樹木樹幹内の<14>^C濃度の緯度依存性

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In the last report, a Japanese Cypress in Central Japan and a Seraya in Sabah-Malaysia were analyzed for ^<14>C concentration of annual rings (AD 1945-1983). Each of annual rings for the Japanese Cypress was devided radially into 3-4 consecutive sections. The ^<14>C concentrations, δ^<14>C, of the sections were measured with a Tandetron Accelerator Mass Spectrometer in Nagoya University, compared with those of atmospheric CO_2. The good agreement was found between them. This suggested evidently that the δ^<14>C values of the tree rings could be used to estimate the δ^<14>C values of atmospheric ^<14>CO_2 in the past. δ^<14>C variation of annual rings for the Japanese Cypress 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 transforming CO_2 from stratosphere to troposphere. By using a variation pattern of δ^<14>C common to Japanese Cypress and Seraya, the average growth rate of the Seraya, that has no annual rings, was estimated to be 5.5mm/year. And a latitude dependence of the δ^<14>C variation was found for annual rings of the trees (6°N-42°N). This phenomena seemed to be closely related with the mechanism of global mixing for bomb-produced ^<14>CO_2 in the atmosphere. In this report the concentrations of ^<14>C in annual rings of tree stems growing in the southern hemisphere were measured with the Tandetron Accelerator Mass Spectrometer. The rapid increase in atmospheric <14>CO_2 was caused by the nuclear weapon tests since 1950. The same increase of ^<14>C concentration was found in tree stems. Because the nuclear weapon tests were mainly performed at mid- and high latitude in northen hemisphere, the atmospheric ^<14>C concentration has latitude dependence betewen 1954-1967,but that in the southern hemisphere was independent of latitude. Our study showed the ^<14>C concentration in the stems grown in the southern hemisphere. And we discussed latitude dependence of the ^<14>C concentration in trees on the earth. Using excess ^<14>C as a tracer and the process to presume the time when a section had formed in a tree. 1. The ^<14>C concentration in the trees which had grown south of latitude 7°S were independent of latitude and remained constant. 2. The ^<14>C concentration of a section in a tree on the earth is necessary equal to that in the atmosphere at the latitude where the tree had grown and at the time when the section is formed. The δ^<14>C values of the tree rings can be used to estimate those of atmospheric ^<14>CO_2. There are no individual variations in ^<14>C Concentration. 3. The time when the ^<14>C concentration in a tree showed the maximum value differed with the latitude where the tree had grown. 4. By considering the δ^<14>C variations of annual rings of Japanese Cypress, Merkusii pine, Teak, Parana Pine, and Lingue, the residence time was about 1-2 years for transforming CO_2 from northern hemisphere to southern hemisphere. 5. This phenomena seemed to be closely related with the mechanism of global mixing for bomb-produced ^<14>CO_2 in the the troposphere. There are two big circulations in the troposphere on the earth. One goes from the equator to the north, another from the equator to the south. This mechanism of global mixing for bomb-produced ^<14>CO_2 in the atmosphere causes the time difference of 1-2 years in the ^<14>C concentrations in the southern hemisphere.
名古屋大学の論文

樹木樹幹内の<14>^C濃度の緯度依存性

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