RecentPb,Cs andAm accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)

Over the past 50 years,210Pb,137Cs and241Am have been abundantly used in reconstructing recent sediment and peat chronologies. The study of global aerosol-climate interaction is also partially depending on our understanding of222Rn-210Pb cycling, as radionuclides are useful aerosol tracers. However, in comparison with the Northern Hemisphere, few data are available for these radionuclides in the Southern Hemisphere, especially in the South Indian Ocean. A peat core was collected in an ombrotrophic peatland from the remote Amsterdam Island (AMS) and was analyzed for210Pb,137Cs and241Am radionuclides using an underground ultra-low background gamma spectrometer. The210Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (137Cs and241Am) that are related to nuclear weapon tests. We compared the AMS210Pb data with an updated210Pb deposition database. The210Pb flux of 98 ± 6 Bq·m-2·y-1derived from the AMS core agrees with data from Madagascar and South Africa. The elevated flux observed at such a remote location may result from the enhanced222Rn activity and frequent rainfall in AMS. This enhanced222Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The210Pb flux at AMS is higher than those derived from cores collected in coastal areas in Argentina and Chile, which are areas dominated by marine westerly winds with low222Rn activities. We report a137Cs inventory at AMS of 144 ± 13 Bq·m-2(corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.