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. 2018 Jun 12;115(24):6141-6146.
doi: 10.1073/pnas.1719420115. Epub 2018 May 29.

Fluctuating Radiocarbon Offsets Observed in the Southern Levant and Implications for Archaeological Chronology Debates

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Free PMC article

Fluctuating Radiocarbon Offsets Observed in the Southern Levant and Implications for Archaeological Chronology Debates

Sturt W Manning et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Considerable work has gone into developing high-precision radiocarbon (14C) chronologies for the southern Levant region during the Late Bronze to Iron Age/early Biblical periods (∼1200-600 BC), but there has been little consideration whether the current standard Northern Hemisphere 14C calibration curve (IntCal13) is appropriate for this region. We measured 14C ages of calendar-dated tree rings from AD 1610 to 1940 from southern Jordan to investigate contemporary 14C levels and to compare these with IntCal13. Our data reveal an average offset of ∼19 14C years, but, more interestingly, this offset seems to vary in importance through time. While relatively small, such an offset has substantial relevance to high-resolution 14C chronologies for the southern Levant, both archaeological and paleoenvironmental. For example, reconsidering two published studies, we find differences, on average, of 60% between the 95.4% probability ranges determined from IntCal13 versus those approximately allowing for the observed offset pattern. Such differences affect, and even potentially undermine, several current archaeological and historical positions and controversies.

Keywords: archaeology; calibration; radiocarbon; radiocarbon offsets; southern Levant.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
(A) Map showing location of study area and sampled sites, TZM and BADG. (B) The time periods covered by the TZM J. phoenicea known-age tree-ring chronology and its cross-dating versus the existing chronology (24, 25).
Fig. 2.
Fig. 2.
(A) The 14C ages from the known-age JJ samples, and previously published dates on known-age annual plant matter from Egypt (7), plotted against the NH radiocarbon calibration curve (IntCal13) (1) (1σ errors shown). (B) Differences between the JJ 14C ages and IntCal13 and comparison of these trends versus 5-y moving averages of reconstructed precipitation for southern Jordan (24) and regional temperature from Red Sea corals (28). (C) Overall offsets in 14C ages between the JJ samples and IntCal13 by laboratory, showing (light gray) the neutral prior (0 ± 20) versus the calculated posterior densities from each laboratory’s data versus IntCal13 (red and blue regions) (27).
Fig. 3.
Fig. 3.
(A) Comparison of the JJ 14C data by laboratory versus both IntCal13 (1) and SHCal13 (2) (1σ errors shown). Known-age tree-ring 14C measurements from Bcharrê, (northern Lebanon), Stavros tis Psokas (western Cyprus), and Çatacık (western Turkey), are also shown (44). (B). OxA data on other known age NH tree rings (61, 62) versus IntCal13 (1). (C) Overall 14C years offset OxA NH data in B versus IntCal13; light gray region shows the neutral prior (0 ± 20) versus the calculated posterior region (blue) (27).
Fig. 4.
Fig. 4.
(A) IntCal13 14C calibration curve ∼1200–700 BC approximately adjusted by 24 ± 5 14C years in the periods where curve taphonomy suggests a substantive JJ offset might apply based on Fig. 2 and SI Appendix, Fig. S3 (27). (B) (Bottom, vertical bars) Comparison of the calibrated calendar age ranges at 68.2% and 95.4% probability with, and without, both the average 19 ± 5 14C years offset or the approximate JJ adjusted IntCal13 14C calibration curve for the date sets from Tel Rehov (14) modeled as a sequence in OxCal (27), and the boundaries labeled as indicated from a rerun of the Bayesian chronological model from Khirbat en-Nahas (18). (Top, stars) Comparison of the noncommon (nonoverlapping), versus common (overlapping) ranges calculated when comparing the JJ adjusted ranges versus those from IntCal13 expressed as a percentage value: 0% (gray line) equates to exactly the same ranges; the larger percentage numbers indicate progressively less overlap. The average differences across the 17 comparisons are (i) for the 68.2% most likely ranges = 162% and (ii) for the 95.4% most likely ranges = 60%.

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