Flexible paleoclimate age-depth models using an autoregressive gamma process

Radiocarbon dating is routinely used in paleoecology to build chronologies of lake and\npeat sediments, aiming at inferring a model that would relate the sediment depth with\nits age. We present a new approach for chronology building (called "Bacon") that has\nreceived enthusiastic attention by paleoecologists. Our methodology is based on\ncontrolling core accumulation rates using a gamma autoregressive semiparametric model\nwith an arbitrary number of subdivisions along the sediment. Using prior knowledge about\naccumulation rates is crucial and informative priors are routinely used. Since many\nsediment cores are currently analyzed, using different data sets and prior\ndistributions, a robust (adaptive) MCMC is very useful. We use the t-walk (Christen and\nFox, 2010), a self adjusting, robust MCMC sampling algorithm, that works acceptably well\nin many situations. Outliers are also addressed using a recent approach that considers a\nStudent-t model for radiocarbon data. Two examples are presented here, that of\na peat core and a core from a lake, and our results are compared with other approaches.