Annually resolved radiocarbon (14C) measurements on tree rings led to the discovery of abrupt variations in 14C production attributed to large solar flares. We present new results of annual and subannual 14C fluctuations in tree rings from a middle-latitude sequoia (California) and a high-latitude pine (Finland), analyzed for the period 1030–1080 CE, to trace a possible impact of the Crab supernova explosion, occurring during the Oort minimum of solar activity. Our results indicate an increase of Δ14C around 1054/55 CE, which we estimate is higher in magnitude than the cyclic variability due to solar activity at a 2σ significance level. The net signal appears to be synchronized in the studied locations. Several sources of this event are possible including γ-rays from the Crab supernova, an unusually weak solar minimum or a solar energetic particle incident. More data are needed to provide more insight into the origin of this 14C event.

El Maye is a community located in the municipality of Ixmiquilpan, Hidalgo, in the central region of Mexico. During the late Postclassic period (1350–1521 AD), the Aztecs controlled the area through the establishment of a dual-headed system, one part belonging to the Aztec government and the other to the local government. El Maye was the local government center for the Ixmiquilpan territory under the Aztec domain. The residential units of El Maye archaeological site were constructed in 6 different occupational phases, with the presence of large rooms, stucco floors and walls, offerings, and a variety of ceramics belonging to the late Aztec III ceramic period (1400–1520 AD). The Axis Project of the Mezquital Valley (PEVM-ENAH) and the Accelerator Mass Spectrometry Laboratory (LEMA-UNAM) have undertaken a collaborative study of the El Maye site by performing absolute radiocarbon accelerator mass spectrometry (14C AMS) dating. For a better understanding of the emergence and development of El Maye, a series of AMS 14C dates of charcoal and bone samples recovered from different stratigraphic levels, was performed. This allowed us to locate the occupation of the site between 1320 and 1625 cal AD.

Travertine precipitated during the past ca. 120 years, from thermal waters in one of the historical Spas of the Buda Thermal Karst (Hungary) was investigated using radiocarbon (14C). The age of the deposit is based on the historic date of the structure on which the travertine was deposited. A textural study of the travertine buildup using a ~22-cm-long diamond-core crosscutting was undertaken. The original aim of the study was to improve our understanding of the controls and possibly also the rate of travertine-precipitation. In addition to characteristic, mm-scale, regular laminations, 0.5–1.0 cm dark-colored intervals were also observed in the core. Correlation of these latter textural changes with well-known changes in the water management of the Spa was greatly hindered by the lack of age data from the interior of the core. Therefore, in addition to the two known points (beginning in 1883 AD and ending 2004 AD) at least one age-datum point, somewhere inbetween, was necessary. Since the timespan of the core obviously included the 1960s of the last century, we expected that the 14C anomaly related to the atmospheric nuclear tests of those years could be detected by isotope-geochemistry. This paper gives a brief overview of the textural features of the investigated travertine and presents the dataset proving the incorporation of considerable amounts of atmospheric carbon in the carbonate precipitate, which, indeed, facilitated the indirect dating of the part of the core containing “bomb” 14C, and this helped us to unfold the factors controlling the observed textural changes of the travertine.

Radiocarbon (14C) has been instrumental in clarifying how people came to inhabit the expanse of Pacific Oceania, now supporting an “incremental growth model” that shows a number of long-distance sea-crossing migrations over the last few millennia. A crucial step in this narrative involved the initial settlement of the remote-distance Oceanic region, in the case of the Mariana Islands around 1500 BC. The Marianas case can be demonstrated through delineation of stratigraphic layers, dating of individual points or features within those layers, redundant dating of samples in secure contexts, localized and taxon-specific corrections for marine samples, and cross-constraining dating of superimposed layer sequences. Based on the technical and methodological lessons from the Marianas example, the further steps of the incremental growth model will continue to be refined across Pacific Oceania. Many of these issues may be relevant for broader research of ancient settlement horizons in other regions.

We undertook a strengths, weaknesses, opportunities, and threats (SWOT) analysis of Northern Hemisphere tree-ring datasets included in IntCal20 in order to evaluate their strategic fit with the demands of archaeological users. Case studies on wiggle-matching single tree rings from timbers in historic buildings and Bayesian modeling of series of results on archaeological samples from Neolithic long barrows in central-southern England exemplify the archaeological implications that arise when using IntCal20. The SWOT analysis provides an opportunity to think strategically about future radiocarbon (14C) calibration so as to maximize the utility of 14C dating in archaeology and safeguard its reputation in the discipline.

Faunal assemblages from the pre-Contact period sites Frisby-Butler and Hornblower II on Marthaʼs Vineyard, Massachusetts, USA, remain unstudied since excavation during the 1980s. This project establishes radiocarbon (14C) dates from faunal remains and evaluates occupation and abandonment at each site. 14C measurements were collected from 17 specimens and 13 dates from previous analyses were re-examined. Dates were identified from the archaeological time periods Transitional Archaic (2700–3700 BP), Early Woodland (2000–2700 BP), and Late Woodland (450–1200 BP) at Frisby-Butler. Occupation likely represented seasonal visitations during autumn and winter to hunt based on white-tailed deer (Odocoileus virginianus) demographic profiles. A combined dataset of new and re-calibrated 14C measurements from Hornblower II date to the Late Archaic (3700–6000 BP), Early Woodland, Middle Woodland (1200–2000 BP), and Late Woodland periods. Settlement was focused on gathering warm-weather foods like demersal fish and lakebirds. Together, the sites demonstrate periodic seasonal use of the southwest coast of the island throughout the Late Holocene and fit within an established regional pattern in southern New England.

Connecting calendar ages to radiocarbon (14C) ages, i.e. constructing a calibration curve, requires 14C samples that represent, or are closely connected to, atmospheric 14C values and that can also be independently dated. In addition to these data, there is information that can serve as independent tests of the calibration curve. For example, information from ice core radionuclide data cannot be directly incorporated into the calibration curve construction as it delivers less direct information on the 14C age–calendar age relationship but it can provide tests of the quality of the calibration curve. Furthermore, ice core ages on 14C-dated volcanic eruptions provide key information on the agreement of ice core and radiocarbon time scales. Due to their scarcity such data would have little impact if directly incorporated into the calibration curve. However, these serve as important “anchor points” in time for independently testing the calibration curve and/or ice-core time scales. Here we will show that such information largely supports the new IntCal20 calibration record. Furthermore, we discuss how floating tree-ring sequences on ice-core time scales agree with the new calibration curve. For the period around 40,000 years ago we discuss unresolved differences between ice core 10Be and 14C records that are possibly related to our limited understanding of carbon cycle influences on the atmospheric 14C concentration during the last glacial period. Finally, we review the results on the time scale comparison between the Greenland ice-core time scale (GICC05) and IntCal20 that effectively allow a direct comparison of 14C-dated records with the Greenland ice core data.

Quality control procedures have been developed at the Laboratoire de Mesure du Carbone 14 (LMC14) national laboratory throughout the years of operation. Routine procedures are applied to sample preparation depending on their composition and their size. The tuning of the ARTEMIS AMS facility, hosted by the LMC14 laboratory, uses an accurate procedure. A batch of unknown samples is measured with accompanying samples (primary and secondary standards and blanks), which give a powerful set of data to control the quality of each measurement. A homemade database has been created to store the sample information and study the evolution of the accompanying samples. The LMC14 laboratory participated in the Sixth International Radiocarbon Intercomparison, SIRI. The results are presented here, with statistical tests to assess the quality of the preparations and measurements done at the LMC14 national laboratory. To obtain a reliable radiocarbon (14C) age by AMS, 1 mg of sample is required in routine analysis. Recently, the LMC14 developed a new procedure dedicated to microsamples, allowing the size of samples to be reduced and contributing to opening 14C dating to materials that were previously unreachable. This new procedure has been successfully tested on valuable Cultural Heritage samples: lead white mural paintings.

Bayesian analysis of radiocarbon (14C) dates in North American archaeology is increasing, especially among archaeologists working in deeper time. However, historical archaeologists have been slow to embrace these new techniques, and there have been only a few examples of the incorporation of calendar dates as informative priors in Bayesian models in such work in the United States. To illustrate the value of Bayesian approaches to sites with both substantial earlier Native American occupations as well as a historic era European presence, we present the results of our Bayesian analysis of 14C dates from the earlier Guale village and the Mission period contexts from the Sapelo Shell Ring Complex (9MC23) in southern Georgia. Jefferies and Moore have explored the Spanish Mission period deposits at this site to better understand the Native American interactions with the Spanish during the 16th and 17th centuries along the Georgia Coast. Given the results of our Bayesian modeling, we can say with some degree of confidence that the deposits thus far excavated and sampled contain important information dating to the 17th-century mission on Sapelo Island. In addition, our modeling of new dates suggests the range of the pre-Mission era Guale village. Based on these new dates, we can now say with some degree of certainty which of the deposits sampled likely contain information that dates to one of the critical periods of Mission period research, the AD 1660–1684 period that ushered in the close of mission efforts on the Georgia Coast.

The sources and fate of radiocarbon (14C) in the Dead Sea hypersaline solution are evaluated with 14C measurements in organic debris and primary aragonite collected from exposures of the Holocene Ze’elim Formation. The reservoir age (RA) is defined as the difference between the radiocarbon age of the aragonite at time of its precipitation (representing lakeʼs dissolved inorganic carbon [DIC]) and the age of contemporaneous organic debris (representing atmospheric radiocarbon). Evaluation of the data for the past 6000 yr from Dead Sea sediments reveal that the lakeʼs RA decreased from 2890 yr at 6 cal kyr BP to 2300 yr at present. The RA lies at ~2400 yr during the past 3000 yr, when the lake was characterized by continuous deposition of primary aragonite, which implies a continuous supply of freshwater-bicarbonate into the lake. This process reflects the overall stability of the hydrological-climate conditions in the lakeʼs watershed during the late Holocene where bicarbonate originated from dissolution of the surface cover in the watershed that was transported to the Dead Sea by the freshwater runoff. An excellent correlation (R2=0.98) exists between aragonite ages and contemporaneous organic debris, allowing the estimation of ages of various primary deposits where organic debris are not available.

The curves recommended for calibrating radiocarbon (14C) dates into absolute dates have been updated. For calibrating atmospheric samples from the Northern Hemisphere, the new curve is called IntCal20. This is accompanied by associated curves SHCal20 for the Southern Hemisphere, and Marine20 for marine samples. In this “companion article” we discuss advances and developments that have led to improvements in the updated curves and highlight some issues of relevance for the general readership. In particular the dendrochronological based part of the curve has seen a significant increase in data, with single-year resolution for certain time ranges, extending back to 13,910 calBP. Beyond the tree rings, the new curve is based upon an updated combination of marine corals, speleothems, macrofossils, and varved sediments and now reaches back to 55,000 calBP. Alongside these data advances, we have developed a new, bespoke statistical curve construction methodology to allow better incorporation of the diverse constituent records and produce a more robust curve with uncertainties. Combined, these data and methodological advances offer the potential for significant new insight into our past. We discuss some implications for the user, such as the dating of the Santorini eruption and also some consequences of the new curve for Paleolithic archaeology.

Reversals and plateaus in the radiocarbon (14C) calibration curve lead to similar 14C ages applying to a wide range of calendar dates, creating imprecision, ambiguity, and challenges for archaeological dating. Even with Bayesian chronological modeling, such periods remain a problem when no known order—e.g., a stratigraphic sequence—exists, and especially if site durations are relatively short. Using the reversal/plateau AD 1480–1630 and the archaeology of northeastern North America as our example, we consider possible strategies to improve chronological resolution across such reversal/plateau periods in the absence of stratigraphic sequences, including uses of wood-charcoal TPQs from even very short wiggle-matches, and site phase duration constraints based on ethnohistoric and archaeological evidence.

Aeolian deposits are widely distributed in the middle Yangtze River Basin (YRB), central China. The formation of those aeolian deposits (including aeolian sands and loess deposits) represented the deterioration of local environment. Previous geochronological studies have shown that both aeolian sands and loess began to be deposited in the last interglacial (~100 ka). In this study, a total of four and six accelerator mass spectrometry radiocarbon (AMS 14C) samples were collected from a sand hill and a loess section, respectively, in the Jiujiang area to refine their chronology. Charcoals extracted from bulk samples were employed for AMS 14C dating. The sand layer at the lower part of the HG-C section is sandwiched by two mud layers dated to 26,670–26,285 and 24,480–24,180 cal BP, respectively. Therefore, we infer that aeolian activities in this region started at ~25 ka BP, which was significantly younger than that of previous studies. Meanwhile, thick loess began to deposit leeward of the sand hills in this region. Based on the AMS14C chronology and provenance tracing, we conclude that the loess was essentially the fine-grained aeolian deposits. Our results suggest that topography and vegetation cover have an important effect on the spatial distribution of aeolian deposits in this region.

The adoption of a new funerary ritual with all its social and cognitive meanings is of great importance to understanding social transformations of past societies. The first known occurrence of cremation in the territory corresponding to modern Belgium dates back to the Mesolithic period. From the end of the Neolithic onward, the practice of cremation was characterized by periods in which this rite was predominant and periods of contractions, defined by a decrease in the use of this funerary ritual. This paper aims to quantify such phenomenon for the first time by modeling discontinuities in burial practices through kernel density analysis of 1428 radiocarbon (14C) dates from 311 archaeological sites located in Belgium from the Mesolithic to the Middle Ages. Despite possible taphonomic and sampling biases, the results highlight the existence of periods with a large uptake of cremation rite followed by periods of contractions; such discontinuities took place in correlation with changes in the socio-economical structure of local communities, as, for example, during the later Middle Bronze Age and at the end of the Roman Period.