δ14 CO2 Record from Schauinsland
Ingeborg Levin and Bernd Kromer
Institut für Umweltphysik,
University of Heidelberg, D-69120,
Period of Record
December 1976 - 1996
All air samples at Schauinsland have been collected from a ventilated intake stack approximately 7m above the ground. Bi-weekly integrated CO2 samples from about 15-20 m3 of air have been continuously collected by dynamic quantitative absorption in carbonate-free sodium hydroxide (NaOH) solution. Air has been pumped through a rotating glass tube filled with a packed bed of Raschig rings (hard glass) to enlarge the surface of the absorbing NaOH solution (200 ml of 4 normal NaOH). The CO2 absorption is quantitative and samples represent mean values of 10 days to 2 weeks. In the laboratory, the samples are extracted from the NaOH solution in a vacuum system by adding hydrochloric or sulfuric acid. 13C analyses of the CO2 are by mass spectrometry and 14C analyses are by high precision proportional counting, after purification of the CO2 sample over charcoal (Schoch et al. 1980, Kromer and Münnich 1992). δ13C values are given relative to the V-PDB standard (Hut 1987) with the overall precision of a single analysis reported to be +/- 0.15 per mil (Levin and Kromer 1997). δ14C data are given relative to the NIST oxalic acid activity corrected for decay (Stuiver and Polach 1977) with the precision of a single δ14C measurement reported to be +/- 3-5 per mil (Levin and Kromer 1997).
More details on the sampling methods and laboratory procedures are provided in Levin et al. (1980), Schoch et al. (1980), Levin et al. (1985), and Kromer and Münnich (1992).
Black Forest mountain range close to Schauinsland
Summit, forest environment
47°55' N, 7°55' E
1205 m above MSL
This time series from Schauinsland coupled with the record from Vermunt, offers 35 years of 14CO2 since the nuclear test ban treaty in 1962. Levin et al. (1985) consider this time series from Schauinsland to be representative of the higher altitude 14CO2 level over central Europe. On the basis of close agreement between the 14CO2 records from Schauinsland and Vermunt, Levin et al. (1985) suggest the two records are indicative of the 14CO2 level of tropospheric CO2 above Central Europe.
Levin and Kromer (1997) observed the δ14CO2 to show a steady and approximately exponential decrease from 1977 to 1996 with a time constant of 16.3 +/-0.2 years. This is a consequence of bomb 14C still equilibrating with the world oceans and the biosphere, as well as an ongoing input of 14C-free fossil fuel CO2 into the atmosphere. The Schauinsland record shows a seasonal pattern with minimum values occurring during the winter half year. Levin and Kromer (1997) explained these annual minima being in part due to larger fossil fuel contamination in winter than in summer.
δ13C analyses from the Schauinsland samples show mean seasonal variations with an amplitude of +/- 0.4 per mil, caused by atmosphere-biosphere exchange and a mean decrease from 1977 to 1996 of δ13C = -0.017 per mil yr -1. This trend is mainly due to an increasing burden of fossil fuel CO2 in the atmosphere, depleted in 13C/12C ratio, and compares well to trends measured at other stations in mid-to-high northern latitudes (Levin and Kromer 1997).
- Hut, G. 1987. Stable isotope reference samples for geochemical and hydrological investigations. In Report to the Director General, IAEA, Vienna.
- Kromer, B., and K.O. Münnich. 1992. CO2 gas proportional counting in radiocarbon dating - review and perspective. In Radiocarbon After Four Decades: an Interdisciplinary Perspective (R.E. Taylor, A. Long, and R. Kra, eds.) Springer-Verlag, New York, 184-197.
- Levin, I., and B. Kromer. 1997. Twenty years of high precision atmospheric 14CO2 observations at Schauinsland station, Germany. Radiocarbon (in press).
- Levin, I., K.O. Münnich, and W. Weiss. 1980. The effect of anthropogenic CO2 and 14C sources on the distribution of 14C in the atmosphere. In Proceedings of the 10th International Radiocarbon Conference (M. Stuiver and R. Kra, eds.) Radiocarbon 22(2):379-91.
- Levin, I., B. Kromer, H. Schoch-Fischer, M. Bruns, M. Münnich, D. Berdau, J.C. Vogel, and K.O. Münnich. 1985. 25 years of tropospheric 14C observations in central Europe. Radiocarbon 27(1):1-19.
- Levin, I., R. Graul, and N.B.A. Trivett. 1995. Long-term observations of atmospheric CO2 and carbon isotopes at continental sites in Germany. Tellus 47B:23-34.
- Schoch, H.M., Bruns, K.O. Münnich and M. Münnich. 1980. A multicounter system for high precision C-14 measurements. In Proceedings of the 10th International Radiocarbon Conference (M. Stuiver and R. Kra, eds.) Radiocarbon 22(2):442-47.
- Stuiver, M., and H.A. Polach. 1977. Discussion: Reporting of 14C data. Radiocarbon 19(3):355-63.
CITE AS: Levin, I., and B. Kromer. 1997. δ14CO2 records from Schauinsland. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.