Differential human bone remodeling rates and implications for the temporal resolution of geoprofiling isotopes

Isotopic analysis of human skeletal remains helps individuate decedents in forensic contexts by providing diet and residence information during life. The time represented (adolescence, middle adulthood) and the amount of time averaged (years, decades) depends on a bone's remodeling rate (RMR). Measuring isotopic values of multiple bones with different RMRs has been used to detect an individual's residential mobility and major changes in dietary practices. However, RMRs for the majority of human bones have not been adequately quantified, so the temporal resolution of bone isotopes is not well known. Here we utilized reported fraction modern radiocarbon (F¹⁴C) values of known decedents to estimate RMRs for the following elements, structures, and phases: cortical and trabecular femoral collagen, cortical tibial collagen and bioapatite, cortical and trabecular rib collagen, cortical occipital and parietal collagen, and trabecular vertebral collagen. Non-parametric comparisons yielded several significant RMR differences; the largest between the collagen phase of femoral cortex (3.3 %/year) and vertebral trabeculae (14.3 %/year). Tibial collagen and bioapatite also yielded different RMRs, 3.7 %/year and 5.0 %/year, respectively. As a result, dietary models that combine bioapatite and collagen phases may mix temporal scales. Turnover intervals exceeded 20 years for all cortical structures, potentially indicating that isotopic values represent much younger periods in an individual's life than previously thought. Additional studies are warranted that integrate histomorphometry and bomb pulse ¹⁴C dating of multiple elements, structures, and phases from known decedents to improve the temporal resolution of bone isotopes.