[A-AS21] Atmospheric Chemistry

[AAS21-19] Variations in the atmospheric Ar/N2 and APO observed at Tsukuba, Ochi-Ishi, Hateruma and Minamitorishima, Japan

*Shigeyuki ISHIDOYA¹, Shohei MURAYAMA¹, Yasunori TOHJIMA², Kazuhiro TSUBOI³, Hidekazu MATSUEDA³, Shoichi TAGUCHI¹, Prabir Patra⁴, Hiroaki KONDO¹ (1.National Institute of Advanced Industrial Science and Technology (AIST), 2.National Institute for Environmental Studies (NIES), 3.Meteorological Research Institute (MRI), 4.Japan Agency for Marine-Earth Science and Technology (JAMSTEC))

Keywords:Atmospheric Ar/N2 ratio, Atmospheric Potential Oxygen (APO), Air-sea heat flux

Atmospheric Ar/N₂ ratio is a unique tracer of spatiotemporally-integrated air-sea heat fluxes, and expected to be a new tool to validate changes in the global ocean heat content (e.g. Keeling et al. 2004; Cassar et al., 2008). The Ar/N₂ ratio is also useful to estimate thermal and biological components of Atmospheric Potential Oxygen (APO = O₂ +1.1xCO₂) separately, so that it will contribute to better understanding of the oceanic carbon cycle. Therefore, we have developed a high-precision measurement system of the atmospheric Ar/N₂ ratio and APO (Ishidoya and Murayama, 2014), which is applicable both for continuous observations and analyses of discrete flask air samples, and started systematic observations of the Ar/N₂ and APO at Tsukuba (36N, 140E) and Hateruma Island (24N, 124E), Japan since 2012 and at Cape Ochi-Ishi (43N, 146E) and Minamitorishima Island (24N, 154E), Japan since 2013. Clear seasonal cycles of the Ar/N₂ ratio were observed at all the sites, and the peak-to-peak amplitudes of the seasonal cycles were in the range of 15 - 50 per meg. The observed amplitudes were found to be significantly larger than those calculated using atmospheric transport models and the seasonal air-sea N₂ fluxes climatology (TransCom fluxes; Garcia and Keeling et al., 2001) with a scaling factor to convert changes in the atmospheric N₂ concentration to those in the Ar/N₂ ratio (Blaine, 2005). We will also present preliminary estimations of the thermal and the biological APO at our sites by using the observed seasonal Ar/N₂ and APO cycles.

Acknowledgements
We would like to acknowledge N. Oda and F. Shimano, Global Environmental Forum, and many staffs of Japan Meteorological Agency for their supporting the observations.

References
Blaine, T. (2005) Continuous Measurements of Atmospheric Argon/Nitrogen as a Tracer of Air-Sea Heat Flux: Models, Methods, and Data. PhD Thesis, University of California, San Diego.
Cassar, N. et al. (2008) An improved comparison of atmospheric Ar/N₂ time series and paired ocean-atmosphere model predictions. J. Geophys. Res., 113, D21122. DOI: 10.1029/2008 JD009817.
Garcia, H. & Keeling, R. (2001) On the global oxygen anomaly and air-sea flux. J. Geophys. Res, 106, 31155-31166.
Ishidoya, S. & Murayama, S. (2014) Development of high precision continuous measuring system of the atmospheric O₂/N₂ and Ar/N₂ ratios and its application to the observation in Tsukuba, Japan. Tellus B, 66, 22574, http://dx.doi.org/ 10.3402/tellusb.v66.22574.
Keeling, R. et al. (2004) Measurement of changes in atmospheric Ar/N₂ ratio using a rapid-switching, single-capillary mass spectrometer system. Tellus B, 56, 322-338.