Ice core record of the 13C/12C ratio of atmospheric CO2 in the past two centuries

The release of carbon into the atmosphere due to the activities of humans has caused an increase in concentration as well as a change in the isotopic composition of atmospheric carbon dioxide. CO2 derived from fossil fuel combustion and from biomass destruction have δ13C values of ∼−25‰ (compared to the atmospheric value of ∼−7‰) and are thus depleted in 13C. We have measured δ13C of CO2 separated from air trapped in bubbles in ice samples from an ice core taken at Siple Station in Antarctica, in which it has been possible to demonstrate the atmospheric increase of CO2 (ref. 1) and methane2 with high time resolution. The isotopic results, together with the CO2 record from the same ice core, yield information on the sources of excess carbon dioxide and provide a data base for testing the consistency of global carbon cycle models