Isotopic composition of atmospheric O2 in ice linked with deglaciation and global primary productivity

International audienceIn photosynthesis, O2 is continuously formed from H2O and released to the atmosphere. Coupled with respiration, photosynthesis forms a loop in which oxygen isotopes are exchanged between O2 and H2O. During the ice ages, sea water was enriched in δ18O by ∼1.3‰ relative to the present value1. Continental waters in the areas of high primary productivity exchange rapidly with the oceans. They probably presented a similar isotopic enrichment. Since the δ18O of glacial water was greater than at present, we would expect that the δ18O of atmospheric O2 was also greater than at present. Fireman and Norris2 and Horibe et al.3 have measured the δ18O of O2 from the glacial atmosphere by analysing trapped gases in ice cores. However, their data are either too few or too imprecise to demonstrate whether δ18O of atmospheric O2 has, in fact, varied. Here we present data on the changes, during the past 22 kyr approximately, in the δ18O of atmospheric O2 trapped in the ice core Dome C (East Antarctica, 74° S, 124° E). The results show that the isotopic composition of atmospheric O2 has indeed varied along with that of sea water, and that the δ18O (O2) record offers a tool for studying several important aspects of the global cycles of O2 and H2O in relation to the climate