Quantifying Inter-Laboratory Variability in Stable Isotope Analysis of Ancient Skeletal Remains

Over the past forty years, stable isotope analysis of bone (and tooth) collagen and hydroxyapatite has become a mainstay of archaeological and paleoanthropological reconstructions of paleodiet and paleoenvironment. Despite this method’s frequent use across anthropological subdisciplines (and beyond), the present work represents the first attempt at gauging the effects of inter-laboratory variability engendered by differences in a) sample preparation, and b) analysis (instrumentation, working standards, and data calibration). Replicate analyses of a 14C-dated ancient human bone by twenty-one archaeological and paleoecological stable isotope laboratories revealed significant inter-laboratory isotopic variation for both collagen and carbonate. For bone collagen, we found a sizeable range of 1.8 % for d13Ccol and 1.9 % for d15Ncol among laboratories, but an interpretatively insignificant average pairwise difference of 0.2 % and 0.4 % for d 13Ccol and d15Ncol respectively. For bone hydroxyapatite the observed range increased to a troublingly large 3.5 % for d 13Cap and 6.7 % for d18Oap, with average pairwise differences of 0.6 % for d 13Cap and a disquieting 2.0 % for d 18Oap. In order to asses