CONCENTRATION OF ATMOSPHERIC CARBON DIOXIDE AT THE JAPANESE ANTARCTIC STATION, SYOWA

Continuous measurement of the atmospheric CO_2 concentration was initiated at Syowa Station in February 1984. Variation of CO_2 concentration at this station can be divided into three components such as secular trend, seasonal cycle and irregular variation after removing contaminated data. The secular trend was variable with time. The increase rate of CO_2 concentration was low from 1984 to 1986,but it became very high in 1987 and 1988. This change may be related to the 1987 ENSO event. The average rate of annual CO_2 increase over the 5 years was about 1.6 ppmv (yr)^. The average seasonal CO_2 cycle showed minimum and maximum concentrations in mid-April and early in October and its peak-to-peak amplitude was about 1.1 ppmv. The seasonal cycle including irregular parts was variable from year to year, but there was no indication of long-term expansion of the amplitude. The irregular CO_2 variation observed, especially from February to August, had a high correlation with the air mass exchange by synoptic scale weather disturbances