Atmospheric Δ¹⁴CO₂ trend in Western European background air from 2000 to 2012

Long-term measurements of atmospheric Δ¹⁴CO₂ from two monitoring stations, one in the European Alps (Jungfraujoch, Switzerland) and the other in the Black Forest (Schauinsland, Germany), are presented. Both records show a steady decrease, changing from about 6‰ per year at the beginning of the century to only 3‰ per year on average in the last 4 yr. A significant seasonal variation of Δ¹⁴CO₂ is observed at both sites with maxima during late summer and minima in late winter/early spring. While the Δ¹⁴C maxima are similar at Jungfraujoch and Schauinsland, the minima at Schauinsland are lower by up to 10‰, due to a larger influence from ¹⁴C-free fossil fuel CO₂ emissions in the footprint of the Schauinsland station in winter. Summer mean Δ¹⁴C values at Schauinsland are considered best suited as input for studies of biospheric carbon cycling in mid-northern latitudes or for dating of organic material of the last half century.