Danny McCarroll

Ten timbers from the spire scaffold of Salisbury Cathedral were dated using a combination of ring‐width dendrochronology, stable oxygen isotopic dendrochronology and radiocarbon dating. Seven timbers were coeval and assigned a combined empirical felling date range of 1352–1378, which was further refined to 1351–1359 (OxCal 95.4%). These results would indicate that the scaffold was not a 1320s construction but instead built later in the 14th century. The remaining sampled timbers produced a precise felling date of spring 1737 and are coincident with documented repair work in 1738.

We test a recent prediction that stable carbon isotope ratios from UK oaks will display age-trends of more than 4‰ per century by measuring >5400 carbon isotope ratios from the late-wood alpha-cellulose of individual rings from 18 modern oak trees and 50 building timbers spanning the 9th–21st centuries. After a very short (c.5 years) juvenile phase with slightly elevated values, the number of series that show rising and falling trends is almost equal (33:35) and the average trend is almost zero. These results are based upon measuring and averaging the trends in individual time-series; the ‘mean of the slopes’ approach. We demonstrate that the more conventional ‘slope of the mean’ approach can produce strong but spurious ‘age-trends’ even when the constituent series are flat, with zero slope and zero variance. We conclude that it is safe to compile stable carbon isotope chronologies from UK oaks without de-trending. The isotope chronologies produced in this way are not subject to the ‘segment length curse’, which applies to growth measurements, such as ring width or density, and have the potential to retain very long-term climate signals.

Oxygen isotope ratios from oak tree rings are used to extend the May–August precipitation totals of the England and Wales precipitation series back to 1201 ce. The agreement between instrumental and reconstructed values is unusually strong, with more than half of the variance explained and standard verification tests passed. The stability of this relationship is confirmed using split‐period calibration and verification. This allows the reconstruction to be variance‐scaled to the full length of the instrumental series back to 1766. Direct comparison with historical reports of very wet and dry summers show good agreement. Near‐constant replication, with a minimum of 10 timbers sourced from historic buildings across central southern England ensures signal strength does not change over time. Summers during the late 20th century appear anomalously dry and those of the 21st century very close to the pre‐20th century average with no evidence in the record of prolonged ‘megadroughts’ across England and Wales.

We thank Helama and Matskovsky (2019, https://doi.org/10.1177/0959683616652709) for their interest in our work. They argue that we should use Regional Curve Standardization (RCS) to identify trends in our oxygen isotope series and to detrend them prior to climate reconstruction. We disagree.

Ring‐width dendrochronology, based on matching patterns of ring width variability, works best when trees are growing under significant environmental (climatic) stress. In the UK, and elsewhere in the temperate mid‐latitudes, trees generally experience low stress, so dating is more difficult and often fails. Oxygen isotopes in tree rings passively record changes in the isotopic ratios of summer precipitation, so they carry a strong common signal, which offers potential for cross‐dating. A master chronology covering the period 1200–2000 ce was constructed using the oxygen isotope ratios of the latewood cellulose of oak samples from central England. Two independent chronologies, developed to verify the isotopic signal, were combined (n = 10 trees) and the method was evaluated by dating timbers of known age and historical timbers that could not be dated by ring‐width dendrochronology, from both within and beyond the central England region. The agreement between samples and the master chronology is exceptionally strong, allowing the dating of timbers with far fewer rings than is normally the case for ring‐width dendrochronology. Tree‐ring oxygen isotope values are more suited to correlation analysis than tree‐ring widths, so it is possible to provide t‐values that conform to Student's t‐distribution and can be converted into probabilities of error. A protocol for assigning dates using ‘stable‐isotope dendrochronology’ is proposed, which has the potential to revolutionize the dating of wooden structures and artefacts, allowing the dating of short and invariant ring sequences from young, fast‐grown trees. Such samples are commonplace throughout the historical building and archaeological records and were, until now, considered impossible to date. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd

The recent development of an oxygen isotope (δ¹⁸O) master chronology for south central England (1200–2000 AD) has successfully demonstrated reliable cross-dating between the master chronology and undated samples from vernacular and high-status buildings. The method is well suited to complacent, wide-ringed samples, which are commonplace throughout the UK historic buildings archive and often fail to date by ring-width dendrochronology, or remain unsampled. This paper outlines briefly the isotope dating technique, and describes the application of the method to a number of case studies where ring-width dendrochronology has been unable to provide a robust date. The close association between ring-width dating and stable isotope dendrochronology is explored and its wider potential considered. Note: For illustrations of the buildings used in the case studies, see “Stable Isotope Tree-ring Dates: List 1,” doi:10.1080/03055477.2019.1660956.