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

In 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

Findings from an in-depth annual tree-ring radiocarbon inter-comparison

The radiocarbon calibration curve so far contains annually resolved data only for a short period of time. With accelerator mass spectrometry (AMS) matching the precision of decay counting, it is now possible to efficiently produce large datasets of annual resolution for calibration purposes using small amounts of wood. The radiocarbon inter-comparison on single-year tree-ring samples presented here is the first to investigate specifically possible offsets between AMS laboratories at high precision. The results show that AMS laboratories are capable of measuring samples of Holocene age with an accuracy and precision that is comparable or even goes beyond what is possible with decay counting, even though they require a thousand times less wood. It also shows that not all AMS laboratories always produce results that are consistent with their stated uncertainties. The long-term benefits of studies of this kind are more accurate radiocarbon measurements with, in the future, better quantified uncertainties.Additional co-authors: Douglas J Kennett, Timothy D J Knowles, Margot Kuitems, Todd E Lange, Fusa Miyake, Marie-Josée Nadeau, Toshio Nakamura, J Philip Naysmith, Jesper Olsen, Takayuki Omori, Fiona Petchey, Bente Philippsen, Christopher Bronk Ramsey, G V Ravi Prasad, Martin Seiler, John Southon, Richard Staff, Thibault Tun

Re-evaluation of the New Oxalic Acid standard with AMS

ISSN:0168-583XISSN:1872-958

Kibworth Harcourt Mill, Langton Road, Kibworth Harcourt, Harborough, Leicestershire: Ring-width Dendrochronology and Radiocarbon Wigglematching of additional Oak Timbers

An original set of samples taken in 2004 were re-assessed, and an additional 21 timbers were sampled, along with one measured by digital photography. Some timbers are thought to have been derived from the same parent trees, and a new site master made from the ring-width series of 17 trees was made. One later timber was dated individually. Radiocarbon wiggle-matching was undertaken on the main post, which could not be dated by ring-width dendrochronology. The main post was found to have come from a tree felled after cal AD 1574–1620 (95% probability), but probably after cal AD 1584–1605 (68% probability). Spring vessels for AD 1774 were found on four timbers, pushing the construction date for the majority of the mill a year later than previously found. Some elements of the cross tree appear to have come from trees felled in AD 1791–1824, which may suggest that the trestle has been replaced. A packing piece under a cross tree dates to after AD 1845

High Precision 14C Analysis in Small Seawater Samples

ISSN:0033-822

Bourn Mill, Caxton End, Bourn, Cambridgeshire: ring width dendrochronology, radiocarbon wiggle-matching and oxygen isotope analysis of elm and oak timbers

Samples were taken from 21 of the various timber elements of the mill, including both oak and elm timbers. Conventional ring-width dendrochronology established that the main post was most likely felled in the first half of the sixteenth century, making this the earliest main post of a post mill yet dated. Felling dates for the sheers and front sheer spacer of spring AD 1703 and spring AD 1707 also indicated a previously unknown rebuilding phase, which is earlier than the known partial- destruction of the mill during a storm in AD 1741. Other weak statistical matches between the ring-width series of oak and elm timbers were explored using other scientific dating techniques. The combined analysis confirmed that these other surviving timbers in the trestle probably date from repairs undertaken in AD 1874 and AD 1931 but suggested that many other timbers in the buck are eighteenth-century survivals

Comparability of radiocarbon measurements in dissolved inorganic carbon of seawater produced at ETH-Zurich

Radiocarbon observations (Δ14C) in dissolved inorganic carbon (DIC) of seawater provide useful information about ocean carbon cycling and ocean circulation. To deliver high-quality observations, the Laboratory of Ion Beam Physics (LIP) at ETH-Zurich developed a new simplified method allowing the rapid analysis of radiocarbon in DIC of small seawater samples, which is continually assessed by following internal quality controls. However, a comparison with externally produced 14C measurements to better establish an equivalency between methods was still missing. Here, we make the first intercomparison with the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility based on 14 duplicate seawater samples collected in 2020. We also compare with prior deep-water observations from the 1970s to 1990s. The results show a very good agreement in both comparisons. The mean Δ14C of 12 duplicate samples measured by LIP and NOSAMS were statistically identical within one sigma uncertainty while two other duplicate samples agreed within two sigma. Based on this small number of duplicate samples, LIP values appear to be slightly lower than the NOSAMS values, but more measurements will be needed for confirmation. We also comment on storage and preservation techniques used in this study, including the freezing of samples collected in foil bags.ISSN:0033-822

Girlington Hall, Ovington, County Durham: Tree-Ring Analysis and Radiocarbon Wiggle-Matching of Oak and Elm Timbers

Analysis was undertaken on samples from the roof and ceiling structures of the hall and cross-wing resulting in the construction of three site sequences: GRLNSQ01 contains 34 oak samples and spans the period AD 1268–1440; GRLNSQ02 contains 13 oak samples and spans the period AD 1412–1579; GRLNSQ03 contains six elm samples but remains undated. In the hall, a series of reused common rafters, thought to have been from the original roof, have been dated to AD 1436, whilst two purlins are somewhat later being felled in AD 1579 and AD 1594–1619. The ground- and first-floor ceiling frames, thought to be later alterations, utilise timber felled in AD 1579, but the first floor ceiling also incorporates some timber felled in the period AD 1435–60. In the cross-wing, the roof timbers have been dated as being felled in AD 1439 and AD 1440, whilst the ground-floor ceiling frame also contains timber felled in AD 1440. The first-floor ceiling frame, again thought to be a later alteration, contains some timbers felled in the period AD 1435–60 and others potentially representing more than one period of felling in the mid/late sixteenth century. Radiocarbon dating was undertaken on single-ring samples from two elm timbers (GRL-N18 and GRL-N20) from the 158 year undated site sequence GRLNSQ03. Wiggle-matching of these results indicates that the timbers in this site sequence, from the hall roof, were probably felled around cal AD 1700