14C Analysis Research Articles

New palaeolimnological record from West Anatolia (Paleo‐Kuleönü Lake) provides new information on the activity of the Gölcük volcanism and the distribution of the Santorini Minoan eruption

AbstractAnatolia, which had active volcanoes during the Pleistocene and Holocene periods, was also influenced by volcanic eruptions around the Eastern Mediterranean. Therefore, tephrochronology is an important research topic in palaeoenvironmental studies conducted in Anatolia. This study focuses on the geochemical characteristics, chronologies and source areas of six different tephra layers identified in a 16 m sediment core obtained from Paleo‐Kuleönü Lake in the Lake District of West Anatolia. Whole‐rock geochemistry is used to determine the geochemical characteristics and source of the tephra layers, micro X‐ray fluorescence analysis is used to determine relative element changes throughout the cores, and 14C analysis is performed to establish the chronologies. The geochemistry of the Paleo‐Kuleönü Lake tephra layers is consistent with the Gölcük volcanism located in West Anatolia province and the Minoan eruption within the Aegean volcanic province. The layers that resemble the geochemistry of the Gölcük volcanism accumulated at ~33 218 cal a bp (PLK‐19‐1; 30 cm), ~32 267 cal a bp (PLK‐19‐2: 18 cm), ~31 597 cal a bp (PLK‐19‐3; 8 cm), ~31 300 cal a bp (PLK‐19‐4; 17 cm) and ~26547 cal a bp (PLK‐19‐5; 13 cm) and are associated with the last eruptive cycle (Cycle III) of the volcanism. The closest tephra layer to the surface in the sediment core, designated as PLK‐19‐6 (~1.5 cm), shows geochemical similarities with the Santorini Minoan eruption. However, according to our data, the age of the tephra layer is ~4717 bp/~5542 cal a bp, which is inconsistent with the widely accepted date for the Minoan eruption in the literature. The discrepancy between the geochemical match and chronological inconsistency is discussed in the context of the results presented in the paper.

Bomb radiocarbon dating and age estimation of European eel (Anguilla anguilla) of Norway

Abstract Age estimates from bomb 14C dating conflict with a well-recognized age reading protocol (grinding, polishing and staining in the sagittal plane) for otoliths of European eel (Anguilla anguilla). Proper alignment of calculated hatch years for 14C measurements taken from the earliest otolith growth—among the smallest otolith extractions to date for successful 14C analysis due to the advent of gas-AMS—was not achieved using age estimates from an accepted method. The realignment of otolith 14C values to a tropical bomb 14C reference chronology, which is most applicable to the Sargasso Sea as the natal origin of European eel, led to an increase of the original age estimates by 8 to 32 years. A maximum age of approximately 46 years was determined for the European eel specimen with the most massive otolith, of which mass is a reasonable proxy for age and was instrumental in identifying age estimate discrepancies. By extending the otolith mass-to-age relationships from this study to the most massive otoliths available from archived otoliths of Norway, an increase of up to several decades from the original otolith age estimates was discovered, leading to support for a potential lifespan of 70–100 years in the natural environment.

No time to die: Radiocarbon chronology of the funerary monument of El Amarejo 1 and burial practices during the Bronze Age in the Southern Meseta, Spain

Abstract This paper presents the radiocarbon context of the megalithic monument El Amarejo 1, situated in the corridor of Almansa in the southern region of La Meseta in Spain. The monument was constructed using small and medium-sized masonry, comprising a short corridor and two separate chambers in which burials were carried out. The results of the 14C analyses of each of the 11 individuals documented indicate that the monument was in use between approximately 1900 and 1200 cal BC. Bayesian modeling of the radiocarbon dates allows for the proposition of hypotheses regarding the construction, utilisation dynamics, and abandonment of the monument. The combination of these new data with the analysis of the 14C dating of other burials from the Bronze Age of La Mancha reveals a complex and heterogeneous panorama. The evidence presented and analyzed in this paper suggests that burial practices associated with fortified settlements and their domestic areas shared space and time with the construction of megalithic monuments located near settlements.

Investigating the impact of COVID-19 on the atmospheric 14C trend and fossil carbon load at urban and background sites in Hungary

Abstract The study analyses in situ CO2 mole fraction, 14CO2, and fossil based excess CO2 mole fraction (Cfoss) data at Hegyhátsál (HUN) rural monitoring station (Central Europe) supplemented by passive monitoring of 14C content of tree-rings. Through the observed period (2014–2020) we focused on revealing trends in atmospheric CO2 and 14C levels, particularly during the year of the first COVID lockdown, in comparison to the preceding five years. In addition, monthly integrated samples of atmospheric CO2 and tree-rings from the six years were subjected to 14C analysis. The passive tree-ring measurements focuses on two major urban areas (Budapest and Debrecen) in Hungary, along with the rural monitoring site. Results show a steady increase in CO2 levels at HUN between 2014 and 2020. The calculated fossil based excess CO2 concentrations for the initial year of COVID are in good agreement with the previous five-year averages both at 115 m and 10 m elevations. These results also show seasonal variations of CO2 mole fractions, peaking in winter and decreasing in summer. Tree-ring results from Debrecen show a good alignment with the results of the atmospheric monitoring station, and it does not show a significant fossil contribution in the urban background area during the vegetation periods. Tree-ring results from Budapest show a stronger fossil contribution compared to the Debrecen ones. Our atmospheric CO2 results do not show a large decrease in fossil CO2 atmospheric contribution during the first lockdown. We found that the use of this passive CO2 monitoring technique can provide a valuable tool for investigating such differences.

A new portable sampler of atmospheric methane for radiocarbon measurements

Abstract. Radiocarbon (14C) is an optimal tracer of methane emissions, as 14C measurements enable distinguishing between fossil methane and biogenic methane (CH4). However, 14C measurements in atmospheric methane are still rare, mainly because of the technical challenge of collecting enough carbon for 14C analysis from ambient air samples. In this study, we address this challenge by advancing the system in Zazzeri et al. (2021) into a much more compact and portable sampler and by coupling the sampler with the MICADAS (MIni CArbon DAting System) accelerator mass spectrometry (AMS) system at ETH Zurich, using a gas interface. Here, we present the new sampler setup, the assessment of the system contamination and a first inter-laboratory comparison with LARA (Laboratory for the Analysis of Radiocarbon with AMS) at the University of Bern. With our sampling line, we achieved a very low blank, 0.7 µgC compared to 5.5 µgC in Zazzeri et al. (2021), and a sample precision of 0.9 %, comparable with other measurement techniques for 14CH4, while reducing the sample size to 60 L of air. We show that this technique, with further improvements, will enable routine 14CH4 measurements in the field for an improved understanding of CH4 sources.

Evaluating possible sources of error in tree-ring 14C data using multiple trees across South America

Abstract A limitation in fine-tuned tree-ring radiocarbon (14C) data is normally associated with overall data uncertainty. Tree-ring 14C data variance as a result of sample heterogeneity can be reduced by adopting best practices at the time of sample collection and subsequent preparation and analysis. Variance-reduction of 14C data was achieved by meticulous sample handling during increment core or cross-sectional cuttings, in-laboratory wood reductions, and cellulose fiber homogenization of whole rings. To demonstrate the performance of those procedures to final 14C results, we took advantage of the replicated data from assigned calendar years of two Pantropical post-1950 AD tree-ring 14C reconstructions. Two Cedrela fissilis Vell. trees spaced 22.5 km apart, and two trees of this species together with one Peltogyne paniculata Benth tree spaced 0.2 to 5 km apart were sampled in a tropical dry and moist forest, respectively. Replicate 14C data were then obtained from grouped tree-ring samples from each site. A total of 88% of the replicated 14C results fell into a remarkably consistent precision/accuracy range of 0.3% or less, even though multiple tree species were used as pairs/sets. This finding illustrates how adopting a few simple strategies, in tandem with already established chemical extraction procedures and high-precision 14C analysis, can improve 14C data results of tropical trees.

Radiocarbon age-offset measurements reveal shifts in the transport mechanism and age of permafrost-derived organic carbon from Burial Lake, arctic Alaska from MIS 3 to present

The stability of arctic permafrost and the carbon it contains are currently threatened by a rapidly warming climate. Burial Lake, situated in northwestern arctic Alaska, is underlain by continuous permafrost and has a uniquely rich set of paleoclimate proxy data that comprise a 40-ka record of climate and environmental change extending well into Marine Isotope Stage (MIS) 3. Here, we examine the relationship between erosion, subsurface hydrology, and primary productivity from the Burial Lake sediments to improve our understanding of the links between climate, hydrology, sediment transport, and carbon mobility. The record is developed with radiocarbon (14C) age-offsets from two independent methods used to date the lake sediments: 1) 14C measurements on paired bulk sediment and plant macrofossils from the same stratigraphic layer of lake sediment and 2) ramped pyrolysis-oxidation (RPO) 14C analysis that separates fractions of organic carbon (OC) from a single bulk sediment sample based on thermochemical differences through continuous heating. As lakes capture and archive OC transported from the watershed, changes in the amount and relative age of permafrost-derived OC mobilized during past climatic variations can be documented by examining how age-offsets change over time. The Burial Lake sediment revealed higher age-offsets during the cold Last Glacial Maximum (LGM; ∼29-17 ka) than the comparatively warmer post-glacial (∼17 ka-present) and the MIS 3 interstadial (∼40-29 ka) periods. The relatively warm, wet climate of the post-glacial period promoted both terrestrial and aquatic productivity, resulting in increased OC deposition, and it likely favored transport via subsurface flow of dissolved OC (DOC) sourced from soils. This resulted in a greater flux of contemporary OC relative to ancient OC into the lake sediment, lowering the average age offset to ∼2 ka. In contrast, the low-productivity conditions of the LGM resulted in slow soil accumulation rates, leaving ancient OC in a shallower position in the soil profile and allowing it to be easily eroded in the form of particulate OC (POC). Although the amount of total OC deposited in the lakebed during the LGM is small relative to post-glacial deposition, the majority is ancient, which leads to a relatively high average age offset of ∼9 ka. Finally, climate and environmental conditions of the MIS 3 interstadial were intermediate between those of the post-glacial and the LGM. As with post-glacial sediments, a relatively large amount of OC is present; however, the vast majority of it is ancient (more similar to the LGM), and it produces an average age offset of ∼6 ka. The Burial Lake radiocarbon record demonstrates the complexities of the thaw and mobilization of permafrost OC in arctic Alaska, including the balance between production, transport, deposition, remobilization, and preservation. This record highlights the importance of considering factors that both enhance and inhibit erosion (i.e. vegetation cover, lake level, precipitation) and the mechanisms of OC transport (i.e. subsurface flow or erosion) in predictions of future permafrost response to changes in climate.

Stable isotope of Mesolithic remains of Pila wernei of the Nile area, Sudan: A tool for palaeoenvironment reconstruction

The article deals with stable isotopes of oxygen and carbon on current and archaeological semi-aquatic gastropod shell of the Pila wernei from Sudan and reports some new 14C analyses on archaeological Pila specimens. This, with the aim of obtaining new information on climatic and environmental changes in the al-Khiday area during the first phase of Holocene. The Pila shells come from a well-preserved shell midden present at al-Khiday and dated 8700-7000 cal yr BP. The area of al-Khiday was inhabited since at least 10 ka. Pila wernei species has never been studied in detail; this study demonstrates that the O and C isotope composition of aragonite shell is able to record the environmental and diet changes during the gastropod life. The comparison between the isotope data obtained on present-day and archaeological shells show a prevalence of C4 plants and higher rainfall during the Mesolithic. Two climatic fluctuations have been recognised: the first one indicating wetter conditions from 8650-8400 to 8500-8050 cal yr BP (decrease of the δ18O values), the second one pointing less wetter conditions from 8500-8050 to 7850-7600 cal yr BP (increase of δ18O values). Despite the difficulties in studying semi-aquatic gastropods due to their lifestyle habit, the identification of climatic fluctuations in the Early Holocene confirms the reliability of this proxy for climatic reconstructions. Despite the high number of isotopic analyses (1556) used in this work, they were not sufficient to mirror the fast climate changes characterising the studied period and finally obtain a detailed reconstruction for nearly the two millennia considered. Nonetheless, future projects may benefit greatly from unveiling the shell-environment relationship of the species.

Recent sedimentology at the grounding zone of the Kamb Ice stream, West Antarctica and implications for ice shelf extent

Sediment accumulating beneath floating ice contains a record of ice dynamics in polar regions where in situ observations are rare. In 2019 a hole was melted through a 590m-thick region of the Ross Ice Shelf ∼5 km seawards of the Kamb Ice Stream (KIS) grounding line (82.7841°S, 155.2626°W) to access the seafloor. Imagery from a remotely operated vehicle (ROV, Icefin) shows ocean current-generated ripples likely formed by tidal flow parallel to the grounding line (GL). Observed current speeds <0.15 m s−1 suggest these bedforms may be relict. Larger, dm-scale, ‘furrows’ parallel to the former direction of KIS flow may relate to past grounding line processes. A 0.49 m-long gravity core collected from the seafloor contains weakly stratified diamicton. The sediment matrix comprises variable mixtures of reworked Tertiary biogenic silica, predominantly diatoms, and arkose material. Sediment εNd values of ∼7 are consistent with derivation from the WAIS, as is the U-Pb age distribution and modelled late Holocene ice flows. Ramped pyrolysis 14C analysis shows all fractions are either >30 ka or 14C dead. By contrast, 210Pb-210 activity of >30 Bq Kg−1 indicates deposition within the last 120 years. The combination of features suggests rapid rainout deposition from melting of a sediment-laden basal debris layer as the GL retreated, followed by some reworking by ocean currents and little modern accumulation. Although Tertiary diatoms are abundant, unambiguously Late Quaternary forms are absent and we speculate on the implications for Ross Ice Shelf stability. [239 wds]

FIRST δ13C RESULTS WITH A NEW CONNECTION BETWEEN THE EA-IRMS SYSTEM AND THE GAS INJECTION SYSTEM AT COLOGNEAMS

ABSTRACTThis work presents the integration of an elemental analyzer (EA) and an isotope ratio mass spectrometer (IRMS) into the 6 MV AMS system at the Institute for Nuclear Physics, University of Cologne. The AMS measurement of δ13C values for IAEA-C6 reference material resulted in –11.39(226)‰, compared to –10.28(32)‰ obtained by IRMS. The EA-IRMS system was also tested with IAEA-C3, IAEA-C5, and IAEA-C7 reference materials, yielding –24.79(9), –25.18(15), and –14.76(18)‰ respectively. Compared to the IAEA information values given as –24.91(49), –25.49(72) and –14.48(21)‰ respectively. To investigate an observed sample mass dependency, environmental samples from Spitzbergen were examined, showing δ13C values of –25.17(55), –25.80(31), and –26.17‰ in Cologne, while Hamburg recorded –24.8(1), –25.5(1), and –26.2(13)‰. In summary, this new setup could enable online analysis and quasi-simultaneous measurements of 14C, δ13C, and δ15N for ultra-small samples, utilizing precise δ13C values from IRMS for fractionation correction of the 14C/14C isotopic ratio.

Cosmogenic radionuclides in meteorites from the Otway Massif blue ice area, Antarctica: An unusual, well‐preserved H5 chondrite strewn field

AbstractThe US Antarctic Search for Meteorites (ANSMET) discovered a dense cluster of 88 ordinary chondrites with a total mass of more than 100 kg on a blue ice area (BIA) of 1.6 × 0.3 km2 near the Otway Massif, Grosvenor Mountains, Antarctica. The larger masses (weighing up to 29 kg) were found at one end of an oval‐shaped pattern and the smaller masses (50–200 g) at the other end. We measured concentrations of the cosmogenic radionuclides 10Be (half‐life—1.36 × 106 year) and 36Cl (3.01 × 105 year) in the metal fraction of 17 H chondrites, including 14 fragments of this cluster, to verify the hypothesis that this meteorite cluster on the Otway Massif BIA represents a meteorite strewn field produced by the atmospheric breakup of a single meteoroid. The 10Be and 36Cl concentrations confirm that 10 out of 14 H chondrites from different locations within this small area are paired fragments of the same meteorite fall, while the four other H chondrites represent two additional—smaller—falls. The radionuclides suggest a pre‐atmospheric mass of 200–400 kg for the large pairing group, suggesting that 25%–50% of the meteoroid survived atmospheric entry. Based on the distribution of the paired H chondrites and evidence of their common cosmic‐ray exposure history in space, we conclude that most of the 88 meteorites within this small area represent a meteorite strewn field. The small size of the strewn field suggests that the meteoroid entered at a steep angle (&gt;60°), while the low amount of fusion crust on most meteorite surfaces most likely indicates atmospheric break up at low altitude, while additional fragmentation of a large surviving fragment may have occurred during impact on the ice. This well‐documented strewn field provides a good opportunity to apply model simulations of the atmospheric fragmentation of this object as a function of entry angle, velocity, and meteoroid strength. Cosmogenic 14C analyses in two members of the Otway Massif pairing group yield a terrestrial age of 15.5 ± 1.5 kyr, which represents the time elapsed since this meteorite fell on Earth. The excellent preservation of an Antarctic meteorite strewn field suggests that the Otway Massif BIA represents a relatively stagnant blue ice field.

Stable Isotopic Evidence of Paleorecharge in the Northern Gulf Coastal Plain (USA)

Stable isotope abundances (δ18O and δ2H) in regional aquifers can provide important paleoclimate information. However, identifying paleoclimate signals can be complicated by cross-formational mixing and, potentially, by isotopic diffusion between aquifers and confining units. We examine controls on δ18O and δ2H distributions in the Wilcox aquifer of the northern Gulf Coastal Plain (USA). We sampled groundwater for δ18O, δ2H, Cl−, and 36Cl along a ~300 km downgradient transect. We developed a simplified, 1D numerical model of groundwater flow and 18O transport to assess the possible importance of isotopic diffusion between the aquifer and its confining units. Along the inferred flowpath, δ18O and δ2H values were depleted by as much as 1.3 and 8.2‰, respectively, as the Wilcox aquifer transitioned from unconfined to confined. However, they then gradually rose farther downgradient by up to 1.1 and 8.6‰. Chlorine-36 analyses and 14C analyses (from other studies) indicate that groundwater ages range from ~103 yr to ~8 × 105 yr. Modeling results indicate that the effect of diffusion on isotopic abundances is limited, whereas Cl− data indicate that cross-formational flow is limited. Therefore, we posit that confined groundwater in our study reflects a Pleistocene paleorecharge signal.

Coprocessing of cashew nut shell liquid and phenol model compounds with VGO in a pilot-scale FCC riser

The feasibility of coprocessing of waste biomass resource cashew nut shell liquid (CNSL) with vacuum gas oil (VGO) to produce bio-based fuel has been demonstrated in a pilot riser. Herein, the effects of reaction temperature, catalyst to oil ratio (C/O), CNSL blending ratio, CNSL feed position and ZSM-5 addition on the product distribution and quality of CNSL coprocessing with VGO were analyzed in detail. CNSL was a suitable bio-based feedstock for coprocessing because any proportion of CNSL blended with VGO for coprocessing was feasible with no difficulties occurring in the system. The addition of CNSL could improve conversion and liquefied petroleum gas (LPG) yield in fluid catalytic cracking (FCC) while maintaining high gasoline yield. Compared to CNSL, phenol or guaiacol with a smaller kinetic diameter was more likely to cause catalyst deactivation. GCxGC-MS analysis of liquid products showed that the oxygenate content in the liquid products was low, and cashew phenol could be cracked, cyclized, dehydrogenated, and converted to naphthol, and further dehydrated and converted to naphthalenes. 14C analysis showed that the biocarbon content of LPG and gasoline produced from CNSL coprocessing was high, indicating that CNSL coprocessing was meaningful.

Palaeoenvironmental reconstruction of Holocene calcareous tufas distributed over a manganese deposit in Mexico

The Holocene calcareous tufa deposits are located in the north-central sector of the state of Hidalgo, Mexico. These deposits outcrop on the Upper Jurassic Chipoco Formation in the Molango Manganese District. Calcareous tufa deposits correspond to carbonate formations of inactive tufas disconnected from the current hydrological network. To better understand the textural, geochemical, and biological characteristics and environmental conditions during their formation, a detailed study involving field analysis, X-ray diffraction analysis, X-ray fluorescence analysis, and morphometric analysis with light microscopy, and scanning electron microscopy was carried out. Similarly, 14C analysis was undertaken to determine the age of the deposit. On this basis, two biofacies were defined, one with stem structures and the other with Phyto clasts, bryophytes (Plagiomnium cuspidatum), and copepods, limited both at the base and the top by lenticular-shaped erosive surfaces and sigmoidal clinoforms. These bio facies formed in lacustrine and paludal environments, and barrier waterfalls. From a geomorphological point of view, the accumulations of these calcareous tufas originated on slopes and/or at the foot of karstic springs, where the accumulation of material originated from the height of the spring with respect to the bottom of the valley, giving rise to a set of stepped tuffaceous plains with a wedge-shaped profile, colonized by important masses of bryophyte mounds, copepods, and vascular plants. This suggests a swampy environment where sedimentation took place in shallow water accumulations, where there is clear evidence of exposure and pedogenetic modification, indicating wet and dry episodes that translate into seasonal fluctuations in the water table. Six mineral phases were observed including silicates, carbonates and arsenates. The 14C analysis indicates that the plant found in the charcoal sample within the calcareous tufa deposit is of Holocene age.

Dual-carbon isotope analysis of benzene polycarboxylic acids for tracking black carbon across different environments

Black carbon (BC) is ubiquitous in the environment and is a significant component of the refractory carbon pool. However, its sources, biogeochemical processes, and environmental residence times are poorly understood. One important reason is that the technical protocols for isolating/analyzing BC vary across different matrices, thereby bringing inconsistency among studies on BC in different environment media. Benzene polycarboxylic acids (BPCA), produced by nitric acid oxidation of the condensed aromatic structure that is common in BC and BC-like substances, has been proven to be a useful molecular proxy for tracking BC in the Earth's surface. Here, we introduce a new technical approach for the compound-specific dual-carbon isotope (δ13C and Δ14C) analysis of BPCA. The BPCA compounds are isolated using preparative liquid chromatography, in which trifluoroacetic acid is used in the mobile phase instead of phosphoric acid. This allows complete removal of solvent from the isolated BPCA fraction, so that conversion of BPCA isolates into CO2 can be done by conventional oxidation methods for off-line Δ14C analysis with accelerator mass spectrometry. Liquid chromatography (void column)-stable carbon isotope ratio mass spectrometry is employed to measure δ13C of the isolated BPCA, leaving as much BPCA carbon amount as possible for 14C analysis. Blockage of oxidation chamber due to incomplete oxidation of other organic acids in the samples is avoided thanks to preliminary isolation of BPCA. We tested the approach by applying it to solid and dissolved BC species in a suite of environmental reference materials, including maize char, coal, riverine natural organic matter (NOM 2R101N), marine sediment (SRM 1941b), urban dust (SRM 1649b), and coke-polluted soils. We assessed the offsets of BPCA-δ13C and BPCA-Δ14C values caused by procedural carbon contaminations to correct measured carbon isotopic values. Paired δ13C-Δ14C data of individual BPCA were plotted to validate and demonstrate the ability of this dual carbon isotope technique in tracking BC across different environmental matrices. We observed slightly different δ13C-Δ14C signatures among individual BPCA, indicating that the less condensed BC may have younger apparent radiocarbon ages.

Asian monsoonal temperature and environmental changes since the penultimate deglaciation as revealed by alkenones and alkanes in sediments from the northern South China Sea

A new alkenone sea surface temperature (SST) record from the South China Sea (SCS) over the last 170 ka has been reported here. Our analysis of magnetic susceptibility and AMS 14C dating on the top portion of the core suggests that this record dates to the Marine Isotope Stage (MIS) 6. As indicated in Termination I and II, SST changes are correlated with clear glacial/interglacial cycles and likely dominated by atmospheric CO2 and Western Pacific Warm Pool temperature changes. But the two Terminations were different in magnitude. In Termination I, the minimum and maximum SSTs are 24.5 °C and 27.5 °C, respectively, showing a smaller rise (3 °C) than in Termination II (24–28.3 °C). The n-alkane indices, such as average chain length (ACL) and carbon preference index (CPI), exhibited high/low values during glacial/interglacial periods, and possible more arid climate during MIS 6 than MIS 2. During Termination II, the maximum surface warming in the SCS is accompanied by a progressive lag of approximately 7000 years in relation to maximum summer insolation until Termination I, when they are nearly synchronous. According to the study, SSTs are continuously changing and are influenced by solar insolation, global ice volume changes, and ocean–atmosphere interactions across hemispheres.

Testing and assessment of high-precision and high-accuracy AMS-radiocarbon measurements at Nanjing University, China

AbstractIn 2018, an Ionplus 200 kV MIni-CArbon DAting System (MICADAS) accelerator mass spectrometer (AMS) was installed at the Laboratory of AMS Dating and the Environment, Nanjing University (NJU-AMS Laboratory), China. The NJU-AMS Laboratory is largely devoted to research on radiocarbon dating and 14C analysis in fields of earth, environmental and archaeological sciences. The laboratory has successfully employed various pretreatment methods, including routine pretreatment of tree rings, buried wood and subfossil wood, seeds, charcoal, pollen concentrates, organic matter, and shells. In this study, operational status of the NJU-AMS is presented, and results of radiocarbon measurements made on different sample types are reported. Measurements on international standards, references of known age, and blank samples demonstrate that the NJU-AMS runs stably and has good reproducibility on measurement of single samples. The facility is capable of measuring 14C in samples with the precision and accuracy that meet the requirements for investigating annual 14C changes, history-prehistory age dating, and Late Quaternary stratigraphic chronology research.

Alligator gar as a centenarian species: extending lifespan estimates using bomb radiocarbon and laser ablation–accelerator mass spectrometry

Context The potential lifespan of alligator gar (Atractosteus spatula) is currently unknown. A previous study applied bomb radiocarbon (14C) dating to establish ages &gt;60 years, but maximum age was limited by the rise of bomb-produced 14C in the 1950s. Aims An exceptionally large specimen (2.6 m, 148 kg) was captured in Mississippi and otolith growth zones revealed an age estimate of 95 years. This specimen provided an opportunity to apply new technology to validate the lifespan of alligator gar. Methods Developments in accelerator mass spectrometry (AMS) led to technology that measures 14C continuously from carbonates (laser ablation-AMS), as opposed to single sample 14C analysis. Key results Use of laser ablation AMS on the 2.6-m alligator gar otolith, and two smaller fish aged &gt;60 years, supported ages that were older than original estimates by 5–20 years. Conclusions Our study indicates that alligator gar age can be underestimated for the largest fish, maximum recorded length is 2.6 m based on a historical photograph, and lifespan is at least 75–95 years with support for an age of 100 years for the 2.6-m fish. Implications An increase in lifespan of this magnitude would affect our understanding of population dynamics and recovery efforts.

Biomass Burning Greatly Enhances the Concentration of Fine Carbonaceous Aerosols at an Urban Area in Upper Northern Thailand: Evidence From the Radiocarbon‐Based Source Apportionment on Size‐Resolved Aerosols

AbstractTo study the role of biomass burning (BB) in air pollution at upper‐northern Thailand, the source apportionment of size‐resolved carbonaceous aerosols from Chiang Mai was carried out based on the radiocarbon (14C) analysis. The fraction of modern carbon (F14C) was generally decreased with particle size increasing and with the highest and lowest values of 0.90 ± 0.04 and 0.61 ± 0.04, respectively. Elemental carbon, regardless of emission sources, and BB‐derived organic carbon (OCbb) showed unimodal size distribution patterns with peaks at 0.43–0.65 μm. Fossil‐fuel derived‐OC (OCf) displayed a bimodal mode with the major peak at 2.1–10 μm, and the minor one at 0.43–0.65 μm. The biogenic secondary organic aerosols (BSOA) showed a typical fine‐mode unimodal size distribution pattern during the high BB (HBB) season, and a bimodal mode during the low BB season. The BSOA concentration increased by 189% ± 80% due to the interaction with open BB plums during HBB season, which was quantified by a 14C‐involved random forest model. Besides, the concentration of biogenic primary organic aerosols also showed a significant increment during the HBB season, especially in sub‐microns. Our results highlight the critical importance of controlling open fires to reduce air pollutants and the potential exposure risk.

ASSESSING 14C BLANKS IN THE SMALL-SCALE ANALYSIS OF N-ALKANE COMPOUND-SPECIFIC-RADIOCARBON-ANALYSIS

ABSTRACTCompound-specific radiocarbon analysis (CSRA) provides the possibility to date sample material at a molecular level. N-alkanes are considered as specific compounds with high potential to CSRA. As these compounds originate from plant waxes, their radiocarbon (14C) analysis can provide valuable information about the age and origin of organic materials. This helps to reconstruct and understand environmental conditions and changes in vegetation in the past. However, CSRA has two main challenges: The small sample size of CSRA samples, making them extremely sensitive to blank effects, and the input of unknown amounts of extraneous carbon during the analytical procedure. According to the previous study from Sun and co-workers, we used different-sized aliquots of leaves Fagus sylvatica (nC27, nC29) and Festuca rubra agg (nC31, nC33) as modern standards and two commercial standards (nC26, nC28) as fossil standards for blank determination. A third commercial standard (nC27) with predetermined radiocarbon content of F14C = 0.71 (14C age of 2700 BP) serves to evaluate the blank correction. We found that the blank assessment of Sun and co-workers is also applicable to n-alkanes, with a minimum sample size of 15 µg C for dependable CSRA dates. We determined that the blank introduced during the analytical procedure has a mass of (4.1 ± 0.7) µg carrying a radiocarbon content of F14C = 0.25 ± 0.05. Applying the blank correction to a sediment sample from Lake Holzmaar (Germany) shows that all four isolated n-alkanes have similar 14C ages. However, the bulk material of the sediment and branches found in the sediment core are younger than the CSRA dates. We conclude that the disparity between the actual age of analysed organic material and the age inferred from radiocarbon results, which can occur in sediment traps due to delayed deposition, is the reason for the CSRA age.