著者

遠嶋 康徳

出版者

日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.44, no.3, pp.77-93, 2010

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Observation of the change in atmospheric O₂ concentration, combined with atmospheric CO₂ observation, provides complementary information about the global carbon cycle. This is based on the fact that O₂ and CO₂ fluxes are tightly coupled during terrestrial photosynthesis, respiration, and fossil fuel and biomass burning, but are less or decoupled during the sea-air gas exchanges. Especially, the long-term O₂ changes can be used to partition the sequestration of fossil fuel CO₂ release between ocean and terrestrial biosphere. In this review, we examine the parameters used for the partitioning calculation, including - O₂: C exchange ratios for the terrestrial photosynthesis/respiration and fossil fuel burning. In early atmospheric O₂ studies, the net oceanic O₂ flux was assumed to be zero because of the low solubility of O₂ in seawater in comparison with that of CO₂. However, recent studies have suggested that the upper-ocean warming, reducing the solubility of O₂ and the oceanic ventilation, causes net oceanic O₂ outgassing. We also review approaches to estimate the net oceanic O₂ fluxes. Finally, using the updated fossil CO₂ emission estimates and recently reported warming rates of the global upper ocean, we recalculate the ocean and terrestrial carbon sinks based on the previously reported atmospheric O₂ observations.