One of the difficulties in reporting accurate radiocarbon results from compound-specific radiocarbon analysis (CSRA) is the lack of suitable process standard materials to correct for the amount and 14C content of carbon added during extensive sample processing. We evaluated the use of n-alkanes extracted from modern grass material (1.224±0.006 fraction modern) as process standards for CSRA. The n-alkanes were isolated using preparative capillary gas chromatography (PCGC) from two independent chemical extraction methods applied to the grass. Since this was our first assessment of the 14C content of the grass n-alkanes, we corrected for extraneous carbon derived from PCGC isolation using commercially available single compounds of modern and 14C-free content. Results were consistent across the two extraction methods showing that the C29n-alkane has a fraction modern value that is within 1σ of the bulk value of the grass while C31n-alkane and less abundant n-alkanes have values within 2σ of the bulk value of the grass. C29 and C31n-alkanes were the most abundant n-alkanes in the grass and, as such, the more feasible for collection of sufficient amounts of carbon for accelerator mass spectrometry (AMS) analysis. Our results suggest that choosing a grass n-alkane with an elution time closest to that of the unknowns may be advisable due to possibly greater effect from GC column bleed (14C-free) at later elution times. We conclude that C29 and C31n-alkanes in modern grass of known 14C content can be used as in-house standards to correct for the addition of 14C-free carbon during sample preparation for 14C analysis of n-alkanes.

Atmospheric Δ14CO2 measurements are useful to investigate the regional signals of anthropogenic CO2 emissions, despite the currently scarce observational network for Δ14CO2. Plant samples are an easily attainable alternative, which have been shown to work well as a qualitative measure of the atmospheric Δ14CO2 signals integrated over the time a plant has grown. Here, we present the 14C analysis results for 89 individual maize (Zea mays) plant samples from 51 different locations that were gathered in the Netherlands in the years 2010 to 2012, and from western Germany and France in 2012. We describe our sampling strategy and results, and include a comparison to a model simulation of the Δ14CO2 that would be accumulated in each plant over a growing season. Our model simulates the Δ14CO2 signatures in good agreement with observed plant samples, resulting in a root-mean-square deviation (RMSD) of 3.30‰. This value is comparable to the measurement uncertainty, but still relatively large (20–50%) compared to the total signal. It is also comparable to the spread in Δ14CO2 values found across multiple plants from a single site, and to the spread found when averaging across larger regions. We nevertheless find that both measurements and model capture the large-scale (>100 km) regional Δ14CO2 gradients, with significant observation-model correlations in all three countries in which we collected samples. The modeled plant results suggest that the largest gradients found in the Netherlands and Germany are associated with emissions from energy production and road traffic, while in France, the 14CO2 enrichment from nuclear sources dominates in many samples. Overall, the required model-based interpretation of plant samples adds additional uncertainty to the already relatively large measurement uncertainty in Δ14CO2, and we suggest that future fossil fuel monitoring efforts should prioritize other strategies such as direct atmospheric sampling of CO2 and Δ14CO2.

Age estimation has been a limiting factor in the study of giant columnar cacti. In order to test the feasibility of using radiocarbon methods to estimate the age of the giant cardon cacti (Pachycereus pringlei), we selected six sites spanning the latitudinal and precipitation range of the species in the Baja California peninsula. In each site, we selected four individuals of different heights and sampled a spine from the lowest areole in the stem. The age of the spine was estimated using 14C dating, and the mean annual growth rate of the plant was calculated dividing the height of the lead shoot by the plant’s age. Mean annual growth rate was 0.098 m/yr, with values varying between 0.03 and 0.23 m/yr. Within the range of plants sampled, mean annual growth rates were significantly correlated with the height of the plant (r 2=0.82, P<0.0001), and no other site-specific variable such as precipitation or latitude was a significant predictor of mean annual growth rates. A model integrating mean growth rate versus height showed that relatively small differences in growth rates between plants accumulate during the plants’ lifetime, so that plants of similar size may have very different ages. We conclude that 14C dating provides a robust method to explore the growth and demography of columnar cacti.

Dissolved inorganic carbon (DIC) in groundwater is used to estimate the residence time based on radiocarbon concentration. DIC is usually extracted by a gas-strip or precipitation (SrCO3 or BaCO3) method. In this study, the gas-strip and precipitation methods of DIC were applied to both artificially prepared NaHCO3 solutions and natural groundwater to estimate the certainty of the two methods for 14C dating. 14C values obtained by the gas-strip method for NaHCO3 solutions with distinct salinity, DIC, and 14C concentrations were close to the theoretically predicted 14C value based on the 14C value of NaHCO3 powder. Conversely, the 14C value obtained by the precipitation method always showed higher values than the predicted values. The difference in 14C value between the gas-strip and precipitation methods was assumed to be caused by the contamination of modern carbon in the NaOH solution used in the precipitation method. The contamination of modern carbon derived from the NaOH solution during precipitation was found to range from less than 1 mg/L to about 1 mg/L. The applicability of the precipitation method for groundwater should be considered carefully according to the DIC, 14C concentration of groundwater, and purpose of the study being conducted.

The radiocarbon content of dissolved organic carbon (DOC) in rivers, lakes, and other non-saline waters can provide valuable information on carbon cycling dynamics in the environment. DOC is typically prepared for 14C analysis by accelerator mass spectrometry (AMS) either by ultraviolet (UV) oxidation or by freeze-drying and sealed tube combustion. We present here a new method for the rapid analysis of 14C of DOC using wet chemical oxidation (WCO) and automated headspace sampling of CO2. The approach is an adaption of recently developed methods using aqueous persulfate oxidant to determine the δ13C of DOC in non-saline water samples and the 14C content of volatile organic acids. One advantage of the current method over UV oxidation is higher throughput: 22 samples and 10 processing standards can be prepared in one day and analyzed in a second day, allowing a full suite of 14C processing standards and blanks to be run in conjunction with samples. A second advantage is that there is less potential for cross-contamination between samples.

This article presents a modified method for extraction of dissolved inorganic carbon (DIC) from seawater for radiocarbon measurement by accelerator mass spectrometry (AMS). Standard tests indicate that the extraction efficiencies of DIC are >96%, and the respective precisions of Δ14C-DIC and δ13C-DIC analyses are 6‰ and 0.1‰ or better. Using the method, we report Δ14C-DIC profiles collected from the shelf and slope in the East China Sea (ECS) of the northwest Pacific Ocean. Both the DIC concentration and Δ14C-DIC in the shelf and slope regions seem primarily affected by the Kuroshio Current. It is estimated that 54–65% of the bottom water in the shelf region could be from the intrusion of Kuroshio intermediate water, which carries a high concentration and low Δ14C values of DIC, and which influenced the DIC and its 14C signature on the shelf. Compared with the Δ14C-DIC profiles at other sites in the northwest Pacific reported previously, it appears that the Δ14C-DIC distributions are mainly controlled by the major oceanic currents in the region, and large variations in Δ14C-DIC occurred mostly in the upper 800 m of the water column. The similarity of Δ14C-DIC at depth suggests that the deep-water circulation patterns have been relatively stable in the northwest Pacific Ocean in the last 20 yr.

Corals of the Hawaiian Archipelago are well situated in the North Pacific Gyre (NPG) to record how bomb-produced radiocarbon has been sequestered and transported by the sea. While this signal can be traced accurately through time in reef-building corals and used to infer oceanographic processes and determine the ages of marine organisms, a comprehensive and validated record has been lacking for the Hawaiian Archipelago. In this study, a coral core from Kure Atoll in the northwestern Hawaiian Islands was used to create a high-resolution bomb 14C record for the years 1939–2002, and was then used with other 14C measurements in fish otoliths and seawater to explore differences and similarities in the bomb 14C signal throughout the Hawaiian Archipelago. The Kure Atoll sample series produced a well-defined bomb 14C curve that, with some exceptions, was similar to other coral 14C records from the Hawaiian Archipelago. Subtle differences in the coral 14C records across the region may be explained by the large-scale ocean circulation patterns and decadal cycles of the NPG. The most rapid increase of 14C, in the 1950s and 1960s, showed similar timing across the Hawaiian Archipelago and provides a robust basis for use of bomb 14C dating to obtain high-precision age determinations of marine organisms. Reference otoliths of juvenile fish demonstrated the use of the post-peak 14C decline period as a viable reference in the age validation of younger and more recently collected fishes, and effectively extended the utility of bomb 14C dating to the latest 30 yr.

In order to map the freshwater reservoir effect (FRE) variability of the Loire River and its tributaries, spatial and temporal carbon isotope (13C and 14C) analyses of the dissolved inorganic carbon (DIC) were conducted. Sites were selected to represent the diversity of geological settings, soil type, and land use. Results show a large spatial variability of 14C FRE ranging between 135 and 2251±30 yr, objectively correlated to DIC contents and alkalinity. Deeper investigations of the relationship between 14C activity of DIC and environmental variables show that the geological substrate is the dominant factor in the 14C reservoir effect, and far more influential than the river flow discharge.

Charcoal is widely used for radiocarbon dating in archaeological and paleoenvironmental studies. Reliable 14C dating requires appropriate chemical treatment to remove postdeposition contamination from the charcoal samples. This study assesses two pretreatments: acid-base-acid (ABA) and acid-base-oxidation with stepped combustion (ABOx-SC). In addition to 14C, the effects of the treatments on the chemical structure and composition of charcoal were studied using Fourier transform infrared spectroscopy (FTIR) and C/H/O elemental analysis. Samples of pine wood charred in the laboratory at 270, 300, 400, 500, and 600°C, and environmental samples of charred pine wood from pyroclastic flow deposits in southern Kyushu, Japan, were tested. The laboratory-charred samples showed that NaOH treatment removed highly hydrophilic organic components derived from endogenous and exogenous organic materials in the samples and that oxidation treatment caused the oxidative degradation of molecules in samples starting from its edges. The ABA-treated environmental charcoal yielded younger 14C dates than the ABOx-treated samples, probably owing to the effects of remaining organic contaminants bound to the edges of the aromatic molecular structures produced by the original pyrolysis. Meanwhile, it was found that ABA-SC treatment can reduce contaminants as effectively as ABOx-SC treatment. This implies that the stepped combustion (SC), not the chemical oxidation, is the key to reduce contaminant residue left after ABA and ABOx treatments. The results in this study indicate that the investigation of the structural and compositional changes of charcoal during its pretreatment is useful for assessment of the reliability of the 14C ages.

Lightweight concrete was widely used and mainly spread during the Roman period. This technology was used in the West Church, Umm el-Jimal, Jordan. The date of construction of the West Church is debated and different dates have been suggested based on its architectural styles and comparisons with other churches. This research aims to radiocarbon date the construction of the dome (church), archaeometrically characterize the mortar, and determine the source of the scoria. Three charcoals and two broken pieces comprising scoria from the mortar of the fallen dome and six large scoria samples from Quais cone were collected. The research used different analytical methods including accelerator mass spectrometry 14C, X-ray diffraction, petrographic microscopy, inductively coupled plasma mass spectrometry, and scanning electron microscopy-energy dispersive X-ray spectroscopy. 14C determinations dated the dome (church) to the Late Roman–Early Byzantine periods, which contradicted the archaeological data. Analytical results showed that the mortar is lime-based and hydraulic. The similarities in the mineralogical composition, macroscopic and microscopic features, and chemical composition (compared statistically) of the scoria samples and the short distance between Umm el-Jimal and the Quais volcanic cone very likely indicate that the Quais volcanic cone is the source of the scoria used in the fallen dome.

This article presents new radiocarbon evidence from the Middle Bronze Age palatial site of Tel Kabri (Israel). The final phase of the palace (Phase III) can be dated to Middle Bronze Age II, with an end date around the transition from Middle Bronze II to III or very early in Middle Bronze III. According to our 14C data, the end of Tel Kabri Phase III (and thus the transition from Middle Bronze II to III) can be dated to ~1700 BC. This date is about 50–100 yr earlier than traditional chronological models for the Middle Bronze Age propose (~1650 BC according to the traditional chronology or ~1600 BC according to the low chronology). 14C data from Tel Kabri thus add additional evidence for a higher Middle Bronze Age chronology for the Levant, consistent with recent 14C evidence from Tell el-Dabca (Egypt), Tel Ifshar (Israel), and Tell el-Burak (Lebanon).

Tell Abu en-Ni‘aj, an agrarian Early Bronze IV village in the northern Jordan Valley, Jordan, provides a series of 24 accelerator mass spectrometry (AMS) seed dates spanning seven stratified phases of occupation. Bayesian analysis of these ages reveals that habitation at Tell Abu en-Ni‘aj began between 2600 and 2500 cal BC and ended just before 2000 cal BC. This sequence provides the longest radiocarbon record of occupation for an Early Bronze IV settlement in the southern Levant and pushes the beginning of the Levantine Early Bronze IV earlier than proposed previously. When integrated with 14C dates from an array of sites in the southern Levant, Egypt, and Lebanon, this evidence aligns with recent 14C-based chronologies calling for earlier ages for Early Bronze I–III, details Early Bronze IV chronology through the course of this period, and corroborates the date of the Early Bronze IV/Middle Bronze Age transition ~2000 cal BC.

The absolute chronology of the Kura-Araxes (KA) culture in the Southern Caucasus still represents a challenge due to the fragmentation and inadequacy of the radiocarbon record, as well as the inconsistencies in material typologies in the region. Recent archaeological fieldwork at the site of Aradetis Orgora in the Shida Kartli region of Georgia revealed four occupation levels dating to the KA II phase according to the local relative chronology. 14C samples were collected from reliable contexts and further selected according to reliability criteria, taking into account both archaeological issues and lab procedures. FTIR was applied in order to determine the preservation of charcoals and to monitor the efficiency of lab treatments on all the samples. Only accurate 14C measurements were selected for Bayesian analysis incorporating stratigraphic information. Two models were run, the second of which simulated intervals corresponding to unexcavated stratigraphy or due to a lack of samples. In this article, the available 14C dates for the KA occupation at Aradetis are presented for the first time and analyzed using Bayesian principles. The results of Bayesian modeling suggest that the occupation of the excavated KA II levels cover the period between 3040–2810 BC (simple model) or 3090–2720 BC (interval model).

In the Valencia region of Spain, the dominant use of natural caves for collective burials during the Late Neolithic and Chalcolithic periods has been documented. Collective burials are central to the hypothesis about social relationships in Copper Age societies from Iberia, and key to interpreting kinship-based societies. Les Llometes (Alcoi, Alicante) is one of the biggest collective burial sites existing in eastern Iberia. This article presents the direct 14C dates on 25 skeletal remains at the site. The results indicate that the site was used as a burial place from the end of the 5th millennium cal BC until the end of the 4th millennium cal BC, and is a first milestone for future studies that will shed light on the transition towards social structure through the use of a cemetery space. Moreover, this research is one of the few investigations of Late Neolithic collective burials in Iberia that comprises an extensive accelerator mass spectrometry (AMS) 14C data set of almost all the individuals reported at a single site. This case also serves to highlight the utility of revisiting materials from historic excavations by 14C dating all the skeletal remains that define the minimum number of individuals, and therefore ensuring a more complete picture of the prehistoric human record.

Excavations from 2009–2010 in Armadale, Isle of Skye, Scotland, encountered a burial site with seven cists, pits containing cremation burials, a kerbed cairn, and a small stone and post circle. Twenty-one radiocarbon measurements were taken from single entities of wood charcoal, carbonized residue on pottery, and cremated human bone. A site chronology has been constructed using a Bayesian approach that considers the stratigraphic contexts and feature formation processes. The site was host to thousands of years of discontinuous human activity beginning with little understood Mesolithic and Neolithic components. Modeling estimates that mortuary activity at the site began in the Early Bronze Age in 2220–1985 cal BC (95% probability) and to have ended in 1880–1660 cal BC (95% probability). The span of activity during this burial component is estimated to be 140–520 yr (95% probability) in the primary Bayesian model and 50–470 yr (95% probability) in an alternative model. These modeling results demonstrate that human burial at Armadale was an infrequent event and further suggest that the memory of the location and social role of Armadale as a burial ground persisted throughout much of the Early Bronze Age.