Measurements of the natural abundance of radiocarbon in biomarker molecules can be used to elucidate the biogeochemical roles of marine bacteria and archaea in the oceanic water column. However, the relatively low concentration of biomass, especially below the euphotic zone, inevitably results in small sample sizes for compound-specific analyses. In ultra-microscale 14C measurements, which we define as measurements on samples smaller than 25g C, the process of isolating pure compounds and preparing them for measurement adds significant background carbon. This additional blank carbon can contribute up to 40% of the total sample mass; therefore, it is necessary to quantify all components of the processing blank in order to make appropriate corrections. Complete propagation of error is critical in order to report the correct analytical uncertainty. The carbon blank is composed of at least 3 different sources: i) those that scale in proportion to the mass of the sample; ii) sources that contribute a constant mass of blank, e.g. closed-tube combustion; and iii) contaminants from vacuum lines and/or other aspects of sample handling that are difficult to quantify. We approached the problem of correcting for the total sample processing blank by deriving a 4-part isotopic mass balance based on separating the 3 exogenous components from the sample. Subsequently, we derived the appropriate equations for the full propagation of error associated with these corrections. Equations for these terms are presented. Full treatment of a set of raw data is demonstrated using compound-specific 14C data from the North Central Pacific water column.

The traditional chronology of ancient Israel in the 11th-9th centuries BCE was constructed mainly by correlating archaeological phenomena with biblical narratives and with Bible-derived chronology. The chronology of Cyprus and Greece, and hence of points further west, are in turn based on that of the Levant. Thus, a newly proposed chronology, about 75100 yr lower than the conventional one, bears crucial implications not only for biblical history and historiography but also for cultural processes around the Mediterranean. A comprehensive radiocarbon program was initiated to try and resolve this dilemma. It involves several hundreds of measurements from 21 sites in Israel. Creating the extensive databases necessary for the resolution of tight chronological problems typical of historical periods involves issues of quality control, statistical treatment, modeling, and robustness analysis. The results of the first phase of the dating program favor the new, lower chronology.

Two lacustrine sediment sequences, La Olla 1 and Laguna del Sauce Grande, on the southern coast of Buenos Aires Province, Argentina, were investigated for carbon reservoir effects, which may influence age-depth chronologies. Fruits of the submerged macrophyte Ruppia cf. maritima from the La Olla 1 sequence, and gastropod shells of Heleobia parchappii from the Laguna del Sauce Grande core, were radiocarbon dated. In addition, terrestrial plant remains and shells of living specimens were dated to assess the presence and magnitude of a reservoir effect. A reservoir age of about 800 14C yr is estimated for the aquatic plant samples of La Olla 1 for the early Holocene. The reservoir effect is attributed to the inwash of 14C-deficient bicarbonate from the surrounding sand dunes. The decay of marine organisms and salt spray are likely the main sources of 14C-deficient carbon. The magnitude of the reservoir effect is consistent with marine reservoir offsets reported for the region. The 14C measurements on shells of living and fossil specimens of Heleobia parchappii indicate the absence of a reservoir effect at Laguna del Sauce Grande, which may be due to the large size and shallow nature of the lake. This study shows how the reservoir ages of 2 close-by lakes in very similar geological settings can be largely different. These results have significant implications for the interpretation of 14C dates from lacustrine deposits in the region.

A new compact accelerator mass spectrometry (AMS) system dedicated to the measurement of radiocarbon has been commissioned at the Accium BioSciences headquarters in Seattle. The entire facility (including ancillary laboratories for the preparation of graphite targets) has been designed to handle samples with a wide range of 14C concentrations. In this paper, we discuss the technical details of the new facility and present performance test results demonstrating state-of-the-art capabilities. In particular, modern samples can be readily measured with 0.3% precision and accuracy, machine background levels are consistently in the low 1016 (14C/12C), and chemical background is approximately equivalent to a fraction of modern of 0.004. In addition, when 100-times-modern samples were processed, no increase in background was observed, either during sample processing or during AMS measurement. This corresponds to a dynamic range for 14C analysis of 6 orders of magnitude.

The problem of a hiatus at about 61005300 BP (about 49004200 cal BC) in the prehistoric chronology of the Cis-Baikal region in Siberia is discussed. Based on a critical evaluation of existing evidence, there was no discontinuity found in the cultural sequence between the Kitoi and Serovo/Glazkovo complexes of the Neolithic, and the proposed hiatus may be an artifact based on underestimation of solid data. Conventional 14C dates are presented that were generated in the 1980s to early 2000s for Cis-Baikal prehistoric burial grounds, and were later dated by the accelerator mass spectrometry (AMS).

The brackish Lake Obuchi in Rokkasho, Japan, is adjacent to the first Japanese commercial nuclear fuel reprocessing facilities, which are now undergoing performance testing, with commercial operation scheduled to start in 2007. Preparatory surveys were made by measuring the background levels of radiocarbon for water, aquatic biota, and sediment samples using accelerator mass spectrometry (AMS) in order to study the potential effects of 14C released by the plant to the 14C concentration in aquatic samples. Concentrations of 14C in Futamata River in 2004 ranged from 102 +/- 0.5 to 109 +/- 0.6 pMC (average 106 +/- 0.6 pMC), while 14C concentrations in brackish water from Lake Obuchi and in seawater were 89 +/- 0.5 to 104 +/- 0.4 pMC (average 98 +/- 0.5 pMC) and 82 +/- 0.6 to 102 +/- 0.4 pMC (average 93 +/- 0.5 pMC), respectively. The relationship between 14C concentration and salinity showed a negative correlation (r = 0.68, P < 0.01, n = 20). 14C concentration in selected aquatic biota (i.e. fish, benthos, and seagrass) from 2003 to 2004 ranged from 105 0.7 to 107 0.6 pMC and in zooplankton and phytoplankton was 103 +/- 2.4 to 105 +/- 1.7 pMC. The depth profile of 14C in 3 core sediment samples from Lake Obuchi showed maximum concentrations from 103 +/- 0.5 to 106 +/- 0.5 pMC at 520 cm depth. The vertical profile of 14C concentration in the sediment did not follow global atmospheric 14C fallout. We confirmed that the background level of 14C concentration in aquatic samples in brackish Lake Obuchi before operation of the reprocessing plant was similar to the concentration (~106 pMC) in the recent atmosphere.