Discovery of annual growth in a modern olive branch based on carbon isotopes and implications for the Bronze Age volcanic eruption of Santorini

Yael Ehrlich,Lior Regev,Elisabetta Boaretto

doi:10.1038/s41598-020-79024-4

Yael Ehrlich, Lior Regev + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-79024-4

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Journal: Scientific Reports	Publication Date: Jan 12, 2021
Citations: 13	License type: open-access

Affiliation: Weizmann Institute of Science

Abstract

The volcanic eruption of Santorini in the Bronze Age left detectable debris across the Mediterranean, serving as an anchor in time for the region, synchronizing chronologies of different sites. However, dating the eruption has been elusive for decades, as radiocarbon indicates a date about a century earlier than archaeological chronologies. The identification of annual rings by CT in a charred olive branch, buried alive beneath the tephra on Santorini, was key in radiocarbon dating the eruption. Here, we detect a verified annual growth in a modern olive branch for the first time, using stable isotope analysis and high-resolution radiocarbon dating, identifying down to the growing season in some years. The verified growth is largely visible by CT, both in the branch’s fresh and charred forms. Although these results support the validity of the Santorini branch date, we observed some chronological anomalies in modern olive and simulated possible date range scenarios of the volcanic eruption of Santorini, given these observed phenomena. The results offer a way to reconcile this long-standing debate towards a mid-sixteenth century BCE date.

Highlights

Radiocarbon dating places the eruption in the late seventeenth century B CE6,7, nearly a century in disagreement, generating a long-standing debate[8] which has not been settled to this day[9,10,11,12]
Matching multiple radiocarbon measurements to the radiocarbon calibration curve generally gives a narrower date range compared to one radiocarbon measurement, which could potentially be matched to several areas on the calibration curve, resulting in a broader possible date range
The radiocarbon date for the eruption based on the olive branch, considering only that the samples taken from the branch are a sequence, is 1625–1567 BCE, at 1σ (68.2%) confidence interval[7]

Summary

Introduction

Radiocarbon dating places the eruption in the late seventeenth century B CE6,7, nearly a century in disagreement, generating a long-standing debate[8] which has not been settled to this day[9,10,11,12]. The radiocarbon date for the eruption based on the olive branch, considering only that the samples taken from the branch are a sequence, is 1625–1567 BCE, at 1σ (68.2%) confidence interval[7] This result is obtained by calibrating the radiocarbon age against the updated standard calibration curve, I ntCal2014. We take advantage of this phenomenon and combine it with detailed structural studies of olive wood using micro-CT and chronological studies at a resolution of 1–2 years using radiocarbon dating Dating at such high resolution is possible for a unique period of time beginning in the early 1960s, due to massive nuclear weapon testing in the atmosphere. This testing resulted in a sharp and nearly twofold increase in atmospheric radiocarbon levels, termed the “bomb peak”. As the change in radiocarbon levels was relatively fast and dramatic, the difference between one year and another during the “bomb peak” is significant, which allows for a sequence of samples from this specific period to be radiocarbon dated at a nearly-annual (but sometimes sub-annual) r esolution[30]

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