検索画面に戻る Go Research

	(240Kb)

[Ｂ−７.５　Study on geochemical cycles of carbon dioxide by measurements of its isotope ratio and oxygen/nitrogen ratio in the atmosphere]

[Contact person]

[Total Budget for FY1996-2000]

　46,618,000 Yen
　(FY 2000; 15,963,000 Yen)

［Abstract］

　Estimation of carbon dioxide budget in the atmosphere is important issue to asses the future increase of CO₂. Growth rate of carbon dioxide was known to change every year. Such a variation may to be related to CO₂ budget in nature. In this study, we focused on isotope ratio of carbon dioxide and oxygen concentration change associated with the CO₂ growth. These two parameters can give us useful information on the CO₂ budget in the atmosphere. To observe these parameters, bottle sampling of background air over the Pacific was carried out with two ships-of-opportunity and by using two monitoring stations (Hateruma Island and Cape Ochi-ishi). Carbon isotope ratio (1995-2000) showed latitudinal gradient and clear seasonal variation with a long-term change. Isotopic budget calculation showed that the CO2 source flux from land biosphere increased in 1998 with a small increase of CO2 sink flux by the ocean, followed by changing to ocean as a source in late 1998. Then land biosphere changed to sink in 1999. Gradually ocean became sink again in 2000.
　The 3-year record (Ju1.1997-Jun.2000) and 2-year record (Dec.1998-Nov.2000) of the O₂/N₂ ratios clearly showed seasonal variations, which inversely co-vary with variations in the CO₂ mixing ratio. The changing rates of CO₂ mixing ratio and O₂/N₂ ratio at Hateruma were 2.1±0.1 ppm/yr and -3.7±0.5 ppm/yr, respectively. Assuming that the CO₂ production rate by fossil fuel consumption during the same period is 6.6 GtC/yr, these observed CO₂ and O₂/N₂ trends correspond to the land biotic and oceanic uptakes of 1.5±1.0 GtC/yr and 0.9±1.1 GtC/yr, respectively.

［Key Words］

　Carbon dioxide, Carbon isotope ratio, Oxygen concentration, Pacific ocean, bottle sampling, Hateruma