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Original Articles

Time and space variations of the carbon isotopic ratio of tropospheric carbon dioxide over Japan

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Pages 258-274 | Received 14 Jul 1992, Accepted 02 Nov 1992, Published online: 18 Jan 2017
 

Abstract

CO2 samples collected in the troposphere over Japan during the period from April 1984 to November 1990 were analyzed for δ3C with a precision of better than 0.03 %. The amplitudes of the seasonal cycles of δ3C and CO2 concentration decreased with increasing height, with a phase delay of about 1 month between the lower and upper troposphere. From a comparison of the observed seasonal variation of the CO2 with that of δ3C, it was found that the rate of change in δ3C with respect to the CO2 concentration is about –0.05 %/ppmv. This suggests that the seasonal CO2 cycle over Japan is mainly produced by seasonally-dependent biospheric activities. However, air transport from different latitudes is also important for the seasonal CO2 cycle, particularly in the upper troposphere. δ3C decreased secularly at an average rate of about –0.04 %/year, due mainly to combustion of fossil fuel with isotopically light CO2. Interannual variations of δ3C, superimposed on the long-term trend, were also observed, which were approximately opposite in phase with those of the CO2 concentration. The comparison of both interannual variations suggested that the cause could be primarily attributed to an imbalance in the CO2 exchange between the atmosphere and the biosphere rather than between the atmosphere and the oceans.