Multimodal-TERESA, a 210Pb-based radiometric dating model for recent sediments under largely varying rates of supply

Lead-210 from natural atmospheric fallout is widely used in multidisciplinary studies for dating recent sediments. In anthropogenically-impacted and/or high energy systems the Pb-210 flux onto the sediments may show non-random temporal variability, leading to the failure of classical dating models. The problem of how identifying and dating such cases remained unsolved, and it is the goal of the present work. Empirical evidences from varved sediments prove that initial activity concentrations of excess Pb-210 (Pb-210(exc)) and sediment accumulation rates (SARs) show large and independent temporal variability. M-TERESA model describes such variability by using multimodal frequency distributions and decodes the chronology from the Pb-210(exc) versus mass depth profile. The new model can solve scenarios with largely varying rates of supply, which fall beyond the limits of the piecewise versions of the classical models. Its use is demonstrated with some complex Pb-210(exc) profiles from varved sediments and synthetic cores for which an alternative and complete reconstruction of palaeofluxes and SARs is possible. The paper is supported by a wide set of supplementary material, including numerical codes for applying TERESA. The proposed methods are also useful for improving the reliability of routinely applications of the Pb-210-based radiometric dating of recent sediments.