A detailed investigation of pretreatment protocols for high precision radiocarbon measurements of annual tree-rings

Much discussion has revolved around proper sample types and pretreatment methods to generate a calibration dataset that would allow for the most accurate representation of an unknown sample's calendar age. Since the development of radiocarbon dating, tree-rings have played a vital role in the creation of global calibration datasets, with these samples being subjected to varying degrees of both physical and chemical pretreatments. With an international move away from multi-ring composite measurements and toward higher resolution annual and/or sub-annual measurement of radiocarbon content, and with the on-set of a major new research project using, primarily the highly resinous North American Bristlecone Pine, we set out to review sample preparation procedures. The question became; which fraction, and therefore how much pretreatment is really necessary in order to extract the most representative and replicable C¹⁴ determination in a tree-ring for any given growth year, and could it be both specimen as well as species dependent? For this study, a total of four samples were chosen. These samples consisted of two rings from two different years from Bristlecone Pine and two rings from these same years from Irish Oak. These rings were each treated with a series of progressively more aggressive chemical treatments allowing for the extraction of different fractions from each ring. An analysis of the different pretreatment methods, as well as interspecies variance, is discussed.