The North Sea is considered a unique heritage site that yielded a huge amount of zoological and archaeological data. More than 200 palaeozoological and archaeological fossil bone samples from the North Sea bed are dated by 14C. About 2/3 of these dated bones are Pleistocene in age; the majority of the bones are from extinct species (in particular woolly mammoth); about 1/3 of the sample date to the Holocene. The presented dataset is important in its kind, but interpretation is limited because of a lack of context of the finds. The stable isotopes (13C, 15N) of the dated samples provide additional information on palaeoenvironmental conditions and dietary habits in the past. We present primarily a Groningen list of data; a few fossils dated in other laboratories are included for completeness.

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.

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.

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.

We report new accelerator mass spectrometry radiocarbon (AMS 14C) dates of bones from humans, animals, and fish from grave 12 of the Lebyazhinka V Eneolithic burial ground in the middle Volga River region, Russia. Earlier conventional dates established a chronology. This has to be adjusted by new insights: the date has to be corrected for reservoir effects. For this purpose we redated bone from a human, and for herbivore and freshwater fauna from the same context, and included measurements of the stable isotopes δ13C and δ15N. The reservoir offset for the human appears to be about 700 14C yr.

The volcanic mega event of the Minoan Santorini eruption constitutes a time anchor in the 2nd millennium BCE that is inherently independent of archaeology and political history. It was a geological event. Yet the dimension of time in geology is not different than in archaeology or human history. Why then does archaeological dating usually place the Minoan Santorini eruption in the 18th Dynasty around 1500 BCE, whilst radiocarbon dating of the volcanic event at Akrotiri (Thera) yielded a calibrated age of 1646–1603 cal BCE, a difference of more than a century? The crux of the problem lies apparently in the correlation between archaeological strata and political history. We present radiocarbon dates of Ashkelon Phases 10 and 11 in comparison to Tell el-Dabca and the Santorini eruption, based only on 14C dating. Tell el-Dabca Phase D/2 is slightly older than the volcanic event. But Phase D/1 or Phase C/2-3 could have witnessed the eruption. Ashkelon Phase 11 has similar radiocarbon dates as Tell el-Dabca Phases E/2, E/1 and D/3, all being significantly older than the Minoan eruption. It seems that the duration of Ashkelon Phase 10 includes the temporal occurrence of the Minoan Santorini eruption within the Second Intermediate Period.

The relic “the sack of Saint Francesco” has for the first time been investigated by scientific means. The sack is kept at the Franciscan Friary of Folloni near Montella in southern Italy. According to legend, the sack appeared on the doorstep of the Friary in the winter of 1224 containing bread sent from St Francesco (St Francis of Assisi), who at that time was in France. The bread was allegedly brought to the friary by an angel. We analyzed samples of the sack to obtain a radiocarbon (14C) date and to search for any remaining traces of bread. The 14C date yielded a calibrated age range of AD 1220–1295 (2σ), which places the textile in the right timeframe according to the legend. Chemical analysis by gas-chromatography with mass spectrometric detection (GC-MS) revealed the presence of ergosterol (5, 7, 22-ergostatrien-3b-ol), a known biomarker of brewing, baking, or agriculture. In this paper we have further substantiated the validity of ergosterol as a biomarker for the past presence of bread. It appears that there is a fine correspondence between the Franciscan legend and the two most decisive scientific methods relevant for analyzing the sack. Although it is not proof, our analysis shows that the sack indeed could be authentic.

In this response to the reply by Shahack-Gross and Finkelstein (2017), we present additional data of our research at Horvat Haluqim. This includes phytolith percentages and multicellular phytolith stomata in a thin section of a layer in Terraced Field 12, dated by radiocarbon (14C) to the Late Bronze–Early Iron Age. We also show thin-section evidence of aggrading sediment laminations in this terraced field. A new 14C date is given of the Early Islamic Period in Terraced Field 7, as differences in terrace wall architecture are highlighted. We revisit the interpretation by Shahack-Gross and Finkelstein in relation to herd management. Our 14C dates attest that terrace agriculture based on runoff/floodwater irrigation occurred in the Negev Highlands during several periods, including the Iron Age.

Shahack-Gross and Finkelstein (2015) further developed their theory, based on microarchaeology, that there was no agriculture in the Negev Highlands during the Iron Age. We critically evaluate their article in this rejoinder and propose that their conclusion is an example of overinterpretation from a small amount of indirect data. Based on phytoliths in two courtyards and a few rooms, i.e. structures not related to farming, they construed the absence of agriculture during the Iron Age in an area of 2000 km2. We present new radiocarbon, macroarchaeological, and microarchaeological data of Horvat Haluqim, showing that agriculture in the Negev Highlands based on runoff/floodwater capture and related terrace wall construction did not begin with the Roman–Byzantine period. Terrace agriculture in the Negev is older and includes also the Iron Age.

The mid-Holocene eruption of Aniakchak volcano (Aniakchak II) in southwest Alaska was among the largest eruptions globally in the last 10,000 years (VEI-6). Despite evidence for possible impacts on global climate, the precise age of the eruption is not well-constrained and little is known about regional environmental impacts. A closely spaced sequence of radiocarbon dates at a peatland site over 1000 km from the volcano show that peat accumulation was greatly reduced with a hiatus of approximately 90–120 yr following tephra deposition. During this inferred hiatus no paleoenvironmental data are available but once vegetation returned the flora changed from a Cyperaceae-dominated assemblage to a Poaceae-dominated vegetation cover, suggesting a drier and/or more nutrient-rich ecosystem. Oribatid mites are extremely abundant in the peat at the depth of the ash, and show a longer-term, increasingly wet peat surface across the tephra layer. The radiocarbon sample immediately below the tephra gave a date of 1636–1446 cal yr BC suggesting that the eruption might be younger than previously thought. Our findings suggest that the eruption may have led to a widespread reduction in peatland carbon sequestration and that the impacts on ecosystem functioning were profound and long-lasting.

Humans colonized the Balearic Islands 5–4 ka ago. They arrived in a uniquely adapted ecosystem with the Balearic mountain goat Myotragus balearicus (Bovidae, Antilopinae, Caprini) as the only large mammal. This mammal went extinct rapidly after human arrival. Several hypotheses have been proposed to explain the extinction of M. balearicus. For the present study ancient DNA analysis (Sanger sequencing, Roche-454, Ion Torrent), and pollen and macrofossil analyses were performed on preserved coprolites from M. balearicus, providing information on its diet and paleo-environment. The information retrieved shows that M. balearicus was heavily dependent on the Balearic box species Buxus balearica during at least part of the year, and that it was most probably a browser. Hindcast ecological niche modelling of B. balearica shows that local distribution of this plant species was affected by climate changes. This suggests that the extinction of M. balearicus can be related to the decline and regional extinction of a plant species that formed a major component of its diet. The vegetation change is thought to be caused by increased aridity occurring throughout the Mediterranean. Previous hypotheses relating the extinction of M. balearicus directly to the arrival of humans on the islands must therefore be adjusted.

During the Pleistocene, the coastal marine bivalve mollusc Mya arenaria became extinct in northwest Europe. The species remained present in North America. Datings of Mya shells found in northern Denmark and the southern Baltic Sea suggest that repopulation of northwest European coasts already occurred before Columbus’ discovery of America (1492), possibly facilitated by Viking (Norse) settlers at Greenland and northeast North America. In this paper we report on findings of M. arenaria at five locations in the coastal landscape of the Netherlands: polders reclaimed from the Wadden Sea and the former estuaries of Oer-IJ and Old Rhine. The shells from four of these locations also date before 1492 AD.

Radiocarbon calibration based on dendro-chronology and U-series dated corals yield a calibration curve (INTCAL98) well into the Late Glacial, back to ca. 15,600 calendar years ago. Beyond this limit, various calibration curves are produced, mainly based on laminated sediments and various carbonates dated by U-series isotopes. Such calibration curves now cover the complete 14C dating range of about 45,000 years, but are not consistent with each other. Each calibration method (other than dendro-chronology) has its own assumptions and pitfalls. Thus far, the calibration curve obtained from Lake Suigetsu laminated sediments is the only terrestrial (atmospheric) one.

We present a revised relative mean sea-level (MSL) curve for the Rhine-Meuse delta, western Netherlands, for the period 7900-5300 cal yr BP. The revision is based on a series of new and previously unpublished local groundwater-level index data from buried Late Glacial aeolian dunes in the lower Rhine-Meuse delta, and reinterpretation of existing data.

The new index data consist of (AMS and conventional) radiocarbon dates of samples, collected from the base of peat formed on dune slopes, near Vlaardingen (21 index points), Hillegersberg (one index point), and Hardinxveld-Giessendam (10 index points). The Vlaardingen data represent the coast-nearest Rhine-Meuse delta local water-level record, which therefore is highly indicative for sea-level change. Pollen and macrofossil analysis, and dating of paired samples was carried out to assess the reliability of the groundwater-level index data.

The revision of the MSL curve involves: (1) a significant (0 to >1 m) upward adjustment for the period 7900-7300 cal yr BP; (2) a downward adjustment of <0.25 m for the period 6650-5300 cal yr BP. The new data indirectly support the reliability of the part of the curve for the period 7300-6650 cal yr BP. A longitudinally fairly uniform river gradient of 2.5-3.0 cm/km in the lower Rhine-Meuse delta during the period 6650-5600 cal yr BP can be inferred from the data sets. A significant river gradient extended further towards the coastline than previously thought and it may be that also the revised MSL curve reflects river-gradient effects. An increased floodbasin effect (stronger intra-coastal tidal damping) seems to have developed in the lower Rhine-Meuse delta in de period 7500-6600 cal yr BP, and was probably a complex response to a major avulsion of the Rhine.

Botanical microfossils, macroremains and oribatid mites of a Weichselian interstadial deposit in the central Netherlands point to a temporary, sub-arctic wetland in a treeless landscape. Radiocarbon dates and OSL dates show an age between ca. 54.6 and 46.6 ka cal BP. The vegetation succession, starting as a peat-forming wetland that developed into a lake, might well be linked with a Dansgaard-Oeschger climatic cycle. We suggest that during the rapid warming at the start of a D-O cycle, relatively low areas in the landscape became wetlands where peat was formed. During the more gradual temperature decline that followed, evaporation diminished; the wetlands became inundated and lake sediments were formed. During subsequent sub-arctic conditions the interstadial deposits were covered with wind-blown sand. Apart from changes in effective precipitation also the climate-related presence and absence of permafrost conditions may have played a role in the formation of the observed sedimentological sequence from sand to peat, through lacustrine sediment, with coversand on top. The Wageningen sequence may correspond with D-O event 12, 13 or 14. Some hitherto not recorded microfossils were described and illustrated.

Radiocarbon dating of peat has its intrinsic problems. This is often caused by mobile organic fractions. For the Weichselian Pleniglacial, another methodological problem arises: the limit of the 14C dating method. This is discussed in terms of bulk (i.e. non-selected material, generally dated conventionally) vs AMS (i.e. selected botanical remains) dates, contamination, background and calibration, guided by a series of peat samples from the Belgian/Dutch border.

An olive branch is traditionally a symbol of peace, but not necessarily in the context of chronological problems in the Eastern Mediterranean region and the Near East during the second millennium BC. Cherubini et al. (above) strongly attack the radiocarbon dating by Friedrich et al. (2006) of an ancient olive branch, buried by volcanic tephra during the Minoan Santorini eruption. The criticism stems from their investigation of growth rings in modern olive trees on Santorini. The authors attempt with additional arguments, beyond their botanical investigation, to defend the traditional low chronology of the Santorini eruption of around 1500 BC. However, they ignore other crucial publications with radiocarbon dates concerning the Santorini eruption. In this response, we evaluate and negate their main arguments, and present our own conclusions.

The chronology of long Upper Pleistocene loess sequences in Eurasia is based on combined pedostratigraphy and radiocarbon dating of high-quality charcoal. The accuracy of such a chronology depends on the reproducibility and precision of the 14C dates. However, certain dates may show discrepancies with regard to their chronostratigraphic context based on series of coherent dates. In order to evaluate the consistency and variation in the 14C dates obtained from small charcoal pieces, this question was tested on a set of spruce wood remains with well-preserved tree rings found in the Middle Pleniglacial loess-loam sequence of Kurtak (central Siberia). Tree-ring analysis of five fairly large wood pieces from three successive layers, dated to about 30.0, 30.8, and 32.2–32.5 ka BP previously, was done by continuous sampling of 90–150 rings on each wood piece. This enabled direct comparison of the succession of tree rings with the 14C dates. A total of 133 dates was obtained for the five wood pieces. The results show fluctuations in the 14C dates within a time range between 1000 and 2000 yr. Four possible causes for such variation will be discussed herein: (1) internal variability of the AMS dating method; (2) outliers; (3) variations in the 14C background; and (4) external factors such as past atmospheric 14C variations.

The dolmen known as Shepsi was accidentally discovered on the Black Sea coast (Tuapse region, Russia). Radiocarbon dates show that the classic trapezoidal construction of the Caucasian dolmens with a port-hole appeared in the region as early as 3250 BC. The distinctive structural characteristic for dolmens of that time was a floor slab laid between the side slabs, which were embedded in the ground. The material complex and 14C dates show that this type of dolmen coexisted with the Novosvobodnaya-type of the Maikop culture, located on the northern slope of the main Caucasus ridge. This leads to a new hypothesis concerning the regional origin and further development of the megalithic structures in the western Caucasus.

Late Neolithic graves excavated at Tell Sabi Abyad, Syria, have been dated by radiocarbon. This series of 46 human bone dates represents a sequence of cemeteries that is analyzed by Bayesian methodology. The dates show continuous use of the northeastern slope of the mound as a burial ground throughout the Initial Pottery Neolithic to the Halaf period.