Calcite‐CO₂ mixed into CO₂‐free air: a new CO₂‐in‐air stable isotope reference material for the VPDB scale

Abstract

In order to generate a reliable and long-lasting stable isotope ratio standard for CO 2 in samples of clean air, CO 2 is liberated from well-characterized carbonate material and mixed with CO 2 -free air. For this purpose a dedicated acid reaction and air mixing system (ARAMIS) was designed. In the system, CO 2 is generated by a conventional acid digestion of powdered carbonate. Evolved CO 2 gas is mixed and equilibrated with a prefabricated gas comprised of N 2 , O 2 , Ar, and N 2 O at close to ambient air concentrations. Distribution into glass flasks is made stepwise in a highly controlled fashion. The isotopic composition, established on automated extraction/measurement systems, varied within very small margins of error appropriate for high-precision air-CO 2 work (about AE0.015% for d 13 C and AE0.025% for d18 O). To establish a valid d 18O relation to the VPDB scale, the temperature dependence of the reaction between 25 and 478C has been determined with a high level of precision. Using identical procedures, CO 2 -in-air mixtures were generated from a selection of reference materials; (1) the material defining the VPDB isotope scale (NBS 19, d To quantitatively control the extent of isotope-scale contraction in the system during mass spectrometric measurement other available international and local carbonate reference materials (L-SVEC, IAEA-CO-1, IAEA-CO-8, CAL-1 and CAL-2) were also processed. As a further control pure CO 2 reference gases (Narcis I and II, NIST-RM 8563, GS19 and GS20) were mixed with CO 2 -free synthetic air. Independently, the pure CO 2 gases were measured on the dual inlet systems of the same mass spectrometers. The isotopic record of a large number of independent batches prepared over the course of several months is presented. In addition, the relationship with other implementations of the VPDB-scale for CO 2 -in-air (e.g. CG-99, based on calibration of pure CO 2 gas) has been carefully established. The systematic high-precision comparison of secondary carbonate and CO 2 reference materials covering a wide range in isotopic composition revealed that assigned d-values may be (slightly) in error. Measurements in this work deviate systematically from assigned values, roughly scaling with isotopic distance from NBS 19. This finding indicates that a scale contraction effect could have biased the consensus results. The observation also underlines the importance of cross-contamination errors for high-precision isotope ratio measurements.As a result of the experiments, a new standard reference material (SRM), which consists of two 5-L glass flasks containing air at 1.6 bar and the CO 2 evolved from two different carbonate materials, is available for distribution. These 'J-RAS' SRM flasks ('Jena-Reference Air Set') are designed to serve as a high-precision link to VPDB for improving inter-laboratory comparability.a CopyrightThe isotopic composition and concentration of CO 2 in atmospheric air are useful parameters, required for deriving carbon-flux information between atmospheric, terrestrial, ...

Jena Reference Air Set (JRAS): a multi-point scale anchor for isotope measurements of CO<sub>2</sub> in air

“…The first of the two calcites, MAR-J1, with δ 13 C VPDB ∼ +2 ‰, has characteristics (isotopic composition, trace elements, grain size) that are almost identical to NBS 19, the primary scale anchor for Vienna Pee Dee Belemnite (VPDB). The second calcite, OMC-J1, is also similar to NBS 19, but not as close as MAR-J1 (see Ghosh et al, 2005). It was chosen as a compromise after a long and unsuccessful search for an ideal candidate to serve as a second anchor point to the VPDB isotope scale.…”

“…It was chosen as a compromise after a long and unsuccessful search for an ideal candidate to serve as a second anchor point to the VPDB isotope scale. Ideally, this point should be close to that of atmospheric CO 2 ; however, OMC-J1 provides an adequate range between the two anchor points with a δ 13 C value of about −4 ‰ on the VPDB scale (Ghosh et al, 2005).…”

Atomic weights of the elements 2005 (IUPAC Technical Report)

“…L-SVEC lithium carbonate (NIST RM 8545) was selected as the low-13 C content scale anchor because EA δ 13 C values of amounts as small as 0.3 mg are statistically identical and carbonates are easily prepared for analysis using H 3 PO 4 . L-SVEC was assigned a δ 13 C consensus value of -46.6 ‰ based on high accuracy measurements [32].…”

“…Recommended δ 13 C values (on a scale anchored by L-SVEC equals -46.6 ‰) were determined for three CO 2 gases (NIST RM 8562, RM 8563, and RM 8564) and three calcium carbonate reference materials (IAEA-CO-1, IAEA-CO-8, and NBS 18) because high-quality data were available [27,32]. Uncertainties of reference material values on this scale are improved by factors up to two or more (Fig.…”

Prerequisites for application of hyperbolic relaxed eddy accumulation on managed grasslands and alternative net ecosystem exchange flux partitioning

“…This, as well as the CO 2 mixing ratio analysis, were accomplished in the isotope and trace gas laboratory of the Max Planck Institute in Jena, Germany. All 13 C isotopic signatures in this study were analyzed in relation to 13 C isotopic abundances in the international standards VPDB (Vienna Pee Dee Belemnite; Brand et al, 2009;Wendeberg et al, 2011;JRAS scale;Ghosh et al, 2005;Wendeberg et al, 2011). The precision in the laboratory of 0.012 ‰ for δ 13 C (for more detailed information about the laboratory analysis see Werner et al, 2001), the application of a hyperbolic deadband (hyperbolic relaxed eddy accumulation, HREA; Bowling et al, 1999b) and comprehensive REA system and component laboratory tests made the resolution of up-and downdraft isotope ratio and mixing ratio differences possible, and consequently the determination of δ 13 C isofluxes (Wichura, 2009;Ruppert et al, 2012).…”