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Articles de revues sur le sujet « Isotopic disequilibrium »

Auteur : Grafiati
Publié le 8 mars 2025

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1

Thaler, Caroline, Amandine Katz, Magali Bonifacie, Bénédicte Ménez et Magali Ader. « Oxygen isotope composition of waters recorded in carbonates in strong clumped and oxygen isotopic disequilibrium ». Biogeosciences 17, no 7 (3 avril 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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2

Gamnitzer, U., A. B. Moyes, D. R. Bowling et H. Schnyder. « Measuring and modelling the isotopic composition of soil respiration : insights from a grassland tracer experiment ». Biogeosciences Discussions 8, no 1 (5 janvier 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 et H. Schnyder. « Measuring and modelling the isotopic composition of soil respiration : insights from a grassland tracer experiment ». Biogeosciences 8, no 5 (26 mai 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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4

Ishimura, T., U. Tsunogai, S. Hasegawa, F. Nakagawa, T. Oi, H. Kitazato, H. Suga et T. Toyofuku. « Variation in stable carbon and oxygen isotopes of individual benthic foraminifera : tracers for quantifying the magnitude of isotopic disequilibrium ». Biogeosciences 9, no 11 (8 novembre 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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5

Lee, Dongho, et Scott J. Carpenter. « Isotopic disequilibrium in marine calcareous algae ». Chemical Geology 172, no 3-4 (février 2001) : 307–29. http://dx.doi.org/10.1016/s0009-2541(00)00258-8.

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6

Abart, R. « Isotopic Disequilibrium During Metasomatic Vein Formation ». Mineralogical Magazine 58A, no 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, no 4 (1 août 2007) : 273. http://dx.doi.org/10.2113/gselements.3.4.273.

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8

Antonelli, Michael A., Tushar Mittal, Anders McCarthy, Barbara Tripoli, James M. Watkins et Donald J. DePaolo. « Ca isotopes record rapid crystal growth in volcanic and subvolcanic systems ». Proceedings of the National Academy of Sciences 116, no 41 (23 septembre 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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9

To, Dominic. « Isotopic Disequilibrium of Uranium in Kansas Groundwaters ». Transactions of the Kansas Academy of Science (1903-) 93, no 1/2 (1990) : 38. http://dx.doi.org/10.2307/3628127.

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10

Sugiura, N., K. Hashizume, Y. Miura, K. Kiyota et S. Zashu. « Cosmogenic nitrogen isotopic disequilibrium observed in meteorites ». Meteoritics 30, no 6 (novembre 1995) : 646–53. http://dx.doi.org/10.1111/j.1945-5100.1995.tb01162.x.

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11

Ebner, Pirmin Philipp, Hans Christian Steen-Larsen, Barbara Stenni, Martin Schneebeli et Aldo Steinfeld. « Experimental observation of transient <i>δ</i><sup>18</sup>O interaction between snow and advective airflow under various temperature gradient conditions ». Cryosphere 11, no 4 (25 juillet 2017) : 1733–43. http://dx.doi.org/10.5194/tc-11-1733-2017.

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Abstract. Stable water isotopes (δ18O) obtained from snow and ice samples of polar regions are used to reconstruct past climate variability, but heat and mass transport processes can affect the isotopic composition. Here we present an experimental study on the effect of airflow on the snow isotopic composition through a snow pack in controlled laboratory conditions. The influence of isothermal and controlled temperature gradient conditions on the δ18O content in the snow and interstitial water vapour is elucidated. The observed disequilibrium between snow and vapour isotopes led to the exchange of isotopes between snow and vapour under non-equilibrium processes, significantly changing the δ18O content of the snow. The type of metamorphism of the snow had a significant influence on this process. These findings are pertinent to the interpretation of the records of stable isotopes of water from ice cores. These laboratory measurements suggest that a highly resolved climate history is relevant for the interpretation of the snow isotopic composition in the field.
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12

Neumann, Thomas A., et Edwin D. Waddington. « Effects of firn ventilation on isotopic exchange ». Journal of Glaciology 50, no 169 (2004) : 183–94. http://dx.doi.org/10.3189/172756504781830150.

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AbstractA new model of isotopic diffusion in the upper few meters of firn tracks the isotopic composition of both the ice matrix and the pore-space vapor through time in two dimensions. Stable isotopes in the vapor phase move through the firn by diffusion along concentration gradients and by advection. Wind-driven ventilation carries atmospheric water vapor into the firn, where it mixes with existing pore-space vapor. Unlike previous models, our model allows disequilibrium between pore-space vapor and the surrounding snow grains. We also calculate the isotopic effects of ventilation-driven sublimation and condensation in the firn. Model predictions of isotopic diffusion in firn compare favorably with existing diffusion models. Model results quantify what other investigators have suggested: isotopic change in the upper few meters is more rapid than can be explained by the Whillans and Grootes (1985) model; isotopic equilibration with atmospheric vapor is an important component of post-depositional isotopic change; and ventilation enhances isotopic exchange by creating regions of relatively rapid sublimation and condensation in the firn.
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13

Ishimura, T., U. Tsunogai, S. Hasegawa, F. Nakagawa, T. Oi, H. Kitazato, H. Suga et T. Toyofuku. « Variation in stable carbon and oxygen isotopes of individual benthic foraminifera : tracers for quantifying the vital effect ». Biogeosciences Discussions 9, no 5 (31 mai 2012) : 6191–218. http://dx.doi.org/10.5194/bgd-9-6191-2012.

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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 (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 vital effect in different species is correlated with inter-individual 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 vital effect established in this study, we can reconstruct the δ13C values of dissolved inorganic carbon in bottom water by correcting foraminiferal isotopic compositions for the isotopic shift resulting from the vital effect. Our findings will allow the use of isotope data for all benthic foraminifera as more reliable proxies for reconstructing past bottom water conditions and evaluating global carbon cycling.
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14

Fastovsky, D. E., M. A. Arthur, N. H. Strater et A. Foss. « Freshwater Bivalves (Unionidae), Disequilibrium Isotopic Fractionation, and Temperatures ». PALAIOS 8, no 6 (décembre 1993) : 602. http://dx.doi.org/10.2307/3515035.

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15

COMPARINI, E., R. DAL PASSO, C. PESCATORE et M. UGHI. « ON A MODEL FOR THE PROPAGATION OF ISOTOPIC DISEQUILIBRIUM BY DIFFUSION ». Mathematical Models and Methods in Applied Sciences 19, no 08 (août 2009) : 1277–94. http://dx.doi.org/10.1142/s0218202509003784.

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We consider a model for the distribution of radionuclides in the ground water around a deep repository for used nuclear fuel, based on the assumption that different isotopes of the same chemical element A contribute jointly to the chemical potential of A. In this hypothesis, the total flux Ji of a particular isotope Ai of an element A has two components, one due to the interaction of Ai with the solvent molecules B, the other with the kin isotopes. We study some qualitative properties of the solution in the physically relevant assumption that the first of these components is negligible. In this assumption the problem reduces to a parabolic equation for the total concentration of the element A, possibly coupled with hyperbolic equations for the concentrations of the single isotopes.
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16

Iles, Kieran A., Janet M. Hergt et Jon D. Woodhead. « Modelling Isotopic Responses to Disequilibrium Melting in Granitic Systems ». Journal of Petrology 59, no 1 (1 janvier 2018) : 87–113. http://dx.doi.org/10.1093/petrology/egy019.

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17

Paull, Charles K., et William M. Balch. « Oxygen isotopic disequilibrium in coccolith carbonate from phytoplankton blooms ». Deep Sea Research Part I : Oceanographic Research Papers 41, no 1 (janvier 1994) : 223–28. http://dx.doi.org/10.1016/0967-0637(94)90034-5.

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18

Sandoval, D. N., E. Greaves et S. Melendez. « Uranium and thorium isotopic disequilibrium in Venezuelan hot springs. » GEOCHEMICAL JOURNAL 21, no 2 (1987) : 43–49. http://dx.doi.org/10.2343/geochemj.21.43.

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19

Dran, J. C., Y. Langevin et J. C. Petit. « Uranium isotopic disequilibrium : Reappraisal of the alpha-recoil effect ». Chemical Geology 70, no 1-2 (août 1988) : 126. http://dx.doi.org/10.1016/0009-2541(88)90557-8.

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Toulhoat, Pierre, et Catherine Beaucaire. « Géochimie des eaux liées au gisement d'uranium de Cigar Lake (Saskatchewan, Canada) et apport des isotopes de l'uranium et du plomb comme guides de prospection ». Canadian Journal of Earth Sciences 30, no 4 (1 avril 1993) : 754–63. http://dx.doi.org/10.1139/e93-061.

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The primary objective of this study is a better understanding of the chemical evolution of the waters crossing the Cigar Lake (Saskatchewan, Canada) uranium ore deposit and, once described, to investigate the behavior of the lead and uranium isotopes and to test their use as guidelines in exploration. The underground waters around the Cigar Lake ore deposit were sampled by pumping bore holes or by air lifting. Isotopic analyses of U and Pb and chemical analyses of the major elements and of some trace elements (Ba, Ra, U) were completed. Based on these results, a model is proposed to explain the genesis and evolution of the waters and also to account for the water–minerals equilibria. The saturation indices of uraninite and coffinite were determined by way of oxidation–reduction potentials calculated on the basis of measured Fe contents. The waters saturated with these minerals, which are also the most reduced, are systematically located directly above or across the ore deposit. These saturation indices, as well as the calculated oxidation–reduction potentials, are good guidelines for hydrogeochemical exploration in the Cigar Lake orebody setting; however, they must be used only in a relative fashion. Furthermore, the 234U/238U disequilibrium measurements and the U concentration in the waters permit the recognition of waters having percolated through the mineralized zones (higher U concentrations, lower disequilibria). The nature of the mineralization is probably responsible for the coexistence of the two evolutionary trends within the mineralized zones; in the high-grade zones, the disequilibria are low, whereas in the zones of disseminated mineralization or in halos surrounding the orebody, the disequilibria are greater, reflecting the prevailing influence of selective dissolution of 234U in the zones where exchange surfaces between the mineral carrying U and the solution are more important. The measurement of Pb isotopic ratios in the waters also permits of a clear characterization of waters that have percolated through the ore deposit: in this case, the Pb isotopic ratios are enriched in radiogenic Pb. [Journal Translation]
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21

Vance, E. R., et M. Gascoyne. « Isotopic disequilibrium effects in leaching of natural uraninite and thorianitc ». Geochimica et Cosmochimica Acta 51, no 9 (septembre 1987) : 2593–94. http://dx.doi.org/10.1016/0016-7037(87)90310-3.

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22

McConnaughey, Ted. « 13C and 18O isotopic disequilibrium in biological carbonates : I. Patterns ». Geochimica et Cosmochimica Acta 53, no 1 (janvier 1989) : 151–62. http://dx.doi.org/10.1016/0016-7037(89)90282-2.

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23

Spötl, Christoph, et Augusto Mangini. « U/Th age constraints on the absence of ice in the central Inn Valley (eastern Alps, Austria) during Marine Isotope Stages 5c to 5a ». Quaternary Research 66, no 1 (juillet 2006) : 167–75. http://dx.doi.org/10.1016/j.yqres.2006.03.002.

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AbstractCalcitic flowstones are present in fractures of a Pleistocene breccia near Innsbruck, Austria, and record periods of carbonate precipitation in the unsaturated zone between 101,500 ± 1500 and 70,300 ± 1800 yr, constrained by U-series disequilibrium dates. The occurrence of these speleothems, their low carbon isotopic composition, and the lack of infiltrated siliciclastic material demonstrate that the central Inn valley – which harbored one of the most extensive valley glaciers during the last glacial maximum – was ice-free during Marine Isotope Stages 5c to 5a. Climatically warm periods are separated by distinct drops in the oxygen isotopic composition of the speleothem calcite, attributed to strong and possibly seasonally biased atmospheric cooling. During these intervening stadials, which mirror those identified in the Greenland ice cores and marine sea-surface temperature records, calcite deposition apparently came to a halt, but the Inn Valley remained ice-free. The youngest calcite layer formed between ∼74,000 and ∼70,000 yr and places a maximum age limit on the likely expansion of alpine glaciers during the Marine Isotope Stage 5/4 transition, consistent with other speleothem records.
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Apolinarska, Karina, Krzysztof Pleskot, Aleksandra Pełechata, Michał Migdałek et Mariusz Pełechaty. « Seasonal deposition of authigenic calcite out of isotopic equilibrium with DIC and water, and implications for paleolimnological studies ». Journal of Paleolimnology 66, no 1 (23 mars 2021) : 41–53. http://dx.doi.org/10.1007/s10933-021-00184-y.

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AbstractWe conducted year-round, monthly monitoring of the stable isotope composition of DIC and water in hypereutrophic Lake Kierskie, western Poland, along with isotope measures of calcite collected in sediment traps installed at 16 and 30 m water depth in the lake. Isotope data were supplemented by previously published data on physico-chemical variables in the lake water column. We sought to determine how carbon and oxygen isotopic disequilibria in calcite deposited in the lake’s laminated sediments vary seasonally, and what factors drive this variability. Deposition of calcite out of equilibrium with DIC and water was documented over the entire study period. For δ18O, the disequilibrium difference between successive months far exceeded the amplitude of the seasonal variability in the isotope composition of water. The biggest difference between the measured and calculated δ13Ccalcite and δ18Ocalcite values was observed during late autumn and winter sediment resuspension and redeposition (2.4‰ and 5.4‰, respectively). In the spring, δ13Ccalcite and δ18Ocalcite offsets from equilibria, 0.5‰ and 1.3‰, respectively, resulted from rapid precipitation of large calcite crystals. During summer, intense productivity and processes related to calcifying algae (“vital effects”) caused lower δ13C (0.5–1.8‰) and δ18O (2.8–2.9‰) in calcite. Differences between isotope values of calcite collected from the two water depths were small, and might have resulted from different settling velocities of small and large crystals, and/or preferential dissolution of smaller grains. We suggest that winter laminae should be excluded from isotope studies of varved sediments whenever possible, as they likely contain redeposited carbonate in which the isotope value is not indicative of conditions in the lake at the time of laminae formation. We also recommend supplementing isotope analysis of calcite in varved lake sediments with seasonally resolved analysis of carbonate content. It appears that major shifts in the proportion of carbonate deposited across seasons can cause notable changes in mean annual values of δ18Ocalcite and δ13Ccalcite, even if DIC and water isotopic compositions remain stable.
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van der Velde, I. R., J. B. Miller, K. Schaefer, G. R. van der Werf, M. C. Krol et W. Peters. « Terrestrial cycling of <sup>13</sup>CO<sub>2</sub> ; by photosynthesis, respiration, and biomass burning in SiBCASA ». Biogeosciences 11, no 23 (1 décembre 2014) : 6553–71. http://dx.doi.org/10.5194/bg-11-6553-2014.

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Abstract. We present an enhanced version of the SiBCASA terrestrial biosphere model that is extended with (a) biomass burning emissions from the SiBCASA carbon pools using remotely sensed burned area from the Global Fire Emissions Database (GFED), (b) an isotopic discrimination scheme that calculates 13C signatures of photosynthesis and autotrophic respiration, and (c) a separate set of 13C pools to carry isotope ratios into heterotrophic respiration. We quantify in this study the terrestrial exchange of CO2 and 13CO2 as a function of environmental changes in humidity and biomass burning. The implementation of biomass burning yields similar fluxes as CASA-GFED both in magnitude and spatial patterns. The implementation of isotope exchange gives a global mean discrimination value of 15.2‰, ranges between 4 and 20‰ depending on the photosynthetic pathway in the plant, and compares favorably (annually and seasonally) with other published values. Similarly, the isotopic disequilibrium is similar to other studies that include a small effect of biomass burning as it shortens the turnover of carbon. In comparison to measurements, a newly modified starch/sugar storage pool propagates the isotopic discrimination anomalies to respiration much better. In addition, the amplitude of the drought response by SiBCASA is lower than suggested by the measured isotope ratios. We show that a slight increase in the stomatal closure for large vapor pressure deficit would amplify the respired isotope ratio variability. Our study highlights the importance of isotope ratio observations of 13C to assess and improve biochemical models like SiBCASA, especially with regard to the allocation and turnover of carbon and the responses to drought.
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Livnat, A., et J. Kronfeld. « Paleoclimatic Implications of U-Series Dates for Lake Sediments and Travertines in the Arava Rift Valley, Israel ». Quaternary Research 24, no 2 (juillet 1985) : 164–72. http://dx.doi.org/10.1016/0033-5894(85)90003-1.

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The Sayif travertines and lacustrine limestones cropping out in the northern Arava Valley, a region of extreme aridity, have been dated by the 230Th/234U disequilibrium method. The consistency between the stratigraphic position and the apparent ages at each of the sampling sites strongly supports the reliability of the ages. Most of the ages fall within two clusters that are coincident with ages representative of oceanic oxygen-isotope stages 5 and 7. The colder intervening stage 6 was not a period of substantial travertine formation. During the warmer global episodes of isotopic stages 5 and 7 the arid south of Israel apparently was considerably wetter than at present.
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Borodulina, Galina, Igor Tokarev et Evgeny Yakovlev. « Isotope Composition of Natural Water in Lake Onega Basin ». Water 15, no 10 (13 mai 2023) : 1855. http://dx.doi.org/10.3390/w15101855.

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In 2009–2018, the isotopic composition of oxygen and hydrogen in the atmospheric precipitation, groundwater and river and lake water of Lake Onega basin was studied. The weighted annual isotope composition of precipitation at Petrozavodsk was δ18O = −11.7‰ and δ2H = −84‰ and varied from −30.9 to −4.1‰ for δ18O and from −23 to −22‰ for δ2H. The isotopic composition of the water in Lake Onega was relatively uniform from −11.5 to −9.3‰ for δ18O and from −85 to −71‰ for δ2H. In the bays, the isotopic composition of the water varied more substantially than in the central part of the lake due to the river runoff during springtime flooding. In late summer, the concentrations of deuterium and oxygen-18 increased in the lake water, and figurative points on the δ2H vs. δ18O diagram shifted above the meteoric line. The absorption of the isotopically heavy summer precipitation and disequilibrium isotope fractionation during evaporation led to the enrichment of the lake water by heavy isotopes. Experiments were conducted to estimate the evaporation influence on the isotope enrichment of the residual water, and a comparison of the obtained isotope data with the experimental function showed that commonly, about 4% and up to 12% of water was lost during the spring and summer, respectively. In the water of the tributaries, the abundance of the deuterium and oxygen-18 varied in a wider scale than in the lakes, from −14.4 to −9.1‰ for δ18O and from −102 to −73‰ for δ2H. An evaporation loss of up to 35% was found for the rivers in late summer, and this value was proportional to the area of lakes and wetlands in the elementary watershed. The initial isotope composition of the water in the tributaries prior to evaporation was estimated to be δ18O ≈ −14.1‰ and δ2H ≈ −103‰ on average and crossed the approximation and meteoric lines. This estimation was close to the average composition of the groundwater, i.e., δ18O ≈ −13.4‰ and δ2H ≈ −94‰ on the Lake Onega catchment. The slightly increased isotope depletion of the calculated composition in the initial river water in comparison with the groundwater was the result of the contribution of the spring snowmelt water, which had a significant influence on the lake water balance.
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Simonetti, Antonio, et Keith Bell. « Isotopic disequilibrium in clinopyroxenes from nephelinitic lavas, Napak volcano, eastern Uganda ». Geology 21, no 3 (1993) : 243. http://dx.doi.org/10.1130/0091-7613(1993)021<0243:idicfn>2.3.co;2.

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Fleischer, Robert L. « Alpha-recoil damage : Relation to isotopic disequilibrium and leaching of radionuclides ». Geochimica et Cosmochimica Acta 52, no 6 (juin 1988) : 1459–66. http://dx.doi.org/10.1016/0016-7037(88)90216-5.

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Fantle, Matthew S., B. Davis Barnes et Kimberly V. Lau. « The Role of Diagenesis in Shaping the Geochemistry of the Marine Carbonate Record ». Annual Review of Earth and Planetary Sciences 48, no 1 (30 mai 2020) : 549–83. http://dx.doi.org/10.1146/annurev-earth-073019-060021.

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Carbonate sediments and rocks are valuable archives of Earth's past whose geochemical compositions inform our understanding of Earth's surface evolution. Yet carbonates are also reactive minerals and often undergo compositional alteration between the time of deposition and sampling and analysis. These changes may be mineralogical, structural, and/or chemical, and they are broadly referred to as diagenesis. Building on work over the past 40 years, we present an overview of key carbonate diagenesis terminology and a process-based framework for evaluating the geochemical impacts of carbonate diagenesis; we also highlight recent experimental and field observations that suggest metal isotopes as valuable diagenetic indicators. Our primary objectives are to demonstrate the value of coupling quantitative and analytical approaches, specifically with regard to metal isotopes and Mg/Ca, and to focus attention on key avenues for future work, including the role of authigenesis in impacting global geochemical cycles and the isotopic composition of the rock record. ▪ Quantitative frameworks utilizing well-understood diagenetic indicators and basic geochemical parameters allow us to assess the extent of diagenetic alteration in carbonate sediments. ▪ The reactivity, duration of reaction, and degree of isotopic or elemental/chemical disequilibrium determine the extent to which carbonates may be altered. ▪ Metal isotopic ratios (δ44Ca, δ26Mg, 87Sr/86Sr) can be used to constrain the extent and rate of carbonate recrystallization. ▪ Diagenetic signals may be globally synchronous, while diagenetic fluxes may impact global geochemical cycles.
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Hegner, E., T. K. Kyser et L. Hulbert. « Nd, Sr, and O isotopic constraints on the petrogenesis of mafic intrusions in the Proterozoic Trans-Hudson Orogen of central Canada ». Canadian Journal of Earth Sciences 26, no 5 (1 mai 1989) : 1027–35. http://dx.doi.org/10.1139/e89-083.

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Sm–Nd isotopic data from five mafic intrusions in the La Ronge – Lynn Lake Domain indicate crystallization between 1.88 and 1.79 Ga. The data from a single intrusion in the Glennie Lake Domain suggest a slightly younger age of about 1.71 Ga. These results indicate a cogenetic origin of the mafic intrusions with the associated volcanic and plutonic rocks.Initial εNd values vary from +4.5 to −0.6 and can be modeled by mixing Proterozoic mantle-derived magmas with ≤17% Archaean crust or subduction of ≤3% sediment similar to pelites from the Wollaston Domain. The initial εNd value of 0 for a Late Proterozoic Mackenzie dike is compatible with an origin from mantle sources affected by Hudsonian subduction processes.Rb–Sr data indicate variable and generally high initial 87Sr/86Sr isotopic ratios, which reflect, in part, isotopic redistribution during metamorphism. δ18O values of coexisting clinopyroxene, orthopyroxene, and plagioclase indicate isotopic disequilibrium. Plagioclase samples show variable degrees of enrichment in 18O due to isotopic exchange with metamorphic fluids that probably also affected Rb and Sr.
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Schmittner, Andreas, et Nathaniel J. Fillman. « Carbon and carbon-13 in the preindustrial and glacial ocean ». PLOS Climate 3, no 7 (8 juillet 2024) : e0000434. http://dx.doi.org/10.1371/journal.pclm.0000434.

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Despite their importance for Earth’s climate and paleoceanography, the cycles of carbon (C) and its isotope 13C in the ocean are not well understood. Models typically do not decompose C and 13C storage caused by different physical, biological, and chemical processes, which makes interpreting results difficult. Consequently, basic observed features, such as the decreased carbon isotopic signature (δ13CDIC) of the glacial ocean remain unexplained. Here, we review recent progress in decomposing Dissolved Inorganic Carbon (DIC) into preformed and regenerated components, extend a precise and complete decomposition to δ13CDIC, and apply it to data-constrained model simulations of the Preindustrial (PI) and Last Glacial Maximum (LGM) oceans. Regenerated components, from respired soft-tissue organic matter and dissolved biogenic calcium carbonate, are reduced in the LGM, indicating a decrease in the active part of the biological pump. Preformed components increase carbon storage and decrease δ13CDIC by 0.55 ‰ in the LGM. We separate preformed into saturation and disequilibrium components, each of which have biological and physical contributions. Whereas the physical disequilibrium in the PI is negative for both DIC and δ13CDIC, and changes little between climate states, the biological disequilibrium is positive for DIC but negative for δ13CDIC, a pattern that is magnified in the LGM. The biological disequilibrium is the dominant driver of the increase in glacial ocean C and the decrease in δ13CDIC, indicating a reduced sink of biological carbon. Overall, in the LGM, biological processes increase the ocean’s DIC inventory by 355 Pg more than in the PI, reduce its mean δ13CDIC by an additional 0.52 ‰, and contribute 60 ppm to the lowering of atmospheric CO2. Spatial distributions of the δ13CDIC components are presented. Commonly used approximations based on apparent oxygen utilization and phosphate are evaluated and shown to have large errors.
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Veinott, Geoffrey I., et R. Jack Cornett. « Carbon isotopic disequilibrium in the shell of the freshwater mussel Elliptio complanata ». Applied Geochemistry 13, no 1 (janvier 1998) : 49–57. http://dx.doi.org/10.1016/s0883-2927(97)00053-x.

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Engel, J., J. Woodhead, J. Hellstrom, R. Maas, R. Drysdale et D. Ford. « Corrections for initial isotopic disequilibrium in the speleothem U-Pb dating method ». Quaternary Geochronology 54 (octobre 2019) : 101009. http://dx.doi.org/10.1016/j.quageo.2019.101009.

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35

Bajwa, B. S., et H. S. Virk. « Autoradiography for U, Th, and isotopic disequilibrium study of Siwalik fossil bones ». Environment International 22 (janvier 1996) : 379–82. http://dx.doi.org/10.1016/s0160-4120(96)00135-3.

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Kil, Youngwoo, Haemyeong Jung et Kyounghee Yang. « Li isotopic disequilibrium of the Cenozoic subcontinental lithospheric mantle in East Asia ». Geosciences Journal 20, no 5 (23 septembre 2016) : 597–607. http://dx.doi.org/10.1007/s12303-016-0024-y.

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37

Grose, Christopher J., et Juan C. Afonso. « Chemical Disequilibria, Lithospheric Thickness, and the Source of Ocean Island Basalts ». Journal of Petrology 60, no 4 (2 mars 2019) : 755–90. http://dx.doi.org/10.1093/petrology/egz012.

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Abstract We examine REE (Rare-Earth Element) and isotopic (Sr–Hf–Nd–Pb) signatures in OIB (Ocean Island Basalts) as a function of lithospheric thickness and show that the data can be divided into thin- (&lt;12 Ma) and thick-plate (&gt;12 Ma) sub-sets. Comparison to geophysically constrained thermal plate models indicates that the demarcation age (∼12 Ma) corresponds to a lithospheric thickness of about 50 km. Thick-plate OIB show incompatible element and isotopic enrichments, whereas thin-plate lavas show MORB-like or slightly enriched values. We argue that enriched signatures in thick-plate OIB originate from low-degree melting at depths below the dry solidus, while depleted signatures in MORB and thin-plate OIB are indicative of higher-degree melting. We tested quantitative explanations of REE systematics using melting models for homogeneous fertile peridotite. Using experimental partition coefficients for major upper mantle minerals, our equilibrium melting models are not able to explain the data. However, using a new grain-scale disequilibrium melting model for the same homogeneous lithology the data can be explained. Disequilibrium models are able to explain the data by reducing the amount of incompatible element partitioning into low degree melts. To explore new levels of detail in disequilibrium phenomena, we employ the Monte-Carlo Potts model to characterize the textural evolution of a microstructure undergoing coarsening and phase transformation processes simultaneous with the diffusive partitioning of trace elements among solid phases and melt in decompressing mantle. We further employ inverse methods to study the thermochemical properties required for models to explain the OIB data. Both data and theory show that OIB erupted on spreading ridges contain signatures close to MORB values, although E-MORB provides the best fit. This indicates that MORB and OIB are produced by compositionally indistinguishable sources, although the isotopic data indicate that the source is heterogeneous. Also, a posteriori distributions are found for the temperature of the thermomechanical lithosphere-asthenosphere boundary (TLAB), the temperature in the source of OIB (Tp, oib) and the extent of equilibrium during melting (i.e. grain size). TLAB has been constrained to 1200–1300°C and Tp, oib is constrained to be &lt;1400°C. However, we consider the constraints on Tp, oib as a description of all OIB to be provisional, because it is a statistical inference from the global dataset. Exceptional islands or island groups may exist, such as the classical ‘hotspots’ (Hawaii, Reunion, etc) and these islands may originate from hot sources. On the other hand, by the same statistical arguments their origins may be anomalously hydrated or enriched instead. Mean grain size in the source of OIB is about 1–5 mm, although this is also provisional due to a strong dependence on knowledge of partition coefficients, ascent rate and the melting function. We also perform an inversion in which partition coefficients were allowed to vary from their experimental values. In these inversions TLAB and Tp, oib are unchanged, but realizations close to equilibrium can be found when partition coefficients differ substantially from their experimental values. We also investigated bulk compositions in the source of OIB constrained by our inverse models. Corrections for crystallization effects provided ambiguous confirmations of previously proposed mantle compositions, with depleted mantle providing the poorest fits. We did not include isotopes in our models, but we briefly evaluate the lithospheric thickness effect on isotopes. Although REE data do not require a lithologically heterogeneous source, isotopes indicate that a minor enriched component disproportionately contributes to thick-plate OIB, but is diluted by high-degree melting in the generation of thin-plate OIB and MORB.
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38

Clark, Alexander J., Ismael Torres-Romero, Madalina Jaggi, Stefano M. Bernasconi et Heather M. Stoll. « A clumped isotope calibration of coccoliths at well-constrained culture temperatures for marine temperature reconstructions ». Climate of the Past 20, no 9 (20 septembre 2024) : 2081–101. http://dx.doi.org/10.5194/cp-20-2081-2024.

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Abstract. Numerous recent studies have tested the clumped isotope (Δ47) thermometer on a variety of biogenic carbonates such as foraminifera and bivalves and showed that most follow a common calibration. However, there may be a difference between biogenic-carbonate-based calibrations and the most recent inorganic carbonate calibrations that are assumed to have formed close to isotopic equilibrium. Biogenic calibrations such as those based on foraminifera from seafloor sediments suffer from uncertainties in the determination of the calcification temperatures. Therefore, well-constrained laboratory cultures without temperature uncertainty can help resolve these discrepancies. Although the sample size requirements for a reliable Δ47 measurement have decreased over the years, the availability and preservation of many biogenic carbonates are still limited and/or require substantial time to be extracted from sediments in sufficient amounts. Coccoliths, on the other hand, are abundant and often well-preserved in sediments, and they are a potential interesting target for palaeoceanography. We thus determined the Δ47–temperature relationship for coccoliths due to their relative ease of growth in the laboratory. The carbon and oxygen isotopic compositions of coccolith calcite have limited use in palaeoenvironmental reconstructions due to physiological effects that cause variability in the carbon and oxygen isotopic fractionation during mineralization. However, the relatively limited data available suggest that clumped isotopes may not be significantly influenced by these effects. We cultured three species of coccolithophores under controlled carbonate system conditions with CO2(aq) concentrations between 5 and 45 µM, pH between 7.9 and 8.6 units, and temperatures between 6 and 27 °C. Our well-constrained results agree with a previous culture study that there are no apparent species- or genus-specific vital effects on the Δ47–temperature relationship in coccolithophores despite significant deviations from equilibrium in the C and O isotopic composition. We find that while varying environmental parameters other than temperature does not have a significant effect on Δ47, changing the parameters yields coccolith Δ47–temperature calibrations that agree within 1.2 ppm. Our coccolith-specific Δ47–temperature calibration with well-constrained temperatures shows a consistent, positive offset of 2–3 °C to the inorganic carbonate calibrations, which point to as yet unknown coccolith-specific disequilibrium effects. Thus, we suggest the use of our coccolith-specific calibration for further coccolith palaeoceanographic studies and that calibrations derived from laboratory-grown biogenic carbonates are desirable to reinforce the confidence of clumped-isotope-based temperature reconstructions in palaeoceanography.
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Sheldon, Nathan D. « Using Carbon Isotope Equilibrium to Screen Pedogenic Carbonate Oxygen Isotopes : Implications for Paleoaltimetry and Paleotectonic Studies ». Geofluids 2018 (10 décembre 2018) : 1–11. http://dx.doi.org/10.1155/2018/5975801.

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Stable isotope compositions of pedogenic carbonates (δ13Ccarb, δ18Ocarb) are widely used in paleoenvironmental and paleoaltimetry studies. At the same time, both in vertical stratigraphic sections and in horizontal transects of single paleosols, significant variability in δ18Ocarb values is observed well in excess of what could reasonably be attributed to elevation changes. Herein, a new screening tool is proposed to establish which pedogenic carbonate δ18Ocarb compositions reflect formation in isotopic equilibrium with environmental conditions through the use of the co-occurring δ13Corg composition of carbonate-occluded or in profile organic matter, where Δ13C = δ13Ccarb – δ13Corg. Based upon 51 modern soils from monsoonal, continental, and Mediterranean moisture regimes, Δ13C = +15.6 ± 1.1‰ (1σ), which closely matches theoretical predictions for carbonates formed at carbon isotope equilibrium through Fickian diffusion. Examples from both disequilibrium and equilibrium cases in the geologic record are examined, and it is shown that previous δ18Ocarb records used to infer Cenozoic uplift in southwestern Montana do not provide any constraint on paleoelevation because >90% of the pedogenic carbonate isotopic compositions are out of equilibrium. Guidelines for future paleoaltimetry studies include collection of both vertical stratigraphic sections and lateral transects, of at least three nodules per horizon, petrographic screening of nodules for diagenesis, collection of at least one independent proxy for paleoclimate or paleovegetation, and screening δ18Ocarb values using Δ13C measured for each paleosol.
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40

Knesel, Kurt M., et Jon P. Davidson. « Isotopic disequilibrium during melting of granite and implications for crustal contamination of magmas ». Geology 24, no 3 (1996) : 243. http://dx.doi.org/10.1130/0091-7613(1996)024<0243:iddmog>2.3.co;2.

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Gonfiantini, Roberto, Staf Valkiers, Philip D. P. Taylor et Paul De Bièvre. « Using isotopic disequilibrium of CO2 to model gas adsorption in mass spectrometric measurements ». International Journal of Mass Spectrometry and Ion Processes 161, no 1-3 (février 1997) : 15–26. http://dx.doi.org/10.1016/s0168-1176(96)04527-2.

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Wilson, Siobhan A., Shaun L. L. Barker, Gregory M. Dipple et Viorel Atudorei. « Isotopic Disequilibrium during Uptake of Atmospheric CO2into Mine Process Waters : Implications for CO2Sequestration ». Environmental Science & ; Technology 44, no 24 (15 décembre 2010) : 9522–29. http://dx.doi.org/10.1021/es1021125.

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43

Kil, Youngwoo. « Lithium isotopic disequilibrium of minerals in the spinel lherzolite xenoliths from Boeun, Korea ». Journal of Geochemical Exploration 107, no 1 (octobre 2010) : 56–62. http://dx.doi.org/10.1016/j.gexplo.2010.06.006.

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Chen, Lie-Meng, Fang-Zhen Teng, Xie-Yan Song, Rui-Zhong Hu, Song-Yue Yu, Dan Zhu et Jian Kang. « Magnesium isotopic evidence for chemical disequilibrium among cumulus minerals in layered mafic intrusion ». Earth and Planetary Science Letters 487 (avril 2018) : 74–83. http://dx.doi.org/10.1016/j.epsl.2018.01.036.

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45

Davies, Gareth R., et Simone Tommasini. « Isotopic disequilibrium during rapid crustal anatexis : implications for petrogenetic studies of magmatic processes ». Chemical Geology 162, no 2 (janvier 2000) : 169–91. http://dx.doi.org/10.1016/s0009-2541(99)00123-0.

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46

Comparini, E., et M. Ughi. « Initial behaviour of the characteristics in the propagation of isotopic disequilibrium by diffusion ». Mathematical Methods in the Applied Sciences 34, no 13 (6 mai 2011) : 1627–37. http://dx.doi.org/10.1002/mma.1470.

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Mazzone, Peter, et Norman K. Grant. « Mineralogical and isotopic evidence for phenocryst-matrix disequilibrium in the Garner Mountain andesite ». Contributions to Mineralogy and Petrology 99, no 2 (juin 1988) : 267–72. http://dx.doi.org/10.1007/bf00371467.

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Li, Shuguang, Liu Yican, Shutong Xu et Yongfei Zheng. « Effects of retrograde-zoning of garnet on Sm-Nd isotopic dating of eclogite and oxygen isotopic disequilibrium between eclogitic minerals ». Science in China Series B : Chemistry 45, S1 (décembre 2002) : 28–37. http://dx.doi.org/10.1007/bf02932204.

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Smellie, John A. T. « Uranium-series disequilibrium studies of drillcore Km3 from the Kamlunge test-site, northern Sweden ». Mineralogical Magazine 49, no 351 (avril 1985) : 271–79. http://dx.doi.org/10.1180/minmag.1985.049.351.14.

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AbstractStudies of the U decay series (238U-234U-230Th) have been carried out on samples from unaltered bedrock and highly altered fracture/crush zones from drillcore Km3 (Kamlunge test-site). The fracture zones are characterized by abundant iron oxide coatings (hematite and hydroxy iron oxides) resulting from the passage of hydrothermal solutions coeval with the Lina granite intrusion. Enrichments of U and Th, thought to be due to co-precipitation (or preferential sorption) processes together with the iron-oxides, are also present.The isotopic results show that out of a total of twelve rock samples measured, six indicate isotopic disequilibrium mostly due to unequal depletions of 234U and 238U; one near-surface sample indicated some minor assimilation of U. The major fracture zones generally indicate removal of total U. This has resulted from interaction with groundwaters which are still marginally oxidizing, even at depths of 375 m.Isotopic disequilibrium has occurred within recent geological times, i.e. during the last 0.5 Ma as imposed by the half-lives of 234U and 230Th. In terms of radioactive disposal considerations, the results are important in that: (1) the investigated bedrock environment (100–500 m) is generally reducing; however (2) there is some evidence to indicate that rock/water interactions, leading to the removal of total U, have resulted from the presence of less reducing groundwaters within those large-scale fracture/crush zones which intersect the bedrock surface.
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Jackson, Matthew G., Stanley R. Hart, Nobumichi Shimizu et Jerzy S. Blusztajn. « The87Sr/86Sr and143Nd/144Nd disequilibrium between Polynesian hot spot lavas and the clinopyroxenes they host : Evidence complementing isotopic disequilibrium in melt inclusions ». Geochemistry, Geophysics, Geosystems 10, no 3 (mars 2009) : n/a. http://dx.doi.org/10.1029/2008gc002324.

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