鍾乳石に記録された山口県秋吉台カルスト地域の植生変遷(<特集>炭酸塩の地球化学)

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Speleothems record successive information on terrestrial paleoenvironment. The vegetation change in the Akiyoshi-dai Plateau, Yamaguchi Prefecture, was examined using the δ^<13>C values of a stalagmite formed in the grassland area. The stalagmite δ^<13>C values largely reflect those of the soil CO_2 derived from organic carbon associated with the δ^<13>C values dependent on the vegetation type. The soil δ^<13>C values in the forest areas (-23〜-21‰) were lower than that in the grassland area (-15‰). A 50/50 contribution from rock carbonate (+3‰) and the soil CO_2 resulted in HCO_3^- with δ^<13>C values reflecting the vegetation. When the seepage water was exposed to cave air of a lower CO_2 concentration, the speleothems were formed from the water in the cave. The δ^<13>C values of the speleothems in the forest areas were in the range of -7.8〜-5.5‰, whereas that in thegrassland area was -4.3‰. The 7 cm growing stalagmite sample from the Kitayamakita-no-yokoana Cave in the grassland was found to have recorded the artificial vegetation change in the Akiyoshi-dai Plateau as variations in the δ^<13>C values of the carbonate. The average growth rate of a separate stalagmite (24μm y^<-1>) formed under circumstances similar to the stalagmite examined in the Akiyoshi-dai Plateau made it possible to estimate that yearly burning of the dead grass on the Akiyoshi-dai Plateau had started about 400 years ago.
日本地球化学会の論文
2006-08-25

鍾乳石に記録された山口県秋吉台カルスト地域の植生変遷(<特集>炭酸塩の地球化学)

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