Controls on Sr isotopic evolution in lacustrine systems: Eocene green river formation, Wyoming
Amalia C. DoebbertClark M. JohnsonAlan R. CarrollBrian L. BeardJeffrey T. PietrasMeredith K. RhodesBrooke Ann NorstedL. Ashley Throckmorton
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Green River Formation
δ18O
δ18O
Carbon fibers
Isotope Analysis
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The stable isotope change in the Yamzho Lake Basin is discussed based on the observed results of stable isotope of precipitation,river and lake water in 2004 and on the stable isotope fractionation model in a closed lake.This study shows that the present-5.9‰ of Yamzho Lake δ18O is related to the eventual steady lake δ18O after evaporation enrichment under the relative humidity of around 54%~58%.It is also found that the input δ18O to the closed lake has also affected the eventual δ18O after evaporation enrichment.However,the impact of the lake water temperature has little effect on the steady lake δ18O.The lake itself has a strong adjustment to the input δ18O change.For the large change of input δ18O,the Yamzho Lake δ18O can reach another steady state in less than 50 years.
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Water cycle
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Stable isotopic composition of fossil ostracode is used as an ideal proxy for paleo-lake sedimentary environments.Over the last three decades,measurements of the δ13C and δ18O values of ostracode shells have been extensively used in lake palaeoenvironmental reconstruction.Many methods for sample preparation have been applied in stable isotope measurements of ostracode shells from lake sediments.However,for stable isotope measurements of biocarbonate samples,different methods will probably affect the resolution,reproducibility and inter-laboratory comparison of the measurement results.In this paper,previous methods of sample preparation for biocarbonate isotopic measurements are compared,with their effects on δ13C and δ18O analyses evaluated.The results suggest that different methods will not result in remarkable differences in δ13C and δ18O measurements of lake ostracode shells.Therefore,sample cleaning procedure is considered unnecessary for such analyses.
δ18O
Isotopic ratio
Isotope Analysis
Proxy (statistics)
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The δ2H and δ18O values in water bodies are essential to the management of water resources because of the ability to insight into hydrological processes. In this study, we have measured and analyzed the major ions (Na+, K+, Ca2+, Mg2+, Cl–, SO24– and HCO–3 ) and stable H-O isotopes (δ2H and δ18O) for fifteen surface water samples collected from the Xinbian River in Suzhou, northern Anhui Province, China. The results show that all of the water samples are classified to be Na-HCO3 type, and the mean values of δ2H and δ18O are –42.93‰ and –5.36‰, respectively. Gibbs diagram and the relationship between δ2H and δ18O indicate that both water chemistry and stable isotopes in river water are mainly controlled by evaporation. Correlation analysis reveals that a significant correlation between major ions and δ18O. Predictors (K+, SO24– and HCO–3 ) have been selected by optimal subset regression analysis were used to model the δ18O values in the river water. Moreover, the residuals of the model were normally distributed and values between –0.2‰ to 0.2‰ for most water samples, suggesting a strong relationship between the observed and predicted δ18O values.
δ18O
Isotope Analysis
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Ostracod
δ18O
Authigenic
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Using the MUGCM simulations,the variation features of stable isotopes in precipitation,amount effect and relationship between δD and δ18O,on the diurnal,monthly and yearly time scales in Yunnan Province,China,are analyzed.There is significant amount effect for the isotopes in precipitation,whether on the diurnal time scale or on the monthly or the yearly time scales.Compared with the measured values,the simulated δ18O in precipitation shows the stronger correlation with precipitation.For the single station,the local meteoric water line(LMWL) is simulated well at Mengzi and Tengchong,however at Simao and Kunming,the simulated results do not reproduce truly the measured relationship between δD and δ18O in precipitation with the higher LMWL slopes,which implies that the model may overestimate the depletion of the HDO over such a particular areas like Yunnan.
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Diurnal temperature variation
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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 crystallization 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 to 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.
Disequilibrium
δ18O
Equilibrium fractionation
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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.
Disequilibrium
δ18O
Equilibrium fractionation
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