25 Years of Tropospheric 14C Observations in Central Europe

A long-term mountain station series of tropospheric 14 C data for the period 1959 to 1984 is presented. This series is considered representative of the higher altitude 14 C level over central Europe. Even tree-ring 14 C levels from a rural ground level site in southern Germany are consistently lower (by Δ 14 C depression = −15‰ if compared with the mountain station summer average in atmospheric CO 2 ). The rural tree-ring series is considered to represent the additional continental Suess effect at ground level without local contamination. This Suess effect decreases gradually with the distance from the ground ( ie , source) level. We therefore estimate the additional continental Suess effect in the vegetation period to be Δ 14 C depression = −5‰ for the mountain station and −20‰) for a rural ground level site, respectively. Based on this assumption, yearly mean tropospheric 14 C levels corrected for fossil fuel contamination and representative of the Northern Hemisphere are provided for use in global carbon cycle models.