Abstract
Fallout radionuclides, potential global indicators of the Anthropocene, raise questions about their preservation in bogs. This study evaluates the reliability of <sup>241</sup>Am records in acidic, ombrotrophic peat cores. The <sup>241</sup>Am source is the radioactive decay of the short-lived <sup>241</sup>Pu (half-life 14.29 years) present in fallout from atmospheric nuclear weapons testing. We assessed 35 peat cores from 30 European and North American sites, collected over three decades for trace metal deposition studies. Each core underwent independent <sup>210</sup>Pb dating. We excluded 10 cores due to significant <sup>241</sup>Am peak quantification uncertainty. Of the remaining 25 cores, 22 displayed a single <sup>241</sup>Am peak and 3 exhibited two peaks with similar activities. Among the 22 single-peak cores, 18 were within 10 years of AD 1963, with 10 within 5 years. For 10 of these 22 cores, <sup>14</sup>C dates from the atmospheric bomb pulse curve were compared, showing ≤ 10 years of difference, with 7 cores ≤ 5 years from the <sup>210</sup>Pb CRS model AD 1963. Factors contributing to age discrepancies included analytical limitations in <sup>241</sup>Am measurements, peat accumulation rates affecting <sup>241</sup>Am activities, post-depositional migration of <sup>241</sup>Pu and/or <sup>241</sup>Am, uncertainties in <sup>210</sup>Pb age-modelling, and limited <sup>14</sup>C samples. The utility of <sup>241</sup>Am as an Anthropocene marker depends on the accepted uncertainty level in defining this epoch. The detection of <sup>241</sup>Am in 35 cores, validated in 22 cores, suggests a hemispheric Anthropocene onset. The bomb pulse curve of <sup>14</sup>C in bogs could serve as an alternative marker. Common <sup>137</sup>Cs post-depositional migration in ombrotrophic peatlands contrasts with its immobility in minerotrophic peatlands, suggesting the latter may also retain nuclear weapons test fallout, including <sup>241</sup>Am.
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