NONSEASONAL 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 Rn-222 monitoring, that enables us to characterize direct air injections from South Africa into subantarctic areas.