The relationship between the phosphate and structural carbonate fractionation of fallow deer bioapatite in tooth enamel

Rationale The species-specific relationship between phosphate (delta O-18(P) values) and structural carbonate (delta O-18(C) values) oxygen isotope ratios has been established for several modern and fossil animal species but until now it has not been investigated in European fallow deer (Dama dama dama). This study describes the relationship between phosphate and structural carbonate bioapatite in tooth enamel of extant fallow deer, which will help us further understand the species' unique environmental and cultural history. Methods The oxygen isotope composition of phosphate (delta O-18(P) value) and structural carbonate (delta O-18(C) value) of hydroxylapatite was determined in 51 modern fallow deer tooth enamel samples from across Europe and West Asia. The delta O-18(C) values were measured on a GV IsoPrime dual-inlet mass spectrometer and the delta O-18(P) values on a temperature-controlled elemental analyser (TC/EA) coupled to a DeltaPlus XL isotope ratio mass spectrometer via a ConFlo III interface. Results This study establishes a direct and linear relationship between the delta O-18(C) and delta O-18(P) values from fallow deer tooth enamel (delta O-18(C) = +9.244(+/- 0.216) + 0.958 * delta O-18(P) (+/- 0.013)). Despite the successful regression, the variation in delta O-18 values from samples collected in the same geographical area is greater than expected, although the results cluster in broad climatic groupings when Koppen-Geiger classifications are taken into account for the individuals' locations. Conclusions This is the first comprehensive study of the relationship between ionic forms of oxygen (phosphate oxygen and structural carbonate) in fallow deer dental enamel. The new equation will allow direct comparison with other herbivore data. Variable delta O-18 values within populations of fallow deer broadly reflect the ecological zones they are found in which may explain this pattern of results in other euryphagic species.