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ABSTRACT. We present studies of 9 modern (up to 400-yr-old) peat sections from Slovenia, Switzerland, Austria, Italy, and Finland. Precise radiocarbon dating of modern samples is possible due to the large bomb peak of atmospheric 14 C concentration in 1963 and the following rapid decline in the 14 C level. All the analyzed 14 C profiles appeared concordant with the shape of the bomb peak of atmospheric 14 C concentration, integrated over some time interval with a length specific to the peat section. In the peat layers covered by the bomb peak, calendar ages of individual peat samples could be determined almost immediately, with an accuracy of 2-3 yr. In the pre-bomb sections, the calendar ages of individual dated samples are determined in the form of multi-modal probability distributions of about 300 yr wide (about AD 1650(about AD -1950. However, simultaneous use of the post-bomb and pre-bomb 14 C dates, and lithological information, enabled the rejection of most modes of probability distributions in the pre-bomb section. In effect, precise age-depth models of the post-bomb sections have been extended back in time, into the "wiggly" part of the 14 C calibration curve.Our study has demonstrated that where annual resolution is concerned, tissues of Sphagnum are the only representative material for 14 C dating, although even samples of pure Sphagnum collected from a very thin slice of the peat section contain tissues grown in different years, so they integrate the atmospheric 14 C signal over a period of time. This time period (0.5-8 yr, depending on the site) seems to correlate with the peat accumulation rate, but it also depends on how the sampled peat sections were handled. When constructing age-depth models, for some peat sections we used the strategy of multi-stage 14 C dating. This led to a drastic reduction in the uncertainty of the age-depth models, by dating only a few additional samples in the profile.Our study is the first in which peat sections from the late pre-bomb time (AD 1900(AD -1960 have been precisely dated at a high temporal resolution. In this time interval, 14 C ages of all the samples dated were younger than those derived from the atmospheric calibration curve, apparently due to the effect of integration. Evidently, the determination of calendar ages based on 14 C dating of single peat samples from that interval may be affected by a serious error if the possibility of integration is ignored.

The concentration of radiocarbon, 14C, in the atmosphere depends on its production rate by cosmic rays, and on the intensity of carbon exchange between the atmosphere and other reservoirs, for example the deep oceans. For the Holocene (the past approximately 11,500 years), it has been shown that fluctuations in atmospheric radiocarbon concentrations have been caused mostly by variations in the solar magnetic field. Recent progress in extending the radiocarbon record backwards in time has indicated especially high atmospheric radiocarbon concentrations in the Younger Dryas cold period, between 12,700 and 11,500 years before the present. These high concentrations have been interpreted as a result of a reduced exchange with the deep-ocean reservoir, caused by a drastic weakening of the deep-ocean ventilation. Here we present a high-resolution reconstruction of atmospheric radiocarbon concentrations, derived from annually laminated sediments of two Polish lakes, Lake Gosciaz and Lake Perespilno. These records indicate that the maximum in atmospheric radiocarbon concentrations in the early Younger Dryas was smaller than previously believed, and might have been caused by variations in solar activity. If so, there is no indication that the deep-ocean ventilation in the Younger Dryas was significantly different from today's.

ABSTRACT. Seven radiocarbon laboratories: Åbo/Aarhus, CIRCE, CIRCe, ETHZ, Poznań, RICH, and Milano-Bicocca performed separation of carbonaceous fractions suitable for

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ABSTRACT.A line for preparation of graphite targets for accelerator mass spectrometry (AMS) radiocarbon dating has been built in the Gliwice 14 C Laboratory. The AMS 14 C measurements of our targets are performed in the Leibniz-Labor für Altersbestimmung, Kiel, Germany. The quality of our line has been tested in two series of AMS 14 C measurements of background and Ox-II standard samples and by measurements of the amount of CO 2 released during combustion of sample-free quartz tubes. Most background contamination in the first series was introduced during combustion, which has been greatly reduced by baking quartz tubes vacuum-sealed with CuO and Ag. The residual contamination (ca. 1.5 µg C) seems to come mostly from the quartz tubes themselves. At present, most of the contamination of the background is introduced during graphitization. The reproducibility of background preparations is satisfactory, especially for samples larger than 1.5 mg, when it is better than ± 0.09 pMC. Despite still significant contamination with low-14 C carbon during the graphitization process (corresponding to 1.2 ± 0.2% of 14 C-free carbon), the good reproducibility of the results allows us to use our line in routine 14 C dating.

Absolute dating of mortars is crucial when trying to pin down construction phases of archaeological sites and historic stone buildings to a certain point in time or to confirm, but possibly also challenge, existing chronologies. To evaluate various sample preparation methods for radiocarbon (14C) dating of mortars as well as to compare different dating methods, i.e. 14C and optically stimulated luminescence (OSL), a mortar dating intercomparison study (MODIS) was set up, exploring existing limits and needs for further research. Four mortar samples were selected and distributed among the participating laboratories: one of which was expected not to present any problem related to the sample preparation methodologies for anthropogenic lime extraction, whereas all others addressed specific known sample preparation issues. Data obtained from the various mortar dating approaches are evaluated relative to the historical framework of the mortar samples and any deviation observed is contextualized to the composition and specific mineralogy of the sampled material.

ABSTRACT. Carbonate binders from mortars and plasters as well as charcoal fragments sampled at the ancient settlement of Hippos (Sussita) have been subjected to radiocarbon dating by gas proportional counting (GPC) and accelerator mass spectrometry (AMS). Hippos is situated on the east coast of the Sea of Galilee (32°46 / N, 35°39Έ) at the top of a hill in the Golan Heights area, Israel. According to historical-archaeological data, the town had functioned since the 3rd century BC until AD 749, when it eventually crumbled into ruins after an earthquake. The appropriate sample selection and preparation based on the results of pétrographie observations permitted us to distinguish different phases involved in the expansion of the settlement. More than 200 samples were taken from the settlement and subjected to pétrographie and chemical analyses. Of the 200 total samples, about 20 were selected for dating. Here, we present the first 10 results of 14 C dating carried out for Hippos. The oldest sample dated thus far gave an age corresponding with the 2nd century BC to 1 st century AD-probably indicating an old Roman temple, on the base of which the North-West church (NWC) was later erected. The next dates extend up to the 8th century AD, the age related to the last phase of settlement inhabitation. Research is continuing as new excavations take place.