Deep-sea sediment mixing by bioturbation is ubiquitous on the seafloor, and it can be an important influence on the fidelity of paleoceanographic records. Bioturbation can be difficult to quantify, especially in the past, but diffusive models based on radioactive tracer profiles have provided a relatively successful approach. However, a singular, constant mixing regime is unlikely to prevail in a region where dynamic oceanographic changes in the bottom water environment are a consequence of paleoclimatic variability. In this study, foraminiferal stable isotopes, radiocarbon (14C) dating, and 230Th fluxes are utilized to understand the sediment mixing history in the easternmost region of the North Pacific. In the uppermost sediment, a 12,000-yr offset between planktonic foraminifera species N. incompta and G. bulloides is observed that coincides with age plateaus at 2000–2500 yr for N. incompta and 15,000–16,000 yr for G. bulloides despite coincident glacial-interglacial shifts in δ18O of benthic species. These age plateaus, particularly for G. bulloides, are a result of changing foraminiferal abundance related to assemblage shifts and carbonate preservation changes since the last glacial period, providing a window into the extent of mixing in the past. The 14C and stable isotope results can be simulated using an iterative model that couples these changes in foraminiferal abundance with variability in mixing depth over time. The best-fit model output suggests that the deepest, or most intense, mixing of the past 30,000 yr (30 kyr) may have occurred during the Holocene. Even though changes in mixing affect the 14C and δ18O of planktonic species that have dramatically varying abundance, substantial age control is nevertheless provided by δ18O measurements on the more consistently abundant benthic foraminifera Uvigerina, thus allowing the construction of a reliable chronology for these cores.

Organic material and a few tree trunks have been recovered from the shrinking ice deposits of Velebit Mountain, Croatia. Ten radiocarbon (14C) dates, seven new measurements and three recalibrated ones, from three cave ice deposits were evaluated. The new data argue for the preservation of a ~1000-yr-old deposit in the Kugina Ice Cave and a <500-yr-old accumulation in the Ledena Pit. A 14C age suggests that the ice in the lower section of Vukušić cave ice deposit is very likely older than 3500 yr. The work is in progress to verify this suggestion. Evaluation of the temporal distribution of the calibrated ages of the 14C-dated vegetal remains allowed constraining the accumulation and ablation history of cave ice in the northern and central Velebit. Periods lacking vegetal remains in these cave ice deposits (before the 11th century and in the 15th century) tend to match with similar patterns from other cave ice deposits from the Eastern Alps and the Swiss Jura Mountains, suggesting large-scale coherence regulating European cave ice mass balance changes over the past ~1200 yr.

Because the 14C calibration curves IntCal and SHCal are based on data from temperate latitudes, it remains unclear which curve is more suitable for archaeological and paleoenvironmental records from tropical South America. A review of climate dynamics reveals a significant influx of Northern Hemisphere air masses and moisture over a substantial part of the continent during the South American Summer Monsoon (SASM). Areas affected by the SASM receive unknown amounts of input from both hemispheres, where an argument could be made for either curve. Until localized tree-ring data can resolve this, we suggest using a mixed calibration curve, which accounts for inputs from both hemispheres, as a third calibration option. We present a calibration example from a crucial period of environmental and cultural change in the southern Lake Titicaca. Given our current lack of data on past ∆14C variation in South America, our calibrations and chronologies will likely change in the future. We hope this paper spurs new research into this topic and encourages researchers to make an informed and explicit choice of which curve to use, which is particularly relevant in research on past human–environmental relationships.

The Varna I cemetery, on the Bulgarian Black Sea coast, is one of the most remarkable sites in European prehistory, with the world’s earliest large-scale assemblage of gold artifacts. Modeling of the first series of 14 accelerator mass spectrometry (AMS) dates yielded a duration of occupation at the site of ca. 150 years, ~4600–4450 cal BC. However, there were insufficient paired human–animal dates for a full consideration of the question of the marine reservoir effect. Here, a fuller set of 71 dates from 53 graves is presented. We identify a small reservoir effect in a number of individuals based on 14C, as well as carbon and nitrogen stable isotopes. We test the effect of this by building a series of different Bayesian models. Our favored model, including a correction for some of the human determinations, shows activity at the cemetery starting at 4596–4516 cal BC and ending 4427–4341 cal BC (at 95.4% probability). The overall span of activity covers ~120–260 years (93.6% prob.). The modeling shows that Varna I falls toward the beginning of the Bulgarian Late Copper Age.

Biogeochemical analyses of eastern oysters (Crassostrea virginica) are frequently included in environmental monitoring and paleoecological studies because their shells and soft tissues record environmental and dietary signals. Carbon isotopes in the mineral phase of the shell are derived from ambient bicarbonate and dissolved inorganic carbon (DIC), while organic carbon present in soft tissue is of dietary origin. Mineral-bound organic matter within the carbonate shell matrix (“conchiolin”) is studied less frequently. The purpose of this study was to compare carbon isotope composition (δ13C and Δ14C) of conchiolin to those of shell carbonates and soft tissues in eastern oysters and assess the extent to which conchiolin can provide insight into paleoecological records. Eleven oyster specimens were live-collected from Apalachicola Bay, USA, as well as a set of environmental samples (water, sediment, and terrestrial plants). Overall, the δ13C values in all studied oyster tissue types record environmental signals related to carbon sources, with conchiolin being enriched in 13C by an average of 2.3‰ relative to bulk soft tissues. Δ14C values in oyster shell carbonates generally reflect the marine versus riverine source of DIC, while conchiolin Δ14C values are impacted by variable relative contributions of young and old organic matter. Environmental samples indicate a significantly large difference in Δ14C among sources, from –127‰ in particulate organic matter to approximately +15‰ in DIC. Conchiolin is significantly depleted in 14C relative to other tissue types, by as much as 56.6‰, posing a major obstacle to the use of conchiolin as an alternative material for radiocarbon dating.

The total 14C content and its partition between inorganic and organic species were measured on irradiated Zy-4 samples from a CANDU spent fuel rod transferred from Cernavoda Nuclear Power Plant (NPP). Long-term leaching tests and accelerated corrosion tests were carried out to measure the 14C release and corrosion rate, respectively, in chemical conditions relevant to cementitious environment. Experimentally measured 14C inventory was compared to the theoretically one predicted based on the irradiation history and impurity content of Zy-4 by means of ORIGEN computations. CANDU SF claddings have a 14C content of around 2 × 104 Bq/g of Zy-4, mainly as organic compounds (more than 99%). The total 14C content measured by acid dissolution/wet oxidation method is in good agreement with the value estimated by ORIGEN simulations for an average burn-up of 7 MWd/kgU. The total 14C released as dissolved species after 18 days and 18 months of Zy-4 immersing in alkaline solution are similar, indicating that a small amount of 14C was available as instant release fraction (0.05% from the initial 14C content) followed by a very low release rate that could not be measured by liquid scintillation counting. In alkaline conditions, 14C is released predominantly (∼70%) as soluble species, but also inorganic 14C was measured as gaseous species. From the soluble 14C released during leaching test, more than 60% was found to be as organic species. Generally, corrosion rates values ranging between 46 and 130 nm/yr were measured by the linear polarization resistance method. In addition, defects and cracks were observed on the oxide layer by scanning electron microscopy (SEM) investigation.

Ecse Mound is a burial mound in the Hortobágy region of eastern Hungary. Built by prehistoric nomadic peoples from the east, it now stands on the border between two modern settlements. The construction of the mound was assumed to be related to representatives of the Pit Grave Culture populating the area between the Late Copper and Bronze Ages. This theory considered similarities in shape, orientation, and stratigraphy of this mound with other absolute-dated ones in the Hortobágy region alone. The mound comprises two construction layers as indicated by magnetic susceptibility and on-site stratigraphic observations. According to detailed sedimentological, geochemical analyses of samples taken from the bedrock, artificial stratigraphic horizons, and the overlying topsoil, there is a marked similarity between the soil forming the body of the mound in both artificial horizons and the underlying bedrock soil. In contrast the pedological, geological character of the modern topsoil is utterly different. According to our dating results, the uppermost stratigraphic horizon is coeval with the absolute-dated mounds in the region, assigning it to the period of the Pit Grave Culture. However, the lower anthropological horizon is older and dates to between the Early and Late Copper Ages.

Recent multidisciplinary research indicates that prehistoric agriculture innovation promoted permanent human settlements of areas up to 3400 m above sea level (asl) in the northern Tibetan Plateau, but when and how ancient humans extensively occupied areas above that altitude remains uncertain. In this paper, we investigated 12 archaeological sites situated above 3600 m asl in the Yushu autonomous prefecture, east-central Tibetan Plateau, to explore this issue. We determined the ages of five sites using the radiocarbon (14C) dating method and identified animal bones sampled from three sites. The dating results show that humans occasionally occupied the Yushu area around 900 BC, and permanently inhabited the area between AD 540 and 1620. Preliminary faunal identifications indicate human-raised livestock including yak, sheep, and horse during the latter period. Stone-constructed tombs and rock painting were found at some investigated sites, suggesting humans perhaps engaged in a pastoral lifestyle during the very late Holocene in the high altitude Yushu area, where nomadic livestock production remains the current primary subsistence strategy focus.

Although radiocarbon accelerator mass spectrometry (14C AMS) surpasses conventional radiometric methods in many aspects, they still represent an interesting alternative, especially for studies unconstrained by sample size. Here we showed that the gas proportional counting technique can be used for bone samples, processed only by a simple ABA method, and ethanol, distilled from wine samples. The feasibility of the described methods was verified by successful dating of 11 well-preserved vertebrate bones of modern to 21 kyr BP age excavated from different caves in Slovakia from which collagen was also extracted, as well as by determination of 14C concentration in two modern western Slovakia vintages, which matches well the atmospheric Δ14C level for the respective region and grape vegetation period. Various empiric factors affecting the yield of the thoroughly tested procedures used for processing of samples and their optimization parameters are discussed as well.

The gas release and speciation of carbon species from irradiated and unirradiated Zircaloy-4 samples, representative for the fuel cladding as used in Belgian nuclear power plants, were studied in a saturated Ca(OH)2 solution in anaerobic conditions. This environment is relevant for the Belgian Supercontainer design, as perceived for the geological disposal of high-level nuclear waste. To achieve this, we performed simple immersion and potentiostatic corrosion tests. Potentiodynamic polarization curves, recorded prior to the potentiostatic tests, revealed that irradiation seems to induce changes on the Zircaloy-4 corrosion behavior, such as a shift of the corrosion potential. Potentiostatic corrosion tests on unirradiated Zircaloy-4 provided a corrosion rate of ~54 nm/yr over a 7 day-experiment, whilst a corrosion rate of only ~4 nm/yr was calculated for the irradiated sample. Gas chromatography revealed that during simple immersion tests, which lasted 195 days, hydrogen, methane, ethane, and CO2 were produced, with methane being the major compound. Assuming that all carbon released from the metal was transformed into gaseous compounds, this yields to a corrosion rate ranging from 57 to 84 nm/yr for the irradiated sample. However, caution has to be taken on these corrosion rate and more tests should be performed to confirm these results.

We evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation. Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield 176±40 kg C m−2 to 225±58 cm of peat depth. Estimated peat basal ages ranged from 5100 to 11,100 cal BP. The long-term apparent rate of carbon accumulation over the entire peat profile was 22±2 g C m−2 yr−1. Plot location within the study area did not affect carbon accumulation rates, but estimated basal ages were younger in profiles from plots closer to the bog lagg and farther from the bog outlet. In addition, carbon accumulation varied considerably over time. Early Holocene net carbon accumulation rates were 30±6 g C m−2 yr−1. Around 3300 calendar BP, net carbon accumulation rates dropped to 15±8 g C m−2 yr−1 until the last century when net accumulation rates increased again to 74±57 g C m−2 yr−1. During this period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate may reduce net carbon accumulation in peat in this and other southern boreal peatlands. Furthermore, our we caution against historical interpretations extrapolated from one or a few peat cores.

Radiometric dating of glacier ice is an essential tool where stratigraphic dating methods cannot be applied. This study focuses on Alpine glacier ice and presents a new sample preparation system for dating of glacier ice samples via radiocarbon (14C) dating of the microscopic particulate organic carbon (POC) fraction incorporated in the ice matrix. An adaptable, low-cost inline filtration-oxidation-unit (REFILOX) has been developed, which for the first time unifies all sample preparation steps from ice filtration to CO2 quantification in one closed setup. A systematic 14C investigation of modern European aerosol samples revealed that a POC combustion temperature of 340°C provides the best representation of the real sample age. A very low process blank of maximally 0.3±0.1 µgC now enables 14C dating of high Alpine ice samples, where POC concentrations are generally low (typically 10–50 µgC/kg), in an ice sample mass range of 300–500 g. In a first successful application, the method was used to obtain age constraints for an ice core from the cold, high Alpine firn saddle Colle Gnifetti (Switzerland). Analysis of the bottom ice core sections revealed a basal age of 4171–3923 cal yr BP but also a so far enigmatic discontinuity in the age-depth relationship.

Considering the impact of coastal dynamics on the radiocarbon (14C) marine reservoir effect (MRE), upwelling has the potential of enhancing marine influence, usually 14C depleted. Freshwater input can contribute either to increased reservoir offsets, when dead carbon from rock weathering is available, but also towards an atmospheric 14C signal, when the presence of terrestrial organic matter from catchment prevails. An overview of the MRE studies based on shellmounds on the coast of Rio de Janeiro reveals a pattern of negative local corrections for Saquarema and Rio das Ostras but positive values for Cabo Frio island, suggesting the presence of cold upwelling waters in Cabo Frio at 1.6–1.2 cal kBP. New results for a shellmound on the Ilha Grande island, in the western portion of the Rio de Janeiro coast, revealed a negative value at about 3 ka. We discuss distribution of MRE values and temporal variability in the region and their relation to ocean dynamics, continental input and the choice of marine organisms used for ∆R determination. A comparison of local reservoir offsets for the Saquarema region obtained from fish otolith and mollusk shells revealed similar ΔR distributions, showing that both materials can be equally used.

The vertical distribution of soil organic carbon (SOC) with depth and its horizontal pattern is influenced by the topography and relief of the surface, due to lateral redistribution of soil material along slopes. Spatial and temproral variability of these changes is frequently due to human impacts on the landscape. In our study, the results of these processes were studied in detail in a small sub-catchment in a forested hillslope section using radiocarbon (14C) dating of SOC and embedded datable material (charcoal, artifacts) from soil profiles with colluvial accumulations. Events with accelerated material redistribution could be identified as an accumulation of a 40-cm-thick colluvial layer between cal BC 410–360 (2σ) and cal AD 430–580 (2σ). Later colluvial deposition resulted in thinner accumulations (cal AD 1120–1220 [2σ] 30 cm; cal AD 1810–1920 [2σ] 21 cm). As the earliest human impact, we found soil transformation from cal BC 1290–1130 (2σ). The depth-age model for SOC compiled according to the average SOC age and its depth showed different characteristics on middle-slope and down-slope position, with rates of 48.0 yr×cm–1 and 22.0 yr×cm–1 respectively, which indicates the importance of topographic position of soils in SOC redistribution processes.

This paper examines the marine reservoir effect for Tomales Bay, a 25.5-km-long tidal estuary along the northern coast of California. We determined the regional ∆R through radiocarbon (14C) measurements of pre-1950 shells from a museum collection as well as archaeologically recovered shell samples from a historical railroad grade of known construction date. These results are compared against four sets of paired shell and bone samples from two local archaeological sites. Our results indicate little spatial variation along the inner bay, but the proposed ∆R value is lower than those previously reported for nearby areas along the Pacific Coast. We also note potential variability in regional ∆R of approximately 200 14C years for the late Holocene, and comparison with an older paired bone and shell sample points toward more significant temporal variation earlier in time.

The total 14C content and its speciation (inorganic/organic) were measured in spent ion exchange resins (SIERs) received from Cernavoda Nuclear Power Plant (NPP). Also, 14C release from SIERs was investigated by desorption tests carried out in alkaline solution relevant for cementitious environment disposal. The method used for total 14C measurement consists of combustion in oxygen-rich atmosphere, while for speciation measurements, both in SIERs and in desorption solutions, an analytical method based on acid stripping and wet oxidation was applied. Around 97% from the total 14C inventory measured on the Cernavoda SIERs (33.7 kBq/g) was found to be in inorganic form and only 7% as organic 14C. Under alkaline conditions, 14C could be released both as gaseous and as soluble species: from the total 14C present in the SIERs samples around 7% was released as inorganic 14C in the gas phase and 79% as dissolved species (mainly as inorganic 14C). These percentages were obtained for unconditioned SIERs in NaOH solution. The SIERs will be immobilized in a suitable matrix for disposal, and the presence of Ca ions dissolved in cement pore water favor precipitation of 14C and consequently the amount of 14C released from disposal area should be lower.

We report ∆14C measurements of cellulose extracted from near monthly tree ring growth for the 1960s of a white oak that grew in western Oregon, USA. Comparison with ∆14C measurements of atmospheric CO2 reveals that the tree ring ∆14C values were equal to or lower than those in atmospheric CO2 at the time of ring formation. We suggest that the low tree ring ∆14C values during the period 1962–1963 were caused by the presence of an atmospheric front or blocking between subpolar and temperate air masses that delayed the arrival of the bomb signal at the tree’s site.

We performed a new series of measurements on samples that were part of early measurements on radiocarbon (14C) dating made in 1948–1949. Our results show generally good agreement to the data published in 1949–1951, despite vast changes in technology, with only two exceptions where there was a discrepancy in the original studies. Our new measurements give calibrated ages that overlap with the known ages. We dated several samples at four different laboratories, and so we were also able to make a small intercomparison at the same time. In addition, new measurements on samples from other Egyptian materials used by Libby and co-workers were made at UC Irvine. Samples of tree rings used in the original studies (from Broken Flute Cave and Centennial Stump) were obtained from the University of Arizona Laboratory of Tree-Ring Research archive and remeasured. New data were compared to the original studies and other records.

Radiocarbon (14C) is one of the key radionuclides for the performance and safety assessment of a radioactive waste disposal, due to its high activity concentration in waste materials from the nuclear cycle and to its mobility. The measurement of the 14C content in spent ion exchange resins from nuclear reactors is important for the safety assessment of the disposal concept and for the choice of the appropriate treatment/disposal method. Ion exchange resins are commonly used in nuclear reactors as filters for the purification of process liquids or wastes streams and they retain molecules containing radioactive isotopes, among which is 14C. Their efficiency, both as filters and as waste containers, is strictly connected with the morphology. The preservation of spherical shape upon aging is one of the key parameters for their quality assessment and for the evaluation of the potential release of 14C during storage conditions. In this study, the change in IERs morphology during storage periods has been investigated in order to verify correlation with 14C release. Both brand new and aged specimens have been studied in order to assess the quality of the resins after 10 yr of storage and to contribute to the understanding of 14C release mechanisms.

A large collection of maize macro-specimens has been gathered from archaeological sites across the American continent, but only a few have been directly dated by accelerator mass spectrometry (AMS). We recently conducted two new excavations in several rock shelters of Tehuacán valley (San Marcos, Coxcatlán, and Purrón) and uncovered 132 non-manipulated macro-specimens of maize suitable for morphological and paleogenomic analysis, including many complete cobs, stalks, internodes, and leaves. Direct AMS dates for 43 samples found in San Marcos or Coxcatlán confirm the previously reported chronologies for these sites. By contrast, a cob found in Purrón was dated to 3060±30 before present (3360–3180 cal BP) (2σ), demonstrating that maize was present at that site at least 1500 calendar years earlier than previously expected, and suggesting that other specimens of similar age are still likely to be found in the southeastern region of the Tehuacán valley. A global comparison of macro-specimen chronology across the continent shows that the current archaebotanical record does not yet reflect the chronology of dispersal from central Mexico to northern or southern regions, opening the possibility for finding the missing links in subsequent expeditions within Mexico and Central America.