Probability distributions of calibrated dates for samples older than AD 1950. The radiocarbon age gives ambiguous calibrated dates for all samples; i.e. wood is formed in the period between 1650 and 1950. Samples with conventional radiocarbon ages of more than 200 years might have been formed as far back as the 16th century. Roman numerals refer to locations of samples in the core (Fig. 3). Horizontal lines below probability distributions represent the 1 (upper) and 2 sigma ranges of calibrated dates.