ESTIMATING THE AMOUNT OF 14CO2 IN THE ATMOSPHERE DURING THE HOLOCENE AND GLACIAL PERIODS

Radiocarbon has been used to define parameters for modeling past, recent, and future CO2/carbon amounts in the atmosphere and in other environmental compartments. In the present paper, we estimate the amount of C-14 in the atmosphere by calculating the molar activity of (CO2)-C-14 (quantity of (CO2)-C-14 molecules per mol of air). Data on the reconstruction of the past concentration of atmospheric CO2 from Antarctic ice cores and Delta C-14 activities from the IntCal09 calibration curve were applied. The results obtained indicate that cosmogenic production had a dominant influence on the C-14 amount in the atmosphere between 50 and 20 ka BP, when the CO2 concentrations were relatively stable, with a slowly decreasing trend. The decreasing C-14 activity (Delta C-14) between 20 and 2 ka BP seems to be caused predominantly by a dilution of atmospheric (CO2)-C-14 by input of CO2 with a depleted amount of C-14 (probably from deeper oceanic layers), which is evident from a comparison with the Delta C-14 and molar activity time series. A strong linear relation was found between the C-14 activity and CO2 concentration in the air for the period 20-2 ka BP, which confirms a dominant influence of atmospheric dilution of (CO2)-C-14. The observed linear relation between the CO2 and Delta C-14 levels persists even in the prevailing part of the Holocene. Likewise, the quantity of (CO2)-C-14 in the atmosphere (calculated as molar activity) during the prevailing part of the deglacial period (20-11 ka BP) was surprisingly increasing, although a decreasing trend in the C-14 cosmogenic production rate could be expected.