Dataset Information

Statistical clumped isotope signatures.

ABSTRACT: High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (?average) isotopic composition of the involved atoms. We show here that this referencing convention leads to apparent negative clumped isotope anomalies (anti-clumping) when the indistinguishable atoms originate from isotopically different populations. Such statistical clumped isotope anomalies must occur in any system where two or more indistinguishable atoms of the same element, but with different isotopic composition, combine in a molecule. The size of the anti-clumping signal is closely related to the difference of the initial isotope ratios of the indistinguishable atoms that have combined. Therefore, a measured statistical clumped isotope anomaly, relative to an expected (e.g. thermodynamical) clumped isotope composition, may allow assessment of the heterogeneity of the isotopic pools of atoms that are the substrate for formation of molecules.

SUBMITTER: Rockmann T

PROVIDER: S-EPMC4989146 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Statistical clumped isotope signatures.

Röckmann T T Popa M E ME Krol M C MC Hofmann M E G ME

Scientific reports 20160818

High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (≈average) isotopic compos ...[more]

PMID: 27535168

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Project description:RationaleClumped isotope geochemistry examines the pairing or clumping of heavy isotopes in molecules and provides information about the thermodynamic and kinetic controls on their formation. The first clumped isotope measurements of carbonate minerals were first published 15 years ago, and since then, interlaboratory offsets have been observed, and laboratory and community practices for measurement, data analysis, and instrumentation have evolved. Here we briefly review historical and recent developments for measurements, share Tripati Lab practices for four different instrument configurations, test a recently published proposal for carbonate-based standardization on multiple instruments using multi-year data sets, and report values for 21 different carbonate standards that allow for recalculations of previously published data sets.MethodsWe examine data from 4628 standard measurements on Thermo MAT 253 and Nu Perspective IS mass spectrometers, using a common acid bath (90°C) and small-sample (70°C) individual reaction vessels. Each configuration was investigated by treating some standards as anchors (working standards) and the remainder as unknowns (consistency standards).ResultsWe show that different acid digestion systems and mass spectrometer models yield indistinguishable results when instrument drift is well characterized. For linearity correction, mixed gas-and-carbonate standardization or carbonate-only standardization yields similar results. No difference is observed in the use of three or eight working standards for the construction of transfer functions.ConclusionsWe show that all configurations yield similar results if instrument drift is robustly characterized and validate a recent proposal for carbonate-based standardization using large multiyear data sets. Δ47 values are reported for 21 carbonate standards on both the absolute reference frame (ARF; also refered to as the Carbon Dioxide Equilibrated Scale or CDES) and the new InterCarb-Carbon Dioxide Equilibrium Scale (I-CDES) reference frame, facilitating intercomparison of data from a diversity of labs and instrument configurations and restandardization of a broad range of sample sets between 2006, when the first carbonate measurements were published, and the present.

Dataset Information

Statistical clumped isotope signatures.

Publications

Statistical clumped isotope signatures.

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