Americium-241 in peat bogs as a global marker of the beginning of the Anthropocene: examples from Europe and North America
Notice bibliographique
Résumé
Fallout radionuclides are being considered as potential global indicators of the beginning of the Anthropocene, yet questions persist about their preservation in bogs. This study assessed the reliability of 241 Am records in peat cores from acidic, ombrotrophic bogs. The source of 241 Am (half-life 432.7 years) in these natural archives is radioactive decay of the short-lived plutonium isotope 241 Pu (half-life 14.329 years) present in fallout from the atmospheric testing of nuclear weapons. We leveraged previously gathered data to gauge the congruence of 241 Am records with 210 Pb dates, examining the alignment of the 241 Am activity peak with the depth corresponding to the year AD 1963, as determined using the 210 Pb constant rate of supply (CRS) model. Our analysis employed 35 peat cores from 30 sites across Europe and North America, collected over the last three decades for trace metal deposition studies. Each core underwent independent 210 Pb dating. Among the 35 cores, 10 were excluded because of significant uncertainty in 241 Am peak quantification. Among the remaining 25 cores, 22 displayed a single 241 Am peak and 3 exhibited two peaks with similar 241 Am activities. Of the 22 cores with a single peak, 18 were within 10 years of AD 1963, with 10 of those being within 5 years. For 10 of the 22 cores, 14 C dates obtained from the atmospheric bomb pulse curve enabled comparison, with 9 showing ≤10 years of difference and 7 of those showing ≤5 years from the 210 Pb CRS model AD 1963. Factors contributing to age discrepancies included (i) analytical limitations of 241 Am measurements in peat using gamma spectrometry, (ii) the impact of peat accumulation rates on 241 Am activities, i.e., dilution effects, (iii) post-depositional migration of 241 Pu and (or) 241 Am, (iv) uncertainties introduced during 210 Pb age-modelling, and (v) the limited number of samples dated using 14 C. The usefulness of 241 Am as an Anthropocene marker (assuming AD 1963) hinges on the accepted uncertainty level in defining this epoch. Detection of 241 Am through gamma spectrometry was statistically validated as a real peak in 22 out of a total of 35 cores: this fraction (63%) is within the range reported in other studies. Given that the cores were gathered from 16 European and 14 North American sites, these peaks can be taken to denote the hemispheric onset of the Anthropocene. Lastly, common post-depositional migration of 137 Cs in ombrotrophic peatlands contrasts with its immobility in minerotrophic peatlands, where the presence of mineral matter and neutral pH inhibit its movement. This observation suggests that fens and swamps, characterized by minerotrophic conditions, may also serve as repositories of nuclear weapons test fallout, including 241 Am.
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Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».