Stable-Isotope Ratios and Concentration of CO2in Air from Polar Ice Cores

Abstract

Analyses of air trapped in an ice core from the South Pole indicate that the CO2concentration may have increased by about 10 ppm and that the13C/12C ratio decreased slightly in the thirteenth century. These changes, if really of atmospheric origin, must be due to a significant input into the atmosphere of CO2, either of biogenic or of oceanic origin.18O/16O ratios in CO2from different ice cores are much lower than those which have been observed in atmospheric carbon dioxide. A possible explanation is that the CO2has equilibrated isotopically with the ice. We have calculated equilibrium isotope-fractionation factors between ice and carbon dioxide and found that the observed18O/16O ratios of CO2are indeed near isotopic equilibrium with the ice. This indicates that an exchange of oxygen atoms probably occurs between ice and included CO2.