Radiocarbon Content Research Articles

THE RADIOCARBON SAMPLE ARCHIVE OF TRONDHEIM

ABSTRACTAtmospheric CO2 samples have been collected by the Trondheim Radiocarbon Laboratory since the 1960s. The remaining material from the measurements has been precipitated as CaCO3 and stored in glass containers. We investigated some of the stored samples to assess whether the material could still be used for remeasurements of atmospheric radiocarbon (14C) content, or if it has been contaminated during the years of storage. We attempted different methods to clean the carbonate and release the CO2 for new measurements. The results indicate that the older samples before 1970 show a significant change in 14C content compared to the original measurements, and that our cleaning methods have only little effect. Later samples from the 1970s, which were archived in glass containers with a different lid, show a lower contamination that, however, still leads to an added uncertainty of several pMC and makes these samples unreliable.

CENTENNIAL TO MILLENNIAL-SCALE FLUCTUATIONS OF THE LAKE SUIGETSU ATMOSPHERIC 14C RECORD REPRESENT AUTHENTIC 14C FEATURES OVER LAST GLACIAL-TO-DEGLACIAL TIMES

ABSTRACT Short-term fluctuations in atmospheric radiocarbon (14C) concentration mark the tree-ring record for the last ∼15 kyr. Terrestrial macrofossils from sediment cores of Lake Suigetsu, Japan, extend this record of fluctuations back to >35 cal ka BP. Their significance, however, is under debate since the signal-to-noise ratio of the Suigetsu record is low and progressively decreases with increasing age. Coherent semi-millennial-scale structures of the Suigetsu 14C record have nevertheless been identified by three different techniques, namely visual inspection, analyses of the first derivative of 14C vs. calendar age, and Bayesian spline inflections of 14C concentration vs. calendar age, and hence appear objectively real. These 14C fluctuations correlate closely with those of the tree-ring-based 14C master record ∼10–14 cal ka. Thus, Suigetsu fine structures attain global significance and may properly reflect atmospheric 14C variability back to ∼35 cal ka. Carbonate-based 14C records from speleothems and ocean sediments are far smoother and form, together with Suigetsu and other data, the backbone of the IntCal20 record >14 cal ka that largely lacks the Suigetsu fine structure. 14C decay reduces 14C-signal amplitudes over time, so Holocene-style 14C signals of solar modulation disappear in the noise beyond ∼10 cal ka. The remaining older 14C fine structures had larger forcings, most likely linked to climate and carbon cycle, especially ocean-atmosphere CO2 exchange, and thus contain valuable information about these factors. They may also provide global stratigraphic tie points to correlate 14C records of oceanic plankton sediments and climate signals independent of problems with local 14C reservoir effects.

Radiocarbon evidence for the stability of polar ocean overturning during the Holocene

Proxy-based studies have linked the pre-industrial atmospheric p_{{rm{CO}}_{2}} rise of ∼20 ppmv in the mid- to late Holocene to an inferred increase in the Southern Ocean overturning and associated biogeochemical changes. However, the history of polar ocean overturning and ventilation through the Holocene remains poorly constrained, leaving important gaps in the assessment of the feedbacks between changes in ocean circulation and the carbon cycle in a warm climate state. The deep-ocean radiocarbon content, which provides a measure of ventilation, responds to circulation changes on centennial to millennial time scales. Here we present absolutely dated deep-sea coral radiocarbon records from the Drake Passage, between South America and Antarctica, and Reykjanes Ridge, south of Iceland, over the Holocene. Our data suggest that ventilation in the Antarctic circumpolar waters and North Atlantic Deep Water is surprisingly invariant within proxy uncertainties at our sampling resolution. Our findings indicate that long-term, large-scale polar ocean overturning has not been disturbed to a level resolvable by radiocarbon and is probably not responsible for the millennial atmosphere p_{{rm{CO}}_{2}} evolution through the Holocene. Instead, continuous nutrient and carbon redistribution within the water column following deglaciation, as well as changes in land organic carbon stock, might have regulated atmospheric CO2 budget during this period.

The effects of diet and beauty products on the uptake and storage of 14C in hair and nails: ramifications for the application of bomb pulse dating to forensic anthropological casework

Radiocarbon dating is a useful tool in the examination of unknown human remains. Recent studies have shown that the analysis of hair and nail samples can provide a highly accurate estimation of the year of death (YOD). However, little research has examined factors that may influence the uptake and storage of 14C in these tissues, such as diet, or the use of beauty products. This study measured the level of 14C in human hair and nail samples collected from living individuals to determine whether diet, and the use of hair dye or nail polish, has a significant impact on the estimation of YOD. The results of this study showed that diet did not appear to impact the radiocarbon content in human hair and nail, and thus should not be considered a limitation when analysing samples obtained from unidentified human remains. The use of nail polish, and in the majority of cases, hair dye, did not significantly impact the 14C concentration in nails and hair. While the results of this study are preliminary, they suggest that in most cases, both hair and nail can be successfully analysed using radiocarbon dating to estimate an individual’s YOD. However, best practice should involve the analysis of multiple tissue types, to minimise any error that may be introduced as a result of the decedent’s use of beauty products.

Newly designed glass apparatus to conduct stepwise dissolution experiment for radiocarbon using fish otoliths

Isotopes and trace elements extracted from fish otoliths have been widely used to understand different fish habitats. Otoliths can track the life-long histories of fish habitats and can supplement the information that is often difficult to reconstruct using tagging methods. Due to the advancement of radiocarbon measurement techniques, small quantities can be prepared for this purpose, and radiocarbon can be used to understand the migration history by referring to the variations of radiocarbon in the surface ocean. One major drawback of otolith isotope methods is the length of time it takes to collect samples by milling before each sample can be measured by accelerator mass spectrometry. Sequential acid digestion systems can potentially offer a solution whereby each dissolution step can provide information of otolith growth. Here we designed a glass apparatus that can be used for this purpose. We tested the otoliths from the western Pacific roughy (Hoplostethus japonicus) caught in Suruga Bay off the coast of Japan to see if their otoliths can provide reliable information in reconstructing their life history. The results show radiocarbon concentrations in the otoliths gradually decreased, indicating the habitat depth of analyzed individuals gradually shifted from deep to shallow water demonstrating the promise of this method to understand fish habitats. This is consistent with expected behavior considering the oceanography of the region. Thus, stepwise dissolution using a newly designed glass apparatus, proposed here, can aid marine fish ecological studies using otoliths.

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.

Isotopic and microbial evidence for biodegradation of diluted bitumen in the unsaturated zone

The oil sands region in Western Canada is one of the world's largest proven oil reserves. To facilitate pipeline transport, highly viscous oil sands bitumen is blended with lighter hydrocarbon fractions to produce diluted bitumen (dilbit). Anticipated increases in dilbit production and transport raise the risk of inland spills. To understand the behaviour of dilbit in the unsaturated or vadose zone following a surface spill, we ran parallel dilbit and conventional heavy crude exposures, along with an untreated control, using large soil-filled columns over 104 days. Phospholipid fatty acids (PLFAs), biomarkers for the active microbial population, were extracted from column soil cores. Stable carbon isotope contents (δ13C) of individual PLFAs and radiocarbon contents (Δ14C) of bulk PLFAs were characterized over the course of the experiment. The Δ14CPLFA values in soils impacted by dilbit (−221.1 to −54.7‰) and conventional heavy crude (−259.4 to −97.9‰) indicated similar levels of microbial uptake of fossil carbon. In contrast, Δ14CPLFA values in the control column (−46.1 to +53.7‰) reflected assimilation of more recently fixed organic carbon. Sequencing of 16S ribosomal RNA genes extracted from soil cores revealed a significant increase in the relative abundance of Polaromonas, a known hydrocarbon-degrader, following exposure to both types of oil. This study demonstrates that in the first several months following a surface spill, dilbit has a similar potential for biodegradation by a native shallow subsurface microbial community as conventional heavy crude oil.

Determination of Radiocarbon Content in Bio-Oil Samples by Mini Carbon Dating System in the Gliwice Radiocarbon and Mass Spectrometry Laboratory

Abstract The applications of isotopes are used by many European countries to investigate environmental changes. A compact modern accelerator mass spectrometry (AMS) system known as Mini Carbon Dating System (MICADAS) is used in Gliwice Radiocarbon and Mass Spectrometry Laboratory for determining the 14C content in different environmental samples including liquid fuels. For radiocarbon measurement using MICADAS, the liquid samples are accurately prepared using the tin capsules for liquids for combustion in elemental analyser (EA) and graphitisation in the AGE system. In this study, the determination of 14C content in three different bio-oil samples and one reference sample of 100% biomass was conducted. Bio-oil samples were prepared using tin capsules for liquids sealed in the second capsules for solids to avoid sample evaporation while the reference sample was prepared using the tin capsule for solids for combustion in EA and graphitisation in the AGE system. Based on the 14C measurement results, one of the bio-oils was not produced from the analysed reference biomass. Two others were determined as a mixture of bio- and fossil components, and based on 14C the bio-carbon content was calculated. For all samples, the 14C measurement showed reproducible and reliable results.

First dating of a rock painting in Ẓufār (Sultanate of Oman): Low energy plasma oxidation radiocarbon sampling

We successfully measured four radiocarbon dates on two specimens of a black geometric rock painting with a fragment in jeopardy of naturally spalling off in the wall of a rock shelter in the Ẓufār region, in the south of the Sultanate of Oman. Extraction of carbon dioxide (CO2) for radiocarbon dating of the binder in the black pigment of the rock painting specimen was conducted in the plasma oxidation laboratory at the Office of Archeological Studies in Santa Fe, NM. The radiocarbon content was measured on the Swiss ETH-Zürich accelerator mass spectrometer MICADAS. The dates obtained agreed with one another within the statistical uncertainty and the average date of the four samples was 1500 ± 35 radiocarbon years BP. The calendric equivalents of the average date results in calendric calibration date ranges that span the mid-fifth through mid-seventh centuries (440–453 CE, 478–496 CE, and 534–646 CE). This research demonstrates that it is possible to date the black paintings of the Jebel al-Qara’ area of Oman; this is the first pictogram that was dated using radiocarbon dating in the region.

CHARACTERISTICS OF PINE NEEDLES EXPOSED TO MULTI-SOURCE POLLUTION IN SILESIA: RADIOCARBON CONCENTRATION IN PINE NEEDLES AND ELEMENTAL ANALYSIS OF THE NEEDLES’ SURFACE DEPOSITS

ABSTRACTWe present here the analysis of the radiocarbon concentration and the components deposited on 2-year-old Pinus sylvestris L. needles collected in 2021, which were exposed to air contaminants for approximately two years. The needles were collected from seven sampling sites located near roads, households, and industrial factories in Silesia, the most industrialized part of Poland. The radiocarbon concentration was investigated using liquid scintillation spectrometry. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to quantitatively analyze the elements deposited on the surface of pine needles. The depletion of the radiocarbon concentration in pine needles relative to clean air was observed at most of the investigated sites. Although it has been observed that in the research area, the fossil fuel CO2 emission ranging from 0.4 to 3%, we cannot exclude that Suess effect may be underestimated due to biomass burning and mixing of the 14CO2 origin from different sources. A significant amount of silicon, nitrogen, and sulfur was commonly found in samples, Metal elements of Ca, Fe, Al, Mg, and K were also present in most samples. Heavier elements of Fe and Ti were present in higher concentrations only in needles obtained from sites nearer to the heat and power plant in Łaziska Górne.

Reductions in California's Urban Fossil Fuel CO2 Emissions During the COVID‐19 Pandemic

AbstractFossil fuel carbon dioxide (CO2) emissions (ffCO2) constitute the majority of greenhouse gas emissions and are the main determinant of global climate change. The COVID‐19 pandemic caused wide‐scale disruption to human activity and provided an opportunity to evaluate our capability to detect ffCO2 emission reductions. Quantifying changes in ffCO2 levels is especially challenging in cities, where climate mitigation policies are being implemented but local emissions lead to spatially and temporally complex atmospheric mixing ratios. Here, we assess ffCO2 emission patterns associated with pandemic‐induced changes to human activity using direct observations of on‐road CO2 mole fractions in the Los Angeles (LA) urban area and analyses of the radiocarbon (14C) content of annual grasses collected by community scientists throughout California, USA. With COVID‐19 mobility restrictions in place in 2020, we observed a significant reduction in ffCO2 levels across California, especially in urban centers. In LA, on‐road CO2 enhancements were 60 ± 16% lower than the corresponding period of 2019 and rebounded to pre‐pandemic levels by 2021. Plant 14C analysis indicated ffCO2 reductions of 5 ± 10 ppm in 2020 relative to pre‐pandemic observations in LA. However, ffCO2 emission trajectories varied substantially by region and sector as COVID‐related restrictions were relaxed. Further development of these techniques could aid efforts to monitor decarbonization in cities, especially in developing countries without established CO2 monitoring infrastructure.

STUDY OF BIO-BASED CARBON FRACTIONS IN TIRES AND THEIR PYROLYSIS PRODUCTS

ABSTRACTWasted tires are the great source of fuel and valuable components but could be a cause of environmental and land pollution. This study shows the detailed method for the determination of radiocarbon isotope (14C) concentration in tires and their pyrolysis products. Samples are taken from truck and passenger car tires in the form of shredded rubber, pyrolysis oil and recovered carbon black. Liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) techniques were used for the investigation at Gliwice Radiocarbon and Mass Spectrometry Laboratory, and National Laboratory for Age Determination, Trondheim, Norway. The results are in good agreement. Radiocarbon concentration of the rubber varies significantly because of its complex structure and composition within the tires. The 14C concentration values were found to be higher in pyrolytic oil compared to rubber, and greater in truck tires rather than car tires.

Sediment organic matter compositional changes in a tropical rift lake as a function of water depth and distance from shore

Little is known of modern carbon cycling in East African rift lakes. These large tropical systems with anoxic bottom waters can act as test cases for carbon cycling under future climate change scenarios as well as key sediment repositories for paleolimnology studies and fossil fuel generation. This study is the first to combine stable and radiocarbon isotopic information on bulk sediment and biomarkers (n-alcohols) in an African rift lake by investigating surface sediments collected on a nearshore to offshore transect in northern Lake Malawi. This study is also the first to report radiocarbon content in water column particulate organic, dissolved organic and inorganic carbon from an African rift lake. General surface-sediment trends with increasing water depth were an increase in %TOC, and decreases in grain size, δ13C and C/N. Carbon radioisotope analyses showed that bulk sedimentary organic matter was modern across the transect. Biomarker data indicated a primarily aquatic origin for sedimentary organic matter at offshore sites; terrestrial material dominated the n-alcohol signature closest to the shore. Protokerogen stable isotope signatures were similar, and radiocarbon was somewhat depleted relative to bulk sediment organic matter. As compared to bulk organic matter, lipids were 13C-depleted throughout the sampling transect and 14C-depleted at the most nearshore location. This indicates an aged lipid carbon source and likely significant diagenetic alteration of modern sources prior to deposition in nearshore sediments, perhaps a combination of soil erosion, in-river processing, sediment resuspension and mobilization, and preferential degradation of younger organic matter in the oxic nearshore region.

Modelling cosmic radiation events in the tree-ring radiocarbon record

Annually resolved measurements of the radiocarbon content in tree-rings have revealed rare sharp rises in carbon-14 production. These ‘Miyake events’ are likely produced by rare increases in cosmic radiation from the Sun or other energetic astrophysical sources. The radiocarbon produced is not only circulated through the Earth’s atmosphere and oceans, but also absorbed by the biosphere and locked in the annual growth rings of trees. To interpret high-resolution tree-ring radiocarbon measurements therefore necessitates modelling the entire global carbon cycle. Here, we introduce ‘ticktack’ (https://github.com/SharmaLlama/ticktack/), the first open-source Python package that connects box models of the carbon cycle with modern Bayesian inference tools. We use this to analyse all public annual 14Ctree data, and infer posterior parameters for all six known Miyake events. They do not show a consistent relationship to the solar cycle, and several display extended durations that challenge either astrophysical or geophysical models.

Factors controlling SOC stability in colluvial soils under contrasting climate and soil weathering conditions

AbstractAlthough agricultural colluvial soils are important storage for soil organic carbon (SOC), the mechanisms underlying colluvial (cumulative soils) SOC stability have received little attention so far. In this study, we aim to understand to what extent the main controls on colluvial SOC stability differ from those observed in non‐colluvial soils. Paired soil profiles (non‐colluvial versus colluvial) were collected from five sites which differ in climate, soil geochemical background and cultivation history. Topsoil (0–10 cm) and subsoil (30–50 cm) were analysed for SOC fractions, mineral composition, potential soil respiration and radiocarbon content. Our analysis showed that for non‐colluvial soils, climate, cultivation history and weathering degree have significant effects on potential soil respiration. In contrast, for colluvial soils, the most influential factor for potential soil respiration was the rate of accretion and this was independent of climatic and geochemical context. Furthermore, accretion rates indirectly affected potential soil respiration by interacting with the degree of weathering of deposited soil. This changed the mineral matrix of colluvial soil settings and thereby may enhance soil mineral‐related SOC stabilisation mechanisms. Together, these results suggest that the dominant controls on SOC stability in colluvial soils differ from those in non‐colluvial soils, and the soil accretion rate is the most important control on colluvial SOC stability in agricultural systems.Highlights The dominant controls on SOC stability in colluvial and non‐colluvial soils were compared. Climate and mineral weathering predominantly control SOC stability in non‐colluvial soils. In contrast, the accretion rate is the key factor controlling colluvial SOC stability. Accretion rate drives the role of mineral weathering in colluvial SOC stability.

Method validation for determination of 14C with the use of CO2 absorption method

The CO2 absorption method is applicable for analyzing radiocarbon content in environmental samples. Since this method is characterized with low accuracy and sensitivity, optimization and improvement are needed. In the Laboratory for Liquid Scintillation Spectrometry at Jožef Stefan Institute, internal method validation was performed. The main aim of this validation was to set optimal and controlled conditions that would improve the total uncertainty. For that purpose, we investigated the effect of three parameters on the final results: size of the trap, flow rate and combination of trapping mediums. All measurements were performed on ultra-low level liquid scintillation counter Quantulus™ 1220. The counting efficiency was determined with the use of the external standard method (SQP(E)) and standard addition method. We recognized the use of a big trap, thus use of a balance with a readability of 0.01 g, as the most significant contributor to the total uncertainty. A small trap, flow rate of 0.1 L/min and a mixture of CarbonCount™ and CarbonTrap™ proved to be the most suitable parameters. Using a small trap instead of a big one lowered the relative uncertainty from 2.4% to 0.01%, causing a decrease in the total uncertainty from 4.7% to 3.2%.

RADIOCARBON DATING OF CHARCOALS FROM HISTORICAL MORTARS FROM TÝŘOV AND PYŠOLEC CASTLES.

Organic inclusions in lime binders provide useful samples for radiocarbon dating of historical objects. Two Czech castles Týřov and Pyšolec from Late Middle Ages were explored, and tens of charcoals were found in their walls. The radiocarbon content of the charcoals was measured with accelerator mass spectrometry. The dating results showed that none of the charcoals were younger than the known historical ages (Týřov: 1260 - 1270, Pyšolec: 1300 - 1340), but some were considerably older. Two charcoals from Pyšolec castle dated to Palaeolithic, likely originating from fluvial sediments added as an aggregate to the mortar. When excluding these two charcoals, the others indicated most likely dates being 50-100y older than the building dates of the castles. This systemic effect corresponds to the age of wood used for lime burning and shall be accounted for when dating mortars using charcoals.

THE MIYAKE EVENT IN 993 CE RECORDED IN OAK SUB-ANNUAL TREE RINGS FROM KUJAWY (POLAND)

ABSTRACTThis article presents measurements of the radiocarbon (14C) concentration in sub-annual tree rings. Samples of earlywood (EW) and latewood (LW) from dendrochronologically dated tree rings (English oak, Quercus robur) from Kujawy, near Kraków (Poland), spanning the years of 990–997 CE, are extracted and their 14C content is measured at the Center for Applied Isotope Studies at the University of Georgia, USA. The EW and LW data show a gradual increase in the Δ14C values between 991–995 CE, which are similar to those observed by Rakowski et al. (2018). An increase of 10.3 ± 2.6‰ in Δ14C for the EW data, and 8.6 ± 2.6‰ for the LW data has been recorded for this period. Using this data, it is possible to estimate the time period for when a major historical event occurred, which seems to have been in the late summer (September –2/+1 month) of 993 CE.

Dramatic Lockdown Fossil Fuel CO2 Decrease Detected by Citizen Science-Supported Atmospheric Radiocarbon Observations.

COVID-19 lockdowns resulted in dramatic changes to fossil fuel CO2 emissions around the world, most prominently in the transportation sector. Yet travel restrictions also hampered observational data collection, making it difficult to evaluate emission changes as they occurred. To overcome this, we used a novel citizen science campaign to detect emission changes during lockdown and engage youth in climate science. Citizen scientists collected grass samples from their garden or local park, from which we analyzed the radiocarbon content to infer the recently added atmospheric fossil fuel CO2 mole fraction at each sampling location. The local fossil fuel CO2 mole fractions during lockdown were compared with a “normal” nonlockdown period. Our results from 17 sites in five cities around New Zealand demonstrate dramatic reductions in traffic emissions of 75 ± 3% during the most severe lockdown restriction period. This is consistent with sparse local traffic count information and a much larger decrease in traffic emissions than reported in global aggregate estimates of emission changes. Our results demonstrate that despite nationally consistent rules on travel during lockdown, emission changes varied by location, with inner-city sites typically dominated by bus traffic showing smaller decreases in emissions than elsewhere.

Tracking local radiocarbon releases from nuclear power plants in southern Ontario (Canada) using annually-dated tree-ring records

Understanding the radiocarbon ( 14 C) content of atmospheric carbon dioxide (CO 2 ) underlies many fields of research. This study shows how one can track the influence of nuclear power plants at the local and regional scale in Canada’s largest urban area. This area is subject to significant 14 CO 2 depletion due to CO 2 emissions from fossil fuel burning. Tree cores collected across southern Ontario in 2018 show that tree-rings dated annually record the same decadal trends as atmospheric measurements at a background site. Tree cores taken closer to 14 CO 2 or fossil fuel sources reflect those local influences. Data of 14 C from a site 20 kilometer downwind from a nuclear power plant is highly correlated (R 2 =0.76) with annually reported emissions from the plant for 2009-2018. Extending the analysis back to the 1990s shows that the emissions of 14 CO 2 were 4-8 times higher than those at present. At that time, 14 CO 2 emissions were sufficiently strong to affect a remote background monitoring site. Concerning the urban fossil fuel CO 2 emission signature, 14 CO 2 in the cellulose of a tree from downtown Toronto has an extremely depleted Δ 14 C signature. The local signal from traffic emissions overshadows any 14 CO 2 from nuclear emissions in the region. This study suggests that, with more cores to reflect the emissions of nuclear 14 CO 2 before 1990 and more suitable urban sampling locations (i.e., representative of a neighborhood rather than one road), this approach has potential to better track the long-term impact of urbanization and nuclear power plants in Canada, and potentially elsewhere around the globe.