Observed and modeled seasonal variation of 13C, 18O and 14C of atmospheric CO Happo, a remote site in Japan, and a comparison with other records

Measurements of the C-13/C-12 and O-18/O-16 ratios and C-14 Of atmospheric CO were carried out for 2 years (1997 and 1998) at Happo (36 degrees 41'N, 137 degrees 48'E, 1840 m above sea level) in Japan. This is the first measurement of time series for isotopic compositions of CO at a remote site in Asia. The seasonal cycle of the O-18/O-16 ratio shows a maximum of 19%0 (Vienna SMOW) in February and a minimum of 2 parts per thousand in July. This minimum value is heavier than the values reported for high latitude in the Northern Hemisphere, and this indicates that CO from fossil fuel combustion, which has a large O-18/O-16 ratio, affects midlatitude in the Northern Hemisphere considerably. On the contrary, the C-13/C-12 ratio shows a clear seasonal variation with little scatter; maximum -24.5 parts per thousand (Vienna Peedee belemnite) in April and minimum -28.5 parts per thousand in July-August. The seasonal variation at Happo has different values and phases compared to those in the Southern Hemisphere and in the northern high latitude. (CO)-C-14 concentration at Happo is similar to that at high latitude in the Northern Hemisphere. A simple box model calculation is presented for these seasonal variations, and the model reproduces the observed seasonal cycles of CO concentration, O-18/O-16 ratio, and (CO)-C-14 concentration within the limitations of the simplified model, but not C-13/C-12 ratio. To reproduce the spring maximum of CO concentration, an enhanced CO production from biomass burning or other CO sources in spring are inferred in east Asia.