Tree rings radiocarbon

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. 

The next problem was which trees to measure. Many tree ring sequences can be counted with an accuracy of about one year. Those which are not yet tied to modern sequences by overlapping ring patterns (said to be "floating"), can be dated in favorable cases with an accuracy of about 30 years by radiocarbon dating, depending on the age and the number of radiocarbon measurements which are made. 

Figure 27. Radiocarbon age vs. chronological age of tree rings vs. years 4000—...

Clark, R. M., Renfrew, C., "Tree-Ring Calibration of Radiocarbon Dates and the Chronology of Ancient Egypt, Nature (1973) 243, 266. 

Floating Tree-Ring Chronologies Using Radiocarbon Dates, Archaeometry (1972) 14,519. 

The isotopic isolation of in each tree ring had crucial implications for future radiocarbon studies and continues to be very much a part of current research. Specifically, the examination of the radiocarbon contents in tree-ring-dated samples of wood provided the principal data that permits an in-depth examination of the assumption that the production of radiocarbon by cosmic rays had been maintained at a constant level. For archaeologists especially, it is important to know if there have been... 

Significant interpretative problems in the use of radiocarbon values are apparent immediately when the C-dated tree ring data are examined (Figures 3 and 4). If we ignore for the moment the short-term perturbations, the radiocarbon and dendrochronological values approximately agree ( 1-3%) for the last 2000 years. However, as one moves back in time from about the beginning of the Christian era, there is an increas-... 

The question of whether variations in content in wood samples taken from western North America can be used to document worldwide secular variations in radiocarbon values seemingly has been answered by studies of the concentrations in tree rings from Patagonia, Argentina, Canada, and Europe. The maximum contemporaneous deviation noted was between the southern and northern hemisphere, but it did not exceed... 

Friedrich M., Kromer B., Spurk M., Hofmann J., and Kaiser K. F. (1999) Paleo-environment and radiocarbon calibration as derived from Late Glacial/Early Holocene tree-ring chronologies. Quat. Int. 61, 27-39. 

Kromer B. and Spurk M. (1998) Revision and tentative extension of the tree-ring based C calibration, 9,200-11,855 cal BP. Radiocarbon 40, 1117-1125. 

The pre-industrial atmospheric G/ G values, R, have been determined from radiocarbon measurements of tree rings, and the value of is based on hundreds of deep ocean DI G measurements,... 

FIG. 5.5. Long term variation in atmospheric activity as determined from tree rings. (From H. E. Suess, La Jolla Radiocarbon Lab.)... 

The size of tree rings can be related to CO2 content, where the number of rings indicates the age of the tree. The amount of CO2 in ice can be directly measured from portions of polar ice in different layers obtained by drilling. The age of CO2 can be determined by radiocarbon dating and other methods. 

In radiocarbon dating, a reasonable assumption is that the ratio of carbon-14 to carbon-12 in the atmosphere has been relatively constant for the past 50,000 yr. However, because variations in solar activity control the amount of carbon-14 produced in the atmosphere, that ratio can fluctuate. We can correct for this effect by using other kinds of data. Recently scientists have compared carbon-14 data with data from tree rings, corals, lake sediments, ice cores, and other natural sources to correct variations in the carbon-14 clock back to 26,000 yr. 

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