Information on the CO2 Cycle from Ice Core Studies

Information on the history of the atmospheric CO 2 content and the 13 C/ 12 and 14 C/C ratios is recorded in natural ice. Measurements on samples from very cold accumulation regions show that CO 2 is occluded not only in air bubbles, but also in the ice lattice. The two CO 2 components are of similar size. It is very difficult to measure CO 2 in the bubbles and CO 2 in the ice lattice separately. By melting the samples and extracting the evolving gases in two fractions, it is possible to estimate CO 2 concentration in the bubbles and the ice lattice. Enrichment or depletion of CO 2 in the bubbles by exchange with the ice is difficult to estimate. Information about this effect is expected from 13 C/ 12 C analysis on the extracted CO 2 fractions. To investigate whether atmospheric CO 2 content was different during the last glaciation than during the present one, sets of 16 and 20 samples distributed over the last 40,000 years from the two deep ice cores from Camp Century (North Greenland) and Byrd Station (West Antarctica) were measured. The time scales for the two cores are based on a rheological model. Results and conclusions are: — The data series from both cores show similar trends correlated to a certain degree to the δ 18 O profiles. — For both cores, the values for the CO 2 concentration of the first fraction, considered to best represent the atmospheric composition, show lower values during glaciation than in the Holocene, with a minimum before the end of glaciation. — Low CO 2 concentrations in the first fractions (200ppm) of certain samples are a strong indication that the atmospheric CO 2 concentration during last glaciation was lower than during the postglacial. These low concentrations indicate that, at that time, CO 2 concentration in the atmosphere could have been lower than today by a factor of 1.5. Possible explanations for such a change in atmospheric CO 2 content as well as its influence on atmospheric 14 C/C ratio and on the radiation balance is discussed.