09:45 〜 10:00
[AAS11-10] Diurnal, seasonal, and interannual variations in δ18O of atmospheric O2 and its application to evaluate natural/anthropogenic changes in oxygen, carbon, and water cycles
キーワード：大気中O2の安定同位体比、大気中O2/N2比
Variations in the δ18O of atmospheric O2, δ18Oatm, is an indicator of biological and water processes associated with the Dole-Morita effect (DME). We detected diurnal, seasonal, and interannual variations of δ18Oatm firstly based on observations at Tsukuba, Japan. The average diurnal δ18Oatm cycle reached a minimum during the daytime, and its amplitude was larger in summer than in winter. We found that use of δ18Oatm enabled separation of variations of atmospheric δ(O2/N2) into contributions from biological activities and fossil fuel combustion. The average seasonal δ18Oatm cycle reached at a minimum in summer, and the peak-to-peak amplitude was about 2 per meg. A box model that incorporated biological and water processes reproduced the general characteristics of the observed diurnal and seasonal cycles. A slight but significant secular increase of δ18Oatm occurred during 2013–2022. Secular changes in δ18Oatm were also simulated by using the box model considering long-term changes of terrestrial gross primary production, photorespiration, and δ18Oatm of leaf water (δ18OLW). We calculated changes of δ18OLW using a three-dimensional model, MIROC5-iso (Okazaki and Yoshimura, 2017). The observed secular increase of δ18Oatm was reproduced by the box model that incorporated the isotopic effects associated with the DME from Bender et al. (1994), while the simulated δ18Oatm showed secular decrease when the model incorporated the isotopic effects from Luz and Barkan (2011). Therefore, long-term observations of δ18Oatm and better understanding of the DME are indispensable, for an application of δ18Oatm to constrain long-term changes in global GPP and photorespiration. These findings were reported by Ishidoya et al. (2025) recently.
Acknowledgements
This study was partly supported by JSPS KAKENHI (grant nos. 22H05006, 23H00513, 22H04938, and 22K14095) and the Global Environment Research Coordination System from the Ministry of the Environment, Japan (grant nos. METI1953)
Reference
Bender, M., et al., The Dole effect and its variations during the last 130,000 years as measured in the Vostok ice core, Global Biogeochem. Cycles, 8(3), 363–376, 1994.
Luz, B. & Barkan, E.: The isotopic composition of atmospheric oxygen, Global Biogeochem. Cycles, 25, GB3001, 2011.
Ishidoya, S., et al., Diurnal, seasonal, and interannual variations in δ(18O) of atmospheric O2 and its application to evaluate natural and anthropogenic changes in oxygen, carbon, and water cycles, Atmos. Chem. Phys., in press, 2025.
Okazaki, A. & Yoshimura, K.: Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction, Clim. Past, 13, 379–393, 2017.
Acknowledgements
This study was partly supported by JSPS KAKENHI (grant nos. 22H05006, 23H00513, 22H04938, and 22K14095) and the Global Environment Research Coordination System from the Ministry of the Environment, Japan (grant nos. METI1953)
Reference
Bender, M., et al., The Dole effect and its variations during the last 130,000 years as measured in the Vostok ice core, Global Biogeochem. Cycles, 8(3), 363–376, 1994.
Luz, B. & Barkan, E.: The isotopic composition of atmospheric oxygen, Global Biogeochem. Cycles, 25, GB3001, 2011.
Ishidoya, S., et al., Diurnal, seasonal, and interannual variations in δ(18O) of atmospheric O2 and its application to evaluate natural and anthropogenic changes in oxygen, carbon, and water cycles, Atmos. Chem. Phys., in press, 2025.
Okazaki, A. & Yoshimura, K.: Development and evaluation of a system of proxy data assimilation for paleoclimate reconstruction, Clim. Past, 13, 379–393, 2017.