HR: 14:25h
AN: A42D-04    [PDF]
TI: Towards A New Air-CO2 Isotopic Scale Based On Air Reference Material Generated From Carbonates
AU: * Ghosh, P
EM: pghosh@bgc-jena.mpg.de
AF: Stable Isotope Laboratory Max-Planck-Institute for Biogeochemistry, Hans-Knell-Strasse 10,, Jena, 07745 Germany
AU: Brand, W A
EM: wbrand@bgc-jena.mpg.de
AF: Stable Isotope Laboratory Max-Planck-Institute for Biogeochemistry, Hans-Knell-Strasse 10,, Jena, 07745 Germany
AB: Carbon and oxygen stable isotope ratios of atmospheric carbon dioxide provide important, independent information about carbon sources and sinks. Combined with CO2 mole fraction measurements, 13CO2 measurements can be used to quantitatively separate fluxes between atmosphere and terrestrial biosphere from fluxes between atmosphere and ocean. Highly precise and accurate isotopic data are needed for deriving accurate flux information using inverse modeling. For example, a change of just 0.02 % in 13C translates into an equivalent of 1.0 x 109 metric tons of carbon in models of surface fluxes. Such high degree of precision is possible, provided different laboratories agree on a common scale. Existing practice of using a carbonate reference material (NBS19) to unify scales has shown inadequate to this process in the past. Instead, CO2 admixture to CO2-free air where the CO2 is generated from a carbonate similar to NBS-19 in composition and texture has been proposed. We describe here an acid reaction and air mixing station (ARAMIX) setup at the Max Planck Institute for Biogeochemistry which is capable to introduce CO at ambient levels into an air mixture (without CO2) at the required precision level. This mixing station is used for generating CO2 by a conventional acid reaction ( at 47 C the carbonate powder is reacted with pure ortho-phosphoric acid) and mixing the reaction gas with synthetic air. The mixture is distributed into several glass flasks (5l volume, 1.6 bar) attached to the system. Such flask air samples were measured using two different extraction / mass spectrometer systems established previously in the Jena isotope facility. Using the same protocol we have generated CO2-in-air mixtures from NBS-19 and other internationally available carbonate standards for assigning isotopic values to our new carbonate reference material (MAR J1). The isotopic record in a number of batches prepared over months will be discussed. In addition, the relationship with existing CO2-in-air scales (e.g. CG-99, based on a pure CO2 gas) have been evaluated by direct CO2 admixture to synthetic air using the same setup.
DE: 4806 Carbon cycling
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting