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The Lagoa Salgada is located in the Paraíba do Sul river delta plain on the coast of Rio de Janeiro state, Brazil, and is one of the few lagoons in the world that have well-developed recent stromatolites. Lagoa Salgada is a hypersaline lagoon formed in a very complex environmental system subjected to terrestrial and oceanic influences under different sea level regimes and climate variations. In addition, sediment and stromatolites are characterized by unusually positive inorganic δ13C VPDB values. For this reason, it has been the target of several geological and paleoenvironmental studies, which, in their great majority, require a geochronological technique in order to determine the changes in the environment over time. When radiocarbon (14C) dating is used, it is necessary to consider some details as the source of 14C in the environment and perform 14C ages calibration accordingly. In the present paper, a bibliographic survey was carried out in order to review the data treatment and improve the environmental evolution discussion based on accurate calibration. Using the Marine20 curve and an undetermined ΔR, we generated growth and depositional models to establish an overview of the formation of this lagoon. [ABSTRACT FROM AUTHOR]

Due to fluctuations in past radiocarbon (14$$ {}^{14} $$C) levels, calibration is required to convert 14$$ {}^{14} $$C determinations Xi$$ {X}_i $$ into calendar ages θi$$ {\theta}_i $$. In many studies, we wish to calibrate a set of related samples taken from the same site or context, which have calendar ages drawn from the same shared, but unknown, density f(θ)$$ f\left(\theta \right) $$. Calibration of X1,...,Xn$$ {X}_1,\dots, {X}_n $$ can be improved significantly by incorporating the knowledge that the samples are related. Furthermore, summary estimates of the underlying shared f(θ)$$ f\left(\theta \right) $$ can provide valuable information on changes in population size/activity over time. Most current approaches require a parametric specification for f(θ)$$ f\left(\theta \right) $$ which is often not appropriate. We develop a rigorous non‐parametric Bayesian approach using a Dirichlet process mixture model, with slice sampling to address the multi‐modality typical within 14$$ {}^{14} $$C calibration. Our approach simultaneously calibrates the set of 14$$ {}^{14} $$C determinations and provides a predictive estimate for the underlying calendar age of a future sample. We show, in a simulation study, the improvement in calendar age estimation when jointly calibrating related samples using our approach, compared with calibration of each 14$$ {}^{14} $$C determination independently. We also illustrate the use of the predictive calendar age estimate to provide insight on activity levels over time using three real‐life case studies. [ABSTRACT FROM AUTHOR]

The Chronos 14Carbon-Cycle Facility is a new radiocarbon laboratory at the University of New South Wales, Australia. Built around an Ionplus 200 kV MIni-CArbon DAting System (MICADAS) Accelerator Mass Spectrometer (AMS) installed in October 2019, the facility was established to address major challenges in the Earth, Environmental and Archaeological sciences. Here we report an overview of the Chronos facility, the pretreatment methods currently employed (bones, carbonates, peat, pollen, charcoal, and wood) and results of radiocarbon and stable isotope measurements undertaken on a wide range of sample types. Measurements on international standards, known-age and blank samples demonstrate the facility is capable of measuring 14C samples from the Anthropocene back to nearly 50,000 years ago. Future work will focus on improving our understanding of the Earth system and managing resources in a future warmer world. [ABSTRACT FROM AUTHOR]

Following some 30 years of radiocarbon research during which the mathematical principles of 14C-calibration have been on loan to Bayesian statistics, here they are returned to quantum physics. The return is based on recognition that 14C-calibration can be described as a Fourier transform. Following its introduction as such, there is need to reconceptualize the probabilistic 14C-analysis. The main change will be to replace the traditional (one-dimensional) concept of 14C-dating probability by a two-dimensional probability. This is entirely analogous to the definition of probability in quantum physics, where the squared amplitude of a wave function defined in Hilbert space provides a measurable probability of finding the corresponding particle at a certain point in time/space, the so-called Born rule. When adapted to the characteristics of 14C-calibration, as it turns out, the Fourier transform immediately accounts for practically all known so-called quantization properties of archaeological 14C-ages, such as clustering, age-shifting, and amplitude-distortion. This also applies to the frequently observed chronological lock-in properties of larger data sets, when analysed by Gaussian wiggle matching (on the 14C-scale) just as by Bayesian sequencing (on the calendar time-scale). Such domain-switching effects are typical for a Fourier transform. They can now be understood, and taken into account, by the application of concepts and interpretations that are central to quantum physics (e.g. wave diffraction, wave-particle duality, Heisenberg uncertainty, and the correspondence principle). What may sound complicated, at first glance, simplifies the construction of 14C-based chronologies. The new Fourier-based 14C-analysis supports chronological studies on previously unachievable geographic (continental) and temporal (Glacial-Holocene) scales; for example, by temporal sequencing of hundreds of archaeological sites, simultaneously, with minimal need for development of archaeological prior hypotheses, other than those based on the geo-archaeological law of stratigraphic superposition. As demonstrated in a variety of archaeological case studies, just one number, defined as a gauge-probability on a scale 0–100%, can be used to replace a stacked set of subjective Bayesian priors.

A new method for automated construction of 14C-based archaeological chronologies, called Barcode Seriation (BS), is introduced. The application of BS is demonstrated for medium-sized (N~50 sites) datasets of the early Neolithic cultures Starčevo/Körös/Criş, LBK-I, and Vinča A. The BS-method is easy to apply, but nevertheless allows construction of 14C-chronologies at comparatively high dating precision. The key to BS is a new timing discriminator (TD), designed for leading/trailing edge shape-analysis of summed probability distributions of 14C-ages (SPDs). In functional terms, the TD works as an Analog-to-Digital Converter. The SPD signal digitisation, in turn, supports large-scale 14C-database analysis on different levels of data confinement (e.g. by sites, periods, periods, cultures, phases) as well as on large geographic scales (regional-continental). Due to the compactness of the chosen graphic-output topology, the combined BS/TD-technology supports ordination and plotting of very large 14C-datasets, but leaving room in graphic representation for the chronology to be shown in context with other records e.g. from palaeoenvironmental, archaeobiological, and palaeaoclimatological studies. The feasibility of routine application of the new method is demonstrated by case-comparisons at high dating-resolution for the sites of Pityerdomb (Hungary), Vráble (Slowakia), Versend-Gilencsa (Hungary), Vinča-Belo-Brdo (Serbia), and at two LBK-sites ('Lüsse' and 'Unteres Feld') both located in the Ammer Valley near Tübingen (Germany). The new methodology is complemented with studies towards the application of Gauge Theory in support of archaeological 14C-analysis. [ABSTRACT FROM AUTHOR]

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To resolve an inconsistency around AD 1895 between radiocarbon (14C) measurements on oak from the British Isles and Douglas fir and Sitka spruce from the Pacific Northwest, USA, we measured the 14C content in single-year tree rings from a Scots pine tree (Pinus sylvestris L.), which grew in a remote location in Saltdal, northern Norway. The dataset covers the period AD 1864–1937 and its results are in agreement with measurements from the US Pacific coast around 1895. The most likely explanation for older ages in British oak in this period seems to be 14C depletion associated with the combustion of fossil fuels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

For a century, archaeologists have puzzled over the enigma of successful whaling unfolding with no predecessors prior to the last two millennia. The emergence of social complexity is linked with the appearance of the Old Bering Sea (OBS) aesthetic engraved on walrus ivory implements found in sites with large cemeteries and thick middens. Significantly, many OBS sites co-occur with major haulout locations for Pacific walrus, whose procurement engendered relationships that, along with seafaring or hunting technology, were the pivotal drivers that fostered whaling. Our revision of extant 14C assays to correct for marine carbon produces a younger 'Low' chronology placing the OBS florescence between AD 650–1250, with its earliest phase Okvik and allied Ipiutak communities from AD 300 to 600. The lithic technology of OBS is distinctive in its notched bifaces with affinities to 3000-year-old Chukchi Archaic assemblages. Later influences on OBS development include Ipiutak lithic technology and suggest migration, and either adversarial, or trading relationships with Alaska. The acquisition of rare commodities (driftwood, iron and obsidian) contributed to differential success and resulted in inequality recorded in burials. [ABSTRACT FROM AUTHOR]

This paper evaluates chronological trends in the presence and absence of domestic animal bone (sheep, goat, and cattle) and pottery in Namaqualand, the proposed gateway to the rest of South Africa for early herders or hunter-gatherers with sheep and ceramics. We update date calibrations with local ΔR corrections and mixtures of recent calibration curves and include five previously unpublished dates. We use histograms of calibrated medians, sorted in 100-year bins, to assess sustained regional patterns with dates associated with domestic animal bone and pottery (n = 73). While too small to be useful as a population proxy, the current set of dates does reveal three pulses of occupation separated by two clear gaps, which we evaluate with a Bayesian model of three sequential phases. The model's boundaries are used as estimates of the dates of Early (AD 80–210), Middle (AD 490–790), and Late (AD 1180–1690) occupational phases separated by two substantial lapses of 280 and 380 years, respectively. The alternating phases of presence and absence are suggestively correlated with climate shifts, leading to a discussion of the idea that effective moisture was a crucial factor in choosing whether to occupy Namaqualand. The set of archaeological dates has greater temporal and spatial resolution than many regional climate data, so we suggest that these trends may more accurately reflect the variable conditions specific to Namaqualand, at least until they are refined by future climate research. [ABSTRACT FROM AUTHOR]

The Last Glacial–Interglacial Transition (LGIT; 15,000–11,000 cal BP) was characterized by complex spatiotemporal patterns of climate change, with numerous studies requiring accurate chronological control to decipher leads from lags in global paleoclimatic, paleoenvironmental, and archaeological records. However, close scrutiny of the few available tree-ring chronologies and radiocarbon-dated sequences composing the IntCal13 14C calibration curve indicates significant weakness in 14C calibration across key periods of the LGIT. Here, we present a decadally resolved atmospheric 14C record derived from New Zealand kauri spanning the Lateglacial from ~13,100–11,365 cal BP. Two floating kauri 14C time series, curve-matched to IntCal13, serve as a 14C backbone through the Younger Dryas. The floating Northern Hemisphere (NH) 14C data sets derived from the YD-B and Central European Lateglacial Master tree-ring series are matched against the new kauri data, forming a robust NH 14C time series to ~14,200 cal BP. Our results show that IntCal13 is questionable from ~12,200–11,900 cal BP and the ~10,400 BP 14C plateau is approximately 5 decades too short. The new kauri record and repositioned NH pine 14C series offer a refinement of the international 14C calibration curves IntCal13 and SHCal13, providing increased confidence in the correlation of global paleorecords. [ABSTRACT FROM AUTHOR]

The calibration of radiocarbon measurements is based on a number of mathematical assumptions that are rarely considered by users of the various available calibration programs. As 14C ages take on mathematical properties best known from quantum physics, a quantum theoretical approach provides a useful basis to evaluate the reliability of processes of calibration and Bayesian modelling of radiocarbon datasets. We undertake such an evaluation here through a consideration of the mathematics of calibration, the normalization process, and through an archaeological case study. We demonstrate that the normalization function deemed necessary for 14C histogram shape-correction is identical to the default prior widely used in Bayesian calibration. We highlight flaws in default Bayesian calibration algorithms which may affect archaeological studies that are overly reliant on high calibration precision, especially when based on relatively small (N<100) sample sizes. The observed differences between algorithms have consequences for radiocarbon models that claim sub-generational (~25–30 calendar years) precision. [ABSTRACT FROM AUTHOR]

This work reports the first high-precision 14 C-AMS dating of holocellulose from a Brazilian subtropical species for the period 1927–1997, with the goal to identify suitable Southern American tree species that will serve as benchmarks for improving the calibration of the 14 C time-scale for the Southern Hemisphere (SH). The tree rings analyzed here came from a single tree of Paraná pine ( Araucaria angustifolia ) growing at 22°50′S, 46°04′W (Camanducaia, Minas Gerais, Brazil). A slight depletion of atmospheric 14 C after 1927 AD was observed, due to the Suess effect. Our 14 C results also showed the rise and rapid decrease of atmospheric 14 C concentrations associated with the detonation of nuclear weapons during the late 50s, and its subsequent uptake by other large C sinks. Current 14 C data can be used for the study of the global carbon cycle, forensic sciences applications, and the determination of the age and growth rate of tropical trees without annual ring patterns. The remarkable overall agreement of our tree-ring/ 14 C data with the SH Zone 1–2 compilation dataset shows this subtropical tree species' potential to refine the 14 C calibration curve. [ABSTRACT FROM AUTHOR]

Radiocarbon (C) dates are the most important means for determining the age of Holocene archaeological deposits. The theoretical physical basis of this method is by now unassailable, having been consistently tested and refined over two generations. However, the means by which this method has been applied and the interpretation of these results remain as key issues, particularly for complex archaeological discoveries that substantially affect our understanding of world prehistory and social evolution. Many factors can produce uncertainty or variation in the C concentrations of samples, even those that have been selected from the same archaeological context or event. A number of recent studies have also addressed the ways in which ambiguities and irregularities in the C calibration curve can affect the interpretation of archaeological dates and temporal patterns. Of greatest concern, however, is a growing practice of using only one or two samples to date a significant prehistoric context or event. The date of these events, usually relative to other human activities, often holds important theoretical implications for evolutionary anthropology and related disciplines. In this article, we demonstrate that such a practice is rarely adequate or acceptable. Rather, proper procedure requires a suite of dates that permit statistical verification that the deposit or event itself is being correctly dated. We present a detailed case study that highlights the importance of analyzing multiple samples of C from significant archaeological contexts. [ABSTRACT FROM AUTHOR]

Radiocarbon-dated marine mammal remains from emergent Arctic coastlines have frequently been used to reconstruct Holocene sea-ice histories. The use of such reconstructions has hitherto been complicated by uncertain marine reservoir corrections precluding meaningful intercomparisons with data reported in calibrated or sidereal years. Based on an exhaustive compilation of previously published marine mammal radiocarbon dates (both live-harvested materials and subfossils) from the Canadian Arctic Archipelago (CAA), new, statistically-derived δ13C and ΔR values are provided. Average δ13C values are: −16.1 ± 1.1‰ (bone collagen; n = 193) for bowhead (Balaena mysticetus); −14.4 ± 0.5‰ (n = 44; dentine) for beluga (Delphinapterus leucas); −14.8 ± 1.9‰ (teeth and tusks; n = 18) and −18.0 ± 4.7‰ (n = 9; bone collagen) for walrus (Odobenus rosmarus). ΔR values are 170 ± 95 14C years for bowhead (n = 23) and 240 ± 60 14C years for beluga (n = 12). Scarce data preclude calculation of meaningful, statistically robust walrus ΔR. Using the new ΔR values, an expanded and revised database of calibrated bowhead dates (651 dates; many used in previous CAA sea-ice reconstructions) shows pronounced late Quaternary spatio-temporal fluctuations in bone abundance. Though broadly resembling earlier bowhead subfossil frequency data, analysis of the new expanded database suggests early- and mid-Holocene increases in whale abundance to be of longer duration and lower amplitude than previously considered. A more even and persistent spread of infrequent low-abundance remains during “whale free” intervals is also seen. The dominance of three eastern regions (Prince Regent Inlet & Gulf of Boothia; Admiralty Inlet; Berlinguet Inlet/Bernier Bay) in the CAA data, collectively contributing up to 88% of all subfossil remains in the mid-Holocene, is notable. An analysis of calibrated regional sea-level index points suggests that severance of the Admiralty Inlet-Gulf of Boothia marine channel due to isostatically-driven regression may have played a significant role in enhanced whale mortality during this interval. Comparisons between the newly calibrated bowhead data and other regional sea-ice proxy data further highlight spatial and temporal discrepancies, potentially due to regional asynchronicities and variable sensitivities in proxy response to climate and oceanographic forcing. However, the limited number of deglacial–postglacial marine records continues to hamper extensive intercomparisons between marine mammal and other proxy datasets. Nevertheless, an examination of assumptions inherent in linking bowhead subfossil frequencies, population densities, and sea-ice thickness and distribution, shows that such relationships are highly complex. Factors such as broad sea-ice preferences, variable mortality rates and causes, long distance carcass transport, variable coastline and basin/channel geometries, and changing emergence rates all complicate the correlation of whale bone abundance to sea-ice histories. [ABSTRACT FROM AUTHOR]

In this paper we explore the meaning of the word probability, not in general terms, but restricted to the field of radiocarbon dating, where it has the meaning of ‘dating probability assigned to calibrated 14C-ages’. The intention of our study is to improve our understanding of certain properties of radiocarbon dates, which – although mathematically abstract – are fundamental both for the construction of age models in prehistoric archaeology, as well as for an adequate interpretation of their reliability.

In order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or ΔR value. This study measured the ΔR on both known-age pre-bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of South Africa: the southwestern Cape and Namaqualand. Pooling the data by region produces ΔR values that are similar enough to use a west coast weighted mean ΔR of 146 ± 85 14C years to correctly calibrate marine shell or mixed marine and terrestrial 14C ages. There are however temporal differences in ΔR throughout the Holocene, which we compare with proxy data for upwelling and sea surface temperatures. [ABSTRACT FROM AUTHOR]

Abstract: The debate about the complex issues of human development during the Middle to Upper Palaeolithic transition period (45–35 ka BP) has been hampered by concerns about the reliability of the radiocarbon dating method. Large 14C anomalies were postulated and radiocarbon dating was considered flawed. We show here that these issues are no longer relevant, because the large anomalies are artefacts beyond plausible physical limits for their magnitude. Previous inconsistencies between 14C radiocarbon datasets have been resolved, and a new radiocarbon calibration curve, IntCal09 (), was created. Improved procedures for bone collagen extraction and charcoal pre-treatment generally result in older ages, consistent with independently dated time markers. [Copyright &y& Elsevier]

Abstract: The high potential of the varved sediments of Lake Suigetsu, central Japan, to provide a purely terrestrial radiocarbon calibration model and a chronology of palaeoclimatic changes has been widely recognised for the last two decades. However, this potential has not been fully realised since the only available long sediment core from the lake (‘SG93’) was extracted from a single bore hole and was therefore interrupted by gaps of unknown duration between successive core sections. In the summer of 2006, a new sediment core (‘SG06’) was recovered from the lake. Four separate boreholes were drilled and the parallel sets of cores recovered were found to overlap completely, without gaps between segments. This new record provides the ability to test existing atmospheric radiocarbon calibration models, as well as to assess the scale of inter-regional leads and lags in palaeoclimatic changes over the last Glacial–Interglacial cycle. Multi-disciplinary analyses from SG06 are still ongoing, but a reliable description of the sedimentary sequence needs to be provided to the wider science community before major outputs from the project are released, thereby allowing fully-informed critical evaluation of all subsequent releases of data based on the SG06 record. In this paper, we report key litho-stratigraphic information concerning the SG06 sediment core, highlighting changes in the clarity of annual laminations (varves) with depth, and possible implications for the mechanism of the climate change. We also discuss the potential of the SG06 record to meet the fundamental goals of the INQUA-INTIMATE project. [Copyright &y& Elsevier]

Abstract: The development of a calibration of atmospheric radiocarbon (∆14C) is a significant scientific goal because it provides the means to link the numerous 14C dated paleoclimate records to a common timescale with absolutely dated records, and thereby improve our understanding the relationships between the carbon cycle and climate change. Currently, few calibration datasets that directly sample the atmospheric 14C reservoir are available beyond the end of the dendro-dated Holocene tree ring record at 12.6kyr BP (Before 1950 AD). In the absence of suitable true atmospheric records, 14C calibrations beyond this age limit are based largely on marine data, that are complicated by the marine reservoir effect, which may have varied over the glacial cycle. In this paper, we present a high-resolution record of U–Th series and 14C measurements from Hulu Cave speleothem H82, spanning 10.6–26.8kyr BP. Corrections for detrital 230Th are negligible, and the contribution of 14C-free geologic carbon to the speleothem calcite is small (5–6%) and is stable across major climate shifts. The time series provides a 16kyr record of atmospheric ∆14C as well as an updated age model for the existing Hulu Cave δ18O record. The 14C data are in good overall agreement with existing marine and terrestrial 14C records, but comparisons with the Cariaco Basin marine ∆14C record through the deglacial interval reveal that the Cariaco reservoir age appears to have varied during parts of the Younger Dryas and Heinrich Stadial 1 cold events. This highlights the importance of developing extended high-resolution marine and terrestrial 14C records as a means of detecting changes in ocean circulation over the glacial cycle. [Copyright &y& Elsevier]

Abstract: The radiocarbon dating method relies on calibration through an independent dating method. Dendrochronology is an ideal partner of radiocarbon, because tree-rings are close-to-perfect archives of the atmospheric 14C level, and the tree-ring time scale can be built beyond doubt with high replication. Over the past 30 years, several stages of 14C calibration data sets have been constructed from the work of tree-ring laboratories in Europe and North America. This process is outlined and the present state is documented. In turn, 14C age fluctuations, caused mainly by helio-magnetic changes, can be used to anchor floating tree-ring sections to the calendar scale with a precision of a few decades. [Copyright &y& Elsevier]

All scientists who study the late Quaternary are confronted by the problem of radioa carbon calibration. Since 1969, numerous highafrequency time series have been developed through the use of several stable isotopes (e.g., 6180). Such time series are inefficient as dating methods because too many age possibilities are obtained for a given unique value. However, the Bayesian framework permits incorporation of these time series as a prior assumption on ages in order to improve calibrated ages obtained from a more precise absolute dating approach such as that using radiocarbon. The method is tested on data obtained from the Gigny cave (French Jura). Highly discontinuous posterior distributions are obtained with narrow highest posterior density regions. Thus, when the radiocarbon method alone gives large uncertainties, the incorporation of 6180 values of meteoric waters largely diminishes these uncertainties. [ABSTRACT FROM AUTHOR]

We present a new set of 14C ages obtained by accelerator mass spectrometry (AMS) on planktonic foraminifera from a deep-sea core collected off the Iberian Margin (MD952042). This site, at 37°N, is distant from the high-latitude zones where 14C reservoir age is large and variable. Many independent proxies — alkenones, magnetic susceptibility, ice-rafted debris, foraminifera stable isotopes, abundances of foraminifera, pollen, and dinoflagellates — show abrupt changes correlative with Dansgaard-Oeschger and Heinrich events of the last glacial period. The good stratigraphic agreement of all proxies — from the fine to the coarse-size fractions — indicates that the foraminifera 14C ages are representative of the different sediment fractions. To obtain reliable 14C ages of foraminifera beyond 20,000 14C yr B.P., we leached the shells prior to carbonate hydrolysis and subsequent analysis. For a calendar age scale, we matched the Iberian Margin U37K′ profile with that of Greenland Summit δ18O. Both are proxies for temperature, which in models varies synchronously in the two areas. The match creates no spurious jumps in sedimentation rate and requires only a limited number of tie points. Except for ages older than 40,000 14C yr B.P., Greenland''s GISP2 and GRIP records yield similar calendars. The 14C and imported calendar ages of the Iberian Margin record are then compared to data — from lacustrine annual varves and from corals and speleothems dated by U–Th — previously used to extend the calibration beyond 20,000 14C yr B.P. The new record follows a smooth pattern between 23,000 and 50,000 cal yr B.P. We find good agreement with the previous data sets between 23,000 and 31,000 cal yr B.P. In the interval between 33,000 and 41,000 cal yr B.P., for which previous records disagree by up to 5000 cal yr, the Iberian Margin record closely follows the polynomial curve that was previously defined by an interpolation of the coral ages and runs between the Lake Suigetsu and the Bahamian speleothem data sets. [Copyright &y& Elsevier]

Radiocarbon dating is the most widely applied and reliable dating technique for providing chronological control during Marine Isotope Stage 3 (MIS3; ∼60–27 cal kyr BP). Past variations in the atmospheric concentration of radiocarbon mean a calibration curve is required. IntCal20 and SHCal20 calibration curves covering MIS3 are presently largely based on non-atmospheric records which, in combination with larger radiocarbon (14C) dating uncertainties, results in significant smoothing and reduced resolution in calibration curve structure. Floating tree ring radiocarbon chronologies that are wiggle-matched to other palaeo records (particularly to Hulu Cave speleothems) have the potential to provide detailed structure to the MIS3 portion of extant calibration curves. New Zealand subfossil kauri (Agathis australis) trees are long-lived and are useful for constructing temporally-floating MIS3 atmospheric radiocarbon datasets. This paper presents extant and emerging data from several important Northland subfossil kauri locations (Omaha, Babylon Coast, Bream Bay, Kai Iwi Lakes, Mangawhai). We show the span of seven floating MIS3 kauri sequences (individual trees and chronologies) from which sequential radiocarbon series covering a total of 7556 years is now in development (representing 23% of the period 60–27 cal kyr BP). We also report radiocarbon dates for an additional 34 ancient kauri from MIS3 that can provide additional coverage. After these floating subfossil wood sequences have been produced, close to 40% of MIS3 (12,420 years) will be covered by contiguous subfossil kauri radiocarbon measurements. Based on our findings, we discuss the prospects and limitations for obtaining a highly resolved and precise atmospheric radiocarbon calibration curve comprehensively covering MIS3 using subfossil kauri. [ABSTRACT FROM AUTHOR]

The Younger Dryas/Holocene transition (YD/H) in the sediments of Kråkenes Lake, western Norway, is well marked both lithologically and palaeobiologically at 756.5 cm in the investigated core. A series of 70 AMS radiocarbon dates on terrestrial plant macrofossils and the NaOH-soluble fraction of lake sediment was measured between 585 and 840 cm, covering the time span c. 10 440 to 7915 BP on the radiocarbon timescale. Forty-three of these dates above 760 cm were wiggle-matched against the German oak- pine dendro-calibration curve (IntCal 93) with recent corrections in both the oak and the pine sections. With an increase in age of the pine dendro-series of 200 6 20 yr, the calendar age of the YD/H lithostratigraphic boundary at Kråkenes is estimated to 11 530 [sup +40] [sub -60] cal. BP. By using a date of 9750 BP (11 170 cal. BP) on the transition between the 10 000 and 9600 14 C plateaux as a time marker, this result is compared with recent results from other archives. It is consistent with many of them, including the GRIP ice core, German pine series, Lake Gościaż, south Swedish lakes, and Baltic varves, suggesting that the Younger Dryas-Holocene transition in the North Atlantic region occurred within the range 11 500–11 600 cal. BP. [ABSTRACT FROM AUTHOR]