Challenges and limitations of the 210Pb sediment dating method: Results from an IAEA modelling interlaboratory comparison exercise

The 210Pb sediment dating is the most widely used method to determine recent (~100–150 years) chronologies and sediment accumulation rates in aquatic environments and has been used effectively for reconstruction of diverse environmental processes associated with global change. Owing to the relative accessibility of the 210Pb methodology, many environmental chronologies have been produced, but not always critically assessed. Sometimes, sedimentary processes such as compaction, local mixing, erosion, or episodic sedimentation are not taken into account, nor the validity of the fundamental premises and proper estimation of uncertainties assessed. A Pb-210 dating interlaboratory comparison modelling exercise was designed within the framework of the IAEA (International Atomic Energy Agency) Coordinated Research Project “Study of temporal trends of pollution in selected coastal areas by the application of isotopic and nuclear tools” (CRP K41016), to identify potential problems associated with the use of 210Pb dating models and to suggest best practices to obtain reliable reconstructions. The exercise involved 14 laboratories worldwide with different levels of expertise in the application of the 210Pb dating methods. The dating exercise was performed using 210Pb, 226Ra and 137Cs activity data from two sediment cores (coastal and lacustrine sediments), and the participants were requested to provide their 210Pb chronologies based on dating models. This modelling exercise evidenced the limitations and constraints of 210Pb method when supplementary and validation information is not available. The exercise highlighted the relevance of solid understanding of the fundamentals, assumptions and limitations of the 210Pb dating method and its validation, and allowed identifying key aspects to improve the reliability of 210Pb dating process, including: a critical examination and interpretation of the 210Pb activity depth profile; an appropriate selection of the 210Pb dating model according to the characteristics of the 210Pb activity profile and the environmental setting taking into account sediment compaction in the calculations; a sound identification of the 210Pb equilibrium depth and the estimation of the 210Pb inventory ensuring the best possible estimation of interpolated 210Pb values when needed; and the use of independent markers to corroborate the age models. © 2020