The IntCal20 Northern Hemisphere radiocarbon age calibration curve (0-55 kcal BP)

Abstract

Radiocarbon ages cannot provide absolutely-dated chronologies for archaeological or palaeoenvironmental studies directly, but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently-dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international radiocarbon calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends to c. 13,900 cal BP as a fully atmospheric record. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree rings, terrestrial and marine sediments, speleothems, and corals, using improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the radiocarbon ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere for the pre-Holocene. Here we provide an overview of new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences from the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences throughout the radiocarbon timescale.