Calibration and radiocarbon dating

Arguably, few research topics engage so many different fields of science and have such a profound impact on our understanding of Earth and Solar science as the history of C in the Earth's atmosphere and the surface and deep oceans.Over the past decade we have witnessed a remarkable development and proliferation of accelerator mass spectrometers; these instruments have reduced the counting time by a factor of 100 and reduced the sample size by a factor of 1000 compared to the classic B-counting systems.Over this time interval, the Caricao data set used by Int Cal04 differs by more than 200 years from the tree ring and our coral calibration data.The photo images of the Cariaco sediment layering (Hughen et al., 2004) shows very weak to indistinct layers in the 13,250 to 14,000 year interval where the offset of Cariaco data with the tree ring and coral data sets is most apparent.We recommend that researchers and editors always list their raw radiocarbon ages and laboratory sample identification code and simply identify the calibration version used for their calibrated ages.This permits anyone to revise calibrated ages as our calibration curve is periodically updated over the next three years.In a series of published papers and manuscripts soon to be published, we present our analytical techniques in detail (Mortlock et al., 2005; Chiu et al., 2005a) and the geochemical (Cao et al., 2005) and geophysical (Chiu et al., 2005b, 2005c) explanations for the departure of radiocarbon dates from the true calendar ages and compare our results to other radiocarbon calibration data.

The curve will be updated every year on Jan 1 and versions are identified as Fairbanks followed by the month and year such as Fairbanks0107 for the upcoming version.It is estimated that nearly 90% of all measurements made at the more than 50 active accelerator mass spectrometry laboratories are radiocarbon dates.This dramatic increase in the number of radiocarbon dates is driving the demand for a radiocarbon calibration program that spans the entire radiocarbon timescale from the present to 55,000 years BP.In our radiocarbon calibration paper (Fairbanks et al., 2005), we present paired C age determinations (Lawrence Livermore National Lab and Leibniz-Labor for Radiometric Dating and Isotope Research Christian-Albrechts University Kiel) that span the entire range of the radiocarbon dating technique and present a radiocarbon calibration curve based on a Bayesian statistical model with rigorous error estimations.Due to the importance of an accurate and precise radiocarbon calibration curve, we have measured many samples in duplicate and validated the quality of the samples by dating the older samples with redundant U dates.

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