14C concentrations in tree stems, 1

The 14C concentrations in trees sampled at various latitudes were measured with a Tandetron Accelerator Mass Spectrometer at Nagoya University. The growing periods of the parts for 14C measurements were estimated by the relationship between meteorological conditions and the appearance of anatomical features of annual rings such as false rings, latewood formation, and so on. The following results were obtained: 1. The latitude dependence of the 14C variation is found in tree stems as well as in the atmosphere. 2. The 14C concentrations in tree stems are almost equal to those in the atmosphere at the latitude where the tree had grown and at the time when the sampled section is formed. Therefore the 14C concentrations in the atmosphere are estimated by those of the tree stems. 3. The time when the 14C concentration in the tree showed its maximum value has difference of 1 - 2 years with that of the latitude where the tree had grown. 4. This phenomena seemed to be related closely with the mechanism of global mixing of 14CO2 produced by atmospheric nuclear weapon tests. This mechanism causes a time lag of 14C variation between northern and southern hemisphere. (author)