VARIATIONS OF CARBON ISOTOPIC RATIO OF ATMOSPHERIC CARBON DIOXIDE OVER JAPAN

• Main Authors: ナカザワ タカキヨ, モリモト シンジ, アオキ シュンジ, タナカ マサユキ, Takakiyo NAKAZAWA, Shinji MORIMOTO, Shuhji AOKI, Masayuki TANAKA
• Format: Report
• Language: English
• Published: ABSTRACT 1992
• Subjects: Polar meteorology and glaciology; Proceedings of the NIPR Symposium on Polar Meteorology and Glaciology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3752; http://id.nii.ac.jp/1291/00003752/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3752&item_no=1&attribute_id=18&file_no=1

Carbon dioxide samples collected in the troposphere over Japan during the periods from April 1984 to November 1990 were analyzed for the carbon isotope ratio, δ^<13>C, with a precision of 0.03‰ (one standard deviation). The seasonal cycle of δ^<13>C decreased with increasing height, with a phase delay of about one month between the lower and upper troposphere, which was quite similar to that of the CO_2 concentration. It was found from the observed seasonal cycles of the CO_2 concentration and δ^<13>C that the rate of change in δ^<13>C with respect to the CO_2 concentration is about -0.05‰ per ppmv. This implies that the seasonal CO_2 cycle over Japan is mainly induced by seasonally dependent biospheric activities. However, the air transport from different latitudes is also important for the seasonal CO_2 cycle, especially in the upper troposphere. δ^<13>C decreased secularly at an average rate of about -0.03‰ per year due mainly to combustion of fossil fuels with lighter CO_2 relative to the atmospheric CO_2. Irregular variations of δ^<13>C with the periods of two or three years, superimposed on the secular trend, were also observed; they were almost in phase with these of the CO_2 concentration. From the comparison of both irregular variations, it was found that the cause could primarily attributed to the imbalance in CO_2 exchange between the atmosphere and biosphere in association with climate change, rather than between the atmosphere and oceans.