Recent Developments in Calibration for Archaeological and Environmental Samples

J van der Plicht,S Talamo,T J Heaton,C Bronk Ramsey,E M Scott

doi:10.1017/rdc.2020.22

J van der Plicht, S Talamo + Show 3 more

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https://doi.org/10.1017/rdc.2020.22

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Abstract

ABSTRACTThe curves recommended for calibrating radiocarbon (14C) dates into absolute dates have been updated. For calibrating atmospheric samples from the Northern Hemisphere, the new curve is called IntCal20. This is accompanied by associated curves SHCal20 for the Southern Hemisphere, and Marine20 for marine samples. In this “companion article” we discuss advances and developments that have led to improvements in the updated curves and highlight some issues of relevance for the general readership. In particular the dendrochronological based part of the curve has seen a significant increase in data, with single-year resolution for certain time ranges, extending back to 13,910 calBP. Beyond the tree rings, the new curve is based upon an updated combination of marine corals, speleothems, macrofossils, and varved sediments and now reaches back to 55,000 calBP. Alongside these data advances, we have developed a new, bespoke statistical curve construction methodology to allow better incorporation of the diverse constituent records and produce a more robust curve with uncertainties. Combined, these data and methodological advances offer the potential for significant new insight into our past. We discuss some implications for the user, such as the dating of the Santorini eruption and also some consequences of the new curve for Paleolithic archaeology.

Highlights

The main backbone of radiocarbon (14C) calibration has been and will continue to be tree rings dated by dendrochronology, for the time periods where this is possible
The dramatic onset of the Younger Dryas (YD) is characterized by a steep slope in the calibration curve, corresponding to an increase of about 5% in the atmospheric 14C content (Δ14C ≈ 50‰) and which signifies the shutdown of the “ocean conveyor” (Broecker 1997)
Even here, we need to be somewhat careful with our interpretation as the IntCal20 estimate still retains two distinct peaks suggesting the two most likely periods for the last ring are either ca. 1605 calBC (3555 calBP) or ca. 1595 calBC (3545 calBP). Both these IntCal20based potential calendar dates are more recent than the calendar age estimate obtained using IntCal13 by about 5–15 years showing the effect of the calibration curve change assuming the validity of the olive wood wiggle match

Summary

INTRODUCTION

The main backbone of radiocarbon (14C) calibration has been and will continue to be tree rings dated by dendrochronology, for the time periods where this is possible. Both these IntCal20based potential calendar dates are more recent than the calendar age estimate obtained using IntCal (or earlier curves) by about 5–15 years showing the effect of the calibration curve change assuming the validity of the olive wood wiggle match. The recalibration with IntCal provides a new time span for this important human fossil, placing his calendar age back in time, between 41,180–39,190 calBP at 68.2% confidence, and at 41,900–37,700 calBP at 95.4% confidence (see Figure 5) This shift to older ages of the presence of Homo sapiens at the site implies a longer overlap with Neanderthals in this region. For Arcy-sur-Cure the ranges are between 42,080–41,270 calBP at 68.2% and 42,370–40,780 calBP (Figure 5)

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