14C Measurements Research Articles

Preliminary investigation of the local marine reservoir effect in port JOLI harbour, NOVA scotia using archaeological M. arenaria shells

Port Joli Harbour, situated on the southwest coast of the maritime province of Nova Scotia, Canada, has the highest density of shell midden deposits in Atlantic Canada. The terrestrial radiocarbon chronology points to continuous human occupation of the harbour from 1685 cal yr BP to 250 cal yr BP. Despite the abundance of the soft-shell clams Mya arenaria at shell midden sites throughout the harbour they have not been incorporated into the chronology, nor have they been used to study the local marine reservoir effect in the harbour. We report 12 new 14C measurements on archived Mya arenaria from the same depositional contexts as previously dated charcoal and terrestrial mammal bone samples from two shell middens in Port Joli Harbour. From these shell-charcoal and shell-bone pairs, we present preliminary calculations of local marine reservoir corrections (ΔR) for the harbour. The ΔR values are highly variable and are overall more positive than the pre-bomb values reported for the Scotian Shelf. The variability of these values highlights the challenges in calculating ΔR values from archived archaeological samples but also the opportunities to include high-resolution analysis of ΔR variations in discussions on human-environment interactions in coastal settings during the late Holocene. We suggest that the chondrophore may be more favourable for calculating first order estimates of ΔR to be used in future archaeological calibrations, while high resolution analysis of the ventral margin region is useful for climate reconstructions. We recommend that more 14C measurements from M. arenaria shells be obtained from either distinct features or rapidly deposited middens in Port Joli Harbour. A suite of temporally and geographically precise ΔR values for the harbour will not only allow for the study of middens that are at risk of coastal erosion and lack charcoal for 14C dating but will also allow for the reconstruction of past climate conditions and refine our understanding of late Holocene human-environment interactions in the North Atlantic.

Bomb-radiocarbon in the Northern Indian Ocean

Bomb-radiocarbon is a useful tracer to study ocean circulation and air-sea CO2 exchange processes. In the present study bomb radiocarbon distribution in dissolved inorganic carbon of the Northern Indian Ocean around late 2010s has been evaluated. In the late 2010s surface waters in the Northern Indian Ocean had ∆14C values ranging between 9 and 17 ‰ which is comparable or even higher than that of the contemporaneous atmospheric ∆14C values. Water column measurements showed that the bomb 14C inventory in the Arabian Sea and the Bay of Bengal has increased between 1990s and 2010s. During the same period, the eastern and western equatorial Indian Ocean showed either no change or a slight decline in the water column bomb 14C inventory. These bomb 14C inventory values were also used to estimate the air-sea CO2 exchange rate and net CO2 flux over the Northern Indian Ocean region. Bomb 14C-based estimate of net CO2 flux from the Arabian Sea is 75 ± 24 Tg C yr−1 and the Bay of Bengal is 1 ± 7 Tg C yr−1, which is comparable to the estimates reported by previous investigations in the region. The present observations show that the bomb 14C is being transferred to the deeper depths of the ocean, emphasizing the need for continued 14C measurements to gain further insights into subsurface processes in the region.

Extreme solar storms and the quest for exact dating with radiocarbon.

Radiocarbon (14C) is essential for creating chronologies to study the timings and drivers of pivotal events in human history and the Earth system over the past 55,000 years. It is also a fundamental proxy for investigating solar processes, including the potential of the Sun for extreme activity. Until now, fluctuations in past atmospheric 14C levels have limited the dating precision possible using radiocarbon. However, the discovery of solar super-storms known as extreme solar particle events (ESPEs) has driven a series of advances with the potential to transform the calendar-age precision of radiocarbon dating. Organic materials containing unique 14C ESPE signatures can now be dated to annual precision. In parallel, the search for further storms using high-precision annual 14C measurements has revealed fine-scaled variations that can be used toimprove calendar-age precision, even in periods that lack ESPEs. Furthermore, the newly identified 14C fluctuations provide unprecedented insight into solar variability and the carbon cycle. Here, we review the current state of knowledge and share our insights into these rapidly developing, diverse research fields. We identify links between radiocarbon, archaeology, solar physics and Earth science to stimulate transdisciplinary collaboration, and we propose how researchers can take advantage of these recent developments.

Local hydrology control of radiocarbon in stalagmites from the Kyusendo Cave, Kumamoto, Japan

Stalagmite is an important archive of paleoclimate especially in the region of the East Asian Monsoon. Despite the widespread use of radiocarbon (14C) dating to explore past environmental changes, the contribution of a14C-free carbon fraction leached from soil and/or host rocks during stalagmite formation, known as the dead carbon fraction (DCF), impedes its application to stalagmite chronology. Thus, uranium series dating is preferentially used to determine stalagmite ages. However, both U/Th and 14C dating can be applied to stalagmite samples, U/Th can be used to calibrate the radiocarbon ages by assuming a relatively constant DCF contribution over time. Studies exploring DCF changes from glacial to interglacial periods remain scarce, suggesting that temporal and speleothem-specific DCF studies are needed. Here, we present findings on DCF changes over the last 38 ka in speleothems obtained from southwestern Japan. Our analysis includes measurements of both 14C in drip water and speleothem calcite alongside U/Th dating of three stalagmites collected from Kyusendo Cave, located in southern Japan. The DCFs reconstructed from these stalagmites exhibited variations of 37.8%–73.9% between 4.2 and 38.3 ka, which exceeded the typical DCF values reported previously. Intra-test variations of the DCF values in Kyusendo Cave also revealed differences of up to 30%–40% among the three stalagmites. A higher drip water DCF and dripping rate showed a strong negative correlation, indicating that variations in DCF may reflect changes in local hydrology. The study findings suggest that speleothem-specific and temporally varied DCF should be considered in paleoclimate reconstructions using speleothems.

The potential of in situ cosmogenic 14CO in ice cores as a proxy for galactic cosmic ray flux variations

Abstract. Galactic cosmic rays (GCRs) interact with matter in the atmosphere and at the surface of the Earth to produce a range of cosmogenic nuclides. Measurements of cosmogenic nuclides produced in surface rocks have been used to study past land ice extent as well as to estimate erosion rates. Because the GCR flux reaching the Earth is modulated by magnetic fields (solar and Earth's), records of cosmogenic nuclides produced in the atmosphere have also been used for studies of past solar activity. Studies utilizing cosmogenic nuclides assume that the GCR flux is constant in time, but this assumption may be uncertain by 30 % or more. Here we propose that measurements of 14C of carbon monoxide (14CO) in ice cores at low-accumulation sites can be used as a proxy for variations in GCR flux on timescales of several thousand years. At low-accumulation ice core sites, 14CO in ice below the firn zone originates almost entirely from in situ cosmogenic production by deep-penetrating secondary cosmic ray muons. The flux of such muons is almost insensitive to solar and geomagnetic variations and depends only on the primary GCR flux intensity. We use an empirically constrained model of in situ cosmogenic 14CO production in ice in combination with a statistical analysis to explore the sensitivity of ice core 14CO measurements at Dome C, Antarctica, to variations in the GCR flux over the past ≈ 7000 years. We find that Dome C 14CO measurements would be able to detect a linear change of 6 % over 7 ka, a step increase of 6 % at 3.5 ka or a transient 100-year spike of 190 % at 3.5 ka at the 3σ significance level. The ice core 14CO proxy therefore appears promising for the purpose of providing a high-precision test of the assumption of GCR flux constancy over the Holocene.

Demystifying the tropics: FTIR characterization of pantropical woods and their α-cellulose extracts for past atmospheric 14C reconstructions

To ensure unbiased tree-ring radiocarbon (14C) results, traditional pretreatments carefully isolate wood cellulose from extractives using organic solvents, among other chemicals. The addition of solvents is laborious, time-consuming, and can increase the risk of carbon contamination. Tropical woods show a high diversity in wood-anatomical and extractive composition, but the necessity of organic-solvent extraction for the 14C dating of these diverse woods remains untested. We applied a chemical treatment that excludes the solvent step on the wood of 8 tropical tree species sampled in South-America and Africa, with different wood-anatomical and extractive properties. We analyzed the success of the extractive removal along with several steps of the α-cellulose extraction procedure using Fourier Transform Infrared (FTIR) spectroscopy and further confirmed the quality of 14C measurements after extraction. The α-cellulose extracts obtained here showed FTIR-spectra free of signals from various extractives and the 14C results on these samples showed reliable results. The chemical method evaluated reduces the technical complexity required to prepare α-cellulose samples for 14C dating, and therefore can bolster global atmospheric 14C applications, especially in the tropics.

Last ice sheet recession and landscape emergence above sea level in east-central Sweden, evaluated using in situ cosmogenic 14C from quartz

Abstract. In situ cosmogenic 14C (in situ 14C) in quartz provides a recently developed tool to date exposure of bedrock surfaces of up to ∼ 25 000 years. From outcrops located in east-central Sweden, we tested the accuracy of in situ 14C dating against (i) a relative sea level (RSL) curve constructed from radiocarbon dating of organic material in isolation basins and (ii) the timing of local deglaciation constructed from a clay varve chronology complemented with traditional radiocarbon dating. Five samples of granitoid bedrock were taken along an elevation transect extending southwestwards from the coast of the Baltic Sea near Forsmark. Because these samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. In contrast, in situ 14C concentrations in an additional five samples taken from granitoid outcrops above the highest postglacial shoreline, located 100 km west of Forsmark, should reflect local deglaciation ages. The 10 in situ 14C measurements provide robust age constraints that, within uncertainties, compare favourably with the RSL curve and the local deglaciation chronology. These data demonstrate the utility of in situ 14C to accurately date ice sheet deglaciation, and durations of postglacial exposure, in regions where cosmogenic 10Be and 26Al routinely return complex exposure results.

Determination of radiocarbon content in liquid fuel blends by accelerator mass spectrometry and liquid scintillation counting in the gliwice radiocarbon and mass spectrometry laboratory

Abstract The increase in biobased material usage requires the methods of verification to investigate the actual content of biocarbon in such materials, including liquid fuels. The determination of biocarbon in liquid samples using 14C required adaptation of existing sample preparation methods. In this study, both accelerator mass spectrometry (AMS) and liquid scintillation counting (LSC) methods were used to determine the content of 14C in six different liquid fuel blends produced from purely bio-based hydrotreated vegetable oil (HVO) and a 14C-free petrodiesel sample (ON/UF-BC). The results obtained for pure petrodiesel provide background values. The results indicate a good agreement between LSC and AMS, and a linear correlation between the 14C measurement results for blended samples and HVO content affirmed the reproducibility between the two methods. The repeatability of AMS results was tested on 10 aliquots of one of the blends, and the results were deemed reproducible.

An Approach for Assessing Human Respiration CO2 Emissions Using Radiocarbon Measurements and Bottom‐Up Data Sets

AbstractCarbon dioxide (CO2) is a major greenhouse gas in the atmosphere and has large impacts on climate change. Its fossil fuel (CO2ff) and biogenic (CO2bio) sources are well investigated, while CO2 emissions from human respiration (CO2hr), a subset of CO2bio, have received less attention. Especially as a source of carbon emissions in densely populated megacities, the role of CO2hr emissions in the carbon cycles was largely neglected. Here we fully characterize the respiratory CO2 emission rates (CERs) of Chinese people for the first time. Using the example of the megacity Beijing in China, we estimate the CO2hr emissions and present a method for quantifying its fraction in the atmospheric CO2 based on radiocarbon (14C) measurements and inventory data sets. The results show that males and females have similar age trends in CERs, but the gender difference is significant, especially between the ages of 20 and 60, the average CERs was 33% higher for males than for females (P < 0.05). The CO2hr emissions were about 22.2 ± 0.6 kt CO2 per day, which was equivalent to 7.5% of daily CO2ff emissions in winter. The proportion is likely to be twice in summer due to the seasonal fluctuations of fossil fuel emissions. More importantly, the respiratory emissions could increase atmospheric CO2 concentration by about 2 ppm, accounting for 14% ± 6% of average CO2bio concentration in winter. This study highlights the importance of human respiration in carbon emissions in megacities and has implications for a better understanding of the regional carbon budget.

Development of pixelated silicon detector for AMS study

A pixelated silicon detector (PSD) has been developed for the position-sensitive detector on a focal plane of an accelerator mass spectrometry (AMS) system in Yamagata University (YU). The YU-AMS system measures the relative abundances of the carbon isotopes 14C, 13C, and 12C for radiocarbon dating. The beam of the rare isotope 14C is transported to the focal plane of the AMS system. When the focal plane detector is position-sensitive to the beam, it can be utilized for beam diagnostics on the AMS beamline to achieve 14C measurement with high accuracy. To investigate the characteristics of the PSD, α particles from 241Am were irradiated on the PSD. A beam test using 14C was also performed to evaluate the size and position of the 14C beam on the focal plane of the YU-AMS system.

Variable aging and storage of dissolved black carbon in the ocean

During wildfires and fossil fuel combustion, biomass is converted to black carbon (BC) via incomplete combustion. BC enters the ocean by rivers and atmospheric deposition contributing to the marine dissolved organic carbon (DOC) pool. The fate of BC is considered to reside in the marine DOC pool, where the oldest BC 14C ages have been measured (>20,000 14C y), implying long-term storage. DOC is the largest exchangeable pool of organic carbon in the oceans, yet most DOC (>80%) remains molecularly uncharacterized. Here, we report 14C measurements on size-fractionated dissolved BC (DBC) obtained using benzene polycarboxylic acids as molecular tracers to constrain the sources and cycling of DBC and its contributions to refractory DOC (RDOC) in a site in the North Pacific Ocean. Our results reveal that the cycling of DBC is more dynamic and heterogeneous than previously believed though it does not comprise a single, uniformly "old" 14C age. Instead, both semilabile and refractory DBC components are distributed among size fractions of DOC. We report that DBC cycles within DOC as a component of RDOC, exhibiting turnover in the ocean on millennia timescales. DBC within the low-molecular-weight DOC pool is large, environmentally persistent and constitutes the size fraction that is responsible for long-term DBC storage. We speculate that sea surface processes, including bacterial remineralization (via the coupling of photooxidation of surface DBC and bacterial co-metabolism), sorption onto sinking particles and surface photochemical oxidation, modify DBC composition and turnover, ultimately controlling the fate of DBC and RDOC in the ocean.

Spatial Variation in Transit Time Distributions of Groundwater Discharge to a Stream Overlying the Northern High Plains Aquifer, Nebraska, USA

AbstractGroundwater transit time distributions (TTDs) describe the spectrum of flow‐weighted apparent ages of groundwater from aquifer recharge to discharge. Regional‐scale TTDs in stream baseflow are often estimated from numerical models with limited calibration from groundwater sampling and suggest much younger groundwater discharge than has been observed by discrete age‐dating techniques. We investigate both local and regional‐scale groundwater TTDs in the Upper Middle Loup watershed (5,440 km2) overlying the High Plains Aquifer in the Nebraska Sand Hills, USA. We determined flow‐weighted apparent ages of groundwater discharging through the streambed at 88 discrete points along a 99 km groundwater‐dominated stream segment using 3H, noble gases, 14C, and groundwater flux measurements at the point‐scale (<7.6 cm diameter). Points were organized in transects across the stream width (3–10 points per transect) and transects were clustered in five sampling areas (10–610 m in stream length) located at increasing distances along the stream. Groundwater apparent ages ranged from 0 to 8,200 years and the mean groundwater transit time along the 99 km stream is >3,000 years. TTDs from upstream sampling areas were best fit by distributions with a narrow range of apparent ages, but when older groundwater from downstream sampling areas is included, the regional TTD is scale dependent and the distribution is better described by a gamma model (α ≈ 0.4) which accommodates large fractions of millennial‐aged groundwater. Observations indicate: (a) TTDs can exhibit spatial variability within a watershed and (b) watersheds can discharge larger fractions of old groundwater (>1,000 years) than commonly assumed.

Sources and high burial efficiency of fossil organic carbon in small bays and implication for coastal carbon cycle

Coastal seas receive and store large amounts of organic carbon (OC) from land and ocean, thereby playing a crucial role in the global carbon cycle. Understanding factors that influencing OC sources and burial efficiencies in coastal areas have been challenging. We selected the Jiaozhou Bay (JZB) and its surrounding rivers heavily affected by human activities as a case study small bay. We presented bulk parameters of grain size, sediment surface area (SSA), TOC content and carbon isotopes (δ13Corg and Δ14Corg), terrestrial biomarkers (∑C27 + C29 + C31n-alkanes) and marine biomarkers (brassicasterol and dinosterol) in surface sediments and suspended particulates. Our results showed low TOC and biomarker contents in the Dagu River Estuary from the west of the JZB associated with coarse sediments and lower SSA. To estimate the OC proportions, we applied a three-end member mixing model based on TOC δ13Corg and biomarker ratios and obtained the OC contribution from phytoplankton (average 52 %), soil (average 34 %) and wetlands (average 14 %). A transect from east to west of the JZB was selected to further assess the OC age composition based on radiocarbon isotopic (14C) measurements for a new perspective. The lower Δ14Corg values in the east revealed fossil OC contributions from human activities, such as petroleum pollutant inputs from sewage outlets. Based on a dual‑carbon isotope (δ13Corg and Δ14Corg) mass balance mixing model, the OC contributions were 40 %, 34 %, 14 %, 12 % from fossil carbon, phytoplankton, wetlands and soil, respectively. The very high burial efficiency of fossil OC in JZB (111 ± 19 %) indicated that small bays such as the JZB could be an important sedimentary carbon sink.

Atmospheric Δ14C in the northern and southern hemispheres over the past two millennia: Role of production rate, southern hemisphere westerly winds and ocean circulation changes

The variations of atmospheric Δ14C over the past two millennia are classically attributed to changes in its production rate in the upper atmosphere, which in turn is related to changes in solar activity and the Earth's magnetic field. However, the potential contribution of atmospheric and oceanic circulation changes during this period has not been precisely quantified. This has been achieved here using a coupled climate model simulating explicitly the evolution of the different carbon isotopes, driven by a new estimate of 14C production derived from 10Be measurements, and using different production rates for each hemisphere. Our results confirm that changes in global and hemispheric atmospheric Δ14C are primarily driven by changes in production rate. The very good agreement between our results and observed atmospheric Δ14C also highlights the strong consistency of current interpretations of 10Be and 14C measurements. By contrast, the interhemispheric difference in atmospheric Δ14C is controlled by changes in the intensity of southern hemisphere westerly winds (SHWW) that impact atmosphere-ocean exchange and the upwelling of 14C depleted water masses in the Southern Ocean. Changes in deep water formation in both hemispheres or open ocean polynyas in the Southern Ocean only have a small impact on atmospheric Δ14C over that period. When driven by changes in the SHWW proportional to three existing reconstructions of the Southern Annular Mode (SAM) index, the model reproduces some key characteristics of the observed interhemispheric Δ14C gradient. These include the low values in the 15th century and the peak in the 16th century, but there are also clear differences between the experiments and Δ14C observations. This suggests that while SAM reconstructions capture some robust features in the centennial variability, large uncertainties remain.

Development and applications of accelerator mass spectrometry methods for measurement of 14C, 10Be and 26Al in the CENTA laboratory

Terrestrial and extraterrestrial radioisotope research has been strongly dependent on the development of analytical methods which would enable to trace radioisotopes at low concentrations in subgram samples (e.g., in tree rings, ice cores, meteorites, etc.). Accelerator mass spectrometry (AMS) has become the most sensitive technique for ultralow-level analysis of long-lived radioisotopes, such as 14C, 10Be and 26Al. We review developments and applications carried out in the CENTA laboratory, and describe a recently installed fully equipped AMS line, designed for analysis of long-lived radioisotopes from tritium to curium.

Contribution of fossil and biomass-derived secondary organic carbon to winter water-soluble organic aerosols in Delhi, India

Delhi, among the world's most polluted megacities, is a hotspot of particulate matter emissions, with high contribution from organic aerosol (OA), affecting health and climate in the entire northern India. While the primary organic aerosol (POA) sources can be effectively identified, an incomplete source apportionment of secondary organic aerosol (SOA) causes significant ambiguity in the management of air quality and the assessment of climate change. Present study uses positive matrix factorization analysis on the water-soluble organic aerosol (WSOA) data from the offline-aerosol mass spectrometry (AMS). It revealed POA as the dominant source of WSOA, with biomass-burning OA (31–34 %) and solid fuel combustion OA (∼21 %) being two major contributors. Here we use water-solubility fingerprints to track the SOA precursors, such as oxalates or organic nitrates, instead of identifying them based on their O:C ratio. Non-fossil precursors dominate in more oxidized oxygenated organic carbon (MO-OOC) (∼90 %), a proxy for aged secondary organic carbon (SOC), by coupling offline-AMS with 14C measurements. On the contrary, the oxidation of fossil fuel emissions produces a large quantity of fresh fossil SOC, which accounts for ∼75 % of less oxidized oxygenated organic carbon (LO-OOC). Our study reveals that apart from major POA contributions, large fractions of fossil (10–14 %) and biomass-derived SOA (23–30 %) contribute significantly to the total WSOA load, having impact on climate and air quality of the Delhi megacity. Our study reveals that large-scale unregulated biomass burning was not only found to dominate in POA but was also observed to be a significant contributor to SOA with implications on human health, highlighting the need for effective control strategies.

Determination of carbon-14 in marine biota using oxidation combustion and gel suspension liquid scintillation counting

In this study, we report a new analytical method for determination of 14C in marine biota utilizing oxidation combustion separation combined with CaCO3 suspension of precipitates for liquid scintillation counting (LSC). The main factors affecting the oxidation combustion efficiency of tube combustion furnace and the counting efficiency of the LSC were systematically investigated and optimized. Under the optimal combustion conditions, the combustion recovery of carbon ranged from 85.6 % to 92.4 % for five marine samples. And the method achieved a detection limit of 0.13 Bq/g for 14C and repeatability of 3.9–9.1 %. The analytical turnover time was 6 h, and up to six samples could be processed simultaneously. Assessment of uncertainty components showed that the uncertainty in counting was the largest contributor, followed by combustion recovery and counting efficiency. The developed method enables reliable measurement of 14C in marine biota, providing valuable analytical tool for risk assessment purposes.

ACHIEVING LOW BACKGROUNDS DURING COMPOUND-SPECIFIC HYDROXYPROLINE DATING: HPLC COLUMN EFFECTS

ABSTRACT Accelerator mass spectrometry (AMS) radiocarbon (14C) dating is central to the development of robust chronologies in archaeological and paleoenvironmental contexts spanning the last 50,000 years. For dates to be accurate, samples must be free of exogenous carbon contamination. At the Oxford Radiocarbon Accelerator Unit (ORAU), considerable advancements in the dating of bone collagen have been made through the development of a high performance liquid chromatography (HPLC) method for the dating of the amino acid hydroxyproline, which can mitigate the effects of carbon contamination. However, recent changes in ligand manufacturing methods for the mixed-mode column used in the ORAU protocol (Primesep A, SIELC Technologies; IL, USA) have resulted in unacceptably high analytical backgrounds. Prior to the manufacturing change, backgrounds of > 50k BP were achievable. Since the manufacturing change, a mean background of 32.5k BP has been measured. Due to column bleed, the Primesep A is therefore no longer suitable for 14C measurement of hydroxyproline from older material. Here, we present background data and the chromatography conditions used to isolate hydroxyproline using an alternative column, a preparative-scale Newcrom AH, which shows promising potential as an alternative for the routine isolation and AMS dating of hydroxyproline—especially approaching the age and mass limits of the method.

Making the case for an International Decade of Radiocarbon.

Radiocarbon (14C) is a critical tool for understanding the global carbon cycle. During the Anthropocene, two new processes influenced 14C in atmospheric, land and ocean carbon reservoirs. First, 14C-free carbon derived from fossil fuel burning has diluted 14C, at rates that have accelerated with time. Second, 'bomb' 14C produced by atmospheric nuclear weapon tests in the mid-twentieth century provided a global isotope tracer that is used to constrain rates of air-sea gas exchange, carbon turnover, large-scale atmospheric and ocean transport, and other key C cycle processes. As we write, the 14C/12C ratio of atmospheric CO2 is dropping below pre-industrial levels, and the rate of decline in the future will depend on global fossil fuel use and net exchange of bomb 14C between the atmosphere, ocean and land. This milestone coincides with a rapid increase in 14C measurement capacity worldwide. Leveraging future 14C measurements to understand processes and test models requires coordinated international effort-a 'decade of radiocarbon' with multiple goals: (i) filling observational gaps using archives, (ii) building and sustaining observation networks to increase measurement density across carbon reservoirs, (iii) developing databases, synthesis and modelling tools and (iv) establishing metrics for identifying and verifying changes in carbon sources and sinks. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

A NEW RAMPED OXIDATION-14C ANALYSIS FACILITY AT THE NEIF RADIOCARBON LABORATORY, EAST KILBRIDE, UK

ABSTRACTSample materials such as sediments and soils contain complex mixtures of different carbon-containing compounds. These bulk samples can be split into individual fractions, based on the temperature of thermal decomposition of their components. When coupled with radiocarbon (14C) measurement of the isolated fractions, this approach offers the advantage of directly investigating the residence time, turnover time, source, or age of the different components within a mixed sample, providing important insights to better understand the cycling of carbon in the environment. Several laboratories have previously reported different approaches to separate radiocarbon samples based on temperature in what is a growing area of interest within the research community. Here, we report the design and operation of a new ramped oxidation facility for separation of sample carbon on the basis of thermal resistance at the NEIF Radiocarbon Laboratory in East Kilbride, UK. Our new instrumentation shares some characteristics with the previously-reported systems applying ramped oxidation and/or ramped pyrolysis for radiocarbon measurement, but also has several differences which we describe and discuss. We also present the results of a thorough program of testing of the new system, which demonstrates both the reproducibility of the thermograms generated during sample combustion, and the reliability of the radiocarbon measurements obtained on individual sample fractions. This is achieved through quantification of the radiocarbon background and analysis of multiple standards of known 14C content during standard operation of the instrumentation.