Twenty years of atmospheric 14CO2 observations at Schauinsland station, Germany

We present and discuss quasi-continuous long-term (CO2)-C-14 observations from the continental background station Schauinsland (48 degrees N, 8 degrees E, 1205 m asl, Black Forest, southern Germany). The observed steady decline of atmospheric (CO2)-C-14 from 1977 to 1996 can be described by a single exponential function with an e-folding time of(16.3 +/- 0.2) yr. Summer means (May to August) in atmospheric (CO2)-C-14 at Schauinsland compare within Delta(14)C = +/-4 parts per thousand with measurements made on individual rings from a tree grown in the near vicinity of the Schauinsland site. Both data sets are slightly depleted by up to 5 parts per thousand if compared to maritime background measurements of atmospheric (1)4CO(2) made at Izana, Tenerife. This is due to the influence of fossil fuel CO2 emissions over the European continent as well as generally in mid latitudes of the Northern Hemisphere. delta(13)C analyses from the Schauinsland samples show mean seasonal variations with an amplitude of +/-0.4 parts per thousand, caused by atmosphere-biosphere exchange, and a mean decrease from 1977 to 1996 of delta(13)C = -0.017 parts per thousand yr(-1). This trend is mainly due to an increasing quantity of fossil fuel CO2 in the atmosphere, depleted in C-13/C-12 ratio, and compares well to trends measured at other stations in mid-to-high northern latitudes.