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The radiocarbon (14C) dating facility at the Centre for Isotope Research, University of Groningen went through a major upgrade in 2017 and this included installation of a MICADAS accelerator mass spectrometer (AMS). In the first 18 months, we performed 4000 sample and 3000 reference measurements. A careful evaluation of those measurement results is presented, to characterize the various sources of uncertainty and to ultimately assign, for every sample measurement, a realistic expanded uncertainty. This analysis was performed on the measurements of secondary references and sample duplicates in various phases of their processing steps. The final expanded uncertainty includes both the 14C measurement uncertainties and uncertainties originating from pretreatment steps. Where the 14C measurement uncertainty includes straightforward uncertainties arising from Poisson statistics, background subtraction, calibration on Oxalic Acid II and δ13C correction, the uncertainties originating from pretreatment steps are based on the spread of actual measurement results for secondary references and sample duplicates. We show that the 14C measurement uncertainty requires expansion, depending on the number of processing steps involved prior to a 14C measurement, by a maximum factor of 1.6 at our laboratory. By using these expansion (multiplication) factors, we make our reported uncertainty both more realistic and reliable.
The last decade has seen the development of a range of new statistical and computational techniques for analysing large collections of radiocarbon (14C) dates, often but not exclusively to make inferences about human population change in the past. Here we introduce rcarbon, an open-source software package for the R statistical computing language which implements many of these techniques and looks to foster transparent future study of their strengths and weaknesses. In this paper, we review the key assumptions, limitations and potentials behind statistical analyses of summed probability distribution of 14C dates, including Monte-Carlo simulation-based tests, permutation tests, and spatial analyses. Supplementary material provides a fully reproducible analysis with further details not covered in the main paper.
We present two new Bayesian 14C models using IntCal20 that incorporate 17 new calibrated AMS ages for Early Bronze IV Tell Abu en-Ni‘aj and Middle Bronze Age Tell el-Hayyat, located in the northern Jordan Valley, Jordan. These freshly augmented suites of carbonized seed dates now include 25 AMS dates from Tell Abu en-Ni‘aj and 31 AMS dates from Tell el-Hayyat. The modeled founding date for Tell Abu en-Ni‘aj strengthens an emerging high chronology for Early Bronze IV starting by 2500 cal BC, while the end of its habitation by 2200 cal BC may exemplify a regional pattern of increasingly pervasive abandonment among late Early Bronze IV settlements in the Southern Levant. In turn, our modeled date for the Early Bronze IV/Middle Bronze Age transition at Tell el-Hayyat around 1900 cal BC pushes this interface about a century later than surmised traditionally, and its abandonment in Middle Bronze III marks an unexpectedly early end date before 1600 cal BC. These inferences, which coordinate Bayesian AMS models and typological ceramic sequences for Tell Abu en-Ni‘aj and Tell el-Hayyat, contribute to an ongoing revision of Early and Middle Bronze Age Levantine chronologies and uncoupling of their attendant interpretive links between the Southern Levant and Egypt.
We here present a comparison of methods for the pretreatment of a batch of tree rings for high-precision measurement of radiocarbon at the Aarhus AMS Centre (AARAMS), Aarhus University, Denmark. The aim was to develop an efficient and high-throughput method able to pretreat ca. 50 samples at a time. We tested two methods for extracting α-cellulose from wood to find the most optimal for our use. One method used acetic acid, the other used HCl acid for the delignification. The testing was conducted on background 14C samples, in order to assess the effect of the different pretreatment methods on low-activity samples. Furthermore, the extracted wood and cellulose fractions were analyzed using Fourier transform infrared (FTIR) spectroscopy, which showed a successful extraction of α-cellulose from the samples. Cellulose samples were pretreated at AARAMS, and the graphitization and radiocarbon analysis of these samples were done at both AARAMS and the radiocarbon dating laboratory at Lund University to compare the graphitization and AMS machine performance. No significant offset was found between the two sets of measurements. Based on these tests, the pretreatment of tree rings for high-precision radiocarbon analysis at AARAMS will henceforth use HCI for the delignification.
We present a new biennial record of radiocarbon (14C) measured in Danish oak. The new record covers the years 1251–1378 CE, thereby spanning the Grand Solar Minimum known as the Wolf Minimum. Two oak samples from every other year were measured at the AMS facility at Aarhus University (Denmark), resulting in an average precision of 1.4‰ for the record. Spectral analysis of the new record revealed two peaks at 27 and 9.1 years, which could indicate the Hale cycle was lengthened and the Schwabe cycle shortened during the Wolf Minimum, but it is also possible that the amplitude of the Schwabe cycle was too small to be accurately identified with the acquired precision of this record. The record was bandpass filtered to investigate the variability of the amplitude in different bands, which showed a dampening of the amplitude during the second half of the Wolf Minimum in bands centered on the Schwabe and the Hale cycle, respectively. A reconstruction of the solar modulation function, Φ, also showed a periodicity of ca. 9 years, and indicated that the Wolf Minimum was preceeded by one cycle of decreased solar activity.
Medieval manuscripts are invaluable archives of the written history of our past. Manuscripts can be dated and localized paleographically, but this method has its limitations. The Fragmenta membranea manuscript collection at the National Library of Finland has proved difficult to date using paleographic methods. Radiocarbon dating has been applied to manuscripts of parchment before, but a systematic protocol for radiocarbon dating of parchment has not been established with a minimally destructive sampling strategy. In this work, we have established a radiocarbon dating procedure for parchments combining a clean-room based chemical pretreatment process, elemental analyzer combustion, automatic graphitization and accelerator mass spectrometry (AMS) measurements to reduce the AMS target size from a typical 1 mg of carbon. Prolonged acid treatment resulted in improved dating accuracy, since this is consistent with the manufacturing process of medieval parchment involving a lime bath. Two different combustion processes were compared. The traditional closed tube combustion (CTC) method provided a well-established though labor-intensive way to produce 1 mg AMS targets. The Elemental Analyzer-based process (EA-HASE, Elemental Analyzer Helsinki Adaptive Sample prEparation line), is designed for fast combustion and smaller sample sizes. The EA-HASE process was capable of reproducing the simulated radiocarbon ages of known-age samples with AMS graphite target sizes of 0.3 mg of carbon, corresponding to a 3 mm2 area of a typical medieval parchment. The full potential of the process to go down to as little as 50 μg will be further explored in the future in parallel to studies of sample-specific contamination issues.
A new series of 19 radiocarbon dates provides new insights on the human settlement activity in central Ukraine. The paper presents data from the Early Holocene until the establishment of Trypillian mega-sites in the late Vth mill. BC. Our new dates from a long sequence of the site of Melnychna Krucha refine the chronology of the Middle and Late Mesolithic and local ceramic-bearing “Buh-Dniester” culture. Additional dates were obtained on bones from Linear Pottery culture sites and Trypillian sites of stages A3 and B1.
Radiocarbon (14C) dating has been widely used to determine the age of deposits, but there have been frequent reports of inconsistencies in age among different dating materials. In this study, we performed radiocarbon dating on a total of 33 samples from 8-m-long sediment cores recovered from the wetland of the Muljangori volcanic cone on Jeju Island, South Korea. Ten pairs of humic acid (HA) and plant fragments (PF) samples, and three pairs of HA and humin samples, from the same depths were compared in terms of age. The PF were consistently younger than the HA. Interestingly, the age difference between HA and PF samples showed a long-term change during the past 8000 years. To test whether there was an association between this long-term age difference and climate change, we compared with the carbon/nitrogen (C/N) ratios and total organic carbon isotope (δ13CTOC) values of the sediments, as indicators of the relative abundance of terrestrial and aquatic plants; these parameters showed similar long-term trends. This suggests that the increasing (decreasing) trend in age difference was influenced by long-term dry (wet) climate change.
Oracle bone script developed into a sophisticated writing system in Shang Dynasty of China more than 3000 years ago. The systematic scientific dating of oracle bones had not been previously reported. Here we present radiocarbon (14C) dates measured from the sequential samples of oracle bones that pertain to the Shang kings. The results indicate that King Wu Ding (who is called Wu Ting in some literature) reigned during 1254 BC to 1197 BC, and the Shang Dynasty terminated around 1041 BC. It also points that the Li group in the sequence of oracle bones is most probably related to the time of King Wu Ding and Zu Geng.
The article presents the results of the absolute dating of 31 pre-Columbian funerary bundles excavated on the Cerro Colorado site located in the northern part of the Peruvian Central Coast, where the Chancay culture developed in the last centuries before the Spanish invasion. The typical custom in this region was to wrap the dead with textiles and a vegetal material, by which the bundle was created. The funerary bundles of the Cerro Colorado differed in terms of the complexity, quantity and quality of the materials used (especially textiles and metal ornament). Before our project, there was not a single radiocarbon (14C) date for an undisturbed Chancay tomb, which made it impossible to understand the temporal dependency between the elaborated, standard, and modest bundles. Our results finally shed light on their proper chronological position, also demonstrating that the most elaborate bundles were created between the 13th and 15th centuries.
Radiocarbon (14C) dating was performed for various types of precious coral colony fragments collected from the Ashizuri fishing field, around 100–200 m deep, off the southwest coast of Kochi Prefecture, Japan, to understand the historical background of one of the largest precious coral fishing fields in Japan. The 14C ages of the 55 specimens range from ~7500 years ago to the modern. Most of the measured samples were older than 1871, when fishing activities of precious corals began in Kochi Prefecture. These results suggest that most of the deaths of the precious coral colonies were due to natural causes, such as natural mortality, predation, or various forms of environmental degradation, and not strictly related to destructive fishing practices. Additionally, precious corals started inhabiting the study area at least ~7500 years ago, when the marine condition became similar to that of today after the Last Glacial Period. This study is the first to focus on the age of dead precious coral fragments and has revealed that they might be an important fossil resource that could lengthen the timespan of precious coral fishery. This additional time may enable us to establish reasonable and effective regulations for sustainable fishery.
Pleistocene human remains are rare inland on the Iberian Peninsula. Most are considered Neandertals, but anthropological analyses and direct dating are rare. Recently, we published a study of a navicular from this region found in the Torrejones Cave. The results showed it differed from that of Neandertals and it was re-identified as Homo sapiens. Following the previous stratigraphic and biochronologic descriptions, we suggested that it could correspond to an Upper Paleolithic human, since the navicular was apparently recovered in the Late Pleistocene from an in situ unit. Direct radiocarbon dating from this fossil (4855–5036 cal BP), believed to be the only Paleolithic Homo sapiens from inland Iberia, as well as other hominin and faunal remains from the site, show that the human bones actually date to the Chalcolithic. The unexpectedly recent chronology for the navicular implies that there is no evidence of human fossils from the Upper Paleolithic in Torrejones Cave. Thus, any date from the Middle/Upper Paleolithic human record should be taken with caution until in-depth paleoanthropological, stratigraphical and/or direct dating studies are conducted. Extraordinary caution is recommended when human remains are recovered from apparently Paleolithic units in contexts bearing Holocene sepulchral units on the uppermost levels and/or some evidence of bioturbation.
The AD 775 peak in Δ14C (henceforth, M12) was first measured by Miyake et al. and has since been confirmed globally. Here we present earlywood and latewood Δ14C values from tree rings of pinyon pine (Pinus edulis) from Mummy Cave, Canyon de Chelly National Monument, Chinle, Arizona, USA, for the period AD 770–780. These data reconfirm the timing of M12 and show a small rise in Δ14C in AD 774 latewood. Allowing for the delay in lateral transfer of radiocarbon produced at high latitude, this suggests that 14C peak production occurred in late winter or spring of AD 774. Additionally, Δ14C decreased slightly in the earlywood of AD 775 and increased in the latewood of AD 775 to a higher level than that observed in AD 774.
The San Pedro de Atacama oases, located in northern Chile’s hyperarid Atacama Desert, have been occupied for at least 3000 years. Here, we examine cemetery use in the oases, with emphasis on the Middle Period (ca. AD 400–1000). By modeling of a large corpus (n=243) of radiocarbon dates, over 90% of which are direct AMS assays of human bone collagen, we attempt to establish a temporal framework by which to explore the establishment of formalized social inequality in this period. Modeling of these dates at three locally defined scales (all ayllus, inter-ayllu, and intra-ayllu) permit heretofore unavailable insights into the chronological and spatial dimensions of life and mortuary activity in the oases and allow us to better contextualize patterns of social inequality during the dynamic Middle Period. The results of this modeling indicate two distinct peaks of occupation during the Middle Period in San Pedro and document significant temporal variability in cemetery use patterns on both inter- and intra-ayllu scales. These results stress the importance of local social and environmental factors to the occupation of the oases and provide crucial chronological structure for future archaeological and bioarchaeological research in the region.
For most of human history, funerary burial has been unusual. Archaeology shows a shift in funerary practices in postglacial hunter-gatherers, in parts of Europe during the Late Mesolithic. This is documented by the burial grounds in the Tagus and Sado valleys in the southwestern Iberian Peninsula, Portugal, where ca. 376 burials were excavated. This study presents a chronology for the burial activity in these sites and contextualizes the start and end activity phases within regional environmental changes and cultural developments. The dataset consists of 76 14C dates on human bone (19 new, 57 published) including new dates from contexts in Portugal outside these valleys. Bayesian chronological models were defined in OxCal, and protein carbon contributions of marine foods were estimated by the Bayesian mixing model FRUITS. The results indicate a broader timeframe for the Late Mesolithic in Portugal, than previously suggested, starting during a period of significant environmental changes, ca. 8500–8300 cal BP, and ending ca. 7000 cal BP. The burial activity decreased during the establishment of Neolithic farmers in southwestern Iberia from ca. 7450 cal BP, however, these burial grounds continued to be used by Mesolithic hunter-gatherers, showing that diverse social structures and worldviews coexisted for several generations.
We explore marine reservoir effects (MREs) in seal bones from the northern Bering and Chukchi Seas regions. Ringed and bearded seals have served as dietary staples in human populations along the coasts of Arctic northeast Asia and North America for several millennia. Radiocarbon (14C) dates on seal bones and terrestrial materials (caribou, plants seeds, wood, and wood charcoal) were compared from archaeological sites in the Bering Strait region of northwestern Alaska to assess MREs in these sea mammals over time. We also compared these results to 14C dates on modern seal specimens collected in AD 1932 and 1946 from the Bering Sea region. Our paired archaeological samples were recovered from late Holocene archaeological features, including floors from dwellings and cache pits, that date between 1600 and 130 cal BP. 14C dates on seal bones from the northern Bering and Chukchi Seas show differences [R(t)] of 800 ± 140 years from to their terrestrial counterparts, and deviations of 404 ± 112 years (ΔR) from the marine calibration curve.
Accelerator mass spectrometry (AMS) dating of pollen concentrates is often used in lake sediment records where large, terrestrial plant remains are unavailable. Ages produced from chemically concentrated pollen as well as manually picked Pinaceae grains in Yellowstone Lake (Wyoming) sediments were consistently 1700–4300 cal years older than ages established by terrestrial plant remains, tephrochronology, and the age of the sediment-water interface. Previous studies have successfully utilized the same laboratory space and methods, suggesting the source of old-carbon contamination is specific to these samples. Manually picking pollen grains precludes admixture of non-pollen materials. Furthermore, no clear source of old pollen grains occurs on the deglaciated landscape, making reworking of old pollen grains unlikely. High volumes of CO2 are degassed in the Yellowstone Caldera, potentially introducing old carbon to pollen. While uptake of old CO2 through photosynthesis is minor (F14C approximately 0.99), old-carbon contamination may still take place in the water column or in surficial lake sediments. It remains unclear, however, what mechanism allows for the erroneous ages of highly refractory pollen grains while terrestrial plant remains were unaffected. In the absence of a satisfactory explanation for erroneously old radiocarbon ages from pollen concentrates, we propose steps for further study.
Eurasian steppes experienced frequent cultural transfers, human migration, and diffusion of techniques during the Bronze Age. The Hami Oasis is one of the most dynamic areas and has attracted multiple cultural flows. It is an important area that connects various routes of the Tianshan Corridor with the Hexi Corridor in western China. The Tianshanbeilu cemetery is the largest Bronze Age cemetery in Hami. Thirty-seven new radiocarbon dates allowed us to establish a new and more accurate chronology for Tianshanbeilu. Our results showed that the Tianshanbeilu cemetery was used from approximately 2022–1802 cal BC and remained in use from 1093–707 cal BC. This indicates that Tianshanbeilu is the earliest and longest-used known cemetery in eastern Xinjiang. By incorporating the typology of artifacts and stratigraphic relationships, the development of the Tianshanbeilu cemetery was divided into four phases. The first phase was from 2011–1672 cal BC, the second phase was from 1660–1408 cal BC, the third phase was from 1385–1256 cal BC, and the fourth phase was from 1214–1029 cal BC.
This study describes a procedural blank assessment of the ultraviolet photochemical oxidation (UV oxidation) method that is used to measure carbon isotopes of dissolved organic carbon (DOC) at the National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS). A retrospective compilation of Fm and δ13C results for secondary standards (OX-II, glycine) between 2009 and 2018 indicated that a revised blank correction was required to bring results in line with accepted values. The application of a best-fit mass-balance correction yielded a procedural blank of 22.0 ± 6.0 µg C with Fm of 0.30 ± 0.20 and δ13C of –32.0 ± 3.0‰ for this period, which was notably higher and more variable than previously reported. Changes to the procedure, specifically elimination of higher organic carbon reagents and improved sample and reactor handling, reduced the blank to 11.0 ± 2.75 µg C, with Fm of 0.14 ± 0.10 and δ13C of –31.0 ± 5.5‰. A thorough determination of the entire sample processing blank is required to ensure accurate isotopic compositions of seawater DOC using the UV oxidation method. Additional efforts are needed to further reduce the procedural blank so that smaller DOC samples can be analyzed, and to increase sample throughput.
Fungal hyphae associated with tree roots extending into the surrounding substrate are suspected to have to contaminated buried plant material with recent carbon in two examples and to have resulted in erroneously young radiocarbon ages. This problem might be overcome by choosing sampling sites far from trees or by analyzing the lignin component of samples, although the latter is presently difficult.