CO2 RECORD BETWEEN 40 AND 8 KYR BP FROM THE GREENLAND ICE CORE PROJECT ICE CORE

CO2 ice-core records show an increase in the atmospheric concentration of 80-100 parts per million by volume (ppmv) from the last glacial ma ximum (LGM) to the early Holocene. We present CO2 measurements perform ed on an ice core from central Greenland, drilled during the Greenland Ice Core Project (GRIP). This CO2 profile from GRIP confirms the most prominent CO2 increase from the LGM, with a mean concentration of 200 ppmv, to the early Holocene with concentrations between 290 and 310 p pmv. Some structures of the new CO2 record are similar to those previo usly obtained from the Dye 3 ice core (Greenland), which indicated a d ilemma between Greenland and Antarctic CO2 records [Oeschger et al., 1 988]. Both Greenland cores show high CO2 values for rather mild climat ic periods during the last glaciation, whereas CO2 records from Antarc tica do not show such high CO2 variations during the glaciation and, f urthermore, the CO2 values in the early Holocene are about 20-30 ppmv higher in the GRIP record than in Antarctic records. There is some evi dence that the difference could be due to chemical reactions between i mpurities in the ice leading to an increase of the CO2 concentration u nder certain conditions. If in situ processes can change the CO2 conce ntration in the air bubbles, the question arises about how reliably do CO2 records from ice cores reflect the atmospheric composition at the time of ice formation. The discrepancies between the CO2 profiles fro m Greenland and Antarctica can be explained by in situ production of e xcess CO2 due to interactions between carbonate and acidic species. Si nce the carbonate concentration in Antarctic ice is much lower than in Greenland ice, CO2 records from Antarctica are much less affected by such in situ-produced CO2.