serac: a R package for ShortlivEd RAdionuclide Chronology of recent sediment cores

Abstract

Short-lived radionuclides are measured in surface sediment to provide a geochronology for the past century. Age-depth models can be produced from 210Pbex activity-derived sedimentation rates and confirmed by 137Cs and 241Am activities that are result of fallout from nuclear weapon tests and the Chernobyl accident. Different methods of age depth modelling using such data require expertise in lake sedimentation processes. Here, we present a package, serac, that allows the user to compute an age-depth model, output a graph and an age model as a text file, and provide metadata using the free open-source statistical software R. serac ensures the reproducibility of age-depth or age-mass depth models and allows testing of several 210Pbex models (CFCS, CIC, CRS) and sedimentation hypotheses (changes in the sedimentation rates, instantaneous deposits, varved sedimentation, etc.). Using several case studies, including lakes and lagoon in different environments, we demonstrate the use of the programme in diverse situations that may be encountered. The rising number of sediment cores in recent palaeo studies and the need to correlate them require reproducible methods. serac is a user-friendly code that enables age model computation for the past century and encourages the standardisation of outputs.