Measurements of stable isotopic ratios of atmospheric CO2 have been made at Syowa Station, Antarctica since 1986. The average peak-to-peak amplitude of the seasonal cycle of δ13C was about 0.04‰ with the maximum in autumn and the minimum in spring. From comparison with the seasonal cycle of the CO2 concentration, it was speculated that air with high CO2 concentration influenced by exchange between the atmosphere and the biosphere and/or combustion of fossil fuel arrives at the station from late fall to early spring, while oceanic origin air with low CO2 is transported from late spring to summer. The average increase rate of δ13C of atmospheric CO2 between 1986 and 1990 was about -0.02‰/year. Interannual variations of δ13C, superimposed on the long-term trend, were also seen. These were approximately opposite in phase to those of the CO2 concentration. The comparison of both interannual variations suggests that the principal cause could be an imbalance in the CO2 exchange between the atmosphere and the biosphere. On the other hand, δ18O of atmospheric CO2 showed a clear seasonal cycle with the maximum in summer and minimum in winter, which may also be related to the seasonally-dependent atmospheric transport.
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|Published - 1996