The concentration of atmospheric carbon dioxide at the Japanese Antarctic Station, Syowa

Precise and continuous measurements of the atmospheric CO₂ concentration have been made at Syowa Station, Antarctica since February 1984. The diurnal CO₂ variation was hardly observable throughout the year. The secular CO₂ trend was variable with time, showing slow increase in 1984, 1986 and 1988 and rapid increase in 1985 and 1987. The annual CO₂ increase was especially large in 1987, which may be related to the 1986/1987 ENSO event. The average rate of annual CO₂ increase over the last 5 years was about 1.6 ppmv yr^-1. The average seasonal CO₂ cycle showed minimum and maximum concentrations in mid-April and early in October, respectively, and its peak-to-peak amplitude was about 1.1 ppmv. The measured seasonal cycle was variable from year to year, but there was no indication of a long-term increase of the amplitude. It was found that irregular CO₂ variations with amplitudes of 0.2 ppmv at most and periods of a few weeks show high correlation with airmass exchange by synoptic scale weather disturbances. The results from Syowa are compared with those from the South Pole and Cape Grim, Tasmania.