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

1997, Journal of Geophysical Research

CO2 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 CO2 measurements performed 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 ppmv. Some structures of the new CO2 record are similar to those previously obtained from the Dye 3 ice core (Greenland), which indicated • dilemm• between Greenland •nd Antarctic CO2 records [Oeschger et al., 1988]. Both Greenland cores show high CO2 values for rather mild climatic periods during the last glaciation, whereas CO2 records from Antarctica do not show such high CO2 variations during the glaciation and, furthermore, the CO2 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 CO2 concentration under certain conditions. If in situ processes can change the CO2 concentration 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 from Greenland and Antarctica can be explained by in situ production of excess CO2 due to interactions between carbonate and acidic species. Since 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. ing the Holocene, pronounced differences occur between Antarctic and Greenland CO2 records during periods of the glaciation between 20 and 40 kyr B.P., where the CO2 profile from Dye 3 (Greenland) shows several fast variations of the order of 50 parts per million per volume (ppmv), while the Byrd and Vostok fluctuations of no more than 20 ppmv. If both profiles would reflect unadulterated atmospheric concentrations, then this implies an interhemispheric difference up to about 50 ppmv during certain periods. On the basis of the present knowledge of the atmospheric carbon cycle, such large interhemispheric concentration differences can be excluded. High CO2 values found in the Dye 3 core between 20 and 40 kyr B.P. are parallel with mild climatic periods, the so-called Dansgaard-Oeschger events. One possible explanation for the high CO2 concentration during the Dansgaard-Oeschger events in the Dye 3 core is melt layers, which contain air considerably enriched in CO2 [Neftel et el., 1982]. It was one of the important goals of the Greenland Ice Core Project (GRIP) to solve the CO2dilemma mentioned by Oeschger et el. [1988]. The above explanation is not very likely because the new drill site at Summit (central Greenland) was selected also due to its current low mean annual temperature 26,539 26,540