All age–depth models are wrong, but are getting better

The construction of accurate age-depth relationships and a realistic assessment of their uncertainties is one of the fundamental prerequisites for comparing and correlating late Quaternary stratigraphical proxy records. Four widely used age-depth modelling routines - CLAM, OxCal, Bacon and Bchron - were tested using radiocarbon dates simulated from varved sediment stratigraphies. All methods produce mean age-depth models that are close to the true varve age, but the uncertainty estimation differs considerably among models. Age uncertainties are usually underestimated by CLAM, whereas age uncertainties produced by Bchron are often too large. With OxCal and Bacon, the setting of model-specific parameters influences the estimated uncertainties, which vary from too large to too small. The variability of sediment accumulation rates is underestimated by CLAM but overestimated by Bacon and Bchron. Bayesian age-depth models mainly improve the assessment of uncertainties of age-depth models.