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Prehistoric shell mounds can be useful for the quantification of the radiocarbon marine reservoir effect (MRE) and, at the same time, knowledge about the MRE allows for the establishment of robust chronologies for these sites. This creates a loop in which the archaeological setting has a dual role: it is part of both the method and the application. Therefore, it is paramount to address these sites from both archaeological and environmental perspectives, investigating their origin and diagenesis in order to overcome biases caused by post-depositional alterations. In this study, samples of bone, charcoal and shell from a Late Holocene shell mound in Southern Brazil, the Sambaqui de Cabeçuda, were analyzed following a multidisciplinary approach to disentangle the complex relationships between archaeology and the environment. We performed X-ray diffraction, radiocarbon dating, stable isotopes (δ13C, δ18O, δ15N) and anthracology analyses as well as Bayesian Chronological Models and Isotope Mixing Models to assess the local MRE and to reconstruct the diet of Cabeçuda builders. Our results reveal a negative local correction for the MRE (ΔR = –263 ± 46 14C yr), expected for the lagoon next to the site, and diets with considerable intakes of marine proteins. We examine the implications of these results for the chronology of the site and discuss a series of complications when performing MRE studies using shell mound sites.

As a contribution towards a regional environmental context of human-climate interactions, the ICDP co-funded Chew Bahir Drilling Project, a part of the HSPDP (Hominin Sites and Paleolakes Drilling Project), recovered ~280-m long cores of sedimentary strata through continental scientific drilling in southern Ethiopia. The fluvio-lacustrine coring locality in the Chew Bahir basin is situated near key archaeological and paleoanthropological sites, such as the Omo-Kibish where the Omo 1 and 2 Homo sapiens fossils were recovered.Here we present the 620,000-year environmental record from Chew Bahir that provides an extraordinary opportunity to examine the potential influence of climate variability on hominin evolution, cultural innovation and dispersal during the Middle to Late Pleistocene. The near-continuous Chew Bahir record documents 13 environmental episodes that differ in length and character, potentially inducing habitat changes influencing hominin biological and cultural transformation. We infer that long-lasting and relatively stable humid conditions from ~620,000–275,000 years BP (Episodes 1–6) were interrupted by several abrupt and extreme hydroclimatic oscillations. This phase coincided with the appearance of high anatomical diversity in hominin groups. During Episodes 7–9 (~275,000–60,000 years BP), a pronounced pattern of climatic cyclicity was paralleled by the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of H. sapiens in eastern Africa, and a key phase of human social and cultural innovation. Episodes 10–12 (~60,000–10,000 years BP), marked by high-frequency climate oscillations, is contemporaneous with the global dispersal of H. sapiens, facilitated by continued technological innovation and the alignment of humid pulses between eastern Africa and the eastern Mediterranean.Prospectively, the Chew Bahir record represents a crucial component for the Middle and Late Pleistocene in the ongoing efforts of the scientific community (future and upcoming ICDP-funded projects) to address questions in Africa across four topical core areas: paleoclimate, paleoenvironment, basin evolution, and modern lake systems.

A new chronological study of the LBK in the central Polish lowlands shows that it emerged later, lasted for a shorter period, and ended sooner than has been supposed up till now. LBK communities emerged, probably in the middle of the 53rd century cal BC, to form an enclave in the central Polish lowlands, probably as a result of colonisation from loess areas in the south of Poland. Settlement steadily intensified throughout the 52nd century cal BC, reaching its peak at the beginning of Phase III. In the middle of the 51st century cal BC there followed an abrupt decline or collapse, and LBK occupation of the lowlands had probably ended completely by the end of that century. There followed an appreciable gap before the re-emergence of settlement in the form of the Late Band Pottery culture (LBPC), characterised by significantly sparser settlement, changed dwelling structures and contacts with hunter-gatherer groups. A start to the wider task of comparing the situation in the central Polish lowlands with other regional sequences is made principally by reviewing similar formal modelling of a post-LBK hiatus in the Rhineland. Possible factors causing the LBK decline are discussed, including climatic downturn, population boom and bust, warfare, cultural malaise, disease and internal social conflict. None of these is overwhelmingly convincing on its own, and one of the many challenges for continuing research in the Polish lowlands and beyond will be to find further specific evidence to decide which of this range of possibilities is most plausible in specific contexts.

The Marine20 radiocarbon (14C) age calibration curve, and all earlier marine radiocarbon calibration curves from the IntCal group, must be used extremely cautiously for the calibration of marine 14C samples from polar regions (outside ~ 40ºS – 40ºN) during glacial periods. Calibrating polar 14C marine samples from glacial periods against any Marine calibration curve (Marine20 or any earlier product) using an estimate of ΔR, the regional 14C depletion adjustment, that has been obtained from samples in the recent (non-glacial) past is likely to lead to bias and overconfidence in the calibrated age. We propose an approach to calibration that aims to address this by accounting for the possibility of additional, localized, glacial 14C depletion in polar oceans. We suggest, for a specific polar location, bounds on the value of ΔR_20 (θ) during a glacial period. The lower bound ΔR_20^Hol may be based on 14C samples from the recent non-glacial (Holocene) past and corresponds to a low-depletion glacial scenario. The upper bound, ΔR_20^GS, representing a high-depletion scenario is found by increasing ΔR_20^Hol according to the latitude of the 14C sample to be calibrated. The suggested increases to obtain ΔR_20^GS are based upon simulations of the Hamburg Large Scale Geostrophic Ocean General Circulation Model (LSG OGCM). Calibrating against the Marine20 curve using the upper and lower ΔR_20 bounds provide estimates of calibrated ages for glacial 14C samples in high- and low-depletion scenarios which should bracket the true calendar age of the sample. In some circumstances, users may be able to determine which depletion scenario is more appropriate using independent paleoclimatic or proxy evidence.

Several scientific expeditions surveyed the ocean during the 19th century, gathering a wealth of interdisciplinary data as well as samples of different kinds. The latter are currently held by museums worldwide, and are the subject of study in different sciences, offering a unique opportunity to access information which is not readily available elsewhere. This is the case for research involving the offset in 14C (or radiocarbon) activity between the ocean and the atmosphere, termed the Marine Reservoir Effect (MRE), which is responsible for apparent 14C ages in marine material. The quantification of this discrepancy is crucial for the 14C dating tool since corrections must be applied for the accurate calibration of marine 14C ages. Nevertheless, the difficulty of finding suitable material for assessing the MRE contributes to the current scenario of scarce and patchy data. Here we propose the use of samples collected during well-documented 19th-century scientific expeditions in order to overcome the lack of information that prevents the use of many museum specimens in MRE studies. Approximately 60 mollusk shells and a sea urchin, collected from the coast of Brazil, were analysed for their radiocarbon age, δ13C and δ18O. The MRE is variable, with considerably high values occurring at specific spots along the shoreline. The data indicate a rather large area of upwelling influence on the southeastern coast of Brazil and possible dissolution of 14C-free limestone in the northeast. The results shed light on processes affecting the 14C concentration of Brazilian coastal waters, bearing implications for palaeoenvironmental and archaeological studies performed in the region. Moreover, the data generated in this study will be useful for the validation of 14C simulations in numerical models. Finally, this paper offers a discussion of the importance of natural history collections which looks beyond the preservation of our biodiversity.

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.

Radiocarbon dating and Bayesian chronological modelling have provided precise new dating for the henge monument of Mount Pleasant in Dorset, excavated in 1970–1. A total of 59 radiocarbon dates are now available for the site and modelling of these has provided a revised sequence for the henge enclosure and its various constituent parts: the timber palisaded enclosure, the Conquer Barrow, and the ditch surrounding Site IV, a concentric timber and stone monument. This suggests that the henge was probably built in the 26th century calbc, shortly followed by the timber palisade and Site IV ditch. These major construction events took place in the late Neolithic over a relatively short timespan, probably lasting 35–125 years. The principal results are discussed for each element of the site, including comparison with similar monument types elsewhere in Britain and Ireland, and wider implications for late Neolithic connections and later activity at the site associated with Beaker pottery are explored.

Connecting calendar ages to radiocarbon (14C) ages, i.e. constructing a calibration curve, requires14C samples that represent, or are closely connected to, atmospheric14C 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 the14C age–calendar age relationship but it can provide tests of the quality of the calibration curve. Furthermore, ice core ages on14C-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 core10Be and14C records that are possibly related to our limited understanding of carbon cycle influences on the atmospheric14C 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 of14C-dated records with the Greenland ice core data.

Oxygen isotope ratios from oak tree rings are used to extend the May–August precipitation totals of the England and Wales precipitation series back to 1201 CE. The agreement between instrumental and reconstructed values is unusually strong, with more than half of the variance explained and standard verification tests passed. The stability of this relationship is confirmed using split‐period calibration and verification. This allows the reconstruction to be variance‐scaled to the full length of the instrumental series back to 1766. Direct comparison with historical reports of very wet and dry summers show good agreement. Near‐constant replication, with a minimum of 10 timbers sourced from historic buildings across central southern England ensures signal strength does not change over time. Summers during the late 20th century appear anomalously dry and those of the 21st century very close to the pre‐20th century average with no evidence in the record of prolonged ‘megadroughts’ across England and Wales.

In much of Europe, the advent of low-input cereal farming regimes betweenc.ad800 and 1200 enabled landowners—lords—to amass wealth by greatly expanding the amount of land under cultivation and exploiting the labour of others. Scientific analysis of plant remains and animal bones from archaeological contexts is generating the first direct evidence for the development of such low-input regimes. This article outlines the methods used by the FeedSax project to resolve key questions regarding the ‘cerealization’ of the medieval countryside and presents preliminary results using the town of Stafford as a worked example. These indicate an increase in the scale of cultivation in the Mid-Saxon period, while the Late Saxon period saw a shift to a low-input cultivation regime and probably an expansion onto heavier soils. Crop rotation appears to have been practised from at least the mid-tenth century.

Analyses of radiocarbon dates (all corrected for the freshwater reservoir effect) and associated stable isotope values obtained from the skeletal remains of ~650 individuals provide many new insights about Middle Holocene hunter–gatherers (HGs) of the Cis-Baikal region, Eastern Siberia. The new radiocarbon evidence clarifies the culture history of the region by defining better the boundaries between the chronological (archaeological periods) and cultural (mortuary traditions) units, as well as our understanding of the transitions between them. Furthermore, differences between the four archaeological micro-regions with regard to the timing and duration of these culture historical units have come into focus for the first time. In terms of dietary patterns, the Early Neolithic foragers of the Angara and Southwest Baikal trended towards a greater reliance on aquatic foods. A similar trend was found in the Late Neolithic (LN) Isakovo group on the Angara, while the LN Serovo group in the Little Sea trended towards an increased dietary reliance on terrestrial game. In the Early Bronze Age HGs, a mosaic of dietary patterns was found: some groups experienced dietary shifts (frequently emphasizing different foods), while other groups displayed stability. Such differences were found even between close neighbours. All these results suggest significant variation in patterns of culture change within and between archaeological periods, mortuary traditions, and micro-regions. Some cultural patterns developed at a quick pace, others much more slowly; some appear to have collapsed rapidly, while others probably went through a more gradual transition to a different pattern. Additionally, this large set of radiocarbon dates allows novel insights into patterns of cemetery use: some seem to have been used continuously, others only sporadically, and some show long periods of disuse. Moreover, some cemeteries of the same mortuary tradition were apparently in use substantially earlier than others were even established. In sum, Cis-Baikal Middle Holocene HG strategies underwent a range of changes not only at the boundaries between relevant culture historical units but also within such units. New insights suggest considerable spatio-temporal variation in the nature, pace, and timing of these developments.

A considerable amount of bioarchaeological research – including AMS14C dating and stable carbon and nitrogen isotope analyses (δ13C and δ15N) – has been undertaken on the hunter-gatherers from the area west of Lake Baikal, known as Cis-Baikal. No such work has previously been reported for the east side of the lake, Trans-Baikal. Here, we present new radiocarbon dates and isotopic results for twenty individuals from the Fofanovo cemetery, located along the Selenga River on the southeast coast of Lake Baikal. Once corrected for an old carbon effect using regression equations developed for Cis-Baikal, the radiocarbon results form 4 chronological clusters: 1) Late Mesolithic (LM), around 7950cal BP (n=3); 2) Late Neolithic (LN), between ca. 6000 and 5500cal BP (n=5); 3) LN to EarlyBronze Age(EBA), between ca. 4900 and 4500cal BP (n=2); and the largest cluster 4) later EBA, around 3700cal BP (n=10). The LM Cluster 1 dates indicate that formal cemetery use in Trans-Baikal may have begun earlier than in Cis-Baikal. Clusters 2 and 3 reveal a previously unidentified LN component to the cemetery. Additionally, the EBA Cluster 4 appears to be largely synchronous with the EBA in Cis-Baikal. As a group, the Fofanovo individuals are isotopically distinct from the Middle-Holocene hunter–gatherers in the microregions of Cis-Baikal, exhibiting a combination of low δ13C values (−19.4±0.9‰) but high δ15N values (15.2±0.8‰). This likely reflects the distinctive isotopic ecology of the lower Selenga River, combined with use of aquatic resources from Lake Baikal itself. While further sampling is needed to test its robustness, a statistically significant difference between the LN (n=6) and EBA (n=11) was found, suggesting a greater reliance on the seasonal resources of the Selenga River during the EBA. Further analyses on these and other individuals from the cemetery are planned and will undoubtably provide additional insights into hunter-gatherer subsistence adaptations and dietary variation in Trans-Baikal, highlighting both differences and similarities with those of Cis-Baikal.

Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al . undermine our model.

Leads, lags, or synchronies in climatic events among different regions are key to understanding mechanisms of climate change, as they provide insights into the causal linkages among components of the climate system. The well-studied transition from the Lateglacial to early Holocene (ca. 16–10 ka) contains several abrupt climatic shifts, making this period ideal for assessing the spatio-temporal structure of climate change. However, comparisons of timings of past climatic events among regions often remain hypothetical because site-specific age scales are not necessarily synchronised to each other. Here we present new pollen data (n = 510) and mean annual temperature reconstruction from the annually laminated sediments of Lake Suigetsu, Japan. Suigetsu's 14C dataset is an integral component of the IntCal20 radiocarbon calibration model, in which the absolute age scale is established to the highest standard. Its exceptionally high-precision chronology, along with recent advances in cosmogenic isotope studies of ice cores, enables temporally coherent comparisons among Suigetsu, Greenland, and other key proxy records across regions. We show that the onsets of the Lateglacial cold reversal (equivalent to GS-1/Younger Dryas) and the Holocene were synchronous between East Asia and the North Atlantic, whereas the Lateglacial interstadial (equivalent to GI-1/Bolling-Allerod) started ca. two centuries earlier in East Asia than in the North Atlantic. Bimodal migration (or ‘jump’) of the westerly jet between north and south of the Tibetan plateau and Himalayas may have operated as a threshold system responsible for the abruptness of the change in East and South (and possibly also West) Asia. That threshold in Asia and another major threshold in the North Atlantic, associated with switching on/off of the Atlantic meridional overturning circulation (AMOC), were crossed at different times, producing a multi-centennial asynchrony of abrupt changes, as well as a disparity of climatic modes among regions during the transitional phases. Such disparity may have disturbed zonal circulation and generated unstable climate during transitions. The intervening periods with stable climate, on the other hand, coincided with the beginnings of sedentary life and agriculture, implying that these new lifestyles and technologies were not rational unless climate was stable and thus, to a certain extent, predictable.

Authors thank the National Natural Science Foundation of China grants NSFC 41888101 and NSFC 41731174, the 111 program of China (D19002), U.S. NSF Grant 1702816, and the Malcolm H. Wiener Foundation for support for research that contributed to the IntCal20 curve. The work on the Swiss and German YD trees was funded by the German Science foundation and the Swiss National Foundation (grant number: 200021L_157187). The operation in Aix-en-Provence is funded by the EQUIPEX ASTER-CEREGE, the Collège de France and the ANR project CARBOTRYDH (to EB). The work on the correlation of tree ring 14C with ice core 10Be was partially supported by the Swedish Research Council and the Knut and Alice Wallenberg foundation. M. Butzin is supported by the German Federal Ministry of Education and Research (BMBF) through the PalMod project (grant number: 01LP1505B). S. Talamo and M. Friedrich. are funded by the European Research Council under the European Union’s Horizon 2020 Research and Innovation Programme (grant agreement No. 803147-RESOLUTION, awarded to ST). C. Turney would like to acknowledge support of the Australian Research Council (FL100100195 and DP170104665). P. Reimer and W. Austin acknowledge the support of the UKRI Natural Environment Research Council (Grant NE/M004619/1). 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. Publisher PDF

Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa. Here we analyse a 200,000-year multi-proxy paleoclimate record from Chew Bahir, a tectonic lake basin in the southern Ethiopian rift. Our record reveals two modes of climate change, both associated temporally and regionally with a specific type of human behavior. The first is a long-term trend towards greater aridity between 200,000 and 60,000 years ago, modulated by precession-driven wet-dry cycles. Here, more favorable wetter environmental conditions may have facilitated long-range human expansion into new territory, while less favorable dry periods may have led to spatial constriction and isolation of local human populations. The second mode of climate change observed since 60,000 years ago mimics millennial to centennial-scale Dansgaard-Oeschger cycles and Heinrich events. We hypothesize that human populations may have responded to these shorter climate fluctuations with local dispersal between montane and lowland habitats.

This research investigates two factors influencing the ability of tree-ring data to provide accurate 14C calibration information: the fitness and rigor of the statistical model used to combine the data into a curve; and the accuracy, precision and reproducibility of the component 14C data sets. It presents a new Bayesian spline method for calibration curve construction and tests it on extant and new Southern Hemisphere (SH) data sets (also examining their dendrochronology and pretreatment) for the post-Little Ice Age (LIA) interval AD 1500–1950. The new method of construction allows calculation of component data offsets, permitting identification of laboratory and geographic biases. Application of the new method to the 10 suitable SH 14C data sets suggests that individual offset ranges for component data sets appear to be in the region of ± 10 yr. Data sets with individual offsets larger than this need to be carefully assessed before selection for calibration purposes. We identify a potential geographical offset associated with the Southern Ocean (high latitude) Campbell Island data. We test the new methodology for wiggle-matching short tree-ring sequences and use an OxCal simulation to assess the likely precision obtainable by wiggle-matching in the post-LIA interval.

When and where the process of state formation took place in the biblical kingdom of Judah is heavily debated. Our regional project in the southwestern part of Judah, carried out from 2007 to the present, includes the excavation of three Iron Age sites: Khirbet Qeiyafa, Tel Lachish, and Khirbet al-Ra’i. New cultural horizons and new fortification systems have been uncovered, and these discoveries have been dated by 59 radiometric determinations. The controversial question of when the kingdom was able to build a fortified city at Lachish, its foremost center after Jerusalem, is now resolved thanks to the excavation of a previously unknown city wall, dated by radiocarbon (14C) to the second half of the 10th century BCE.

The development of chronologies relies on integrating information from a number of different sources. In addition to direct dating evidence, such as radiocarbon dates, researchers will have contextual information which might be an environmental sequence or the context in an archaeological site. This information can be combined through Bayesian or other types of age-model. Once a chronology has been developed, this information can be used to estimate, for example, chronological uncertainties, rates of change, or the age of material which has not been directly dated.Dealing with the information associated with chronology building is complicated and re-evaluation of chronologies often requires structured information which is hard to access. Although there are many databases with primary dating information, these often do not contain all of the information needed for a chronology. The Chronological Query Language (CQL) developed for OxCal was intended to be a convenient way of pulling such information together for Bayesian analysis. However, even this does not include much of the associated information required for reusing data in other analyses.The IntChron initiative builds on the framework set up for the INTIMATE (Integrating Ice core, Marine and Terrestrial Records) chronological database (Bronk Ramsey et al. 2014) and is primarily an information exchange format and data visualization tool which enables users to pull together the types of information needed for chronological analysis. It is intended for use with multiple dating methodologies and while it will be integrated with OxCal, is intended to be an open format suitable for use with other software tools. The file format is JSON which is easily readable in software such as R, Python and MatLab. IntChron is not primarily intended to be a data depository but rather an index of sites where information is stored in the relevant format. As an initial step, databases of radiocarbon dates from the Oxford Radiocarbon Accelerator Unit (including those for the NERC radiocarbon facility), the RESET tephra database, the INTIMATE chronological database and regional radiocarbon databases for Egypt and Southern Africa are all linked. The intention is that users of OxCal will also be able to make published data accessible to others and to store working data, visible only to the user, to be used with the associated analysis tools. The IntChron site allows data from third party sources to be accessed through a representational state transfer (REST) application programming interface (API) in a number of different formats (JSON, csv, txt, oxcal) and associated bibliographic information in BibTeX format.The aim of the IntChron initiative is to make it easy for users to provide data (in the single JSON format with limited minimum requirements) as well as to access data and tools, while promoting robust chronologies including realistic estimates of uncertainties. It is hoped that this will help to bring the chronological research communities to a point where data access is as easy as it is in some other fields. This is particularly important for Early Career Researchers and for those seeking to use large datasets in novel ways.

The radiocarbon dating method is supported by highly refined calibration data empirically obtained from environmental archives. Nevertheless, marine calibration remains problematic due to the spatiotemporally variable Marine Reservoir Effect (MRE). The currently accepted curve for radiocarbon calibration in the ocean is a global curve, partly derived by numerical modelling from its atmospheric counterpart. As such, this curve cannot account for the effects of local phenomena, strongly correlated with 14C signatures in seawater (e.g., ocean dynamics and continental input). Although the radiocarbon community has suggested the use of regional calibration curves that would better represent the heterogeneous ocean reservoir, a reasonable method for their construction has not yet been proposed. We directly address this longstanding issue in radiocarbon research by exploring the output of a model for the temporal evolution of the MRE. The limitations of this model are inherited by our method, and this hinders the use of the regional curves derived here in many regions of the world ocean. Nevertheless, the approach described in this paper remains valid regardless of the chosen model and our preliminary results show that, with the future development of accurate and highly resolved models for the MRE, this method may be a promising alternative to the use of ΔR values in the process of marine calibration.

Bayesian chronological modelling of radiocarbon dates from the Brochtorff Circle at Xagħra, Gozo, Malta (achieved through the ToTL and FRAGSUS projects), provides a more precise chronology for the sequence of development and use of a cave complex. Artefacts show that the site was in use from the Żebbuġ period of the late 5th/early 4th millennium cal BC to the Tarxien Cemetery phase of the later 3rd/early 2nd millennia cal BC. Absolutely dated funerary activity, however, starts with a small rock-cut tomb, probably in use in the mid to late fourth millennium cal BC, in the Ġgantija period. After an interval of centuries, burial resumed on a larger scale, probably in the thirtieth century cal BC, associated with Tarxien cultural material, with the use of the cave for collective burial and other depositions, with a series of structures, most notably altar-like settings built from massive stone slabs, which served to monumentalise the space. This process continued at intervals until the deposition of the last burials, probably in the twenty-fourth century cal BC; ceremonial activity may have ended at this time or a little later, to be followed by occupation in the Tarxien Cemetery period. The implications for the development of Neolithic society on Malta are discussed, as well as the changing character of Neolithic Malta in comparison to contemporary communities in Sicily, peninsular Italy and southern Iberia. It is argued that underground settings and temples on Malta may have served to reinforce locally important values of cooperation and consensus, against a wider tide of differentiation and accumulation, but that there could also have been increasing control of the treatment of the dead through time. The end of the Maltese Neolithic is also briefly discussed.

Sea-level change is thought to influence the frequencies of volcanic eruptions on glacial to interglacial timescales. However, the underlying physical processes and their importance relative to other influences (for example, magma recharge rates) remain poorly understood. Here we compare an approximately 360-kyr-long record of effusive and explosive eruptions from the flooded caldera volcano at Santorini (Greece) with a high-resolution sea-level record spanning the last four glacial–interglacial cycles. Numerical modelling shows that when the sea level falls by 40 m below the present-day level, the induced tensile stresses in the roof of the magma chamber of Santorini trigger dyke injections. As the sea level continues to fall to −70 or −80 m, the induced tensile stress spreads throughout the roof so that some dykes reach the surface to feed eruptions. Similarly, the volcanic activity gradually disappears after the sea level rises above −40 m. Synchronizing Santorini’s stratigraphy with the sea-level record using tephra layers in marine sediment cores shows that 208 out of 211 eruptions (both effusive and explosive) occurred during periods constrained by sea-level falls (below −40 m) and subsequent rises, suggesting a strong absolute sea-level control on the timing of eruptions on Santorini—a result that probably applies to many other volcanic islands around the world. Sea-level lowstands over the last 360,000 years strongly controlled the timing of eruptions of the Santorini Volcano, according to an analysis of tephras and sea-level records, as well as numerical modelling of the underlying magma chamber.

Yuzhniy Oleniy Ostrov in Karelia, northwest Russia, is one of the largest Early Holocene cemeteries in northern Eurasia, with 177 burials recovered in excavations in the 1930s; originally, more than 400 graves may have been present. A new radiocarbon dating programme, taking into account a correction for freshwater reservoir effects, suggests that the main use of the cemetery spanned only some 100-300 years, centring on ca. 8250 to 8000 cal BP. This coincides remarkably closely with the 8.2 ka cooling event, the most dramatic climatic downturn in the Holocene in the northern hemisphere, inviting an interpretation in terms of human response to a climate-driven environmental change. Rather than suggesting a simple deterministic relationship, we draw on a body of anthropological and archaeological theory to argue that the burial of the dead at this location served to demarcate and negotiate rights of access to a favoured locality with particularly rich and resilient fish and game stocks during a period of regional resource depression. This resulted in increased social stress in human communities that exceeded and subverted the 'normal' commitment of many hunter-gatherers to egalitarianism and widespread resource sharing, and gave rise to greater mortuary complexity. However, this seems to have lasted only for the duration of the climate downturn. Our results have implications for understanding the context of the emergence-and dissolution-of socio-economic inequality and territoriality under conditions of socio-ecological stress.

Reversing the field Do terrestrial geomagnetic field reversals have an effect on Earth's climate? Cooper et al. created a precisely dated radiocarbon record around the time of the Laschamps geomagnetic reversal about 41,000 years ago from the rings of New Zealand swamp kauri trees. This record reveals a substantial increase in the carbon-14 content of the atmosphere culminating during the period of weakening magnetic field strength preceding the polarity switch. The authors modeled the consequences of this event and concluded that the geomagnetic field minimum caused substantial changes in atmospheric ozone concentration that drove synchronous global climate and environmental shifts. Science , this issue p. 811

Stable oxygen isotope dendrochronology is an effective precision-dating method for fast grown, invariant (complacent) tree-rings and for trees growing in moist, temperate climatic regions where growth may not be strongly controlled by climate. The method works because trees preserve a strong common isotopic signal, from summer precipitation, and therefore do not need to be physiologically stressed to record a dating signal. This study explores the working hypothesis that whilst tree species may differ in their eco-physiology, leaf morphology and wood anatomy they will record an isotopic signal in their growth rings that is sufficiently similar to enable their precise dating against isotopic reference chronologies developed using dated oak tree rings from the same region. Modern and historical samples from six species (sweet chestnut, English elm, ash, alder, European beech and black poplar) were analysed and their oxygen isotopic variability was compared against an oak master chronology previously developed for central southern England. Whilst differences in the relative strength of the agreement between the different species and the master chronology are apparent, the potential for interspecies dating is demonstrated convincingly. The ability to date non-oak species using stable oxygen isotopes opens-up new opportunities for science-based archaeology and will improve understanding of a largely-unexplored, but significant part of the European historical buildings archive.

The Lake Baikal region of southern Siberia has a rich mortuary record that has provided the most comprehensive isotopic database for palaeodietary studies of north-temperate hunter-gatherers in the world, permitting more detailed reconstructions and finer-grained research questions than are usually possible. Building on previous work, this study contributes new δ13C, δ15N, and AMS radiocarbon dating results from the cemeteries of Verkholensk (n = 44) in the Upper Lena River micro-region and Ulan-Khada (n = 19) in the Little Sea micro-region. Our results reveal that the Late Neolithic (LN, 5570–4600 cal BP) individuals at Verkholensk exhibit higher δ15N values than in the Early Bronze Age (EBA, 4600–3700 cal BP), suggesting a shift to a more terrestrial diet, possibly in response to climate-induced environmental changes. In addition, EBA individuals at Verkholensk differ in both δ13C and δ15N from those at the nearby site of Obkhoi, suggesting territorial divisions at a surprisingly small scale, although there is a diachronic component that needs to be considered, highlighting the need for additional work on freshwater reservoir corrections for the Upper Lena micro-region. The Ulan-Khada EBA results are consistent with the ‘Game-Fish’ and ‘Game-Fish-Seal’ dietary patterns previously identified in the Little Sea micro-region. The now substantial Little Sea micro-region EBA dataset—— allows for more subtle differences in diet to be identified, namely that EBA females with Game-Fish-Seal diets for the whole of the Little Sea sample display significantly lower mean δ13C values than their male counterparts, providing some of the first evidence for sex-based dietary distinctions in Lake Baikal. A small number of δ13C and/or δ15N outliers were identified at both Verkholensk and Ulan-Khada that may support previous suggestions of individual mobility between the Upper Lena and Little Sea micro-regions. Exploratory use of δ18O isotopes in bone collagen offers a novel line of support for this scenario, confirming a number of independently identified outliers.

The new IntCal20 radiocarbon record continues decades of successful practice by employing one calibration curve as an approximation for different regions across the hemisphere. Here we investigate three radiocarbon time-series of archaeological and historical importance from the Mediterranean-Anatolian region, which indicate, or may include, offsets from IntCal20 (~0–22 14C years). While modest, these differences are critical for our precise understanding of historical and environmental events across the Mediterranean Basin and Near East. Offsets towards older radiocarbon ages in Mediterranean-Anatolian wood can be explained by a divergence between high-resolution radiocarbon dates from the recent generation of accelerator mass spectrometry (AMS) versus dates from previous technologies, such as low-level gas proportional counting (LLGPC) and liquid scintillation spectrometry (LSS). However, another reason is likely differing growing season lengths and timings, which would affect the seasonal cycle of atmospheric radiocarbon concentrations recorded in different geographic zones. Understanding and correcting these offsets is key to the well-defined calendar placement of a Middle Bronze Age tree-ring chronology. This in turn resolves long-standing debate over Mesopotamian chronology in the earlier second millennium BCE. Last but not least, accurate dating is needed for any further assessment of the societal and environmental impact of the Thera/Santorini volcanic eruption.

T.J. Heaton is supported by a Leverhulme Trust Fellowship RF-2019-140\9, “Improving the Measurement of Time Using Radiocarbon”. M Butzin is supported by the German Federal Ministry of Education and Research (BMBF), as Research for Sustainability initiative (FONA); www.fona.de through the PalMod project (grant numbers: 01LP1505B, 01LP1919A). E. Bard is supported by EQUIPEX ASTER-CEREGE and ANR CARBOTRYDH. Meetings of the IntCal Marine Focus group have been supported by Collège de France. 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/. Publisher PDF

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 in14C determinations, and its consequences on calibration which we address through the provision of predictive intervals on the curve; improvements to the modeling of rapid14C 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 Khao Wong Prachan Valley of central Thailand is one of four known prehistoric loci of copper mining, smelting and casting in Southeast Asia. Many radiocarbon determinations from bronze-consumption sites in north-east Thailand date the earliest copper-base metallurgy there in the late second millennium BC. By applying kernel density estimation analysis to approximately 100 new AMS radiocarbon dates, the authors conclude that the valley's first Neolithic millet farmers had settled there by c. 2000 BC, and initial copper mining and rudimentary smelting began in the late second millennium BC. This overlaps with the established dates for Southeast Asian metal-consumption sites, and provides an important new insight into the development of metallurgy in central Thailand and beyond.

We test a recent prediction that stable carbon isotope ratios from UK oaks will display age-trends of more than 4‰ per century by measuring >5400 carbon isotope ratios from the late-wood alpha-cellulose of individual rings from 18 modern oak trees and 50 building timbers spanning the 9th–21st centuries. After a very short (c.5 years) juvenile phase with slightly elevated values, the number of series that show rising and falling trends is almost equal (33:35) and the average trend is almost zero. These results are based upon measuring and averaging the trends in individual time-series; the ‘mean of the slopes’ approach. We demonstrate that the more conventional ‘slope of the mean’ approach can produce strong but spurious ‘age-trends’ even when the constituent series are flat, with zero slope and zero variance. We conclude that it is safe to compile stable carbon isotope chronologies from UK oaks without de-trending. The isotope chronologies produced in this way are not subject to the ‘segment length curse’, which applies to growth measurements, such as ring width or density, and have the potential to retain very long-term climate signals.

Humans have been adapting to more demanding habitats in the course of their evolutionary history. Nevertheless, environmental changes coupled with overpopulation naturally limit competition for resources. In order to find such limits, reconstructions of climate and population changes are increasingly used for the continent of our origin, Africa. However, continuous and high-resolution records of climate-human interactions are still scarce. Using a 280 m sediment core from Chew Bahir*, a wide tectonic basin in southern Ethiopia, we reconstruct the paleoenvironmental conditions during the development of Homo sapiens. The complete multiproxy record of the composite core covers the last ~600 ka , allowing tests of hypotheses about the influence of climate change on human evolution and technological innovation from the Late Acheulean to the Middle/Late Stone Age, and on dispersal within and out of Africa. Here we present results from the uppermost 100 meters of the Chew Bahir core, spanning the last 200 kiloyears (ka). The record shows two modes of environmental change that are associated with two types of human mobility. The first mode is a long-term trend towards a more arid climate, overlain by precession-driven wet-dry alternation. Through comparison with the archaeological record, humid episodes appear to have led to the opening of ‘green’ networks between favourable habitats and thus to increased human mobility on a regional scale. The second mode of environmental change resembles millennial-scale Dansgaard-Oeschger and Heinrich events, which seem to coincide with enhanced vertical mobility from the Ethiopian rift to the highlands, especially in the time frame between ~65–21 ka BP. The coincidence of climate change and human mobility patterns help to define the limiting conditions for early Homo sapiens in eastern Africa.___________________* cored in the context of HSPDP (Hominin Sites and Paleolakes Drilling Project) and CRC (Collaborative Research Centre) 806 “Our way to Europe”

What role did climate dynamics play in the evolution and dispersal of Homo sapiens within and beyond Africa, and in key cultural innovations? Were gradual climatic changes, rapid shifts from wet to dry, or short-term climate flickers the main driver of human evolution and migration? As a contribution towards an enhanced understanding of those possible human-climate interactions the Chew Bahir Drilling Project, part of the Hominin Sites and Paleolakes Drilling Project (HSPDP) and the Collaborative Research Center (CRC) 806 “Our way to Europe”, recovered two ~280 m-long sediment cores from a deep, tectonically-bound basin in the southern Ethiopian rift in late 2014. The Chew Bahir record covers the past ~600 ka of environmental history, a critical time period that includes the transition from the Acheulean to the Middle Stone Age, and the origin and dispersal of Homo sapiens. Here we present the results from our multi-proxy study of the Chew Bahir 280 m-long composite core, providing a detailed and high-resolution record of eastern Africa’s climate oscillations during the last ~600 ka. To determine sediment age we used a Bayesian model to combine ages derived from radiocarbon dating of ostracodes, optically-stimulated luminescence (OSL) dating of quartz, Argon-Argon (40Ar/39Ar) dating of feldspar grains from some key (micro)tephra layers, and correlation on the basis of geochemistry of a tephra unit in the core to a known and dated tephra in the outcrop. We used high-resolution geophysical and geochemical indicators, such as the established aridity proxy K, sediment colour and authigenic minerals to differentiate between climate fluctuations on different time scales and magnitudes. Our results show that the full proxy record from Chew Bahir can be divided into three phases with similar trends in central tendency and dispersion. Phase I from ~600 to ~430 kyr BP shows a long-term shift from humid to arid conditions while slightly increasing the variability and ending with the most extreme oscillations between full humidity and extreme aridity. The transition into Phase II (~430 to ~200 kyr BP) is marked by a pronounced millennial-scale humidity increase. Phase II reflects generally more humid conditions and there is evidence of double humidity increase tendency. Firstly, between ~430 and ~315 kyr BP (Phase IIa), and again from ~280 to ~195 kyr BP (Phase IIb), with only slight changes in long-term variability. Since ~200 kyr BP (Phase III), a long-term aridification trend sets in, similar to Phase I, but with a distinct increase in variability and amplitudes. All of these changes would have had significant implications for shaping our ancestors’ living environments, both broadening and limiting their options in response to the different degrees and rates of climatic stress. The Chew Bahir record, one of the very few long terrestrial environmental records from continental eastern Africa, can contribute to testing the influence of low versus high latitude climate change in driving the expansion, contraction and fragmentation of early human habitats.

Calibration is a key element of the radiocarbon dating methodology and the underlying Bayesian statistical approach taken, and algorithms used, are well established and used in calibration software and associated analysis packages. These calibration methods are based on a calibration curve which provides a mean estimate for the radiocarbon isotope ratio (fractionation corrected) expected in samples, and the associated standard uncertainty, both as a function of time (or calendar age). The measured samples also have their radiocarbon isotope ratio reported in the same form and so the calibration process involves comparison of the sample radiocarbon measurements with the calibration curve at different points on the calendar age scale. This then yields a probability distribution function, with associated highest probability density ranges, for the sample calendar age. We discuss here how improvements in the construction of the IntCal20 curve offer new opportunities, enabling users to obtain more from the calibration curve than previously possible and address some of the limitations of previous calibration approaches.Previous approaches to calibration assumed that the values of the calibration curves at any time were normally distributed around their estimated mean. However, there are time periods where the distribution of these curves are not well represented by such a normal distribution. This is potentially significant even for calibrations of single samples. The new IntCal20 curve generates multiple possible calibration curves, providing us with the opportunity to identify and adapt to such non-normality. A second limitation of previous approaches to calibration arises when multiple determinations are used within a broader chronological model. In such cases the usual assumption is that the calibrated uncertainties are independent. This is certainly not the case if all the samples are the same age (which is currently addressed by combination before calibration) but also is potentially wrong if the samples are close enough in age for there to be correlated uncertainty in the calibration curve. Again, using the collection of possible curves provided in the construction of IntCal20, rather than just the summary curve, we look at possible solutions to this challenge. The implications for high-precision chronologies are also discussed.

The construction of the new IntCal20 calibration curve was undertaken using a number of new statistical approaches (Heaton et al. 2020), when compared to previous versions. This was partly due to the nature of some of the new datasets; partly to improve the robustness of the curve; and partly to address particular aspects of radiocarbon within the Earth System such as reservoir effects, incorporation of geological carbon in speleothems, and the uncertainties associated with different timescales. Here the main approaches taken are summarised with a perspective on their strengths and potential weaknesses.In particular, the high-resolution extensions to the Hulu speleothem radiocarbon record (Cheng et al. 2018) allow it to be used to anchor the chronology for other key records (Suigetsu, Cariaco, and the Pakistan and Iberian Margins), providing a coherence in the timescale not possible before. Further, for the first time, we incorporate time varying marine reservoir ages, constrained by the Hamburg Large Scale Geostrophic Ocean General Circulation Model (LSG OGCM)(Butzin et al. 2020). In addition, work on the relationship to the Greenland ice core timescales (Adolphi et al. 2018) enables us to make direct comparison between radiocarbon dated records and the ice core timescale and here we report on tools to assist with this.Along with the update to the calibration curve itself, the associated tools for calibration, age-depth modelling and Bayesian modelling have also been updated to make best use of the new resolution and characteristics of the curve. Here we summarise updates to Bacon, Calib and OxCal.Heaton, TJ. et al (2020) The IntCal20 approach to radiocarbon calibration curve construction: A new methodology using Bayesian splines and errors-in-variables Radiocarbon: in review.Cheng, H. et al. (2018) Atmospheric 14C/12C changes during the last glacial period from Hulu Cave. Science, 362(6420), pp.1293-1297. doi:10.1126/science.aau0747Adolphi, F. et al. (2018) Connecting the Greenland ice-core and U/Th timescales via cosmogenic radionuclides: Testing the synchronicity of Dansgaard-Oeschger events. Climate of the Past, 14, pp.1755-1781. doi:10.5194/cp-2018-85Butzin, M. et al. (2020) A short note on marine reservoir age simulations used in IntCal20. Radiocarbon: in press.