A regional marine reservoir correction (Delta-R) of 33 +/24 14C yr for southern Brazil was obtained from 6 marine shell samples collected in the states of Santa Catarina and Paran. This work also presents a R estimation of 8 +/17 14C yr for the southern and southeastern Brazilian coast from the states of Rio de Janeiro to Santa Catarina, obtained by including 7 ages published in previous works. The high variability of R in modern and Holocene samples from the Brazilian coast is also discussed.

Californias San Miguel Island contains over 600 archaeological sites, some occupied as early as 12,000 yr ago and most located along the islands north coast. Archaeologists have long believed the south coast to have been marginal or largely uninhabited. Burial of some landforms by sand dunes deposited after historical overgrazing, the lack of systematic survey, and a dearth of radiocarbon dating have also contributed to an underestimation of the intensity of human land use along the south coast of San Miguel Island. Our recent reconnaissance and dating of shell middens on the islands south coast indicate more intensive occupation than previously thought, with numerous south coast sites spanning at least the past 9000 yr, and demonstrate the utility of combining systematic archaeological reconnaissance and radiometrics in reconstructions of human settlement and historical ecology in coastal environments.

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 14C concentration in 1963 and the following rapid decline in the 14C level. All the analyzed 14C profiles appeared concordant with the shape of the bomb peak of atmospheric 14C 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 1650-1950). However, simultaneous use of the post-bomb and pre-bomb 14C 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 14C calibration curve. Our study has demonstrated that where annual resolution is concerned, tissues of Sphagnum are the only representative material for 14C 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 14C 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 14C 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 1900-1960) have been precisely dated at a high temporal resolution. In this time interval, 14C ages of all the samples dated were younger than those derived from the atmospheric ccalibration curve, apparently due to the effect of integration. Evidently, the determination of calendar ages based on 14C dating of single peat examples from that interval may be affected by a serious error if the possibility of integration is ignored.

The Delta-14C content of surface waters in and around the Cariaco Basin was reconstructed from radiocarbon measurements on sub-annually sampled coral skeletal material. During the late 1930s to early 1940s, surface waters within and outside of the Cariaco Basin were similar. Within the Cariaco Basin at Islas Tortugas, coral Delta-14C averages -51.9 +/3.3ppm. Corals collected outside of the basin at Boca de Medio and Los Testigos have Delta-14C values of -53.4 +/3.3ppm and -54.3 +/2.6, respectively. Additional 14C analyses on the Isla Tortugas coral document an ~11 decrease between ~1905 (-40.9 +/4.5ppm) and ~1940. The implied Suess effect trend (-3ppm/decade) is nearly as large as that observed in the atmosphere over the same time period. If we assume that there is little to no fossil fuel 14CO2 signature in Cariaco surface waters in ~1905, the waters have an equivalent reservoir age of ~312 yr.

A variety of analytical procedures involve breaking open a glass or quartz vessel containing a gaseous sample, and then quantitatively collecting the sample gases for analysis. In order to do this, a variety of "tube crackers" have been used. This paper discusses an alternate tube cracker that offers numerous advantages over those that have been discussed previously in the literature.

Nearly a decade ago, a different chronology than the conventional absolute chronology for the early Iron Age in Israel was suggested. The new, lower chronology transfers Iron Age I and Iron Age IIA contexts in Israel, traditionally dated to the 11th and 10th centuries BCE, to the 10th and 9th centuries, respectively. Thus, it places the Iron I/IIA transition at about 920-900 BCE. This alternative chronology carries important implications for Israelite history, historiography, and Bible research, as well as for the chronologies of other regions around the Mediterranean. Relevant radiocarbon data sets published to date, which were measured at different sites by different laboratories, were claimed to be incompatible. Therefore, the question of agreement between laboratories and dating methods needs to be addressed at the outset of any study attempting to resolve such a tight chronological dilemma. This paper addresses results pertaining to this issue as part of a comprehensive attempt to date the early Iron Age in Israel based on many sites, employing different measuring techniques in 2 laboratories. The intercomparison results demonstrate that: a) the agreement between the 2 laboratories is well within the standard in the 14C community and that no bias can be detected in either laboratory; and b) calculating the Iron I|IIa transition in 3 different ways (twice independently by the measurements obtained at the 2 labs and then by combining the dates of both) indicates that the lower chronology is the preferable one.

Dating sediments which have accumulated over the last few hundred years is critical to the calibration of longer-term paleoclimate records with instrumental climate data. We attempted to use wiggle-matched radiocarbon ages to date 2 peat profiles from northern England which have high-resolution records of paleomoisture variability over the last ~300 yr. A total of 65 14C accelerator mass spectrometry (AMS) measurements were made on 33 macrofossil samples. A number of the age estimates were older than expected and some of the oldest ages occurred in the upper parts of the sequence, which had been dated to the late 19th and early 20th century using other techniques. We suggest that the older 14C ages are the result of contamination by industrial pollution. Based on counts of spheroidal carbonaceous particles (SCPs), the potential aging effect for SCP carbon was calculated and shown to be appreciable for samples from the early 20th century. Ages corrected for this effect were still too old in some cases, which could be a result of fossil CO2 fixation, non-SCP particulate carbon, contamination due to imperfect cleaning of samples, or the reservoir effect from fixation of fossil carbon emanating from deeper peat layers. Wiggle matches based on the overall shape of the depth-14C relationship and the 14C minima in the calibration curve could still be identified. These were tested against other age estimates (210Pb, pollen, and SCPs) to provide new age-depth models for the profiles. New approaches are needed to measure the impact of industrially derived carbon on recent sediment ages to provide more secure chronologies over the last few hundred years.

Xinzhai is an important archaeological site discovered 40 yr ago and recently re-excavated in the Henan Province, dynasty of China. Radiocarbon measurements on bone samples from this site were performed at the Peking University AMS facility (PKU-AMS) and the Vienna University AMS facility (VERA). Calibrated ages were obtained with the computer program OxCal. The results of these measurements are presented and the related chronology is discussed.