David L. Dettman escribis:
> One of our students is working on the stable isotope ratios of carbonate
> dust blowing around Tucson. One of the issues involved is alteration of the
> original composition through interaction of this very fine carbonate powder
> with atmospheric water vapor and CO2. It is well known in the 14C community
> that fine grain carbonate powder will pick up modern CO2 and give anomalous
> ages. This got me to thinking about the old standard NBS-20 and whether
> interaction with atmosphere can result in measurable shifts in either d13C
> or d18O. Can anyone describe the problems that led to the abandonment of
> NBS-20? Did the increased variability (or trend in composition) show up in
> oxygen or in carbon or both?
> Throughout the 1980s we used NBS-20 at the Univ. of Michigan. The
> original supply was split into small amounts and each was sealed and stored
> in a desiccator. We never saw any drift in its measured composition.
> Many thanks,
> David Dettman
>
> David Dettman [log in to unmask]
> Dept. of Geosciences ph. (520) 621-4618
> Univ. of Arizona FAX (520) 621-2672
> Gould-Simpson Bldg.
> Tucson, AZ 85721