Implications of a 400 year tree ring based C-13/C-12 chronology

The significance of a 400 year (1550-1950 AD) C-13/C-12 chronology from a juniper from the Sinai Peninsula has been reassessed. A calibration of the isotope data covering the period 1740-1950 was carried out using the C-13/C-12 Of CO2 trapped in ice cores and a carbon isotope fractionation model. The calibration indicated a surprising constancy of C-i/C-a (concentration of CO2 in the leaf intercellular space to that in the atmosphere) during this time period. Using this procedure of calibration, when the pre-1740 tree ring record was examined in terms of the C-13/C-12 of the atmospheric CO2, significant variations were indicated. These variations, comparable to that imposed by anthropogenic causes occurred between 1700 and 1850 AD. Obviously, such variations in the C-13/C-12 of atmospheric carbondioxide is unlikely, but rather these should reflect variations in the C-i/C-a, ratio. Interestingly, the atmospheric C-13/C-12 variations deduced from this tree ring record parallels the C-14 variations in the atmosphere during the same period. Since the C-14 variations (at least prior to 1850 AD) have been linked to solar activities and by implication to climate, covariation between C-13/C-12 and C-14 Supports the hypothesis that the marked shifts in C-13/C-12 prior to 1850 resulted from a climate-induced perturbation in the The combined calibration procedure and comparison with C-14 provides a more useful approach to interpret C-13/C-12 time series in trees.