New guidelines for delta C-13 measurements

Consistency of delta C-13 measurements can be improved 39-47% by anchoring the delta C-13 scale with two isotopic reference materials differing substantially in C-13/C-12. It is recommended that delta C-13 values of both organic and inorganic materials be measured and expressed relative to VPDB (Vienna Peedee belemnite) on a scale normalized by assigning consensus values of -46.6 parts per thousand to L-SVEC lithium carbonate and +1.95 parts per thousand to NBS 19 calcium carbonate. Uncertainties of other reference material values on this scale are improved by factors up to two or more, and the values of some have been notably shifted: the delta C-13 of NBS 22 oil is -30.03 parts per thousand