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Is ^<14>C concentration higher for plants growing at high altitude Tibetan Plateau than those at the sea level?(Proceedings of the 20^<th> Symposium on Chronological Studies at the Nagoya University Center for Chronological Research in 2007)

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  • 標高5000mのチベット高原に生育する植物は低地の植物より ^<14>C濃度が高いのか?(第20回名古屋大学年代測定総合研究センターシンポジウム平成19(2007)年度報告)

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Abstract

To answer a question whether ^<14>C concentration is higher for plants growing at high altitude locations than those growing at the sea level, we recently have collected plants samples from four sites at different altitudes: (1) plants from Lake Pumayum area at the altitude of 5030m; (2) plant samples from the suburbs of Lhasa city at the altitude of 4000m; (3) needle leaves from pine tree at 2600m-high location of Mt. Fuji; and (4) needle leaves from pine trees growing in the Higashiyama Campus of Nagoya University. The plant samples were rinsed with distilled water, treated chemically by an acid- alkali-acid treatment, and finally dried in an electric oven. A part of the samples were combusted to produce CO_2 and the produced CO_2 was changed to graphite for ^<14>C measurements with an AMS ^<14>C system at Nagoya University. The measured ^<14>C concentration was given in a ratio of sample ^<14>C/^<12>C to that of standard. For both sample and standard, isotopic fractionation was corrected. In addition, the decrease of ^<14>C concentration by radioactive decay for a standard from AD1950 to the year of sample collection was also corrected. ^<14>C concentrations were highest for the plant samples from Lake Pumayum showing a value of 1.081±0.016 in average, followed by the values of 1.055±0.005 for plants near Lhasa city, the values of 1.051±0,002 for plants from Mt. Fuji, and finally 1.017±0.003 for pine needles from Nagoya University. This clear altitude dependence may be explained preferably by Suess effect that is a dilution effect of modern ^<14>C concentration with dead carbon, containing no ^<14>C, produced by combustion of fossil fuel. The estimated altitude dependence of ^<14>C atom production is not strong and the resulting altitude dependence of ^<14>C concentration of CO_2 can fade out quickly by the strong air-mass mixing in the troposphere.

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