Search

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]

Copyright of Documenta Praehistorica is the property of Documenta Praehistorica and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

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]

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]

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]

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]