Accelerator Mass Spectrometry Research Articles

Palaeoclimatic shifts in the Central Ganga Basin during the Middle- to Late Holocene: Exploring the 4.2 ka arid event and its implications in northern India

The Central Ganga Basin is one of the most densely populated regions of India. It is agriculturally diverse and contributes much to the Indian economy. The region has housed numerous ancient and mediaeval empires. This study presents a continuous record of the paleomonsoon from the Chandrika Devi lake, Lucknow district of Uttar Pradesh, India which is linked with paleo vegetational shifts over the last ~6000 years (5871–75 cal yr BP). The chronology of the lake core is based on three accelerated mass spectrometry (AMS) radiocarbon and two Optically Stimulated Luminescence (OSL) dates. The multiproxy data (grain size, major and trace element ratio, total organic carbon (TOC wt%), carbon isotopes (δ13Corg‰) and pollen), suggest that the lake was initially a part of the Gomti river that began to transform into a lake at ~5000 cal yr BP with weakening of the Indian summer monsoon (ISM) in the Central Ganga Basin. The lake formation was completed at ~4100 cal yr BP under the influence of the 4.2 ka arid event. This phase marks the beginning of human presence as well as agricultural activities in the lake region with the appearance of Cerealia pollen and other agricultural taxa. The agricultural activity surrounding the lake catchment peaked at ~3000 cal yr BP. The lake gradually shrank and became a marshy lowland at ~75 cal yr BP. Our study is significant because it is the first comprehensive multiproxy study from the Lucknow region in the Central Ganga Basin on paleomonsoonal variability and its relationship to human activity, agricultural practices during the Late-Holocene with a focus on the 4.2 Ka arid event. Also, pollen record suggests that the changes in agriculture and human activity began just after 4.2 ka arid event in the study area.

The Metabolism and Disposition of Brepocitinib in Humans and Characterization of the Formation Mechanism of an Aminopyridine Metabolite.

<s><s></s></s> Brepocitinib is an oral once-daily Janus kinase 1 and Tyrosine kinase 2 selective inhibitor currently in development for the treatment of several autoimmune disorders. Mass balance and metabolic profiles were determined using accelerator mass spectrometry in six healthy male participants following a single oral 60 mg dose of 14C-brepocitinib (~300 nCi). The average mass balance recovery was 96.7% {plus minus} 6.3% with the majority of dose (88.0% {plus minus} 8.0%) recovered in urine and 8.7% {plus minus} 2.1% of the dose in recovered in feces. Absorption of brepocitinib was rapid, with maximal plasma concentrations of total radioactivity and brepocitinib achieved within 0.5 hours after dosing. Circulating radioactivity consisted primarily of brepocitinib (47.8%) and metabolite M1 (37.1%) derived from hydroxylation at the C5' position of the pyrazole ring. Fractional contributions to metabolism via cytochrome P450 (CYP) enzymes were determined to be 0.77 for CYP3A4/5 and 0.14 for CYP1A2 based on phenotyping studies in HLM. However, additional clinical studies are required to understand the potential contribution of CYP1A1. Approximately 83% of the dose was eliminated as N-methylpyrazolyl oxidative metabolites, with 52.1% of the dose excreted as M1 alone. Notably, M1 was not observed as a circulating metabolite in earlier metabolic profiling of human plasma from a multiple ascending study with unlabeled brepocitinib. Mechanistic studies revealed M1 was highly unstable in human plasma and phosphate buffer, undergoing chemical oxidation leading to loss of the 5-hydroxy-1-methylpyrazole moiety and formation of aminopyrimidine cleavage product M2. Time dependent inhibition and trapping studies with M1 yielded insights into the mechanism of this unusual and unexpected instability. Significance Statement This work describes the mass balance and metabolic profile of brepocitinib in human, a JAK1/TYK2 inhibitor being developed for treatment of autoimmune diseases.

Magnetic Response to the Source‐To‐Sink Environmental Changes in the Bay of Bengal Since ∼60 ka

AbstractThe terrestrial magnetic minerals of marine sediments are utilized to track the climatic changes in the source area and the dynamic characteristics of sedimentation processes. However, due to the varied source‐to‐sink environments, the magnetic response to ambient climate cannot be generalized. Here, we conducted systematic environmental magnetic analyses on core CJ04‐50 from the Ninetyeast Ridge and investigated its magnetic response to source‐to‐sink environmental changes. Core CJ04‐50 covers the last 60 Kyr based on accelerator mass spectrometry (AMS) 14C dating and the relative paleointensity (RPI) record. Rare earth element (REE) results suggest that the terrestrial materials are fed by the Ganges‐Brahmaputra (G‐B) and Irrawaddy/Indo‐Burma Ranges. High/low magnetic mineral content corresponds to strong/weak terristrial input during the cold/warm period. This pattern differs from that in the East Asian marginal seas, which have a high magnetic mineral content in warm periods. It might be attributed to the heavier Indian summer monsoon (ISM) precipitation than that of East Asian summer monsoon. Excessive moisture (&gt;1,500 mm/year) would not favor the formation and preservation of magnetic minerals in the source area during interglacials. By contrast, the enhanced physical weathering during glacials results in more magnetic contributions. A significant local magnetite dissolution occurred at the layer of Middle MIS 3, which may be caused by the non‐steady state diagenesis following deposition.

Late Holocene decoupling of lake and vegetation ecosystem in response to centennial-millennial climatic changes in arid Central Asia: A case study from Aibi Lake of western Junggar Basin

Central Asian lakes are crucial for sustaining fragile oasis ecosystems in arid regions. Understanding the response of ecosystems in these lake basins to climate change is essential for predicting future variations in these ecosystems. Aibi Lake is a notable terminal lake in arid Central Asia. In this study, a 95 cm lacustrine sediment core was drilled from Aibi Lake to investigate the response of lacustrine and terrestrial ecosystems in the lake basin to climate change over the past 3200 years. Accelerator mass spectrometry (AMS) 14C dating and multi-proxy analyses of diatoms, pollen, grain size, total organic content (TOC), total nitrogen (TN), and total hydrogen (TH) are applied to the sediment core. The grain size and geochemical results show that the lake experienced elevated levels and improved productivity and nutrition during the periods of 708–181 BCE, 0–740 CE, and 1428–1900 CE. The periods align with the Roman Warm Period, Dark Age Cold Period, and Little Ice Age, respectively. For the past 3200 years, benthic diatoms have consistently been the dominant species in the lake. During the climatic transition periods of the Dark Age Cold Period, Medieval Warm Period, and Little Ice Age, there were significant changes in the abundance and survival of certain species of diatoms. Specifically, the halophilic species (Nitzschia dissipata and Nitzschia hungarica), basophilic species (Synedra acus), and the nutrition level-relevant species (Navicula menisculus) experienced notable shifts. These changes ultimately resulted in a noticeable alteration in the structure and function of the diatom community. Over the past 3200 years, the lake ecosystem has undergone three noticeable regime shifts. In contrast, the vegetation in the lake catchment has remained relatively stable, primarily consisting of desert steppe. These results suggest that aquatic ecosystems in arid central Asia are more susceptible and exhibit more rapid responses to climate change compared to terrestrial vegetation.

A microCT assessment of archaeological parenchyma from three riverine shell middens dating to the early Holocene, Yongjiang River Basin, Guangxi, southern China

Archaeobotanical investigations at three riverine shell midden sites dating to the early Holocene – Baozitou, Shichuantou and Nabeizui – in the Yongjiang River Basin, Guangxi, southern China have identified charred fragments of archaeological parenchyma. A subset of the archaeological parenchyma was assessed using X-ray micro-computed tomography (microCT), which enabled virtual histological examination of the interior of parenchyma fragments. The microCT scanning identified a fragment of lotus root (Nelumbo nucifera), a possible immature fig fruit (poss. Ficus sp.), cooked food fragments, and less diagnostic elements, some of which derive from underground storage organs (USOs), including a bud/bulb and potentially an aroid. The fragment of lotus root from Nabeizui was directly radiocarbon dated using Accelerator Mass Spectrometry to 8770–8544 cal BP. A new AMS radiocarbon chronology based on Canarium nutshells for the three sites indicates that they were all used during the early Holocene. These findings contribute to the understanding of broad spectrum plant use by hunter-gatherer-fisher communities in southern China during the early Holocene, as well as showing the potential of microCT imaging for the analysis of archaeological parenchyma from this region.

Flood events in the lower reaches of the Yellow River: OSL and radiocarbon dating on the Anshang site

The lower reaches of the Yellow River have witnessed numerous episodes of flooding and considerable shifts in its course. Examining flood records within the Yellow River basin offers invaluable insights into ancient human settlements, agricultural practices, trade routes, and technological advancements of ancient Chinese civilizations. However, dating these fluvial sediments poses a considerable challenge due to either the scarcity of organic material for radiocarbon (14C) dating or the potential incomplete bleaching of sediments for optically stimulated luminescence (OSL) techniques. This study focused on the Anshang site located in Henan Province, we obtained OSL ages from distinct grain size fractions of quartz and cross-verified them with independent acceleration mass spectrometry (AMS) 14C ages. The findings revealed that both coarse quartz grains (CG) and medium quartz grains (MG) underwent complete bleaching in silt-dominated flood deposits and shallow lacustrine deposits. Conversely, the OSL ages of CG and MG quartz were notably overestimated by approximately 3–6 ka in silty clay-dominated flood deposits. Upon comparing the OSL ages with AMS 14C ages, it was evident that bulk organic matter AMS 14C ages aligned with CG OSL ages in shallow lacustrine deposits, but they appeared older than CG OSL ages in flood deposits. However, the AMS 14C ages from plant demonstrated good consistency. Consequently, we successfully identified flood-lacustrine sediments dating back to approximately ∼13 ka, ∼8–3 ka, ∼2.6 ka, ∼1 ka, and the last few hundred years, aligning well with historical documentation and earlier research. The regional evidence presented herein enhances our understanding of the applicability of OSL dating and AMS 14C dating in fluvial-lacustrine sediments. Armed with these new ages, we constructed a reference chronology for archaeological localities situated in the fluvial sediments of the lower reaches of the Yellow River.

MONITORING OF MODERN CARBON FRACTION IN DISPOSABLE PACKAGING

ABSTRACT Radiocarbon (14C) methodology was used to investigate the presence of biocarbon in different bio-based disposable packaging products. Packaging waste contributes to a municipal solid waste, which is increasing environmental concerns and resulting in the enhancement of EU regulations that aim to reduce packaging waste. The 14C amount in samples reflects how much of the biocarbon has been used. In this study, the concentration of 14C was determined in commonly used types of disposable packaging, such as cups, plates, straws, cutlery, and baking paper. Samples were made of materials such as paper, wheat bran, sugarcane, and wood. The mean concentration of the 14C isotope, measured by the accelerator mass spectrometry (AMS) technique, is greater than 100 pMC in all tested samples, indicating that the samples are modern. The relatively high 14C concentration values in the waterproof layer of the sample indicate that bioplastic, rather than plastic, was used in its production. The highest 14C isotope concentration values were measured for samples that used the oldest biomass (wood and paper), and the lowest for products from current crops (sugarcane and wheat bran), which is consistent with the trend of changes in 14C concentration in the biosphere. The study also addresses the problem of heterogeneity and representativeness of subsamples.

Development and carbon accumulation dynamics of a minerotrophic fen during the last millennium, northeast China

Peatlands are terrestrial ecosystems with high carbon sequestration efficiency, providing critical feedback on climate change. It is crucial to understand how peatland development and carbon accumulation respond to various factors to reveal the future direction of carbon reservoirs under changing climatic conditions. To assess the impact of climate and hydrological conditions on the development and carbon accumulation of peatlands, 15 peat core samples were analyzed to examine the processes of lateral expansion in the Dongfanghong (DFH) peatland, a minerotrophic fen located in the Changbai Mountains of northeast China. Accelerator Mass Spectrometry 14C, total organic carbon, dry bulk density, testate amoebae, δ13C of α-cellulose in Carex spp. and plant macrofossil analyses were conducted on a high-resolution peat core. The proxies were used to calculate carbon accumulation rate (CAR) and reconstruct water table depth as well as surface moisture and vegetation development of the DFH peatland. Our findings indicated that the DFH peatland was initiated at 1011 cal. CE and experienced paludification during the last millennium. The expansion of the DFH peatland was primarily determined by hydrological conditions rather than climatic factors such as total solar irradiance and regional temperature. The rapid expansion between 1500 and 1700 cal. CE was likely resulted from relatively low precipitation and a decrease in water table/surface moisture. CAR generally correlated with total solar irradiance, regional temperature, and precipitation, suggesting that climate may be crucial for CAR in DFH peatlands over multi-centennial timescales. However, the increased CAR under relatively dry conditions suggested that the CAR were regulated by hydrological conditions over a centennial timescale. This study highlighted the important roles of climate and hydrological conditions in the lateral expansion and CAR of the peatland in minerotrophic fen and that there may be a threshold for hydrology during the process of peatland development and carbon accumulation.

RETREATMENT OF BONE MATERIAL IN THE GLIWICE RADIOCARBON LABORATORY USING ULTRAFILTRATION

ABSTRACT Preparation of bones for radiocarbon (14C) dating is still quite a challenge for researchers. The methods are being tested and improved, to increase reliability of dating results and to verify the previous ones. In this work, a set of gelatine samples, extracted from Cervus elaphus and Cervus canadensis bones from various sites in Europe and a set of human bones from archaeological sites in Poland were subjected to retreatment using ultrafiltration in Gliwice Radiocarbon Laboratory. The tested samples represent a wide range of ages, from older than 40,000 14C years BP to modern. The prepared material was subjected to the measurement of C/N atomic ratios and 14C dating using the accelerator mass spectrometry (AMS) technique. Also, the stable isotopes (δ13C and δ15N) values were determined. In a few cases ultrafiltration allows to improve gelatine quality for long-stored samples, by increasing the %C and %N as well as decreasing C/Nat ratios. Nevertheless, this effect was not observed for majority of the samples. Remeasurements of long-term stored samples give mostly the same 14C ages for ultrafiltered ones and for those without ultrafiltration.

Effects of long-term application of inorganic fertilizers and organic amendments on the turnover rates of fractionated soil organic carbon and their determining factors in paddy fields

ABSTRACT To investigate how the long-term application of inorganic fertilizer and organic amendments affects the turnover rates of organic matter in physico-chemically fractionated components in paddy soils and how their rates are related to their amounts, we studied the effect of variable management of inorganic fertilizer and organic amendments for > 50 years on the ∆14C values of accumulated soil organic carbon (SOC) in fractionated components of 5 soil samples from three paddy fields. SOC was fractionated into four components based on their physico-chemical properties: (1) light fraction (LF) derived from plant residues, (2) heavy fraction (HF) containing stable aggregates, (3) oxidizable fraction (OxF) and (4) non-oxidizable fraction (NOxF) forming organo-mineral complexes with fine-textured minerals. The ∆14C values were determined by accelerator mass spectrometry using graphitized samples. The ∆14C values of SOC in NOxF (from −305‰ to − 90.5‰) were much lower than those of HF (from −123‰ to − 3.7‰) and OxF (from −215‰ to 21.0‰). Lowest values for NOxF suggested slowest turnover rates as expected, and higher and comparable values for OxF and HF implied much faster turnover rates of SOC in OxF compared with upland soils. This could be one of the characteristics of SOC dynamics in paddy soils, probably reflecting repeated puddling of plow layer soils. ∆14C values in all the fractions increased in response to the application of inorganic fertilizer and organic amendments, suggesting faster turnover rate. Soils with clayey and weathered characteristics had the lowest ∆14C values, or slowest turnover rates among the study fields. The relationship between the ∆14C value and the amount of accumulated C for HF, OxF and NOxF indicated that the more the SOC accumulated, the faster the turnover rate of the SOC was, regardless of the fractions, and the relationship of the HF was considerably different from those of OxF and NOxF. In conclusion, these results can be the basis for understanding the C dynamics and for improving soil fertility status and soil C sequestration in paddy soils.

CHRONOLOGICAL STUDY OF COLLECTIVE BURIALS IN THE NORTHERN IBERIAN PLATEAU: ANALYSIS OF RADIOCARBON DATES ON HUMAN BONES FROM THE MEGALITHIC COMPLEX OF LA LORA (BURGOS, SPAIN)

ABSTRACT This paper offers a temporal analysis of the megalithic group of La Lora in the context of northern Iberian Plateau megalithism. For this purpose, 67 accelerator mass spectrometry radiocarbon (AMS 14C) dates were obtained on human bone from the minimum number of individuals recovered from nine tombs. This is the first systematic dating project carried out in this dolmen group and has enabled the chronology of the main funerary series to be updated. The results reveal that the actual funerary use dates mainly to the 4th millennium BC, although, as deduced from the archaeological material, some tombs were reused in later periods. Additionally, the significant architectural polymorphism of the group, consisting mainly of simple dolmens and large corridor tombs, suggested a temporal evolution to monumentality. However, the dating shows a more complex reality, since it is likely that the large tombs functioned as funerary pantheons during the 4th millennium BC, characterized by a cyclical and recurrent use. In contrast, the simpler structures were preferred to be of shorter use and restricted to the first half of the 4th millennium.

Accelerator mass spectrometry measurements of 233U in groundwater, soil and vegetation at a legacy radioactive waste site

Low-level radioactive wastes were disposed at the Little Forest Legacy Site (LFLS) near Sydney, Australia between 1960 and 1968. According to the disposal records, 233U contributes a significant portion of the inventory of actinide activity buried in the LFLS trenches. Although the presence of 233U in environmental samples from LFLS has been previously inferred from alpha-spectrometry measurements, it has been difficult to quantify because the 233U and 234U α-peaks are superimposed. Therefore, the amounts of 233U in groundwaters, soils and vegetation from the vicinity of the LFLS were measured using accelerator mass spectrometry (AMS). The AMS results show the presence of 233U in numerous environmental samples, particularly those obtained within, and in the immediate vicinity of, the trenched area. There is evidence for dispersion of 233U in groundwater (possibly mobilised by co-disposed organic liquids), and the data also suggest other sources of 233U contamination in addition to the trench wastes. These may include leakages and spills from waste drums as well as waste burnings, which also occurred at the site. The AMS results confirm the historic information regarding disposal of 233U in the LFLS trenches. The AMS technique has been valuable to ascertain the distribution and environmental behaviour of 233U at the LFLS and the results demonstrate the applicability of AMS for evaluating contamination of 233U at other radioactive waste sites.

Case studies of three geological archives for rare radionuclide measurements using accelerator mass spectrometry

Long-lived radionuclides in our environment provide important information on natural and anthropogenic processes. Their presence and concentration reflect the balance of production and decay. Geological archives store such information and the nuclides can be chemically extracted from the bulk sample. Accelerator mass spectrometry (AMS) represents a sensitive method to quantify those nuclides at natural levels. Three different terrestrial archives are discussed here as examples for radionuclide extraction using various chemical separation methods for subsequent AMS measurements. We focus on sample preparation for the cosmogenic radionuclides 10Be and 26Al, various anthropogenic actinide isotopes such as U, Pu, and Am as well as the astrophysically interesting nuclides 41Ca, 53Mn, and 60Fe. The processed materials cover samples with masses between a few mg and up to a few hundred kg and protocols are presented for the quantitative extraction of some 10,000 atoms of cosmogenic or interstellar origin per sample and even as low as a few hundred actinide atoms.

Radiocarbon dates from Curaçao’s oldest Archaic site extend earliest island settlement to ca. 5700 cal BP

Due to its proximity to coastal South America and settlement during the early phase of insular Caribbean occupation, Curaçao’s archaeological record offers potential evidence for early overwater exploration and regional interaction. Here, we report new accelerator mass spectrometry (AMS) dates on charcoal from C-1426 at Saliña Sint Marie, an Archaic rockshelter site that extends Curaçao’s occupation back to 5735–5600 cal BP, some 290–850 years earlier than the established settlement chronology. This finding makes the C-1426 rockshelter Curaçao’s earliest known archaeological site and among the oldest in the insular Caribbean. We describe the site and the archaeological context of dating and conclude by considering the implications of Curaçao’s revised occupation chronology for initial Caribbean settlement.

Temporal variation and pollution status of heavy metals in core sediments from Jiangsu intertidal area, China

Eight heavy metal concentrations were analyzed from a 60.35-m-long sediment core in the Jiangsu intertidal area, China. Based on the lithofacies characteristics, mean grain size, downcore distributions of elements, and accelerator mass spectrometry (AMS) 14C and optically stimulated luminescence (OSL) data, the sediments in the core were divided into three units that formed during marine isotope stages 4 (MIS 4), MIS 3, and MIS 1. Except for Cd, all the other heavy metals had the lowest average concentrations in U3, which formed during MIS 4 with the coarsest sediment, representing a fluvial deposit. Most of the heavy metals were positively correlated with Al, Fe, and the total organic carbon (TOC), indicating these metals had the same sources. Pearson's correlation coefficient, enrichment factor, geoaccumulation index, and principal component analysis suggested that there was no element enrichment or contamination in the core sediments and that all heavy metals were naturally sourced.

Understanding the pharmacokinetic journey of Fc-fusion protein, rhIL-7-hyFc using complementary approach of two analytical methods, accelerator mass spectrometry and ELISA.

Antibody-based therapeutics (ABTs), including monoclonal/polyclonal antibodies and fragment crystallizable region (Fc)-fusion proteins, are increasingly used in disease treatment, driving the global market growth. Understanding the pharmacokinetic (PK) properties of ABTs is crucial for their clinical effectiveness. This study investigated the PK profile and tissue distribution of efineptakin alfa, a long-acting recombinant human interleukin-7 (rhIL-7-hyFc), using enzyme-linked immunosorbent assay (ELISA) and accelerator mass spectrometry (AMS). Totally, four rats were injected intramuscularly with 1mg/kg of rhIL-7-hyFc containing 14C-rhIL-7-hyFc, which was prepared via reductive methylation. Serum total radioactivity (TRA) and serum rhIL-7-hyFc concentrations were quantified using AMS and ELISA, respectively. The TRA concentrations in organs were determined by AMS. Serum TRA peaked at 10hours with a terminal half-life of 40hours. The rhIL-7-hyFc exhibited a mean peak concentration at around 17hours and a rapid elimination with a half-life of 12.3hours. Peak concentration and area under the curve of TRA were higher than those of rhIL-7-hyFc. Tissue distribution analysis showed an elevated TRA concentrations in lymph nodes, kidneys, and spleen, indicating rhIL-7-hyFc's affinity for these organs. The study also simulated the positions of 14C labeling in rhIL-7-hyFc, identifying specific residues in the fragment of rhIL-7 portion, and provided the explanation of distinct analytes targeted by each method. Combining ELISA and AMS provided advantages by offering sensitivity and specificity for quantification as well as enabling the identification of analyte forms. The integrated use of ELISA and AMS offers valuable insights for the development and optimization of ABT.

RADIOCARBON AND URANIUM PROFILES IN MARINE GASTROPODS AROUND THE JAPANESE ARCHIPELAGO

ABSTRACT In this study, we investigate the distribution of radiocarbon and uranium in the calcified opercula of Turbo sp. collected from Ryukyu region and Chiba, Japan, to explore the potential of U/Th dating using mollusks collected from the Japanese archipelago. We acquired high-resolution radiocarbon and uranium concentration measurements using single-stage accelerator mass spectrometry and laser ablation−inductively coupled plasma−mass spectrometry. Our results show that uranium in the opercula of modern Turbo sp. is unevenly distributed at concentrations 1000 times less than those in coral skeletons. Radiocarbon found in the calcified opercula samples record ambient seawater radiocarbon values as well as coral skeletons. Uranium in the calcified opercula of Holocene Turbo marmoratus were also unevenly distributed and concentrated within the opercula in a different manner than observed in modern samples, suggesting uranium exchange after death. Our results suggest variable uptake of uranium isotopes into mollusk shells and highlights the need for rigorous sample selection criteria when choosing mollusks species for U/Th dating around Japan.

A novel post-1950 CE atmospheric 14C record for the tropics using absolutely dated tree rings in the equatorial Amazon

In this study, we present a comprehensive atmospheric radiocarbon (14C) record spanning from 1940 to 2016, derived from 77 single tree rings of Cedrela odorata located in the Eastern Amazon Basin (EAB). This record, comprising 175 high-precision 14C measurements obtained through accelerator mass spectrometry (AMS), offers a detailed chronology of post-1950 CE (Common Era) 14C fluctuations in the Tropical Low-Pressure Belt (TLPB). To ensure accuracy and reliability, we included 14C-AMS results from intra-annual successive cuts of the tree rings associated to the calendar years 1962 and 1963 and conducted interlaboratory comparisons. In addition, 14C concentrations in 1962 and 1963 single-year cuts also allowed to verify tissue growth seasonality. The strategic location of the tree, just above the Amazon River and estuary areas, prevented the influence of local fossil-CO2 emissions from mining and trade activities in the Central Amazon Basin on the 14C record. Our findings reveal a notable increase in 14C from land-respired CO2 starting in the 1970s, a decade earlier than previously predicted, followed by a slight decrease after 2000, signaling a transition towards the fossil fuel era. This shift is likely attributed to changes in reservoir sources or global atmospheric dynamics. The EAB 14C record, when compared with a shorter record from Muna Island, Indonesia, highlights regional differences and contributes to a more nuanced understanding of global 14C variations at low latitudes. This study not only fills critical spatial gaps in existing 14C compilations but also aids in refining the demarcation of 14C variations over South America. The extended tree-ring 14C record from the EAB is pivotal for reevaluating global patterns, particularly in the context of the current global carbon budget, and underscores the importance of tropical regions in understanding carbon-climate feedbacks.

Separation of Lipoproteins for Quantitative Analysis of 14C-Labeled Lipid-Soluble Compounds by Accelerator Mass Spectrometry.

To date, 14C tracer studies using accelerator mass spectrometry (AMS) have not yet resolved lipid-soluble analytes into individual lipoprotein density subclasses. The objective of this work was to develop a reliable method for lipoprotein separation and quantitative recovery for biokinetic modeling purposes. The novel method developed provides the means for use of small volumes (10-200 µL) of frozen plasma as a starting material for continuous isopycnic lipoprotein separation within a carbon- and pH-stable analyte matrix, which, following post-separation fraction clean up, created samples suitable for highly accurate 14C/12C isotope ratio determinations by AMS. Manual aspiration achieved 99.2 ± 0.41% recovery of [5-14CH3]-(2R, 4'R, 8'R)-α-tocopherol contained within 25 µL plasma recovered in triacylglycerol rich lipoproteins (TRL = Chylomicrons + VLDL), LDL, HDL, and infranatant (INF) from each of 10 different sampling times for one male and one female subject, n = 20 total samples. Small sample volumes of previously frozen plasma and high analyte recoveries make this an attractive method for AMS studies using newer, smaller footprint AMS equipment to develop genuine tracer analyses of lipophilic nutrients or compounds in all human age ranges.

AMS 14C DATING AND STABLE ISOTOPE ANALYSIS ON AN 8-KYR OYSTER SHELL FROM TAIPEI BASIN: SEA LEVEL AND SST CHANGES

ABSTRACT Seven accelerator mass spectrometry radiocarbon (AMS 14C) dates (7260±106∼7607±95 BP averaged 7444±103 BP) on a giant oyster shell, collected from an ancient shore of the Taipei Basin, are similar to the LSC (liquid scintillation counting) 14C age (7260±46 BP) of a grass sample inside the shell. The calibrated 14C ages of the C. gigas by Marine20 are 7490±240∼7805±230 cal BP (average 7660±96 cal BP), generally agreed with the calibrated LSC 14C ages of the grass and the oyster shell. Combined with other 14C ages of shoreline samples in the Taipei Basin, it is evident that sea level rose from 8600 to 7600 cal BP and reached a stand higher than modern sea level. During this marine transgression, the sedimentation rate along the shoreline was very high because 14C dating was not able to detect age differences for 4–5 m thick sediment sequences. Sixty-nine analyses of δ18O and δ13C from the oldest part of the shell exhibit clear seasonal cycles, with a 4-year period of growth in the 5.5-cm section. According to the δ18O values, the ancient oyster grew in a warmer-than-present shoreline environment, suggesting that the current absence of the giant oyster in Taiwan is not due to warming conditions.