This paper presents radiocarbon dates of terrestrial macrofossils from Lakes Gościąż and Perespilno, Poland. These data agree very well with most of the German pine calibration curve. In the Late Glacial, they generally agree with the data from Lake Suigetsu, Japan, and indicate constant or even increasing 14C age between 12.9 and 12.7 ka BP, rapid decline of 14C age around 12.6 ka BP, and a long plateau 10,400 14C BP around 12 ka BP. Correlation with corals and data from the Cariaco basin seems to support the concept of site-speficic, constant values of reservoir correction, in contradiction to those introduced in the INTCAL98 calibration. Around the Allerød/Younger Dryas boundary our data strongly disagree with those from the Cariaco basin, which reflects large discrepancy between calendar chronologies at that period. The older sequence from Lake Perespilno indicates two periods of rapid decline in 14C age, around 14.2 and 13.9 ka BP.

We have studied DNA adduction with 14C-labeled nicotine and nicotine-derived nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), by accelerator mass spectrometry (AMS) in mouse liver at doses equivalent to low-level exposure of humans. The dose ranges of nicotine and NNK administered were from 0.4 μg to 4.0×102 μg kg b.w.-1, and from 0.1 μg to 2.0×104 μg kg b.w.-1, respectively. In the exposure of mice to either nicotine or NNK, the number of DNA adducts increased linearly with increasing dose. The detection limit of DNA adducts was 1 adduct per 1011 nucleotide molecules. This limit is 1–4 orders of magnitude lower than that of other techniques used for quantification of DNA adducts. The results of our animal experiments enabled us to speculate that nicotine is a potential carcinogen. According to the procedure for 14C-labeled-NNK synthesis, we discuss the ultimate chemical speciation of NNK bound to DNA. From the animal tests we derived a directly perceivable relation between tobacco consumption and DNA adduction as the carcinogenic risk assessment.

Tufa is a superficial, secondary deposit of calcium carbonate which accumulates on precipitation from emergent spring waters. It occurs as discrete, localized masses in regions of calcareous country rock.

In the United Kingdom, deposits vary widely in structure and thickness but little is known of the rate of deposition. Some deposits contain laminae assumed to represent annual growth increments and which should contain a 14C and stable isotope record related to the original water from which it was precipitated.

Investigations are reported on tufa from, three areas of different limestones in the United Kingdom (Northwest Yorkshire, South Derbyshire and North Oxfordshire).

Hydrologically, the dating of tufa by 14C involves the same problems as the dating of groundwater. In the case of actively forming tufa, however, it is possible to derive a sequence of measurements, beginning with present day deposition, which clearly demonstrates the applications of age corrections.

At Gordale Scar, Northwest Yorkshire, a profiling study of laminated tufa appears to show bomb trial 14C to a depth of 18mm below the surface, with almost constant values around 50 percent modern (raw data) from 18 to 48mm below the surface. The 14C content of surface tufa lies within the seasonal range of 14C measurements from the parent stream waters.

Results of 50 percent modern in the sequence are consistent with the simplest correction procedures based on δ13C balance and the observed δ13C change on tufa precipitation is a practical demonstration of the fractionation factor ∊13. However, the application of corrections to active, surface tufa and parent waters collected monthly over a period of study (14 months) from all three sites, produce results higher than would be expected from published world 14C levels.

Many studies use radiocarbon dates on estuarine shell material to build age-depth models of sediment accumulation in estuaries in California, USA. Marine 14C ages are typically older than dates from contemporaneous terrestrial carbon and local offsets (ΔR) from the global average marine offset need to be calculated to ensure the accuracy of calibrated dates. We used accelerator mass spectrometry (AMS) 14C dating on 40 pre-1950 salt marsh snail and clam shells previously collected from four California estuaries. The average ΔR and standard deviation of 217 ± 129 14C yr is consistent with previous calculations using mixed estuarine and marine samples, although the standard deviation and resulting age uncertainty was higher for our estuarine calculations than previous studies. There was a slight but significant difference (p = 0.024) in ΔR between epifaunal snails (ΔR = 171 ± 154 14C yr) and infaunal clams (ΔR = 263 ± 77 14C yr), as well as between samples from individual estuaries. However, a closer examination of the data shows that even for the same species, at the same estuary, ΔR can vary as much as ∼500 14C yr. In some cases, the bulk of this variation occurs between samples collected by different collectors at different times, potentially indicating time dependence in carbon sources and ΔR variation. These variations could also be attributed to differences in collection location within a single estuary and resulting spatial differences in carbon sources. Intertidal specimens located in the high marsh may have lower ΔR than fully marine counterparts because of increased terrestrial 14C input. The large variations in ΔR here highlight the need for conservative chronological interpretations, as well as the assumption of wide uncertainties, when dating samples from estuarine sources.

Radiocarbon values of groundwater in main aquifers of the extremely arid Negev Desert and the Arava Valley, southern Israel, are used for studying the underground flow regime, particularly the complex connections between different aquifers and mixing of water bodies. The study shows that 14C can serve as a hydrological tracer in arid environments and that groundwater dating may be possible (although not very accurate) even in this extremely arid environment (precipitation, <50 mm/yr), where there is almost no vegetation. There are several aquifers in this region, some of which are deep (deeper than 500 m) and regional and contain mainly fossil water, while others are local and restricted to the Arava, much shallower (50–200 m) and are thought to contain historical to recent waters. Most of the current recharge to these shallow unconsolidated aquifers comes from flash floods that flow from the mountains rising on both sides of the valley. The groundwater in the deep aquifers has low 14C values (usually <5 pMC), implying old ages (preliminary ages >26,000 yr). Groundwater in the shallow aquifers characterized by higher 14C values (up to 60–70 pMC) imply younger ages and faster groundwater flow (recent recharge). This is also supported by the presence of tritium in some of the samples. A few exceptional values are explained by the unique mixing of water from different sources; another is due to a technical failure in the well.

This paper presents a suite of new accelerator mass spectrometry (AMS) radiocarbon measurements from the Ayacucho Valley of Peru and discusses their implications for the timing and nature of the collapse of the Wari Empire. Analysis of these and previously published dates from the region indicate that there is little evidence for state political authority in Ayacucho prior to the end of the 7th century. Dated human remains from the polity's eponymous capital indicate that the authority of the state's rulers persisted at least as late as the mid-11th century. Dates from rural sites in the Ayacucho Valley suggest continuity of occupation and folk material culture following Wari's disintegration. Finally, AMS measurements of bone from 2 large extramural ossuaries represent the first absolute dates associated with Chanca ceramics and suggest that this archaeological/ethnohistoric culture appeared in the valley at about AD 1300.

Results of measurements in an underground laboratory, 70m of water equivalent below surface, are given. Background values of proportional gas counters with volumes between 16cc and 1.5L are lower by a factor of 2—4.5 compared to the values in the previously used laboratory (7m w.e.). High counting gas pressures, up to 5 at CH4 and up to 36 at P-10, enable the use of relatively small counters with correspondingly small background contributions from the walls. A separation of the residual background into different components is attempted, distinguishing a pressure dependent volume effect and surface correlated contributions. It can be shown that the selection of radioactively pure counter construction material is very important for a good low level counting system.

We used moss increment counting to obtain well-defined samples of the topmost peat layers of two Sphagnum fuscum hummocks. The two ombrotrophic bogs, Lakkasuo in central Finland and Korvinsuo in eastern Finland, are of different ages, covering 3 and 9 ka, respectively. Using AMS dating, we traced bomb-produced 14C through the topmost parts of the two peat profiles. A well-defined 14C activity peak was found in both sequences dating the corresponding layer to ad 1965. A comparison between the maximum peat activities and the corresponding atmospheric values for the period of interest provides an opportunity to evaluate the amount of CO2 emanating from the decaying peat bog, and taken up by the living sphagnum plants.

Considerable variations in δ13C values were also observed. These variations indicate, at least partly, annual variations in the emission rate of CO2 from decomposition of older peat in the bog, and are connected with climatic factors such as temperature and precipitation.

This list consists mainly of dates obtained from analysis during 1967 and 1968 of archaeologic and geologic samples. The last section deals essentially with climatic, palynologic, and sea level variation problems. All measurements of atmospheric CO2 made periodically from 1962 until end of 1970 are also published here. In agreement with international convention, all dates have been calculated on the basis of the C14 half-life of 5568 years and 95% of NBS oxalic acid as the modern reference year.

The following list presents dates on a portion of the samples measured at ISOTOPES during 1967 and 1968 and measurements made previously for which either complete sample data has been recently received, or, in some cases, deferred due to the editorial load in preparing the definitive list.

The production rate of 14C during the Holocene averaged 2.4 ± 0.2 atoms 14C/cme 2 sec. Neutrons produced by galactic cosmic rays account for 90% of the 14C production with the remaining 10% resulting from neutrons produced by protons from solar flares. Production and decay of 14C can be reconciled by including 14C permanently or temporarily stored in sediments. Sedimentary reservoirs contain ca 30% of all terrestrial 14C. The lagoons, bays, marshes and deltas of the coastal wetlands alone account for 12% of the 14C inventory. The capacity of the coastal wetlands to store carbon has become the subject of renewed interest.

The following list of dates contains all measurements made during 1973, ie, since our last list (R, 1973, v 15, p 451–468). We have installed this year a Nuclear Enterprises NIM system to be used with our 2.5L Oeschger-type proportional counter (Philips), in addition to our 6L and 1L proportional counters which have worked consistently with Beckman Lowbeta electronics. The Philips counter has been calibrated relative to the Beckman electronics and we are now calibrating it relative to the NIM system.

Precision 14C analyses have been performed on samples comprising 1 to 4 annual rings from the south-central European dendrochronologic sequence of sub-fossil oak wood covering the period 1930 to 3100 bc. Apart from a major deviation in the 29th century bc, the 14C fluctuations have amplitudes of ca 10‰ and a possible periodicity of 90 years. A 14C peak at 2190 bc has a rise- and decay-time of <20 years indicating rather abrupt changes in the production rate of 14C. The 14C calibration curve derived from these data can be used for precise dating of the Early Bronze Age in the Near East.

Bayesian methods have been widely used to address the Iron Age chronological debate in Israel, which has implications for the entire eastern Mediterranean Iron Age chronology. However, a consensus has not been reached. This is largely because radiocarbon dates of materials in this period lie on an oscillation in the calibration curve. This study focuses on the modeling of 14C dates from the Iron I and Iron II periods, discusses the underlying assumptions and limitations of existing Bayesian chronologies, and proposes the use of a more appropriate model that allows for the phase transitions not being instantaneous. The new trapezoidal model sheds light on the probable duration of the transitions between the Iron Age phases.

We describe a simple method for trapping low concentrations of CO2 present in gas mixtures, such as air and soil respiration, using a zeolite molecular sieve (type 13x) for environmental carbon isotope studies. We employ reusable molecular-sieve cartridges and a lightweight battery-driven pumping system, developed to enable CO2 collection in difficult and dangerous terrain or under extreme climatic conditions. The results of a small field experiment suggest that CO2 could be quantitatively trapped on and recovered from the 13x molecular sieve, without any fractionation of the stable carbon isotope. The δ13C of CO2 was also independent of the amount of air ≤18 liters and rate at which it was collected, i.e. ≤ 1 liter of air/min.

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

The marine radiocarbon reservoir effect (MRE) occurs as a spatially and temporally dependent variable owing to localized changes in oceanic water composition. This study investigates ΔR values (deviations from the global average MRE whose ΔR = 0) during the period 500–1350 BP for the east coast of Scotland, where a complex estuarine system exists that drains into the semi-enclosed North Sea basin. Due to the availability of suitable archaeological samples, the data set has a distinct Medieval focus that spans the area from Aberdeen in the north to East Lothian in the south. Many of the ΔR values are not significantly different from 0 (the global average), but there are occasional excursions to negative values (max –172 ± 20) indicating the presence of younger water. These values show greater variability compared to other published data for this general region, suggesting that considerable care must be taken when dating marine derived samples from archaeological sites on the east coast of Scotland.

We report on the present status of the Lawrence Livermore AMS spectrometer, including sample throughput and progress towards routine 1% measurement capability for 14C, first results on other isotopes and experience with a multisample high-intensity ion source.

Eleven woolly mammoth bone samples from Lugovskoe (central West Siberian Plain, Russia) were radiocarbon dated in 3 laboratories: Institute of Geology, Novosibirsk; Oxford University, Oxford; and Christian Albrechts University, Kiel. Each laboratory used its own protocol for collagen extraction. Parallel dating was carried out on 3 samples in Novosibirsk and Oxford. Two results are in good agreement. However, there is a major discrepancy between 2 dates obtained for the third sample. The dates obtained so far on the Lugovskoe mammoths range from about 18,250 BP to about 10,210 BP. The Lugovskoe results thus far confirm the possibility of woolly mammoth survival south of Arctic Siberia in the Late Glacial after about 12,000 BP, which has important implications for interpreting the process of mammoth extinction. The site has also produced the first reliable traces of human occupation from central Western Siberia at the Late Glacial, including unique direct evidence of mammoth hunting.

This date list includes most of the archaeologic and geologic samples dated in this laboratory since publication of our last date list (R, 1975, v 17, p 196-215) as well as many samples dated previously which lacked adequate sample information.