最終氷期の古富士泥流中に発見された埋没ヒノキ年輪の炭素同位体組成

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タイトル別名
  • サイシュウ ヒョウキ ノ コ フジ デイリュウチュウ ニ ハッケンサレタ マイ
  • Stable carbon isotope composition of tree rings of a Japanese cypress from the Old-Fuji mudflow, of the last glacial period.

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The δ^<13>C fluctuation of tree rings in two Japanese cypress (Chamaecyparis obtusa) samples, one from the last glacial period and another from the present time, is examined. Each annual growth ring was divided into four or five segments, consisting of three earlywood segments and two latewood segments or no division of latewood, in order to measure seasonal variations within a year. The last glacial sample has about 400 annual growth rings and the mean ring width is 0.71 mm. Pith and sapwood were not present. Seasonal variations were measured for about 10 successive annual tree rings. A secular trend analysis is presented covering 100 years. The isotopic composition for three years was measured for a modern sample from Mt. Amagi, Izu Peninsula. The tree grew over a period of about 200 years, from 1794 A.D. to 1986 A.D., and the mean ring width is 1.27 mm. The carbon isotope composition of glacial period samples shows that the range is from -23.77 to -21.08 ‰, the mean value is -22.16 ± 0.40 ‰ and the mean seasonal fluctuation in each tree ring is 1.20 ± 0.32 ‰. That of modern samples shows that the range is from -23.00 to -21.41 ‰, the mean value is -22.29 ± 0.45 ‰ and the mean seasonal fluctuation is 0.73 ± 0.38 ‰. Assuming the δ^<13>C values of cellulose in the Hinoki tree rings directly reflected those of atmospheric CO_2 and the secular trend in depletion of δ^<13>C values via the Suess effect, these results give good agreement with the trend of depletion in atmospheric δ^<13>C values of CO_2 ascertained by ice core analysis and C4 plant analysis. There are poor correlations between seasonal fluctuations of isotope data and dendrochronological data influenced by climatic factors.

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