The chemical extraction of soil organic carbon (SOC) fractions from soils often does not produce satisfactory results for radiocarbon dating. In this study, a sequential pyrolysis technique was investigated. The soil was pyrolyzed at temperatures of 200, 400, 600, and 800 °C to partition organic carbon into pyrolytic volatile (Py-V) and pyrolytic residue (Py-R) fractions. The preliminary results show that the 14C dates of both fractions become progressively older as the pyrolysis temperature is increased. In addition, the ages of the Py-V fractions are consistently younger than the corresponding Py-R fractions extracted at the same temperature. Experimental results of known-age paleosol samples indicate that the Py-V fractions obtained between 600 and 800 °C yield the most reliable ages. This technique provides a new approach to improve the accuracy of 14C dating of loess-paleosol sequences.

Establishing precise age-depth relationships of high-alpine ice cores is essential in order to deduce conclusive paleoclimatic information from these archives. Radiocarbon dating of carbonaceous aerosol particles incorporated in such glaciers is a promising tool to gain absolute ages, especially from the deepest parts where conventional methods are commonly inapplicable. In this study, we present a new validation for a published 14C dating method for ice cores. Previously 14C-dated horizons of organic material from the Juvfonne ice patch in central southern Norway (61.676°N, 8.354°E) were used as reference dates for adjacent ice layers, which were 14C dated based on their particulate organic carbon (POC) fraction. Multiple measurements were carried out on 3 sampling locations within the ice patch featuring modern to multimillennial ice. The ages obtained from the analyzed samples were in agreement with the given age estimates. In addition to previous validation work, this independent verification gives further confidence that the investigated method provides the actual age of the ice.

A dedicated sample processing line for the extraction of dissolved inorganic carbon (DIC) from seawater and groundwater for accelerator mass spectrometry (AMS) radiocarbon analysis has been developed at CEDAD, the Center for Dating and Diagnostic of the University of Salento, Lecce, Italy. The features of the new system are presented together with tests carried out to determine its functionality and background levels. The first results obtained at CEDAD for analyzing seawater samples taken from the Northern Adriatic compare well with results obtained for the same samples analyzed at ETH Zurich.

The National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility at the Woods Hole Oceanographic Institution has developed an automated system for high-throughput, low-cost analysis of radiocarbon in carbonate samples (e.g. corals, carbonaceous sediments, speleothems, etc.). The method bypasses graphitization and pretreatment, and reduces costs to about 1/5th the price of a graphite-based 14C carbonate analysis, with a throughput of 60 unknowns per day and an analytical precision of better than 2%. Additionally, a simple mixing experiment indicated that extensive cleaning of carbonate samples to remove organic material is not necessary.

Various carbon structures, including carbon nanofilament (CNF), single-wall carbon nanotube (SWCNT), multi-wall carbon nanotube (MWCNT), and pyrolytic graphite sheet (PGS), were exposed in air to determine how they vary according to carbon structure and air temperature. CNF is the carbon structure used in accelerator mass spectrometry (AMS) radiocarbon dating (Santos et al. 2007). When CNF and MWCNT were exposed in cold air (3 or −18 °C) for longer than 6 hr, their 14C/12C ratio increased (>5 × 10–14). When heated in an oven (200 or 250 °C) for longer than 12 hr, their 14C/12C ratio decreased. However, when SWCNT and PGS were exposed in air cooled to 3 °C for 12 hr, their 14C/12C ratio did not increase. This phenomenon is very curious, and is useful for the development of a storage method for carbon samples made by reduction reactions of CO2.

Radiocarbon dating of plant remains is often difficult due to the complete dissolution of the samples in the alkaline step of the ABA pretreatment. At the VERA laboratory, this problem was encountered frequently when numerous Bronze and Early Iron Age samples from the eastern Mediterranean were dated in the course of the special research program SCIEM2000 and in other collaborations with archaeologists focused on that area and time period. For these samples, only a 14C age determination of the humic acid fraction was possible. Humic acids from archaeological samples are always assessed as a second-choice material for 14C dating. It is assumed that the 14C ages may be affected by the presence of humic acids originating from other (younger) organic material, e.g. from soil horizons located above a sample. Therefore, when humic acids are dated a verification of the dates is crucial. To address this basic requirement, we started some time ago to date both fractions of charred seeds, wood, and charcoal samples whenever available, i.e. the residue after the ABA treatment and the humic acids extracted from the samples in the alkaline step. The results of this comparison showed that for the investigated eastern Mediterranean archaeological sites, 50 (out of 52) humic acid dates were in agreement with the 14C dates of the respective ABA-treated samples. Statistical analysis of the age differences leads to the conclusion that the extracted humic acids originated from the samples themselves or from contemporaneous material and were not appreciably contaminated by extraneous material of different age.

A modified sealed tube Zn reduction method based on Khosh et al. (2010) has been developed to graphitize ultra small-mass samples ranging from 4–15 μg carbon (C) for accelerator mass spectrometry (AMS) radiocarbon measurements. In this method, the reagent TiH2 is removed from the previous method while the amounts of Zn and Fe powder remain the same. The volume of the sealed reactor is further reduced by ∼40% to ∼0.75 cm3 and the graphitization temperature is lowered to 450 °C. Graphite targets produced by this method generally yield 12C+1 currents of about 0.5 μA per 1 μg C, similar to the small mass (15–100 μg C) sealed tube Zn reduction method previously reported by Khosh et al. (2010) when measured on the same AMS system at KCCAMS, University of California, Irvine. Change of Fe powder to Sigma-Aldrich (400-mesh) has yielded further improved backgrounds over Fe powder of Alfa Aesar (325-mesh). Modern C background from combustion and graphitization is estimated to be 0.2–0.8 μg C, and dead-C background to be 0.1–0.4 μg C. The accuracy and precision of ultra small-mass samples prepared by this method are size and 14C content dependent, but is usually ±4–5% for the smallest sample size of ∼4–5 μg C with modern 14C content. AMS on-line δ13C measurement that allows for correction of both graphitization and machine-induced isotopic fractionation is the key for applying the sealed tube Zn reduction method to ultra small-mass sample graphitization.

It is important to evaluate each step in radiocarbon analysis to ensure that the whole process is as efficient and accurate as possible. Aerosol filter samples contain a myriad of carbonaceous compounds with varying resistance to oxidation. Complete combustion of the sample is thus of great importance to ensure that the graphitized sample is representative of the original filter sample. We have evaluated sealed tube combustion of μg-sized aerosol samples using different types and amounts of reagents. Successful analysis of aerosol samples as small as 20 μg C was possible following small changes to our standard on-line method. The sealed tube combustion method performs well for standard samples containing 11 μg C.

Use of coral skeletons to determine growth histories of reefs situated in warm, clear tropical waters is well established. Recently, however, there has been increasing awareness of the significance of reefs occurring in environments that are considered as marginal for coral growth, such as turbid inshore settings characterized by episodes of elevated turbidity, low light penetration, and periodic sediment burial. While these conditions are generally considered as limiting for coral growth, coral reefs in these settings can exhibit high live coral cover and species diversity, and thus can be both ecologically and geologically significant. Turbid-zone reefs are also commonly concentrated along eroding shorelines with many analogues to erosional shorelines developed during the Holocene transgression. A growing number of studies of these previously undocumented reefs reveal that the reef deposits are detrital in nature, comprising a framework dominated by reef rubble and coral clasts and set within a fine-grained terrigenous sediment matrix. In addition to the recognized effects of diagenesis or algal encrustations on the radiocarbon signature of coral samples, episodic high-energy events may rework sediments and can result in age reversals in the same stratigraphic unit. As in other reef settings, the possibility of such reworking can complicate the reconstruction of turbid-zone reef growth chronologies. In order to test the accuracy of dating coral clasts for developing growth histories of these reef deposits, 5 replicate samples from 5 separate coral clasts were taken from 2 sedimentary units in a core collected from Paluma Shoals, an inshore turbid-zone reef located in Halifax Bay, central Great Barrier Reef, Australia. Results show that where care is taken to screen the clasts for skeletal preservation, primary mineralogical structures, and δ13C values indicative of marine carbonate, then reliable 14C dates can be recovered from individual turbid reef coral samples. In addition, the results show that these individual clasts were deposited coevally.

We have developed a simple, rapid method to screen carbonates for survey applications, which provides radiocarbon dates with decreased precision at lower cost. The method is based on previous work by Longworth et al. (2011) and involves mixing pulverized CaCO3 with Fe powder, followed by pressing into aluminum target holders for direct 14C accelerator mass spectrometry (AMS) measurements. An optimum beam current averaging ∼10% of those produced by >0.7 mg C graphite targets was obtained for carbonate samples of 0.3–0.5 mg (0.04–0.06 mg C). The precision of the method was evaluated by measuring triplicates of 14C reference materials, as well as by comparing results from this rapid method with results from high-precision AMS measurements on graphite (typically 0.2–0.3%). Measurement reproducibility was ∼1.8% (1σ) for samples <10 ka BP, and it increased drastically for older samples. However, t tests on paired samples resulted in p values greater than 0.05, indicating a good correlation between this survey method and the conventional one. An average blank (calcite) of 0.0075 Fm (∼39 ka BP) was achieved. The simplicity of the technique allowed us to process and measure 72 deep-sea coral samples in less than 25 hr.

Four charcoal samples from loess key sites in Austria, Moravia, and western Ukraine were submitted to ABOx (acid-base oxidation) pretreatment to compare results with the classical ABA (acid-base-acid) method. For this purpose, charcoal samples already dated in Groningen laboratory were selected from 3 archaeological sites: Molodova V in western Ukraine (subunit 10–1, ∼32.6 ka BP), Willendorf II in Austria (unit C4, ∼32.1 ka BP and unit C8, ∼38.9 ka BP) and Vedrovice V in Moravia (unit 4, upper part of Bohunice soil, ∼39.5 ka BP). Each selected charcoal sample has been homogenized and divided into 3 subsamples, which were submitted to ABA in Groningen and to ABA and ABOx pretreatments in Oxford. The results show that the ABOx dates are older than the ABA dates. Nevertheless, down to ∼40 ka BP ABOx and Groningen ABA dates appear in good agreement within a time interval of ∼1 millennium at 1σ. However, Groningen ABA pretreatment produces older dates than the Oxford ABA pretreatment. Both Oxford ABOx and Groningen ABA pretreatments provide sets of dates in good agreement with the chronological background of each selected site.

The Artemis accelerator mass spectrometry (AMS) facility, installed in 2003 in Saclay, France, is devoted to radiocarbon measurements. Samples are submitted by scientists in the fields of Quaternary geology, environmental sciences, and archaeology. The entire preparation process, originally optimized for samples with about 1 mg of carbon, has been tested in recent years for samples with a lower carbon content. In particular, we prepared and measured carbonate and organic background and reference samples ranging in mass from 0.01 to 1 mg C. These tests helped define our protocol's practical limits and determine necessary improvements. Furthermore, our experiments demonstrated that satisfactory graphitization yields (80% and higher) and low background values can be obtained with samples down to 0.2 mg of carbon. For handling smaller samples, we developed a specific process. We tested smaller reactors (5 mL in volume) and adapted the reduction parameters (H2 pressure and temperature) accordingly. We also tested the effect of a chemical water trap on graphitization yields and 14C results. This paper presents in detail the aforementioned developments and reports the 14C results obtained for background and standard small samples prepared with the modified reactors.

Since installation of the new accelerator at INFN-LABEC in Florence in 2004, the workload has progressively increased in the radiocarbon dating laboratory, requiring a faster sample preparation throughput and greater versatility to allow for a larger variety of treated materials. The “standard” sample preparation line is based on an elemental analyzer (EA) for the combustion of the pretreated samples, and a vacuum line where the CO2 is collected and then converted to graphite. This line has been recently redesigned while maintaining the EA, since this instrument provides us reliable and fast sample combustion and separation of gases. The volumes were optimized and all the mechanical parts (e.g. the fittings) were changed in order to improve the vacuum level, thus decreasing the possibility of contamination; finally, the number of graphitization reactors was doubled (from 4 to 8). In those rare cases involving samples characterized by a complex nearly graphitic structure (e.g. burnt residues), the EA might not guarantee a complete combustion. For these samples, we successfully tested the new sample preparation line that has been recently installed at LABEC and especially dedicated to aerosol samples. This line is equipped with a custom-made combustion oven able to heat to 1000 °C. The subsequent gas separation is accomplished by chemical and thermal traps. As an example, the dating of organic matter collected from an Etruscan bronze statue will be presented and discussed.

We document chemical laboratory procedures and results on international comparison samples at the Hertelendi Laboratory of Environmental Studies, Debrecen, Hungary. We also show results using the new MICADAS system and compare these results to internationally recognized standards and blank materials. The newly developed sample preparation system in HEKAL can handle samples as 1) organic material, 2) cellulose fraction of plant, 3) bones, 4) carbonate and shell, and 5) dissolved inorganic carbon of groundwater. The results of radiocarbon measurements on intercomparison samples confirm the reliability of the sample preparation system at HEKAL Lab and also the good performance of the MICADAS 14C system. The blank levels for each type of sample of 1 mg C carbon content are well reproducible, ∼0.3–0.5 pMC.

Compound specific radiocarbon measurements can be made instantaneously using a gas chromatograph (GC) combustion system coupled to a 14C AMS system fitted with a gas ion source. Samples below 10 μg C can be analyzed but the precision is reduced to 5–10% because of lower source efficiency. We modified our GC for CH4 and CO2 analysis and injected samples multiple times to sum data and increase precision. We attained a maximum precision of 0.6% for modern CO2 from 25 injections of 27 μg C and a background of ≃0.5% (40 kyr) for ancient methane. The 14C content of dissolved CO2 and CH4 in water samples collected at a deep-sea hydrothermal vent and a serpentine mud volcano was measured and the results for the vent sample are consistent with previously published data. Further experiments are required to determine a calibration and correction procedure to maximize accuracy.

Measurements of the radiocarbon abundance in 5 samples of bis(2–ethylhexyl) phthalate (DEHP) isolated from Stilton cheese were made by accelerator mass spectrometry (AMS) to determine the fraction of carbon originating from contemporary biogenic sources. DEHP is classified as a “priority hazardous substance” by the European Union, a probable human carcinogen by the United States Environmental Protection Agency, and is suspected to be a human endocrine disrupter. Measurement of its 14C abundance in a specific food indicates whether its presence is due to contamination from industrially synthesized DEHP or a naturally inherent component. A method was developed to determine the contemporary carbon fraction of DEHP in a fatty food matrix at concentrations of 0.14 mg/kg. Five 90–μg quantities of DEHP were extracted from 12 kg of Stilton cheese and isolated by silica gel, size exclusion, and high-performance liquid chromatography (HPLC). Masses of samples were determined by gas chromatography mass spectrometry (GC-MS) analyses prior to combustion and manometry afterwards. The purity of DEHP carbon mass in each isolate was determined by multivariate deconvolution of GCMS fragmentation spectra obtained from measurements of standards and isolates, and ranged from 88.0 ± 1.8% to 92.3 ± 1.1% (n = 5, 1σ). Concurrently processed isolation method blanks contained from 0.15 ± 0.04 to 1.52 ± 0.06 μg (n = 3, 1σ) DEHP per sample and significant quantities of pre- and post-chromatographic extraneous carbon contamination. The mean 14C-corrected contemporary carbon fraction of DEHP in the isolates was 0.235 ± 0.073 (1σ; and ± 0.091 at the 95% confidence level), revealing that the majority of DEHP in Stilton cheese results from anthropogenic sources, but with a significant naturally occurring component.

Dating of the amino acid hydroxyproline from bone collagen has been shown to produce accurate and reliable radiocarbon dates. This article presents further application of the method demonstrating it can be used to obtain dates for both low-collagen and contaminated bones, extending the capability of 14C dating archaeological bone from conventional limits imposed by alternative pretreatment methods. The method therefore has the potential for significantly benefiting the accelerator mass spectrometry (AMS) dating community in the 14C dating of archaeological bone.

When humans consume foods from different radiocarbon reservoirs offset in age to the atmosphere, inaccuracies in the 14C date of bone collagen can occur. Mesolithic human skeletons from the Iron Gates section of the Lower Danube Valley have yielded reservoir offsets of up to ∼500 yr. This has been demonstrated through direct dating of bulk collagen from human bones and the remains of ungulate bone projectile points that were found embedded in them (Cook et al. 2001). We present improvements to a novel HPLC method for the detection and separation of underivatized amino acids using a water-only mobile phase free of organic or inorganic modifiers, ensuring very low carbon backgrounds. Our hypothesis is that direct 14C dating of single essential and non-essential amino acids might allow an improvement in the dating accuracy for reservoir-affected human bones. The method facilitates separation of less polar amino acids (mostly “essential”), currently not possible in the recently published protocol. We discuss methodological developments, demonstrate carbon backgrounds, and present analytical approaches to minimize their effects. We validate the precision and accuracy of the method by accelerator mass spectrometry (AMS) dating relatively modern and 14C-dead, known-age bone standards. Finally, we apply the method to the dating of single amino acids from bone samples with a proven ∼500–yr carbon reservoir effect from Mesolithic burials at the Iron Gates sites. We investigate whether differences can be found in AMS dates for essential and non-essential amino acids since, although contemporaneous, these are expected to derive from dietary sources with differing 14C reservoirs.

OxCal is a widely used software package for the calibration of radiocarbon dates and the statistical analysis of 14C and other chronological information. The program aims to make statistical methods easily available to researchers and students working in a range of different disciplines. This paper will look at the recent and planned developments of the package. The recent additions to the statistical methods are primarily aimed at providing more robust models, in particular through model averaging for deposition models and through different multiphase models. The paper will look at how these new models have been implemented and explore the implications for researchers who might benefit from their use. In addition, a new approach to the evaluation of marine reservoir offsets will be presented. As the quantity and complexity of chronological data increase, it is also important to have efficient methods for the visualization of such extensive data sets and methods for the presentation of spatial and geographical data embedded within planned future versions of OxCal will also be discussed.

Bayesian methods have been widely used to address the Iron Age chronological debate in Israel, which has implications for the entire eastern Mediterranean Iron Age chronology. However, a consensus has not been reached. This is largely because radiocarbon dates of materials in this period lie on an oscillation in the calibration curve. This study focuses on the modeling of 14C dates from the Iron I and Iron II periods, discusses the underlying assumptions and limitations of existing Bayesian chronologies, and proposes the use of a more appropriate model that allows for the phase transitions not being instantaneous. The new trapezoidal model sheds light on the probable duration of the transitions between the Iron Age phases.