Estimating the Amount of 14 CO 2 in the Atmosphere During the Holocene and Glacial Periods

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