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

Abstract

Over the past 50 years, Pb,Cs and Am 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 ofRn-Pb 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 Pb,Cs and Am radionuclides using an underground ultra-low background gamma spectrometer. ThePb Constant Rate of Supply (CRS) model of peat accumulations is validated by peaks of artificial radionuclides (Cs and Am) that are related to nuclear weapon tests. We compared the AMSPb data with an updated Pb deposition database. ThePb flux of 98 ± 6 Bq·m·y 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 Rn activity and frequent rainfall in AMS. This enhancedRn activity itself may be explained by continental air masses passing over southern Africa and/or Madagascar. The Pb 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 lowRn activities. We report a Cs inventory at AMS of 144 ± 13 Bq·m (corrected to 1969). Our data thus contribute to the under-represented data coverage in the mid-latitudes of the Southern Hemisphere.

Holocene dynamics of the southern westerly winds over the Indian Ocean inferred from a peat dust deposition record

“…Radiocarbon and calibrated ages are shown in Table 1. The 210 Pb, 137 Cs and 241 Am results are published in Li et al (2017). The 210 Pb Constant Rate Supply model is in good agreement with post-bomb 14 C ages.…”

Comment on: “A novel approach to peatlands as archives of total cumulative spatial pollution loads from atmospheric deposition of airborne elements complementary to EMEP data: Priority pollutants (Pb, Cd, Hg)” by Ewa Miszczak, Sebastian Stefaniak, Adam Michczyński, Eiliv Steinnes and Irena Twardowska

“…The distribution of 210 Pb (half-life: 22.26 years) in the uppermost peat layers is indeed an argument for the preservation of Pb atmospheric signals in ombrotrophic peat cores. Moreover, a multimethod approach allows a cross-check of 210 Pb age depth models, and in most of the ombrotrophic peat cores the 210 Pb-based constant rate of supply (CRS) age-depth models (Appleby and Oldfield, 1978;Appleby, 2001) are in good agreement with pollen chronological markers (Appleby et al, 1997) as well as with 14 C Bomb Pulse Curve, 137 Cs and 241 Am markers, and tephrochronological dating in various locations (Goodsite et al, 2001;Givelet et al, 2003, Piotrowska et al 2009Li et al, 2017;Davies et al, 2018). E. Experimental studies strongly support Pb immobility.…”

A High–Resolution Accumulation Record of Arsenic and Mercury after the First Industrial Revolution from a Peatland in Zoige, Qinghai–Tibet Plateau

“…Based on previous studies, 137 Cs is a typical anthropogenic radionuclide that has been released into the atmosphere since nuclear weapon invention and testing. Figure 2 shows three significant time points for 137 Cs release (1952 yr-20 cm, beginning of extensive nuclear testing; 1963 yr-13 cm, peak of nuclear testing; 1986 yr-8 cm, Chernobyl incident) [43,44]. Alt-…”

“…Based on previous studies, 137 Cs is a typical anthropogenic radionuclide that has been released into the atmosphere since nuclear weapon invention and testing. Figure 2 shows three significant time points for 137 Cs release (1952 yr-20 cm, beginning of extensive nuclear testing; 1963 yr-13 cm, peak of nuclear testing; 1986 yr-8 cm, Chernobyl incident) [43,44]. Although 137 Cs showed significant trends reflecting radioactivity incidences worldwide, previous studies indicate significant challenges when reconstructing the recent chronology by this method, probably due to the mobility and diffusion of 137 Cs, which is especially the case in minerotrophic peatland [42,43,45,46].…”