ALBERT

Beschreibung: The radiocarbon activity of carbon collected by vacuum distillation from a single partially saturated tuff began to decline after approximately 60% of the water and carbon had been extracted. Disproportionate changes in 14C activity and δ13C during distillation rule out simple isotopic fractionation as a causative explanation. Additional phenomena such as matrix diffusion and ion exclusion in micropores may play a role in altering the isotopic value of extracted carbon, but neither can fully account for the observed changes. The most plausible explanation is that distillation recovers carbon from an adsorbed phase that is depleted in 14C relative to DIC in the bulk pore water.

Beschreibung: Since 1996, the Mongolian-American Expedition to Northern Mongolia has been excavating in the Egiin Gol Valley. The goal of this research has been to examine the competing hypotheses explaining the emergence of pastoral nomadism and the evolution of nomadic complexity. The chronological placement of burials and sites in the survey area has been a key facet of this research. At present, these investigations have generated 10 radiocarbon dates from archaeological contexts. Presented here are the previoulsy unpublished 14C dates and some comments on their significance.

Beschreibung: A first-order ΔR correction value for marine samples is presented based on 3 radiocarbon determinations of known-age marine shells from Samoa.

Beschreibung: A 23-yr record of the measuring accuracy of the Copenhagen radiocarbon dating laboratory has retrospectively been provided through a true blind test. A total of 92 samples of oak from old tree trunks were dated in the period 1971 to 1993 and their dendrochronological age determined independently. The 14C activity of the dendrochronological samples measured in the Copenhagen radiocarbon laboratory was compared to the activity of the tree rings of the same age measured by Stuiver and Pearson (1993) for calibration purposes. The average difference was found to be 54 ± 72 14C yr. The results further indicate that the actual standard deviation is only 7% higher than that quoted by the laboratory. The investigation has shown a long-term stability of laboratory accuracy with no systematic laboratory variations either with respect to sample age or to the time of measurement from 1971 to 1993.

Beschreibung: We have studied 6 reference sections of bog and lake sediments in the Leningrad and Novgorod provinces to develop a geochronological scale for vegetational and paleoclimatic changes in northwestern Russia during the Late Glacial and Holocene. Every 10-cm layer along the peat and gyttja sections (4–8.5 m thick) was investigated palynologically and the great majority of them were radiocarbon dated. Using the data obtained, standard palynological diagrams were plotted and vegetation history reconstructed. The palynozones indicated on the diagrams were related to the climatic periods and subperiods (phases) of the Blytt-Sernander scheme. On the basis of 230 14C dates obtained, we derived the geochronology of climatic periods and phases, as well as the chronology for the appearance and areal distribution of forest-forming tree species. The uppermost peat layers were dated by using the “bomb effect”. We compared the stages of Holocene vegetation and paleoclimatic changes discovered for the Leningrad and Novgorod provinces with the those obtained for Karelia, which we had studied earlier using the same methodology.

Beschreibung: Since 1994, the Institute of Geological Sciences has undertaken an environmental monitoring program to measure radiocarbon levels in territory adjacent to active nuclear power plants (NPP). We determined 14C concentrations in natural objects from areas contiguous to Ignalina NPP as well as 14C background concentration in areas remote from the NPP. In the environs of the Ignalina station comparatively elevated levels of 14C were observed in vegetation and waters of Lake Drisvyaty. This appears to be a consequence of release of carbon radioisotope into the atmosphere and probably into waters of the lake during operation of the nuclear reactor.

Beschreibung: We studied a 12.6-m-long sequence from Lake Abiyata (Central Ethiopia) to establish a reliable and accurate chronology for use in global paleoclimatic reconstructions. The 26 accelerator mass spectrometry radiocarbon (AMS 14C) ages, performed on carbonates and organic matter, define 2 parallel chronologies, representing the complete Holocene period. However, these chronologies show a significant discrepancy from 500 to 900 BP in depth; ages obtained on carbonates were always older than those on organic matter. The hydrogeological and geochemical behavior of the Lake Abiyata basin has shed light on this discrepancy. We found that the carbonate crystallization is due mainly to the mixing of lake waters with groundwaters from the multi-layered aquifer contained in the 600-m-thick basement of the lake. The 14C activity of total dissolved inorganic carbon (TDIC) measured by AMS from bottom and surface lake waters (111.4 and 111.8 pMC, respectively) confirms that the mixing occurs at the water-sediment interface. This evidence of groundwater participation in the carbonate crystallization calls into question the current paleoclimatic reconstructions based on inorganic carbonates in lakes. Specific attention should thus be given to the respective proportions of each end-member in the mixing for the quantitative estimation of the groundwater input. This will help to validate the paleoenvironmental reconstructions and to highlight an eventual diagenetical evolution of inorganic carbonates during burial, via the study of pore waters.

Beschreibung: A method is presented for calibrating radiocarbon ages based on statistical analysis of a large number of randomly distributed dates. One interesting feature of this method is that it is internal; that is, it allows one to extend a known calibration curve further back in time by using only 14C dates, with no reference to any other dating technique. A serious difficulty in implementing this method lies in assembling a sample of dates with the correct statistical properties.

Beschreibung: Measurements on same-age tree-ring samples from proximal Ural Mountain trees by the Ioffe Institute research group and at the University of Arizona demonstrate a variance corresponding to a standard deviation of ±5.1% for Ioffe compared to ±2.1% for Tucson. There is also a calibration difference of 4.3 ±1.2 ‰. Comparison of the same years measured in Seattle on wood from the Pacific Northwest shows an offset of 2.2 ± 0.5 ‰. This is not a calibration error, but rather is expected from the well-documented evidence for divergence and upwelling of 14C-depleted CO2 along the west coast of North America.

Beschreibung: Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30°E during the WOCE-France CIVA1 campaign in February 1993. Our principal objective was to complement the Southern Ocean's sparse existing data set in order to improve the 14C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured 14C is consistent with the θ-S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in 14C, whereas surface waters south of the PF are depleted in 14C. A distinct old 14C signal was found for the contribution of the Pacific Deep Water (PDW) to the return flow of Circumpolar Deep Waters (CDW). Comparison to previous measurements shows a 14C decrease in surface waters, consistent with northward displacement of surface waters, replacement by old deep waters upwelled at the Antarctic Divergence, and atmospheric decline in 14C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb 14C when in the Southern Ocean south of 45°S, motivated us to develop a new approach that relies on a simple mixing model and on chlorofluorocarbon (CFC) measurements also taken during CIVA1. This approach leads to inventories for CIVA1 that are equal to or higher than those calculated with previous methods. Differences between old and new methods are especially high south of approximately 55°S, where bomb 14C inventories are relatively modest.

Beschreibung: We describe a new methodology for separating organic temper from archaeological ceramics from Brazilian Amazonia. These experimental procedures were designed to directly date ceramic samples by accelerator mass spectrometry (AMS). An evaluation of the total carbon indicates the samples’ potential for dating.

Beschreibung: A promising species for tropical dendrochronology is Pinus lagunae, a pine tree found in Baja California Sur (Mexico) around lat 23.5°N. In 1995, we sampled a total of 27 wood cores from 13 Pinus lagunae trees in Sierra La Victoria (23°36'N, 109°56'W), just north of Sierra La Laguna, at an elevation of 1500–1600 m. Selected trees were locally dominant, but their ring-width patterns could not be crossdated. To test the hypothesis that visible growth layers in Pinus lagunae are formed annually, we measured radiocarbon amounts in individual rings by means of accelerator mass spectrometry (AMS). Twenty-three 14C measurements were used to trace the location of the 1963–64 “bomb spike” in 3 wood increment cores. By comparing the location of that δ14C extreme with the number of visible radial wood increments, it was possible to conclude that 2 cores had a number of locally absent rings, while the 3rd one included a few years with more than one growth layer. Therefore, ring-width patterns of sampled Pinus lagunae were not consistent from one tree to another, most likely because of climatic regime in combination with microsite features. While the possibility of generating Pinus lagunae tree-ring chronologies cannot entirely be ruled out, the development of dendrochronological proxy records of climate from coniferous species in tropical North America should focus on species and sites that experience a more pronounced seasonality.

Beschreibung: This paper summarizes radiocarbon measurements of mainly botanical samples from the Iceman (“Ötzi”) and from his discovery site, an Alpine glacier at the Austrian-Italian border. The results were obtained by accelerator mass spectrometry (AMS) at 3 different laboratories (Vienna, Austria; Uppsala, Sweden; Gif-sur-Yvette, France) between 1992 and 1997. All the dates, except 2, are consistent with the time period 3360–3100 BC, as previously determined from bone and tissue samples from the Iceman himself. The 2 exceptional dates from wooden artifacts suggest that the site of the Iceman was used as a mountain pass for millennia prior to and after the lifetime of “Ötzi”.For a 2nd sample complex, we studied logs from the beginning of salt mining in the world's oldest salt mines at Hallstatt in Upper Austria. 14C AMS measurements were performed in Vienna on spruce samples found in the prehistoric mines and from a log-house on the surface. Data evaluation included “wiggle matching” of different sets of tree rings. The results suggest that salt mining in the Hallstatt region took place in the 14th–13th century BC, well before the so-called Hallstatt period.We discuss in some detail the chemical pretreatment of the samples and the data evaluation. We also present a comprehensive survey of 14C dates available in the literature concerning both botanical remains from the vicinity of the Iceman and from the earliest salt mining in Hallstatt.

Beschreibung: A recent publication on directly dated basketry specimens from the western United States (Berger et al. 1998, Radiocarbon 40(2):615–20) contained some misleading information, and in a few cases discussed radiocarbon ages from unacknowledged sources. We provide the missing original citations along with some clarifications. We focus especially on the age of distinctive Fort Rock and Multiple Warp–style sandals, for which we provide additional previously unreported 14C ages. Direct dates on fibers from Fort Rock sandals from 3 different sites range in age from 10,500 cal BP to about 9200 cal BP. Contextual evidence suggests that Multiple Warp sandals may date as early as 6600 cal BP, but the few directly dated specimens are less than 1000 yr old.

Beschreibung: We present results that validate a new wet oxidation, stepped-combustion procedure for dating “old” charcoal samples. An acid–base–wet oxidation (ABOX) pretreatment procedure has been developed that is used in place of the conventional acid-base-acid (ABA) pretreatment. Combustions and graphitizations are performed in a vacuum line that is insulated from the atmosphere by a second backing vacuum to eliminate the risk of atmospheric leakage into the line at any stage of the procedure. Combustions are performed at 3 temperatures (330 °, 630 ° and 850 °) with a graphite target produced from the CO2 evolved during each combustion step. In this way, the removal of any contamination can be monitored, and a high degree of confidence can be placed on the final age. The pretreatment, combustion, graphitization, and measurement blank for the procedure, based on the analysis of a “radiocarbon-dead” graphite, is 0.5 ± 0.5 μg C (1σ, n=14), equivalent to 0.04 ± 0.02 pMC or an “age” of approximately 60 ka for a 1 mg graphite target. Analyses of a “radiocarbon-dead” natural charcoal after ABOX pretreatment and stepped combustion suggest that the total blank (including contamination not removed by pretreatment) may be higher than for graphite, ranging up to 0.10 ± 0.02 pMC. Additional experiments confirm good agreement with accepted values for the international low-14C “New Kauri” standard (0.16–0.25 pMC). They also confirm excellent reproducibility, with 3 separate dates on different aliquots of a charcoal sample from Ngarrabullgan Cave (Queensland, Australia) ranging from 35.2 to 35.5 ka 14C BP. It is also demonstrated that the ABOX pretreatment, in conjunction with the new vacuum line described here, is able to remove contamination not removed by the conventional ABA pretreatment, suggesting that the technique can be used to produce reliable 14C dates on charcoal up to at least 50 ka.

Beschreibung: Bone samples from the Greenland Viking colony provide us with a unique opportunity to test and use 14C dating of remains of humans who depended upon food of mixed marine and terrestrial origin. We investigated the skeletons of 27 Greenland Norse people excavated from churchyard burials from the late 10th to the middle 15th century. The stable carbon isotopic composition (δ13C) of the bone collagen reveals that the diet of the Greenland Norse changed dramatically from predominantly terrestrial food at the time of Eric the Red around AD 1000 to predominantly marine food toward the end of the settlement period around AD 1450. We find that it is possible to 14C-date these bones of mixed marine and terrestrial origin precisely when proper correction for the marine reservoir effect (the 14C age difference between terrestrial and marine organisms) is taken into account. From the dietary information obtained via the δ13C values of the bones We have calculated individual reservoir age corrections for the measured 14C ages of each skeleton. The reservoir age corrections were calibrated by comparing the 14C dates of 3 highly marine skeletons with the 14C dates of their terrestrial grave clothes. The calibrated ages of all 27 skeletons from different parts of the Norse settlement obtained by this method are found to be consistent with available historical and archaeological chronology. The evidence for a change in subsistence from terrestrial to marine food is an important clue to the old puzzle of the disappearance of the Greenland Norse, obtained here for the first time by measurements on the remains of the people themselves instead of by more indirect methods like kitchen-midden analysis.

Beschreibung: We present a simple method for manually separating pollen concentrates for radiocarbon accelerator mass spectrometry (AMS) dating using a mouth pipetting system. The required equipment is readily available from scientific equipment supply houses at minimal cost. Pollen samples from lake sediments required about 4 h of hand picking, whereas samples from marine sediments required about 8 h labor. Pollen dates from marine sediments were much older than expected. We are attempting to resolve whether this is due to contamination of the pollen or the presence of significant quantities of old reworked pollen. Pollen dates from lake sediments associated with Mazama Ash were consistent with other published ages; however, replicate dates on pollen samples from above the ash were consistently older than the surrounding sediment. Our results suggest that caution must be used when interpreting pollen dates if the potential for sediment reworking is present.

Beschreibung: We describe a comprehensive study of carbon isotopes in several karst springs and their environs in a contemporary karst environment in the region of the Cracow-Wieluñ Upland and Western Tatra Mountains, Southern Poland. We collected samples of water, plants and carbonate deposited on aquatic plants, and obtained 13C values and 14C concentrations. We also investigated a group of the youngest calcium carbonates from caves where deposition is still being observed or ceased no more than a few hundred years ago. The determination of a 14C dilution factor (q) in these carbonates allows us to determine the “true” radiocarbon ages of old speleothems from caves in the area under investigation and enables the use of old speleothems as suitable material for extending the 14C calibration time scale, the “Absolute” age having been determined by U/Th or amino acid racemization (AAR) dating methods. Measurements of δ13C and 14C concentrations were made on dissolved inorganic carbon (DIC) extracted from water samples. Calculated values of q range from 0.55 to 0.68 and δ13C values range from −10% to −13% versus VPDB with mean values equal to 0.65 and −12%, respectively. Results indicate that the dissolution process of limestone bedrock is a closed system with the dominating contributor being biogenic carbon dioxide.Isotopic composition of carbon in contemporary plants collected at the karstic springs at 3 localities is highly diverse, with different species distinctly varying in both q and δ13C values. Extremely light values of 13C (under −40%), observed in Algae and Hyloconium splendens, are correlated with 14C concentrations that are much lower than 100 pMC. Small systematic changes of isotopic composition were found in plants of the same species collected along streams at various distances from the spring. The youngest calcium carbonates from different caves show a relatively high scatter of both δ13C values and 14C concentration. The lower reservoir effect for 14C is observed in samples with higher value of δ13C, indicating equilibrium conditions in the sedimentation of carbonate. Pazdur et al. (1995b) presented 14C dating results and paleoclimatic interpretation of 170 14C analyses of 89 speleothems from 41 caves obtained through 1994. Investigations continued until early 1997, during which time a speleothem, JWi2, was dated by 14C, U/Th and AAR dating methods, and its stable isotope composition (δ13C and δ18O) analyzed in detail (reported here). Carbon isotope analyses indicate very large differences among results obtained by U/Th, AAR, and 14C dating methods.

Beschreibung: We present an analysis of radiocarbon dates on Dead Sea Scrolls that have a bearing on the question of the Scroll documents’ relation to Christian origins. We assess details of dating reports, discuss paleographical evidence, and consider the content of the documents. When collated, these findings may be seen as compatible with a view that personalities mentioned in the Scrolls were contemporary with the founders of Christianity.

Beschreibung: Three modes of reporting 14C activities are in use, in part analogous to the internationally accepted (IAEA) conventions for stable isotopes: (1) absolute activity, the specific activity of 14C or the activity per gram of carbon; (2) activity ratio, the ratio between the absolute activities of a sample and the standard; and (3) relative activity, the difference between the absolute activities of a sample and standard material, relative to the absolute standard activity. The basic definitions originate from decisions made by the radiocarbon community at its past conferences. Stuiver and Polach (1977) reviewed and sought to specify the definitions and conventions. Several colleagues, however, have experienced inadequacies and pitfalls in the definitions and use of symbols. Furthermore, the latter have to be slightly amended because of the use of modern measuring techniques.This paper is intended to provide a consistent set of reporting symbols and definitions, illustrated by some practical examples.

Beschreibung: The spatial and temporal distribution of 145 radiocarbon dates on 66 Australian stick-nest rat middens (Muridae: Leporillusspp.) range from modern to 10,900 ± 90 BP. As in American packrat middens, age frequency follows a logarithmic decay, both continentally and at major sites. This is probably a result of natural decay processes. Unlike American middens of similar age, relatively few range changes in plant distribution have been detected in Australia. The distribution of14C ages and the associated midden materials provide important paleoenvironmental information from the arid interior of Australia. The middens record subtle changes in vegetation and dramatic changes in the fauna unlike those interpreted from sites on the coastal rim or the southeastern periphery of the arid zone.

Beschreibung: Twenty-two radiocarbon activity measurements were made by accelerator mass spectrometry (AMS) on 2 Holocene stalagmites from Belgium (Han-stm1b) and from southwest France (Vil-stm1b). Sixteen thermal ionization mass spectrometric (TIMS) U/Th measurements were performed parallel to AMS analyses. The past dead carbon proportion (dcp) due to limestone dissolution and old soil organic matter (SOM) degradation is calculated with U/Th ages, measured calcite 14C activity and atmospheric 14C activity from the dendrochronological calibration curves. Results show that the dcp is different for the 2 stalagmites: between 10,800 and 4780 yr from present dcp=17.5% (σ=2.4; n=10) for Han-stm1b and dcp=9.4% (σ=1.6; n=6) between 3070 and 520 yr for Vil-stm1b. Despite a broad stability of the dcp during the time ranges covered by each sample, a slight dcp increase of about 5.0% is observed in the Han-stm1b sample between 8500 and 5200 yr. This change is synchronous with a calcite δ13C increase, which could be due to variation in limestone dissolution processes possibly linked with a vegetation change. The dcp and δ13C of the 2 studied samples are compared with 5 other modern stalagmites from Europe. Results show that several factors intervene, among them: the vegetation type, and the soil saturation leading to variable dissolution process systems (open/closed). The good correlation (R2=0.98) between the U/Th ages and the calibrated 14C ages corrected with a constant dcp validates the 14C method. However, the dcp error leads to large 14C age errors (i.e. 250–500 yr for the period studied), which is an obstacle for both a high-resolution chronology and the improvement of the 14C calibration curves, at least for the Holocene.

Beschreibung: We tested the feasibility of dating freshwater and terrestrial molluscs from the semiarid and arid zone in China, since these types of shell material deposit only aragonite to form their shell structure, and shell integrity can be easily observed using X-ray diffraction. We also tested the possibility of estimating microenvironmental changes from shell δ13C values, but variations within shell populations preclude the use of these values as a reliable indicator. Reservoir ages were calculated for living shells of the same species as fossil shells by using their measured 14C ages, which were recalculated using an average value of atmospheric 14C activity for the years spanning their time of collection as the modern standard. The results indicate that freshwater and terrestrial shells are potentially useful as dating material, provided extreme care is taken in their collection and other datable material (in this case wood and pollen) is within the profile to act as a comparison.

Beschreibung: Basal 14C dates from a core of the mire at Puerto del Hambre (53°36'21″S, 70°55'53″W), located within the area of glaciation in Estrecho de Magallanes–Bahía Inútil, Chile, are no older than 14,455 ± 115 yr BP. The 14C dates are on samples from which screening isolated autochthonous plant remains. Previous 14C dates of 15,800 ± 200, 16,590 ± 320, and 16,290 ± 140 yr BP are from bulk samples collected from similar basal increments at the site during 3 separate, independent coring operations. The previous suite of 14C dates was suspected to be contaminated by older carbon in the light of chronological evidence, which indicates a 14C age of approximately 14,850 yr BP for glaciation elsewhere in southern Chile. Contamination by “infinitely old” carbon reworked from nearby Tertiary beds and redeposited at Puerto del Hambre is evidently the cause for the older 14C dates.

Beschreibung: A suite of 6 bone gelatin accelerator mass spectrometry (AMS) radiocarbon dates for Rattus exulans Peale and associated beta decay 14C dates for Austrovenus stutchburyi shell are presented for 4 middens at Pauatahanui, Wellington, New Zealand. Mean calibrated age ranges of Rattus exulans (520–435 BP and 350–330 BP at 95% confidence level) and shell (465–375 BP at 95% confidence level) from the 4 midden sites overlap. The agreement between Rattus exulans bone gelatin dates and associated shell provides an inter-sample comparison of 14C dating using both gas counting (beta decay) and AMS dating techniques. We examine the adequacy of the standard gelatinization treatment for bone samples, which has been employed consistently at the laboratory since 1995.

Beschreibung: Accelerator mass spectrometric (AMS) radiocarbon analyses of live-collected, prebomb samples of shell carbonates of the land snails Rabdotus dealbatus and R. alternatus from Texas were carried out to quantify the characteristic age anomalies of land snails from limestone areas. Age anomalies are similar for the two species; they average +700 yr and vary by ±180 yr (1σ) among samples. Serial analysis of 1 shell reveals a significant ontogenetic trend in 14C age anomalies, with older apparent ages (up to 1200 yr) in the apical part of the shell and younger and uniform ages in the last whorl. No trend in age anomalies was found across a broad range of rainfall conditions (from 300 to 1000 mm mean annual rainfall).

Beschreibung: Single-year and decadal radiocarbon tree-ring ages are tabulated and discussed in terms of 14C age calibration. The single-year data form the basis of a detailed 14C age calibration curve for the cal ad 1510–1954 interval (“cal” denotes calibrated). The Seattle decadal data set (back to 11,617 cal BP, with 0 BP = ad 1950) is a component of the integrated decadal INTCAL98 14C age curve (Stuiver et al. 1998). Atmospheric 14C ages can be transformed into 14C ages of the global ocean using a carbon reservoir model. INTCAL98 14C ages, used for these calculations, yield global ocean 14C ages differing slightly from previously published ones (Stuiver and Braziunas 1993b). We include discussions of offsets, error multipliers, regional 14C age differences and marine 14C age response to oceanic and atmospheric forcing.

Beschreibung: As first shown by Bard et al. (1990a), high-precision 230Th-234U ages can be used successfully to calibrate the radiocarbon time scale beyond the high-precision tree-ring calibration that now reaches 11,900 cal bp (Kromer and Spurk 1998). Using mass spectrometric techniques, we measured 14C and 230Th ages on new samples collected from boreholes drilled off the islands of Tahiti and Mururoa (French Polynesia) in order to complement the database previously obtained on Barbados corals (Bard et al. 1990a, 1993).

Beschreibung: The focus of this paper is the conversion of radiocarbon ages to calibrated (cal) ages for the interval 24,000–0 cal BP (Before Present, 0 cal BP = AD 1950), based upon a sample set of dendrochronologically dated tree rings, uranium-thorium dated corals, and varve-counted marine sediment. The 14C age–cal age information, produced by many laboratories, is converted to Δ14C profiles and calibration curves, for the atmosphere as well as the oceans. We discuss offsets in measured l4C ages and the errors therein, regional 14C age differences, tree–coral 14C age comparisons and the time dependence of marine reservoir ages, and evaluate decadal vs. single-year 14C results. Changes in oceanic deepwater circulation, especially for the 16,000–11,000 cal BP interval, are reflected in the Δ14C values of INTCAL98.

Beschreibung: Oak and pine samples housed at the Institute of Botany, University of Hohenheim, are the backbone of the early Holocene part of the radiocarbon calibration curve, published in 1993 (Becker 1993; Kromer and Becker 1993; Stuiver and Becker 1993; Vogel et al. 1993). Since then the chronologies have been revised. The revisions include 1) the discovery of 41 missing years in the oak chronology and 2) a shift of 54 yr for the oldest part back into the past. The oak chronology was also extended with new samples as far back as 10,429 BP (8480 BC). In addition, the formerly tentatively dated pine chronology (Becker 1993) has been rebuilt and shifted to an earlier date. It is now positioned by 14C matching at 11,871-9900 BP (9922–7951 BC) with an uncertainty of ±20 yr (Kromer and Spurk 1998). With these new chronologies the 14C calibration curve can now be corrected, eliminating the discrepancy in the dating of the Younger Dryas/Preboreal transition between the proxy data of the GRIP and GISP ice cores (Johnsen et al. 1992; Taylor et al. 1993), the varve chronology of Lake Gościąż (Goslar et al. 1995) and the pine chronology (Becker, Kromer and Trimborn 1991).

Beschreibung: We report radiocarbon calibration data based on the revised German oak and pine series. The age range of the absolutely dated German oak series has been extended to 10,430 cal bp. The German pine series is tentatively linked to the oak series by 14C, and now reaches back to 11,871 cal bp (±20 yr). The revisions of the tree-ring time scale of the German oak chronology solved long-standing apparent discrepancies in the mid-Holocene 14C calibration data sets. The calibration data set based on the floating German pine is now in close agreement with the Preboreal part of 14C calibration series obtained from most varve chronologies and corals.

Beschreibung: The Queen's University of Belfast, Northern Ireland and University of Waikato, Hamilton, New Zealand radiocarbon laboratories have undertaken a series of high-precision measurements on decadal samples of dendrochronologically dated oak (Quercus patrea) and cedar (Libocedrus bidwillii) from Great Britain and New Zealand, respectively. The results show a real atmospheric offset of 3.4 ± 0.6% (27.2 ± 4.7 14C yr) between the two locations for the interval ad 1725 to ad 1885, with the Southern Hemisphere being depleted in l4C. This result is less than the value currently used to correct Southern Hemisphere calibrations, possibly indicating a gradient in Δ14C within the Southern Hemisphere.

Beschreibung: This paper presents radiocarbon results from a single Diploastrea heliopora coral from Vanuatu that lived during the Younger Dryas climatic episode, between ca. 11,700 and 12,400 calendar yr bp. The specimen has been independently dated with multiple 230Th measurements to permit calibration of the 14C time scale. Growth bands in the coral were used to identify individual years of growth. 14C measurements were made on each year. These values were averaged to achieve decadal resolution for the 14C calibration. The relative uncertainty of the decadal 14C data was below 1% (2σ). The data are in good agreement with the existing dendrochronology and allow for high-resolution calibration for most years. Variations in the fine structure of the 14C time series preserved in this specimen demonstrate sporadic rapid increases in the Δ14C content of the surface ocean and atmosphere. Certain sharp rises in Δ14C are coincident with gaps in coral growth evidenced by several hiatuses. These may be related to rapid climatic changes that occurred during the Younger Dryas. This is the first coral calibration with decadal resolution and the only such data set to extend beyond the dendrochronology-based 14C calibration.

Beschreibung: This study, which was carried out in the southern Brazilian Amazon region (Rondônia state and Humaitá, Southern Amazon state), presents and discusses the significance of carbon isotope data measured in soil profiles collected across natural boundaries of forest to savanna vegetation. The main objective of this study was to evaluate the expansion-regression dynamics of these vegetation units in relation to climate changes during the Holocene. 14C data from charcoal, soil organic matter (SOM) and its component humin fraction indicate that the organic matter in the studied soils is essentially Holocene in origin. 13C data indicate that C3 type plants were the dominant vegetation at all study areas in the early Holocene, and during the entire Holocene, in the forest sites of Central Rondônia state and in the forest site 50 km from the city of Humaitá. 13C data also indicate that C4 plants have influenced significantly the vegetation at the transitional forest and the Cerrado (wooded savanna) sites of Southern Rondônia state and the forest ecosystem located 20 km from the Humaitá city. These typical C4 type isotopic signatures probably reflect a drier climate during the mid-Holocene. The 13C records representing probably the last 3000 yr show an expansion of the forest, due to a climatic improvement, in areas previously occupied by savanna vegetation. These results and other published data for the Amazon region indicate that the areas representing today's forest-savanna boundaries have been determined by significant vegetation changes during the Holocene. The boundary between forest and savanna vegetation seems to be quite sensitive to climatic change and should be the focus of more extensive research to correlate climate and past vegetation dynamics in the Amazon region.

Beschreibung: We present a radiocarbon chronology of key Sayan-Altai monuments from the Scythian period, based on a statistical analysis of dates produced in the 1980s and now supplemented with new dates. These new 14C dates were produced for samples from the Tuekta-1 barrows (burial mounds) and were measured both in St. Petersburg and Groningen. These tree-ring samples were fitted to the calibration curve. Chronologies were established for the Arzhan, Tuekta-1 and Pazyryk-5 barrows. The time of the construction of the Arzhan and Pazyryk-5 barrows is the 9th and late 5th–4th centuries bc, respectively, and agrees with archaeology. According to new data obtained, the time of the Tuekta-1 barrow construction is some years older than has been accepted thus far by archaeologists.

Beschreibung: This note describes point and interval estimation of a settlement time from a collection of radiocarbon dates. An application concerning the settlement time of New Zealand is presented.

Beschreibung: By comparing the radiocarbon age of the soils under burial mounds of known archaeological age with the surface-exposed (background) soils of the surrounding landscapes, we may evaluate the rates of humus renewal in these soils. In the cold climate of the mideastern areas of the Russian plains, the value of humus rejuvenation coefficient decreases. This shows that humus renewal is 5–10 times slower than in the warmer climate of the southern regions. Using the obtained data on the rejuvenation rate of humus substances, we can determine the age of paleosols and study the dynamics of the carbon exchange processes in the biosphere.

Beschreibung: Three very different Canadian soils—clay soils of the St. Lawrence Lowlands, sandy forest soils of the Ottawa Valley, and organic-rich sediments from a wetland on the Canadian Shield—have been cored, sliced and separated into different density fractions, and the radiocarbon content of these soil fractions measured. In two of the areas sampled, cores were obtained close to operating nuclear reactors, as well as from beyond their region of influence. As a consequence, it has been possible to ascertain the depths of penetration of both the weapons-testing pulse (peaking in 1963), and a 25–50-yr chronic reactor input of 14C.The percentage of carbon stored in different density fractions varied with soil type. Turnover times for bulk soil organic carbon, estimated from soil degassing rates, have been compared with those predicated on the residual “bomb” 14C in background cores, and/or on the ratio of reactor-emitted 14C retained in the soils to the total deposited during the lifetime of operation. Residence times for the heavy carbon fraction present at depths below the influence of anthropogenic inputs have also been estimated.The accumulated data will be incorporated in a revised soil model, adjusted for the parameters deemed to be most important to carbon turnover rates under Canadian conditions.

Beschreibung: Organic matter in sediments and suspended matter is a complex mixture of constituents with different histories, sources and stabilities. To study these components in a suspended matter sample from the Ems-Dollard Estuary, we used combined molecular analysis with pyrolysis/gas chromatography/mass spectrometry and stable and radioactive carbon isotope analyses of the bulk and separated chemical fractions. Carbohydrates and proteins, ca. 50% of the total organic carbon (TOC), are much younger than the bulk sample and have a somewhat higher δ13C value. Lipids and the final residue are considerably older and have lower δ13C values. The final residue, ca. 17% of the total carbon, consists mainly of aliphatic macromolecules that could be derived from algae or terrestrial plants. The δ13C value points to a marine origin.

Beschreibung: Radiocarbon activities and uranium isotopic disequilibria were measured in water samples from both the sandy Pleistocene coastal aquifer and within the upper Cretaceous Judea Group carbonate aquifer of northwestern Israel. The samples in both aquifers exhibit a decrease in 14C activity that is concomitant to the growth in 234U-excess. This suggests that under specific conditions, 234U-excess dating of groundwater can be used to corroborate 14C dates, while offering the possibility of extending the range of dating of groundwater beyond that of 14C.

Beschreibung: Radiometric and AMS radiocarbon dating of a 6-m sediment core from Loch Ness, Scotland, indicates that it represents perhaps the very end of the Late Pleistocene, and the first ca. 7500 yr of the Holocene. Counts of laminations observed in the Holocene section of the core suggest that they are present in sufficient number to constitute annual laminations (varves), an hypothesis consistent with the pollen record, which contains a sequence of zones representative of the Early, Middle and part of the Late Holocene regional vegetation history. On the basis of BSEM and X-ray studies of sediments, and modern seston trap data, the laminations are believed to be produced by winter floods, which introduce increased silt loading into the Loch. Sediment for the rest of the year is mostly composed of clay-sized material. This hypothesis is being further tested, however, by continuing sedimentological and microfossil studies.Time-depth relations for the core based on calibrated 14C dates and lamination counts, respectively, illustrate the close correspondence between the two sets of data. The latter are therefore now being used to develop a varve chronology for the Holocene for Loch Ness. This will then in turn be used for further chronological studies, and for investigations of palaeoclimatic variations over the eastern North Atlantic, to which the signal of lamination thickness in the sediments is thought to be particularly sensitive. They may also eventually be used for calibration studies, employing 14C dating of specific carbon compounds, or groups of compounds extracted from the sediment using modern organic geochemical methods.

Beschreibung: The carbonate hydrochemistry of groundwater from the Hvinningdal aquifer (Denmark) was studied by radiocarbon (accelerator mass spectrometry (AMS)) and δ13C measurements as a preliminary step towards 14C groundwater dating. The 14C concentrations varied between 30 and 100 percent modern carbon (pMC) in apparent contradiction with tritium (3H) data, which in most cases indicate a post-bomb date. The dilution of 14C can be explained as being due to the combined effect of dissolution of old soil carbonate and oxidation of old organic carbon. The last effect proved to be essential. To calculate this correction the dissolved oxygen concentration was used together with the δ13C values. The combined corrections bring the 14C concentrations up to post-bomb levels in better agreement with the 3H data.

Beschreibung: A newly operating accelerator mass spectrometry (AMS) facility such as VERA has to go through an extensive testing phase in order to establish optimal conditions for 14C measurements, especially in the field of archaeological samples where an overall precision of 0.5% is desirable.We discuss the results of our measurements at the milligram carbon level as they relate to long-term stability, reproducibility, precision and isotope fractionation.

Beschreibung: The first radiocarbon dates for the famous monuments of European Scythia were produced for the Kelermes, Seven Brothers, Solocha and Chertomlyk barrows (burial mounds) by both accelerator mass spectrometry (AMS) and conventional methods. The obtained 14C dates confirmed the traditional archaeological chronology, which was based on the analysis of written data and typological comparisons of Scythian artifacts with similar objects found in the Ancient East and Greece. The 14C dates for the European Scythian monuments are compared with the Asian ones. The 14C chronology of the European Scythian monuments shows chronological synchronisms between the Asiatic and European monuments. The calibrated ages for the investigated barrows generally agree with the archaeological data.

Beschreibung: The Earth is within the Contemporaneous Solar Maximum (CSM), analogous to the Medieval Solar Maximum (MSM). If this analogy is valid, solar activity will continue to increase well into the 21st century. We have completed 75 single-ring and 10 double-ring measurements from ad 1065 to ad 1150 to obtain information about solar activity during this postulated analog to solar activity during the MSM. δ14C decreases steadily during the period ad 1065 to ad 1150 but with cyclical oscillations around the decreasing trend. These oscillations can be successfully modeled by four cycles. These four frequencies are 1/52 yr-1, 1/22 yr-1, 1/11 yr-1, and 1/5.5 yr, i.e., the 4th harmonic of the Suess cycle, the Hale and Schwabe cycles and the 2nd harmonic of the Schwabe cycle.

Beschreibung: 14C dating with the new Vienna Environmental Research Accelerator (VERA) began with the age determination of a mummified marmot found in the Austrian Alpine region. Soft tissue and bones of the marmot were used for the investigation. For comparison, bone material from known-age samples was also processed and measured. These exercises showed that 14C dating with VERA is reliable, and since that time various samples from archaeological context have been dated.We also studied the applicability of the 14C method in forensic sciences to determine the time of death of human individuals. 14C/12C measurements of samples from different organic human material (bone collagen, lipids from bone and bone marrow, hair) were performed and compared with the tropospheric “bomb peak” values to transform the measured ratios into “calibrated ages”. For specific substances with rapid turnover rates, this gives an estimate for the time of death of the individual. In our study, lipids and hair yield reasonable times of death, whereas the collagen fraction from bones, which has a relatively long turnover time, is not suitable for this purpose.

Beschreibung: We illustrate here the combined use of geographic information system (GIS) technology and a radiocarbon database for analysis of the environmental components and ancient sites in Western Siberia during the period 10–45 ka bp. In total, 230 14C dates from 75 Late Pleistocene outcrops and Paleolithic sites were used to generate paleolandscape maps and to establish the features of the spatiotemporal distribution of Paleolithic sites.

Beschreibung: Accelerator mass spectrometry (AMS) at the milligram level is routinely performed, but it is difficult to go substantially below 100 μg of carbon. We discuss various approaches for sample preparation, machine operation and data evaluation, to meet the special requirements of 14C AMS measurements at the microgram-carbon level. Furthermore, we present first results obtained at the Vienna Environmental Research Accelerator (VERA) from 14C measurements of a snow sample from Gaithersburg, Maryland, USA, prepared at the National Institute of Standards and Technology (NIST).

Beschreibung: The majority of samples processed at the National Ocean Sciences AMS Facility (NOSAMS) thus far were collected as part of the World Ocean Circulation Experiment (WOCE). Due to the long storage time (2–3 yr) required to analyze thousands of samples on the accelerator mass spectrometer (AMS), a test was designed and implemented to determine the effects, if any, of storage time on 14C concentration. We find no systematic offsets in AMS measurements made over a 5-yr period between a total of 16 replicate sets from surface and deep water collected at the same locality. Furthermore, the average δ14C value from the deepwater AMS replicates (-213.1%, std. dev. 7.3) agrees very closely with the conventional 14C results published for GEOSECS (-212.7%) from station 320 taken 20 yr earlier.A total of 73 WOCE shipboard replicate sets (162 AMS measurements) were analyzed with a mean precision of 4.3%. AMS results from 20 more shipboard replicate sets (44 AMS measurements) submitted as CO2 from the Stable Isotope Laboratory (SIL) at the University of Washington were analyzed with a mean precision of 3.4%. These results suggest no significant difference between water stripping methods used in each preparation lab.To assess reproducibility, we calculate a pooled estimate of σ for replicates called s, which we use as an approximation of σTOT for a given sample type. The s for WOCE seawater replicates is 4.9% and 5.8% for SIL gas replicates. These numbers demonstrate an overall reproducibility of seawater AMS results at NOSAMS that is in line with reported errors. We take the difference between total error s and machine error as the overall standard deviation of combined uncertainties associated with preparation of samples and with AMS. For seawater samples processed at NOSAMS, σSPL is calculated to be 2.4%, and for the SIL gas replicates it is 4.8%.Reproducibility of samples prepared with an acid hydrolysis technique is demonstrated using 24 coral samples submitted in triplicate by Dr. R. G. Fairbanks of Lamont Doherty Earth Observatory. Seventy-two replicates were prepared and analyzed at NOSAMS with a mean reported precision of 1.2%. The pooled estimate s for the Fairbanks triplicates is 2.6%. We calculate a laboratory reproducibility uncertainty for coral hydrolysis samples of 2.2%.In 1993, NOSAMS participated in the Third International Radiocarbon Intercomparison (TIRI) Study. We report here 60 AMS analyses of the six TIRI test materials, five of which are organic carbon samples, to validate sample-processing methods for organic carbon sample AMS analyses at NOSAMS.

Beschreibung: In May 1995 an impressive karstic cave possessing dozens of burials dating to the main phase of the Chalcolithic Period (ca. 4500–3500 bce) was discovered in Peqi'in in the high hills of Galilee in northern Israel. It was subsequently excavated over the course of the following months. The large amount of unique ceramic ossuaries and the variety of burial offerings shed light, for the first time, on this critical societal development period in a region where its remains have rarely been found. Although the major significance of the cave is as a mortuary center, it was also utilized in a domestic capacity some centuries previously, during the generally less familiar Early Chalcolithic Period. We present here the dating of 22 14C samples collected from these separate phases of cave use. Their interpretation should aid in understanding of the absolute dating of the Chalcolithic Period and its relation to the period preceding its inception.

Beschreibung: With 〉40 14C dates, mainly on bones and charcoal, the site at Son Mas is the only megalithic sanctuary on the Balearic Islands that has been dated by 14C in detail. Although soil erosion made stratigraphy difficult and the monument was cleaned out regularly during its long use, the results demonstrate that the site was occupied from the Pretalayotic (Chalcolithic) until the Roman period. The aim of this study was not only to date the construction and the use of the sanctuary, but also to correlate this monument, by means of dispersion diagrams, with the other prehistoric sites situated within the same valley. The dates were also used to compare the site with the generally accepted chronology of the Balearic archipelago (Mallorca, Menorca, Ibiza and Formentera).

Beschreibung: We present results that demonstrate the potential of the Packard Tri-Carb® Model 2770TR/SL for radiocarbon dating. For 2 g of sample benzene, a stable background count rate of 0.307 cpm and a stable counting efficiency of 64.78% were determined using a 13–75 keV counting window. Changes to the mathematical routines for t-SIE (quench indicating parameter) calculation and a reduction in the activity of the external standard have enabled stability of the t-SIE to be achieved, and combined with the use of a suitable balance point counting window; all of these factors give the stability of performance required for 14C dating. Calculations based on the above parameters indicate that the limit of detection for 2 g samples, counted for 5000 min, is 〉48,900 yr bp. The great advantage of this system is that these data were acquired using inexpensive standard 7-mL low potassium borosilicate glass vials. Vial holders manufactured from BGO reduced the background to 0.15 cpm with a minimum effect on efficiency (64.46% for 13–75 keV). A similar calculation of the limit of detection gave 〉51,700 bp. The use of the BGO vial holders in other instruments employing time-resolved liquid scintillation counting (TR-LSC) (Models 2250CA and 2260XL) also brought about significant improvements in detection limits.

Beschreibung: To obtain a better understanding of the relationship between calcrete genesis and the results of different absolute dating methods, thermoluminescence (TL), radiocarbon (14C) and uranium/thorium (U/Th) were applied to coeval sample; take from a very young calcrete profile in Namibia. The methodically different ages reflect the characteristics of the applied dating methods, the genetics of calcrete and different events of calcrete genesis. The conventional 14C ages and the TL dates cover the last 50 ka, while the corresponding U/Th dates of coeval samples are many times larger, Uranium-series dates are not related to the deposition of the host material or to its cementation if the ages are smaller than ca. 120 ka. The TL clock is set to zero during eolian transport and the corresponding radiometric ages of the quartz and feldspar grains date the time of their deposition. The 14C ages of the cement correspond, on the other hand, to a time shortly after the onset of the cementation and long before its termination. In the case of very old calcrete, the mixture of young and old cement results in ambiguous ages if they cannot be confirmed by an independent technique.

Beschreibung: A recent broad study of the background of all types of low-level beta and gamma detectors has now made it possible to analyze its components more reliably and with greater detail. This general analysis is developed further here for gas proportional and liquid scintillation counters used in radiocarbon dating. The background of gas counters, which is dominated by secondary cosmic gamma radiation, is now well understood and can be described quantitatively. The background of liquid counters is less well understood and can only be described semiquantitatively, its analysis resting partly on estimates. Methods to reduce the background of both types of systems are described and their effectiveness discussed. This analysis may help in evaluating the quality of existing systems as well as in designing better ones.

Beschreibung: We present here new radiocarbon dates for the different barrows (burial mounds) of the nomadic tribes of the Scythian period in the Khakassia and Tuva regions (Central Asia). The time scale of these barrows is compared with the elite barrows of the Sayan-Altai. In agreement with archaeological evidence, some barrows in Khakassia are chronologically close in time to the Arzhan barrow. The first 14C dates produced for the barrows from the Tuva region belong to a later Scythian period, compared with the elite Arzhan barrow. We determined the final stage of the barrow construction, but to establish the starting time, more dates are necessary (both by dendrochronology and 14C).

Beschreibung: A new set of radiocarbon dates from a rockshelter in Mendoza, Argentina addresses the question of the temporal overlap between the presence of an unidentified extinct ground sloth (cf., Mylodontidae) and evidence of human activity. Dung balls on the cave floor, evidently deposited by sloth, are overlain by charcoal, apparently of cultural origin. 14C dates, mostly on charcoal and dung from this shelter, calibrated using recently published curves, as well as the stratigraphy of the deposits from which the samples were collected, suggest that any co-occurrence of humans and ground sloths in this region was brief. In contrast, the single date on mylodon dermal ossicles from this shelter suggests significant time overlap. Replication of this date as well as obtaining new high-precision 14C analyses from this site will be the next priority.

Beschreibung: We measured radiocarbon ages of 11 pieces of ancient Japanese documents by accelerator mass spectrometry (AMS). The purpose of this study is to compare the relationship between the calibrated 14C age and the historical age of Japanese paper samples. Calibrated ages of nine pieces agree with their historical ages, indicating that Japanese ancient documents can be used for 14C dating in the recent historic period. On the other hand, the 14C age of paper that was used for reinforcement of a sutra is ca. 300 yr older than the historical age of the sutra. This shows that the sutra was repaired with old paper.

Beschreibung: We discuss results of 14C dating peat of palsa of different regions of Northern Eurasia. We apply these dates to determine the age of active palsa growth during different periods of the Holocene in permafrost zone.

Beschreibung: We present δ13C data from both bulk organic sediment samples and terrestrial plant macrofossils from five high-resolution sedimentary sequences from the United Kingdom from which extensive multiproxy data sets have been obtained. These span the last glacial-interglacial transition. Chronological control has been provided by radiocarbon dating and/or tephrochronology. The results demonstrate that significant shifts in bulk organic δ13C can be identified at key climatic transitions in most of the sites. The data are affected by site-specific influences that restrict their use as chronological markers. However, terrestrial plant macrofossil records are more consistent and reveal shifts that appear to be synchronous and which therefore offer a basis for interregional correlation as well as significant paleoenvironmental information.

Beschreibung: β-counting software programs were developed and installed in new PCs for operation under a Windows® NT workstation. The new software programs allow us to simultaneously control several β-counting systems, either remotely or from within the laboratory. This setup is much less expensive than our previous arrangement, which required a separate PC for each counter.

Beschreibung: 14C is one of the radionuclides that are produced to different degrees by neutron-induced reactions in all types of nuclear reactors. Part of the 14C created is continuously released into the surrounding environment during normal operation as airborne effluents in various chemical forms (such as CO2, CO and hydrocarbons) through the ventilation system of the plant. Because of the biological importance of carbon and the long half-life of 14C, it is of interest to measure the releases and their incorporation into living material. We report here on the 14C activity concentrations in annual tree rings and the air around two Swedish nuclear power plants, as well as the background 14C activity levels from two reference sites in southern Sweden from 1973–1996. We used both accelerator mass spectrometry (AMS) and decay counting in the investigation.

Beschreibung: Through the establishment of radiocarbon chronozones relating common geological events within lacustrine and eolian sediments from five profiles representative of loess yuan (tablelands), river valley and northwest margin features of the Loess Plateau, we propose a series of stratigraphic divisions within the last 30 ka. The focus of this detailed study involves stratigraphic relationships contributing to evidence of Younger Dryas events, with the recognition of cold-dry, cool-wet and cold-dry periods represented within the Heiheze silt, Midiwan peat and Liushuwan eolian sand. The stratigraphic profiles reflect century-scale fluctuations of the East Asian monsoons. The precursor events enable us to place the Pleistocene/Holocene boundary at 10,000 bp.

Beschreibung: We report on a review of 14C production and release from the nuclear industry in the United Kingdom (UK). Using earlier predictions (Bush, White and Smith 1984) it is estimated that a total of 1764 TBq of 14C would have been produced in UK graphite-moderated reactors up to the end of 1995, and 135 TBq of this total would have been released. Release rates, based on reported discharges, of 5.1 and 0.93 TBq GW(e)a-1 have been derived for Magnox reactors and Advanced Gas Cooled Reactors (AGRs), respectively. Using these new figures, cumulative discharges of 14C up to 1995 from reactors have been estimated at 531 TBq. The combination of these reactor discharges and the reported discharges from Sellafield (388 TBq) and Amersham (52 TBq) suggest a total cumulative release of 971 TBq of 14C up to the end of 1995.

Beschreibung: Accurate radiocarbon ages were obtained from terrestrial moss from two drill holes in Tern Lake deposits, Antarctica, using liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS). The results show that the lake deposits have been accumulating since the end of the last glacial epoch ca. 12,600 cal BP at the rate of 0.13–1.1 mm a-1. We discuss the validity of 14C ages of Antarctic lake deposits, with respect to the latitude effect of 14C productivity, the reservoir effect, the environment effect and the hard-water effect.

Beschreibung: We calculated apparent increment values based on the radiocarbon dates of 21 Estonian ombrotrophic mires (raised bogs). For short periods, the values vary significantly, but the integrated increment for the total complex of ombrotrophic peat shows a strong increasing tendency with decreasing peat age. This is probably due to the decay of accumulated organic matter. Our hypotheses concern the mechanisms of decay and methods for increasing the reliability of the interpolation and extrapolation of 14C data.

Beschreibung: Time series of δ14C, δ13C, and concentration of atmospheric CO2 covering the last 12 years are available at the Kraków sampling site (southern Poland) representing an urban area exposed to anthropogenic pollution of both local and regional origin. The samples represent continuous monitoring in biweekly intervals. Observations covering the time period 1983–1994 show a linear decrease of the 13C/12C ratio (δ13C = −9.6% in Jan. 1983) with a slope of −0.02% a−1. The decreasing tendency in the case of 14C (δ14C = 221% in January 1983) is weaker with a broad minimum in 1991 (δ14C = 124%) and subsequent gradual increase by ca. 10%, coinciding with a substantial reduction of coal consumption in Poland (26% reduction in 1991–1994 for heat and electricity production), partly compensated in agglomerations by increased gas consumption. The 12-year record of the CO2 concentration in Kraków points to a constant value fluctuating at a high level (average: 373 ppmv) reaching a maximum yearly average of 376 ppmv. These carbon isotope signatures were used for the separation of fossils from biogenic and “background” components, reflecting the strength of relevant sources. The monthly mean of the fossil component varies from ca. 10 ppmv in June to 27.5 ppmv in March while the yearly mean decreased ca. 16 ppmv since 1991.

Beschreibung: A living spruce tree was collected near the explosion center of the Tunguska event that occurred in 1908. We measured annual ring width and studied anatomical features to reconstruct the possible vegetational changes caused by the biological aftereffects of the Tunguska explosion. δ14C of annual rings from 1908 to 1910 was measured with a Tandetron accelerator mass spectrometer. The annual ring width decreased rapidly in 1908–1912, drastically increased in 1913, and decreased gradually thereafter. Traumatic resin ducts were observed in the transition zone between early- and latewood of the annual ring formed in 1908. We thus reconstruct these vegetational changes in the Tunguska forest: the Tunguska explosion damaged forest trees severely for ca. 3 yr, releasing rich nutrients from burned plants into the soil, and subsequently the vegetation was stimulated to recover by decreased socio-biological competition and better lighting conditions. δ14C values range from −28.2 to −1.5% for Tunguska spruce, and from −29.7 to 12.6% for Hinoki cypress. These fluctuations are within the ranges presented in Stuiver and Becker (1993), suggesting no evidence of anomalies of cometary origin in carbon isotopic composition. We found no significant difference between δ14C of Tunguska spruce and of Hinoki cypress.

Beschreibung: We present results of 14C dating of several tree-ring series from the Late Glacial and Early Holocene, analyzed at the Heidelberg University radiocarbon laboratory. Although these are floating series, they contribute high-resolution information about the variability of atmospheric 14C during those periods.

Beschreibung: Interlaboratory comparisons have been widely used in analytical chemistry and radiochemistry as an important part of ongoing quality assurance programs. The 14C community has been no exception in this respect, and in just under 20 years, there have been a number of significant and very extensive interlaboratory trials organized by individual laboratories and the International Atomic Energy Agency (IAEA) to the benefit of the 14C community (both labs and users) (Otlet et al. 1980; ISG 1982; Scott et al. 1990; Rozanski et al. 1992; Scott et al. 1992; Gulliksen and Scott 1995). The comparisons have varied widely in terms of sample type and preparation, but all have had as their primary goal the investigation of the comparability of results produced under possibly quite different laboratory protocols. As techniques have been developed and new labs formed, the reference materials created as a result of the intercomparisons have presented an opportunity for checking procedures and results. Users have been reassured by the existence of regular comparisons as one sign of the concern that laboratories have to ensure highest quality results, but also confused about how to make use of the results from past exercises in the interpretation of sets of dates from many laboratories. The laboratories have also learned valuable lessons from participation in such studies. These have included identification of systematic offsets and additional sources of variation and in studies which have used realistic samples requiring pretreatment, chemical synthesis and counting, it has been possible to identify the stage at which such problems have arisen and to quantify the relative contributions to the overall variation. In this paper, we will briefly review the comparisons so far, draw some conclusions from their findings, and make proposals for the future organization of intercomparisons.

Beschreibung: We discuss the possibility of dating ice wedges by the radiocarbon method. We show as an example the Seyaha, Kular and Zelyony Mys ice wedge complexes, and investigated various organic materials from permafrost sediments. We show that the reliability of dating 18O variations from ice wedges can be evaluated by comparison of different organic materials from host sediments in the ice wedge cross sections.

Beschreibung: Tree trunks and wood fragments in minerotrophic fen peat that accumulated as the result of a jökulhlaup in the outwash plain of Unteraarglacier were radiocarbon-dated using conventional ß-counting. Different pretreatment methods were tested on two wood samples to determine the reliability of our dates. We dated the wood compounds after extended acid-alkali-acid treatment, as well as extraction of cellulose and lignin. The results of the samples Picea (B-6687) and Pinus cent-bra (B-6699) show insignificant differences of 〈 1σ.The 14C dates represent retreat of Unteraarglacier due to warmer and/or drier phases in the Holocene compared to modern climate conditions. The glacier was at least several hundred meters smaller in extent than today ca. 8100–7670 bp, 6175–5780 bp, 4580–4300 bp, 4100–3600 bp and 3380–3200 bp. The 14C dates suggest a ca. 2000-yr cyclicity of tree growth in the area covered by the present Unteraarglacier. The most intense warm and dry period occurred between 4100 bp (probably extending back to 4580 bp) and 3600 bp, with growth of fen peat between 3800 and 3600 bp attributed to wetter conditions.

Beschreibung: The need for increased quality assurance for radiocarbon measurements performed by the monitoring laboratories at nuclear stations has spurred the introduction of a number of interlaboratory comparisons. We organized two such intercomparisons: the first set, circulated in 1994, consisted of two milk samples, one containing current global levels of 14C, the other containing an added spike of 14C-methylated casein. The second set, circulated in 1995, consisted of two samples of natural vegetation growing on the site of the Chalk River Laboratories (CRL), containing two different levels of 14C, both well above global background. The response to our invitation to participate in these studies was very encouraging; six laboratories took part in the first intercomparison, eleven in the second. The list included both monitoring laboratories and those whose main function is 14C dating. Understandably, some of the latter preferred not to analyze the higher-activity samples. The results in 3 of the 4 data sets were consistent with a statistical distribution based on the reported errors. This report provides details of two intercomparisons, including the preparation of the samples, which may now be considered potential secondary reference materials, the range of analytical techniques in use at the participating laboratories, and a statistical analysis of the results returned to us.

Beschreibung: One explanation for the radiocarbon dates on the Shroud of Turin being younger than the time of Christ is that the heat from a fire, which scorched a portion of the Shroud, may have affected the 14C content (dates) on the shroud by affecting molecular exchange between the fabric and atmospheric carbon. This report describes a laboratory test on the susceptibility of cellulose, in the form of cotton, to incorporate carbon from CO2 while it is heated in a closed tube with carbon dioxide until the cotton considerably darkened. To maximize the effect of this hypothetical process, we simulated the shroud material with cotton that had a 14C level of 0.55 modern (55 pMC, equivalent to 4800 yr), and the atmosphere with pure CO2, which had a 14C level of 1.3 modern (130 pMC). No measurable 14C transferred from the gas phase to the solid phase. The implication of this test is that scorching is an unlikely mechanism to affect the apparent age of cellulose-like material.

Beschreibung: The chief objective of this paper is to improve our understanding of the Neolithic in eastern Hungary using absolute chronological data. To accomplish this we calibrated new measurements as well as previously published dates. The up-to-date, standardized evaluation of 147 calibrated measurements showed temporal overlaps between archaeological cultures defined on the basis of ceramic styles. The average timespan of tell settlements of 285 yr was obtained using radiocarbon dates from four major settlements in eastern Hungary: Berettyóújfalu-Herpály, Hódmezővásáhely-Gorzsa-Cukortanya, Öcsöd-Kováshalom and Polgár-Csőszhalom.