Radiocarbon calibration

Figure 11. Hustedt pH categories (26), diatom-inferred pH values (weighted averaging), calibration radiocarbon dates, 210Pb dates, and pH periods in the history of Lilia Oresjon, southwest Sweden. Each bar and point represents one of the 700 samples analyzed from each 0.5-cm interval from the 350-cm-long core. (Reproduced with permission from reference 68. Copyright 1990 Royal Society of London.)...

Figure 2. Left Chronological table of Sardinian prehistory from the Middle Neolithic to the Middle Bronze Age, based on calibrated radiocarbon dates. Right Map of Sardinia with the location of the four sites where the skeletal remains tested were recovered.

When dealing with radiocarbon dates, Bayesian statistics provides a useful framework for the integration of information from different sources and is widely used in archeology and environmental science. This is partly because of the non-normal nature of the uncertainties in calibrated radiocarbon measurements but also because such methods are very flexible and allow the inclusion of many different kinds of underlying model. 

For samples from some carbon reservoirs, the conventional contemporary standards may not define a zero age. A reservoir corrected radiocarbon age can sometimes be calculated by documenting the apparent age exhibited in control samples and correcting for the observed deviation. Reservoir effects are most often observed in samples from marine environments and fresh water lakes. A calibrated radiocarbon age takes into consideration the fact that " C activity in living organisms has not remained... 

Geochemist William Shotyk s analysis of the lead content of ice core samples reveals a 15,000-year history of lead levels. (Note Dates are based on calibrated radiocarbon dating. Because the core was retrieved in two segments, a break in data occurs between 2060 and 3200 years before present.)... 

Despite the inherent problems associated with in speleothems, recent work by Beck et al. (2001) has focused attention on this topic because they demonstrated that in certain circumstances the dcp correction may be sufficiently well constrained that calibration of the radiocarbon timescale might be possible. Speleothems have an advantage over marine corals (e g., Bard et al. 1990, 1998 Edwards et al. 1993), which have been used to extend the calibration curve, because they provide continuous records and are less likely to be affected by post-depositional alteration. Beck et al. (2001)... 

Kitagawa H van der Plicht J (2000) Atmospheric radiocarbon calibration beyond 11,900 cal BP from Lake Suigetsu laminated sediments. Radiocarbon 42 369-380 Ku T-L (2000) Uranium-Series Methods. In Quaternary Geochronology Methods and Applications. 

Vogel JC, Kronfeld J (1997) Calibration of radiocarbon dates for the late Pleistocene nsing U/Th dates on stalagmites. Radiocarbon 39 27-32... 

Hughen, K. A., J. T. Overpeck, S. J. Lehman, M. Kashgarian, J. Southon, L. C. Peterson, R. Alley, and D. M. Sigman (1998), Deglaciation changes in ocean circulation from an extended radiocarbon calibration, Nature 391, 65-68. 

Pearson, G. W. and M. Stuiver (1993), High-precision bidecadal calibration of the radiocarbon time scale 500-2500 BC, Radiocarbon 35, 25-33. 

Ramsey, C. B. (2005), OxCal Radiocarbon Calibration Software, http //www.rlaha. ox.ac.uk/orau/oxcal.htm. 

It is well known that the radiocarbon age does not correspond to the real calendar age of an organism, since Equation (16.2) is based on assumptions that are true only to a first approximation namely, the hypothesis of a constant value of 14/f0 over time in the past. [ 10] An accurate calibration curve[ll,12] has thus to be used to convert the tRC value of a measured sample into its true age. For a complete discussion on this topic, the already cited literature on radiocarbon dating can be considered for reference. In contrast, the focus of this chapter is on how to measure the radiocarbon age tRC, i.e. how to measure uR(t). Assuming, as explained above, 14/f0 and t in Equation (16.2) are known, it is indeed clear that a measurement of 14/ (f) allows us to determine the radiocarbon age. 

The case of Oetzi (or the Iceman), the frozen mummy found in 1991 on the Alps on the border between Austria and Italy and now kept at the Archaeological Museum of Bolzano (Italy), is also well known. AMS radiocarbon measurements from the laboratories of Zurich[78] and Oxford[79] on tissue and bone samples from the Iceman dated him to 4550 19 years BP. When calibrated, this radiocarbon age corresponds to three probable calendar time intervals between 3350 BC and 3100 BC. Consistent measurements were obtained by dating some of his equipment and also botanic remains from the discovery site. [80] In this context, it is important to note that dating of Oetzi represents a good example of the relevance of the behaviour of the calibration curve in the final precision of a radiocarbon measurement. Actually, in this case, despite a very high precision of the radiocarbon age ( 19 years), the special trend in the calibration curve around the dated period, i.e. in particular the so-called wiggles, prevents a more exact and unambiguous absolute age determination. 

Figure 16.6 Calibration of the radiocarbon ages of the Cortona and Santa Croce frocks the software used[83] is OxCal v.3.10. Radiocarbon age is represented on the y axis as a random variable normally distributed experimental error of radiocarbon age is taken as the sigma of the Gaussian distribution. Calibration of the radiocarbon agegivesa distribution of probability that can no longer be described by a well defined mathematical form it is displayed in the graph as a dark area on the x axis...

R.E. Taylor, History of radiocarbon dating, lecture presented at Radiocarbon in ecology and earth system science (http //ecology/botany/ufl/radiocarbon07/), University of California, Irvine (2006). (The first radiocarbon revolution is represented by the development of the dating method by Libby and his colleagues the second radiocarbon revolution is considered to be the introduc tion of calibration.)... 

It is important to remember that sometimes, in spite of the excellent performances of an AMS measurement, the final uncertainty on the true calendar age of a sample is a function of the behaviour of the calibration curve in that time interval a small error on the radiocarbon age does not necessarily correspond to a small, or a unique, calendar span on the BC/AD axis. 

C. Bronk Ramsey, Development of the radiocarbon calibration program, Radiocarbon 43,... 

One of the most interesting of the geophysics results from radiocarbon dates is the history of the sun. Apparently, it is registered in fluctuations of the cosmic ray intensity. These are fluctuations of rather short duration in terms of the radiocarbon lifetime, perhaps a century or so, and apparently they are caused by variations in the solar wind due to long-term changes in the solar emissions. This idea has been developed in some detail recently by Dr. Lai and his collaborators. It promises to give us a way of watching the history of the sun over tens of thousands of years. This fine structure on the curve of calibration was discovered by Dr. Suess and others. 

Currie, L. A., Polach, H. A., Exploratory Analysis of the International Radiocarbon Cross-Calibration Data Consensus Values and Interlaboratory Error, Proceedings of the 10th International Radiocarbon Conference, Radiocarbon. 22, 933... 

Radiocarbon years are calibrated from determinations of the 14C activity and stable isotopic carbon ratios of dendrochrono-logically dated tree rings [4]. The stable isotope data are required to normalize the dates to average wood with 613C value of -25 per mil (13C/12C fractionation relative to PDB reference standard). Photosynthetic and other plant physiological processes may produce differential isotopic fractionation between species, within the same species in different localities and even within the same tree under changing environmental conditions. 

Calibration of the Radiocarbon Dating Time Scale, Radiocarbon. 22(3), 947-949 (1980). 

Suess, H. E., Bristlecone pine calibration of the radiocarbon timescale 5200 B.C. to the present, See Olsson 197a, p. 303-311, 1970a. 

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