High precision 14C dating of Holocene peat deposits: A comparison of Bayesian calibration and wiggle-matching approaches

Abstract

The chronologies of five northern European ombrotrophic peat bogs subjected to a large AMS 14C dating effort (32–44 dates/site) are presented here. The results of Bayesian calibration (BCal) of dates with a prior assumption of chronological ordering were compared with a Bayesian wiggle-match approach (Bpeat) which assumes constant linear accumulation over sections of the peat profile. Interpolation of BCal age estimates of dense sequences of 14C dates showed variable patterns of peat accumulation with time, with changes in accumulation occurring at intervals ranging from 20 to 50 cm. Within these intervals, peat accumulation appeared to be relatively linear. Close analysis suggests that some of the inferred variations in accumulation rate were related to the plant macrofossil composition of the peat. The wiggle-matched age–depth models had relatively high chronological uncertainty within intervals of closely spaced 14C dates, suggesting that the premise of constant linear accumulation over large sections of the peat profile is unrealistic. Age models based on the assumption of linear accumulation over large parts of a peat core (and therefore only effective over millennial time-scales), are not compatible with studies examining environmental change during the Holocene, where variability often occurs at decadal to centennial time-scales. Ideally, future wiggle-match age models should be constrained, with boundaries between sections based on the plant macrofossil composition of the peat and physical–chemical parameters such as the degree of decomposition. Strategies for the selection of material for dating should be designed so that there should be enough 14C dates to accurately reconstruct the peat accumulation rate of each homogeneous stratigraphic unit.