Processes affecting the CO2 concentrations measured in Greenland ice

Detailed CO 2 measurements on ice cores from Greenland and Antarctica show different mean CO 2 concentrations for samples at the same gas age. The deviation between Antarctic and Greenland CO 2 records raises up to 20 ppmv during the last millennium. Based on the present knowledge of the global carbon cycle we can exclude such a high mean interhemispheric difference of the CO 2 concentration between high northern and southern latitudes. Diffusive mixing of the air in the firn smoothes out short term variations of the atmospheric CO 2 Concentration. Nevertheless, we observe short term CO 2 variations in Greenland ice in the range of 10–20 ppmv, which cannot represent atmospheric CO 2 variations. Due to the low temperature at Summit, meltlayers can be excluded for most of the ice and they cannot account for the frequent anomalous short term CO 2 variations and the elevated mean CO 2 concentration in the Greenland ice. In this work we give some clues, that in situ production of CO 2 in Greenland ice could build up excess CO 2 after pore close of. Possible chemical reactions are the oxidation of organic carbon and the reaction between acidity and carbonate. We conclude that the carbonate-acidity reaction is the most probable process to explain the excess CO 2 in the bubbles. The reaction could take place in very small liquid-like veins in cold ice, where the mobility of impurities is higher than in the ice lattice. At present, there exists no technique to measure the carbonate concentration in the ice directly. However, a comparison of CO 2 analyses performed with a dry- and a wet-extraction technique allows to estimate the carbonate content of the ice. This estimate indicates a carbonate concentration in Greenland ice of about 0.4 ± 0.2 µ mol/l and a much lower concentration in Antarctic ice. DOI: 10.1034/j.1600-0889.47.issue4.6.x

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