Abstract
Since 1960, at the French station of Dumont d’Urville (Terre Adelie coast), during more or less long periods, we have monitored Rn-222 and its decay product Pb-210, fission products due to atmospheric nuclear tests, and the cosmonuclides Be-7 and P-32. Almost all these species show seasonal variations, whose general features are maximum concentrations during the local summer (December—January), and minima in the middle of winter (June—July). A long-term change in the Pb-210 concentrations was also observed at Dumont d’Urville, for all seasons, with a more-or-less continuous decrease since 1969 to 1986, from 2.5 to 1.5 dpm per 1000 m3. Such variations seem to be quite usual, because an ice core sampled at the South Pole also displays important fluctuations of the Pb-210 concentration in the fresh snow between 1888 and 1974, from 1 to 3 dpm/kg, particularly from 1920 to 1954. The latitudinal profiles of both Rn-222 and Pb-210 showing minima between 40° and 60° South at sea level, the long-range transport of these nuclides from mid-latitudes toward Antarctica should occur through the higher rather through the lower layers of the troposphere. Therefore, the Pb-210 long-term changes observed can be ascribed to global changes of the general circulation in the Southern hemisphere. The concentrations of Pb-210 at Dumont d’Urville, and the ozone vertical column in October at Halley Bay, show common features, more particularly a significant decrease in the 1980s, meaning that changes in the atmospheric circulation occurred in the Antarctic area from the middle of the 1970s, which can partly account for the ozone decrease beside variations of trace species concentrations.
