One century after its initial excavation, this article presents the first absolute chronology for the settlement of Karanis in Egypt. Radiocarbon dates from crops retrieved from settlement structures suggest that the site was inhabited beyond the middle of the fifth century AD, the time at which it was previously believed to have been abandoned. These dates add to the complex picture of population fluctuations and the remodelling and reuse of structures at Karanis. Two dates reach into the middle of the seventh century, placing the abandonment of the site in a period of political and environmental transition that changed the physical and social landscape of the Fayum region and beyond.

Observations of radiocarbon (14C) in Earth’s atmosphere and other carbon reservoirs are important to quantify exchanges of CO2 between reservoirs. The amount of 14C is commonly reported in the so-called Delta notation, i.e., Δ14C, the decay- and fractionation-corrected departure of the ratio of 14C to total C from that ratio in an absolute international standard; this Delta notation permits direct comparison of 14C/C ratios in the several reservoirs. However, as Δ14C of atmospheric CO2, Δ14CO2 is based on the ratio of 14CO2 to total atmospheric CO2, its value can and does change not just because of change in the amount of atmospheric14CO2 but also because of change in the amount of total atmospheric CO2, complicating ascription of change in Δ14CO2 to change in one or the other quantity. Here we suggest that presentation of atmospheric 14CO2 amount as mole fraction relative to dry air (moles of 14CO2 per moles of dry air in Earth’s atmosphere), or as moles or molecules of 14CO2 in Earth’s atmosphere, all readily calculated from Δ14CO2 and the amount of atmospheric CO2 (with slight dependence on δ13CO2), complements presentation only as Δ14CO2, and can provide valuable insight into the evolving budget and distribution of atmospheric 14CO2.

Studies of pre-bomb mollusks live-collected around the Australian coastline have concluded that near-shore marine radiocarbon reservoir effects are small and relatively uniform. These studies are based on limited samples of sometimes dubious quality representing only selective parts of Australia’s lengthy coastline. We systematically examine spatial variability in the marine radiocarbon reservoir effect (ΔR) through analysis of 292 live-collected mollusk samples across the Australian mainland coasts and near-shore islands subject to strict selection criteria. This study presents 233 new ΔR values combined with an evaluation of 59 previously published values. Results demonstrate significant spatial variability in marine radiocarbon reservoir effects across the study region. ΔR values range from 68 ± 24 14C years off the Pilbara region of Western Australia to –337 ± 46 14C years in the southern Gulf of Carpentaria in Queensland. Most sets of local values exhibit internal consistency, reflecting the dominant influence of regional oceanography, including depletion in ΔR values southwards along the eastern Australian coastline coincident with the East Australian Current. Anomalous values are attributed to inaccurate documentation, species-specific relationships with the carbon cycle and/or short-term fluctuations in marine radiocarbon activities. To account for the heterogeneous distribution of marine 14C, we recommend using a location specific ΔR value calculated using the Australian ΔR Calculator, available at: https://delta-r-calc.jcu.io/.

Archaeological dung pellets are time capsules of ancient herbivore diets and gut flora, informing on past agropastoral activity, ecology, and animal health. Improving multi-proxy approaches is key to maximizing this finite archaeological resource. Through experiments with standard pretreatments used in radiocarbon (14C) dating, we address a fundamental problem in maximal multi-proxy analysis: How to chronometrically date individual caprine pellets while conserving as much as possible for additional analyses? We applied acid-alkali-acid (AAA) or acid-only pretreatments to 37 samples of ancient and recent sheep/goat dung pellets from sites in the Negev desert, Israel, measuring weight-loss due to pretreatment. Shavings of outer surfaces and remaining inner pellets of four pairs were dated and compared. We found that (i) sample-specific factors affect pretreatment survivability, including preservation quality and initial sample size; (ii) given sufficient start weight, AAA can be used to pretreat sheep/goat coprolites; (iii) 100 mg appeared a desirable minimum sample weight before pretreatment; and (iv) shavings of coprolites’ outer surface produced 14C dates equivalent to dates obtained from inner coprolites. Whereas standard coprolite analysis protocols discard shavings removed from outer surfaces to avoid contamination, our findings indicate their efficacy for 14C dating. This offers an important addition to workflows for multi-proxy coprolite analysis.

In this paper we evaluate the extent of freshwater reservoir effects (37 samples across 12 locations) and present new data from various archaeological sites in the Eurasian Steppe. Together with a summary of previous research on modern and archaeological samples, this provides the most up-to-date map of the freshwater reservoir offsets in the region. The data confirm previous observations highlighting that FREs are widespread but highly variable in the Eurasian Steppe in both modern and archaeological samples. Radiocarbon dates from organisms consuming aquatic sources, including humans, dogs, bears, aquatic birds and terrestrial herbivores (such as elk feeding on water plants), fish and aquatic mammals, as well as food crusts, could be misleading, but need to be assessed on a case-by-case basis.

Caves containing perennial ice deposits make up a little-known, but emerging part of the cryosphere under increasing scrutiny from the scientific community. M-17, a sag-type ice cave opening at 1879 m asl in the Tolminski Migovec massif of the Julian Alps (NW Slovenia) contains a perennial underground ice deposit whose paleoclimate sensitivity is poorly understood and whose longevity under current climate change is at risk. The past mass balance of this cave is constrained using wood macro-remains embedded in ice. Accelerator mass spectrometry radiocarbon dating of 18 wood samples embedded in ice provides the largest currently available dataset for a subterranean ice deposit in the southern European Alps. The reconstructed chronostratigraphy reveals three main phases of likely positive ice balance around 900–1100 AD, 1200–1300 AD, and 1700–1800 AD, as well as a period of negative mass balance around 1300–1400 AD. The onset of cave glaciation is deemed to have occurred no later than about 900 AD, with evidence of overall positive ice mass balance during multi-decadal periods characterized by cooler-than-average summers and wetter-than-average springs. Conversely, negative mass balance is recorded during a period warmer-than-average summers and dry springs. The cave has experienced ice mass loss since its discovery in the 1980s.

In the late 1950s it was recognized that levels of atmospheric radiocarbon (14C) had not been constant over time. Since then, researchers have sought to document those changes, initially through measurements of known age tree rings and more recently using other archives to create curves to correct or calibrate radiocarbon ages to calendar ages. This paper highlights some, but by no means all, of the efforts to create and extend radiocarbon calibration curves.

The Quaternary Isotope Laboratory (QIL) at the University of Washington was launched in 1969 and directed by Minze Stuiver until his retirement in 1998. Here we review some of the scientific work undertaken in the QIL and the memories of some of Minze’s former students and colleagues.

In this paper we discuss recent developments in documenting the spread of millet across the Eurasian steppes. We emphasize that, despite a recent proposal that millet consumption in southern Siberia can be attributed to the Early Bronze Age (i.e., the late third to early second millennium BC), at present there are no direct data for southern Siberia indicating the consumption of millet prior to the Late Bronze Age, from the 14th century BC. We also present in full the combined stable isotope and 14C datasets from the Minusinsk Basin to support this conclusion.

The Belfast Ramped Pyroxidation/Combustion (RPO/RC) facility was established at the 14CHRONO Centre (Queen’s University Belfast). The facility was created to provide targeted analysis of bulk material for refined chronological analysis and carbon source attribution for a range of sample types. Here we report initial RPO results, principally on background material, but also including secondary standards that are routinely analyzed at 14CHRONO. A description of our setup, methodology, and background (blank) correction method for the system are provided. The backgrounds (anthracite, spar calcite, Pargas marble) reported by the system are in excess of 35,000 14C years BP with a mean age of 39,345 14C years BP (1σ = 36,497–43,800 years BP, N=44) with F14C = 0.0075 ± 0.0032. Initial results for standards are also in good agreement with consensus values: TIRI-B pine radiocarbon age = 4482 ± 47 years BP (N=13, consensus = 4508 years BP); IAEA-C6 ANU Sucrose F14C= 1.5036 ± 0.0034 (N=10, consensus F14C = 1.503). These initial tests have allowed problematic issues to be identified and improvements made for future analyses.

The Glastonbury Lake Village in Somerset, UK, is made up of 90 mounds comprising 40 roundhouses. Excavations between 1892 and 1907 revealed Iron Age structural and material remains unparalleled in Western Europe. The settlement's exact chronology, however, has remained uncertain. Here, the authors present a programme of radiocarbon and dendrochronological dating and chronological modelling on samples from recent excavations. The results indicate that the site was founded in the early second century cal BC, with the last structures being built just over a century later. This new, robust chronology can be used to date a wide range of associated material culture, and complements chronologies established for other Iron Age sites.

To create a reliable radiocarbon calibration curve, one needs not only high-quality data but also a robust statistical methodology. The unique aspects of much of the calibration data provide considerable modeling challenges and require a made-to-measure approach to curve construction that accurately represents and adapts to these individualities, bringing the data together into a single curve. For IntCal20, the statistical methodology has undergone a complete redesign, from the random walk used in IntCal04, IntCal09 and IntCal13, to an approach based upon Bayesian splines with errors-in-variables. The new spline approach is still fitted using Markov Chain Monte Carlo (MCMC) but offers considerable advantages over the previous random walk, including faster and more reliable curve construction together with greatly increased flexibility and detail in modeling choices. This paper describes the new methodology together with the tailored modifications required to integrate the various datasets. For an end-user, the key changes include the recognition and estimation of potential over-dispersion in 14C determinations, and its consequences on calibration which we address through the provision of predictive intervals on the curve; improvements to the modeling of rapid 14C excursions and reservoir ages/dead carbon fractions; and modifications made to, hopefully, ensure better mixing of the MCMC which consequently increase confidence in the estimated curve.

The concentration of radiocarbon (14C) differs between ocean and atmosphere. Radiocarbon determinations from samples which obtained their 14C in the marine environment therefore need a marine-specific calibration curve and cannot be calibrated directly against the atmospheric-based IntCal20 curve. This paper presents Marine20, an update to the internationally agreed marine radiocarbon age calibration curve that provides a non-polar global-average marine record of radiocarbon from 0–55 cal kBP and serves as a baseline for regional oceanic variation. Marine20 is intended for calibration of marine radiocarbon samples from non-polar regions; it is not suitable for calibration in polar regions where variability in sea ice extent, ocean upwelling and air-sea gas exchange may have caused larger changes to concentrations of marine radiocarbon. The Marine20 curve is based upon 500 simulations with an ocean/atmosphere/biosphere box-model of the global carbon cycle that has been forced by posterior realizations of our Northern Hemispheric atmospheric IntCal20 14C curve and reconstructed changes in CO2 obtained from ice core data. These forcings enable us to incorporate carbon cycle dynamics and temporal changes in the atmospheric 14C level. The box-model simulations of the global-average marine radiocarbon reservoir age are similar to those of a more complex three-dimensional ocean general circulation model. However, simplicity and speed of the box model allow us to use a Monte Carlo approach to rigorously propagate the uncertainty in both the historic concentration of atmospheric 14C and other key parameters of the carbon cycle through to our final Marine20 calibration curve. This robust propagation of uncertainty is fundamental to providing reliable precision for the radiocarbon age calibration of marine based samples. We make a first step towards deconvolving the contributions of different processes to the total uncertainty; discuss the main differences of Marine20 from the previous age calibration curve Marine13; and identify the limitations of our approach together with key areas for further work. The updated values for ΔR, the regional marine radiocarbon reservoir age corrections required to calibrate against Marine20, can be found at the data base http://calib.org/marine/.

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

Early researchers of radiocarbon levels in Southern Hemisphere tree rings identified a variable North-South hemispheric offset, necessitating construction of a separate radiocarbon calibration curve for the South. We present here SHCal20, a revised calibration curve from 0–55,000 cal BP, based upon SHCal13 and fortified by the addition of 14 new tree-ring data sets in the 2140–0, 3520–3453, 3608–3590 and 13,140–11,375 cal BP time intervals. We detail the statistical approaches used for curve construction and present recommendations for the use of the Northern Hemisphere curve (IntCal20), the Southern Hemisphere curve (SHCal20) and suggest where application of an equal mixture of the curves might be more appropriate. Using our Bayesian spline with errors-in-variables methodology, and based upon a comparison of Southern Hemisphere tree-ring data compared with contemporaneous Northern Hemisphere data, we estimate the mean Southern Hemisphere offset to be 36 ± 27 14C yrs older.

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.

Radiocarbon calibration is necessary to correct for variations in atmospheric radiocarbon over time. The IntCal working group has developed an updated and extended radiocarbon calibration curve, IntCal20, for Northern Hemisphere terrestrial samples from 0 to 55,000 cal yr BP. This paper summarizes the new datasets, changes to existing datasets, and the statistical method used for constructing the new curve. Examples of the effect of the new calibration curve compared to IntCal13 for hypothetical radiocarbon ages are given. For the recent Holocene the effect is minimal, but for older radiocarbon ages the shift in calibrated ages can be up to several hundred years with the potential for multiple calibrated age ranges in periods with higher-resolution data. In addition, the IntCal20 curve is used to recalibrate the radiocarbon ages for the glaciation of the Puget Lowland and to recalculate the advance rate. The ice may have reached its maximum position a few hundred years earlier using the new calibration curve; the calculated advance rate is virtually unchanged from the prior estimate.

The marine reservoir effect is the difference in radiocarbon (14C) between the atmosphere and the marine surface ocean. To overcome the dating errors induced, it is necessary to correct marine 14C ages for this effect. ΔR is the difference between the marine 14C age and the marine calibration curve based on an ocean-atmosphere box diffusion model, which accounts for the time delay in diffusion of carbon into the ocean from the atmosphere and biosphere. This global assessment, however, requires computation of a regional ∆R value for calibration to cater for studies based on a local scale. In this paper the marine reservoir effect is assessed for the southern and eastern coasts of South Africa using 14C dating on pre-1950 marine shells of known age. The resultant ∆R values enable a more complete understanding of the marine reservoir effect along the southern and eastern coastal zone of South Africa. 14C age determinations were conducted on 15 shell samples of known age and the results, combined with previously published values, were used to calculate regional marine reservoir correction values. The east coast has a weighted mean ∆R of 121±16 14C yr, while the south coast has a weighted mean ∆R of 187±18 14C yr.