CO₂ record between 40 and 8 kyr B.P. from the Greenland Ice Core Project ice core

Abstract

CO 2 ice‐core records show an increase in the atmospheric concentration of 80–100 parts per million by volume (ppmv) from the last glacial maximum (LGM) to the early Holocene. We present CO 2 measurements performed on an ice core from central Greenland, drilled during the Greenland Ice Core Project (GRIP). This CO 2 profile from GRIP confirms the most prominent CO 2 increase from the LGM, with a mean concentration of 200 ppmv, to the early Holocene with concentrations between 290 and 310 ppmv. Some structures of the new CO 2 record are similar to those previously obtained from the Dye 3 ice core (Greenland), which indicated a dilemma between Greenland and Antarctic CO 2 records [ Oeschger et al ., 1988]. Both Greenland cores show high CO 2 values for rather mild climatic periods during the last glaciation, whereas CO 2 records from Antarctica do not show such high CO 2 variations during the glaciation and, furthermore, the CO 2 values in the early Holocene are about 20–30 ppmv higher in the GRIP record than in Antarctic records. There is some evidence that the difference could be due to chemical reactions between impurities in the ice leading to an increase of the CO 2 concentration under certain conditions. If in situ processes can change the CO 2 concentration in the air bubbles, the question arises about how reliably do CO 2 records from ice cores reflect the atmospheric composition at the time of ice formation. The discrepancies between the CO 2 profiles from Greenland and Antarctica can be explained by in situ production of excess CO 2 due to interactions between carbonate and acidic species. Since the carbonate concentration in Antarctic ice is much lower than in Greenland ice, CO 2 records from Antarctica are much less affected by such in situ‐produced CO 2 .