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1.2-1 Methods in Geochemistry and Mineralogy
Time: 14/Sept/2022: 10:30am-12:45pm · Location: A1
Topics: 1.2 Methods in Geochemistry and Mineralogy
A new approach for high-precision triple oxygen isotope analyses of CO2
Universität Göttingen, Germany
1. A. Pack and D. Herwartz, The triple oxygen isotope composition of the Earth mantle and understanding Δ17O variations in terrestrial rocks and minerals. Earth Planet. Sci. Lett. 390, 138-145 (2014).
2. E. Barkan and B. Luz, High precision measurements of 17O/16O and 18O/16O ratios in H2O. Rapid Commun. Mass Spectrom. 19, 3737-3742 (2005).
3. G. A. Adnew, et al., Determination of the triple oxygen and carbon isotopic composition of CO2 from atomic ion fragments formed in the ion source of the 253 Ultra High‐Resolution Isotope Ratio Mass Spectrometer. Rapid Commun. Mass Spectrom. 33, 1363-1380 (2019).
5.5-2 Deciphering past climates and biogeochemical cycles with geochemical proxy archives
Time: 15/Sept/2022: 9:00am-10:15am · Location: A2
Topics: 5.5 Deciphering past climates and biogeochemical cycles with geochemical proxy archives
Isotope fractionation mechanisms involved in carbonate formation revealed by high-precision triple oxygen isotope analyses
1Geowissenschaftliches Zentrum, Georg-August-Universität Göttingen, Goldschmidtstraße 1, 37077 Göttingen, Germany; 2Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicher Str. 49b, 50674 Köln, Germany
The oxygen (δ18O) and clumped (∆47) isotope composition of carbonates are widely used proxies for palaeotemperature. However, Earth surface carbonates are rarely formed in isotope equilibrium but often show oxygen and clumped isotope compositions that do not accurately reflect their crystallisation temperature. Isotopic disequilibrium commonly observed in biogenic carbonates and speleothems is inherited from the dissolved inorganic carbon pool of their parent solutions. A combination of isotope systems, e.g., ∆47–δ18O, ∆47–∆48, can uncover and correct for such kinetic effects .
The analysis of the 17O/16O ratio to the more commonly investigated 18O/16O ratio in carbonates — referred to as the triple oxygen isotope method — expands the traditional oxygen isotope scheme by another dimension and; thereby, allows the identification of fractionation processes involved in carbonate formation. In addition, the triple oxygen isotope method can give insight into the diagenetic history of ancient carbonates and offers the possibility of reconstructing the primary isotope compositions of altered samples .
Here, we report triple oxygen isotope ratios (Δ17O) of various altered and unaltered biogenic (e.g., brachiopods, belemnites) and abiogenic (e.g., speleothems, laboratory precipitates) carbonates. The high-precision measurements were performed on CO2 gas from acid digestion, using tunable infrared laser differential absorption spectrometry (TILDAS) . Based on the results, we will discuss what combination of kinetic isotope fractionation and diagenetic processes could have played a part in the formation of the investigated carbonates.
 Bajnai et al., 2020, Nat Comms;  Wostbrock et al., 2020, GCA;  Pack et al., this conference.
Goldschmidt Lecture 2021 Daniel Herwartz "Beyond isotope proxies: employing triple oxygen isotope systematics in the water cycle and in chemical sediments as quantitative tool"
Time: 15/Sept/2022: 12:15pm-12:45pm · Location: B
Goldschmidt-Lecture | Award 2021
Topics: Plenary Lecture
Beyond isotope proxies: employing triple oxygen isotope systematics in the water cycle and in chemical sediments as quantitative tool
1Univerität zu Köln, Germany; 2Aix Marseille Univ, CNRS, CEREGE, France; 3Georg-August-Universität Göttingen, Germany
Carbonate classic and clumped isotope ratios (δ18O and Δ47) are used to reconstruct paleotemperature. However, kinetic isotope effects (KIE) induce a bias on absolute temperature reconstructions. High precision δ17O measurements provide a refinement proxy to identify the direction and magnitude of KIEs in carbonates. Progress on this new proxy will be discussed.
The basic concept is similar to the combination of conventional oxygen and hydrogen isotope analyses in water. Combined δ18O and δ2H analyses are commonly used to approximate the magnitude of KIEs during evaporation. Triple oxygen isotope measurements in water are now used in a similar fashion. The simultaneous utilization of both trajectories provides a powerful approach to reconstruct quantitative paleoclimate information. We applied this approach to extracted water from ancient gypsum formed in the Atacama Desert and in Cyprus during the Messinian Salinity Crisis. Quantitative information on paleo-humidity and palaeohydrology are obtained. Effectively, this information is derived by quantifying KIE.
In this example, the KIE is related to diffusion of water molecules through air. Other examples of KIE include the breaking of chemical bonds, molecular mixing effects or steady states. Triple oxygen isotope trajectories allow to distinguish between such fundamental processes. Respective concepts will be explained using examples from chert and phosphate triple oxygen isotope systematics.
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