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Radiocarbon, Volume 22, Number 2 (1980)
ABOUT THIS COLLECTION
Radiocarbon is the main international journal of record for research articles and date lists relevant to 14C and other radioisotopes and techniques used in archaeological, geophysical, oceanographic, and related dating.
This archive provides access to Radiocarbon Volumes 1-54 (1959-2012).
As of 2016, Radiocarbon is published by Cambridge University Press. The journal is published quarterly. Radiocarbon also publishes conference proceedings and monographs on topics related to fields of interest. Visit Cambridge Online for new Radiocarbon content and to submit manuscripts.
ISSN: 0033-8222
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Recent Submissions
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Radiocarbon, Volume 22, Number 2 (1980)American Journal of Science, 1980-01-01
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ParticipantsAmerican Journal of Science, 1980-01-01
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Variations of 14C in Oats Grown from 1957 to 1978 in QuebecAnnual atmospheric radiocarbon concentrations for the year 1957 to 1978 are measured through oat seeds grown in the rural region of La Pocatière, Quebec (70 degrees W, 47 degrees N). Results follow the general pattern of other curves obtained from grains elsewhere in the northern hemisphere. Some disagreements suggest a non-uniform mixing process with faster response to stratospheric contamination in definite regions.
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Variations in Radiocarbon Production in the Earth's AtmosphereWe have investigated solar phenomena associated with unusual changes in the production rates of 14C in the atmosphere. 14C is produced in interactions of cosmic ray neutrons with nitrogen in the atmosphere. Intensity of the neutrons varies globally and fluctuates with time as a result of interactions of galactic cosmic rays which generate neutrons with plasma and magnetic fields of the solar wind. We estimate the total mean production rate of 14C for solar cycle 20, specifically 1965 to 1975, to be 2.25 +/- 0.1 nuclei-cm-2sec-1 from galactic cosmic rays alone, with negligible integrated contribution from solar particle events. Annual averages of Rz, the Zurich sunspot number, and the production rate of 14C, n(14C), were related by n(14C) = 2.60 5.53 x 10^(-3) Rz, +/- 3 percent. The contribution of solar flare particles and the zero sunspot limit are discussed with relation to major fluctuations that appear in the radiocarbon versus dendrochronology over short (~100 years) integration times.
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The Radiocarbon Record in Tree Rings of the Last 8000 YearsIt has become generally accepted during the last year that 14C fluctuations, the so-called "wiggles", observed in wood, dated by its tree rings, do indeed exist. Furthermore the La Jolla measurements show that apart from experimental noise, they do not represent random red noise, but characteristic, recurring features. In 1971, Houtermans found indications for the existence of cyclic components and recent Fourier analyses of all the available data by Neftel and Hartwig show a 200-year component. Cyclic oscillations with other periods appear to be present during limited time intervals. The character of the oscillations is not harmonic. The time derivative of many fluctuations is remarkably constant and such that the 14C rises by 1 percent in about 20 years and decreases by 1 percent in slightly more than twice that length of time. The properties of the overall radiocarbon record have to be considered in attempts to explain the variations in terms of variations of the cosmic ray-production rate and changes of the geochemical distribution of radiocarbon.
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Tree-Ring Dating and Radiocarbon Calibration in South-Central EuropeRadiocarbon variations between 3900 and 2800 BC have been established in La Jolla and Groningen using oak tree rings from a 2350-year floating oak series. Comparison of these variations with the bristlecone pine 14C variations provides precise ages for tree-ring dates of Neolithic settlements of Switzerland and Germany over a period of 1400 years. 14C variations measured in Heidelberg in absolutely dated oakring series from AD 250 to 720 show trends similar to those of long-term growth variation of oaks during the same period of time. The influence of the climatic regime on oak growth of this period is discussed.
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The Concept of DC Gain in Modeling Secular Variations in Atmospheric 14CA constraint on radiocarbon reservoir models is that the DC gain of a system (system transfer function at zero frequency) should equal the equilibrium ratio of the atmospheric radiocarbon mass to the production rate. The simple one-box model is essentially a "black box" but the value of the single residence time is theoretically equal to the DC gain. Using a sunspot-production rate algorithm as the forcing function, predictions of the one-box model match the 14C data from AD 1700 to 1900 better than the 3-box, 5-box and box-diffusion models. The more complex models tend to pile up 14C in the atmosphere because their DC gains are too high, and they overattenuate the de Vries "wiggles". The DC gains can be reduced to more acceptable levels by adjusting model parameters, particularly the sizes of the ocean reservoirs. Better fits to the "wiggles" are also obtained by parameter adjustment. Water content of deep-sea sediments constitutes an extra reservoir for dead carbon, and should help reduce system DC gain.
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The Effect of Fossil Fuel and Biogenic CO, on the 13C and 14C Content of Atmospheric Carbon DioxideThe normalization of a measured delta-14C value of atmospheric CO2 to a delta-13C value of -25 per mil does not take into account the presence of fossil fuel and biogenic CO2. In this paper, we try to assess these contaminations as well as the proper 14C content of "clean air".
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The Effect of Anthropogenic CO2 and 14C Sources on the Distribution of 14C in the Atmosphere14C measurements on continuous weekly samples of atmospheric CO2 and hydrocarbons, collected in a rather densely populated area are presented. The deviation of the measured 14C data from the clean air level is primarily due to CO2 from the combustion of fossil fuels. This is confirmed by fossil fuel admixture estimates individually calculated with an atmospheric dispersion model. Up to 10 percent admixture is predicted by this model and observed from the 14C shift for weekly averages, particularly during the winter season. Natural CO2 admixture due to soil respiration, however, even in winter, is of the same order of magnitude, but much larger in the warm season: the considerable variations in CO2 concentration in summer are almost exclusively controlled by natural sources. Using tree leaf samples, we have been able to identify boiling water reactors (BWR) as weak sources of 14CO2. Atmospheric samples taken in the environment of the pressurized water reactors (PWR) Biblis show that the 14C release of these reactors is primarily in the form of hydrocarbon 14C. The source strength of the various power plants, calculated on the basis of our observations in their environment, ranges from 0.5 to 7Ci per year.
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Temporal Variations in Cosmogenic 10Be Production: Implications for Radiocarbon DatingA procedure is outlined for using cosmogenic 10Be variations in polar ice cores and lake or inland sea sediments to correct for 14C production variations in the past. Some of the requirements and problems associated with such a procedure are discussed.
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Temperature-Dependent Seasonal Variation of the Background in Counters Used for Radiocarbon DatingAll background values measured in one of our 14C counters during 1977 were analyzed together with corresponding values for atmospheric pressure, outdoor temperature, and coincidence counting rate for investigation of the possibilities to separate the temperature dependency of the background from the better known atmospheric pressure dependency. The background values were normalized to a common atmospheric pressure and plotted in a time diagram. A seasonal trend with higher background values in winter than in summer shown by this diagram was confirmed by regression analysis. The regression line and the "Standard error of estimate" was calculated for the background values as a function of the atomspheric pressure, on the one hand and as a function of the coincidence counting rate, on the other hand. A comparison showed that the coincidence counting rate in this case was a better parameter than the atmospheric pressure for calculation of the actual background. The approximate consistency of the temperature effects on the background was checked for the years 1976 to 1978.
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Solar Modulation Effects in Terrestrial Production of Carbon-14This paper is concerned with the expected deviations in the production rate of natural 14C on the earth due to changes in solar activity. We review the published estimates of the global production rates of 14C due to galactic and solar cosmic ray particles, and present new estimates of the expected secular variations in 14C production, taking into account the latest information available on galactic cosmic ray modulation and long-term variations in solar activity. Estimated secular variations are related to data on atmospheric 14C/12C ratios based on tree rings. It is concluded that the observed higher frequency wiggles in atmospheric 14C/12C ratios occurring with time scales of about two hundred years and of 1 to 2 percent in magnitude (de Vries, 1958; Suess, 1970a,b; 1979; Damon, Lerman, and Long, 1978), are largely due to solar activity dependent modulation of the galactic cosmic ray flux by solar plasma. These variations override a slowly varying sinusoidal change of about 10 percent in magnitude during the last approximately 8000 years, which is believed to be primarily due to changes in the geomagnetic field. The high frequency modulation effect in 14C production is substantial, about 20 percent, which, considering the response function of the atmosphere (cf Houtermans, Suess, and Oeschger, 1973), is adequate to explain the observed 14C wiggles (also named Suess wiggles or de Vries oscillations) if in the past, periods of large modulation effects and also periods of weak modulation persisted, ie, the sun remained both active and inactive over long periods of time, of the order of several decades to centuries. The pioneering investigations of Eddy (1976; 1977) of the ancient records of solar activity make it plausible that the 14C wiggles in the ancient 14C/12C ratios are primarily due to modulation of galactic cosmic ray flux by a varying sun. Thus, the 14C wiggles are good indicators of solar activity in the past. We also present revised estimates of the production rates of 14C on the earth due to solar flare accelerated cosmic rays and limits of direct accretion of 14C on the earth.
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Some Possibilities for Development of 14C Measurements by Liquid Scintillation CountingThe possibilities of widening the ranges of usage of scintillation counters are studied. As a result of the introduction of the active guard, the background in 14C channel reduces 30 to 75 percent and the stability of background increases. The application of quartz vials and a plastic scintillator as an active guard establishes 14C activity in small amounts of scintillation cocktail (up to 0.1g C) and dates samples with older ages (up to 57,000 years). The parameters of devices are given in case of different amounts of scintillation cocktail.
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Regional Sources of Volcanic Carbon Dioxide and Their Influence on 14C Content of Present-Day Plant Material14C measurements were made on present-day plant material with short integration times (tree leaves and sprouts) in the Eifel area, western Germany, where ancient volcanism produces gaseous emanations of considerable yield. Plants growing near sources emanating 14C-free CO2 show a significant depletion in the period of their growth. The same effect is found in the 14C content of recent samples from the Thera (Santorini) Archipelago/Greece. This mixing of "dead" CO2 may lead to pseudo ages in archaeologic or geologic samples of up to 1600 years in samples from the vicinity of CO2 emanating sources.
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Radiocarbon Variations in Consecutive Single Rings of a 4000-Year-Old Pine from the British IslesAt the Ninth International Radiocarbon Conference a paper was presented concerning possible short-term 14C variations in 4000-year-old red deer antlers (Genius elaphus) found in Neolithic flint mines in Norfolk, England (Burleigh and Hewson, 1980). It was argued, on archaeologic grounds, that the true age of the samples varied by a few years at most. Their radiocarbon ages, however, varied by a considerably greater amount than could be explained by the errors in the measurements. Duplication of the measurements confirmed this unexpected variation. Farmer and Baxter (1972) claimed a significant correlation of atmospheric 14C levels in the northern hemisphere with sunspot number based on radiocarbon assay of single tree rings for the period 1829 to 1865. In contrast, Stuiver (1978) stated that a series of single-year Douglas Fir measurements did not show a statistically significant periodicity. This paper reports measurements made on a series of single-year dendrochronologic samples of approximately the same age as the red deer antlers, which have been carried out at the British Museum Research Laboratory. The results show that the variation in 14C between rings is not statistically significant; some other explanation must be sought for the anomalous antler measurements.
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Radiocarbon in Annual Coral Rings of Belize and FloridaRadiocarbon measurements on a 109-year-old (1868-1977) core of Montastrea annularis coral from Glover Reef, Belize, in the Gulf of Honduras, reveal uptake of fossil fuel CO2 and bomb 14C by surface ocean waters. The history of Delta-14C values revealed by this Belize growth agree remarkably well with results for coral growth from the Florida Straits. It is concluded that these corals are reliable recorders of 14C concentrations of dissolved inorganic carbon (DIOC) in surface waters representative of the Gulf Stream.
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Radiocarbon Dating of Boise Apatite Using Thermal Release of CO2Extraction of carbon from bone hydroxy apatite as CO2 by heating in an oxygen atmosphere is an alternative method to hydrolysis of the bone. Heating in specific steps allows separation of CO2 fractions from different sources, including weakened or sound bone material and secondary deposits. Pretreatments to remove most secondary carbonate and much of the collagen are necessary. Thermogravimetric (weight loss) curves and CO2 release patterns during heating show that the temperature interval for collection of the most reliable CO2 sample for dating purposes lies between 800 and 950 degrees C. Age dates run on such samples support this conclusion.
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Radiocarbon Ages of Shells in Holocene Marine DepositsRadiocarbon dates of marine shells from Central West Greenland, Finnmark, in North Norway, and Dublin Bay, in Ireland, were used in dating relative sea-level changes. When fossil assemblages and formation of marine deposits and their relationship to sea-level were taken into account, the constructed curves of relative sea-level changes agreed with the shell dates. The origin of the shells in the deposits studied varied from site to site, but the dates gave additional information of the formation of marine deposits which could not have been obtained from the study of sediments alone.
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Possibility of Climatically Induced Variations in the 14C and 13C Enrichment Patterns as Recorded by a 3000-Year-Old Norwegian PineThe secular patterns of Deltaand delta-13C measured in wood cellulose are compared with a palaeotemperature index published for the immediate growth region. 14C enrichment shows an overall decrease of ca 20 per mil (Delta) during the 18th and 19th centuries with shorter term (decade) variations superimposed on the general trend. Measured Delta values correlate significantly with the average mean summer temperatures and indicate a linear coefficient of ca -10.2 per mil C-1. Short-term variations in the natural concentration of 14C which are closely related to climatic change may reflect the latitudinal dependence for atmospheric mixing. The secular trend in delta-13C covers a range of 2 per mil but variations of this magnitude reflect influences other than those directly associated with climatic change, eg, possible assimilation of recycled biospheric CO2 during early life and post AD 1850 anthropogenic effects. No evidence was found to suggest a significant correlation between delta-13C and the mean atmospheric temperature during summer growth periods.
