Non-seasonal variations of atmospheric CO2 concentrations at Amsterdam Island

The atmospheric CO₂ monitoring at Amsterdam island has shown a general increasing trend of the increase rate, which shifted from 1.1 ppm year^-1 in January 1981 to 1.8 ppm year^-1 in January 1989. Besides this general trend, three different kinds of variations were observed: (a) seasonal variations, whose magnitude is small at this station, that is less than ± 0.7 ppm; (b) small non-seasonal variations, as in 1985, likely related to changes in the atmospheric transport, also observed in other stations, but with different magnitudes and features; (c) important non-seasonal variations of the order of 1 ppm, negatively correlated to ENSO events of 1983 and 1987, with delays of 6 and 3 to 4 months, respectively. These variations are ascribed to a general change of the CO₂ emissions to the atmosphere, resulting from global climatic perturbations, rather than to transport processes. This is particularly shown at our sampling site through 222Rn monitoring, that enables us to characterize direct air injections from South Africa into subantarctic areas.