ALBERT

Beschreibung: A bibliography of the radiocarbon dating literature for the years 1948-68, which is in the process of compilation, is examined and a format is proposed. A survey of literature growth has also been undertaken. This enables projections of the numbers of publications referring to radiocarbon dating to be made. The estimated number of publications for the year 1978 is compared to literature retrieval obtained by interrogating eight relevant computer data bases. It is concluded that computer information retrieval is not satisfactory. Bibliographic control of radiocarbon dating literature would be best achieved by a bibliography dedicated to the subject and updated at regular intervals.

Beschreibung: Archaeologists began to participate in cross-disciplinary endeavors in the 1930's, albeit on a very limited basis. The passage of time found members of that discipline unprepared for collaboration with physical scientists when W F Libby announced the development of the radiocarbon dating method. Libby proposed to apply to archeologic and geologic samples techniques based on ideas that were completely foreign to archeology …. The initial reactions of archeologists were sometimes amusing but more often significant, for they led to the foundation and emergence of the radiocarbon chronology that has so profoundly affected our understanding of prehistory (Johnson, 1967, p 165).To date, our historical knowledge about the nature, function, and impact of the early (1946-1948) relations between Libby and American archaeologists has come to us in the form of published anecdotes, many of which contain inaccurate information. The author's access to W F Libby's private 14C correspondence, combined with data obtained from interviews with some of the principal participants throughout this period, offers many new or different insights into the nascent years of radiocarbon dating. When, and under what unexpected cricumstances, did Libby first encounter representatives of the achaeologic community? What strategies were employed to facilitate diffusion of knowledge about 14C dating across disciplinary boundaries? How did archaeologists respond to the introduction or “intrusion” into their field of Libby's radioactive age-measurement tool?

Beschreibung: A new 14C detector system containing nine, independently working, CO2 proportional counters is described. The system is designed for a sufficient measuring capacity at a precision level better than σ = ± 2‰, which requires a counting time of about one week per sample. The size of the installation requires a simple and economic design of counters and electronics. A single anticoincidence shield for all counters consists of five newly developed flat counters. The modern counting rate (52cpm) is sensitively checked by running Heidelberg sodium carbonate standard samples wth a counting rate of about 10 times modern. A microcomputer (DEC PDP-11 /03) is used for data acquisition. Recent developments in laboratory techniques (preparation and gaschromatographic purification of samples) are also reported.

Beschreibung: Amino acid composition data and stable isotope ratios (14N, D, and13C) are being evaluated as sources of information to indicate the presence of non-indigenous organics in bone samples intended for 14C analyses. The study is being conducted in the context of the planned measurement of Pleistocene bone samples by a high energy mass spectrometric 14C detection system.

Beschreibung: Annual atmospheric radiocarbon concentrations for the year 1957 to 1978 are measured through oat seeds grown in the rural region of La Pocatière, Québec (70° W, 47° 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.

Beschreibung: The precision quoted on a radiocarbon date is often misleading. Improvement in the accuracy of measurement is discussed together with the use of appropriate precisions. The effect of high accuracy in 14C dating and meaningful precisions are illustrated and applied to radiocarbon time-scale calibration. Intercomparison of such calibrations reveals a significant continuous saw-tooth pattern of short-term periodicity.

Beschreibung: The University of Washington Model FN tandem Van de Graaff accelerator is being used for the measurement of extremely small isotopic abundance ratios, notably 14C/12C and 10Be/9Be, in a joint project of the Nuclear Physics Laboratory (NPL) and the Quaternary Isotope Laboratory (QL). The experimental arrangements and technical developments are described, and some preliminary results on isotopic ratios in carbon and beryllium are presented.

Beschreibung: Δ14C and δ13C values for organic matter in forest and grassland soils, in the presence or absence of earthworms, indicate that it should be possible to quantify the effects of earthworms on soil organic matter by this means. Without earthworms, both in forest and grassland soils, plant debris tends to accumulate on the surface of the mineral soil and little organic matter is incorporated into or is translocated down the soil profile. Where earthworms are present, there is much more marked incorporation of fresh plant debris in the mineral soil. This is shown especially by the pulse of ‘bomb’ carbon and also by the δ13C values.

Beschreibung: 14C and 13C enrichment values are reported for a series of surface soil profiles which represent the progressive transition from mor to mull humus induced by birch (Betula pendula) colonization.Variations in Δ and δ13C, which range between 85 to 154‰ modern and −28.1 to −25.3‰ (PDB), respectively, reflect changes in the rate and mode of organic decomposition. The most marked alterations in soil character occur over the first few decades following the introduction of birch, with clear isotopic evidence for the deeper penetration and accelerated mineralization of organic material.

Beschreibung: High precision radiocarbon measurements (±2.5‰ STD) were carried out on absolutely dated European oak material. These showed that significant short-term atmospheric 14C variations of up to 2 percent occurred between AD 200 and 800. These changes, reflecting a 150-to 180-year periodicity, seem to correlate with the average sunspot activity around that time. In comparison with results obtained by other authors, a very regular pattern of natural atmospheric 14C variations is exhibited.

Beschreibung: The evolution of a tandem accelerator 14C dating system at Chalk River is recounted. Background problems and sources of instability are discussed and solutions are described. Details of sample chemistry and source preparation are presented.

Beschreibung: Pollen analysis as well as 18O/16O results on lake marl show that the Younger Dryas climatic period, between about 11,000 and 10,300 bp, was the last vigorous cold phase of the Würm Glacial. Detailed 14C analyses from a peat bog near Wachseldorn (Switzerland) point to a 14C anomaly in this period. Further indication of a 14C anomaly is given by the observation that, during the Younger Dryas period, the sedimentation rates in several lakes apparently were higher than in adjacent periods; an explanation might be that the 14C time scale was compressed between 11,000 and 10,000 bp, ie, the atmospheric 14C/C ratio varied. If real, this suggested 14C variation would probably be connected to the climatic events during this transition period from Later Glacial to Postglacial.

Beschreibung: 14C 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.

Beschreibung: An MP tandem Van de Graaff accelerator at the University of Rochester has been employed since May 1977 to detect 14C in various terrestrial samples. The carbon sample sizes required are 1mg or less. Dating accuracies based on reproducibility now approach (± 80 years). Measurements have been made on 1850 wood, Australian sucrose, a carbon sample from Mt Shasta, a baby woolly mammoth, and an Egyptian bull mummy wrapping.

Beschreibung: Carbon isotope measurements in soil CO2 are presented and discussed. Soil CO2 concentration and 13C profiles were measured using a new technique. A simple model describing the CO2 transport from the soil to the atmosphere is derived. The finding that CO2 in the soil is richer in 13C than the CO2 leaving the soil is attributed to isotopic fractionation in molecular diffusion.

Beschreibung: Although initial studies in the 1960's established the feasibility of applying the radiocarbon technique directly to ceramics, subsequent analyses have revealed this category of materials to be more complex than previously believed. Consideration of the points at which various types of organic carbon are introduced into ceramic materials by natural or human agencies allows more effective screening of potential sherd samples. It also suggest ways to overcome some of the limiting factors involved in dating ceramics.

Beschreibung: Mollusks living only on ground surface can be expected to give the most reliable results in 14C dating from carbonates of continental origin. One may assume they have a homogeneous biotope and are not affected by any hard-water effect. In order to verify these assumptions and to test shells as routine dating material, results from terrestrial gastropods are compared with other 14C dates from classic biologic material, such as peat, charcoal, or bone, collected in the same archaeologic or geologic levels in miscellaneous places. Two sites were selected for which other chronologic data, such as prehistoric industries or malacologic diagrams were available.All results indicate older values for 14C shell dates. The discrepancy between “normal” and snail dates amounts to 300 to 1200 14C years and remains the same whatever the absolute age of the sample. All 13C values of perfectly cleaned shells are between —5 to —10%, versus PDB. The initial 14C content of shells that is too low may be different according to species, as suggested by 13C variations.Although fairly constant, this deviation of 14C ages generally makes such samples unreliable for most archaeologic studies, which often need more precise results. However, some measurements were performed on microfauna shells from several Würmian loess to show that dating of shells may be useful in fairly ancient geologic sediments for lack of better carbonaceous samples. Good agreement of some snail dates with expected sediment ages point to the importance of proper sample selection and pretreatment that might be checked by 13C measurements.

Beschreibung: Since the publication of our first date list (R, 1966, v 8, p 239-247), our 14C laboratory has produced about 1500 radiocarbon dates, including several hundreds of concordant double determinations, the majority of which were on archaeologic samples. The greater part of the other dates concerned dendrochronologic samples from our Tree Ring Laboratory (Schmidt, 1977; Freundlich, 1977). Several archaeologic dates have already been published in articles on archaeology, preferentially by the respective excavators, in a few instances also by us (eg, Schwabedissen and Freundlich, 1968; Faruggia et al, 1973; Kuper, 1975; Lüning and Zürn, 1977; Hohenschwert, 1978). An extensive compilation of Neolithic dates is in preparation.

Beschreibung: The secular patterns of Δ and δ13C 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% (Δ) during the 18th and 19th centuries with shorter term (decade) variations superimposed on the general trend. Measured Δ values correlate significantly with the average mean summer temperatures and indicate a linear coefficient of ca − 10.2% °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 δ13C covers a range of 2% 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 δ13C and the mean atmospheric temperature during summer growth periods.

Beschreibung: An interlaboratory comparison experiment for 14C measurements has been organized jointly by the Harwell and British Museum laboratories to include the working radiocarbon laboratories of the United Kingdom. The experiment has been run along the lines of that organized by the IAEA for tritium and has explored the problems of sample preparation, verification of equivalent levels, and presentation of results. Samples of benzene representing 5 age equivalent levels between twice modern and 20,000 years old have been prepared and distributed for measurement either by direct counting (liquid scintillation) or full process tests. Preliminary results received show excellent agreement both between laboratories and in comparison with the known relative activities of the prepared solutions. The possibility of extending the experiment to cover different sample types and a wider distribution of testing laboratories is briefly discussed.

Beschreibung: An 18O/16O versus 14C age curve was constructed for unrecrystallized Holocene marine shell samples from Israel that were shown to be homogeneous populations. The surprisingly large variation in the oxygen isotopic composition (1.2‰) between 2600 and 4000 years ago is most probably due to variations in the isotopic composition of the water. This implies that either the excess of evaporation over precipitation or the Nile river discharge must have varied significantly during the Holocene.

Beschreibung: Frequency distributions of more than 300 14C groundwater ages from various regions in northern and southern Sahara reflect the alternating sequence of humid and arid periods in the Sahara during the Holocene and late Pleistocene. A broad frequency maximum between 20,000 and 50,000 years bp indicates a long humid period. During this time span, the northern Sahara received rain from the Western Drift, which is concluded from a west-east decrease of deuterium and oxygen 18 of these groundwaters (continental effect). In the time-slice between 14,000 and 20,000 years bp, groundwater formation was significantly lower due to a cool and (semi-)arid period. In the Holocene, the Saharian climate is characterized by a sequence of dry and wet periods.

Beschreibung: Two Pinus aristata samples submitted by C W Ferguson were separated in different fractions, as was done earlier with Pinus silvestris L from Sweden, to yield different fractions for studies of the pretreatment. One sample in this new series consisted of heartwood and the second of sapwood.The treatment performed in the radiocarbon laboratory involved an acid treatment by boiling, washings, an hydroxide treatment at 80°C, washings and, finally, another acid treatment before being dried before the combustion. The sodium-hydroxide treatment was repeated to yield at least two soluble and two insoluble fractions.The treatment performed by the wood chemists involved extractions with ethanol-benzene and water. The remaining wood was dated but was also used for the production of holocellulose. The extractives were partitioned between ethyl ether and water and that from the older wood was used for the isolation of neutrals, acids, and phenols. In all, 19 fractions of these two wood samples were dated.It is confirmed that a treatment for 30 min in sodium hydroxide at 80°C is not sufficient to remove the extractives from the heartwood or the sapwood. A treatment at 80°C overnight with 1 percent NaOH yielded a sample from the older wood with a 14C content in good agreement with the results predicted from the curve presented by Stuiver (1978). The final statistical uncertainty in the present investigation was ca 4‰. The younger wood yielded results indicating a lower activity than that given by Stuiver.

Beschreibung: To improve reporting of radiocarbon dates, Stuiver and Polach (1977) recommend that reported standard errors should include the error in the applied δ13C value, and suggest estimated mean values for δ13C to be applied when not measured. Based on δ13C data for ca 250 samples measured during 1975-1979, mean values for different materials dated by the Trondheim radiocarbon laboratory have been compiled. All material is from Norway and Svalbard (marine bone collagen). For peat, gyttja, and terrestrial bone material, δ13C should be measured to obtain optimal precision in the dates. For shell, wood, charcoal, and marine bones, the standard error in an estimated δ13C value will only increase uncertainty of a date from ±50 years to ca ±55 years.

Beschreibung: Tufa is a superficial, secondary deposit of calcium carbonate which accumulates on precipitation from emergent spring waters. It occurs as discrete, localized masses in regions of calcareous country rock.In the United Kingdom, deposits vary widely in structure and thickness but little is known of the rate of deposition. Some deposits contain laminae assumed to represent annual growth increments and which should contain a 14C and stable isotope record related to the original water from which it was precipitated.Investigations are reported on tufa from, three areas of different limestones in the United Kingdom (Northwest Yorkshire, South Derbyshire and North Oxfordshire).Hydrologically, the dating of tufa by 14C involves the same problems as the dating of groundwater. In the case of actively forming tufa, however, it is possible to derive a sequence of measurements, beginning with present day deposition, which clearly demonstrates the applications of age corrections.At Gordale Scar, Northwest Yorkshire, a profiling study of laminated tufa appears to show bomb trial 14C to a depth of 18mm below the surface, with almost constant values around 50 percent modern (raw data) from 18 to 48mm below the surface. The 14C content of surface tufa lies within the seasonal range of 14C measurements from the parent stream waters.Results of 50 percent modern in the sequence are consistent with the simplest correction procedures based on δ13C balance and the observed δ13C change on tufa precipitation is a practical demonstration of the fractionation factor ∊13. However, the application of corrections to active, surface tufa and parent waters collected monthly over a period of study (14 months) from all three sites, produce results higher than would be expected from published world 14C levels.

Beschreibung: We here report on two technical research projects of the Quaternary Isotope Laboratory (QL) vis, (1) the use of thermal diffusion isotopic enrichment to extend the technical range of 14C dating, (2) the preparation of samples for ion counting using a Van de Graaff tandem accelerator. The second project is carried out in cooperation with, and partly at, the Nuclear Physics Laboratory.A gain in dating range of 3 to 4 half-lives can routinely be obtained with the QL and the Groningen enrichment systems. The same gain in age range can be obtained for ion counting with a simplified system that requires only 0.5 to 2g of carbon and 3 to 7 days enrichment time.A method to convert CO2 quantitatively via CO into carbon is described. For short intervals the carbon deposit yields good 12C— beams. We also give a different procedure to make graphite-like carbon samples. The preparation of beryllium metal samples is given last.

Beschreibung: The “shielding” efficiency of the guard counters has been a main scope of the present investigation. Our special guard counters consist of closed shells (ca 3cm thick) filled with propane at 1.2 atmospheres pressure. These guard counters are nearly 100 percent efficient against charged particles, and 1 to 2 percent against gamma and neutrons. The efficiency has now been studied more in detail in an arrangement with four guard shells around a 14C counter. For each extra guard shell, the cosmic fraction of the counter background was reduced by ca 13 percent. The reduction does not involve penetrating high energy charged particles, but is related to γ ray showers penetrating the guards. A thicker old lead shield between 14C counter and the guard counters also reduces the background and serves the same purpose. In order to approach underground conditions for the 1.5 liter counter background (0.32 ± 0.01 c/min), most of the shielding material has to be put inside guard shells. An ordinary guard counter combined with an extra guard on top of the iron shield is very efficient. A background of 0.48 ± 0.01 c/min has already been obtained.

Beschreibung: All 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.

Beschreibung: The normalization of a measured δ14C value of atmospheric CO2 to a δ13C value of − 25‰ 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”.

Beschreibung: In 1957 the National Bureau of Standards (NBS) agreed, at the request of James R Arnold, to store and distribute an oxalic acid contemporary carbon-14 standard. In 1978 stocks of this standard were practically gone. We approached Chas Pfizer and Company, Inc, which had provided the original 1000 pounds of oxalic acid to Dr Arnold to see if they could provide another one-batch lot of 1000 pounds of oxalic acid to replace the old standard. This they did generously, at no cost to NBS. The oxalic acid was prepared by fermentation of French beet molasses from the 1977 spring, summer, and autumn harvest using Aspergillus niger var. The acid was separated from the broth as the insoluble calcium salt and reconverted to free acid using sulfuric acid. The free acid was then crystallized, redissolved, filtered, recrystallized, and dried.

Beschreibung: Measurements of 14CO in the lower troposphere show a well-defined seasonal variation between 11 ± 1 molecules cm–3 in summer and 25 ± 2 molecules cm–3 in winterat 51°N. The concentration at 27°N in summer is found to be 4.2 ± 0.7 molecules cm–3. From these data and published 12CO measurements, the average concentration of OH radicals in the troposphere is calculated to be 6.5 ± 2.5 × 105 molecules cm–3 using a 2-D time-dependent model. The corresponding 12CO lifetime is two months; the 14CO lifetime is five months.

Beschreibung: The use of materials having high levels of 14C activity (up to 113 times the activity of modern carbon) enabled a quantitative analysis of the magnitude and sites of memory occurring in the routine synthesis of benzene, via lithium carbide, for radiocarbon dating. Memory may be expressed as the percentage or fractional contribution of carbon from sources other than the original sample in this synthesis. Although tritium and radon contamination have also been found, the major site of memory was the inner surface of the stainless steel reaction vessel used for lithium carbide production. Up to 1 percent memory has been found there under extreme conditions in the routine dating system at Harwell. Values of half to one-third this size were more usual, but even etching and scouring the inner surface of the reaction vessel reduced the memory only by a factor of four. This lower limit is believed to exist because of the carburization and decarburization of steel which occurs at the temperature required for the production of lithium carbide. The levels of memory found are of the same order as the levels of significance associated with present radiocarbon techniques. With the accuracy and extended chronologies expected from direct 14G measurement by accelerator techniques, these levels of memory become increasingly important in the preparation of acetylene and pyrolitic graphite (via lithium carbide) used as target materials. This effect, however, can be limited by lowering the temperature of the carbide reaction stage or by lining or impregnating the lithium carbide reaction vessel with some carbon-impermeable alloy or material.

Beschreibung: Underlying principles and results are presented for our program to use isotopic and chemical methods to quantify anthropogenic and natural sources of carbonaceous pollutants. Radiocarbon data have been obtained with a specially-developed miniature low-level gas counting system which has permitted us to assay samples containing as little as 5mg carbon. Measurements of carbonaceous particles, using chemical selectivity and size fractionation to supplement the radiocarbon data, have revealed major impact from both fossil fuel and vegetative (contemporary) sources on urban aerosols. Residential wood-burning has been specifically identified as an important source of respirable particles. Current investigations are directed toward the carbonaceous gases and the application of the accelerator technique for the assay of radiocarbon in individual chemical fractions containing microgram quantities of carbon.

Beschreibung: Systematic dating of tufa samples has been undertaken to establish a chronology of tufa deposits in Plitvice National Park, Yugoslavia. We conclude that tufa samples give reproducible data within the time span of ≈ 40,000 years up to recent. The 14C/12C ratio of carbon in the ambient biosphere and hydrosphere gives a detailed picture of the distribution of carbon isotopes in the investigated system. Despite the susceptibility of calcareous material to ambient conditions in the hydrosphere, the original 14C composition of tufa has not been substantially changed. A vertical profile which was cut in tufa during pathway construction showed that the tufa isochrones run vertically in the investigated area. The vertical isochrones and the 14C gradient were horizontal due to tufa build-up in Plitvice National Park which occurs on vertical escarpments that have been flooded. The relatively uniform radiocarbon content of most tufa deposits indicates redistribution of radiocarbon during the formation period. While detailed stratigraphy is often obscured, a general chronology of tufa deposits in the investigated area has been established.

Beschreibung: Chemical components in a sea sediment core from the Santa Barbara Basin show the same periodic variations as do stable isotope variations in a Japanese cedar.

Beschreibung: At the Ninth International Radiocarbon Conference a paper was presented concerning possible short-term 14C variations in 4000-year-old red deer antlers (Cervus 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.

Beschreibung: A description is given of an accelerator-based radioisotope measuring system, being supplied to the Universities of Arizona and Toronto and in part to the University of Oxford. This system will be capable of measuring 14C/12C and 13C/12C ratios in milligram samples of cracked acetylene. At present 200µg of carbon obtained from cracked acetylene appears to be adequate for an isotopic ratio determination. Previous performance and new calculations indicate that a precision better than 1 percent will be achieved in a half-hour period only limited by counting statistics. A precision of 0.2 percent will be obtained in a ten-hour period. Using a carbon sample with an age greater than 60,000 years, the measured background 14C/12C ratio will be less than 0.07 percent of modern.

Beschreibung: Radiocarbon activity of successive parts of Pleistocene and Holocene ooids and mollusk shells from the Persian Gulf, Kuwait, was measured. The inner part of the ooids showed the lowest activity and the cement between grains the highest. Radiocarbon activities correspond to the general stratigraphy and to the position of the sediments. Radiocarbon ages of Pleistocene sediments seem to be very low due to recrystallization of aragonite. Higher radiocarbon activity of cement indicates that atmospheric carbon dioxide was involved in the subaerial diagenetic process. The radiocarbon age of well-preserved mollusk shells seems to be lower than their allegedly Pleistocene geologic age.

Beschreibung: During Pleistocene pluvial precipitation was sufficient for the maintenance of groundwater supported lakes and for the accumulation of playa lakes in wind-scoured depressions during the early Holocene pluvial. At places where ground water reaches near to the surface, wells (birs) have been dug and maintained in historic times. These birs have been used as sampling sites for water analyses, including carbon-14 levels, carbon and oxygen stable isotope ratios, tritium concentrations, and chemical data.All the waters from birs analyzed to date produced apparent radiocarbon ages ranging from late historic to early Holocene, and tritium analyses on some of these indicate no recharge during the Atomic age.Sources of error for the radiocarbon analyses, including exchange with atmospheric CO2, respiration by plant roots, and contact with carbonates of considerably older age, were evaluated. None of these factors have such an extreme impact on the measurements as to render the result invalid. Two trends revealed by these data are an increase in apparent age from northwest to southwest and with subsequent extractions at the same site where the hand-dug well was bailed out and sampled four times within two days.We conclude that recharge of shallow ground water occurred in early Holocene time, and some recharge of deeper aquifers may have occurred where infiltration paths permitted. Some recharge occurred in late Holocene (post pluvial) time, but the net trend has been toward hyper-aridity that characterizes the area today.

Beschreibung: The 14C age of charcoal and wood from Lebanon and central Europe is compared partly with the dendrochronologically determined age of the samples and partly with the archaeologically expected value. While the dendrologic values approximately confirm the correction curve of Ralph, Michael, and Han (1973), charcoal of burned layers seemes to be generally 2 to 3 centuries older than expected from contemporary archaeologically retrieved materials.

Beschreibung: Ionium dates for the Upper Lisan Formation in the Dead Sea valley average (10 ± 3) percent higher than a set of radiocarbon dates from the same profiles. No analytical explanation can be found so that the discrepancy may be real for the period 15,000 BP to 35,000 BP (conventional radiocarbon years). This would have implications for the chronology of the Upper Pleistocene.

Beschreibung: Nuclear-weapon produced 14C (or bomb 14C) in the ocean can be traced by simultaneous tritium observations. Data are presented on the general relationship of bomb 14C and tritium in the North Atlantic. For the period 1965 to 1973, the excess 14C to tritium ratios in the surface water vary, systematically, over a factor of 10: the ratios monotonically increase with time, and decrease with latitude, particularly so for the later observations. The sub-surface water ratios show that the mid- and low-latitude water below about the 15° C isothermal horizon (~500m depth) originates from higher northern latitudes, rather than being renewed by local vertical mixing. It is further shown that in the North Atlantic, bomb 14C did not penetrate beyond the horizon where the presently observed 14C concentration is Δ14C = —75‰. Observed concentrations up to about —40‰ can be corrected for a bomb contribution if the tritium concentration is known because the bomb 14C to tritium concentration ratio is rather uniform in this range. A surface water 14C concentration versus time curve is presented for the period since 1957. This curve is based on a North Atlantic mixing model and is fitted to the 14C observations. Making use of a previously published tritium versus time curve obtained by the same model, a time curve for the average excess 14C to tritium ratio in North Atlantic surface water is given. This curve reproduces the observations well. The presented data and theoretical curves show the usefulness of simultaneous 14C and tritium observations for mixing studies and to provide corrections for bomb 14C in sub-surface 14C data in the North Atlantic.

Beschreibung: The characteristics of a one-dimensional vertical advection-diffusion ocean mixing model were examined using temperature, salinity, and bomb 14C measurements made during the GEOSECS program. Vertical advection (W) and eddy diffusion (K) rates for the main oceanic thermocline and CO2 gas exchange rates (E) were determined from the depth distributions of salinity and bomb produced 14C measured in the upper 1000m of the Atlantic and Pacific Oceans. In the Atlantic, the results suggest that vertical diffusion rates are lower in the equatorial region (K = 0.6cm2sec—1) than in the temperate region (K = 1.6cm2sec—1). Upwelling rates were calculated for stations located between about 30° N and 30°S and average 10m yr—1, corresponding to an upward transport of about 10 Sverdrups. Model calculations of the gas exchange rate of CO2 indicate a 2 to 3-fold decrease between temperate latitudes and the equatorial latitudes of the Atlantic. For many of the Pacific GEOSECS stations, the Δ14C depth distribution is distinctly different than in the Atlantic, and cannot be used to calculate unique values of K and W that explain both the salinity and 14C depth distributions.

Beschreibung: This list reports certain 14C measurements completed by December 1979; other projects completed by this time will be reported later. Age calculations are based on 14C half-life of 5568 yr and modern standard of 95% NBS oxalic acid, supplemented by tree rings of pre-industrial wood from a log cut in the 1850's (Tx-540; R, 1970, v 12, p 249). Deviations reported are based on counting statistics of sample, background and modern, and are ± 1σ, except that when sample count approaches either modern or background, 2σ limits are reported. Unless noted, 12C/13C measurements were not made and results are not corrected for 13C fractionation (assumed ratio = −25‰ WRT PDB). Our laboratory uses liquid scintillation counting of benzene, with Li2C2 and vanadium-activated catalyst in preparation; chemical yields range between 95% and 99%. Three counters are employed; a Packard Tri-Carb Model 3002 and 2 Beckman LS230 spectrometers obtained through a grant from the National Science Foundation.

Beschreibung: This list contains analyses completed between January, 1976 and April, 1977. Details of laboratory operation are contained in our first list (R, 1975, v 18, p 205). Samples submitted for analysis are reviewed by a committee consisting of W DeBoer, E Hansen, Anthropology; L Marcus, Biology; W S Newman, D L Thurber, Earth and Environmental Sciences; and Richard Pardi, Radiocarbon Laboratory.

Beschreibung: Palaeomagnetic field strength measurements for the last 50,000 years are summarized. The period before ~12,000 yr bp is characterized by low dipole moments, but high values are associated with the Lake Mungo polarity excursion between ~32,000 and ~28,000 yr bp. The variation since 12,000 yr bp, based on new results from Australia and published data from the Northern Hemisphere has a quasi-cyclic appearance with maxima at ~10,000 and ~3500 yr bp. The geomagnetic record is used to predict variations in atmospheric 14C concentration, and the results are compared with independent comparisons between 14C and other dating methods. Long-term variations in the 14C time-scale are readily explained by known geomagnetic changes.

Beschreibung: The following radiocarbon dates are a partial list of samples measured for a variety of projects and materials since January 1980. Chemical and counting procedures remain the same as indicated in R v 20, p 274-282.

Beschreibung: The concentration of radiocarbon in the earth's atmosphere is used to analyze the complex of problems associated with the study of various astrophysical, geophysical, and geochemical phenomena within the framework of the All-Union problem of Astrophysical Phenomena and Radiocarbon. Effects of the supernovae explosions, solar activity, geomagnetic field and climatic changes in the 14C level in tree-rings are considered.

Beschreibung: Rates of CO2 exchange across the air-water interface in oceans and lakes measured to date by the L-DGO group are summarized. They range from 3 to 38 moles/m2/yr. The possible causes for this range include the differences in salinity, mean wind speed, and pH. Wind tunnel studies comparing fresh water and sea water are required before a satisfactory explanation can be found.

Beschreibung: The distribution of 14C concentrations in the dissolved inorganic carbon in the surface waters of the Pacific Ocean is shown to have a primarily latitudinal pattern with Δ14C maxima at mid-latitudes in both hemispheres and a minimum at the equator. Oceanographic causes of this phenomenon are discussed.

Beschreibung: Most of the 14C measurements reported here were made between October 1978 and October 1979. Equipment, measurement, and treatment of samples are as reported previously (R, 1968, v 10, p 36-37; 1976, v 18, p 290) except for some minor improvements of the electronic equipment. Sediment samples too small to allow pretreatment, are now burned at

Beschreibung: Detailed radiocarbon chronologies from three volcanic crater lakes (maars) in southeast Australia are examined in relationship to the magnetic mineral stratigraphies within lakes, and the magnetic secular variation stratigraphy between lakes. Some implications for magnetic dating are considered.

Beschreibung: The following list includes some measurements made during 1978 and 1979 in the radiocarbon laboratory of the Ecole Nationale Supérieure de Géologie Appliquée et de Prospection Minière (ENSG) de Nancy. Equipment, measurement and treatment of samples are as reported previously (R, 1979, v 21, p 453-464) where the sample is synthesized to benzene. Radiocarbon ages are calculated using the 14C half-life of 5568 years and 95% activity of NBS oxalic acid is used as modern standard. Anthracite coal and Merck commercial benzene are used for the dead carbon run.

Beschreibung: The correlations between atmospheric radiocarbon cencentrations, on the one hand, and solar activity and the earth's magnetic field, on the other, as well as possible relations between surface temperatures and solar activity and the earth's magnetic field are considered. To draw a consistent picture of these relations, the following mechanisms for climatic changes are proposed: The earth's magnetic field and solar activity both influence the fluxes of charged solar particles into the upper stratosphere; higher surface temperatures are positively correlated with higher particles fluxes. Charged particles produce nitric oxide, which controls, to some extent, the ozone destruction and, thus, the ozone inventory in the upper layers of the stratosphere (above the 10 mbar level) in latitudes greater than about 60°. The varying ozone contents in the upper stratosphere affect the radiation balance and the temperatures on the earth's surface. It has been estimated that a reduction, or increase, respectively, of ozone in the layers above 10 mbar warms, or cools, respectively, the earth's surface. A change of ozone in the lower layers of the stratosphere has the opposite effect. The maximum net effect is in the order of ΔTs ≈ 0.3–1 K, in both directions. This hypothesis might be in accordance with an orbital origin of long-term climatic changes.

Beschreibung: Within the United States, the State of California ranks first in recorded earthquake frequencies. Annually, thousands of shocks are registered on seismometers and many hundreds are actually noticed directly by Californians. In modern times, about one quake per year, destructive to property, has occurred, yet the very large and disastrous events approaching magnitude 8 and higher on the Richter scale are spaced a few decades apart: 1857 in Southern California centered on Tejon Pass, 1872 in the Owens Valley, and 1906 in San Francisco. Unfortunately, the historical record for earthquakes is short in California when compared with accounts for Europe or China, both of which list quakes over a time period of some 2000 to 3000 years. In California, the first historically noted event dates to barely 200 years ago, when in 1769, members of an expedition of the Spanish explorer Gaspar de Portola were knocked to the ground along the Santa Ana River during a large earthquake.

Beschreibung: Problems of the statistical interpretation of radiocarbon age measurements of old samples are discussed, based on the notion of fiducial probability distribution. A probability density function of age has been given. A detailed discussion of different facets of the probability distribution of age has led us to the confirmation of the use of 2σ as the best limiting value between the regions of finite and infinite dates. It has been proposed to make use of the principle of constant probability P = 0.68 in the regions of both finite and infinite ages instead of the criterion N + kσ.

Beschreibung: The following date list covers samples dated by the La Jolla Radiocarbon Laboratory during calendar year 1978. All archaeologic, all geologic, and some geochemical and botanical samples measured during that period are included here. Recent measurements of 14C in tree rings and in annual coral rings will be published elsewhere. Plots and discussion of data for corals from Belize and Florida have been published already by Druffel (1980).

Beschreibung: Radiocarbon 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 oak-ring 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.

Beschreibung: The following list includes samples dated at the Institute of Geology, Academy of Sciences of the Estonian SSR in 1978. The measurement of natural 14C activity is performed by 1-channel and 2-channel scintillation devices (Punning & Rajamäe, 1977). Ages are calculated using the half-life of 5568 ± 30 years and 0.95 NBS oxalic acid modern standard with ad 1950 as reference year.

Beschreibung: The present list includes 74 dates of geologic samples determined using the liquid scintillation 14C method at the Geobiochemical sector of the Institute of Zoology and Botany, Academy of Sciences, Estonian SSR.

Beschreibung: Additional 14C data from the atmosphere and ocean have been provided since the ninth 14C conference in 1976. At the moment, one sampling station in the troposphere in each hemisphere seems to give sufficient accuracy for exchange studies. The 14C concentration in the troposphere in December 1978 constituted a mean value of 30 ± 1 percent (Δ14C) above normal level, a concentration that has been reduced to about one half during 12 years. 14C measurements have been performed with intervals of 1 to 4 months in the surface water of the Atlantic, Pacific, and Indian Oceans. In addition to the 14C data observed, the salinity and temperature are also measured. Because of earlier objections against storing sea water in steel drums on board ships for months before treatment, the CO2 has now been flushed out immediately after collection. The reliability of previous measurements has been confirmed with 10 parallel samples. 14C concentration in ocean surface on each location shows some seasonal variation due to variable exchange of water with deeper layers.

Beschreibung: Results presented in this date list have been obtained from Jan 1977 to Dec 1977, but some earlier measurements are also included. All calculations are based on a contemporary value equal to 0.95 of the activity of NBS oxalic acid standard and on the Libby value for the half-life of radiocarbon. Ages are reported as conventional radiocarbon dates in years before AD 1950. No corrections for 13C/12C ratio were made for measurements reported in this list. Errors quoted (±1σ) included estimated overall standard deviations of count rates of the unknown sample, contemporary standard and background (Pazdur & Walanus, 1979). Counting equipment and experimental procedures have been described earlier (Mościcki & Zastawny, 1976, 1977; Pazdur et al, 1978; Pazdur & Pazdur, 1979a). Sample descriptions are based on information provided by the submitters.

Beschreibung: The dating equipment and operating procedures in the Physical laboratory remained as described previously (R, 1974, v 16, no. 1, p 6-9).Dates were calculated using the 5568-year half-life with 1950 as the reference year, the modern standard being 0.95 of the activity of the NBS oxalic acid standard. When done, δ13C was measured on CO2 produced in the combustion of samples, and results are given relative to the PDB standard. All samples were from Ireland.

Beschreibung: We 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 × 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.

Beschreibung: The radiocarbon dates covered in this list were measured during 1978. Chemical and counting procedures are as reported previously (R, 1978, v 20, p 398-404). Age calculations are based on the conventional 14C half-life (5570 yr) and on the contemporary value of 95% of the activity of NBS oxalic acid. Errors quoted correspond to 1σ value which takes into account the counting statistics, the uncertainty in the half-life, and the instability of the counting system. The ages are not corrected for isotopic fractionation in nature.

Beschreibung: The program called Geochemical Ocean Section Study (GEOSECS) was initiated in 1971 and designed to make an oceanic inventory of chemical constituents in the world oceans, partly as a baseline study for future chemical changes, and partly to investigate large-scale oceanic transport and mixing processes. Measured were hydrographic parameters (salinity, temperature, and oxygen vs depth), the carbonate system, the nutrients, and assorted other constituents with heavy emphasis laid on the radioactive substances, radiocarbon, tritium, and radon.

Beschreibung: Procedures and equipment have been described in previous date lists. Except as otherwise indicated, wood, charcoal and peat samples are pretreated with dilute NaOH and dilute H3PO4 before conversion to the counting gas methane; marls and lake cores are treated with acid only. Very calcareous materials are treated with HCL instead of H3PO4.

Beschreibung: The following list sums up the results of radiocarbon age determinations obtained at the Laboratory in 1974-1975. The list is prefaced with a brief description of the measurement procedure and discussion of some methodological aspects of the investigation that result in a higher accuracy of dating.

Beschreibung: The following radiocarbon dates are a partial list of samples measured for a variety of projects and materials since April 1979. Chemical and counting procedures remain the same as indicated in R, v 20, p 274-282.

Beschreibung: Radiocarbon 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 Δ14C 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.

Beschreibung: Claims that forest cutting during the last few decades has contributed significantly to the buildup in atmospheric CO2 have cast doubt on the validity of models used to estimate CO2 uptake by the ocean. In this paper we review the existing models and conclude that the box-diffusion model of Oeschger and his co-workers provides an excellent fit to the average distributions of natural and bomb-produced radiocarbon. We also take the first steps toward a more detailed ocean model which takes into account upwelling in the equatorial zone and deep water formation in the polar zone. The model is calibrated using the distribution of bomb-produced and cosmic ray-produced radiocarbon in the ocean. Preliminary calculations indicate that the fossil fuel CO2 uptake by this model will be greater than that by the box-diffusion model of Oeschger and others (1975) but not great enough to accommodate a significant decline in the mass of the terrestrial biosphere over the past two decades.

Beschreibung: Radiocarbon dating of mollusks and barnacles from fossil shoreline deposits in the Persian Gulf and on the coast of Iranian Makran is being used to assess the extent and rate of recent crustal deformation in the area. Samples are selected with the help of x-ray diffraction and of light and scanning electron microscopy; whenever possible, two or more ages are determined for each locality on monospecific samples. Age/height values have been used to compute local uplift rates by allowing for sea-level fluctuations, but eustatic controversy can be avoided by limiting the analysis to fault chronology and to relative vertical movements between dated sections. Short counting times on large, carefully pretreated samples would supply the numerous, cheap, low-resolution ages required to follow up the preliminary results obtained by the survey.

Beschreibung: The effects of nonconservative sources (inputs) and sinks (outputs) of carbon are indicated by the behavior of Δ14C and δ13C of the total dissolved inorganic carbon (ΣCO2) in San Francisco Bay and Chesapeake Bay. Isotopic distributions and model calculations indicate that in North San Francisco Bay the net CO2 flux to the atmosphere and carbon utilization in the water column are balanced by benthic production. Municipal waste appears to be a dominant source in South San Francisco Bav. In Chesapeake Bay, atmospheric exchange has increased the Δ14C and δ13C in the surface water. Decomposition of organic matter in the water column is indicated to be the dominant source of excess ΣCO2 in the deep water.

Beschreibung: We have determined the 81Kr activity to be (0.067 ± 0.003) decay/min. 1 krypton. Using this activity in conjunction with our new measurement of the 80Kr(n/γ)81Kr reaction cross-section of (12 ± 4)b, we infer that the 81Kr activity is 1.5-2.0 times that which would be calculated using the current cosmic ray flux. This implies that the average cosmic ray intensity in the atmosphere during the 81Kr life-time was greater than the current intensity, a fact that has implications for the 14C time scale.

Beschreibung: In November 1973 the British Museum Research Laboratory acquired a Hewlett Packard 2100A mini-computer for the storage, calculation and retrieval of scientific measurements made on museum objects. A part of the computer's work is the calculation of radiocarbon dates based on the liquid scintillation counting of 14C activities. A system of programs and files has been developed and has been in daily use since August 1974 (Hall and Hewson, 1977).This paper describes changes and improvements to the system to make it more flexible so that it now provides the full range of facilities required by an active 14C laboratory. The reporting procedures in particular have been restructured in the light of experience. The paper will be of interest to all laboratories that have, or hope to have, access to similar mini- or micro-computers.

Beschreibung: A preliminary review is given of the evaluation of the International Cross-Calibration Radiocarbon Data. Consensus values and standard errors are D14C = 508.1 ± 2.0% (ANU Sucrose) and Δ = −2.5 ± 1.5% (1850 Wood). Reporting format follows recommendations of Stuiver and Polach (1977).

Beschreibung: In this paper it is shown that the ability to directly detect a daughter atom, using resonance ionization spectroscopy, in delayed time coincidence with the decay of a parent species promises to drastically reduce the background in low-level counting experiments. In addition, resonance ionization can also be used as an ion source for a mass spectrometer system that is capable of discriminating between isobars.

Beschreibung: Extraction 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°C. Age dates run on such samples support this conclusion.

Beschreibung: The addition of organic materials derived from the upper soil layer yields, for samples at greater depth, younger 14C dates than the date of deposition. To find a criterion for the contamination with younger carbon in a soil sample, we examined the radiocarbon concentrations in two humic acid fractions and humin taken from the same sample. The humic acid extracted from a soil sample was divided into two fractions HA1 and HA2. HA1 is the first fraction extracted by 30 minutes' heating with 2 percent NaOH solution, and HA2 is the second fraction extracted by 2 hours' heating with 2 percent NaOH solution after the extraction of HA1. The residue was assumed as the humin (HM).Many of the peat or soil samples taken from the layer just above the nonpermeable layer contain appreciable amounts of organic materials transported from the upper layer after the sedimentation of the deposits. For the limited number of cases tested here, there is a trend in which the contaminants are selectively extracted by HA1 or HA2. When the soil samples are contaminated the ages of the HA1 and HA2 fractions appeared to differ widely in most cases. Agreement between the HA1, HA2, and HM ages may be used as a criterion for the reliability of the soil dating.

Beschreibung: Cosmic-ray produced atmospheric 39Ar activity (T1/2 = 269 yr) has been determined at 0.11 ±0.012 dpm/lt argon. Ice samples from two profiles in Greenland bore holes showed conclusively that 39Ar dating leads to correct ages. Corrections can be made for possible contamination of the samples with ambient air during field extraction and during laboratory processing by measuring 85Kr in the same samples.The following isotopes: 14C, 39Ar, 85Kr, 3H, partly 32Si, 13C, and 18O were investigated in 20 groundwater samples. Unexpectedly large discrepancies between “14C ages” and “39Ar ages” were observed for many of these samples. For example, a horizontal profile of a confined sandstone aquifer in the Franconian Albvorland showed decreasing 39Ar and 14C activities from respectively, 100 percent to 17 percent and 80 percent to 0.3 percent of modern activity, corresponding to elapsed time periods of 700 and 〉20,000 years, respectively.It seems unlikely that gas exchange through the aquiclude is the cause of this discrepancy. It can neither be explained by only assuming that the water represents a mixing of components with different ages. We detected the possibility of underground production of 39Ar in thermal spring water from Zurzach, Switzerland. Its argon showed higher specific activity than atmospheric argon. Elsewhere, however, samples were found containing no detectable 39Ar activity: two wells of a confined carstic aquifer in Ingolstadt, Germany, show less than 7 percent atmospheric activity.In our opinion, the assumptions on which the 14C method in hydrology are based need to be critically re-examined. It is possible that for some aquifers carbonate exchange between solid and liquid phases in the aquifer changes 14C results to a larger degree than generally assumed.

Beschreibung: A 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 over-attenuate 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.

Beschreibung: A 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.

Beschreibung: There are extended wind-blown sand territories in the northeastern part of the Great Hungarian Plain. Wind-blown sand migration periods were distineuished by means of radiocarbon age determination of charcoal samples found in the same type of a thin soil layer of chernozem character in different sand dune exposures. The ages of the samples were determined by proportional counter, and are around 12 000 years BP. This thin fossil soil layer, which is regionally spread in the northeast Hungarian wind-blown sand areas, presents a chronological mark between the blown sand forms evolved in the last glacial period and in the Holocene.

Beschreibung: This note provides some explanation of the fact that, contrary to the requirements of local isotropy, the skewness S of the streamwise temperature derivative ∂θ/∂x1 has been observed to be a non-zero constant of magnitude of about unity in high-Reynolds-number and high-Péclet-number turbulent shear flows. Measurements in slightly heated homogeneous shear flows and in unsheared grid turbulence suggest that S is non-zero only when the mean shear dU1/dx2 and the mean temperature gradient dT/dx2 are both non-zero. The sign of S is given by –sgn (dU1/dx2).sgn (dT/dx2). For fixed dU1/dx2, S is of the form tanh (αdT/dx2), α being a constant, while for fixed dT/dx2, it is of the form S/S* = 1 − β1 exp (− β2τ), where S* is a characteristic value of S, β1 and β2 are positive constants, and τ can be interpreted as a ‘total strain’. The derivative skewness data in other (inhomogeneous) shear flows are also compatible with the latter relation. Predictions from a simplified transport equation for [formula omitted], derived in the light of the present experimental observations, are in reasonable agreement with the measured values of S. A possible physical mechanism maintaining S is discussed. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: When pure solvent is separated from a solution of non-zero concentration Cb by a semi-permeable membrane, permeable to solvent (water) but not to solute, water flows osmotically across the membrane towards the solution. Its velocity J is given by J = PΔC, where P is a constant and ΔC is the concentration difference across the membrane. Because the osmotic flow advects solute away from the membrane, ΔC is usually less than Cb, by a factor γ which depends on the thickness of and flow in a concentration boundary layer. In this paper the layer is analysed on the assumption that the stirring motions in the bulk solution, which counter the osmotic advection, can be represented as two-dimensional stagnation-point flow. The steady-state results are compared with those of the standard physiological model in which the layer has a given thickness δ and the osmotic advection is countered only by diffusion. It turns out that the standard theory, although mechanistically inadequate, accurately predicts the value of γ over a wide range of values of the governing parameter β = PCbδ/D (where D is the solute diffusivity) if δ is given by where ν is the kinematic viscosity of the fluid and α is the stirring parameter. The final approach to the steady state is also analysed, and it is shown to be achieved in a time scale (D/ν)1/3/αk′ where k′ is a dimensionless number whose dependence on β is computed. Moreover, if β exceeds a certain critical value (≈ 10), the approach to the steady state is not monotonic but takes the form of a damped oscillation (in practice, however, β is unlikely to rise significantly above 1). The theory is extended to the case where the solute concentration is non-zero on both sides of the membrane and in that case it is shown that J is bounded as β → ∞. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: A rational asymptotic theory describing the perturbed flow in a turbulent boundary layer encountering a small two-dimensional hump is presented. The theory is valid in the limit of very high Reynolds number in the case of an aerodynamically smooth surface, or in the limit of small drag coefficient in the case of a rough surface. The method of matched asymptotic expansions is used to obtain a multiple-structured flow, along the general lines of earlier laminar studies. The leading-order velocity perturbations are shown to be precisely the inviscid, irrotational, potential flow solutions over most of the domain. The Reynolds stresses are found to vary across a thin layer adjacent to the surface, and display a singular behaviour near the surface which needs to be resolved by an even thinner wall layer. The Reynolds stress perturbations are calculated by means of a second-order closure model, which is shown to be the minimum level of sophistication capable of describing these variations. The perturbation force on the hump is also calculated, and its order of magnitude is shown to depend on the level of turbulence closure; a cruder turbulence model gives rise to spuriously large forces. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: Steady potential flow around a two-dimensional bubble with surface tension, either free or attached to a wall, is considered. The results also apply to a liquid drop. The flow and the bubble shape are determined as functions of the contact angle β and the dimensionless pressure ratio γ = (pb − ps)/½ρU2. Here pb is the pressure in the bubble, ps = p∞ + ½ρU2 is the stagnation pressure, p∞ is the pressure at infinity, ρ is the fluid density and U is the velocity at infinity. The surface tension σ determines the dimensions of the bubble, which are proportional to 2σ/ρU2. As γ tends to ∞, the bubble surface tends to a circle or circular arc, and as γ decreases the bubble elongates in the direction normal to the flow. When γ reaches a certain value γ0(β), opposite sides of the bubble touch each other. The problem is formulated as an integrodifferential equation for the bubble surface. This equation is discretized and solved numerically by Newton's method. Bubble profiles, the bubble area, the surface energy and the kinetic energy are presented for various values of β and γ. In addition a perturbation solution is given for γ large when the bubble is nearly a circular arc, and a slender-body approximation is presented for β ∼ ½π and γ ∼ γ0(β), when the bubble is slender. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: The evolution of the shape of a slender inviscid drop in an axisymmetric straining motion is studied at low Reynolds numbers. It is found that the shape equation can be solved by polynommals with time-dependent coefficients. A global stability result can be used to show simply that only one possible equilibrium is stable. It is further shown that if the slender drop starts with a long-wavelength waist then it cannot go to this stable equilibrium and must either extend indefinitely or burst. In the class of trinomial shapes, it is shown that the drop either bursts or goes to the stable equilibrium, depending on whether or not the initial shape has a waist. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: Conditions are found for the appearance of non-uniform progressive waves of permanent form from a long-wave modulation of a finite-amplitude Stokes wave on deep water. The waveheight at which the modulated waves can occur is a very slowly decreasing function of the modulation wavelength for values up to 150 times the original wavelength. Some qualitative remarks are made about the problem of determining the stability of the new waves. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: Based on the parabolic approximation, a refraction—diffraction model for linear water waves is developed. With the assumption that the water depth (refraction index) is slowly varying, the model equation describes the forward-scattered wavefield. Two examples are considered in particular: (i) wave diffraction by a long thin barrier on a uniform slope, and (ii) wave convergence over a semicircular step shoal. For the former problem, a similarity solution in terms of Fresnel integrals is obtained for the wavefield in the neighbourhood of the shadow boundary. For the latter problem, the resulting Schrödinger equation is solved numerically. The wavefield near the caustics as well as in the shadow region is obtained and compared with experimental data. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: The coherent structure dynamics in the near field of a circular jet has been experimentally explored by inducing ‘stable’ vortex pairing through controlled excitation (see Zaman & Hussain 1980) and applying phase-averaging techniques. Hot-wire measurements were made in a 7·62 cm air jet with laminar exit boundary layer at the Reynolds number ReD = 3·2 × 104, excited at the Strouhal number StD = 0·85. At a particular phase during the pairing process, spatial distributions of the phase-average longitudinal and lateral velocity perturbations (〈u)〉, 〈v〉), vorticity, streamlines, the coherent and background Reynolds stresses and turbulence intensities have been educed. These data have been obtained for four different locations occupied by the vortices at the same phase (preceding, during, and following the pairing event), in the region 0 〈 x/D 〈 5. Spatial distributions of these measures at four successive phases during the pairing process are also educed in an attempt to further understand the vortex-pairing dynamics. The flow physics is discussed on the basis of measurements over the physical extent of the vortical structures, phase-locked to specific phases of the pairing event and thus do not involve use of the Taylor hypothesis. The computed pseudostream functions at particular phases are compared with the corresponding streamlines drawn by the method of isoclines. Transition of the vortices is examined on the basis of vorticity diffusion, the superimposed random fluctuation field intensities and Reynolds stress and phase-locked circumferential correlation measurements. The peak vorticity drops rapidly owing to transition and interaction of the vortices during pairing but, farther downstream, the decay can be attributed to destruction of the coherent vorticity by the background turbulence Reynolds stress, especially at the locations of the latter's ‘saddle points’. Controlled excitation enhances the initial circumferential coherence of the vortical structures, but is ineffective in delaying turbulent breakdown near the end of the potential core; the breakdown appears to occur through evolution of the circumferential lobe structures. The coherent structure Reynolds stress is found to be much larger than the background turbulence Reynolds stress for 0 〈 x/D ≲ 3, but these two are comparable near the end of the jet potential core. The zone average of the coherent structure Reynolds stress over the cross-section of the merging vortex pair is much larger than that over a single vortical structure either before or after the completion of pairing. During the pairing process, such average correlations are found to be the largest at an early phase of the process while entrainment, turbulent breakdown as well as rapid diffusion of vorticity occur at a later phase. The regions of alternate positive and negative coherent Reynolds stresses associated with the structures and their interactions help explain ‘negative production’. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: Fully developed periodic flow (with non-zero mean) of a Newtonian fluid in a rigid curved tube has been investigated both numerically and experimentally. Results are reported for the mean friction factor, the amplitude ratio and phase angle between flow rate and pressure drop, the axial velocity profile, and the wall shear stress distribution. The numerical results (obtained by a finite difference method) are restricted to rather slow flows (mean Dean number [formula omitted]), while the experimental results (extracted from instantaneous flow rate-pressure drop measurements) extend up to [formula omitted]. A ‘resonant’ interaction between the axial and secondary flows at intermediate frequencies appears to be a characteristic feature of periodic flow in a curved tube. © 1980, Cambridge University Press. All rights reserved.

Beschreibung: This paper reports on an extensive experimental study of the flows due to under-expanded axisymmetric jets impinging on flat plates. The range of plate locations extends to a point where the jet is just subsonic but the main emphasis is on the behaviour in the first shock cell. Plate inclinations from 90° to 30° were investigated by means of comprehensive surface pressure measurements and shadowgraph pictures. Wherever possible, the main features of the results have been reconstructed using inviscid analyses of the wave interactions. The flows are shown to be extremely complex due to the local structure of the free jet and, particularly, due to interactions between shock waves in the free jet and those created by the plate. In the near field, these interactions tend to be the controlling factors but at larger distances from the nozzle, mixing effects become increasingly important. The maximum pressure on the plate when it is inclined can be very much larger than when the plate is perpendicular, owing to the possibility of high pressure recoveries through multiple shock systems. Correlations are presented for some of the main features on perpendicular plates and it is shown that the integrated pressure loads for both normal and inclined plates can be predicted well by a simple momentum balance. © 1980, Cambridge University Press. All rights reserved.