14C Measurements Research Articles

The 6 MV multi-nuclide AMS system at the University of Tsukuba, Japan: First performance report

A horizontal-type 6 MV Pelletron tandem accelerator was installed at the University of Tsukuba, Japan, in September 2014. The first test of the multi-nuclide accelerator mass spectrometry system was performed in March 2016, after two years of construction. This is the first report of its performance. The particle detection system was designed for high-sensitivity detection of 10Be, 14C, 26Al, 36Cl, 41Ca, and 129I. A five-electrode ΔE-E gas-ionization detector was installed as the end station of the detection system. The system background for 14C measurements, with the 4+ charge state at 5.0 MV, has a 14C/12C ratio of ∼2.4 × 10−16. 10Be, 26Al, 36Cl, 41Ca, and 129I have also been successfully detected. The 41Ca/Ca background is ∼3 × 10−15 as a result of improved isobaric separation techniques.

Uptake and translocation of 14C-Carbamazepine in soil-plant systems

Carbamazepine (CBZ) is an antiepileptic drug that is frequently detected in wastewater treatment plants, soil and plants after irrigation with treated wastewater or application of biosolids. However, little information is available on the fate and uptake of CBZ in edible vegetables. In this study, radioautographic visualization of the 14C distribution revealed that 14C-CBZ can be taken up by all three ready-to-eat vegetables. Furthermore, a mass-balance study was conducted to evaluate the dynamic processes of the uptake and translocation of CBZ by 14C labeling. 14C-CBZ was gradually taken up with the growth of vegetables, with maximum uptake ratios of 2.19 ± 0.15, 2.86 ± 0.24 and 0.25 ± 0.05% of applied 14C in celery, carrot and pak choi, respectively. The bioconcentration factors (BCFs) based on 14C measurements ranged from 7.6 to 26.1 for celery, 3.6–12.9 for carrot, and 4.4–44 for pak choi. 14C-CBZ was easily translocated from the roots to the leaves and/or stems. The amendment of biosolids had a significant inhibitory effect on the uptake and translocation of 14C-CBZ from soil.

Estimation of effective porosity in large-scale groundwater models by combining particle tracking, auto-calibration and <sup>14</sup>C dating

Abstract. Effective porosity plays an important role in contaminant management. However, the effective porosity is often assumed to be constant in space and hence heterogeneity is either neglected or simplified in transport model calibration. Based on a calibrated highly parametrized flow model, a three-dimensional advective transport model (MODPATH) of a 1300 km2 coastal area of southern Denmark and northern Germany is presented. A detailed voxel model represents the highly heterogeneous geological composition of the area. Inverse modelling of advective transport is used to estimate the effective porosity of 7 spatially distributed units based on apparent groundwater ages inferred from 11 14C measurements in Pleistocene and Miocene aquifers, corrected for the effects of diffusion and geochemical reactions. By calibration of the seven effective porosity units, the match between the observed and simulated ages is improved significantly, resulting in a reduction of ME of 99 % and RMS of 82 % compared to a uniform porosity approach. Groundwater ages range from a few hundred years in the Pleistocene to several thousand years in Miocene aquifers. The advective age distributions derived from particle tracking at each sampling well show unimodal (for younger ages) to multimodal (for older ages) shapes and thus reflect the heterogeneity that particles encounter along their travel path. The estimated effective porosity field, with values ranging between 4.3 % in clay and 45 % in sand formations, is used in a direct simulation of distributed mean groundwater ages. Although the absolute ages are affected by various uncertainties, a unique insight into the complex three-dimensional age distribution pattern and potential advance of young contaminated groundwater in the investigated regional aquifer system is provided, highlighting the importance of estimating effective porosity in groundwater transport modelling and the implications for groundwater quantity and quality assessment and management.

Monitoring 14C contamination in Chinese research vessels with swipe tests

Since 14C-tracer is widely used in determining oceanic primary production, most research vessels have a history of using 14C labeled sodium bicarbonate solutions for culture experiments. A contamination monitor test (swipe test) prior to each cruise can help to detect and prevent possible 14C contamination before sampling for 14C studies at natural abundance. Here we report 14C measurements of more than 100 swipe samples collected onboard workplaces of seven Chinese research vessels over a four-year period (2012–2016). Five out of seven ships showed no obvious 14C contamination with F14C values lower than 0.2. Two spots of R/V Dongfanghong 2 showed elevated 14C contamination (F14C were as high as 0.831 and 0.573) during 2012–2014. However, the laboratory surface was cleaned by renovation before the next monitoring operation in May to June 2016. R/V Kexue Yihao was found to have elevated 14C on swipe samples, with an F14C up to 0.331 from November to December 2012. During the same cruise, seawater samples for a natural-level DI14C study were also found to be contaminated. Our results highlight the need for stringent screening and protection procedures on research vessels regarding 14C contamination if the cruise involves sampling for natural-level 14C studies. We recommend the undertaking of swipe tests before and after each cruise.

Increasing accuracy for the radiocarbon dating of sites occupied by the first Americans

Genetic analysis of Paleoamerican human remains suggests that people first entered the Americas sometime between ∼14,000 and ∼16,000 years ago. Evaluation of these data requires unequivocal archaeological evidence in a solid geological context that is well dated. Accurately determining the age of late Pleistocene sites is thus crucial in explaining when and how humans colonized the Americas. There are, however, significant challenges to dating reliability, especially when vertebrate fossils (i.e. bones, teeth and ivory) are often the only datable materials preserved at sites.We re-dated vertebrate fossils associated with the North American butchering sites of Wally's Beach (Canada), La Prele [also known as Fetterman (Wyoming)], Lindsay (Montana), and Dent (Colorado). Our work illustrates the crucial importance of sample chemical preparation in completely removing contaminants derived from sediments or museum curation. Specifically, our work demonstrates that chromatographic methods, e.g. preparative High Performance Liquid Chromatography and column chromatography using XAD resins, are currently the only efficient methods for removing environmental and museum-derived contaminants. These advanced techniques yield demonstrably more accurate AMS 14C measurements that refine the ages of these four sites and thereby contribute to advancing our understanding of human dispersals across North America during the late Pleistocene.

Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.

Solar superstorm of AD 774 recorded subannually by Arctic tree rings

Recently, a rapid increase in radiocarbon (14C) was observed in Japanese tree rings at AD 774/775. Various explanations for the anomaly have been offered, such as a supernova, a γ-ray burst, a cometary impact, or an exceptionally large Solar Particle Event (SPE). However, evidence of the origin and exact timing of the event remains incomplete. In particular, a key issue of latitudinal dependence of the 14C intensity has not been addressed yet. Here, we show that the event was most likely caused by the Sun and occurred during the spring of AD 774. Particularly, the event intensities from various locations show a strong correlation with the latitude, demonstrating a particle-induced 14C poleward increase, in accord with the solar origin of the event. Furthermore, both annual 14C data and carbon cycle modelling, and separate earlywood and latewood 14C measurements, confine the photosynthetic carbon fixation to around the midsummer.

The Corded Ware culture in the Eastern Baltic: New evidence on chronology, diet, beaker, bone and flint tool function

Around 2900–2300 cal BCE, mobile stockbreeders introduced the Neolithic Corded Ware culture (CWC) into the Eastern Baltic. Here, a Central or Northern European Neolithic economy and ideology took hold despite differences in burial practices. Although around 90 CWC graves are known in the region their contents have not been intensively studied. Here, we present new AMS radiocarbon (14C) measurements and carbon and nitrogen stable isotope data obtained on human bone collagen, molecular and isotopic data obtained from ceramic beakers, and user-wear data of flint and bone tools from several CWC graves, Benaičiai, Biržai, Krasnasieĺski, Dakudava 5, and Drazdy 12, in Lithuania and Western Belarus. The bone collagen δ13C and δ15N stable isotope data are rather homogenous and demonstrate that the majority of consumed protein was derived from terrestrial resources. Organic residue analysis of two CWC beakers yielded lipids consistent with ruminant carcass and dairy fats, whilst use-wear analyses indicates that bone pins, flint blades and axes were used as grinders, functional tools or had been carefully renewed before deposition respectively.

Heating mollusc shells - A radiocarbon and microstructure perspective from archaeological shells recovered from Kalba, Sharjah Emirate, UAE

This publication aims to shed light on the influence that prior heating (burning) of mollusc shells during human activity may have on the results of radiocarbon dating. We compare the geochemical and mineralogical composition of heated and unheated shells of Anadara uropigimelana and Terebralia palustris recovered from Neolithic and Bronze Age archaeological contexts at Kalba, Sharjah Emirate, in the United Arab Emirates (UAE). Our research examined whether the heating of shells impacts on the determination of reservoir effects, or whether in spite of heating, this material remains a viable material for precise 14C measurements. Our results show that both heated and non-heated shells of A. uropigimelana and T. palustris provide consistent results, although the mineral composition of the shells changes from aragonite to calcite. Our results are important, since some of our selection of shells did not initially appear to have been heated. A heating process will then usually be detected as a greyish, marble like structure when cutting the shells. As a result of this work, we have also developed insights into prehistoric cooking practices of shells collected in Arabia. Our results provide archaeologists and associated researchers with confidence when assessing the results of radiocarbon dating during their studies of shells that might have been heated.

Deglaciation of coastal south‐western Spitsbergen dated with in situ cosmogenic 10Be and 14C measurements

ABSTRACTThe Svalbard–Barents ice sheet was predominantly a marine‐based ice sheet and reconstructing the timing and rate of its decay during the last deglaciation informs predictions of future decay of marine‐based ice sheets (e.g. West Antarctica). Records of ice‐sheet change are routinely built with cosmogenic surface exposure ages, but in some regions, this method is complicated by the presence of isotopic inheritance yielding artificially old and erroneous exposure ages for the most recent deglaciation. We present 46 10Be ages from south‐western Spitsbergen that, when paired with in situ 14C measurements (n = 5), constrain the timing of coastal deglaciation following the last glacial maximum. 10Be and in situ 14C measurements from bedrock along a ∼400‐m elevation transect reveal inheritance‐skewed 10Be ages, whereas in situ 14C measurements constrain 400 m of ice‐sheet thinning and coastal deglaciation at 17.4 ± 1.5 ka. Our in situ 14C‐dated transect, combined with three additional 10Be‐dated coastal sites, show that the south‐western margin of the Svalbard–Barents ice sheet retreated out of the Norwegian Sea between ∼18 and 16 ka. In situ 14C measurements provide key chronological information on ice‐sheet response to the last termination in cases where measurements of long‐lived nuclides are compromised by isotopic inheritance.

Late Glacial Atmospheric Radiocarbon Variations Recorded in Scots Pine (Pinus sylvestris L.) Wood from KwiatkÓw, Central Poland

ABSTRACTOur project aimed to construct a Scots Pine (Pinus sylvestris L.) chronology for part of the Late Glacial and reconstruct changes in the 14C concentrations during this period. Kwiatków (Kolska Basin, central Poland) proved to be very prospective site, in which wood from the end of Allerød was recognized. A level of organic deposits with so-called fossil forest was encountered within the late-Vistulian terrace of the low valley of the Warta river. Dendrochronological analysis of over 267 samples complying to the requirements of the method allowed, at the present stage of the research, to construct a chronology spanning 265 yr. Fifty-two samples (5 consecutive rings each) were subjected to α-cellulose extraction and 14C measurements. Ninety-six results and the wiggle-matching technique anchor the chronology to the period 13,821–13,561 cal BP (Acomb=141.6%) according to the D_Sequence procedure and the IntCal13 calibration curve or to 13,800–13,540 cal BP according to the wiggle-matching technique using the χ2 test and raw data, i.e. the Heidelberg tree-ring sequence.

A New Graphitization System for Radiocarbon Dating with AMS in the Dendrochronological Laboratory at AGH-UST Kraków

AbstractA new vacuum system for the preparation of graphite samples for radiocarbon (14C) measurement using an accelerator mass spectrometer (AMS) was constructed at the Dendrochronological Laboratory in AGH-UST Kraków. The central part of the system is a manual vacuum line for the production of graphite from carbon dioxide for subsequent AMS measurements. The graphitization system can handle up to five samples simultaneously, and the process lasts for approximately 1 hour. The graphitization line was built to support the preparation of wood samples for a project dedicated to dating a subfossil tree from the Younger Dryas period. For this purpose, the chemical preparation procedure for wood samples was optimized to obtain more reliable results. This includes the extraction of α-cellulose to increase the precision of the age determination. The performance of the system was tested with NIST OxII, IAEA standards (IAEA C3, C5, C6, and C8), and background samples. The results of the 13 samples of subfossil wood were tested and are presented. The methodology gives good reproducibility of results obtained for the samples prepared using this system.

A Novel Cellulose-Preparation Method

AbstractThe radiocarbon (14C) dating of contaminated old wood has been seen as a challenge requiring many lengthy procedures, often using strong alkali extractions and carbon-containing solvents. Introduced here is a novel protocol called 2chlorOx, a twice-repeated sequence of alkaline hypochlorite and acidic chlorite oxidations, which is shown to work well for 14C and 13C measurements on both <5000 BP and >50,000 BP wood samples, producing results superior to those from conventional acidic chlorite or acidic dichromate oxidations. The 2chlorOx method employs only inorganic reagents, many samples can be completed in less than one day under normal laboratory conditions, and cellulose prepared in this way is usually paper-white in color.

Different pretreatment methods for 14C dating of Younger Dryas and Allerød pine wood (Pinus sylvestris L.)

Abstract An analysis was performed on samples from a series of well-preserved tree trunks and in situ stumps of Allerod/Younger Dryas age found in Koźmin and Kwiatkow, Kolska Basin, Central Poland. Five different types of wood preparation methods were investigated in three Polish radiocarbon laboratories (Gliwice, Poznan and Krakow) in order to find the most stable, repeatable and reliable procedure. Their effect was tested on the stable carbon isotope ratio (δ13C) and 14C age. Additionally, FTIR spectroscopy was used as a simple technique for obtaining rapid information on the structure of wood constituents and chemical changes taking place in wood due to various chemical treatments. The results of AMS measurements did not show statistically significant differences in radiocarbon ages of samples prepared according to the tested methods. On the other hand, δ13C measurements showed that the smallest scattering results gave α-cellulose obtained by the method BABA + Bleaching (with NaClO2 and HCl) + strong base. Moreover, the mean δ13C values for holo-cellulose samples are higher than those for α-cellulose samples. Studies evidenced that the methods of preparation leading to holo- or α-cellulose gave the same FTIR spectra, while the standard method of the chemical pretreatment of samples for 14C measurements (ABA) preceded by mercerization is insufficient for removing compounds containing aromatic rings.

AMS and upcoming geochronology facility at Inter University Accelerator Centre (IUAC), New Delhi, India

Inter University Accelerator Centre, an ion accelerator centre, is in the process of setting up a national facility for geochronology. It will be a unique and first such facility in the country to provide the latest and exclusive instrumentation for the geochronological related studies to earth scientists of the country. Within this program various instruments are being installed and a 500 kV Pelletron Accelerator for Accelerator Mass Spectrometry (AMS) has already been set up to measure 14C, 10Be and 26Al radionuclides. A sample preparation laboratory having three automated graphitization equipment and one carbonate handling system has also been set up. Other analytical facilities required for geochronological studies have also been established. This paper provides a brief description of new AMS system, graphitization laboratory for sample preparation, routine 14C measurements, 10Be and 26Al measurements and other instruments installed and planned within the geochronology facility at IUAC.

Age ranges of the Tibetan ice cores with emphasis on the Chongce ice cores, western Kunlun Mountains

Abstract. An accurate chronology is the essential first step for a sound understanding of ice core records. However, dating ice cores drilled from the high-elevation glaciers is challenging and often problematic, leading to great uncertainties. The Guliya ice core, drilled to the bedrock (308.6 m in length) along the western Kunlun Mountains on the north-western Tibetan Plateau (TP) and widely used as a benchmark for palaeoclimate research, is believed to reach >500 ka (thousand years) at its bottom. Meanwhile other Tibetan ice cores (i.e. Dasuopu and East Rongbuk in the Himalayas, Puruogangri in the central TP and Dunde in the north-eastern TP) are mostly of Holocene origin. In this study, we drilled four ice cores into bedrock (216.6, 208.6, 135.8 and 133.8 m in length, respectively) from the Chongce ice cap ∼30 km to the Guliya ice core drilling site. We took measurements of 14C, 210Pb, tritium and β activity for the ice cores, and used these values in a two-parameter flow model to establish the ice core depth–age relationship. We suggested that the Chongce ice cores might be of Holocene origin, consistent with the other Tibetan ice cores except Guliya. The remarkable discrepancy between the Guliya and all the other Tibetan ice core chronology implies that more effort is necessary to explore multiple dating techniques to confirm the age ranges of the TP glaciers, including those from Chongce and Guliya.

More Rapid 14C Excursions in the Tree-Ring Record: A Record of Different Kind of Solar Activity at About 800 BC?

ABSTRACTTwo radiocarbon (14C) excursions are caused by an increase of incoming cosmic rays on a short time scale found in the Late Holocene (AD 774–775 and AD 993–994), which are widely explained as due to extreme solar proton events (SPE). In addition, a larger event has also been reported at 5480 BC (Miyake et al. 2017a), which is attributed to a special mode of a grand solar minimum, as well as another at 660 BC (Park et al. 2017). Clearly, other events must exist, but could have different causes. In order to detect more such possible events, we have identified periods when the 14C increase rate is rapid and large in the international radiocarbon calibration (IntCal) data (Reimer et al. 2013). In this paper, we follow on from previous studies and identify a possible excursion starting at 814–813 BC, which may be connected to the beginning of a grand solar minimum associated with the beginning of the Hallstatt period, which is characterized by relatively constant 14C ages in the period from 800–400 BC. We compare results of annual 14C measurements from tree rings of sequoia (California) and cedar (Japan), and compare these results to other identified excursions, as well as geomagnetic data. We note that the structure of the increase from 813 BC is similar to the increase at 5480 BC, suggesting a related origin. We also assess whether there are different kinds of events that may be observed and may be consistent with different types of solar phenomena, or other explanations.

Vitamin B12 added as a fortificant to flour retains high bioavailability when baked in bread

Vitamin B12 deficiency and depletion are common world-wide, particularly in populations that consume low amounts of animal source foods. WHO and the Food Fortification Initiative recommend that wheat flour be fortified with vitamin B12 in regions where intake of B12 is low. The purpose of this pilot study in five participants was to determine if fortification of flour with B12 produced a bread product with intact B12 still present and to determine if healthy elderly absorb sufficient B12 from bread fortified in this manner. High-purity crystalline 14C-B12 was dissolved in water and added to flour (2 µg B12/100 g flour) in a bread maker and made into rolls (average 1.17 kBq (31.5 nCi) 14C-B12 in a total of 0.8 µg B12 per roll). Excess 14C first appeared in plasma 4 h after ingestion of the 14C fortified bread and plasma levels returned almost to background by 72 h. Measurement of 14C in plasma verified that the dose was absorbed into the systemic circulation. The cumulative % dose recovered in urine was 4.8–37.0% (mean = 20.1%). Most of the 14C label in the stool appeared by day 4, and the cumulative % dose recovered in stool was 24.5–43.0% (mean = 31.8%). Bioavailability among the 5 participants, calculated by subtracting the sum of urinary and fecal 14C excretion from the administered dose, was 28.4–63.7% (mean = 48.0%). This study showed that when B12 is added as a fortificant to flour it survives the fermentation and baking processes, and retains ∼50% bioavailability when fed in small doses to healthy subjects. The Recommended Dietary Allowance of B12 for adults is 2.4 µg/d. This recommendation assumes that usual bioavailability of low doses of the vitamin in the crystalline form is 60%, while for the same amount in foods such as meat and fish it is 50%. Our pilot study shows that B12 added to bread as a fortificant in flour was absorbed as well as it is from endogenous food sources such as meat and fish.

Adoption and Evaluation of a sample Pretreatment Protocol for Radiocarbon Dating of Cremated Bones at HEKAL

ABSTRACTA comparative study was undertaken to adopt and evaluate a radiocarbon (14C) preparation procedure for accelerator mass spectrometry (AMS) measurements of cremated bones at our laboratory, including different types of archaeological samples (cremated bone, bone, charcoal, charred grain). All 14C analyses were performed using the EnvironMICADAS AMS instrument at the Hertelendi Laboratory of Environmental Studies (HEKAL) and the ancillary analyses were also performed at the Institute for Nuclear Research (ATOMKI). After the physical and chemical cleaning of cremated bones, CO2 was extracted by acid hydrolysis followed by sealed-tube graphitization and 14C measurement. The supplementary δ13C measurements were also performed on CO2 gas while FTIR was measured on the powder fraction. Based on the FTIR and 14C analyses, our chemical pretreatment protocol was successful in removing contamination from the samples. Good reproducibility was obtained for the 0.2–0.3 mm fraction of blind-tested cremated samples and a maximum age difference of only 150 yr was found for the remaining case studies. This confirms the reliability of our procedure for 14C dating of cremated bones. However, in one case study, the age difference of 300 yr between two cremated fragments originating from the same urn shows that other processes affecting the cremated samples in the post-burial environment can substantially influence the 14C age, so caution must be exercised.

Isotopic terrestrial imprints of solar superflares

The extreme cosmic event that occurred in AD 775 was detected using 14C measurements in tree rings and 10Be, 36Cl abundances in polar ice cores. Perhaps it is the most powerful solar proton event in the past several thousands of years. Simulation of isotope production with the spectra of solar flares observed in the modern era (23.02.56, 04.08.72 etc.) showed that to produce the measured amount of radionuclides, the particle fluence in the AD 775 event has to be by tens - hundreds times greater than the modern powerful solar events. The results of calculations of long-lived cosmogenic radionuclides (14C, 10Be, 36Cl) production in the Earth's atmosphere are presented.