On the 13C record in tree rings. Part I. 13C Variations in northern hemispheric trees during the last 150 years

¹³C data from 26 trees of different northern hemispheric locations are presented covering the time interval of the last 150 years. It has been found that the mean ¹³C data of these trees during the 1850–1920, 1920–1940 and 1960–1975 time intervals decrease with an almost linear slope, while the data in the 1940–1960 time interval are increasing. The total δ¹³C shift since industrialization found from our trees amounts to nearly —29% which is higher than the linear δ¹³C decrease of —1%/100 years due to the biogenic and fossil CO₂ input into the atmosphere, as assumed previously in model calculations of Siegenthaler et al. (1978). The mean data within the given error-probability correspond to those of other authors with the exception of the data for the 1920–1940 time interval. The disturbances in ¹³C data for recording of increasing atmospheric CO₂ levels have been pointed out.