Oceanic uptake and transport of bomb radiocarbon as 14CO2 created by atmospheric nuclear weapons testing in the 1950s and 1960s has been a useful diagnostic for determining the carbon transfer between the ocean and atmosphere. In addition, the distribution of 14C in the ocean can be used as a tracer of oceanic circulation. Results obtained on samples collected in the Gulf of Alaska in the summer of 2002 provide a direct comparison with results in the 1970s during GEOSECS and in the early 1990s during WOCE. The open gyre values are 20–40% lower than those documented in 1991 and 1993 (WOCE), although the general trends as a function of latitude are reproduced. Surface values are still significantly higher than pre-bomb levels (∼ −105% or lower). In the central gyre, we observe Δ14C values that are lower in comparison to GEOSECS (stn 218) and WOCE P16/P17 to a density of ∼26.8 σt. This observation is consistent with the overall decrease in surface Δ14C values and reflects the erosion of the bomb-14C transient. We propose that erosion of the bomb-14C transient is accomplished by entrainment of low-14C water via vertical exchange within the Gulf of Alaska and replenishment of surface and subther-mocline waters with waters derived from the far northwest Pacific.

We analyzed a sediment core from the equatorial Arabian Sea, chronologically constrained by accurate accelerator mass spectrometry (AMS) radiocarbon dates on selected planktonic foraminiferal species, for paleoproductivity variations corresponding to the variations in the Indian Ocean Equatorial Westerlies (IEW). The IEW in turn are positively correlated to the Southern Oscillation Index (SOI), which is a measure of El Niño, Southwest monsoon (SWM), and east African rainfall (EAR). The productivity data show that Indian and east African rainfalls declined from 35,000 calendar yr BP up to the last glacial maximum (LGM), with the maximum El Niño frequency during the last glacial period. From ∼14,500 to ∼2000 calendar yr BP (i.e. core top), we find strengthening SWM and EAR along with declining El Niño frequency.

Calibration (using CALIBomb) of radiocarbon measurements made on the enamel of human teeth from people born during the nuclear era typically produce 2 possible age ranges that potentially reflect the period of tooth formation. These ranges correspond to periods before and after the 1963 atmospheric 14C maximum. Further measurements made on the collagen component of the combined dentine and cementum from the roots of the same teeth enable the appropriate age range to be selected. Using this range and the formation times for individual teeth, we estimated the year of birth of the individuals and compared these to the known dates of birth. The results were relatively accurate and confirmed those of a previous study by another research group. The present study demonstrates that it is possible to produce a good estimate of the year of birth from a single tooth.

Radiocarbon analysis was performed by liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) to assess whether the content of biological components in hydrocarbon fuels could be derived. Different fuel mixtures were prepared containing bioethanol, fossil ethanol, and fossil gasoline. The specific 14C activity of these mixtures was obtained from LSC measurements and directly related to the concentration of carbon originating from the bioethanol (biocarbon). The results were checked via standardized carbon dating procedures and AMS. A good linear correlation exists between the fuel mixture's specific 14C activity and the concentration of biocarbon. Also, the biocarbon fraction of the fuel mixture (the ratio biocarbon : total carbon) and the normalized fraction of biocarbon (%M) showed good linear correlation. Therefore, both relations provide a possibility to quantitatively determine a fuel's biocarbon content by 14C analysis. When the sample composition is known (e.g. resolved by gas chromatography-mass spectroscopy [GC-MS] and nuclear magnetic resonance [NMR]), the amount of particular biological components in a fuel sample can be derived subsequently. For mixtures of bioethanol, fossil ethanol, and gasoline with bioethanol contents in the range of 0.5–2% m/m, it was found that errors in the normalized fraction of biocarbon (%M) were in the range of 25–10%, respectively. For samples with a higher bioethanol content (up to pure bioethanol), the errors in %M were <10%. Errors might be larger if substantial changes in the concentration of atmospheric 14C took place during the growth period of the biofuel feedstock. By taking into account the variation in specific 14C activity of carbon over the last decades, and by modeling simple tree-growth, it could be illustrated that this effect becomes significant only if the biofuel feedstock stopped growing more than 1 decade ago, e.g. with wood from constructions.

The Oxford Radiocarbon Accelerator Unit (ORAU) has used an ultrafiltration protocol to further purify gelatin from archaeological bone since 2000. In this paper, the methodology is described, and it is shown that, in many instances, ultrafiltration successfully removes low molecular weight contaminants that less rigorous methods may not. These contaminants can sometimes be of a different radiocarbon age and, unless removed, may produce erroneous determinations, particularly when one is dating bones greater than 2 to 3 half-lives of 14C and the contaminants are of modern age. Results of the redating of bone of Late Middle and Early Upper Paleolithic age from the British Isles and Europe suggest that we may need to look again at the traditional chronology for these periods.

High freshwater inputs into Scottish sea lochs (fjords) combined with the restricted exchange between sea loch basin water and coastal Atlantic water masses are likely to result in reduced regional marine radiocarbon reservoir ages (R[t]) in these environments. To test this hypothesis, historical, museum-archived shells, collected live on known dates prior to AD 1950 from coastal locations in NW Scotland, were 14C dated to provide a means of determining R(t) and hence the regional deviation (ΔR) from the modeled global surface ocean reservoir age (R). The sea loch data, when combined with 14C dates from the Scottish west coast (Harkness 1983), yield a regional ΔR value of −26 ± 14 yr. The ΔR of sea loch (fjordic) and coastal waters of NW Scotland are statistically different (at a confidence level >95%) from the ΔR value of 17 ± 14 yr reported for UK coastal waters (Reimer 2005; data after Harkness 1983) and are in good agreement with the coastal ΔR value of −33 ± 93 yr reported by Reimer et al. (2002). Therefore, it is recommended that a regional ΔR correction of −26 ± 14 yr should be applied to modern (i.e. pre-bomb but not prehistoric) marine 14C dates from the NW coast of Scotland.

Isotope tracer studies, particularly radiocarbon measurements, play a key role in biological, nutritional, and environmental research. Accelerator mass spectrometry (AMS) is now the most sensitive detection method for 14C, but AMS is not widely used in kinetic studies of humans. Part of the reason is the expense, but costs would decrease if AMS were used more widely. One component in the cost is sample preparation for AMS. Biological and environmental samples are commonly reduced to graphite before they are analyzed by AMS. Improvements and mechanization of this multistep procedure is slowed by a lack of organized educational materials for AMS sample preparation that would allow new investigators to work with the technique without a substantial outlay of time and effort. We present a detailed sample preparation protocol for graphitizing biological samples for AMS and include examples of nutrition studies that have used this procedure.

Within the framework of radioecological studies, 90Sr was determined in wheat grains, soil, and deposition samples. The radiochemical purification of 90Y consisted of liquid-liquid extraction by tributyl phosphate (TBP), followed by hydroxide and oxalate precipitations and, if necessary, the removal of thorium by anion exchange chromatography. The procedure proved to be very robust and reliable, having yttrium yields of 92.7 ± 4.6% for 1-kg wheat samples, 90.9 ± 4.2% for 50-g soil samples, and 90.6 ± 3.2% for wet and dry deposition samples. 90Y was determined by Cerenkov counting and proportional counting. By optimizing the Cerenkov counting window, a figure of merit (FOM) of 4750 could be reached using a Quantulus™ 1220 system. Minimum detectable activities were in the range of 10 mBq.

This paper focuses on the use of the radiocarbon content of marine shells collected along the Portuguese coast as a proxy for the intensity of coastal upwelling off of Portugal. Differences in the 14C ages of closely associated marine mollusk shells and terrestrial material (charcoal or bones) from several Portuguese archaeological contexts seem to be significant throughout the Holocene. ΔR values range from 940 ± 50 to −160 ± 40 14C yr. Five of these values are significantly higher than the modern value (250 ± 25 14C yr), while the remaining values are lower. The modern value was calculated by measuring the 14C content of live-collected, pre-bomb marine mollusk shells. This value is in accordance with an active upwelling of strong intensity that currently occurs off of Portugal. Some primary observations based on data presented here can be made: i) during the Holocene important changes have occurred in the ocean reservoir effect off the Portuguese coast; ii) these fluctuations may be correlated with regional oceanographic changes, namely with changes in the strength of coastal upwelling; and iii) these changes suggest some sort of variability of the climatic factors forcing coastal upwelling off of Portugal.

Recent methodological advances in the use of zeolite molecular sieves for measuring the isotopic signature of CO2 have provided the opportunity to make direct measurements of 14CO2 in various field situations. We linked a portable molecular sieve/pump/IRGA system to a floating chamber to demonstrate the potential of the method to quantify the isotopic signature (δ13C and 14C) of CO2 lost by evasion (outgassing) from surface waters. The system, which was tested on a peatland stream in Scotland, involved 1) an initial period of scrubbing ambient CO2 from the chamber, 2) a period of CO2 build-up caused by surface water evasion, and 3) a final period of CO2 collection by the molecular sieve cartridge. The field test at 2 different sites on the same drainage system suggested that the results were reproducible in terms of δ13C and 14C values. These represent the first direct measurements of the isotopic signature of CO2 lost by evasion from water surfaces.

Volcanic ash soils (Andosols) may offer great opportunities for paleoecological studies, as suggested by their characteristic accumulation of organic matter (OM). However, understanding of the chronostratigraphy of soil organic matter (SOM) is required. Therefore, radiocarbon dating of SOM is necessary, but unfortunately not straightforward. Dating of fractions of SOM obtained by alkali-acid extraction is promising, but which fraction (humic acid or humin) renders the most accurate 14C dates is still subject to debate. To determine which fraction should be used for 14C dating of Andosols and to evaluate if the chronostratigraphy of SOM is suitable for paleoecological research, we measured 14C ages of both fractions and related calibrated ages to soil depth for Andosols in northern Ecuador. We compared the time frames covered by the Andosols with those of peat sequences nearby to provide independent evidence. Humic acid (HA) was significantly older than humin, except for the mineral soil samples just beneath a forest floor (organic horizons), where the opposite was true. In peat sections, 14C ages of HA and humin were equally accurate. In the soils, calibrated ages increased significantly with increasing depth. Age inversions and homogenization were not observed at the applied sampling distances. We conclude that in Andosols lacking a thick organic horizon, dating of HA renders the most accurate results, since humin was contaminated by roots. On the other hand, in mineral soil samples just beneath a forest floor, humin ages were more accurate because HA was then contaminated by younger HA illuviated from the organic horizons. Overall, the chronostratigraphy of SOM in the studied Andosols appears to be suitable for paleoecological research.

The isotopic composition of ancient wood has the potential to provide information about past environments. We analyzed the δ13C, δ18O, and δ2H of cellulose of conifer trees from several cross-sections at each of 9 sites around the Great Lakes region ranging from ∼4000 to 14,000 cal BP. Isotopic values of Picea, Pinus, and Thuja species seem interchangeable for δ18O and δ2H comparisons, but Thuja appears distinctly different from the other 2 in its δ13C composition. Isotopic results suggest that the 2 sites of near-Younger Dryas age experienced the coldest conditions, although the Gribben Basin site near the Laurentide ice sheet was relatively dry, whereas the Liverpool site 500 km south was moister. The spatial isotopic variability of 3 of the 4 sites of Two Creeks age shows evidence of an elevation effect, perhaps related to sites farther inland from the Lake Michigan shoreline experiencing warmer daytime growing season temperatures. Thus, despite floristic similarity across sites (wood samples at 7 of the sites being Picea), the isotopes appear to reflect environmental differences that might not be readily evident from a purely floristic interpretation of macrofossil or pollen identification.

In this paper, we investigate how to achieve high-accuracy radiocarbon measurements by accelerator mass spectrometry (AMS) and present measurement series (performed on archived CO2) of 14CO2 between 1985 and 1991 for Point Barrow (Alaska) and the South Pole. We report in detail the measurement plan, the error sources, and the calibration scheme that enabled us to reach a combined uncertainty of better than ±3%. The δ13C correction and a suggestion for a span (or 2-point) calibration for the 14C scale are discussed in detail. In addition, we report new, accurate values for the calibration and reference materials Ox2 and IAEA-C6 with respect to Oxl. The atmospheric 14CO2 records (1985–1991) are presented as well and are compared with other existing records for that period. The Point Barrow record agrees very well with the existing Fruholmen (northern Norway) record from the same latitude. The South Pole record shows a small seasonal cycle but with an extreme phase with a maximum on January 1st (±13 days). Together with its generally elevated 14C level compared to the Neumayer record (coastal Antarctica), this makes our South Pole data set a valuable additional source of information for global carbon cycle modeling using 14CO2 as a constraint.

Dating ice samples from glaciers via radiocarbon is a challenge that requires systematic investigations. This work describes an approach for extraction and accelerator mass spectrometry (AMS) 14C analysis of the particulate organic carbon (POC) fraction in glacier ice samples. Measurements were performed at VERA (Vienna Environmental Research Accelerator) on ice samples obtained mainly from the non-temperated ablation zone of the Grenzgletscher (Grenz Glacier) system (Monte Rosa Massif, Swiss Alps). The samples were obtained from 2 sampling sites situated roughly on a common flow line. The sample masses used were between 0.3 and 1.4 kg of ice, yielding between 18 and 307 μg of carbon as POC. The carbon contamination introduced during sample processing varied between 5.4 and 33 μg C and originated mainly from the quartz filters and the rinsing liquids used in processing. Minimum sample sizes for successful graphitization of CO2 in our laboratory could be reduced to <10 μg carbon, with a background in the graphitization process of ∼0.5 μg of 40-pMC carbon. Evaluation of the whole procedure via 11 Grenzgletscher samples revealed a surprisingly large scatter of pMC values. We obtain a mean calibrated age of 2100 BC to AD 900 (95.4% confidence level), which is not significantly different for the 2 sampling sites. Discussions of these results suggest that single 14C dates of glacial POC are presently of limited significance. Future improvements with respect to analytical precision and sample characterization are proposed in order to fully explore the POC dating potential.