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Abstract
ABSTRACTRadiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric14C 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 international14C 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 as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable14C 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 the14C 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 marine14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the 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 with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.
Highlights
In most radioactive isotope systems used for dating, a daughter product is available for measurement so that an absolute age can be calculated
The older part of IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals, using improved evaluation of the time and location variable 14C offsets from the atmosphere for each dataset back to ca. 53,970 cal BP with Marine reservoir age (MRA) corrected Cariaco Basin data providing an extension to 55,000 cal BP
The IntCal20 calibration curve plotted with 1 standard deviation predictive envelopes over the full range of the calibration interval (0–55 cal kBP) in 2000-year intervals with all the datasets and uncertainties is provided in online Supplemental Material (Figure S2)
Summary
In most radioactive isotope systems used for dating, a daughter product is available for measurement so that an absolute age can be calculated. For the older part of the timescale it was decided that the revised and extended atmospheric Lake Suigetsu varved sediment macrofossil record still lacked sufficient corroboration to be used as a stand-alone atmospheric record This part of IntCal comprises statistically integrated evidence from floating tree-ring chronologies, terrestrial macrofossils from lake sediments, foraminifera from marine sediments, speleothems, and corals, using improved evaluation of the time and location variable 14C offsets from the atmosphere (reservoir ages, dead carbon fractions) for each dataset. All these data have been combined using a newly developed Bayesian spline approach which has been adapted to optimize the incorporation of a large number of annual tree rings. IntCal is intended for the calibration of Northern Hemisphere atmospheric samples; SHCal the calibration of Southern Hemisphere atmospheric samples (Hogg et al 2020 in this issue); and Marine
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