Variation of atmospheric 14 CO 2 and its spatial distribution

The atmospheric CO is usually presented in the Δ C notation, which cannot reflect its absolute quantity change. This article presents the atmospheric radiocarbon activity concentrations (a , reported in mBq/m ) in recent years at nine observation stations. The a at Schauinsland decrease from 1977 to 1993 but between 1993 and 2003 keeps at a relative steady state. Atmospheric a s were higher in the northern hemisphere than that in the southern hemisphere. The a s in the northern hemisphere show clear seasonal cycle with higher value in winter and lower value in summer, while this seasonality is not obvious in the southern hemisphere. Vegetation plays as a role of sink in summer and a role of source in winter, and atmosphere-biosphere radiocarbon exchange might be the main driver of the a s seasonality. The annual mean a s in both hemispheres show slightly increasing trends since 2002, which may be mainly caused by decreasing air-sea C flux as the air-sea C gradient decline.