Variability in temperature and 14C levels are recorded in coralline aragonite that grew in the Gulf Stream during the past four centuries. In particular, 18O/16O ratios reflect a decrease of ca 1°C in surface water temperature during the latter part of the Little Ice age. 14C levels also rose in the surface waters of the Gulf Stream and in atmospheric CO2 during the Maunder minimum. These observations indicate that ocean circulation may have been significantly different in the North Atlantic around the beginning of the 18th century.

Marine transport of inorganic and organic carbon is simulated by means of a computer model in which the oceans are divided into a high and low latitude region. Water transport (and with it carbon transport) is reproduced 1) as downwelling of surface waters at low latitudes, and 2) in general, as different depth-dependent turbulent diffusion in both deep-sea regions. The model is calibrated with pre-bomb 14C and validated against perturbations of total carbon, 13C/C- and 14C/C-ratios; it is compatible with carbon release from fossil fuels and from biogenic sources.

In early 1982 we attempted to compile information on 14C counting equipment from all laboratories listed in RADIOCARBON. A gratifying number of laboratories cooperated in communicating their data: more than 65% of those in which proportional counters are in operation. Our compilation covers more than 80% of all gas counters used for 14C dating. Unfortunately, the number of parameters determining counter quality as well as the spread in these factors is so large that their separate influence cannot be established beyond statistical doubt. Nevertheless qualitative and semi-quantitative trends are clearly observed. Laboratories are not identified in the data but the calculations and standardization procedures allow the laboratories to identify their own counter data in the graphs. Each plot does not contain a complete compilation of all counters. This is either because of lack of or internally inconsistent information.

As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25μm stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1–2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.

A conventional 14C system with either a 15cm3 or a 100cm3 methane gas proportional counting tube, each constructed from high purity copper, has been used at the Washington State University 14C laboratory for three years (Sheppard, Hopper, Westberg, 1981). The electronic components of this system included highly stable (John Fluke) power supplies, modified pre-amplifiers (Canberra), and NIM amplifiers, single channel analyzers, scalers, timers, etc, (ORTEC). Modules were selected for a highly stable low-noise system. The system was designed to minimize problems generated by ground-loops, electromagnetic noise pick-up, and line noise. It operates in a copper-lined basement room of a four-story brick and concrete building along with a second and older gas proportional system which has three 500cm3 copper counting tubes operated at 2 or 3 atmospheres of methane. Analysis of the older system's background data indicates that the background counting rate of 0.8 counts per minute is virtually independent of atmospheric pressure. It has not been possible to determine the pressure dependence of the small counting tubes.

Due to traces of radium and uranium in most 14C samples, radon appears as a radioactive contamination in the CO2 prepared by combustion. This contamination must be removed by an active purification prodecure or by storing the CO2 prior to measurement. No effective electronic discrimination against radon and its daughter elements can be performed. The necessary storage time until radon has decayed varies widely, especially for marine shells. The latter material, collected from Norway and Svalbard, has been a main object for the present investigation. In a few cases, a measureable amount of radon may be left even after eight weeks. The behavior of radon and its daughter elements in a CO2 proportional counter has been studied.

The extraction of dissolved carbonate species for age dating from a 100L water sample by the direct-precipitation method (DPM) and by the gas-evolution method (GEM) has been investigated. Stable carbon-isotope fractionation between initial and final carbon dioxide evolved was ca 11‰ by GEM and 1‰ by DPM. GEM will produce isotopically lighter carbon dioxide compared with DPM if carbonate recovery is low. Extraction efficiency of > 95% can be achieved by GEM in 3 hours using nitrogen gas at a sweeping rate of 2000cc per minute. DPM requires precipitates to settle overnight to assure > 95% recovery. GEM is little affected by a high concentration of sulfate ions, whereas DPM is greatly affected by sulfate resulting in less yield.

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.

13C isotope analyses of different stages of benzene synthesis have been made to study partial isotope fractionation. More than 60 analyses of carbonates, charcoal, carbon dioxide, and benzene were made in a double collector mass spectrometer. In the first stage of the synthesis (conversion to carbon dioxide) little or no fractionation was observed, beyond the analytical error of the method. Later stages of the process, show a greater and systematic fractionation. The experimental techniques are described.

Controlled feeding experiments demonstrate that the 14C content of the carbonate fraction of fossil avian eggshell should reliably reflect the 14C activity of feed and contemporary atmospheric CO2 regardless of amounts of 14C depleted scratch injested. Consideration of biochemical pathways and exchange rates across lung membranes leads to the possibility that the carbonate fraction may, in some instances, be slightly 14C depleted. 14C dates on eggshell carbonate should require little or no correction. As with marine shell carbonate, normal soil-forming processes may alter the surficial carbon isotopes in eggshell carbonate. 14C dates on the protein fraction should be even more reliable than those on the carbonate fraction, but only if special precautions or separation techniques exclude non-indigenous carbon from the sample. Original protein contents are likely to be too low for conventional 14C dating techniques.

The preparation and calibration of a secondary standard for the INGEIS Radiocarbon Dating Laboratory are presented. This standard is barium carbonate with a specific activity almost twice that of NBS oxalic acid. It was prepared from BaCO3 with high specific activity and commercial potassium carbonate by an isotopic dilution technique. The advantages of this standard are: 1) the preparation is simple and can be achieved with ordinary labware; 2) the production of CO2 by acid attack from this carbonate shows minimum isotopic fractionation. At least, it has less fractionation than wet oxidation of oxalic acid, the problems of which are described in the literature. This standard ensures better reproducibility in activity measurements; 3) despite some problems of activity exchange with atmospheric CO2 concerning carbonates, measurements of activity over a period of about two years have shown no significant deviation from the mean value. A tentative explanation of this phenomenon is also given. The activity ratio between BaCO3 and NBS oxalic acid is given with its error, and the statistical tests used in the calibration are briefly explained. Finally, a control chart for the activity of the standard over a long period is drawn, showing non-significant deviation and supporting the usefulness of this standard.

A system of 10 proportional 14C counters has been designed. The counters have a volume of 35ml and are operated with CO2 at a pressure of 1 bar and a voltage of 3300V. The amplified signals of the counters are fed through an analog multiplexer to the inputs of three discriminators. The Geiger signal is fed to a separate discriminator. A logic circuit selects from these discriminators the alpha, beta, muon, and purity counts which are then stored in a microcomputer (ITT 2020 with 48K RAM), where the necessary calculations are also performed. The purity of the gas sample is monitored by counting a part of the muon spectrum. The alpha and beta pulses are stored during 95% of the measuring period; the remaining 5% is used for registration of the muon and purity pulses. The overall accuracy of the system for modern carbon samples is 2% after a counting period of 6 days.

When 14C signals approach background levels, the validity of assumptions concerning Poisson counting statistics and measurement system stability becomes crucial in interpreting the resultant low-level counting observations. This has been demonstrated in our previous work on detection limits for non-Poisson error and it is critical in our current studies of carbonaceous pollutants, where the 14C signal from just 5 mg C is comparable to that of the background for our miniature gas proportional counters. To assure data quality, our multi-detector system is designed for the on-line monitoring of critical parameters that reflect both the (statistical) nature of the non-Poisson errors and the underlying (physical) causes. It sends >60 bits of information/pulse to a microprocessor which automatically generates, for each counting period, two-dimensional spectra and multiparameter correlation and control charts. To evaluate the validity of long-term counting of 1–10 mg C we use robust (statistical) estimators, optimal counting interval subdivision, and time series analysis of the individual pulses. New opportunities for selective sampling and chemical fractionation which come with the small sample measurement capability have led us to give special attention also to higher control levels, involving e g, isotonic heterogeneity and representative standard materials.

The Harwell system for measuring milligram size samples using Brookhaven miniature gas counters is fully operative. It comprises 12 counters of different sizes which operate simultaneously within a single NaI crystal (300mm diameter × 300mm long) acting as an anti-coincidence guard counter. Brief details are given of the construction and commissioning of the system, including counter assembly, shield design, electronics, data capture, data analysis, and chemical processing and filling procedures. The performance of the system and an overall view of the fields of application for which the counters have important applications are discussed.

A mini-gas-proportional counter prototype of 10ml capacity (at NTP) was constructed of oxygen-free Finnish copper. The counter tube will be one of 16 equivalent tubes of a small-sample gas counting system, which is equipped with passive graded shield made of lead, cadmium, and copper and a dual active anticoincidence shield, consisting of an external cosmic gas-proportional and an internal plastic scintillation guard. The aim of this study was to evaluate the parameters leading to the design of a cost-effective and compact shielding package for mini-counters.

Continuous 14C data of 1 or 2 weekly samples of atmospheric CO2 are presented, collected near two nuclear power plants (NPP-Biblis and NPP-Philippsburg) located in the rather densely populated upper Rhine valley. Tree-leaf and tree-ring samples from the area of a boiling water reactor in northern Germany (NPP-Würgassen) are also presented and discussed. Additional atmospheric 14CO2 samples from two continental ‘clean-air’ stations in Germany and Austria were used as reference for the polluted areas. For January 1982, these samples yield a ‘clean-air’ 14C concentration in central Europe of Δ14C=255±5‰ (7.7pCi/gC = 1.45pCi/m3 air).

The Harwell Low Level measurements Laboratory has been measuring a variety of natural materials from locations close to United Kingdom nuclear installations since 1977. The measurements are made first, to establish the past effects of releases to the atmosphere of 14C as observed from individual tree rings and second, to establish dispersion contours averaged over extended periods. The main study area has been in Cumbria, around the BNFL nuclear installation at Sellafield. 14C, which can be measured to good precision even at values close to the normal natural levels, provides a powerful technique for the provision of practical experimental values much wanted for theoretical dispersion models.

During the past three years radiocarbon assay has emerged as a primary tool in the quantitative assignment of sources of urban and rural particulate pollution. Its use in several major field studies has come about because of its excellent (fossil/biogenic) discriminating power, because of advances in 14C measurements of small samples, and because of the increased significance of carbonaceous particles in the atmosphere. The problem is especially important in the cities, where increased concentrations of fine particles lead to pollution episodes characterized by poor visibility and changes in the radiation balance (absorption, scattering), and immediate and possibly long-term health effects. Efforts in source apportionment in such affected areas have been based on emissions inventories, dispersion modeling, and receptor modeling – ie, chemical and physical (and statistical) characterization of particles collected at designated receptor sites. It is in the last category that 14C has become quite effective in helping to resolve particle sources. Results are presented for studies carried out in Los Angeles, Denver, and Houston which incorporated 14C measurements, inorganic and organic chemical characterization, and receptor modeling. The 14C data indicated wide ranging contributions of biogenic and fossil carbon sources – eg, <10% to 60% contemporary (biogenic) in Houston – depending on meteorological, biological, and anthropological activity. The combined (chemical, isotopic, statistical) data point to sources such as vehicles, wood combustion, power plants, and vegetation.

In recent years in California, smog aerosols have been observed in metropolitan and rural areas. We wondered what the relative contribution is from sources such as fossil fuel combustion (eg, cars, factories) and emissions from trees and other plants. Pollution produced by fossil fuel combustion can be distinguished from biological sources using radioactive carbon. Carbon in fossil organic materials is radioactively dead whereas carbon in living plants contains 14C. Smog particles were collected on clean glass or quartz fiber paper and analyzed in a small volume CO2 proportional counter for 14C content. Results are given for sampling locations at UCLA, El Monte, Riverside, and Lake Tahoe showing the relative contributions of fossil and modern carbon sources ranging from 0 to 74% and 26 to 100% respectively.

An example of how man's contaminants are introduced, deposited, and retained in sediments giving a chronological record of events has been developed for Lake Washington, Seattle. Significant amounts of both inorganic and organic compounds in the environment originate from fossil fuel sources, such as power plants and motor vehicles. Many organic compounds are introduced also from contemporary biogenic materials. Through the combined carbon isotope analysis technique (CCIA), we can distinguish between fossil and contemporary carbon sources classes (using 14C), as well as sources within each class (using 13C). To establish the chronology of the organic carbon pollutant input to the lake sediment, the ages of the layers were determined using 210pb dating techniques. Sediment profiles of trace metals and a fallout radionuclide plutonium were also obtained and compared with the carbon isotope profiles. The results show that the total organic carbon (TOC) concentration correspond to 93% modern carbon before 1905. This 14C concentration in TOC decreased to ∼60% modern in the 1930's and now is between 95 and 80% modern. The lipid fraction is ca 30% modern and the total aromatic hydrocarbon fraction reached a minimum of 5% modern in 1954. The large decrease in 14C of TOC around 1930 is believed to be due to coal dust or fly ash. The trace metal concentration also increased substantially at this time. The pattern observed in the sediment thus reflects the change in the local energy consumption pattern from a predominately coal to an oil-based economy. From the plutonium profile we infer that mixing occurs for 3 or 4 years before the sediment layers are compacted.