performed via the Gompertz equation. Integration of cell life time to match climate information with time delta13C series is also assessed. The delta13C signature from both inter- and intra-annual resolution are tested against three weather variables: photosynthetically active radiation, temperature and precipitation. The results show stronger linear responses from the delta13C time series of the most northern site (Hyytiala, Finland) to the weather variables while the two other study sites (Norunda, Sweden and Loobos, the Netherlands) did not show significant linear relationships at both annual and intra-annual resolution. The approach developed in this study represents a first step in developing a generic method accessible for non-specialists in dendroclimatology for the use of delta13C time series as climate archives.

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