Time to recalibrate those radiocarbon dates?

Radiocarbon dating is probably the most important dating technique for palaeoecological research in the late Quaternary. One complication with 14C dating is that the concentration of 14C in the atmosphere has changed over time due to, for example, solar-driven changes in the 14C production rate. Radiocarbon dates need to be calibrated to correct for this using a calibration curve derived from a huge number of 14C dates on material of known age.

Every few years, the INTCAL community generates an updated 14C calibration curve incorporating new data. This is a fantastic service to the community.

The current version of the calibration curve is INTCAL13, published in 2013. Many palaeoecologists will be working on material (or reviewing manuscripts) where the dates in the age-depth model were calibrated with a previous version of the calibration curve. Should you change to the new version of the calibration curve? This takes some effort, might mean that different papers published on the same core use different calibration curves, but might not make any material difference.

I’m going to explore how much difference it makes below.

Radiocarbon calibration curves

Radiocarbon calibration curves

The main difference between the curves is how far they extend: IntCal13 and IntCal09 go back to 50000 BP; IntCal04 goes back to 26000 BP; and IntCal98 goes back to 24000, but the last 8000 years of this is a straight line.

More detail on the differences between the curves can be seen by plotting the difference of each curve from IntCal13.

Difference from IntCal13

Difference from IntCal13

Before about 12000 years there are substantial differences between the curves. I would want to recalibrate dates if any were older than this.

Difference from IntCal13 in the Holocene

Difference from IntCal13 in the Holocene

During the Holocene, there are some substantial differences between IntCal98 and IntCal13. I would certainly recalibrate any dates calibrated with IntCal98. The differences between IntCal04/09 and IntCal13 are and generally small, but deviate by up to 40 years in a few places.

The uncertainty of the calibration curves have also changed.

Uncertainty in the calibration curves

Uncertainty in the calibration curves

The more recent calibration curves generally have a smaller uncertainty than the older curves. This is especially pronounced before the start of the Holocene.

For chronologies with pre-Holocene dates, it is certainly worth recalibrating and using the latest calibration curve. For Holocene chronologies, the differences between IntCal04/09/13 are probably not enough to change any conclusions except when high precision is required.

About richard telford

Ecologist with interests in quantitative methods and palaeoenvironments
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