12]C relative to the PeeDee belemnite
standard--was completed on each sample with an isotope ratioing mass spectrometer as described by Read et al.
2]) were introduced into a Finnigan Delta C mass spectrometer, and the isotopic composition was quantified relative to a standard reference material: carbon in the PeeDee Belemnite
and molecular nitrogen gas in the air.
where X = sample; and S = the marine carbonate standard Vienna Peedee belemnite
, VPDB (Gao et al.
Data were expressed as the ratio of (13)C/(12)C relative to the PeeDee belemnite
standard and converted to [Delta] as described by Farquhar et al.
Stable isotope determinations were expressed as the permille difference from the international PeeDee Belemnite
standard, where [[Delta].
The isotopic composition of a carbon compound is expressed as [Delta]13C, the proportional deviation of the 13C/12C ratio from the internationally accepted Peedee belemnite
(PDB) carbonate standard (Craig 1957):
18]O value relative to the international reference standard of Vienna PeeDee Belemnite
(VPDB) in [per thousand], where