Recent 210Pb, 137Cs and 241Am accumulation in an ombrotrophic peatland from Amsterdam Island (Southern Indian Ocean)

Publication date: September 2017
Source:Journal of Environmental Radioactivity, Volumes 175–176
Author(s): Chuxian Li, Gaël Le Roux, Jeroen Sonke, Pieter van Beek, Marc Souhaut, Nathalie Van der Putten, François De Vleeschouwer
Over the past 50 years, ²¹⁰Pb, ¹³⁷Cs and ²⁴¹Am 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 of ²²²Rn-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 for ²¹⁰Pb, ¹³⁷Cs and ²⁴¹Am radionuclides using an underground ultra-low background gamma spectrometer. The ²¹⁰Pb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (¹³⁷Cs and ²⁴¹Am) that are related to nuclear weapon tests. We compared the AMS ²¹⁰Pb data with an updated ²¹⁰Pb deposition database. The ²¹⁰Pb flux of 98 ± 6 Bq·m⁻²·y⁻¹ derived 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 enhanced ²²²Rn activity and frequent rainfall in AMS. This enhanced ²²²Rn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The ²¹⁰Pb 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 low ²²²Rn activities. We report a ¹³⁷Cs 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.



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