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The Alaska Peninsula is a landscape defined by volcanic, tectonic, and glacial processes, and life throughout is conditioned on the interactions among them. During the middle Holocene (ca. 4100–3600 yr ago), intense caldera-forming eruptions of the Aniakchak and Veniaminof volcanoes changed the shape of the central portion of the Peninsula dramatically, and had significant and perhaps devastating impacts on both terrestrial and marine biota. Here we evaluate the severity of these impacts by tracking human settlement patterns using 75 unique radiocarbon (14C) age determinations on buried cultural features from the central Alaska Peninsula. Coastal regions were re-colonized within a few hundred years while river systems most proximate to the volcanoes were uninhabited for up to 1500 years following the most severe eruptions. Patterns of human settlement may also document previously unrecorded landscape change throughout the region, and further contribute to our understanding of post-volcanic ecological succession.
Among the oldest remains of living beings to have inhabited the Earth’s surface, there are the stromatolites—laminated sedimentary rocks associated with lithified mats of layered phototrophic microbial communities—which grow in specific environmental conditions. In the present work, we study a recent carbonatic stromatolite from Lagoa Vermelha (Rio de Janeiro, Brazil), a shallow coastal hypersaline lagoon. X-ray diffraction was associated to a depth chronological model defining three different sections based on changes in mineral composition of the stromatolite with increased dolomite content. Although a mean growth rate of 0.19±0.03 mm/yr is observed, the model discloses decreasing growth rates among the sections. Since dolomite formation can be related to high availability of Mg+2, confirmed by an expressive presence of (Ca, Mg)CO3, the lower growth rates were associated to a more arid environment, until approximately 1440 cal AD, with higher temperatures and consequently promoting water evaporation and salinity enhancement.
The freshwater reservoir effect (FRE) for the Schelde basin (Belgium) is assessed for the Roman, Medieval and early Post-medieval periods by comparing historical and archaeological dates from individual archaeological deposits with radiocarbon dates on the remains of freshwater fish and terrestrial mammals from those same deposits. This is the first time such an assessment has been attempted for the Schelde basin. The FRE offsets prove to be substantial for the historical periods considered. They also differ markedly between fish species and between size classes of a single species. These observations have implications for the evaluation of radiocarbon dates obtained on archaeological remains of humans (and animals) with a substantial amount of freshwater fish into their diet. The data obtained in this study suggest that it will not be easy to correct for any FRE.
Ten marine reservoir effect (R) values were obtained from archaeological shell-middens along the San Matías Gulf, North Patagonian Atlantic coast, Argentina. They were determined by accelerator mass spectrometry (AMS) measurements on marine shell (Mytilidae) and charcoal samples (burned, short-lived plants) derived from a common stratigraphic unit. The R values fluctuate between 205±48 and 358±56 14C yr BP from ca. 5300 to ca. 700 14C yr BP with no obvious temporal trend. Calculated ΔR values fluctuate between +30±66 and –162±48 yr during the same time span. Local factors such as restricted connection with the open sea or presence of aged carbonates do not appear to have had an influence on this effect along the gulf coastline. The mean R value obtained (266 ± 51 yr) constitutes a useful value for correcting ages in shells from abundant archaeological deposits recorded in the area since Middle Holocene times.
For many of archaeology’s rarest and most enigmatic bone artifacts (e.g. human remains, bone ornaments, worked bone), the destruction of the 500 mg material necessary for direct accelerator mass spectrometry (AMS) dating on graphite targets would cause irreparable damage; therefore many have not been directly dated. The recently improved gas ion source of the MICADAS (MIni CArbon DAting System) offers a solution to this problem by measuring gaseous samples of 5–100 µg carbon at a level of precision not previously achieved with an AMS gas ion source. We present the results of the first comparison between “routine” graphite dates of ca. 1000 µg C (2–3 mg bone collagen) and dates from aliquots of gaseous samples of <100 µg C (<0.2 mg bone collagen), undertaken with the highest possible precision in mind. The experiment demonstrates the performance of the AixMICADAS in achieving reliable radiocarbon measurements from <0.2 mg collagen samples back to 40,000 14C BP. The technique has great implications for resolving chronological questions for key archaeological artifacts.
We present new marine reservoir ΔR correction terms for the central and northern Kuril Islands. We estimate ΔR from a series of archaeological charcoal-shell pairs from two archaeological sites using standard calibration procedures and Monte Carlo simulation. The combined ΔR estimate for all paired samples for the Kuril samples is 508±127 yr. In the context of available North Pacific Rim ΔR estimates, the new Kuril data support the interpretation of a well-mixed, 14C-depleted North Pacific Subarctic Gyre. For the broader subarctic North Pacific region, a ΔR estimate in the range of 440±127 yr is a reasonable correction for any coastal marine shell date, and may be applied to fish and marine mammal dates for taxa known to reside within these waters throughout their life-histories. This generalization fails as one moves south from Hokkaido along the East Asian coast. There, well-equilibrated subtropical water minimize the ΔR offset.
Over the last decade, archaeologists have turned to large radiocarbon (14C) data sets to infer prehistoric population size and change. An outstanding question concerns just how direct of an estimate 14C dates are for human populations. In this paper we propose that 14C dates are a better estimate of energy consumption, rather than an unmediated, proportional estimate of population size. We use a parametric model to describe the relationship between population size, economic complexity and energy consumption in human societies, and then parametrize the model using data from modern contexts. Our results suggest that energy consumption scales sub-linearly with population size, which means that the analysis of a large 14C time-series has the potential to misestimate rates of population change and absolute population size. Energy consumption is also an exponential function of economic complexity. Thus, the 14C record could change semi-independent of population as complexity grows or declines. Scaling models are an important tool for stimulating future research to tease apart the different effects of population and social complexity on energy consumption, and explain variation in the forms of 14C date time-series in different regions.
Radiocarbon (14C) measurements of foraminifera often provide the only absolute age constraints in marine sediments. However, they are often challenging as their reliability and accuracy can be compromised by reduced availability of adequate sample material. New analytical advances using the MIni CArbon DAting System (MICADAS) allow 14C dating of very small samples, circumventing size limitations inherent to conventional 14C measurements with accelerator mass spectrometry (AMS). Here we use foraminiferal samples and carbonate standard material to assess the reproducibility and precision of MICADAS 14C analyses, quantify contamination biases, and determine foraminiferal 14C blank levels. The reproducibility of conventional 14C ages for our planktic (benthic) foraminiferal samples from gas measurements is 200 (130) yr, and has good precision as illustrated by the agreement between both standards and their reference values as well as between small gas- and larger graphitized foraminiferal samples (within 100±60 yr). We observe a constant contamination bias and slightly higher 14C blanks for foraminifera than for carbonate reference materials, limiting gas (graphite) 14C age determinations for foraminifera from our study sites to ~38 (~42) kyr. Our findings underline the significance of MICADAS gas analyses for 14C on smaller-than-conventional sized foraminiferal samples for paleoclimate reconstructions and dating.
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.
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.
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.
Soil CO2 flux measurement is a key method that can be used to monitor the hazards in an active volcanic area. In order to determine accurately the variations of the CO2 soil emission we propose an approach based on the radiocarbon (14C) deficiency recorded in the plants grown in and around the Solfatara (Naples, Italy). We twice sampled selected poaceae plants in 17 defined sites around the Solfatara volcano. 14C measurements by liquid scintillation counting (LSC) were achieved on the grass samples. The 14C deficiency determined in the sampled plants, compared to the atmosphere 14C activity, ranged from 6.6 to 51.6%. We then compared the proportion of magmatic CO2 inferred to the instantaneous measurements of CO2 fluxes from soil performed by the accumulation chamber CO2 degassing measurement at the moment of the sampling at each site. The results show a clear correlation (r=0.88) between soil CO2 fluxes and 14C activity. The determination of the plants 14C deficiency provides an estimate of the CO2 rate within a few square meters, integrating CO2 soil degassing variations and meteorological incidences over a few months. It can therefore become an efficient bio-sensor and can be used as a proxy to cartography of the soil CO2 and to determine its variations through time
Terrestrial plant remains in the sediments of lakes from semi-arid and arid regions are rare and therefore the establishment of a sediment chronology depends on accurate assessment of the reservoir effect of the lake water. In a study of Genggahai Lake in the Gonghe Basin, northeastern Qinghai-Tibetan Plateau, we used accelerator mass spectrometry radiocarbon (AMS 14C) dating to determine the age of (1) dissolved inorganic carbon in the water (DICLW), (2) macrophyte remains in the uppermost samples of core sediments, (3) living P. pectinatus in the lake, and (4) dissolved inorganic carbon of spring water in the catchment. The results show that the ages of the DICLW (910 14C yr BP on average) were much younger than the ages of the groundwater (6330 14C yr BP on average), which may result mainly from CO2 exchange between the lake water and the atmosphere. In addition, the 14C ages of DICLW and macrophyte remains in the uppermost core sediments varied from site to site within the lake, which we ascribe to the different photosynthesis rates of Chara spp. and vascular plants. The higher photosynthesis rate of Chara spp. decreases lake-water pCO2, which leads to more atmospheric CO2 being absorbed by the lake water, and thereby greatly reducing the age of carbon species in areas dominated by Chara spp. Although Genggahai Lake is well mixed, the differences between the apparent ages of the lake water are significantly modulated by the photosynthesis intensity of submerged plants.
The marine reservoir effect is the difference in radiocarbon (14C) between the atmosphere and the marine surface ocean. To overcome the dating errors induced, it is necessary to correct marine 14C ages for this effect. ΔR is the difference between the marine 14C age and the marine calibration curve based on an ocean-atmosphere box diffusion model, which accounts for the time delay in diffusion of carbon into the ocean from the atmosphere and biosphere. This global assessment, however, requires computation of a regional ∆R value for calibration to cater for studies based on a local scale. In this paper the marine reservoir effect is assessed for the southern and eastern coasts of South Africa using 14C dating on pre-1950 marine shells of known age. The resultant ∆R values enable a more complete understanding of the marine reservoir effect along the southern and eastern coastal zone of South Africa. 14C age determinations were conducted on 15 shell samples of known age and the results, combined with previously published values, were used to calculate regional marine reservoir correction values. The east coast has a weighted mean ∆R of 121±16 14C yr, while the south coast has a weighted mean ∆R of 187±18 14C yr.
Marine insertion indicators in the Vitoria estuary (ES) revealed relative variations in sea level during the Holocene in three sediment cores. Sedimentological, geochemical (C/N ratio), and paleontological (shells and palynomorphs) analysis and 14C dating associated five sedimentary facies to different estuarine deposits. A C/N ratio <10 at the core base indicated organic matter of marine origin. Moving up the cores to 110–150 cm, an abrupt increase in C/N to 26–63 in every core suggests the sudden entry of higher plants into the estuary, potentially the moment sea level retreated. High continental (10,743 palynomorphs/g) and low marine palynomorph concentrations (323 palynomorphs/g) suggest a primarily continental source even during transgression and at high sea level. Around 8973 cal BP, an open bay already existed in the region of Vitoria. Sea level potentially exceeded the current level around 7110 cal BP. The transgressive maximum was at 5567 cal BP. Marine insertion indicators, such as marine shells, low C/N ratios and foraminiferal linings, did not always respond directly to sea level oscillations. These discrepancies probably result from lateral variations in sedimentary deposits from transport patterns and from variations in organic matter and palynomorph preservation due to differences in river and obstacle proximity.
Here, we introduce a new radiocarbon (14C) extraction line operating at the University of Bern, which was designed and built for the extraction of in situ 14C from meteorites. With this system, we achieved two important developments compared to other systems. First, using the MICADAS gas-interface system, 14C can directly be measured from the collected CO2 gas, i.e., without graphitization of the sample. Second, meteorite sample masses as low as ~0.05 g can be used for high precision and reproducibility. Prior to extraction in an oxygen atmosphere held at a pressure of ~20–30 mbar in an iridium crucible at 1600°C for 40 min, samples were preheated for 1 h in a constant oxygen flow at 500°C and continuous pumping. Gas purification followed the method described previously (e.g., Hippe et al. 2009). While the blank levels for preheated samples are low (<2×104 14C atoms), the blanks for non-preheated samples are high, therefore those results cannot be used. We also report preliminary results for the L-chondrite JaH 073. The terrestrial age of 17.7±0.4 ka is in good agreement with previous results for the same sample of this meteorite, confirming that the extraction line, the gas purification system, and the AMS measurements are all reliable.
To date, finding a technique able to effectively isolate the carbon signal from the binder of a mortar is still an open challenge. In this paper, the radiocarbon (14C) dating of one of the most challenging and diffuse types of mortar, the one with pozzolana aggregate, is investigated. Eight mortar samples from three archaeological sites near Rome (Italy) underwent a selection process called Cryo2SoniC. The selected fractions were analyzed by the accelerator mass spectrometry (AMS) 14C technique and compared to known historical references. Additional scanning electron microscopy analysis and petrographic investigations were done, respectively, to check the grain size of the fractions selected by Cryo2SoniC, and further, to characterize the original mortar samples. The masses of carbon yielded from the dated fractions were almost half of those released from some aerial mortars. The 14C dating results were accurate for pozzolana mortars, from buried and unburied structures, with calcination relics and small contamination of secondary calcite. A limitation in the purification protocol was observed on samples with a massive contamination of secondary calcite deposition of ground water origin, occluding porosity and substituting up to the 80% of the original binder matrix.
Sea surface reservoir ages (R) are reported from radiocarbon (14C) measurements of the annual growth bands of coral Siderastrea siderea collected on the Atlantic coast off Martinique Island, in the Lesser Antilles volcanic arc. Mean values of R are similar between 1835 and 1845 during pre-anthropogenic times at 385±30 yr and between 1895 and 1905 at 382±20 yr when there was a huge eruption from the Montagne Pelée volcano in 1902–1903. Limited 14C aging of sea surface (~40 yr) may be due to enhanced volcanic activity. Variability of R is slightly greater during 1835–1845 than during 1895–1905. It is linked to a moderate increase of ∆14C of 5‰, strengthened by a clear increase of δ18O of 0.4‰. This is attributed to a decrease of the northward advection of the South Atlantic Waters into the western tropical North Atlantic and Caribbean Sea and relative enhanced westward flux of the tropical North Atlantic surface waters, the southern waters having lower values of 14C and δ18O than the North Atlantic ones. From 1835 to 1845, the fraction of the South Atlantic Waters transported up to Martinique Island was reduced from 25% to 15%.