Enamel mineralization and compositional time-resolution in human teeth evaluated via histologically-controlled LA-ICPMS profiles

Mammalian dental enamel is of key interest for the reconstruction of past environments. Sequentially mineralizing enamel (e.g. ~15 years in humans) provides a several year-long archive that spatiallyresolved sampling can ‘read’ at high-time resolution, yet how much enamel maturation overprints any primary signal remains underexplored. We report results of a systematic investigation of histologicallydefined compositional profiles from human enamel obtained by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICPMS). By focusing on two time-equivalent, yet topographically contrasting orientations, along the enamel-dentine junction (EDJ) and enamel prisms, we evaluate the compositional effect of enamel secretion vs. maturation throughout varying enamel thickness. These two time-equivalent profiles are compared with those along nominal isogrowth profiles (all relating to enamel secretion), namely neonatal/ Retzius lines (NNL / R) that connect the other two profiles. We focus on Sr/Ca, Pb/Ca, Zn/Ca and Ba/Ca as commonly-utilized proxies of (palaeo)diet, pollution and/or mineralization in both modern and archaeological individuals. Overall, we demonstrate that the elemental ratios investigated behave strongly differently with respect to maturation overprint and that the highest degree of initial signal variability can be retrieved along and closest to the EDJ. The corresponding data will be presented and discussed in the context of mineralization models and mechanisms.