Atmospheric Delta (CO2)-C-14 trend in Western European background air from 2000 to 2012

Long-term measurements of atmospheric Delta(CO2)-C-14 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 parts per thousand per year at the beginning of the century to only 3 parts per thousand per year on average in the last 4 yr. A significant seasonal variation of Delta(CO2)-C-14 is observed at both sites with maxima during late summer and minima in late winter/early spring. While the Delta C-14 maxima are similar at Jungfraujoch and Schauinsland, the minima at Schauinsland are lower by up to 10 parts per thousand, due to a larger influence from Delta(14) C-free fossil fuel CO2 emissions in the footprint of the Schauinsland station in winter. Summer mean Delta C-14 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.