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Literatura académica sobre el tema "Isotopic disequilibrium"

Autor: Grafiati

Publicado: 8 de marzo de 2025

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Artículos de revistas sobre el tema "Isotopic disequilibrium"

Thaler, Caroline, Amandine Katz, Magali Bonifacie, Bénédicte Ménez y Magali Ader. "Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium". Biogeosciences 17, n.º 7 (3 de abril de 2020): 1731–44. http://dx.doi.org/10.5194/bg-17-1731-2020.

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Abstract. Paleoenvironmental reconstructions, which are mainly retrieved from oxygen isotope (δ18O) and clumped isotope (Δ47) compositions of carbonate minerals, are compromised when carbonate precipitation occurs in isotopic disequilibrium. To date, knowledge of these common isotopic disequilibria, known as vital effects in biogenic carbonates, remains limited, and the potential information recorded by δ18O and Δ47 offsets from isotopic equilibrium values is largely overlooked. Additionally, in carbonates formed in isotopic equilibrium, the use of the carbonate δ18O signature as a paleothermometer relies on our knowledge of the paleowaters' δ18O value, which is often assumed. Here, we report the largest Δ47 offsets observed to date (as much as −0.270 ‰), measured on microbial carbonates that are strongly linked to carbonate δ18O offsets (−25 ‰) from equilibrium. These offsets are likely both related to the microorganism metabolic activity and yield identical erroneous temperature reconstructions. Unexpectedly, we show that the δ18O value of the water in which carbonates precipitated, as well as the water–carbonate δ18O fractionation dependence on temperature at equilibrium, can be retrieved from these paired δ18O and Δ47 disequilibrium values measured in carbonates. The possibility to retrieve the δ18O value of paleowaters, sediments' interstitial waters or organisms' body water at the carbonate precipitation loci, even from carbonates formed in isotopic disequilibrium, opens long-awaited research avenues for both paleoenvironmental reconstructions and biomineralization studies.

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Gamnitzer, U., A. B. Moyes, D. R. Bowling y H. Schnyder. "Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment". Biogeosciences Discussions 8, n.º 1 (5 de enero de 2011): 83–119. http://dx.doi.org/10.5194/bgd-8-83-2011.

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Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δefflux) in ecosystems is generally interpreted to represent the actual isotopic composition of respiration (δresp). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δatm) or δresp causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δefflux from δresp (termed disequilibrium effect). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δefflux and δresp. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δatm of −46.9‰ during daytime for 2 weeks. Nighttime δefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. The δefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δresp (see Gamnitzer et al., 2009). Conversely, the δefflux measured using the closed chamber technique differed from these by −11.2‰. Most of this disequilibrium effect (9.5‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δatm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δresp in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δresp or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

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Gamnitzer, U., A. B. Moyes, D. R. Bowling y H. Schnyder. "Measuring and modelling the isotopic composition of soil respiration: insights from a grassland tracer experiment". Biogeosciences 8, n.º 5 (26 de mayo de 2011): 1333–50. http://dx.doi.org/10.5194/bg-8-1333-2011.

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Abstract. The carbon isotopic composition (δ13C) of CO2 efflux (δ13Cefflux) from soil is generally interpreted to represent the actual isotopic composition of the respiratory source (δ13CRs). However, soils contain a large CO2 pool in air-filled pores. This pool receives CO2 from belowground respiration and exchanges CO2 with the atmosphere (via diffusion and advection) and the soil liquid phase (via dissolution). Natural or artificial modification of δ13C of atmospheric CO2 (δ13Catm) or δ13CRs causes isotopic disequilibria in the soil-atmosphere system. Such disequilibria generate divergence of δ13Cefflux from δ13CRs (termed "disequilibrium effect"). Here, we use a soil CO2 transport model and data from a 13CO2/12CO2 tracer experiment to quantify the disequilibrium between δ13Cefflux and δ13CRs in ecosystem respiration. The model accounted for diffusion of CO2 in soil air, advection of soil air, dissolution of CO2 in soil water, and belowground and aboveground respiration of both 12CO2 and 13CO2 isotopologues. The tracer data were obtained in a grassland ecosystem exposed to a δ13Catm of −46.9 ‰ during daytime for 2 weeks. Nighttime δ13Cefflux from the ecosystem was estimated with three independent methods: a laboratory-based cuvette system, in-situ steady-state open chambers, and in-situ closed chambers. Earlier work has shown that the δ13Cefflux measurements of the laboratory-based and steady-state systems were consistent, and likely reflected δ13CRs. Conversely, the δ13Cefflux measured using the closed chamber technique differed from these by −11.2 ‰. Most of this disequilibrium effect (9.5 ‰) was predicted by the CO2 transport model. Isotopic disequilibria in the soil-chamber system were introduced by changing δ13Catm in the chamber headspace at the onset of the measurements. When dissolution was excluded, the simulated disequilibrium effect was only 3.6 ‰. Dissolution delayed the isotopic equilibration between soil CO2 and the atmosphere, as the storage capacity for labelled CO2 in water-filled soil pores was 18 times that of soil air. These mechanisms are potentially relevant for many studies of δ13CRs in soils and ecosystems, including FACE experiments and chamber studies in natural conditions. Isotopic disequilibria in the soil-atmosphere system may result from temporal variation in δ13CRs or diurnal changes in the mole fraction and δ13C of atmospheric CO2. Dissolution effects are most important under alkaline conditions.

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Ishimura, T., U. Tsunogai, S. Hasegawa, F. Nakagawa, T. Oi, H. Kitazato, H. Suga y T. Toyofuku. "Variation in stable carbon and oxygen isotopes of individual benthic foraminifera: tracers for quantifying the magnitude of isotopic disequilibrium". Biogeosciences 9, n.º 11 (8 de noviembre de 2012): 4353–67. http://dx.doi.org/10.5194/bg-9-4353-2012.

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Abstract. Stable carbon and oxygen isotopic compositions (δ13C and δ18O) of benthic foraminiferal carbonate shells have been used to reconstruct past bottom-water environments. However, the details of factors controlling the isotopic disequilibrium between the shells and the surrounding bottom seawater (so-called the "vital effect") are still ambiguous. In this study, we analyzed the isotopic composition of individual benthic foraminifera of multiple species by using a customized high-precision analytical system, and found that the magnitude of the isotopic disequilibrium between benthic foraminiferal shell and the surrounding bottom seawater (δ13CDIC and δ18Owater) in different species is correlated with inter-individual isotopic variations. As a result, we can choose suitable species as bottom-water proxies by using the inter-individual isotopic variations. In addition, by using the simplified interpretation of the inter-individual and inter-species isotopic variations established in this study, we could reconstruct the δ13C values of dissolved inorganic carbon in bottom water by correcting foraminiferal isotopic compositions for the isotopic shift resulting from the isotopic effects (vital effect, microhabitat effect, and many other reported isotopic effects). Our findings will allow the use of isotope data for benthic foraminifera as more reliable proxies for reconstructing past bottom-water conditions and evaluating global carbon cycling.

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Lee, Dongho y Scott J. Carpenter. "Isotopic disequilibrium in marine calcareous algae". Chemical Geology 172, n.º 3-4 (febrero de 2001): 307–29. http://dx.doi.org/10.1016/s0009-2541(00)00258-8.

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Abart, R. "Isotopic Disequilibrium During Metasomatic Vein Formation". Mineralogical Magazine 58A, n.º 1 (1994): 1–2. http://dx.doi.org/10.1180/minmag.1994.58a.1.03.

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Watson, E. B. "Equilibrium and Disequilibrium in Isotopic Series". Elements 3, n.º 4 (1 de agosto de 2007): 273. http://dx.doi.org/10.2113/gselements.3.4.273.

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Antonelli, Michael A., Tushar Mittal, Anders McCarthy, Barbara Tripoli, James M. Watkins y Donald J. DePaolo. "Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems". Proceedings of the National Academy of Sciences 116, n.º 41 (23 de septiembre de 2019): 20315–21. http://dx.doi.org/10.1073/pnas.1908921116.

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Kinetic calcium isotope effects can be used as growth-rate proxies for volcanic and subvolcanic minerals. Here, we analyze Ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects (>2‰) can occur during magmatic plagioclase crystallization. Experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase Ca diffusivity (R/D). Plagioclase phenocrysts from the 1915 Mount Lassen rhyodacite eruption, the ∼650-y-old Deadman Creek Dome eruption, and several mafic subvolcanic orbicules and plagioclase comb layers from Northern California have disequilibrium Ca isotopic compositions that suggest rapid crystal growth rates (>1 cm/y to 15 cm/y). The Ca isotope results, combined with complementary crystal-size distribution analyses, suggest that magmatic rejuvenation (and eruption) events, as reflected in crystal growth times, can be as short as ∼10−3 y. Although mafic systems are predicted to have shorter magmatic rejuvenation periods, we find similarly short timescales in both mafic and silicic systems. These results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption. By focusing on a common mineral such as plagioclase, this approach can be applied across all major magmatic compositions, suggesting that Ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions.

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To, Dominic. "Isotopic Disequilibrium of Uranium in Kansas Groundwaters". Transactions of the Kansas Academy of Science (1903-) 93, n.º 1/2 (1990): 38. http://dx.doi.org/10.2307/3628127.

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Sugiura, N., K. Hashizume, Y. Miura, K. Kiyota y S. Zashu. "Cosmogenic nitrogen isotopic disequilibrium observed in meteorites". Meteoritics 30, n.º 6 (noviembre de 1995): 646–53. http://dx.doi.org/10.1111/j.1945-5100.1995.tb01162.x.

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Tesis sobre el tema "Isotopic disequilibrium"

Lidman, Fredrik. "Isotopic Disequilibrium for Assessment of Radionuclide Transport in Peat Lands : Uranium-Thorium Series Nuclides in a Core from Klarebäcksmossen, Oskarshamn, Sweden". Thesis, Uppsala University, Department of Earth Sciences, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-88889.

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In order to assess the risks that are associated with a deep repository of nuclear waste, it is important to know how different radionuclides behave in different environments. Since some of the most critical radionuclides in nuclear waste such as Ra-226 occur naturally in the environment, it is possible to study their behaviour directly. Peat lands are thought to be one of the most critical ecosystems due to their capability of accumulating large amounts of radioactivity and the possible exposure pathways to man.

Klarebäcksmossen is a peat land situated close to the nuclear power plant in Oskarshamn, which is one of two areas in Sweden where site investigations for a future deep repository are being conducted. In this study a complete peat-gyttja-clay profile from Klarebäcksmossen has been analysed for a large number of both natural and artificial radionuclides using gamma spectrometry. The degree of isotopic disequilibrium between different nuclides in the uranium-thorium series has been used to assess radionuclide migration and accumulation throughout the core.

The measurements indicate that uranium has been accumulated in the gyttja, but mobilised from the clay. Radium, on the other hand, has been leached from the gyttja layers, and the strikingly low Ra-226/Pb-210 ratios show that it might have been very recently. Alternatively, there is a very extensive migration of Rn-222.

In the peat low levels of radioactivity were found for most radionuclides, but with clear differences between minerotrophic and ombrotrophic peat. This may indicate that the uptake of radionuclides by peat mainly is passive. The accumulation rate for the peat has also been determined using Pb-210 dating.

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Pesnin, Marie. "Apports des nouveaux traceurs d'anomalies isotopiques à l'étude des déséquilibres isotopiques dans les biocarbonates". Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASJ033.

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Les biocarbonates produits par les organismes marins tels que les foraminifères ou les coraux sont des archives importantes pour étudier les environnements et climats du passé. Depuis les travaux de H. Urey en 1947, il est établi que la composition isotopique en oxygène-18 (δ18O) des carbonates reflète à la fois la température de formation et le rapport isotopique (18O/16O) de l'eau de mer. Cette relation, supposément fondée sur l'équilibre thermodynamique entre l'eau et le carbonate, peut cependant être perturbée soit par des paramètres environnementaux, soit par des mécanismes biologiques . Chez certains organismes, comme les coraux, ces « effets vitaux » se manifestent par des déséquilibres isotopiques flagrants, qui compliquent l'interprétation d'une partie non négligeable du registre sédimentaire fossile. En réponse à ces problèmes, cette thèse adopte une approche novatrice en tirant partie de nouveaux traceurs isotopiques, les anomalies d'oxygèen-17 (Δ17O) et les « clumped isotopes » (Δ47, Δ48), en complément des mesures traditionnelles de δ13C et δ18O. En travaillant à partir d'échantillons modernes dont les conditions de croissance sont bien documentées, les contraintes supplémentaires fournies par ces traceurs permettent de mieux caractériser les facteurs qui influençent la composition isotopique des biocarbonates.Ce travail a commencé par une première étape exploratoire, visant d'une part (1) à identifier les organismes / cas d'étude à cibler en priorité, en associant des mesures isotopiques à faible résolution spatiale avec des observations in situ fournissant des informations minéralogiques, élémentaires et isotopiques à bien plus haute résolution, et d'autre part (2) à établir des protocoles expérimentaux optimisés pour les techniques instrumentales de pointe utilisées pour les mesures de Δ47/Δ48 (par spectrométrie de masse à très haute sensibilité) et de Δ17O (par VCOF-CRDS, une technologie spectroscopique innovante). Le premier volet de ce travail a donné lieu à la première l'étude publiée sur les clumped isotopes dans les squelettes de bryozoaires. Les résultats mettent en évidence une forte influence de la minéralogie sur le signal Δ47, qui semble résulter d'un simple effet thermodynamique. Par contre, il apparaît que les organismes de certains sites présentent des déséquilibres isotopiques spécifiques, potentiellement associés à la salinité locale. Ces résultats suscitent de nouvelles interrogations sur l'influence de certains paramètres environnementaux sur l'activité de certaines enzymes, en particulier l'anhydrase carbonique qui joue un rôle majeur dans le maintien de l'équilibre isotopique entre l'eau et le carbone inorganique dissous (CID). Le second volet porte sur la caractérisation, chez les coraux d'eau froide, des écarts à l'équilibre dans cinq dimensions isotopique (δ13C, δ18O, Δ17O, Δ47, Δ48), observées ici conjointement pour la première fois. Les observations sur Δ47 et Δ48 sont en accord avec une publication indépendante récente, et cohérentes avec un modèle théorique du CID, suggérant que la signature isotopique des coraux profonds est principalement contrôlée par des effets cinétiques liés à l'absorption du CO₂ métabolique. Cependant, les prédictions de ce même modèle sont en désaccord avec nos mesures de Δ17O (qui ont été depuis confirmées par des observations indépendantes), soulignant la nécessité de réviser certains paramètres du modèle. La richesse des questions nouvelles suscitées par ce travail de thèse illustre l'intérêt de combiner les observations dans un espace multi-isotopique à 5 dimensions avec des modèles théoriques quantitatifs, tout en confrontant ces modèles aux spécificités biologiques de chaque organisme marin, permettant tout à la fois de mieux comprendre les mécanismes de biominéralisation et de quantifier l'influence des effets vitaux dans les biocarbonates sur les paléo-reconstructions
Biocarbonates produced by marine organisms such as foraminifera or corals serve as important archives for studying past environments and climates. Since the work of H. Urey in 1947, it has been established that the oxygen-18 isotopic composition (δ18O) of carbonates reflects both the formation temperature and the isotopic ratio (18O/16O) of seawater. However, this relationship, supposedly based on the thermodynamic equilibrium between carbonate and water, can be disturbed by either environmental parameters or biological mechanisms. In certain organisms, such as corals, these "vital effects" manifest as significant isotopic disequilibrium, complicating the interpretation of a substantial portion of the fossil sedimentary record.In response to these challenges, this thesis adopts an innovative approach by leveraging new isotopic tracers, namely oxygen-17 anomalies (Δ17O) and "clumped isotopes" (Δ47, Δ48), in addition to traditional δ13C and δ18O measurements. By working with modern samples for which growth conditions are well documented, the additional constraints provided by these tracers allow for a better characterization of the factors influencing the isotopic composition of biocarbonates.This work began with an exploratory phase, aimed at (1) identifying the organisms/case studies by combining low spatial resolution isotopic measurements with in situ observations that provide mineralogical, elemental, and isotopic information at much higher resolution, and (2) establishing optimized experimental protocols for cutting-edge instrumental techniques used for Δ47/Δ48 measurements (via ultra-high sensitivity mass spectrometry) and Δ17O (via VCOF-CRDS, an innovative spectroscopic technology).The first part of this work resulted in the first published study on clumped isotopes in bryozoan skeletons. The results highlight a strong influence of mineralogy on the Δ47 signal, which seems to result from a simple thermodynamic effect. However, it appears that organisms from certain sites exhibit specific isotopic disequilibrium, potentially linked to local salinity. These findings raise new questions about the influence of certain environmental parameters on the activity of specific enzymes, particularly carbonic anhydrase, which plays a key role in maintaining isotopic equilibrium between water and dissolved inorganic carbon (DIC).The second part focuses on characterizing isotopic disequilibria in five isotopic dimensions (δ13C, δ18O, Δ17O, Δ47, Δ48) in cold-water corals, observed together here for the first time. The observations on Δ47 and Δ48 are consistent with a recent independent publication and align with a theoretical DIC model, suggesting that the isotopic signature of deep-sea corals is primarily controlled by kinetic effects related to the absorption of metabolic CO₂. However, the predictions of this same model are at odds with our Δ17O measurements (which have since been confirmed by independent observations), underscoring the need to revise certain model parameters.The richness of new questions raised by this thesis highlights the value of combining observations in a five-dimensional multi-isotopic space with quantitative theoretical models, while confronting these models with the biological specifics of each marine organism. This approach enables a deeper understanding of biomineralization mechanisms and allows for a more precise quantification of the influence of vital effects in biocarbonates on paleo-reconstructions

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Truebe, Sarah y Sarah Truebe. "Past Climate, Modern Caves, and Future Resource Management in Speleothem Paleoclimatology". Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621105.

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My research focuses on reconstructing past climate in southern Arizona using cave deposits called speleothems. However, this necessitates a broader perspective than simply a geochemical time series, and therefore, I also investigate modern cave systems using a combination of modeling and observational datasets. Finally, cave deposits are fundamentally non-renewable resources, and sampling for past climate reconstruction can be destructive, unlike other cave uses. My last investigation is focused on developing possible best practice recommendations for paleoclimate scientists and other cave stakeholders moving forward. We developed two new stalagmite records of past climate variability in southern Arizona over the past 7000 years. Past climate reconstruction from two caves (Cave of the Bells and Fort Huachuca Cave) highlights insolation control of southern Arizona hydroclimate from 7000-2000 years before present. Additionally, comparison between two stalagmites with different seasonal sensitivities uncovers a few eras of multi-decade long droughts in southern Arizona, which align with other regional reconstructions of past climates and elucidate forcings on Southwest paleoclimate as emergent from both external (insolation) and internal climate variability in the Pacific and Atlantic Ocean basins. Although the oxygen isotopic signal of cave calcite in speleothems is complex, agreement with these other records indicates that the speleothem records from these caves primarily record a climate signal.Modeling and monitoring of modern caves both helps us interpret paleoclimate records and enhances our understanding of cave systems in their own right. Modeling of Cave of the Bells dripwaters demonstrates the effect of storage and mixing on the dripwater oxygen isotope signal; non-climate processes can imprint on dripwater variability on multidecadal timescales. Monitoring shows that on very small spatial scales, every cave is different, and even sites within the same cave respond uniquely to surface climate. Most notably, calcite oxygen isotopic composition, used to reconstruct past climate, shows seasonal variability unrelated to dripwater and surface rainfall oxygen isotope variability. Substantial oxygen isotope disequilibrium is identified at numerous caves sites in southern Arizona, and this understanding aligns with a growing number of cave studies that demonstrate the long-held assumption of isotopic equilibrium in cave systems may not always be valid or that the way in which we define isotopic equilibrium insufficiently captures the variety of processes controlling the oxygen isotopic composition of speleothems. Overall, however, monitoring can identify stalagmites that are more sensitive to surface climate and less sensitive to these in-cave processes by identifying sites with dripwater variability responses to surface rainfall variability and sites that precipitate close to oxygen isotopic equilibrium. Finally, a major missing component in speleothem research is the fact that speleothems take thousands and sometimes hundreds of thousands of years to form. They are non-renewable resources on human timescales, and habitat for myriad microbes that have yet to be identified. Removal of speleothems for paleoclimate research is one of the only destructive uses of these deposits. With that in mind, I also analyze current methods of collecting speleothems and develop a framework based on two surveys of scientists and stakeholders to assist scientists and managers when evaluating potential methods of incorporating cave conservation into the speleothem sampling process. Thus, I approach caves from a variety of angles and timescales, from the past through the present to the future, illuminating caves as complex scientific and social systems.

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Cuvier, Alicia. "Accumulation de l'uranium, de ses descendants et des éléments traces métalliques dans les sols des zones humides autour des anciennes mines d'uranium". Thesis, Toulouse, INPT, 2015. http://www.theses.fr/2015INPT0104/document.

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L’exploitation minière de l’uranium et les processus de traitement du minerai sont à l’origine d’un marquage potentiel de l’environnement par les descendants des chaînes de désintégration U-Th et des éléments traces métalliques (ETM) associés. Ces contaminants s’accumulent ensuite préférentiellement dans des zones de sédimentation continentales (étangs ou lacs) ou des zones humides (tourbières, berges de rivière) situées à l’aval hydraulique des mines. Les zones humides en particulier sont des milieux sensibles aux changements globaux et à la pression anthropique, situés en général en tête de bassin versant. Cela pose donc un risque en cas relargage des contaminants depuis ces milieux. L’objectif de cette étude est de mettre en place une méthodologie aisément reproductible, y compris aux sites miniers orphelins, et permettant l’identification et la caractérisation des contaminations et la compréhension des mécanismes d’accumulation et des risques de relargage. Cette étude a été réalisée dans l’environnement de l’ancienne mine de Bertholène (Aveyron, 12, France). Les zones d’accumulations préférentielles ont été identifiées par spectrométrie gamma in situ mobile et fixe. Des échantillons de sols, sédiments, végétaux, eaux et tourbes ont été prélevés autour du site, afin (a) de caractériser l’activité des différents descendants des chaînes de l’U et du Th et les contaminations en ETM associées à différentes échelles d’observation, (b) de comprendre les mécanismes d’accumulation et de relargage potentiel et (c) de tracer les sources des contaminants. Les résultats obtenus montrent que l’essentiel de la contamination est localisée dans une zone inondable de l’environnement proximal aval de la mine. Les activités en uranium élevées (U-238 > 20000 Bq.kg-1) et le fort enrichissement des radionucléides du début de chaîne par rapport à la fin de chaîne de l’U-238 traduisent un apport préférentiel d’U-238 et de Th-230, par rapport au Ra-226, lors d’inondations. Les contaminations en ETM associées sont relativement faibles, excepté en Mn, en Ba et en S. Les accumulations en radionucléides et en ETM sont expliquées à la fois par les caractéristiques géochimiques du minerai d’uranium et par les processus de traitement du minerai et des eaux d’exhaure. Les lessivages chimiques réalisés révèlent que les fractions acido-solubles et oxydes amorphes des sols constituent des pièges prépondérants des contaminants et que des variations du pH ou du potentiel d’oxydoréduction pourraient générer des relargages important d’uranium et de radium dans l’environnement. Finalement les déséquilibres radiologiques et les isotopes du plomb sont des traceurs fiables de la contamination associée à l’exploitation d’une mine d’uranium
Uranium mining and uranium ore processing increase the environmental activity of U and Th decay products and trace elements, in particular in case of releases to the adjacent rivers. Contaminants accumulate then preferentially in sedimentation areas (such as ponds or lakes) or in wetlands (peatlands, marshes or riverbanks) located downstream to the mine. Wetlands – generally located at the head of watershed – are particularly sensitive to environmental changes and anthropogenic pressure. This poses a risk of release of contaminants from these accumulation areas. The objective of the present study is to propose an easily reproducible methodology – in particular for the orphan mining sites – to identify and characterize accumulation areas. This study also aims to improve our understanding of the mechanisms of accumulation and release, in these areas. This study was performed around the former mining site of Bertholène (France). Standing and mobile in situ gamma spectrometry is used to accurately locate the accumulation areas. Soils, sediments, vegetation, water and peat are also sampled upstream and downstream of the mine, in order to (a) characterize the activities and the disequilibria of the U-Th decay chains and the associated trace elements according to the scale of observation, (b) understand the mechanisms of accumulation and release and (c) identify the potential sources using geochemical proxies and isotopic analyses. The results obtained show that radionuclides are mainly accumulated in a flooding area located downstream the mine. Strong U-238 activities (> 20000 Bq.kg-1) and strong Ra-226/U-238 and Th-230/Ra-226 activity ratios are recorded, involving preferential inputs of U-238 and Th-230 during flooding events. Trace element contamination is low, except for Mn, Ba and S. Such contaminations are potentially explained by the geochemical composition of the uranium ore and by the past and current processes of ore and water mine. Sequential extractions highlight the importance of the acido-soluble and the amorphous oxides in the trapping of contaminants. Thus, pH or Eh potential changes could induce major releases of uranium to the environment. The large differences in Pb isotope composition between natural soils and uranium ores, as well the activity ratios of the U-238 and decay chain products, make these indicators helpful to identify the soils and the sediments impacted by uranium mining

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Xia, Qikai. "High precision TIMS U-Th disequilibrium dating and C, O, Sr isotope-based multi-proxy palaeoclimatic study of Speleothems in Australia /". [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18421.pdf.

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Williams, Cheryl Ann. "The geochemistry of Mt. Misery volcano, St. Kitts, Lesser Antilles : a combined U-series disequilibria and crystal size distribution study". Thesis, Open University, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340678.

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Brens, Raul Jr. "U-Th-Ba Elemental Fractionation during Partial Melting of Crustal Xenoliths and its Implications for U-series Disequilibria in Continental Arc Rocks". FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/406.

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Understanding U-series isotopic disequilibria of partially melted crust is integral for determining the effect that crustal assimilation has on the U-series signature of magmas. In this work, U, Th and Ba (as a proxy for Ra) elemental abundances were gathered on the quenched glass in partially melted crustal xenoliths of granitic composition using microbeam techniques. The crustal xenoliths, which are found in basaltic lava, from Mirador Volcano in Chile, are old, and can be assumed to be at secular equilibrium, whereas melting occurred during eruption of Mirador in 1979. A comparison of the ratios Ba/Th and U/Th in the partial melts with those of the whole rock reveal how much fractionation has occurred during partial melting. Different ratios of U, Th and Ba compared to the whole rock substantiate fractionation via partial melting. Thus, assimilation of partial melts of crust can play a role in U-series isotopic disequilibria.

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Bosia, Clio. "Les séries radioactives de l'uranium dans les sédiments de la Gandak (Himalaya) : de la roche total aux analyses in situ sur les minéraux séparés". Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAH003/document.

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L’analyse de sédiments totaux et de fractions granulométriques de la rivière Gandak (Himalaya) a montré que la variabilité des séries de l’uranium observée pour les sédiments himalayens est contrôlée par leur évolution minéralogique et granulométrique plutôt que par le mécanisme d’altération. Cette conclusion questionne les travaux antérieurs et souligne la nécessité d’étudier la mobilité des radionucléides à échelle minérale. A cette fin, une approche sur fractions minérales a mis en évidence des processus d’échange entre les minéraux, avec une mobilité significative de 230Th, fortement appauvri dans les zircons, et 226Ra, enrichis en particulier dans la fraction argileuse. Les déséquilibres observés semblent induits par un processus d’altération récent, de quelque ka.Ces résultats sont confirmés par l’analyse des déséquilibres 238U-234U-230Th dans des minéraux par SIMS, qui montre un enrichissement en 230Th à la surface des monazites et une perte de Th (232, 230) dans les zircons
The analysis of total sediments and grain-size fractions from the Gandak river (Himalaya) showed that the Uranium series variability observed for the Himalayan sediments is controlled by their mineralogical and grain-size evolution, rather than by the weathering process.This conclusion called into question the transfer timescale in Himalayan plains estimated by previous works and highlighted the need to explore radionuclide mobility at the mineral scale. For this purpose, an approach on pure mineral fractions pointed out exchange processes between the mineral phases, with a significant mobility of 230Th, strongly depleted in zircon, and 226Ra, particularly enriched in the clay fraction. The observed disequilibria are attributed to a recent weathering process of a few ky. Those observations are confirmed by the SIMS analysis of 238U-234U-230Th disequilibria on mineral grains, which show a 230Th enrichment at the grain surface in monazites and a loss of Th, 230 and 232, in zircons

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Mkaza, Masizole. "Sm-Nd isotopic disequilibrium between minerals in Merenskycyclic units of the Bushveld Complex, South Africa". Thesis, 2009. http://hdl.handle.net/10210/1964.

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Mühlinghaus, Christian [Verfasser]. "The principles of growth and isotopic fractionation of stalagmites : a numerical model to reconstruct temperature and precipitation records from stalagmites grown under disequilibrium conditions / presented by: Christian Mühlinghaus". 2008. http://d-nb.info/990060810/34.

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Libros sobre el tema "Isotopic disequilibrium"

T, Shewschuk. Uranium-series disequilibrium studies of unaltered rocks from the Lac du Bonnet Batholith. Pinawa, Man: AECL, Whiteshell Laboratories, 1997.

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Duffield, Wendell A. A model to help explain Sr-isotope disequilibrium between feldspar phenocrysts and melt in large-volume silicic magma systems. [Menlo Park, Calif.?]: U.S. Dept. of the Interior, U.S. Geological Survey, 1994.

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Uranium-Series Disequilibrium: Applications to Earth, Marine, and Environmental Sciences (Oxford Science Publications). Clarendon Pr, 1992.

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Capítulos de libros sobre el tema "Isotopic disequilibrium"

Giletti, Bruno J. "Isotopic Equilibrium/Disequilibrium and Diffusion Kinetics in Feldspars". En Feldspars and their Reactions, 351–82. Dordrecht: Springer Netherlands, 1994. http://dx.doi.org/10.1007/978-94-011-1106-5_9.

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Attendorn, H. G. y R. N. C. Bowen. "Uranium series disequilibrium dating". En Radioactive and Stable Isotope Geology, 131–53. Dordrecht: Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5840-4_5.

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Ramos, Frank C. y Frank J. Tepley. "11. Inter- and Intracrystalline Isotopic Disequilibria: Techniques and Applications". En Minerals, Inclusions And Volcanic Processes, editado por Keith D. Putirka y Frank J. Tepley III, 403–44. Berlin, Boston: De Gruyter, 2008. http://dx.doi.org/10.1515/9781501508486-012.

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Baskaran, Mark. "Dating of Biogenic and Inorganic Carbonates Using 210Pb-226Ra Disequilibrium Method: A Review". En Advances in Isotope Geochemistry, 789–809. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. http://dx.doi.org/10.1007/978-3-642-10637-8_37.

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Schleucher, J., P. Vanderveer, J. L. Markley y T. D. Sharkey. "Disequilibrium of Chloroplastic Phosphoglucose Isomerase Inferred from Deuterium Isotope Discrimination". En Photosynthesis: Mechanisms and Effects, 3521–24. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-3953-3_821.

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Frank, Norbert y Freya Hemsing. "Dating of Corals and Other Geological Samples via the Radioactive Disequilibrium of Uranium and Thorium Isotopes". En Frontiers in Earth Sciences, 89–100. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-24982-3_6.

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Criss, Robert E. "Nonequilibrium Fractionation and Isotopic Transport". En Principles of Stable Isotope Distribution. Oxford University Press, 1999. http://dx.doi.org/10.1093/oso/9780195117752.003.0006.

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At the Earth’s surface, isotopic disequilibrium is far more common than isotopic equilibrium. Although isotopic equilibrium is approached in certain instances, numerous constituents of the lithosphere, hydrosphere, atmosphere, and biosphere are simply not in mutual isotopic equilibrium. This condition is consistent with the complex and dynamic conditions typical of the Earth’s surface, particularly the large material fluxes, the rapid changes in temperature, and the biological mediation of chemical systems. Fortunately, several aspects of isotopic disequilibrium may be understood in terms of elementary physical laws. For homogeneous phases such as gases or well-stirred liquids, or for cases where spatial gradients in isotopic contents are not of primary interest, then the principles of elementary kinetics can be applied. For cases where isotopic gradients are important, the laws of diffusion are applicable. If two phases are out of isotopic equilibrium, they will progressively tend to approach the equilibrium state with the passage of time. This phenomenon occurs by the process of isotopic exchange, and its rate may be understood by examining isotopic exchange reactions from the viewpoint of elementary kinetic theory. In particular, consider the generalized exchange reaction where A and B are two phases that share a common major element, and A* and B* represent the same phases in which the trace isotope of that element is present. The present analysis is simplified if the exchange reaction is written so that only one atom is exchanged, in which case the stoichiometric coefficients are all unity. For reaction 4.1, kinetic principles assert that the forward and reverse reactions do not, in general, proceed at identical rates, but rather at the rates indicated by the quantities kα and k written by the arrows, multiplied by the appropriate concentrations terms. Assuming that the reaction is first order, then the reaction progress, represented by the quantity dA*/dt, may be expressed by the difference between these forward and reverse rates, as follows: . . . dA*/dt = kα(A)(B*) − k(A*)(B) (4.2) . . . In order to evaluate the exchange process more completely, is important to carefully chose a consistent set of concentrations for substitution equation 4.2.

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Herz, Norman y Ervan G. Garrison. "Applications of Stable Isotopes in Archaeological Geology". En Geological Methods for Archaeology. Oxford University Press, 1998. http://dx.doi.org/10.1093/oso/9780195090246.003.0020.

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Isotopic ratios of elements in natural materials on the earth either have been constant in time and space or have varied as a result of radioactive decay or geochemical fractionation. Elements which show variations in isotopic abundances in different samples and the reasons for these variations have helped resolve many geological and archaeological problems. Radioactive decay has provided absolute dating clocks: for archaeology, the most useful systems have been associated with 14C, 40Ar, and U-disequilibrium series. Variations in isotopic ratios of the stable elements H, C, O, N, S, Sr, and Pb have helped solve problems of provenance, paleoenvironments, and paleodiets. The rationale for isotopic variations of individual elements will determine the types of applications to archaeological geology. The most important applications are the determinations of artifact signatures, paleodiet, and paleoenvironment. Isotopic fractionation of light elements by physical, chemical, and biological processes is controlled by those thermodynamic properties which are determined by atomic weight and electronic configuration. Thermodynamic properties of molecules that are mass and temperature dependent include energy, which decreases with decreasing temperature, and vibrational frequency, which varies inversely in proportion to the square root of the reduced mass. Easily measurable isotopic separation is generally restricted to the lighter elements, that is, with atomic weights less than 40. Because isotopic fractionation is mass dependent, the separation is greater for elements with the greater mass difference between isotopes. The greatest separation is expected for hydrogen (mass 1) versus deuterium (mass 2); the other light elements commonly have isotopic differences closer to 10%. Thus, the lighter isotopes have higher vibrational energy and their chemical bonds are more easily broken. The different reactivity of lighter versus heavier isotopes of an element is responsible for their separation during geochemical and biological processes. Thermodynamic behavior has been considered a principal cause for variations, not in isotopic abundances of the heavier elements Sr and Pb, but rather in abundances of their parent radionuclides: Rb for Sr and U and Th for Pb. Recently, however, P. Budd and others suggested that under nonequilibrium conditions, fractionation could theoretically take place among the lead isotopes.

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"Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals". En Life in the Slow Lane: Ecology and Conservation of Long-Lived Marine Animals, editado por Erica J. Burton, Allen H. Andrews, Kenneth H. Coale y Gregor M. Cailliet. American Fisheries Society, 1999. http://dx.doi.org/10.47886/9781888569155.ch6.

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Abstract. —Radiometric aging of fishes is a recently developed technique using the disequilibria of 210 Pb:226 Ra in calcified structures to determine age. It has been applied successfully to several fish species, but certain limitations have made improvements desirable. Because 226 Ra can be measured directly by counting atoms using isotope-dilution thermal ionization mass spectrometry (TIMS), a new ion-exchange separation technique was developed to isolate small quantities of radium from calcified structures for TIMS determination. The advantages of this new technique are reduced sample mass and processing time, and greater accuracy and precision of radium quantification. We applied this technique to calcified structures from three fish species: otolith cores of Pacific grenadier Coryphaenoides acrolepis and tarpon Megalops atlanticus, and pectoral fin ray cores of Atlantic sturgeon Acipenser oxyrinchus. Annulus-derived age estimates for C. acrolepis were accurate with a confirmed longevity of at least 48 years. Although annulus-derived ages for M. atlanticus were inconsistent with radiometric ages, radiometric aging confirmed that tarpon are longlived; females may exceed 82 years. Radiometric age could not be determined for A. oxyrinchus because 210 Pb activities were greater than could be supported by ingrowth from 226 Ra decay. In this paper we discuss the application and limitations of this technique and its relevance to fisheries management.

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Actas de conferencias sobre el tema "Isotopic disequilibrium"

Fearey, B. L. y B. M. Tissue. "High-resolution spectroscopy of Th and Pa isotopes". En OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.mkk7.

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Doppler-free spectroscopy has been performed on thorium and protactinium isotopes to gain a detailed understanding of the underlying physics of spectral features. Characterizing phenomena such as Lamb dips and optical pumping are important in understanding and optimizing resonance ionization mass spectrometry (RIMS) analysis. Measurement of these isotopes by RIMS is used in U-series disequilibrium dating of geological samples of the last 400,000 years. Isotope shifts and hyperfine structure of 232Th, 230Th, 229Th, 233Pa, and 231Pa are reported for several transitions. The Doppler-free spectra of Th showed an interesting effect, which was strongly dependent on laser power, in which a narrow peak replaced the usual Lamb dip. These results and a detailed analysis will be presented and discussed.

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Tissue, B., G. Loge, J. Olivares y B. Fearey. "Broad- and narrow-band cw lasers in resonance ionization mass spectrometry isotope analysis". En OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.tuz30.

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Resonance ionization mass spectrometry (RIMS) is being developed to measure 230/232Th ratios (~5:105), which are used in U-series disequilibrium dating of geological samples of the last 400,000 years. We will discuss the precision and accuracy of the ratio measurements when resonant excitation with a broad-band dye laser and a narrow-band frequency-doubled Ti:sapphire laser is used. The dye laser is evaluated with and without optogalvanic frequency locking onto a Th transition to provide better reproducibility. The relative advantages and disadvantages of the two excitation sources will be summarized, including 1) narrowband excitation yielding greater isotope selectivity versus 2) broad-band laser excitation providing higher sensitivity (simultaneous excitation of all relevant isotopes and all atoms within the Doppler profile).

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Bouvier, Anne-Sophie, Estelle Rose-Koga, Alexander Robert Lee Nichols y Clémence Le Lay. "Link between Fluids and Stable Isotope Disequilibrium between Melt Inclusions and Host Olivine". En Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.237.

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Macris, Catherine A., Carrie A. Menold, Anat Shahar, Edward Young y Robert T. Rupard. "INTER-MINERAL IRON ISOTOPE FRACTIONATION IN UHP ROCKS: DISEQUILIBRIUM AS A SIGNAL OF HIGH PRESSURE METASOMATISM". En GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-283501.

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Wang, Yang, Shan Ke y Yongsheng He. "Mg Isotope Disequilibrium during Fluid-Fluxed Crustal Anatexis: A Case Study of Migmatites from the Dabie Orogen". En Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.2787.

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Layzell, Anthony, Greg Ludvigson, Jon Smith y Rolfe Mandel. "Assessing Stable Carbon Isotope Disequilibrium in Late Pleistocene Buried Soils of the Great Plains, USA, Using a State Factor Approach". En Goldschmidt2020. Geochemical Society, 2020. http://dx.doi.org/10.46427/gold2020.1427.

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Layzell, Tony, Greg A. Ludvigson, Rolfe D. Mandel y Jon J. Smith. "USING FACTORS OF SOIL FORMATION TO INVESTIGATE STABLE CARBON ISOTOPE DISEQUILIBRIUM IN LATE PLEISTOCENE (MIS 3) BURIED SOILS OF THE CENTRAL GREAT PLAINS, USA". En GSA 2020 Connects Online. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020am-355553.

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Lucarelli, Jamie, Hannah Carroll, Bettina Purgstaller, Martin Dietzel, Aradhna Tripati y Robert Eagle. "Paired Δ₄₇ and Δ₄₈ carbonate clumped isotope data: Standard values, multi-instrument comparisons, mixing effects, and disequilibrium effects". En Goldschmidt2021. France: European Association of Geochemistry, 2021. http://dx.doi.org/10.7185/gold2021.7805.

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Mohamed, Tarek S., Morten Kristensen, Shu Pan, Kang Wang, Soraya S. Betancourt, Carlos Torres-Verdín y Oliver C. Mullins. "In-Reservoir Mixing Dynamics Over Geologic Time of Separate Gas and Oil Charges in Well-Connected Reservoirs". En SPE Annual Technical Conference and Exhibition. SPE, 2023. http://dx.doi.org/10.2118/215051-ms.

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Abstract Many reservoirs experience separate gas and oil charges that can lead to a variety of different outcomes of fluid type and distribution. There has been fundamental uncertainty even as to which charge fluid can arrive first, let alone what fluid dynamic processes can result over geologic time. For high-pressure basins such as the Gulf of Mexico, this mixture can lead to increased solution gas, large GOR gradients and sometimes cause formation of viscous oil and tar at the oil-water contact, impacting aquifer support. In some reservoirs, the present-day outcome of oil and gas mixing over geologic time is clearly established by detailed chemical evaluation of reservoir fluids from many reservoir locations. Our objective is to understand the dynamics of the gas and oil mixing processes. Chemical measurements show that the extent of mixing includes thermodynamic equilibration in young reservoirs by 1) FHZ equation of state (EoS) asphaltene gradients and cubic EoS modeling of solution gas for reservoir fluids, 2) analysis of liquid-phase geochemical biomarkers, and 3) methane carbon isotope analysis. Specifically, in the common charge of primary biogenic gas and oil into reservoirs, methane isotope analysis is unequivocal. We employ reservoir simulation of a point gas charge into oil with various geometries and charge rates to establish parametric conditions which lead to excellent mixing vs those conditions that lead to large, disequilibrium gradients. The roles of compositional diffusion vs. momentum diffusion induced by forced convection are explored both in simulation and overall fluid mechanics analysis, which helps both to validate the results and extend the range of applicable parameters. Modeling results and simple fluid mechanics estimates also establish that there is no possibility that these reservoirs could have a gas charge followed by an oil charge; in the selected reservoirs, oil must have arrived first, followed by a biogenic gas charge. Seismic images of gas chimneys offer guidance regarding how the latter process can take place. Second, modeling results clearly establish a surprisingly wide range of charge conditions that can lead to excellent mixing and equilibration even for a point gas charge. Modeling results also show that for a very fast charge, results are consistent with those expected for CO2 injection and sequestration. The evaluation of geodynamic processes of separate biogenic gas and oil charges into reservoirs has rarely been accomplished. Even the result that biogenic gas charge must occur after oil charge challenges widely-held conventional thinking. In addition, the rapid and thorough mixing (less than 2 million years) of gas and oil charges is unexpected yet readily reproduced by reservoir simulation. The ability to connect CO2 sequestration to a wide range of reservoir studies is a novel way to constrain CCS modeling.

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