Radiocarbon Dating to a Single Year by Means of Rapid Atmospheric ¹⁴C Changes

In the best case, radiocarbon measurements allow artificial objects to be dated with a precision of 10 calendar years when conventional wiggle-matching onto the IntCal09 calibration curve is applied. More precise dating can only be achieved by using annually resolved 14 C calibration data, particularly in timespans when there are rapid changes in atmospheric 14 C concentration. The recently observed jump in atmospheric 14 C concentration of 1.5% between AD 774 and 775, though expected to be rare, is a good example for such a rapid change. We demonstrate by example that is possible to precisely 14 C date the cutting year of a timber in the historically important and well-preserved Holy Cross chapel of the convent St. John the Baptist in Val Müstair, Switzerland.