CO<sub>2</sub>循環における炭酸塩岩溶解の役割 [in Japanese] The role of chemical weathering of carbonate rocks in the geochemical cycle of CO<sub>2</sub> [in Japanese]
Access this Article
Search this Article
The geochemical cycle of CO<sub>2</sub> in a carbonate rock area was discussed by using for an example obtained for Akiyoshi-dai Plateau (Yamaguchi Prefecture), one of the big gest karst plateaus in Japan. The calcium concentration of the baseflow of the groundwater in the area showed seasonal fluctuations, and followed changes in CO<sub>2</sub> concentration in the soil. Soil CO<sub>2</sub> measured in the meadows which cover most of the area varied from a minimum of 0.08% at a soil temperature of 3.8℃, and a maximum of 1.2% at 20.8℃. The calcium concentration in the groundwater is controlled by waterlimestone dissolution equilibrium, under open system conditions depending on the meadow's soil CO<sub>2</sub> concentration. At the runoff peak of groundwater issuing from Akiyoshi-do Cave, which has the biggest drainage basin in Akiyoshi-dai Plateau, 18.5 km<sup>2</sup>, the calcium concentration increases due to the flushing out of water with a long residence time in the deeper phreatic zone. During 1983-1986, a yeary average of 2,100 tons of limestone was dissolved in 2.1×10<sup>7</sup>m<sup>3</sup> of groundwater issuing from Akiyoshi-do Cave, its catchment basin including 16.5km<sup>2</sup> of a limestone area: the mean solutional denudation rate is 51mm/ka. The amounts of CO<sub>2</sub> untilized on chemical weathering in carbonate rock areas in the world, corresponding to the same amounts of chemically weathered carbonate rocks in mol, were estimated by using the limestone denudation rate of 50mm/ka and found to be 8x10<sup>11</sup>kg/y. The role of chemical weathering of carbonate rocks cannot be ignored in the geochemical cycle of CO<sub>2</sub>.
Chikyukagaku 27(1), 21-28, 1993
The Geochemical Society of Japan