Preprints
https://doi.org/10.5194/gchron-2021-13
https://doi.org/10.5194/gchron-2021-13

  17 May 2021

17 May 2021

Review status: this preprint is currently under review for the journal GChron.

Evidence for old carbon contamination in 14C wiggle-match age series for the 946 CE eruption of Changbaishan volcano

Richard N. Holdaway1,2, Ben Kennedy2, Brendan M Duffy3, Jiandong Xu4,5, and Clive Oppenheimer6 Richard N. Holdaway et al.
  • 1Palaecol Research Ltd, P. O. Box 16569, Hornby, Christchurch 8042, New Zealand
  • 2School of Earth Sciences and Environment, University of Canterbury, Private Bag 4800, Christchurch 8041, New Zealand
  • 3School of Earth Sciences, University of Melbourne, Melbourne 3010, Australia
  • 4National Observation and Research Station of Jilin Changbaishan Volcano, Institute of Geology, China 15 Earthquake Administration, Beijing 100029, China
  • 5Key Laboratory of Seismic and Volcanic Hazards, China Earthquake Administration, Beijing 100029, China
  • 6Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, U.K.

Abstract. Volcanic eruptions that are not historically attested are commonly radiocarbon dated by "wiggle matching" sequential 14C measurements of the rings of trees killed by the eruption against an accepted calibration curve. It is generally assumed that carbon laid down in the wood is uncontaminated by 14C-free ("old") carbon, although evidence for contamination is well documented. Often, ill-fitting ring ages are excluded from analysis. The ‘Millennium Eruption' of Changbaishan volcano on the China-DPR Korea border offers a valuable case study in wiggle match dating, since several independent groups reported age estimates before the determination and acceptance of a precise eruption year of 946 CE. Some of the discrepancies and incompatibilities between published dates were attributed to old carbon effects. Here, we apply a new methodology to correct for contamination levels of up to 4.5% old carbon to eight wiggle match date series for the Millennium Eruption. Without discarding ring ages, we find agreement indices as high as, or higher than, those for the published dates, and five of the eight date series yielded high-agreement-index eruption dates closer to 946 CE than the published dates. None of the five yield a best result at zero contamination. Differences between the eruption dates reveal a weak association with the direction of the sampled tree from the caldera, but no relationship with distance. Our results suggest that old carbon contamination is possible over a wide area, potentially leading to over-estimation of eruption ages by years, decades or more, cautioning against over-reliance on wiggle-match ages that are not corroborated by other lines of evidence. Our revised protocol that accounts for contamination offers a way forward in the application of wiggle match dating of eruptions and provides a platform for understanding discrepancies that exist when comparing wiggle match series.

Richard N. Holdaway et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2021-13', Anonymous Referee #1, 01 Aug 2021
  • RC2: 'Comment on gchron-2021-13', Anonymous Referee #2, 08 Sep 2021

Richard N. Holdaway et al.

Richard N. Holdaway et al.

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Short summary
Prehistoric volcanic eruptions are often dated by wiggle matching series of radiocarbon ages on tree rings to standard calibration curves, ignoring potential contamination by 'old' carbon given off by the volcano. We modeled the effects of low amounts of contamination on wiggle match dates for the 10th century Changbaishan eruption and found evidence of contamination in all. We propose a new protocol to identify the presence of contamination, and provide more secure dates for major eruptions.