High-Precision Bidecadal Calibration of the Radiocarbon Time Scale, AD 1950–500 BC and 2500–6000 BC

The radiocarbon ages of dendrochronologically dated wood spanning the AD 1950–6000 BC interval are now available for Seattle (10-yr samples, Stuiver Pearson Pearson & Stuiver 1986). We now find that minor corrections must be applied to the published data sets, and therefore, give new bidecadal radiocarbon age information for 2500–6000 BC, as well as corrected radiocarbon age averages for AD 1950–500 BC. Corrected average 14 C ages for the 500–2500 BC interval are given separately (Pearson & Stuiver 1993). The Seattle corrections (in the 10–30 14 C-yr range) are discussed in Stuiver and Becker (1993), whereas Pearson and Qua (1993) provide information on Belfast corrections (averaging 16 yr). All dates reported here are conventional radiocarbon dates, as defined in Stuiver and Polach (1977). Belfast 14 C ages back to 5210 BC were obtained on wood from the Irish oak chronology (Pearson et al. 1986). Wood from the German oak chronology (Becker 1993) was used by Belfast for the 5000–6000 BC interval. For the overlapping interval (5000–5210 BC), Belfast reports weighted Irish wood/German wood 14 C age averages. The Seattle 14 C ages for the AD interval were either on Douglas fir wood from the US Pacific Northwest, or Sequoia wood from California (Stuiver 1982). The BC materials measured in Seattle were mostly part of the German oak chronology. Thirteen samples (5680–5810 BC) from the US bristlecone pine chronology (Ferguson & Graybill 1983) were measured in Seattle as well. Here, the final Seattle decadal 14 C ages resulted from averaging German oak and bristlecone pine ages.