Composition and consequences of the IntCal20 radiocarbon calibration curve

Radiocarbon calibration is necessary to correct for variations in atmospheric radiocarbon over time. The IntCal working group has developed an updated and extended radiocarbon calibration curve, IntCal20, for Northern Hemisphere terrestrial samples from 0 to 55,000 cal yr BP. This paper summarizes the new datasets, changes to existing datasets, and the statistical method used for constructing the new curve. Examples of the effect of the new calibration curve compared to IntCal13 for hypothetical radiocarbon ages are given. For the recent Holocene the effect is minimal, but for older radiocarbon ages the shift in calibrated ages can be up to several hundred years with the potential for multiple calibrated age ranges in periods with higher-resolution data. In addition, the IntCal20 curve is used to recalibrate the radiocarbon ages for the glaciation of the Puget Lowland and to recalculate the advance rate. The ice may have reached its maximum position a few hundred years earlier using the new calibration curve; the calculated advance rate is virtually unchanged from the prior estimate.