C05_01

Statistical challenges and opportunities when modelling multiple radiocarbon dates

Heaton T¹

¹University Of Sheffield, Sheffield, United Kingdom

The recent explosion in the availability of radiocarbon dates has been accompanied by an ever-increasing interest in the application of data science techniques within the archaeological and environmental science communities. Detailed modelling and computational analyses of large sets of dates have the potential to provide unprecedented inference on our past, on rates of change, and on population dynamics. It is essential however that the methods underpinning these “big-data” analyses are rigorous and robust. This concern is particularly relevant for radiocarbon dating since the need for calibration of the determinations introduces considerable, and complex, uncertainties in our dates that must be incorporated into any inference.

This talk will discuss some of the opportunities, and challenges, for the modelling of multiple radiocarbon dates. We will introduce statistically-rigorous alternatives to summed probability distributions (SPDs) that provide robust predictive calendar age summaries, with accompanying uncertainty bands that are essential to aid inference, as well as improved calibration accuracy. We will also discuss how radiocarbon users might obtain more from the IntCal20 radiocarbon calibration curve. Current approaches to calibration consider the calibration curves as normally-distributed around their published pointwise mean. This simplification results in some potentially crucial information about the calibration curve, such as on its covariance, being entirely lost to calibration users. The new IntCal20 methodology generates multiple possible calibration curve realisations, each representing an entire plausible ¹⁴C history from 55,000 – 0 cal yr BP. Using the collection of these realisations, rather than pointwise means, may provide improved inference for complex modelling.

C05_02

Development of the IntCal database

Bronk Ramsey C¹, Austin W², Bard E³, Bayliss A⁴, Cheng H⁵, Friedrich M⁶, Heaton T⁷, Hogg A⁸, Hughen K⁹, Manning S¹⁰, Muscheler R¹¹, Palmer J¹², Pearson C¹³, Reimer P¹⁴, Reimer R¹⁴, Turney C¹², Wacker L¹⁵, IntCal Working Group

¹University Of Oxford, , United Kingdom, ²University of St Andrews, , United Kingdom, ³Cerege, Aix-en-Provence, France, ⁴Historic England, , United Kingdom, ⁵Xi'an Jiaotong University, , China, ⁶University of Hohenheim, , Germany, ⁷University of Sheffield, , United Kingdom, ⁸University of Waikato, , New Zealand, ⁹Woods Hole Oceanographic Institute, , USA, ¹⁰Cornell University, , USA, ¹¹Lund University, , Sweden, ¹²University of New South Wales, , Australia, ¹³University of Arizona, , USA, ¹⁴Queen's University Belfast, , United Kingdom, ¹⁵ETH Zurich, , Switzerland

The IntCal family of internationally-agreed radiocarbon calibration curves is built upon data from research spanning several decades. Most of the data are presented within primary publications and includes meta-data.  In addition to the curves themselves, the IntCal group have collated these data and (since 2010) made them available for other sorts of analysis through an open-access database portal and to ensure transparency in what has been used in the construction of the ratified calibration curves.  As the database of associated data expands, work is underway to facilitate best practice for new data submissions, make more of the associated metadata available in a structured form, and to help those wishing to work with the data using programming languages such as R, Python and MatLab.  The data is complex because of the range of different types of archive, each with their specific requirements. A restructured interface will include visualisation that enable the data to be plotted and compared without needing to be exported.  This development is building on a general open access data model 'IntChron' designed for the sharing of databases of this kind.  The intention is to include complementary datasets which can be used with the main radiocarbon series to provide new insights into the global carbon cycle. As well as facilitation of access to (and use of) the data by other researchers, this work aims to streamline the generation of new calibration curves.

C05_03

In light of Marine20 – how old is the Greenland shark?

Olsen J¹, Nielsen J², Grønkjær P¹, Steffensen J³

¹Aarhus University, Aarhus, Denmark, ²Greenland Institute of Natural Resources, Nuuk, Greenland, ³University of Copenhangen, Copenhagen, Denmark

In 2016 the longevity of the Greenland shark (Somniosus microcephalus) was determined to 392 ±120 years using radiocarbon analysis of eye lenses of 28 specimens. The age of pre-bomb sharks was determined using the Marine13 radiocarbon calibration curve with the assumption that the carbon source of the eye lens nucleus reflects food webs of potentially different ΔR levels. The common wisdom is that because both the absolute reservoir age R and the regional reservoir ages ΔR are changed with Marine20, then the calibrated ages are more or less unchanged. Nonetheless, what happens when you a Bayesian model with greatly increased error margins?  Here we present an updated age estimate of the longevity of the Greenland shark using Marine20 with updated ΔR values by employing a Bayesian model. Further constrains are added by radiocarbon dating of new specimens from the bomb curve era. To support the new post-bomb eye lens radiocarbon data, a marine reference dataset will be presented based on enamel radiocarbon dating of know-age 29 hooded seals (Cystophora cristata) from West Greenland.

C05_04

Current compilation of recent atmospheric radiocarbon

Hua Q¹, Turnbull J^2,3, Santos G⁴, Rakowski A⁵, Ancapichún S^6,7, De Pol-Holz R⁷, Hammer S⁸, Lehman S⁹, Levin I⁸, Miller J¹⁰, Palmer J^11,12, Turney C¹³

¹Australian Nuclear Science And Technology Organisation, Lucas Heights, Australia, ²Rafter Radiocarbon Laboratory, GNS Science, Lower Hutt, New Zealand, ³CIRES, University of Colorado , Boulder, USA, ⁴Earth System Science, University of California, Irvine, , USA, ⁵Institute of Physics, Center for Science and Education, Silesian University of Technology, Gliwice, Poland, ⁶Postgraduate School in Oceanography, Faculty of Natural and Oceanographic Sciences, Universidad de Concepción, Concepción, Chile, ⁷Centro de Investigación GAIA Antártica (CIGA) and Network for Extreme Environment Research (NEXER), Universidad de Magallanes, Punta Arenas, Chile, ⁸Institut für Umweltphysik, Heidelberg University , Heidelberg, Germany, ⁹INSTAAR, University of Colorado,, Boulder, USA, ¹⁰NOAA Global Monitoring Laboratory, Boulder, USA, ¹¹ARC Centre of Excellence for Australian Biodiversity and Heritage, School of Biological, Earth and Environmental Sciences, University of New South Wales, , Australia, ¹²Chronos 14Carbon-Cycle Facility and the Earth and Sustainability Science Research Centre, University of New South Wales, , Australia, ¹³Division of Research, University of Technology Sydney, , Australia

The last couple of centuries has seen substantial changes in atmospheric radiocarbon driven by the combustion of fossil fuels free of ¹⁴C since the mid-19th century and the injection of bomb-derived radiocarbon into the atmosphere, mostly in the late 1950s and early 1960s. The current compilation of recent atmospheric radiocarbon levels, covering the period from 1950 to 2019, was released late last year. It consists of zonal, hemispheric and global summer data sets for use in carbon-cycle studies and monthly data sets for five zones (Northern Hemisphere zones 1, 2, and 3, and Southern Hemisphere zones 3 and 1-2) for more accurate radiocarbon dating of recent terrestrial samples. After describing the current compilation, the presentation will focus on new and future collections. This discussion includes new data sets such as atmospheric sampling from Alert and Neumayer (Levin et al., 2021), tree rings from Eastern Amazon Basin (Santos et al., in prep.) and southern Chile (De Pol-Holz et al., in prep.). The new data enables the extension to a more recent time period and the improved determination of zonal borders. Autumn and winter plant/seed data during the early bomb period (e.g., Hüls et al. 2021), where atmospheric sampling is not available, can allow an improved compilation of monthly zonal data. Finally, data quality considerations, such as applying dendrochronological methods, tree-ring pre-treatment and replicate radiocarbon analyses, will also be discussed.

Hüls, M. et al. 2021. Radiocarbon 63, 1387-1396.

Levin, I. et al. 2021. Radiocarbon, doi:10.1017/RDC.2021.102

C05_05

Southern Levant calibration regional offsets identified by short-lived archaeological materials

Regev J¹, Regev L¹, Uziel J², Gadot Y³, Ben-Ami D², Mintz E¹, Boaretto E¹

¹Weizmann Institute of Science, Rehovot, Israel, ²Israel Antiquities Authority, Jerusalem, Israel, ³Tel Aviv University, Tel Aviv, Israel

The topic of regional offsets from the northern hemisphere calibration curve has been gaining attention in recent years as part of a community effort to increase the radiocarbon calibration resolution. Usually, the suggested offsets are identified by modern, known-age samples or tree rings, dendrochronologically dated. Our group has developed over the years microarchaeological tools, which enable radiocarbon-aimed field sampling for high-resolution dating and modeling using short-lived charred remains. These analyses can provide confidence in the archaeological context and stratigraphy in relation to such samples. Therefore, once those sequences are wiggle-matched, they follow the calibration curve with very few outliers.

We have encountered two instances, one in the 1st millennium BC and the other in the 3rd millennium BC, in which our modeled results extended beyond the calibration curve with an excess of ¹⁴C by a few permille. Furthermore, we have found the opposite effect of ¹⁴C depletion when dating the historically known-age destruction event of Jerusalem by the Babylonians in 586 BC. In those instances, wherever the calibration curve is not based on single tree rings, some Irish oak and/or bristlecone pine samples were additionally measured.

C05_06

Annual radiocarbon dating of tree rings of the beginning and the end of the Yayoi period, Japan.

Sakamoto M^1,2, Hakozaki M¹, Nakatsuka T³, Ozaki H⁴

¹National Museum of Japanese History, Sakura-shi, Japan, ²The Graduate University for Advanced Studies, Sakura-shi, Japan, ³Nagoya University, Nagoya-shi, Japan, ⁴The University of Tokyo, Bunkyo-ku, Japan

Paddy rice cultivation is thought to have been introduced to Kyushu Island of the Japanese archipelago from mainland China via the Korean Peninsula, but until now no dendrochronological dating of the trees which had been growing at that time on Kyushu Island has been achieved. However, the practical application of oxygen isotope dendrochronology has enabled to date a wide range of tree species and regions and has opened the possibility of developing calibration curves based on its results. In this report, we examine the behavior of radiocarbon ages of the annual rings of a buried chinaberry (Melia azedarach) from 1025 to 927 B.C.E. excavated in Kagoshima, southern Kyushu Island, which is dated by oxygen isotope dendrochronology.

Two datasets of Japanese tree rings were introduced for IntCal20, which made a change in the shapes of the curve from the 1st to 3rd centuries C.E. However, the validity of the revision should be considered by accumulating radiocarbon dating of tree rings. We also measured radiocarbon dates of Japanese zelkova (Zelkova serrata) buried in Miyagi, northeastern prefecture of the Japanese archipelago, which was dated by oxygen isotope dendrochronology (41 B.C.E – 130 C.E.). Although this sample is older than expected age of the end of the Yayoi period, regional offset in radiocarbon age can be discussed by comparing with Korean tree rings (Hong et al., this conference).

This work was supported by JSPS KAKENHI Grant Numbers JP18H03594 and JP22H00026.

C05_07

A pollen ¹⁴C stratigraphy of Lake Suigetsu from 12 to 20 ka BP

Omori T¹, Yamada K², Kitaba I², Nakagawa T²

¹The University Museum, The Uiniversity of Tokyo, Tokyo, Japan, ²Research Centre for Palaeoclimatology, Ritsumeikan University, Shiga, Japan

A radiocarbon stratigraphy of terrestrial fossil pollen grains extracted from Lake Suigetsu’s varved sediment has been established from 12 ka to 20 ka cal BP in multi-decadal resolution. The obtained curve showed i) an overall good agreement with that of terrestrial macro fossils (Bronk Ramsey et al. 2012), and ii) significantly smoother decadal trends than those of the terrestrial macro fossils. These results indicate that the fossil pollen grains are i) as good indicator of the atmospheric radiocarbon concentration as terrestrial leaf fossils, and ii) picking up decadal signals of the atmospheric radiocarbon variability, free from inter-annual scatters which are inevitable with terrestrial leaf fossils. Because pollen grains fix the contemporary atmospheric radiocarbon, the smoothness of the curve should be a good indication of the true radiocarbon variability, rather than the terrestrial radiocarbon reservoir effects. The fact that curve is relatively free from the influence of inter-annual variability, which has been proved to be more significant than was previously believed (Bronk Ramsey et al. 2020, Miyake et al. 2017), implies that the radiocarbon datasets of fossil pollen grains are likely to have stronger power to constrain ages, when used as a radiocarbon calibration model.

C05_08

Semi-millennial structure of the Suigetsu atmospheric ¹⁴C record

Sarnthein M¹, Grootes P¹

¹University of Kiel, Kiel, Germany

Centennial-to-millennial-scale fluctuations in atmospheric ¹⁴C concentration on time-scales from years to millennia have been documented by tree-rings for the last 15 kyr. Further back, terrestrial macrofossils from sediment cores of Lake Suigetsu extend this ¹⁴C record from ~10 ka to 50 ka. The significance of these features is under debate since the signal-to-noise ratio of the record is low. Yet, coherent semi-millennial-scale structures were identified by three different techniques, namely visual inspection, a first derivative of the ¹⁴C-age vs calendar age, and Bayesian spline inflections of ¹⁴C concentration vs calendar age. Accordingly, the semi-millennial features of the noisy Suigetsu ¹⁴C record may be objectively real. Being corroborated by the tree ring-based ¹⁴C master record ~10 to ~15 cal. ka, the features attain global significance and extend the fine-scale variability back to ~35 cal. ka. Carbonate-based ¹⁴C records from ocean sediments and speleothems appear far smoother. Together with data from Suigetsu and floating tree ring sections, these records form the backbone of the IntCal20 record that beyond 15 ka largely misses the Suigetsu fine structure. ¹⁴C decay reduces ¹⁴C-signal amplitudes over time, so Holocene ¹⁴C signals of solar modulation disappear below noise level during earlier times. Accordingly, most ¹⁴C structures visible >15 ka originally had larger signals, most likely, connected to climate, ocean-atmosphere CO₂ exchange, and carbon cycle. During this time, the Suigetsu ¹⁴C fine structure may thus give valuable information about these forcings. Also, it may serve for valuable global stratigraphic correlation of pertinent ¹⁴C records of oceanic plankton sediments.

C05_P01

Radiocarbon analysis of annually published journals

Gautschi P¹, Brehm N¹, Wertnik M¹, Synal H¹, Wacker L¹

¹ETH Zurich, Zurich, Switzerland

The paper of books or journals is typically produced from cellulose extracted from trees. This makes them potentially suitable for radiocarbon dating. However, precise calendar age determination of the measured radiocarbon ages is difficult. Paper production has a lot of unknown factors such as different tree ages, i.e. number of tree rings, which go into the production of cellulose. Additionally, storage time between harvest of a tree and final publication is usually unknown and may vary. Therefore, the atmospheric integration time of a paper product, is an unknown distribution.

A series of 52 annually published journals over the ¹⁴C bomb pulse (1947 - 2021 AD) have been prepared for radiocarbon analysis to study the age assembly and the storage time of trees used for the paper. The measured ¹⁴C concentrations were compared to modelled ¹⁴C concentrations in paper, which are based on a simple tree-ring model and assuming the cellulose was formed from atmospheric CO₂ at the year of formation. Best agreements were obtained assuming a mean age of trees of 40 to 80 years and a relatively short storage time of two years between the harvest of trees and the final publication. Although the measured journals follow the model qualitatively, some significant deviations were observed between individual years of publication.

C05_P02

Barley Mash its history in the Radiocarbon Inter-comparison studies and its role as a modern carbon standard.

Naysmith P¹, Scott M², Dunbar E¹

¹SUERC, East Kilbride, United Kingdom, ²School of Mathematics and Statistics, University of Glasgow,

Over the past 30 years, the format of the radiocarbon (¹⁴C) inter-comparison studies has changed due to the change and development in measurement techniques. The selection of sample types used in these studies has remained constant—namely, natural and routinely dated materials that could subsequently be used as in-house laboratory standard material. Barley Mash, a by-product from the manufacture of malt whisky, is a good example of one of the widely used material from the Intercomparison studies.  Barley from a single year’s growing season is used in the production of whisky, often coming from a single geographical location and is available is large quantities, thus making it a suitable modern carbon reference material. Barley Mash samples have been used ten times in inter-comparison starting with TIRI, in 1992 through to GIRI, in 2021, with the same batch of barley mash being used in multiple inter-comparison studies. In this paper, the barley mash results from all the intercomparisons will be collated and reanalysed.

During the last 19 years, the Barley Mash TIRI A has been used in the SUERC ¹⁴C laboratory as an in-house laboratory standard material resulting in a dataset of several thousand of measurements. Such a rich data set is mined to illustrate some of the benefits arising from the inter-comparison program.

C05_P03

Determination of the influence of air parcels in the Northern and Southern Hemisphere on radiocarbon calibration in Southern America

Ancapichun S¹, Pawlyta J², Rakowski A³, Sieczkowska D⁴

¹Universidad de Concepción, Concepción, Chile, ²AGH, Kraków, Poland, ³SUT, Gliwice, Poland, ⁴University of Warsaw, Warsaw, Poland

The chronology of Machu Picchu was traditionally associated with the period attributed to the reign of Pachacuti Inca Yupanqui. Within the scheme of the so-called historical chronology, proposed by John H. Rowe in 1945, the ascension to power of Pachacuti Inca took place around 1438 CE and the construction of Machu Picchu began by 1450 -1460 CE. Several radiocarbon-dated samples may help to understand the chronology of the construction of llaqta of Machu Picchu, Chachabamba, and Choqesuysuy. However, there is a lack of consensus between different radiocarbon-based Inca chronologies, because of the lack of information of which calibration curves to use: Northern Hemisphere (NH), Southern Hemisphere (SH), or a mixed calibration curve? Thus, the main goal of the present investigation is to develop a new methodological approach to reconstruct a consistent radiocarbon-based Incan chronology, an approach based on the determination, through modeling, of the proportion of NH and SH air parcels arriving at three relevant Inca settlements. We found air parcels contributions from the NH and SH for: Machu Picchu (50% NH and 50% SH), Chamical (29% NH and 71% SH), and Tiquischullpa (41% NH and 59% SH). Thereby, our investigation brings three proportions to mix NH and SH 14C curves, based on an empirical method, for Inca’s radiocarbon dating studies. Our study emphasizes that great attention should be paid when applying radiocarbon calibration to radiocarbon measurements of samples originating in regions under the influence of the atmospheric circulation-boundary between hemispheres. 

C05_P04

Comprehensive update of marine reservoir values for New Zealand coastal waters to inform coastal hazard research

Turnbull J^1,2, Clark K¹, Ferrick T¹, Marshall B³, Howarth J⁴

¹GNS Science, Lower Hut, New Zealand, ²CIRES, University of Colorado, Boulder, USA, ³Te Papa Tongarewa Museum of New Zealand, Wellington, New Zealand, ⁴Victoria University of Wellington, Wellington, New Zealand

Accurate dating of coastal hazard events such as earthquakes and tsunamis typically hinges upon marine radiocarbon ages, and a well-constrained marine reservoir correction is vital to evaluating the size and frequency of large to great subduction earthquakes and tsunamis.     Yet in New Zealand, we have relied on only 31 ∆R values from four locations to estimate ∆R for the entire coastline.  Here we add 170 new measurements to the marine reservoir correction dataset for the mainland New Zealand and evaluated the influence of location, feeding method, living depth, environmental preference and species on the variance in ΔR values. We find there are no significant differences between ΔR values from suspension-feeding organisms compared to browsing/scavenger/carnivore-feeding organisms, and we find little variability between species that prefer estuarine environments to open coastal environments. This means that when dating shells from geological records, we do not need to take particular care to avoid certain species that may have anomalies of carbon precipitation in their shells.  Importantly, location is the dominant control on ∆R variability and we recommend the subdivision of New Zealand into five large regions, each with a different ΔR value.