Annual Variation in Atmospheric 14C Between 1700 BC and 1480 BC

Charlotte Pearson,Lukas Wacker,Gregory Hodgins,Gretel Boswijk,Matthew Salzer,Alex Bayliss,Peter Brewer,Silvia Bollhalder,David Brown

doi:10.1017/rdc.2020.14

Charlotte Pearson, Lukas Wacker + Show 7 more

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https://doi.org/10.1017/rdc.2020.14

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Abstract

ABSTRACTIn 2018 Pearson et al. published a new sequence of annual radiocarbon (14C) data derived from oak (Quercus sp.) trees from Northern Ireland and bristlecone pine (Pinus longaeva) from North America across the period 1700–1500 BC. The study indicated that the more highly resolved shape of an annually based calibration dataset could improve the accuracy of 14C calibration during this period. This finding had implications for the controversial dating of the eruption of Thera in the Eastern Mediterranean. To test for interlaboratory variation and improve the robustness of the annual dataset for calibration purposes, we have generated a replicate sequence from the same Irish oaks at ETH Zürich. These data are compatible with the Irish oak 14C dataset previously produced at the University of Arizona and are used (along with additional data) to examine inter-tree and interlaboratory variation in multiyear annual 14C time-series. The results raise questions about regional 14C offsets at different scales and demonstrate the potential of annually resolved 14C for refining subdecadal and larger scale features for calibration, solar reconstruction, and multiproxy synchronization.

Highlights

This study presents a major new annual calibration dataset based on Irish oak produced at the ETH Accelerator Mass Spectrometry (AMS) Laboratory, Zürich, for the period 1680–1500 BC
An average weighted mean difference of –8.1 ± 1.9 14C yr can be calculated between the Irish oaks and North American pines
Comparison of the oak data with other multidecadal annual 14C time series produced at AA for juniper trees from Turkey (Table 1: 6) from a similar latitude as the bristlecone pine, indicated a difference of –8.4 ± 3.4 14C yr relative to the Irish oak

Summary

Introduction

A recent resurgence of investigations creating records of annual radiocarbon (14C) from calendar dated tree-ring series has demonstrated the potential of such data to expose yearto-year rapid excursions in 14C (e.g. Miyake et al 2012, 2014; Wang et al 2017) and a range of other likely solar driven patterns (e.g. Miyake et al 2017; Park et al 2017; O’Hare et al 2019) that are otherwise obscured in reconstructions based on 5-, 10- or 20-yr blocks of tree-rings (e.g. IntCal13; Reimer et al 2013). A recent resurgence of investigations creating records of annual radiocarbon (14C) from calendar dated tree-ring series has demonstrated the potential of such data to expose yearto-year rapid excursions in 14C What requires further exploration is the utility of longer (multidecadal, multicentennial) 14C time-series from single tree-rings for improving the radiocarbon calibration curve and for better defining 14C variability between laboratories and within the natural environment at a correspondingly high resolution. Pearson et al (2018) showed that between 1700 and 1500 BC, consecutive annual 14C measurements produced at the University of Arizona AMS Laboratory (hereafter AA) on single years from contemporary North American bristlecone pine and Irish oak trees, were within stated error of one another and the majority of the raw data derived from multiyear German and Irish oak samples underlying the IntCal curve (Reimer et al 2013).

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