The approaching obsolescence of 137Cs dating of wetland soils in North America. (1st November 2018)

• Record Type: Journal Article
• Authors: Drexler, Judith Z.; Fuller, Christopher C.; Archfield, Stacey
• Is Part Of: Quaternary science reviews. Volume 199(2018)
• Page Start: 83
• Page End: 96
• Publication Date: 2018-11-01
• Subjects: Anthropocene -- North America -- Radiogenic isotopes -- Uncertainty analysis -- 137Cs mobility -- Best practices; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2018.08.028
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: The peak fallout in 1963 of the radionuclide 137 Cs has been used to date lake, reservoir, continental shelf, and wetland sedimentary deposits. In wetlands such dating is used to project the ability of wetlands to keep pace with sea level rise and develop strategies for mitigating carbon pollution using biological carbon sequestration. Here we demonstrate that reliable 137 Cs profiles are increasingly difficult to obtain from wetland soils. Among 58 soil cores recently collected from a range of wetland types and 137 Cs fallout densities across the United States, 25% contain no identifiable 137 Cs peaks. Less than 40% of 137 Cs ages are consistent with 210 Pb dating. We provide a new measure of 137 Cs peak clarity (τ) for our core dataset by comparing the 50% interquartile range of data around the 137 Cs peak for "ideal" cores profiles determined using 137 Cs fallout data to that of observed core profiles. Our results show that overall τ is approximately 10 times greater for observed cores than ideal cores. The deterioration in the 137 Cs peak has occurred due to radionuclide decay, 137 Cs migration in situ, which is ubiquitous in this study, and 137 Cs amendments from surface waters. Such deterioration likely extends to both Mexican and non-permafrost, Canadian wetlands. We recommend continued use of 137 Cs only if the full bound of dating uncertainty for both 137 Cs and an additional method such as 210 Pb is propagated into estimates of wetland vertical accretion and carbon sequestration.