We conducted a study of relative gas composition changes of CO2, CO and CH4 during the formation of graphite targets using different temperatures, catalysts and methods. Reduction with H2 increases the reaction rate without compromising the quality of the AMS target produced. Methane is produced at virtually any temperature, and the amount produced is greater at very low temperatures. The reduction of CO to graphite is very slow when H2 is not included in the reaction.

The radiocarbon reservoir age correction values (R) for the Russian Far East are estimated as 370 ± 26 yr for the northwestern Sea of Japan, and 711 ± 46 yr for the southern Kurile Islands.

We built a floating, 1382-ring pine chronology covering the radiocarbon age interval of 12,000 to 10,650 BP. Based on the strong rise of Δ14C at the onset of the Younger Dryas (YD) and wiggle-matching of the decadal-scale Δ14C fluctuations, we can anchor the floating chronology to the Cariaco varve chronology. We observe a marine reservoir correction higher than hitherto assumed for the Cariaco site, of up to 650 yr instead of 400 yr, for the full length of the comparison interval. The tree-ring Δ14C shows several strong fluctuations of short duration (a few decades) at 13,800; 13,600; and 13,350 cal BP. The amplitude of the strong Δ14C rise at the onset of the YD is about 40, whereas in the marine data set the signal appears stronger due to a re-adjustment of the marine mixed-layer Δ14C towards the atmospheric level.

A line for preparation of graphite targets for accelerator mass spectrometry (AMS) radiocarbon dating has been built in the Gliwice 14C Laboratory. The AMS 14C measurements of our targets are performed in the Leibniz-Labor für Altersbestimmung, Kiel, Germany. The quality of our line has been tested in two series of AMS 14C measurements of background and Ox-II standard samples and by measurements of the amount of CO2 released during combustion of sample-free quartz tubes. Most background contamination in the first series was introduced during combustion, which has been greatly reduced by baking quartz tubes vacuum-sealed with CuO and Ag. The residual contamination (ca. 1.5 μg C) seems to come mostly from the quartz tubes themselves. At present, most of the contamination of the background is introduced during graphitization. The reproducibility of background preparations is satisfactory, especially for samples larger than 1.5 mg, when it is better than ± 0.09 pMC. Despite still significant contamination with low-14C carbon during the graphitization process (corresponding to 1.2 ± 0.2% of 14C-free carbon), the good reproducibility of the results allows us to use our line in routine 14C dating.

Proficiency testing is a widely used, international procedure common within the analytical chemistry community. A proficiency trial (which VIRI is) often follows a standard protocol, including analysis that is typically based on z-scores, with one key quantity, σp . From a laboratory intercomparison (sometimes called a proficiency trial), we hope to gain an assessment of accuracy (in this case, from dendro-dated samples), laboratory precision (from any duplicate samples), and generally, an overall measure of performance, including measurement variability and hence realistic estimates of uncertainty. In addition, given our stated aim of creating an archive of reference materials, we also gain a determination of consensus values for new reference materials.

VIRI samples have been chosen to deliver these objectives and the sample ages included in the different stages, by design, spanned modern to background. With regard to pretreatment, some samples required intensive pretreatment (e.g. bone), while others required none (e.g. cellulose and humic acid). Sample size was not optimized, and indeed some samples were provided solely for accelerator mass spectrometry (AMS) measurement. In this sense, VIRI presented a more challenging exercise than previous intercomparisons, since by its design in stages, one can explore improvements (or deteriorations) over time in laboratory performance. At each stage, more than 50 laboratories have participated, with an increasing demographic shift towards more AMS and fewer radiometric laboratories.

The A.E. Lalonde accelerator mass spectrometer (3MV, HVEE) was commissioned in early 2014 at the University of Ottawa (Canada). The radiocarbon sample preparation laboratory spent the better part of 2014 undertaking a quality control program, establishing pretreatment protocols, and streamlining sample processing. In the fall of 2014, the first unknown samples were accepted and in the first year of operation well over 1000 targets (~60% unknowns) were analyzed. Here, we present an overview of sample processing protocols and results from routinely measured standards, reference, and blank materials.

Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (δ13C) and nitrogen (δ15N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of δ13C and δ15N showed a distinct enrichment trend down profile with a large (average 13δC = 5.0 and average 15δN= 6.3) and abrupt offset within the uppermost 10–20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 are usually interpreted as a recent change from C4 to C3 dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.

A new National Electrostatic Corporation (NEC) 5MV accelerator mass spectrometer became operational at the Scottish Universities Environmental Research Centre (SUERC) in July 2002. It has 2 Cs sputter negative ion sources: a 134-sample source (S1) for the routine measurement of all species, and a hybrid source (S2) with 40 spaces for radiocarbon measurements with either graphite or CO2 samples. A number of performance tests on graphite samples have been carried out on both sources. A precison of better than 0.3% is feasible for modern samples on a routine basis. The 14C background of the machine and the graphite preparation process blank are 0.04 ± 0.01 and 0.16 ± 0.05 pMC, respectively, indicating that 14C dating back to ~50 kyr BP is possible. The normalized 14C values for a series of reference materials agree well with the IAEA, TIRI, and FIRI consensus values. Routine measurement of 14C has been underway since May 2003. Preliminary results of performance tests on the CO2 gas ion source are also reported.

As an extension of the Bratislava – Tbilisi collaboration, thermonuclear bomb-produced 14C variations in atmospheric CO2 of Bratislava (1967–1987) and in annually produced Georgian wines (1950–1987) are discussed. 14C produced in bomb tests performed in the atmosphere has considerably modified the natural 14C levels in the atmosphere and biosphere. Measurements of 14C in monthly samples of atmospheric CO2 show typical seasonal variations with maxima in summers and deep minima in winters. There is very good agreement between 14C measured in CO2 and in wine samples. Four maxima (1959, 1964, 1970 and 1978) were identified in the wine data. Our results confirm that wines prepared from annually grown grapes without any addition of other substances are good indicators of the 14C content of atmospheric CO2.

Observations of 14C in atmospheric CO2 at four different sites in central Europe, Heidelberg, Westerland, Schauinsland and Jungfraujoch have enabled us to determine individual fossil-fuel contributions to atmospheric CO2 concentration. The data clearly show a decrease of fossil-fuel CO2 with distance from anthropogenic source regions. At Heidelberg during winter we observe 14C/12C ratios up to 10% lower than at the clean air mountain station Jungfraujoch in the Swiss Alps, corresponding to an anthropogenic CO2 contamination level of ca 10% at the Heidelberg site. The Schauinsland and Westerland winter fossil-fuel CO2 concentrations are only ca 1.5 and 2% of the mean concentration, respectively. Our results indicate a strong seasonality in the European fossil-fuel CO2 source with ca 50% lower CO2 emissions during summer if compared to winter fossil-fuel CO2 release. This effect may significantly contribute (by 1–2 ppm) to the observed annual cycle of atmospheric CO2 concentration in northern mid-latitudes.

In August 1980, the National Bureau of Standards (NBS) issued, in the form of oxalic acid, a new International Reference Material of contemporary 14C for use in radiocarbon dating laboratories. This reference material was to replace the 1975 oxalic-acid standard, supplies of which had been practically exhausted in 1978. The preparation of the new oxalic-acid standard was described in a preliminary report, as were, also, the results then available for the activity-concentration ratio of the new to the old standard obtained by a number of leading international laboratories.

With the recent completion of the analysis of all results submitted by the participating laboratories, NBS plans to issue these recently calibrated samples of oxalic acid as an NBS Standard Reference Material. There is, however, no significant difference in the reported value of its activity concentration, relative to that of the 1957 standard, from that given provisionally in 1980.

Subsequent to our report (Cavallo and Mann, 1980) a further measurement of relative activity concentration was reported by the Radiocarbon Laboratory of Peking University. Their value, and that also for δ13C, is insignificantly different from the average value of the results submitted by the eleven laboratories that participated in the international comparison organized by NBS.

The measurements reported have been carried out during 1965 in the Isotope Laboratory of the Institute of Geophysics and Planetary Physics as a continuation of the UCLA date lists I through IV. Samples were analyzed as CO2-gas at one atm in a 7.5 L proportional counter with three energy channels. Dates have been calculated on the basis of a 5568 yr half-life as was recommended by the Sixth International C11 and H3 Dating Conference, June 1965, in Pullman, Washington. The standard for the contemporary biosphere remains as 95% of the count rate of NBS oxalic acid for radiocarbon laboratories. Background determinations have been made with CO2 obtained from marble. The error listed is always at least a one-sigma statistical counting error.

A regional marine reservoir correction (ΔR) of 33±24 14C yr for southern Brazil was obtained from 6 marine shell samples collected in the states of Santa Catarina and Paraná. This work also presents a ΔR estimation of 8±17 14C yr for the southern and southeastern Brazilian coast from the states of Rio de Janeiro to Santa Catarina, obtained by including 7 ages published in previous works. The high variability of R in modern and Holocene samples from the Brazilian coast is also discussed.

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.

We performed radiocarbon measurements using accelerator mass spectrometry (AMS) on 6 stalagmites 3 stalactites and 7 seepage waters from four different caves in Southwest France and Belgium in order to calculate the dead carbon proportion (dcp). All the speleothems studied are modern and annually laminated, which offers the advantage of an accurate chronology, with better than one-year resolution. Coupled with the fact that very little calcite is necessary for an AMS measurement (between 1.5 and 7 yr of calcite deposit), we obtained dead carbon values within an uncertainty limit of ± 1.5%. Results show that the dead carbon proportion varies from 9.2% to 21.9% for calcite deposits and from 3.6% to 21.9% for water. In each sampling site, the dcp is homogeneous. Although the inter-site dcp varies by >11%, its average value of 15.5% ± 4.4 still lies within the uncertainty range of the accepted value of 15% ± 5 (dilution factor of 0.85 ± 0.5). We compare the average dcp of each site with the local geology, vegetation and climate. Given similar geology and temperature the highest dcp values are found under forest cover; dcp difference is up to 9%. However, the Belgian site, which is also under a forest shows a dcp very close to the dcp found under grassland sites of Southwest France, which proves that other unknown factors may play an important role in dissolution processes. Secondary calcite deposition and redissolution in the soil zone or more likely in the fracture system before reaching the cave itself could also explain the inter-site differences. The IAEA isotopic model (Pearson model adapted for open systems) is in good agreement with the measured activities.

The present list represents a major portion of the samples measured since publication of the last date list in 1963. As in previous lists, dates are reported in terms of the 5568 yr half-life. Infinite dates are reported as beyond a limit equal to 2σ above background. Nearly all of the samples were measured in one of three quartz counters with backgrounds of 0.7 to 1.2 cpm per liter of effective counting volume at working pressures of about two atmospheres. The age errors quoted are based only on the standard deviations in counting rates of sample and standards.

The various C14 projects of the Radiocarbon Laboratory have been supported by the National Science Foundation, Grants GP 4879 and GA 1157; the tree ring research has been supported by the Atomic Energy Commission under contract AT (30-1) 2652. Technical assistance has been provided by Carolyn H. Morgan and Terry C. Eisensmith.

In contrast to previous radiocarbon measurement lists, this list contains only known-age samples, most of which formed during the past ten years. The measurements were made largely in order to gain an understanding of the distribution of radiocarbon within the dynamic carbon reservoir both today and at times in the past. Since all materials forming in this reservoir today do not have the same C14/C12 ratio, such an understanding is necessary in order to arrive at the most accurate possible estimate of the age of samples submitted for dating. This is particularly important when high accuracy (i.e., <100 years error) is required on subaerially grown samples and also when attempting to extend the method to samples which formed in reservoirs other than the atmosphere (for example, the ocean and freshwater systems).

The shape of a distribution of calibrated 14C dates displays spurious peaks and troughs, brought about by changes in the slope of the calibration curve interacting with the spreading effect of the stochastic distribution of counting errors. The distortion results in a positive correlation between the numbers of dates per calendar year and the slopes of the calibration curves, for assemblages of archaeological dates from such widely separated areas as British Columbia, South Australia and New Zealand. The distortion also increases the possibility of date reversals, and increases the overall spread of calibrated 14C dates. After taking into account this systematic distortion and inbuilt age of charcoal and wood samples, we estimate dates for the initial settlement and first appearance of fortifications, and infer a likely trend of population growth for prehistoric New Zealand.

The conventional 14C ages of 8 marine shells of known age and 11 marine shells stratigraphically associated with dated wood charcoal show considerable variation from expected ages. One source of this variation is seashore geology; comparison of 6 AMS dates on 3 species of shallow-water, herbivorous gastropod shells from Pleistocene limestone and Holocene volcanic coasts shows that shells from Pleistocene limestone coasts can have apparent, or reservoir, 14C ages up to 620 yr greater than shells of the same species from volcanic coasts. The relatively great variation in apparent ages of Hawaiian marine shells poses problems for their use in dating archaeological sites. For best results, an archaeological marine shell should be sourced to a particular local environment, and the apparent age of shells in that environment determined by dating well-provenienced shells of known age.

The University of Waikato, Hamilton, New Zealand and The Queen's University of Belfast, Northern Ireland radiocarbon dating laboratories have undertaken a series of high-precision measurements on decadal samples of dendrochronologically dated oak (Quercus petraea) from Great Britain and cedar (Libocedrus bidwillii) and silver pine (Lagarostrobos colensoi) from New Zealand. The results show an average hemispheric offset over the 900 yr of measurement of 40 ± 13 yr. This value is not constant but varies with a periodicity of about 130 yr. The Northern Hemisphere measurements confirm the validity of the Pearson et al. (1986) calibration dataset.