Determination of O-16 and O-18 abundance ratios in natural carbon dioxide reservoirs

A mathematical formalism is presented that, based on the relative proportio ns of the O-18/O-16-distinctive CO2 species (CO2)-O-16, (COO)-O-16-O-18, an d (CO2)-O-18 in a given CO2 pool, allows the calculation of O-18/O-16 ratio s for the two different oxygen positions in the CO2 molecules of this parti cular pool. The quantities of the isotopically distinctive CO2 species can be determined as mass peak intensities I-44 (for C16O(2)), I-46 (for (COO)- O-16-O-18), and I-48 (for (CO2)-O-18) by suitable adaptations of convention al mass spectrometric techniques. The delta O-18((1,2)) values obtained for each of the above positions furnish information as to either a probabilist ic ("homogeneous"; with delta O-18((1))=delta O-18((2))) or a nonprobabilis tic ("nonhomogeneous") O-18/O-16 distribution (with delta (18)O((1))not equ al delta O-18((2))) in the respective CO2 pool. Using delta O-18((1,2),) we may consequently obtain information pertaining to the oxygen sources of th e CO2 molecules in the pool as well as to reservoir changes reflected by di fferential diffusion rates of the isotopically distinctive CO2 species that have left and entered the reservoir. This approach may become potentially important for an assessment of the sources and the reservoir dynamics of th e atmospheric CO2 pool. (C) 2000 Elsevier Science B.V.