The Schauinsland CO2 record:: 30 years of continental observations and their implications for the variability of the European CO2 budget -: art. no. 4619

[1] Since 1972, the German Environment Agency (UBA) has been measuring continuously CO2 concentration at Schauinsland station (southwest Germany, 1205 m asl). Because of its vicinity to biogenic and anthropogenic sources and sinks, the Schauinsland CO2 record shows considerable variability. In order to remove these disturbances and derive the large-scale representative "background'' CO2 level for the respective area (southwest Germany) we perform rigorous data selection based on wind speed and time of day. During the past 30 years, the selected CO2 mixing ratios increased by 1.47 ppm per year, following the mean trend in midlatitudes of the Northern Hemisphere. The average seasonal cycle (peak to peak) amplitude has decreased slightly from 13.8 +/- 0.6 ppm in the first decade (1972-1981) to 12.8 +/- 0.7 ppm in the last two decades (1982-2001). This is opposite to other northern latitude sites and is attributed to the decrease of fossil fuel CO2 emissions in the catchment area (southwest Germany and France) and its respective change in the seasonal variation. Except for May and June, monthly mean CO2 mixing ratios at Schauinsland are higher by up to 8 ppm if compared to marine boundary layer air, mainly as a consequence of fossil fuel CO2 emissions in Europe. The CO2 measurements when combined with continuous Rn-222 observations at the same site allow an estimate of the net CO2 flux in the catchment area of Schauinsland: Mean seasonal fluxes compare very well with estimates from a process-oriented biosphere model (SIB-2) as well as from an inverse modeling approach [Peylin et al., 2000]. Annual CO2 fluxes vary by more than a factor of 2, although anthropogenic fossil fuel CO2 emissions show interannual variations of only about 10%. The major part of the variability must therefore be associated to interannual changes of biospheric uptake and release, which are on the order of the total fossil fuel emissions in the same area. This has to be taken into account when reliably quantifying and verifying the long-term carbon balance and emission reduction targets in the European Union.