bluuebunny/crossref_metadata_2025 huggingface dataset:
Geological Survey of Finland Radiocarbon Measurements V
Authors: Heikkinen Aulis
Published: July 2016

The C14 measurements reported here were made in this laboratory between July 1969 and September 1970. The dating system consists of a 0.55 L copper-walled proportional counter (adapted from östlund and Engstrand, 1963, constructed by Outokumpu Oy, Research Lab., Tapiola, Finland) surrounded by a lead cylinder, 1.5 cm thick, placed within an anticoincidence meson detector. The system is encased in selected lead 1.5 cm thick, 7 cm of paraffin wax with ca. 10% boric acid and ca. 20 cm iron. Counter gas is CO2 with which the counter is filled to 228.6 m Hg at a detector temperature of 20°C. Background is 1.50 cpm and net contemporary value is ca. 10.0 cmp.
U.S. Geological Survey, Denver, Colorado Radiocarbon Dates I
Authors: Schroder L. J. , Beetem W. A. , Claassen H. C. , Emerson R. L.
Published: July 2016

The U.S. Geological Survey, at the Denver Federal Center, Lakewood, Colorado assays C14 concentration of water samples using liquid scintillation techniques. The laboratory synthesizes benzene from precipitated barium carbonate using techniques described by Noakes, Kim, and Akers (1967). Three ml of the synthesized benzene is pipetted into a tared, low potassium-40 glass vial. The sample is weighed and 1ml of a scintillation solution is added to the vial. The scintillation solution used is a mixture of 10g PPO and 0.025g dimethyl-POPOP scintillators in 250ml toluene. Calculations of dates are made with the radiocarbon half-life of 5568 years; plus or minus numbers quoted herein are the standard error for the counting of radioactive disintegrations.
Rhodesian Radiocarbon Measurements V
Authors: Sheppard J. G. , Swart E. R.
Published: July 2016

The following list of dates was compiled since 1971, (R., 1971, v. 13, p. 420-431). Procedures of measurements are essentially unchanged from those reported previously (R., 1964, v. 6, p. 31-36; 1966, v. 8, p. 423-429; 1971, v. 13, p. 420-431).
Scottish Universities Research and Reactor Centre Radiocarbon Measurements I
Authors: Harkness D. D. , Wilson H. W.
Published: July 2016

The Radiocarbon Laboratory at the Scottish Universities Research and Reactor Centre was established in August 1971. The laboratory is funded by the Natural Environment Research Council and its main function is geochemical investigations in collaboration with the component bodies of the Council and with grant-aided associations. A dating service is also provided to others.
Birbal Sahni Institute Radiocarbon Measurements I
Authors: Rajagopalan G , Vishnu-Mittre  , Sekar B
Published: July 2016

The Radiocarbon Dating Laboratory of the Institute was established in 1974 primarily to assist in the program of research undertaken by the Institute's Department of Quaternary Palynology (Rajagopalan and Vishnu-Mittre, 1977). The measurements carried out by the Laboratory up to December 1977 are presented in this date list.
Texas A&M University Radiocarbon Dates IV
Authors: Parker R A , Sackett W M
Published: July 2016

Organic and carbonate carbon in sediments deposited in the Cariaco Basin and on the Mississippi River Delta and the total dissolved inorganic carbon in four water column profiles comprise the samples in this list. Except as noted below the samples were processed using the benzene synthesis and other procedures described by Mathews, et al (1972).
Tree-Ring Dating and Radiocarbon Calibration in South-Central Europe
Authors: Becker Bernd
Published: July 2016

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 pine14C 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.
On the Climate-Radiocarbon Relationship: Nitric Oxide and Ozone as Connecting Links Between Radiation and the Earth's Surface Temperatures
Authors: Roedel Walter
Published: July 2016

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.
Radiocarbon Variations in Consecutive Single Rings of A 4000-Year-Old Pine from the British Isles
Authors: Hewson A D , Burleigh Richard
Published: July 2016

At the Ninth International Radiocarbon Conference a paper was presented concerning possible short-term14C 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 atmospheric14C 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 in14C between rings is not statistically significant; some other explanation must be sought for the anomalous antler measurements.
New Measurement of the 81Kr Atmospheric Abundance
Authors: Kuzminov V V , Pomansky A A
Published: July 2016

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.
Mini-Radiocarbon Measurements, Chemical Selectivity, and the Impact of Man on Environmental Pollution and Climate
Authors: Currie Lloyd A , Klouda George A , Cooper John A
Published: July 2016

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.
Temperature Dependent Seasonal Variation of the Background in Counters Used for Radiocarbon Dating
Authors: Håkansson Sören
Published: July 2016

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.
Memory Effects in the Production of Benzene for Radiocarbon Dating
Authors: Radnell C J , Muller A B
Published: July 2016

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.
Isotopic Fractionation of NBS Oxalic 14C Standard and Its Effect On Calculated Age of Materials
Authors: Nehmi Victor A
Published: July 2016

There is much controversy about the significance to radiocarbon dating of isotopic fractionation during the oxidation to CO2 of NBS oxalic acid, the carbon-14 dating standard. To check the effect of fractionation, 30 routine potassium permanganate oxidations of oxalic acid were performed. The isotopic composition of resulting CO2 was determined mass-spectrometrically. δ13C results ranged between —17.7 and —21.2, with an average of —18.9‰ wrt PDB. The effect of not applying an isotopic fractionation correction to NBS oxalic acid when performing age calculations is evaluated.
Low-Level Liquid Scintillation Counting in An Underground Laboratory
Authors: Schotterer Ulrich , Oeschger Hans
Published: July 2016

A commercial liquid scintillation counter (LSC) was tested for its ability of low level counting (LLC) in two underground laboratories (70m of water equivalent cover). Reduction of total background and background components compared to the normal counting laboratory (5m w.e. cover) up to a factor of 9 depending on the energy range and the shielding of counting cell and laboratory walls were obtained. First experiments with a large volume cell (50cc) led to a modern 14C net effect of 425cpm and a corresponding background of 1.6cpm.
Holocene Sea-Level History: Case Study of the Statistical Evaluation of14C Dates
Authors: Geyh Mebus A
Published: July 2016

The limits of the statistical evaluation of14C dates by histograms are discussed. The method of the attempt to establish a global chronology of the short-term eustatic sea-level changes during the Holocene is examined as well as its correlation with the precisely determined Suess wiggles.
Age Structure of Holocene Coastal Sediments: Gulf of Carpentaria, Australia
Authors: Rhodes E G , Polach H A , Thom B G , Wilson S R
Published: July 2016

Shells in beach-ridge and chenier Holocene deposits from the Gulf of Carpentaria, Queensland, have been dated by radiocarbon. Possible contamination of carbonate by post-depositional diagenetic processes, isotopic fractionation, ocean reservoir environmental effect, and association of biological age of sample material with depositional event have been examined in order to validate dating of samples from this environment. A numerical methodology used for comparing ‘groups’ of 14C dates strongly supports morphostratigraphic evidence that time discontinuities occur within both chenier and beach-ridge sequences. Four episodes are recognized in each area, all younger than ca 5800 years ago, the time when sea level reached its postglacial maximum in the Gulf of Carpentaria. To some extent, these episodes are out of phase, reflecting different modes of strandline accumulation.
14C Ages and Magnetic Stratigraphy in Three Australian Maars
Authors: Barton C E , Polach H A
Published: July 2016

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.
The Climatic History of the Eastern Mediterranean as Recorded in Mollusk Shells
Authors: Kaufman Aaron , Magaritz Mordeckai
Published: July 2016

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.
Radioisotope Detection with the Argonne FN Tandem Accelerator
Authors: Kutschera Walter , Henning Walter , Paul Michael , Stephenson E J , Yntema J L
Published: July 2016

A standard heavy ion nuclear structure facility has been used to detect several long-lived radioisotopes by counting the accelerated ions. The problem of eliminating strong isobaric background beams has been solved by combining the energy loss dispersion through a uniform Al foil stack with the high momentum resolution of an Enge split-pole magnetic spectrograph. Radioisotope concentrations in the following ranges have been measured: 14C/12C = 10–12 to 10–13, 26Al/27Al = 10–10 to 10–12, 32Si/Si = 10–8 to 10–14, 36Cl/Cl = 10–8 to 10–11.
Carbon-14 and Carbon-13 in Soil Co2
Authors: Dörr Helmut , Münnich Karl Otto
Published: July 2016

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.
Radiocarbon Concentration in the Atmosphere: 8000-Year Record of Variations in Tree Rings: First Results of a USA Workshop
Authors: Klein Jeffrey , Lerman Juan Carlos , Damon Paul E , Linick Timothy
Published: July 2016

Radiocarbon dates calculated from the ratio of modern carbon-14 activity and sample activity and the half-life of carbon-14 need to be calibrated to compensate for temporal variations in the concentration of carbon-14 in the atmosphere. Development of a suitable calibration scheme has been an ongoing process of the last twenty years, ever since the discovery of variations in historical times of the atmospheric radiocarbon content which parallel climatic and solar phenomena (de Vries, 1958; 1959) and the recent depletion due to industrial effects (Suess, 1955).
Geological Survey of Canada Radiocarbon Dates III
Authors: Dyck W. , Fyles J. G.
Published: July 2016

All C14 measurements in this date list were made with the 2 L counter described in our first date list (GSC I). Ages were calculated on a C14 half life of 5570 ± 30 yr and 0.95 of the activity of the NBS oxalic-acid standard, and are quoted in years before 1950.
Copenhagen Radiocarbon Dates VI
Authors: Tauber Henrik
Published: July 2016

The following list comprises a selected number of measurements made up to November 1963. Age calculations are based on a contemporary value equal to 95% of the activity of the NBS oxalic-acid standard, and on a half life for C14of 5570 ± 30 yr.

Results are expressed in years before 1950 and in the b.c.-a.d. scales. Errors quoted include the standard deviations of the count rates for the unknown sample, the contemporary value, and the background. Calculated errors smaller than 100 yr have been increased by rounding to that figure as a minimum. Sample descriptions have been prepared in collaboration with collectors and submitters.
Berlin Radiocarbon Measurements I
Authors: Kohl G. , Quitta H.
Published: July 2016

The C14Laboratory of the German Academy of Sciences of Berlin (DAW) began to obtain dates in 1961. The focus of research is in archaeology. Samples, coll. in close collaboration with the DAW's Institut für Vor- und Frühgeschichte, are mainly from the Neolithic of central and southeastern Europe, and contribute to the continuing discussion (Milojčić, 1961; Müller-Beck, 1961) of the chronology of this period.
UCLA Radiocarbon Dates VIII
Authors: Berger Rainer , Libby W. F.
Published: July 2016

The measurements reported were made during the 2nd half of 1967 in the Isotope Lab. of the Inst. of Geophysics and Planetary Physics as a continuation of the UCLA date lists I through VII. Samples were analyzed as CO2-gas at close to one atm in a 7.5 L proportional counter with 3 energy channels described earlier. Radiocarbon ages were calculated for uniformity on the basis of a 5568 yr half-life as was recommended by the Sixth International C14and H3Dating Conference, June 1965, in Pullman, Washington. The standard for the contemporary biosphere remains as 95% of the count rate of NBS oxalic acid for radiocarbon labs. Background determinations have been based on CO2obtained from marble. The error listed is always at least a 1σ statistical counting error. In critical cases C13/C12isotope ratio measurements were made to correct the dates for fractionation. All samples were subjected to accepted NaOH and/or HCl pretreatments depending on the individual case as a minimum to exclude contamination.
Tbilisi Radiocarbon Dates I
Authors: Burchuladze A. A.
Published: July 2016

Charcoal from Uplistsikhe village [unlocated], Katlanis Khevi. Archaeologic date: late Bronze age, 12th to 7th centuries B.C. Subm. [n.d.] by D. Khakhutashvili.
Dublin Radiocarbon Dates III
Authors: Dresser P Q
Published: July 2016

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.
University of Lund Radiocarbon Dates XIII
Authors: Håkansson Sören
Published: July 2016

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 <650°C in order to avoid pyrolysis of carbonates that may be present in the samples. Same max combustion temperature is used for samples with suspected graphite contamination. A movable thermocouple (Philips TERMOCOAX TCI 30/50/3) in the combustion zone is used for checking the temperature.
Radon Elimination During Benzene Preparation for Radiocarbon Dating by Liquid Scintillation Spectrometry
Authors: Hood Darden , Hatfield Ronald , Patrick Christopher , Stipp Jerry , Tamers Murry , Leidl Robert , Lyons Barbara , Polach Henry , Robertson Steve , Zhou Weijian
Published: July 2016

Radon gas is a serious contaminant in radiocarbon dating by radiometry. The low specific ionizations associated with the α-particle emitting radon and its β-particle emitting daughters overlap within the 14C counting window. Elimination of radon is therefore imperative for precise 14C age determinations. This paper deals with the sources and mechanism of incorporation of radon affecting 14C dating by liquid scintillation (LS) counting, and reviews conventional radon elimination practices in 14C laboratories. It demonstrates, based on rigorous multichannel and multiparameter α- and β-particle spectral analyses of some 1000 benzene samples, that parent radium is not present and that its daughter radon is quantitatively eliminated during dynamic vacuum recovery of benzene at −78°C. However, the radon-free benzene can be recontaminated by exposure to air containing traces of radon, such as is common in concrete or low-lying laboratories. The use of radon-free air, when exposing the benzene to the atmosphere, and the monitoring of radon counts from the environment and sample benzene in a fixed ‘radon window', are essential prerequisites to the quality control of 14C age determinations in very low background systems.
Study of Background Pulse Spectrum of an LSC System
Authors: Einarsson Sigurđur A , Theodórsson Páll
Published: July 2016

Important advances have been made in reducing the background counting rate of gas proportional counters for14C dating through detailed and systematic study of the background components. Until recently, limited work has been reported on the study of the background of liquid scintillation counters (LSC). During the last few years, commercial systems with greatly reduced background have been introduced. It is shown that the best gas proportional counters and LSC have similar backgrounds for the same amount of sample material. Similar results with less effort may be expected with more detailed and fundamental knowledge of the components of the background of LSC. We report the results of a study of one photomultiplier LSC system where we research all parameters of importance: light collection efficiency, absorbed energy per photo-electron, pulse height spectrum and background counting rate.
New Possibilities for 14C Measurements by Liquid Scintillation Counting
Authors: Aravena Ramon , Drimmie Robert R , Qureshi Riffat M , McNeely Roger , Fabris Sandy
Published: July 2016

Results of intercomparison tests are presented on samples analyzed using gas and liquid scintillation techniques to study the capability of the LKB Quantulus to count an organic solution used for direct absorption of CO2 and samples with low carbon content. Good agreement was obtained for small samples compared to standard sample size and for the direct absorption compared with the traditional techniques.
A Counter System for High-Precision 14C Dating
Authors: Hertelendi Ede , Csongor Éva , Zaborszky Laszlo , Molnar Jozsef , Gal Janos , Györffi Miklos , Nagy Sandor
Published: July 2016

A multicounter radiocarbon dating system was developed applying the experiences of the previous one-channel low-level counting facility. The counter system consists of nine electrolytic copper proportional counters of identical diameters with sensitive volumes of 0.35–0.7dm3 and filled with either methane at high pressure (6 bar) or CO2 at 1 bar. The inner counters are surrounded by an anticoincidence shield consisting of five multiwire proportional flat counters filled with propane. The pulses of the detectors are handled by integrated amplifiers, discriminators and anticoincidence units interfaced to a microprocessor-controlled data evaluation unit. Software is written in BASIC using ASSEMBLER sub-routines. The overall precision of the system for modern carbon samples using high-pressure methane-filled counters (B ≍ 0.7 cpm, S ≍ 14 cpm) is better than 4 after a counting period of seven days.
Variation of Concentration, 14C Activity and 13C/12C Ratios of CO2 in Air Samples from Kitt Peak, Arizona
Authors: Leavitt S W , Long Austin
Published: July 2016

Air was sampled with 5L flasks at Kitt Peak (2100m elev) from 1983 through 1984 at approximately monthly intervals, occasionally supplemented with air samples from urban Tucson ca 75km away (760m elev). The Kitt Peak CO2 concentrations, represented by a yield measurement, fluctuated ca 25% over the monitoring period. The δ13C values (uncorrected for N2O) varied from ca −7.6 to −9.0, with high values (and low CO2 yields) in the late summer consistent with hemispheric seasonal biosphere effects. Tucson air has lower δ13C values and possibly greater CO2 yield suggesting a local fossil-fuel effect. 14C activity of four Kitt Peak samples range from 1.158±.007 to 1.223±.008 as uncorrected fraction of modern, below free air activity of ca 1.250 for 1984 even after correcting for fractionation. The slightly low 14C activity and δ13C values suggest the Kitt Peak air is not quite 100% clean and there may be a local/regional fossil-fuel contribution, but CO2 concentrations are similar to background atmospheric values.
Atmospheric CO2 Exchange With the Biosphere and the Ocean
Authors: Bergh Roger , Nydal Reidar
Published: July 2016

We model the exchange of carbon between the different reservoirs (atmosphere, ocean mixed layer, deep ocean and biosphere). The influence of the biosphere is investigated using two extreme assumptions: 1) no net biospheric effect and 2) biospheric uptake of CO2 proportional to the atmospheric content of CO2 and time-dependent deforestation. Observations of atmospheric CO2 at Mauna Loa and the South Pole may be fit by both these assumptions.
Sources of Carbon to Deep-Sea Corals
Authors: Griffin Sheila , Druffel Ellen R M
Published: July 2016

Radiocarbon measurements in deep-sea corals from the Little Bahama Bank were used to determine the source of carbon to the skeletal matrices. Specimens of Lophelia, Gerardia, Paragorgia johnsoni and Corallium noibe were sectioned according to visible growth rings and/or stem diameter. We determined that the source of carbon to the corals accreting organic matter was primarily from surface-derived sources. Those corals that accrete a calcerous skeleton were found to obtain their carbon solely from dissolved inorganic carbon (DIC) in sea water from the depth at which the corals grew. These results, in conjunction with growth-rate studies using short-lived radioisotopes, support the use of deep-sea corals to reconstruct time histories of transient and non-transient tracers at depth in the oceans.
14C Profiles in the Central Weddell Sea
Authors: Schlosser Peter , Kromer Bernd , Bayer Reinhold , Münnich K O
Published: July 2016

14C data from stations in the central Weddell Sea are presented and discussed using additional parameters (potential temperature, salinity and 3He). The low 14C concentrations of the surface water (≈-90‰) are explained by suppressed gas exchange due to ice cover during the winter and rapid turnover of the surface layer caused by entrainment of Warm Deep Water (WDW) with low 14C concentrations. A simple time-dependent balance calculated for the Surface Water (SW) and the underlying Winter Water (WW) can reproduce the 14C concentrations observed in these layers for 1985. The pre-bomb 14C concentrations are estimated at ≈-130‰ for SW and −140‰ for WW. A strong deviation of the SW 14C concentration observed in 1973 from the calculated value suggest a change in surface circulation and/or air/sea exchange during the period before the Weddell Polynya in 1974. The observed 14C concentrations of the Weddell Sea Bottom Water (WSBW; −135 to −150‰) are only slightly higher than those of the WDW showing that the uptake of bomb 14C in the Weddell Sea is limited. The 14C profiles show a minimum at intermediate depths (≈ 1500m) which is caused by radioactive decay and/or penetration of bomb 14C from shallow and deep layers (WDW and WSBW) into intermediate layers.
Application of 14C AMS Dating to the Chronology of Holocene Glacier Fluctuations in the High Arctic, With Special Reference to Leffert Glacier, Ellesmere Island, Canada
Authors: Blake Weston
Published: July 2016

A series of radiocarbon age determinations obtained by Accelerator Mass Spectrometry (AMS) shows that the front of Leffert Glacier, a major outlet glacier from the Prince of Wales Icefield, Ellesmere Island, was 18+ km behind (west of) its present position for a period of at least 1500 radiocarbon years. A subsequent readvance occurred close to 2000 radiocarbon years ago, as a consequence of the climatic cooling that followed the warm Hypsithermal Interval. A number of other glaciers in the region appear to have behaved in similar fashion.
AMS 14C Dating on the Fossvogur Sediments, Iceland
Authors: Andersen G J , Heinemeier J A N , Nielsen H L , Rud Niels , Thomsen M S , Johnsen Sigfús , Sveinbjörnsdóttir Árný , Hjartarson Árni
Published: July 2016

Several new AMS 14C dates on shells from the Fossvogur sea sediments in southern Iceland are reported. Up till now, researchers have assumed that the Fossvogur sediments formed during the last interglacial period (Eem), some 100,000 years ago. However, a recent 14C determination from this location yielded an age of ca 11,000 yr. Because of the importance of these sediments for the Quaternary chronology of Iceland, further sampling for 14C dating was subsequently initiated. The present results on several shell samples collected from the Fossvogur layers strongly indicate that these sediments were formed during the warm Allerød period toward the end of the last glaciation.
Isotopic Fractionation of Oxygen and Carbon in Lime Mortar Under Natural Environmental Conditions
Authors: van Strydonck Mark J Y , Dupas Michel , Keppens Edward
Published: July 2016

The rate of calcite formation and the isotopic fractionation in lime mortar during the process of mortar setting were examined. The diffusion rate of atmospheric CO2 in the sample is the rate-controlling step of the chemical reaction. A Rayleigh diffusion in the mortar causes an enrichment of 13C and 18O in the samples.
The Influence of Afforestation on Upland Soils: The Use of ‘Bomb 14C’ Enrichment as a Quantitative Tracer for Changes in Organic Status
Authors: Harkness D D , Harrison A F
Published: July 2016

A series of soil samples were collected in November 1984 from five stands of Sitka spruce planted at recorded times between 1951 and 1968. Within a comprehensive program of ecologic and biogeochemical analyses, natural 14C measurements on selected organic components of the 0 to 5cm soil horizons serve to quantify progressive changes induced in the organic carbon inventory and relative to that of the original grassland. Points of particular interest are: 1) an enhanced input of fresh organic matter in the years immediately following planting; this, in parallel with a net decrease in the total carbon content of the topsoil; 2) this freshly introduced carbon predominates in the soil profile even after 30 years of afforestation; 3) during the 15- to 30-year growth period, the soil carbon content remains constant but progressive changes occur in its biogeochemical composition and rate of turnover.
Atmospheric Radiocarbon at the End of the Last Glacial: An Estimate Based on AMS Radiocarbon Dates on Terrestrial Macrofossils From Lake Sediments
Authors: Zbinden Hugo , Andree Michael , Oeschger Hans , Ammann Brigitta , Lotter Andre , Bonani Georges , Wölfli Willy
Published: July 2016

The main purpose of this work is to reconstruct the atmospheric Δ 14C in the glacial-postglacial transition, 14,000 – 10,000 BP, a range not covered by the tree-ring calibration curve. We measured 14C/12C ratios on series of terrestrial macrofossils from sediments of two Swiss lakes. We selected exclusively plant remains of recognizable terrestrial origin that are not affected by hard water and thus reflect atmospheric 14C concentration. Due to the scarcity of such material, we used accelerator mass spectroscopy. Cores of two lakes were measured to eliminate local effects and to check the reproducibility of results. This required a reliable, 14C-independent correlation of the cores, obtained through local pollen zone boundaries 14C ages were obtained as a function of the depth in the cores. If sedimentation rates are known ages can be converted into Δ 14C values. We also attempted estimating sedimentation rates; calculations are based on the Swedish varve chronology. Results were combined to form an entire data set. The Δ 14C curve shows an increase with time during the Allerød and decreases during Preboreal and Bølling periods. Probabilities for these 14C variations are discussed.
Histograms Obtained From Computerized Radiocarbon Age Calibration
Authors: Stuiver Minze , Reimer Paula
Published: July 2016

Two methods of assigning probability values to calendar years are compared by summing distributions for a large number of 14C ages derived from samples initially distributed uniformly in calendar years. The radiocarbon ages are calibrated with both a hypothetical calibration curve and the internationally accepted one. The effect of the calibration curve on an ideal and a random sample population is examined.
A Cyclogram Analysis of the Bratislava 14C Tree-Ring Record During the Last Century
Authors: Attolini M R , Galli Menotti , Nanni Teresa , Povinec Pavel
Published: July 2016

Radiocarbon variations in dated tree-ring samples represent an important tool for the study of the history of solar activity and sun-earth relationships. From this point of view, an investigation of the 11-year radiocarbon cycle is very important. Our cyclogram analysis of the Δ 14C record in tree-ring samples during the last century has confirmed previous results obtained by conventional harmonic analysis, eg, the average amplitude of 2, the phase shift of 3–5 yr for different 11-yr solar cycles, and the anticorrelation dependence of Δ 14C on Wolf sunspot numbers. The observed shorter periodicity (ca 9 yr for Δ 14C compared to 10.5 yr for sunspots), may be due to extra factors in sun-earth relationships.
The Geochemistry and Evolution of Natural Organic Solutes in Groundwater
Authors: Wassenaar Leonard , Aravena Ramon , Fritz Peter
Published: July 2016

This paper describes the organic carbon cycle of the recharge environment of a shallow, sandy aquifer, with an emphasis on the origin, flux and geochemical evolution of dissolved organic carbon using liquid chromatography, carbon isotopes and GC-MS techniques. The two components of DOC investigated are hydrophobic acids and C1-C10 hydrophilic compounds. The 14C activity of these components of the DOC was measured using TAMS.

14C analyses of DOC components may provide an additional tool for groundwater dating. The initial 14C activity of DOC in a recharge zone, however, depends mainly on the residence times and cycling of DOC sources in the recharge environment. Using 14C DOC to estimate groundwater residence times between sampling points along a flow path compares well with residence times estimated on the basis of hydraulic parameters and 14C DIC under closed system conditions.
Radiocarbon Dating of Ostrich Eggshells
Authors: Freundlich Jürgen C , Kuper Rudolph , Breunig Peter , Bertram Hans-Georg
Published: July 2016

Unlike wood charcoal, as found admixed to other cultural remains, ostrich eggshells can be of more direct significance in 14C dating, especially if they were processed to form, eg, eggshell beads. Normally the time span between laying the egg and working the shell beads is short enough to be negligible for 14C dating purposes. Another advantage of eggshell dating is that the carbonate of the shell seems to keep exceptionally well over the millennia, whereas, especially in surface sites in a desert environment, organic material such as wood, charcoal or bone protein tends to decompose. With few comparative test samples, we thought ostrich egg samples would yield 14C dates somewhat too young. The deviation is, however, balanced by performing 13C analyses and a correction for isotope fractionation of ca 350yr.
First Direct AMS Dates on Early Maize From Tehuacán, Mexico
Authors: Long Austin , Benz B F , Donahue D J , Jull A J T , Toolin L J
Published: July 2016

The Tehuacán region in Central Mexico is thought to be the locale of origin of Zea mays, or maize, a cultivated plant pivotal in the development of agriculture in the Americas (MacNeish, 1981, 1985). The age of the earliest maize, and its rate of dispersal are thus important components of cultural development in the New World. We have secured permission from the Federal Government of Mexico to date critical specimens from Tehuacán, which represent what are probably some of the earliest known stages of maize evolution. Twelve Zea mays samples have been dated, six from Cueva San Marcos and six from Cueva Coxcatlán. These were selected as having the best stratigraphic control and correlation with previously dated charcoal samples, and to represent the most ancient maize. Corn from Cueva San Marcos is oldest: four of the six specimens from this cave were within statistics of 4700 BP (uncalibrated). The oldest known domesticated corn is thus no older than 3600 cal BC (dendro-calibrated in calendric years).
The International Radiocarbon Data Base: A Progress Report
Authors: Kra Renee
Published: July 2016

An International Radiocarbon Data Base (IRDB), an online centralized 14C data management and retrieval system has been designed and established to compile, edit and disseminate data to researchers in many scientific fields. The need for such a research tool has been apparent for some years. Since 1985, planning conferences and workshops have addressed the issues of implementing the IRDB. Workshops in Groningen and, most recently in New Haven, have led to consensus on a microcomputer-driven catalogue-type data retrieval management system, selection of an American Advisory Board and the initiation of two pilot projects. A permanent home has been found for the data base at The University of Arizona. It is hoped that our efforts toward international cooperation will culminate with the official launching of this much needed, long overdue enterprise.
Radiocarbon Dating of Intercomparison Samples at the Zagreb Radiocarbon Laboratory
Authors: Horvatinčić Nada , Srdoč Dušan , Obelić Bogomil , Bronić Ines Krajcar
Published: July 2016

The Radiocarbon and Tritium Laboratory of the Rudjer Bošković Institute, Zagreb, participated in the International Collaborative Study (ICS) in all three stages. All measurements were made by proportional counting of methane. We present here a statistical analysis of our results. A comparison with the mean or median values of reported ICS values showed that our results are generally slightly younger.
Gas ProportionalVersusLiquid Scintillation Counting, RadiometricVersusAMS Dating
Authors: Theodórsson Páll
Published: July 2016

I discuss here the basis of a comparison of methods for radiocarbon dating and introduce a new index for the relative merit of a system,factor of counting capacity,that is generally more appropriate than the commonly usedfactor of merit.The merit of a dating system cannot be based on a single figure but other factors must also be considered. A comparison of the gas proportional, liquid scintillation and accelerator mass spectrometry technique is presented that for gas proportional counters is based on a multi-detector system rather than a single detector.
Two Early Sites of Eastern Beringia: Context and Chronology in Alaskan Interior Archaeology
Authors: Erlandson Jon , Walser Rudy , Maxwell Howard , Bigelow Nancy , Cook John , Lively Ralph , Adkins Charles , Dodson Dave , Higgs Andrew , Wilber Janette
Published: July 2016

Between the Alaska Range to the south and the Brooks Range to the north, the Yukon River and its tributaries form an extensive network of waterways leading through the lowlands of interior Alaska deep into the North American continent (Fig 1). Despite the extremely cold winters of this arctic and subarctic landscape, much of the region remained unglaciated during the last 50,000 years. The central Alaskan lowlands are at the west end of the “ice-free corridor,” thought by most prehistorians to be the pathway to the Americas for Asian hunter-gatherers crossing the continental Beringian “landbridge.” Until recently, relatively little was known of the early human prehistory of Alaska's interior. Growing interest in the timing, nature and paleoecological context of the initial peopling of the Americas has prompted excavation at a number of early sites in central Alaska and the adjacent Yukon (see Powers & Hamilton 1978; West 1981; Fagan 1987: 119-134; Hamilton 1989; Powers & Hoffecker 1989).
AMS Dating of Alluvial Sediments on the Southern Tablelands of New South Wales, Australia
Authors: Gillespie Richard , Prosser I. P. , Dlugokencky Edward , Sparks R. J. , Wallace Gavin , Chappell J. M. A.
Published: July 2016

The dating of alluvial deposits is frequently hampered by a lack of good-quality charcoal or other material for radiocarbon samples. We have dated two sites in southeastern Australia using traditional radiometric methods with minimal pretreatment. Results yielded an inconsistent chronology, affected by contamination with younger humic materials. A more consistent and older chronology was achieved using AMS dating of rigorously pretreated samples of fine-grained charcoal. The results have important implications for the radiocarbon dating of many Late Quaternary stratigraphic sequences with low charcoal abundance.
Cosmogenic Nuclides in Ice Sheets
Authors: Lal Devendra , Jull A. J. T.
Published: July 2016

We discuss the nature of the twofold record of cosmogenic nuclides in ice sheets, of nuclei produced in the atmosphere, and of nuclei produced in situ due to interactions of cosmic-ray particles with oxygen nuclei in ice. We show that a wealth of geophysical information, in principle, can be derived from a suitable combination of nuclides in ice deposited at different latitudes. Such knowledge includes temporal changes in the cosmic-ray flux, in the geomagnetic field and in climate. The rate of deposition of cosmogenic atmospheric nuclei in ice depends on the global cosmic-ray flux and a host of climatic factors. The global cosmic-ray flux, in turn, depends on the level of solar activity, and of the geomagnetic dipole field. Thus, the task of deconvolution of the record of cosmogenic nuclides is difficult, but can be facilitated by considering the recently discovered record of in-situ-produced cosmogenic 14C, whose production rate at high latitudes is independent of the geomagnetic dipole field (Lal 1992b). We also present a brief review of work done to date and new prospects for deciphering geophysical records using ice sheets.
Recent and Historical Solar Proton Events
Authors: Shea M. A. , Smart D. F.
Published: July 2016

A study of the solar proton event data between 1954 and 1986 indicates that the large fluence events at the Earth are usually associated with a sequence of solar activity and related geomagnetic storms. This association appears to be useful to infer the occurrence of major fluence proton events extending back to 1934, albeit in a non-homogeneous manner. We discuss the possibility of identifying major solar proton events prior to 1934, using geomagnetic records as a proxy.
High-Precision Decadal Calibration of the Radiocarbon Time Scale, AD 1950–6000 BC
Authors: Stuiver Minze , Becker Bernd
Published: July 2016

The radiocarbon ages of dendrochronologically-dated wood samples, each covering 10 years, are now available for the cal AD 1950–6000 BC age range. The decadal calibration curve constructed from these data comprises 1) the previously published AD 1950–2500 BC portion (Stuiver & Becker 1986), to which minor 14C age corrections were applied, and 2) the new 2500–6000 BC extension.
High-Precision 14C Measurement of German and Irish Oaks to Show the Natural 14C Variations from 7890 to 5000 BC
Authors: Pearson Gordon W. , Becker Bernd , Qua Florence
Published: July 2016

The availability of absolutely (dendrochronologically) dated German oak has allowed the Belfast laboratory to extend its published high-precision 14C measurements of Irish oak (Pearson et al. 1986) by 2680 yr. The samples were selected at contiguous 20-yr intervals, following a precedent adopted and considered satisfactory in previous publications. All samples were measured for at least 200,000 counts within the 14C channel. The statistical counting error, together with the error on standards, backgrounds and applied corrections, give a realistic precision quoted on each sample of ± 2.5‰ (± 20 yr). This error is considered high-precision for sample ages of 7000–8000 BP.
Modeling Atmospheric 14C Influences and 14C Ages of Marine Samples to 10,000 BC
Authors: Stuiver Minze , Braziunas Thomas F.
Published: July 2016

The detailed radiocarbon age vs. calibrated (cal) age studies of tree rings reported in this Calibration Issue provide a unique data set for precise 14C age calibration of materials formed in isotopic equilibrium with atmospheric CO2. The situation is more complex for organisms formed in other reservoirs, such as lakes and oceans. Here the initial specific 14C activity may differ from that of the contemporaneous atmosphere. The measured remaining 14C activity of samples formed in such reservoirs not only reflects 14C decay (related to sample age) but also the reservoir 14C activity. As the measured sample 14C activity figures into the calculation of a conventional 14C age (Stuiver & Polach 1977), apparent 14C age differences occur when contemporaneously grown samples of different reservoirs are dated.