樹木年輪(1945-1983)の^<14>C濃度変動

概要

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A Japanese cypress (Kiso hinoki) grown in Gifu prefecture, Central Japan and a Shorea spruce in Sabah, Malaysia were analyzed for the ^<14>C concentrations of annual tree rings (1945-1983). Each of annual rings (1958-1966) for the hinoki was divided radially into 3 or 4 consecutive sections. The ^<14>C concentrations, Δ^<14>C, of the sections were measured with a Tandetron accelerator mass spectrometer and compared with those of atmospheric CO_2. The good agreement was found between them; this suggested evidently that the Δ^<14>C values of tree rings could be used to estimate the Δ^<14>C values of atmospheric CO_2 in the past. Variations in Δ^<14>C of annual tree rings (1945-1983 ) for the hinoki were found to be closely related with the history of executing the nuclear weapon tests in the atmosphere, by considering that the residence time was about 2 years for transferr-ing CO_2 from stratosphere to troposphere. By using the variation pattern of Δ^<14>C common to most of trees, the average growth rate of the Shorea spruce (ca. 90cm in trunk diameter), having no growth ring, was estimated to be 5.5mm/yr. A latitude dependence of the Δ^<14>C variations was found for annual rings (1963-1970) of trees grown in the northern troposphere (6°N-42°N). This phenomenon seemed to be closely related with the mechanism of global mixing for bomb-produced ^<14>CO_2 in the atmosphere.
日本地球化学会の論文
1987-06-30