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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.

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.

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.

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.

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.

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.

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.

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.

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.

A human skeleton recovered near Kennewick, Washington, USA in 1996 has been dated to the early Holocene on the basis of multiple radiocarbon determinations, an analysis of a style of a temporally diagnostic projectile point found embedded in the ilium of the skeleton, and geological investigations of the locality where the skeleton was recovered. Based on morphological criteria, the Kennewick skeleton, which is one of the most complete early Holocene human skeletons recovered so far in the Western Hemisphere, appears to be more similar to those of modern South Asians and Europeans than to modern Native Americans or to contemporary indigenous populations of Northeast Asia.

In the transition area between the subarctic and subtropical regions in the western North Pacific, vertical distributions of radiocarbon at seven stations were clarified by AMS radiocarbon measurement in 1997. The radiocarbon in intermediate water at those stations indicate (1) direct ventilation of upper intermediate water above 26.6σθ surface and (2) no temporal increment of radiocarbon in the transition area during the last two decades. These results positively suggest that the North Pacific intermediate water is formed in the transition area in the western North Pacific.

Previous reports using archaeological, ethnohistoric, and historic data have proposed that petroleum was extracted by pre-contact aboriginal populations in western Pennsylvania employing wood-lined pits. A suite of AMS-based 14C analyses on total amino acid extracts on nine duplicate samples from a homogenized decadal (10-year) sample of wood taken from a single stake removed from a pit feature at Drake Well Park, Titusville, Pennsylvania, has permitted the calibration of a mean 14C age of 480 ± 15 B.P. to a 2 sigma (95.4%) confidence interval of A.D. 1415-1440. An early fifteenth-century age for this feature supports the view that petroleum exploitation in this region occurred during Late Woodland times.

Well-dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events, and by inference, storms, have varied over the past 10 k.y. in northern New England. We used five sediment cores and radiocarbon dating to develop a chronology of Holocene hydrologic events for the Ritterbush Pond basin, northern Vermont. Chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events. The thickness of some layers suggests hydrologic events at least equal in size to, and probably much larger than, any storm or flood recorded during nearly 300 yr of written regional history. Layer thickness and frequency and, by analogy, storm size and recurrence, change through the Holocene. The largest events occurred 2620, 6840, and 9440 calibrated 14C years before present (cal 14C yr B.P.). The most frequent hydrologic events occurred in three periods: 1750 to 2620, 6330 to 6840, and >8600 cal yr B.P. The recurrence interval of layer deposition during stormy periods averages 130 ± 100 cal yr, whereas the recurrence interval during less stormy periods is longer, 270 ±170 cal yr. The Ritterbush Pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change.

This article presents radiocarbon dates for painted motifs at Red Cliffs, west of Sedona in the northeastern corner of Yavapai County, Arizona. All rock painting shields at the Red Cliffs sites have usually been attributed to the Sinagua. Black pigment from one shield motif and an overlying white dot on another motif yielded uncalibrated radiocarbon dates of 1080 and 550 years B.P., respectively. The black pigment sample dates to a time when the region was extensively used. Assuming that the two shields were painted contemporaneously, the age of the white dot sample suggests that a later cultural group altered Sinagua paintings at Red Cliffs after the Sinagua abandoned the region.

Environmental 14C is well known for its application in carbon dating organic material, as well as its use as a geochemical tracer in the oceans and atmosphere. More recently, 14C in the form of atmospheric 14CO has been used to estimate the concentration of hydroxyl radical, which is the primary oxidant of the atmosphere. This latter application is dependent upon accurate knowledge of the cosmogenic production rate, which has been calculated, but not directly measured. We have measured the atmospheric production rate of 14C near the earth's surface on a 300-meter research tower in Colorado, at the South Pole, at Scott Base, Antarctica, and near Mount Cook, New Zealand. The observed production rate near the surface was 50% of the production rate calculated by an earlier study. We also find that the ‘ground effect’, which causes an increase in the thermal neutron flux resulting in an enhancement of the production rate of 14C, is significantly smaller than calculated in earlier studies.

Radiocarbon measurements have been obtained on contemporary plant samples collected at the site of Monte Verde, Chile, to examine the possibility that a locall4C reservoir effect impinges on the accuracy of thel4C values obtained on previously recovered archaeological samples. Thel4C activity of the modern plants do not reveal any offset from expected contemporaryl4C values and thus provide no support for a major postulated reservoir effect at least for the recent past. Although there is, at present, no direct means of measuring potentiall4C reservoir offsets in the late Pleistocene for this region, we are not aware of any current data that would indicate that there have been major changes during geologically recent times.

We present a simple method for manually separating pollen concentrates for radiocarbon accelerator mass spectrometry (AMS) dating using a mouth pipetting system. The required equipment is readily available from scientific equipment supply houses at minimal cost. Pollen samples from lake sediments required about 4 h of hand picking, whereas samples from marine sediments required about 8 h labor. Pollen dates from marine sediments were much older than expected. We are attempting to resolve whether this is due to contamination of the pollen or the presence of significant quantities of old reworked pollen. Pollen dates from lake sediments associated with Mazama Ash were consistent with other published ages; however, replicate dates on pollen samples from above the ash were consistently older than the surrounding sediment. Our results suggest that caution must be used when interpreting pollen dates if the potential for sediment reworking is present.

We have generated a high resolution coral {Delta}{sup 14}C record spanning the last 50 years to document the seasonal and interannual redistribution of surface waters in the western tropical Pacific. Prebomb (1947{endash}1956) {Delta}{sup 14}C values average {minus}63{per_thousand} and have a total range of 30{per_thousand}. Values begin to increase in 1957, reaching a maximum of 137{per_thousand} in mid-1983. Large interannual variability of up to 80{per_thousand} closely follows the El Ni{tilde n}o-Southern Oscillation (ENSO). During each ENSO warm phase, {Delta}{sup 14}C values begin to increase, reflecting the reduction of low-{sup 14}C water upwelling in the east and the invasion of subtropical water into the western equatorial tropical Pacific. Maximum {Delta}{sup 14}C values are in phase or lag the corresponding sea surface temperature maxima in the eastern tropical Pacific, whereas the rapid return to more negative {Delta}{sup 14}C is in phase with eastern Pacific ENSO indices. The highest-amplitude excursions occur during the 1965/1966 and 1972/1973 events, when the {sup 14}C contrast is highest between the eastern Pacific and subtropics. The 1982/1983 El Ni{tilde n}o, although a larger ENSO event, has a lower {Delta}{sup 14}C amplitude, reflecting the penetration of bomb radiocarbon into the equatorial undercurrent and the reduced contrast in {Delta}{sup 14}C betweenmore » thermocline and subtropical surface waters at that time. This coral record demonstrates the potential for using similar radiocarbon time series for documenting variability in Pacific shallow circulation over interannual and decadal timescales. {copyright} 1998 American Geophysical Union« less

The visual manifestation of the recent Hale-Bopp comet reminds us how telling are those rare objects which suddenly flare in the sky. One can suppose ancient people living by natural light were more compellingly struck by the sight of comets and supernovae, and understandably researchers seek images of them in the shapes of rock-art motifs. An absolute dating contradicts that supposition in respect of a presumed image of the visible supernova of AD 1054.

Relation between submilligram sample size and {sup 14}C activity for sample blanks (wood from Pliocene sediments) and a contemporary standard (oxalic acid) for catalytically reduced graphitic carbon was examined down to 20 micrograms. Mean age of the 1 mg wood sample blanks is now about 51.3 ka (0.168 pMC) while the mean for 20 microgram sample blanks is about 42.9 ka. So far, the lowest value for a 1-mg wood sample blank is about 60.5 ka (0.056 pMC). We have determined a mean {sup 14}C age of about 9.4 ka from a suite of 7 organic extracts from hair, bone, and matting from a mummified human skeleton from Spirit Cave, Nevada. These data indicate that the Spirit Cave human is the third, oldest directly-dated, human skeleton currently known from North America.

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 ( Δ R) 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. DOI: 10.2458/azu_js_rc.55.16384

The Vermilion Lakes site in Banff National Park, Alberta, has yielded cultural remains suggesting a possible sheep-hunting focus during the Paleoindian period and providing evidence for windbreaks or shelters dating as early as 10,300 B.P. Debris flows at this site have separated and preserved six or more cultural components dating between the mid-eleventh and mid-tenth millennia before present. Paleoenvironmental evidence suggests that most of these components date to a period of severe climate. Accelerator and conventional carbon dating of these strata suggest that, for at least part of this time, the detail of the temporal sequence is beyond the resolution of these techniques. Apparent 14C inversions can best be explained by 14C plateaus during key periods of the site's occupation.

The calibration of radiocarbon dates on marine materials involves a global marine calibration with regional corrections. Data from well-associated marine and terrestrial materials in archaeological artifacts from northern Chile indicated that the calibration is valid for the period ad 200–900 and suggest that coastal upwelling intensities during that period were similar to those of the early 20th century.

We report here progress on our technique for14C dating pictographs. We use low-temperature oxygen plasmas coupled with high-vacuum techniques to selectively remove carbon-containing material in the paints without contamination from rock substrates or accretions. We dated >16 pictograph samples that generally agree with ages expected on the basis of archaeological inference. We have shown that carbonate and calcium oxalate decomposition does not occur during our procedure; little mass fractionation is produced. We also used the technique on samples of known14C activity. In each case our results agree with previously determined ages of archaeological charcoal samples. Two samples of the standard Third International Radiocarbon Intercomparison wood yielded ages in near accord with the accepted value. We used14C-free samples to establish that the method and apparatus do not have a significant live carbon background. Each of these determinations supports our conclusion that the technique has the potential of producing accurate and reliable ages. However, background organic material in the basal rocks and accretions can be troublesome, often completely negating the dates obtained.

We report compound-specific radiocarbon analyses of organic matter in ocean sediments from the northeast Pacific Ocean. Chemical extractions and a preparative capillary gas chromatograph (PCGC) were used to isolate phospholipid fatty acids (PLFA) and n-alkanes from 3 cores collected off the coast of California, USA. Mass of samples for accelerator mass spectrometry (AMS) 14C analysis ranged from 13–100 μg C. PLFA extracted from anaerobic sediments in the Santa Barbara Basin (595 m depth) had modern Δ14C values (–20 to +54‰), indicating bacterial utilization of surface-produced, post-bomb organic matter. Lower Δ14C values were obtained for n-alkanes and PLFA from coast (92 m depth) and continental slope (1866 m) sediments, which reflect sources of old organic matter and bioturbation. We present a brief analysis of the blank carbon introduced to samples during chemical processing and PCGC isolation.

THE Black Sea, the world's largest anoxic marine basin, is frequently used as a modern analogue for the formation of organic-rich sediments and carbonaceous rocks1–3, on the widely held assumption that anoxic conditions promote the preferential preservation of organic matter in sediments. Data for testing this hypothesis have so far been equivocal4–7, but here we use radiocarbon ages obtained using accelerator mass spectrometry for the organic fraction of recent Black Sea sediments to estimate the organic carbon accumulation rates. These range from 0.69 to 2.09 g C m−2 yr−1 and are significantly lower than earlier estimates based on varve counting6. Depending on the value taken for the rate of primary production in the Black Sea4,8, between 0.7 and 2.1% of the organic carbon is preserved in the bottom sediments. When compared with carbon accumulation rates in equivalent oxygenated environments9, these results indicate that the modern Black Sea is not a site of anomalously high organic carbon accumulation. This suggests that anoxic conditions in the water column may not be a prerequisite for the preservation of organic matter in marine sediments, and that models of the origin of carbonaceous facies in the geological record may therefore need to be modified.

The ^(14)C reservoir age of the surface ocean was determined for two Holocene periods (4908–4955 and 3008–3066 calendar (cal) B.P.) using U/Th-dated corals from Biscayne National Park, Florida, United States. We found that the average reservoir ages for these two time periods (294 ± 33 and 291 ± 27 years, respectively) were lower than the average value between A.D. 1600 and 1900 (390 ± 60 years) from corals. It appears that the surface ocean was closer to isotopic equilibrium with CO_2 in the atmosphere during these two time periods than it was during recent times. Seasonal δ^(18)O measurements from the younger coral are similar to modern values, suggesting that mixing with open ocean waters was indeed occurring during this coral's lifetime. Likely explanations for the lower reservoir age include increased stratification of the surface ocean or increased Δ^(14)C values of subsurface waters that mix into the surface. Our results imply that a more correct reservoir age correction for radiocarbon measurements of marine samples in this location from the time periods ∼3040 and ∼4930 cal years B.P. is ∼292 ± 30 years, less than the canonical value of 404 ± 20 years.

“Post-maximum-bomb” 14C activities (1964 to the present) provide a natural isotopic signature to obtain information on biomass source age in contemporary food preparations. An analysis of the 14C content in frozen orange juice-containing products purchased in 1996 suggested, in one case, an inferred growth period between 1992 and 1994 for oranges used in the preparation of this commodity. In another case, the 14C analysis indicated an inferred average growth period of 1988−90 for the organics in a “frozen concentrated enriched citrus beverage”. The presence of significant amounts of chemical additives obtained or synthesized from fossil carbon sources can also be documented by measuring 14C content. Keywords: Radiocarbon; carbon isotopes; orange juice; component age

The notable sparseness of human skeletal remains is a characteristic trait of early American prehistory and, therefore, this aspect of the archaeological record is seldom considered in its discussion. In this context, the finding of remains from five individuals dated to the 9th millenium BP on the re-excavations at Bano Nuevo Cave (Andean Central Patagonia, Chile) is particularly interesting. They may not appear excessively old, but several radiocarbon dates (two of them done through AMS directly on the bone of one of the individuals) place them among the very few well-dated early human skeletons throughout the Americas. The small sample size militates against any interpretation of biological affiliation (to say nothing of population movements) and we can only affirm that these people belonged to a generalized “mongoloid stock”, different from historically known Patagonian populations. After a brief presentation of the skeletal evidence and the bone dating methods, we evaluate the relevance of this context with respect to the sparse osteological record of humans in the Americas on the Pleistocene/Holocene transition.

Radiocarbon data from the Cariaco Basin provide calibration of the carbon-14 time scale across the period of deglaciation (15,000 to 10,000 years ago) with resolution available previously only from Holocene tree rings. Reconstructed changes in atmospheric carbon-14 are larger than previously thought, with the largest change occurring simultaneously with the sudden climatic cooling of the Younger Dryas event. Carbon-14 and published beryllium-10 data together suggest that concurrent climate and carbon-14 changes were predominantly the result of abrupt shifts in deep ocean ventilation.

Differences in radiocarbon apparent ages between coexisting planktonic and benthic (B-P) foraminifers in the Santa Barbara Basin contain information about changes in the age (and thus the source) of water entering the basin. The Holocene sequence indicates a greater variability in circulation than previously detected. During the early Holocene, ca. 9 ka, B-P 1 4 C apparent age differences fluctuated between 220 and 560 1 4 C yr, similar to rapid variations seen during the Younger Dryas and the last glacial episode. During the relatively stable middle Holocene (8.5-2 ka), B-P 1 4 C apparent age differences averaged 440 1 4 C yr. After 2 ka, the average B-P 1 4 C apparent age difference increased to 620 1 4 C yr, which has persisted until the present. The shift in B-P 1 4 C apparent age differences likely represents a change in the strength or source of North Pacific Intermediate Water production and is concurrent with changes in regional climate patterns as well as with changes in temperature and accumulation rates measured in the Greenland Ice Sheet Project 2 ice core, suggesting large-scale changes in atmospheric circulation patterns.

The News & Comment article “Kennewick Man's trials continue” by Virginia Morell (10 Apr., [p. 190][1]) reports the continuing legal and administrative conflicts over attempts by anthropologists and others to regain the ability to sample the Kennewick and other early North American skeletons to