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Most extant small ice caps mantling low-relief Arctic Canada landscapes remained cold-based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. As Arctic summers warmed after 1900 CE, ice caps receded, exposing entombed vegetation. The calibrated radiocarbon ages of dead moss collected near ice-cap margins (kill-dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study we reported 94 Last Millennium radiocarbon dates on in situ dead moss collected at the margins of two upland ice complexes on northern Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age ~1240 CE, and further expansion ~1480 CE, coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by re-sampling those previously sampled ice complexes 14 years later, after ~250 m of ice recession. The probability density functions (PDF) of the more recent series of ages matches PDFs of the earlier series, but with a larger fraction of early CE ages; post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances, and were preserved beneath later ice-cap growth. We compare 107 kill dates from the two ice complexes with 79 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDF of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE and a dense early Little Ice Age cluster with peaks at ~1240 and ~1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions ~1880 CE, still visible as zones of limited vegetation cover in remotely sensed imagery. Intervals of widespread ice-cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Modeling (CESM) fully coupled Common Era simulation, suggesting primary forcing of the observed snowline lowerings were both modest declines in summer insolation, and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from sea-ice expansion and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill-dates are mirrored in an annually resolved Common Era record of ice-cap dimensions in Iceland, suggesting this is a circum-North-Atlantic-Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled > 11,000 km2 of north-central Baffin Island, whereas < 100 km2 is glaciated at present. That state approached conditions expected during the inception phase of an ice age, and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance.

Funding information: This work was supported by grants from the National Science Foundation (OCE-2015647 and OCE-2032340 to PAR; OCE- 2032343 to MPH); NERC grant NE/N011716/1 to JWBR and NERC grant NE/M004619/1 to AB. Using new and published marine fossil radiocarbon (14C/C) measurements, a tracer uniquely sensitive to circulation and air-sea gas exchange, we establish several benchmarks for Atlantic, Southern, and Pacific deep-sea circulation and ventilation since the last ice age. We find the most 14C-depleted water in glacial Pacific bottom depths, rather than the mid-depths as they are today, which is best explained by a slowdown in glacial deep-sea overturning in addition to a “flipped” glacial Pacific overturning configuration. These observations cannot be produced by changes in air-sea gas exchange alone, and they underscore the major role for changes in the overturning circulation for glacial deep-sea carbon storage in the vast Pacific abyss and the concomitant drawdown of atmospheric CO2. Publisher PDF

The 14-carbon in animal tissues records the time that the tissues are formed; since the 1960s, using the “bomb curve” for 14 C, the age of animal death can be determined accurately. Using animal tissue samples of known collection and formation dates for calibration, we determine the age of ivory samples from four ivory seizures made by law enforcement agencies between 2017 and 2019. The 14 C measurements from these seizures show that most ivory in the illegal wildlife trade is from animals from recent poaching activities. However, one seizure has a large fraction of ivory that is more than 30 y old, consistent with markings on the tusks indicating they were derived from a government stockpile.

Hamley et al . previously presented multiple lines of evidence that people were present in the Falkland Islands before Europeans and may have brought the now-extinct canid, Dusicyon australis . Stable isotope data reported by Clark et al . indicate that D. australis had a high-trophic, marine diet that terrestrialized following European arrival. This is consistent with our hypothesis of a human mutualism.

The Greenland Ice Sheet (GrIS) is melting in response to a rapidly warming climate. It is imperative to understand GrIS sensitivity to past climate, especially during periods when the ice sheet was smaller than present or possibly absent. The Camp Century ice core from NW Greenland, collected in 1966 and the first ice core to be drilled to the bed of the GrIS, revolutionized our understanding of global paleoclimate since 125 ka. However, basal sediment from the ice core was not fully explored and then sat in storage for decades – until it was re-discovered two years ago. We are now investigating these unique samples from the sub-glacial environment using modern analyses. Here, we present initial results from two samples, the upper and lower portions of >4 m of basal sediment. We applied an array of geochemical analyses to characterize paleoenvironment (lipid biomarkers, δ13C, δ15N), to infer past climatic conditions (δ18O, δD) from frozen pore water, and to determine the exposure and burial history of the sediments below the ice sheet (optically stimulated luminescence [OSL], cosmogenic 10Be, 26Al, and 21Ne). The sub-glacial sediment consists of poorly sorted, reddish-brown, quartz-rich diamict, with paleo-permafrost features in some layers. This material contains woody macrofossils, fungal sclerotia (Cenococcum geophilum), and mosses (Tomenthypnum nitens, Polytrichum juniperinum) that yield a 14C age >55 ka. Woody tissue from the upper and lower samples yield stable δ13C ratios of -26.7±0.1‰ and -29.6±0.1‰ and δ15N ratios of 2.4±0.8‰ and -2.3±0.8‰. Leaf wax (n-alkanoic acid) distributions are similar to modern Arctic shrubs. Frozen pore water yielded δ18O ratios of -23.06±0.08‰ and -21.49±0.08‰, enriched relative to all overlying ice (600 ka. In situ 10Be concentrations in quartz decrease with depth from 7.7±0.1 x104 atoms/g (500-850 µm) and 6.6±0.2 x104 (250-500 µm) in the upper sediment to 1.6±0.1 x104 atoms/g (500-850 µm) and 1.8±0.1 x104 (250-500 µm) in the lower sediment. The 26Al/10Be ratio also decreases with depth. In the upper sediment, 26Al/10Be ratios range between 4.2 and 4.9 indicating > 900 ka of burial. In the lower sediment, 26Al/10Be ratios range from 1.4 to 2.0 indicating >2 Ma of burial. Measured 21Ne/10Be ratios in quartz exceed 1000, which could indicate long-term burial and/or the presence of nucleogenic 21Ne.These results demonstrate that Camp Century basal sediment was exposed under ice-free conditions that supported vegetation similar to today. Cosmogenic data indicate the deeper sediment has been buried for most of the Pleistocene and the OSL date rules out surface exposure of the deeper material at MIS 11. Cosmogenic analysis indicates that the upper sample experienced less burial or more recent re-exposure. These data are consistent with a growing body of evidence indicating a dynamic Pleistocene GrIS, even under a pre-industrial climate system in which atmospheric CO2 concentrations did not exceed ~300 ppm.

Significance This study provides evidence of an enormous solar storm around 2,610 B.P. It is only the third such event reliably documented and is comparable with the strongest event detected at AD 774/775. The event of 2,610 years B.P. stands out because of its particular signature in the radionuclide data [i.e., carbon-14 (14C) data alone does not allow for an unequivocal detection of the event]. It illustrates that present efforts to find such events based solely on 14C data likely lead to an underestimated number of such potentially devastating events for our society. In addition to 14C data, high-resolution records of beryllium-10 and chlorine-36 are crucial for reliable estimates of the occurrence rate and the properties of past solar proton events., Recently, it has been confirmed that extreme solar proton events can lead to significantly increased atmospheric production rates of cosmogenic radionuclides. Evidence of such events is recorded in annually resolved natural archives, such as tree rings [carbon-14 (14C)] and ice cores [beryllium-10 (10Be), chlorine-36 (36Cl)]. Here, we show evidence for an extreme solar event around 2,610 years B.P. (∼660 BC) based on high-resolution 10Be data from two Greenland ice cores. Our conclusions are supported by modeled 14C production rates for the same period. Using existing 36Cl ice core data in conjunction with 10Be, we further show that this solar event was characterized by a very hard energy spectrum. These results indicate that the 2,610-years B.P. event was an order of magnitude stronger than any solar event recorded during the instrumental period and comparable with the solar proton event of AD 774/775, the largest solar event known to date. The results illustrate the importance of multiple ice core radionuclide measurements for the reliable identification of short-term production rate increases and the assessment of their origins.

Time-consuming and expensive radiometric dating techniques limit the number of dates available to construct absolute chronologies for high-resolution paleoclimate reconstructions. A recently developed rapid-screen 14C dating technique reduces sample preparation time and per sample costs by 90%, but its accuracy has not yet been tested on shallow-water corals. In this study, we test the rapid-screen 14C dating technique on shallow-water corals by comparing 44 rapid-screen 14C dates to both high-precision 14C dates and U/Th dates from mid- to late-Holocene fossil corals collected from the central tropical Pacific (2–4°N, 157–160°W). Our results show that 42 rapid-screen 14C and U/Th dates agree within uncertainties, confirming closed-system behavior and ensuring chronological accuracy. However, two samples that grew ∼6500 years ago have calibrated 14C ages ∼1000 years younger than the corresponding U/Th ages, consistent with diagenetic alteration as indicated by the presence of 15–23% calcite. Mass balance calculations confirm that the observed dating discrepancies are consistent with 14C addition and U removal, both of which occur during diagenetic calcite recrystallization. Under the assumption that aragonite-to-calcite replacement is linear through time, we estimate the samples' true ages using the measured 14C and U/Th dates and percent calcite values. Results illustrate that the rapid-screen 14C dates of Holocene-aged fossil corals are accurate for samples with less than 2% calcite. Application of this rapid-screen 14C method to the fossil coral rubble fields from Kiritimati Island reveal significant chronological clustering of fossil coral across the landscape, with older ages farther from the water's edge.

We have developed a simple, rapid method to screen carbonates for survey applications, which provides radiocarbon dates with decreased precision at lower cost. The method is based on previous work by Longworth et al. (2011) and involves mixing pulverized CaCO3 with Fe powder, followed by pressing into aluminum target holders for direct 14C accelerator mass spectrometry (AMS) measurements. An optimum beam current averaging ∼10% of those produced by >0.7 mg C graphite targets was obtained for carbonate samples of 0.3–0.5 mg (0.04–0.06 mg C). The precision of the method was evaluated by measuring triplicates of 14C reference materials, as well as by comparing results from this rapid method with results from high-precision AMS measurements on graphite (typically 0.2–0.3%). Measurement reproducibility was ∼1.8% (1σ) for samples t tests on paired samples resulted in p values greater than 0.05, indicating a good correlation between this survey method and the conventional one. An average blank (calcite) of 0.0075 Fm (∼39 ka BP) was achieved. The simplicity of the technique allowed us to process and measure 72 deep-sea coral samples in less than 25 hr.

The radiocarbon content of whole air provides a theoretically ideal and now observationally proven tracer for recently added fossil-fuel-derived CO2 in the atmosphere (Cff). Over large industrialized land areas, determination of Cff also constrains the change in CO2 due to uptake and release by the terrestrial biosphere. Here, we review the development of a Δ14CO2 measurement program and its implementation within the US portion of the NOAA Global Monitoring Division's air sampling network. The Δ14CO2 measurement repeatability is evaluated based on surveillance cylinders of whole air and equates to a Cff detection limit of 14CO2 budget and from uncertainties in the composition of “background” air against which Cff enhancements occur. As an example of how we apply the measurements, we present estimates of the boundary layer enhancements of Cff and Cbio using observations obtained from vertical airborne sampling profiles off of the northeastern US. We also present an updated time series of measurements from NOAA GMD's Niwot Ridge site at 3475 m asl in Colorado in order to characterize recent Δ14CO2 variability in the well-mixed free troposphere.

The Indonesian Arc represents the subduction of the Indian-Australian plate beneath Asia. It has been the scene of catastrophic tectonic activity, including the recent 2004 M=9.1 Aceh earthquake and resulting Indian Ocean tsunami. We have dated planktonic forams associated with historic tephras (Tambora, 1815 and Krakatau, 1883) in marine sediment cores to determine radiocarbon reservoir ages for 2 locations along the arc. Our best estimates for 19th century regional reservoir corrections (ΔR) are +90 ± 40 yr for surface-dwelling species and +220 ± 40 yr for mixed planktic assemblages containing some upper thermocline species, but scatter in the data suggests that past surface reservoir ages may have varied by about ±100 yr. We used the results of this study to investigate a proposed very large AD 535 eruption at or near Krakatau. We find no evidence for ash from such an eruption, and although this is negative evidence, we consider it sufficiently strong to rule out any possibility that one took place.

The Last Glacial–Interglacial Transition (LGIT; 15,000–11,000 cal BP) was characterized by complex spatiotemporal patterns of climate change, with numerous studies requiring accurate chronological control to decipher leads from lags in global paleoclimatic, paleoenvironmental, and archaeological records. However, close scrutiny of the few available tree-ring chronologies and radiocarbon-dated sequences composing the IntCal13 14C calibration curve indicates significant weakness in 14C calibration across key periods of the LGIT. Here, we present a decadally resolved atmospheric 14C record derived from New Zealand kauri spanning the Lateglacial from ~13,100–11,365 cal BP. Two floating kauri 14C time series, curve-matched to IntCal13, serve as a 14C backbone through the Younger Dryas. The floating Northern Hemisphere (NH) 14C data sets derived from the YD-B and Central European Lateglacial Master tree-ring series are matched against the new kauri data, forming a robust NH 14C time series to ~14,200 cal BP. Our results show that IntCal13 is questionable from ~12,200–11,900 cal BP and the ~10,400 BP 14C plateau is approximately 5 decades too short. The new kauri record and repositioned NH pine 14C series offer a refinement of the international 14C calibration curves IntCal13 and SHCal13, providing increased confidence in the correlation of global paleorecords.

We submit that anomalies in radiocarbon data in archaeological studies should be viewed positively as a stimulus to undertake further targeted research. Additional analyses to resolve anomalies have the potential to provide important insights into heretofore unstudied or incompletely understood depositional or geochemical processes affecting14C values, particularly in certain types of samples and samples from certain types of environments. We consider 2 major categories or sources of14C dating anomalies that we posit are mostly responsible for the vast majority of problematic14C results: anomalous sample contexts and anomalous sample composition. Two additional sources of14C anomalies are much more rarely encountered. Six case studies taken from New World archaeological studies are briefly presented to provide examples of where questions concerning the validity of14C measurements generated additional and ultimately more accurate understandings of temporal relationships. AMS-based14C measurement technology has rendered detailed investigations of14C anomalies routinely feasible.

The “Christmas Cave”, a cave in the Qidron Valley near the Dead Sea and Qumran, has yielded a complex collection of plant-derived rope and fabric artifacts. Using polymerase chain reaction (PCR) to amplify DNA of the samples, we estimated the sizes and determined restriction patterns and base sequences of chloroplast genes, primarily rbcL (gene for the large subunit of ribulose bisphosphate carboxylase). DNA was successfully extracted from all samples, but was limited to sizes of approximately 200–300 base pairs. As expected, the DNA extracted from the samples was identified as coming primarily from flax (Linum usitatissamum L.), but two samples had a significant fraction, and all samples had at least a trace, of hemp (Cannabis sativa L.) DNA. Artifacts from the Christmas Cave were thought to date from Roman times, but it was thought possible that some could be much older. Accelerator mass spectrometry (AMS)-based 14C dating confirmed that the samples contained representatives from both the Roman and Chalcolithic periods. This paper provides a synthesis of DNA, isotope, and literary analysis to illuminate textile history at the Christmas Cave site.

Conventional radiocarbon calculations correct for isotopic fractionation using an assumed value of 2.0 for the fractionation of 14C relative to 13C. In other words, isotopic discrimination in physical and chemical processes is assumed to cause relative shifts in 14C/12C ratios that are exactly double those of 13C/12C. This paper analyzes a 1984 experiment that produced a value for the fractionation ratio in photosynthesis of 2.3, which is used to this day by some researchers in the fields of hydrology and speleothem geochemistry. While the value of 2.3 is almost certainly incorrect, theoretical work suggests that the true value may indeed deviate from 2.0, which would have significant implications for 14C calculations.

Over the past decades, analysis of occluded carbon in phytoliths (opaline silica mineral bodies that form in and between plant cells) has become a workhorse of paleoclimate and archaeological studies. Since different plant types exhibit distinctive phytolith morphologies, their assemblages are used in identifying vegetation histories or food culture adaptations. A few direct radiocarbon AMS measurements of phytoliths have been carried out, but these measurements are difficult due to the low concentrations of phytoliths in some plant species, and the small amount of C per phytolith (14C age are available to verify measurement accuracy and precision, and to check sample preparation protocols. Background corrections are also difficult to address due to the lack of suitable material. In this work, we designed a procedure to quantify a suitable blank using SiO2powder samples (close to the opal structure, and free of14C). The full phytolith extraction showed high carbon contamination components: a) ∼3 μg of modern C and ∼2 μg of dead C. We also performed accuracy tests on large phytolith-occluded carbon samples extracted from soils and harvested plants. The unexpected14C ages in some of the results triggered further investigations of possible sources of carbon contamination.

We present a status report of the accelerator mass spectrometry (AMS) facility at the University of California, Irvine, USA. Recent spectrometer upgrades and repairs are discussed. Modifications to preparation laboratory procedures designed to improve sample throughput efficiency while maintaining precision of 2–3‰ for 1-mg samples (Santos et al. 2007c) are presented.

Primary and secondary standards are essential in radiocarbon analyses for the purpose of reporting and comparing data among laboratories, as well as for internal laboratory data quality control. ANU sucrose is one of the IAEA-certified 14C standards (C-6) with a consensus value of 1.5061 ± 0.0011 fraction modern (Fm). All of our measurements of ANU sucrose (n = 351) as a secondary standard over the last 7 yr result in an average value of 1.5016 ± 0.0005 Fm (2-σ standard error). After applying the same outlier tests used for IAEA reference standards, a weighted average value of 1.5016 ± 0.0002 Fm (n = 294) was calculated. This value is significantly lower than the IAEA C-6 consensus value (t test with unequal variance; p = 0.023). In contrast, our measurements of other secondary standards over the same time period are in excellent agreement with their respective consensus values. Since ANU is the only secondary standard measured in our lab that does not agree with the consensus values, and we have measured a larger number analyses compared to what went into the definition of the consensus value, we suggest that the consensus value of ANU sucrose might be too high by ∼0.0045 ± 0.0011 Fm. Given that some labs routinely use ANU sucrose as a primary standard, our results suggest that revisiting the consensus value of ANU sucrose may be necessary.

Three factors—contamination, a dietary reservoir effect, and a regional δ14C anomaly—are considered as possible contributing explanations for an almost 2-century offset between the historically documented age of 612 BCE and the calibrated ages of 9 14C determinations obtained on 3 human skeletons directly associated stratigraphically with an archaeologically—and historically—defined 612 BCE event at the ancient site of Nineveh in northern Mesopotamia (Iraq). We note that on the order of a 1% (∼80 yr) offset caused by one or a combination of these 3 factors, or other as yet unidentified additional factor(s), would be sufficient to move the average measured 14C age of these bone samples within the major “warp” in the 14C timescale during the mid-1st millennium BCE. We provide what we believe to be sufficient evidence that contamination is not a major factor in the case of these bone samples. At this time, we lack appropriate data to determine with sufficient rigor the degree to which a dietary reservoir effect may be contributing to the offset. At present, a posited regional δ14C anomaly does not appear to be supported on the basis of data from several other localities in the Near East of similar age. One purpose of presenting this data set is to solicit comparisons with 14C values obtained on samples from additional, historically well-documented, known-age archaeological contexts for this time period in this and adjacent regions.

We have developed sample pretreatments for silk for radiocarbon dating. Characteristics of silk under different types of pretreatment were investigated, as well as the behavior of dye and possible contaminants. We found that dye could be removed completely, together with all other foreign materials bigger than 1.2 μm, using a glass microfiber filter after decomposition with 6N HCl. The decomposed proteins were concentrated using Centriprep® ultrafiltration concentrators with 3 different molecular weight cut-offs. By taking a molecular weight fraction—which selects for secondary structures of silk protein—14C dating of silk samples can be made more reliable. This study confirms that uniformly fractured polypeptide chains of silk provide an appropriate fraction for 14C age dating to select silk protein against dye particles and undecomposed foreign contaminants.

The increased detection sensitivity offered by AMS has dramatically expanded the utility of 10 Be. As these applications become more sophisticated attention has focused on the accuracy of the 10 Be standards used to calibrate the AMS measurements. In recent years it has become apparent that there is a discrepancy between two of the most widely used 10 Be AMS standards, the ICN 10 Be standard and the NIST 10 Be standard. The ICN (ICN Chemical & Radioisotope Division) 10 Be AMS standard was calibrated by radioactive decay counting. Dilutions, ranging from 5 × 10 −13 to 3 × 10 −11 10 Be/Be, have been prepared and are extensively used in many AMS laboratories. The NIST 10 Be standard, prepared at the National Institute of Standards and Technology (NIST), is calibrated by mass spectrometric isotope ratio measurements. To provide an independent calibration of the 10 Be standards we implanted a known number of 10 Be atoms in both Si detectors and Be foil targets. The 10 Be concentrations in these targets were measured by AMS. The results were compared with both the ICN and NIST AMS standards. Our 10 Be measurements indicate that the 10 Be/ 9 Be isotopic ratio of the ICN AMS standard, which is based on a 10 Be half-life of 1.5 × 10 6 yr, is 1.106 ± 0.012 times lower than the nominal value. Since the decay rate of the ICN standard is well determined, the decrease in 10 Be/ 9 Be ratio requires that the 10 Be half-life be reduced to (1.36 ± 0.07) × 10 6 yr. The quoted uncertainty includes a ±5% uncertainty in the activity measurement carried out by ICN. In a similar fashion, we determined that the value of the NIST 10 Be standard (SRM4325) is (2.79 ± 0.03) × 10 −11 10 Be/ 9 Be, within error of the certified value of (2.68 ± 0.14) × 10 −11 . The Lawrence Livermore National Laboratory (LLNL) internal standards were also included in this study. We conclude that the 9 Be(n, γ) neutron cross section is 7.8 ± 0.23 mb, without taking into account the uncertainty in the neutron irradiation.

We report on 2 recent developments in an ongoing program of characterizing and improving the National Electrostatics Corp. (NEC) MC-SNICS ion source at University of California (UC) Irvine's Keck AMS laboratory. First, we have investigated the possibility of modifying a large-body (134-sample) MC-SNICS to incorporate the UC Irvine Cs oven and vacuum-insulated Cs feed tube, which provide better confinement of Cs than the standard NEC setup. In our 40-sample source, the feed tube enters the source housing directly below the ionizer assembly. This area cannot be accessed for machining on the 134-sample source, but we have successfully tested a modified geometry where the delivery tube enters the body via the source end flange. Second, we recently installed a second beam profile monitor in the injection line of our spectrometer to allow us to make online emittance measurements. At full output (150 μA of C− at 55 keV), the emittance of our source at 8 kV sputtering voltage is approximately 40π mm mrad.

ΔR values have been calculated based on offsets in radiocarbon values exhibited in a series of stratigraphically paired charcoal and marine shell values, ranging from about 300 to 10,000 BP, excavated from archaeological sites on Cedros Island, Baja California, Mexico. Based on this data, there appears to be the equivalent of about an 800-yr range in inferred ΔR values (-400 to 400 yr) exhibited in Holocene-age marine shells from this portion of the central Baja California coast.

The effect of nitrous oxide (N2O) upon the graphitization of small (∼40 μg of carbon) CO2samples at the ANSTO and University of California, Irvine, radiocarbon laboratories was investigated. Both laboratories produce graphite samples by reduction of CO2over a heated iron catalyst in the presence of an excess of H2. Although there are significant differences between the methods employed at each laboratory, it was found that N2O has no effect upon the reaction at levels of up to 9.3% by volume of CO2. Further, it was systematically determined that more effective water vapor trapping resulted in faster reaction rates. Using larger amounts of the Fe catalyst generally resulted in higher yields or reaction rates (but not both). The effects of changing the type of Fe catalyst on the final yield and reaction rate were less clear.

Previous 14C determinations obtained on two segments of a single mastodon bone recovered from Monte Verde, Chile, were highly discordant, differing by more than 5,000 years. Because of the significance of this site in discussions concerning the earliest peopling of the Western Hemisphere, additional 14C and new δ13C values have been obtained on organic fractions isolated from both segments. The constituent amino acid profiles indicate that both bone segments retain significant amounts of protein (mostly collagen) residues. Four accelerator mass spectrometry-based 14C values obtained on total amino acids and ultrafiltered gelatin fractions—two from each segment—are statistically identical and indicate an age of 12,460 (± 30) BP for the mastodon. This value is concordant with 14C values obtained on other culturally affiliated organics associated with the MV-II levels at this site.

The d 18 O benthic foraminiferal curve and AMS 14 C radiocarbon data provide a representative age model for a southern Bering Sea sediment core (GC-11). Downcore profiles of d 18 Oo fN. pachyderma (s.) and U. auberiana, carbonate and organic carbon contents, species changes in the planktonic foraminifera assemblages and some diatom species show orbital (MIS 1, 2 and 3) and millennium scale variability influenced by the Alaska Current flowing into the studied region. Three warmer episodes in the southern Bering Sea environment were assumed to be synchronous with DO interstadials 8, 12 and 14 (in GISP-2 chronology) during MIS 3. More severe climate and environmental conditions in the southern Bering Sea during MIS 2 occurred synchronously with the LGM within a 17–19 ka time span. Two well pronounced environmental warming events, productivity spikes and changes in the pore water geochemistry, separated by Younger Dryas cooling, were observed at the base of MIS 1 coeval with MWP 1A and 1B. Regional glacial primary productivity based on the calculation of the organic carbon MAR, similar to that found in the far northwestern Pacific, exceeded the Late Holocene values under conditions close to the present day. r 2005 Elsevier Ltd. All rights reserved.

We developed and are testing a system for extracting in situ produced 14 C from quartz. 14 C is liberated from quartz matrix using step-wise heating during which time a spiked carrier gas consisting O 2 –CO–CO 2 –He is flowed through the high-temperature chamber continuously. The total 14 C background is reproducible and typically (2.3 ± 0.2) × 10 6 atoms, and the recovery is consistently greater than 90%. To validate the performance of the system and determine the blank level, we are using quartz samples taken from the Homestake mine (1600 m below the surface), South Dakota. To determine the 14 C release pattern and recovery, we used samples taken from the Transantarctic Mountains, Antarctica.

Radiocarbon (∆14C) measurements of monthly samples from a Galapagos surface coral are among the first data sets from the new Keck Carbon Cycle Accelerator Mass Spectrometry laboratory at the University of California, Irvine. An average ∆14C value of -62‰ is obtained for 144 measurements of samples from monthly coral bands that lived from about AD 1760-1771 (±6 yr). High ∆14C values were found during January through March, when upwelling was weak or absent at the Galapagos Islands. Low ∆14C values were obtained mid-year during strong upwelling. The average seasonal variability of ∆14C was 15-25‰, which is greater than that at other tropical and subtropical locations in the Pacific Ocean because of intense seasonal upwelling at this site. Periods of sustained high ∆14C values were found during 1762-1763 and 1766. A spectral analysis revealed that the spectral density for the ∆14C data displays most of its variance at the 5-yr cycle, which is reflective of El Nino periodicity during the 20th century. Corals reflect the ∆ 14 C in surface DIC and provide time histories of ∆ 14 C on timescales of months to millennia. Records of ∆ 14 C in the surface ocean reveal past variability of surface-subsurface mixing and horizontal current shifts. We report monthly ∆ 14 C measurements from a Galapagos coral representing the 11-yr period AD 1760-1771 (±6 yr). We show that ∆ 14 C is high during the beginning of the year, when trade winds and upwelling were weak, and low ∆ 14 C values during the rest of the year, when wind-driven upwelling was strong.

This paper describes the methods used to develop the Cariaco Basin PL07-58PC marine radiocarbon calibration data set. Background measurements are provided for the period when Cariaco samples were run, as well as revisions leading to the most recent version of the floating varve chronology. The floating Cariaco chronology has been anchored to an updated and expanded Preboreal pine tree-ring data set, with better estimates of uncertainty in the wiggle-match. Pending any further changes to the dendrochronology, these results represent the final Cariaco 58PC calibration data set.

Some of the most valuable paleoclimate archives yet recovered are the multi-proxy records from the Greenland GISP2 and GRIP ice cores. The crucial importance of these data arises in part from the strong correlations that exist between the Greenland δ18O records and isotopic or other proxies in numerous other Northern Hemisphere paleoclimate sequences. These correlations could, in principle, allow layer-counted ice-core chronologies to be transferred to radiocarbon-dated paleoclimate archives, thus providing a 14C calibration for the Last Glacial Maximum and Isotope Stage 3, back to the instrumental limits of the 14C technique. However, this possibility is confounded by the existence of numerous different chronologies, as opposed to a single (or even a “best”) ice-core time scale. This paper reviews how the various chronologies were developed, summarizes the differences between them, and examines ways in which further research may allow a 14C calibration to be established.

We present and compare AMS-14C geochronologies for sediment cores recovered from Lake Titicaca, South America. Radiocarbon dates from three core sites constrain the timing of late Quaternary paleoenvironmental changes in the Central Andes and highlight the site-specific factors that limit the radiocarbon geochronometer. With the exception of mid-Holocene sediments, all cores are generally devoid of macrophyte fragments, thus bulk organic fractions are used to build core chronologies. Comparisons of radiocarbon results for chemically defined fractions (bulk decalcified, humate, humin) suggest that ages derived from all fractions are generally coherent in the post-13,500 yr BP time interval. In the pre-13,500 yr BP time interval, ages derived from humate extracts are significantly younger (300–7000 years) than ages from paired humin residues. Gross age incoherencies between paired humate and humin sub-fractions in pre-13,500 yr BP sediments from all core sites probably reflect the net downward migration of humates. Ages derived from bulk decalcified fractions at our shallow water (90 m) and deep water (230 m) core sites consistently fall between ages derived from humate and humin sub-fractions in the pre-13,500 yr BP interval, reflecting that the bulk decalcified fraction is predominantly a mixture of humate and humin sub-fractions. Bulk decalcified ages from the pre-13,500 yr BP interval at our intermediate depth core site (150 m) are consistently older than humate (youngest) and humin sub-fractions. This uniform, reproducible pattern can be explained by the mobilization of a relatively older organic sub-fraction during and after the re-acidification step following the alkaline treatment of the bulk sediment. The inferred existence of this ‘alkali-mobile, acid-soluble’ sub-fraction implies a different depositional/post-depositional history that is potentially associated with a difference in source material. While internally consistent geochronologies can be developed for the Lake Titicaca sequence using different organic fractions, mobile organic sub-fractions and fractions containing mobile sub-fractions should generally be avoided in geochronology studies. Consequently, we believe humin and/or bulk decalcified ages provide the most consistent chronologies for the post-13,500 yr BP interval, and humin ages provide the most representative ages for sedimentation prior to 13,500 yr BP interval. Using the age model derived from the deep water core site and a previously published isotope-based lake-level reconstruction, we present a qualitative record of lake level in the context of several ice-core records from the western hemisphere. We find the latest Pleistocene lake-level response to changing insolation began during or just prior to the Bolling/Allerod period. Using the isotope-based lake-level reconstruction, we also find the 85-m drop in lake level that occurred during the mid-Holocene was synchronous with an increase in the variability of ice-core δ18O from a nearby icecap, but was not reflected in any of the polar ice-core records recovered from the interior of Antarctica and Greenland.

Fans in the once-glaciated, mountainous landscape of humid-temperate New England preserve a long and unique record of deposition and, thus, of hillslope erosion. By using multiple backhoe trenches and radiocarbon dating of wood and charcoal, we determined the history of five small fans (1900‐14,850 m 3 ) that range in age from historic to $13,320 calibrated (cal.) 14 Cy r

The role of rust in the radiocarbon dating of iron artefacts has been examined experimentally. This was accomplished by re-measuring, using modern accelerator mass spectrometry techniques, the radiocarbon dates of ancient iron-based artefacts that were originally radiocarbon dated 30 years ago by beta counting. The samples were dated with the rust that had accumulated over the last 30 years, which in some cases had consumed most of the original metal. The study also afforded the opportunity to compare beta counting with accelerator mass spectrometry, large and small sample sizes, and old versus new carbon extraction methods. The results demonstrate that in at least some circumstances the carbon in rust can be reliably used for radiocarbon dating. Some experimental observations on iron microstructure and oxidation processes which support these results, are reviewed. The issues of sample size and the role of rust are important because they open up new possibilities for dating iron-based artefacts that had previously been assumed to be unavailable.

Dissolved beryllium-10 concentration profiles in sea water of the East China Sea and the Okinawa Trough in 1993 autumn and 1994 summer have been investigated. The results show that 10 Be concentrations in this area are mainly controlled by surface biological productivity, particle remineralization, and the degree of mixing with the Yangtze River and the Kuroshio waters. During the sampling periods (summer and autumn), the East China Sea was well stratified. Generally, the 10 Be water depth profiles can be divided into three layers: the surface mixed layer, the particulate 10 Be regeneration layer, and the bottom layer. Surface water 10 Be concentrations increase gradually towards the Kuroshio and increase sharply at the edge of the Kuroshio Current. Vertical distributions of 10 Be show that in the summer 10 Be is enriched in the bottom water near the Yangtze River estuary and the bottom water in the middle of the continental shelf. The two enriched areas are separated, probably by an intrusion of the Continental Coastal Water. In the autumn, 10 Be bottom enrichment only occurred in the western part of the East China Sea. This phenomenon is consistent with the seasonal circulation pattern change of currents induced by monsoon winds. The influence on 10 Be by the Kuroshio branch intrusion in the southern East China Sea northeast of Taiwan may be more significant than the Kuroshio main flow. Simple box model results indicate that 10 Be input from the Kuroshio Current is more important than Yangtze River input and atmospheric precipitation. About 81% of 10 Be input to the East China Sea is scavenged into the sediments and 19% of 10 Be flows out of the East China Sea by currents and water exchange. The 10 Be sedimentation flux in the East China Sea is nearly five times of the average global 10 Be production rate, suggesting that the East China Sea is an important sink for 10 Be .

Unleached aliquots of TIRI/FIRI turbidite were analyzed by accelerator mass spectronomy (AMS) over a timespan of 18 months. Individual analyses ranged from 18,090–18,245 yr BP with reported errors between 30–50 yr. The weighted average fraction modern (FM) of these 28 measurements is 0.10378 ± 0.00008 (which equates to 18,199 ± 8 yr BP) and the measurements show a 1 standard deviation scatter of 0.00044 (±35 yr). The fractional error of these results indicates reproducibility of individual measurements at the 4 (1σ) level, which is consistent with the quoted counting-statistics-based errors. Laboratories engaged in the determination of 14C results at reasonably high precision should consider taking advantage of the TIRI and FIRI sample materials in the role of process standards. Additional suites of high-precision data are necessary to refine the accuracy of these sample materials.

A glossy, black deposit covers much of the ceiling and walls of Little Lost River Cave No. 1, Idaho. This site is of particular interest because of the red, orange, and yellow pictographs underlying the coating. Carbon and nitrogen stable isotope analysis has allowed us to better understand the nature and origin of the deposit. With a δ13C value of −20·1‰, δ15N value of +14‰, and a C/N ratio of 5·6 after removal of inorganic carbon from the sample matrix, the deposit appears to have been derived from animal tissue, not plant. Plasma chemical extraction of carbon from the organic material in another sample of the deposit, followed by accelerator mass spectrometric analysis, yielded a minimum uncalibrated radiocarbon age of 2990±50 bp for the paintings. This preliminary evidence suggests that the deposit may be a cooking residue.

Samples from three charcoal pictographs at Ignatievskaya Cave, in the southern Ural Mountains of Russia, have been radiocarbon dated. An advanced antiquity was expected, with some paintings thought to be more than 10,000 years old, as suggested by the imagery. One charcoal painting, for example, resembles a mammoth. The radiocarbon date of that motif, however, dates only to 7370±50 BP. If that motif actually represents a live mammoth, it places mammoth extinction in the Urals nearer to the present than is currently accepted. A charcoal pigment sample, a drawing of lines radiating from a central focus, has also been dated; its age was a few hundred years older than the ‘mammoth’: 7920±60 BP. A charcoal line has been dated with an age of 6030±110 BP. Although radiocarbon analysis was attempted on a red-pigmented painting of a woman, there was not enough organic material in the paint sample to obtain a viable date. Radiocarbon dates on pictographs in Ignatievskaya Cave obtained so far suggest that the paintings may be more recent than has been supposed.

The first meeting of the IntCal04 working group took place at Queen's University Belfast from April 15 to 17, 2002. The participants are listed as co-authors of this report. The meeting considered criteria for the acceptance of data into the next official calibration dataset, the importance of including reliable estimates of uncertainty in both the radiocarbon ages and the cal ages, and potential methods for combining datasets. This preliminary report summarizes the criteria that were discussed, but does not yet give specific recommendations for inclusion or exclusion of individual datasets.

Four sediment cores and twenty-five 14C ages from Ritterbush Pond in northern Vermont provide a detailed and continuous temporal record of Holocene lake and watershed dynamics. Using visual logs, carbon content, magnetic susceptibility, stable isotope signatures, and X-radiography, all measured at 1-cm scale, we identify and date discrete layers of terrestrially-derived sediment in the organic-rich, lacustrine gyttja. These inorganic layers range in thickness from 10 cm and range in grain size and sorting from homogeneous silt to graded sand. AMS radiocarbon ages both from macrofossils within the thickest layers, and gyttja bracketing these layers, provide the basis for correlation among the cores, the dating of 52 basin-wide sedimentation events, and the development of a detailed sedimentation chronology for the Holocene.

δ18O records from the GISP2 and GRIP ice cores are widely used as benchmark paleoclimate chronologies, but there are significant differences between the two time scales. The present study shows that offsets between the two chronologies over the past 14,500 yr do not accumulate gradually, but appear over two short intervals of 100–200 yr. An initial offset of 80 yr occurs close to 3300–3400 yr B.P., and another 100 yr of slip appears at the start of the Younger Dryas. Since these discrepancies are localized, resolving them may be far easier than if large sections of both cores required reexamination.

Juvenile Sebastes jordani individuals sampled in late spring 1995, 1996, and 1997 near Monterey Bay, California, were analyzed for Δ 14 C, δ 13 C, and δ 15 N. As anticipated, a strong negative correlation was found between mean annual juvenile rockfish Δ 14 C and the preceding 3-month average Bakun upwelling index for this region. The sensitivity of this isotopic response by juvenile rockfish to upwelling variations was similar to that previously observed in surface-water inorganic carbon in nearby Half Moon Bay (Robinson 1981). This indicates that the Δ 14 C of surface-dwelling marine fish can be used as a measure of fish feeding in freshly upwelled 14 C-depleted water. However, we found no correlation between this parameter and fish somatic condition as measured by deviations in the regressions of individual fish (1) weight on length, (2) otolith size on fish length, or (3) total lipid content on dry weight. This questions the role upwelling plays in affecting juvenile rockfish condition. Also unrelated to fish condition were fish δ 13 C and δ 15 N, implying that the condition of juvenile S. jordani is unaffected by variation in the consumption of specific, isotopically discernible food resources.

Radiocarbon age determinations are presented on three hieroglyphic texts from Naj Tunich cave in Guatemala containing Maya calendar dates. The ages obtained are on average 110–140 years older than the calendar dates. Several possible reasons are discussed for this discrepancy: one that is applicable to all radiocarbon dates on charcoal, one that applies to rock paintings, and one that is specific for the tropics. Possible problems with the ages ascribed to the Maya calendar dates are also discussed. Even with the potential problems that may exist, these dates still fall within 110–140 years of the ascribed calendar dates. Caution is urged in the interpretation of dates on charcoal pigments from rock paintings; consideration of the “old wood” and “old charcoal” factors is important.

Evaluation of 14C in tree rings provides a measure of the flux of magmatic CO2 from Mammoth Mountain both before and after 1994 when copious diffuse emissions were first discovered and linked to tree kill. We analyzed the annual rings of trees with two main purposes: (1) to track changes in the magnitude of magmatic CO2 emission over time, and (2) to determine the onset of magmatic CO2 emission at numerous sites on Mammoth Mountain. The onset of CO2 emission at different areas of tree kill was determined to be in 1990, closely following the seismic events of 1989. At Horseshoe Lake (HSL), CO2 emission was found to have peaked in 1991 and to have subsequently declined by a factor of two through 1998. The tree-ring data also show that emissions of magmatic carbon from cold springs below the tree-kill areas occurred well before 1989. Trees located on the margins of the kill areas or otherwise away from zones of maximum gas discharge were found to be better integrators of magmatic CO2 emission than those located in the center of tree kills. Although quantitative extrapolations from our data to a flux history will require that a relationship be established between 14C depletion in tree rings and average annual magmatic CO2 flux, the pattern of 14C depletion in tree rings is likely to be the most reliable indicator of the long-term changes in the magnitude of CO2 release from Mammoth Mountain.

This report presents four radiocarbon dates of charcoal pigments from Picture Cave, a site located in a remote wooded area in east-central Missouri. Carbon from charcoal pigments was extracted from three rock drawings on the wall of this cave. The four pigment samples contained sufficient carbon for accelerator mass spectrometric radiocarbon analysis. These black pigment samples (red and white paints are also present in the cave) yielded dates that place their affiliated motifs in a time-frame associated with Cahokia ca. 950 years ago. The dates are somewhat earlier than expected. We discuss the dates in connection with the iconography of the three motif panels tested.

The Tierra Blanca Joven (TBJ) eruption of the Ilopango caldera in central El Salvador was one of the largest Holocene volcanic events in Central America, and its ecological and cultural impacts were felt throughout El Salvador and adjoining areas of Guatemala and Honduras. Early radiocarbon measurements established a ca. A. D. 260 ± 114 calendar date for the eruption. However, a reevaluation of the original 14C dates, in addition to new AMS 14C assays, shows that the TBJ eruption occurred at least a century and a half later than originally estimated. The revised 14C composite supports an Early Classic Period calendar date for the eruption: 1 sigma = A. D. 421(429)526; 2 sigma = A. D. 408(429)536. A review of archaeological settlement, ceramic, and radiocarbon evidence from sites throughout the area of greatest devastation reveals a large-scale demographic collapse following the event. We believe that the population crash was caused both by the biophysical effects of the eruption and by the resulting disarticulation of the "Miraflores" cultural-economic sphere. The affected areas of El Salvador and south-eastern Guatemala did not completely recover until the seventh century A. D.