Oxygen isotope fractionation between human phosphate and water revisited

The oxygen isotope composition of human phosphatic tissues (δ18OP) has great potential for reconstructing climate and population migration, but this technique has not been applied to early human evolution. To facilitate this application we analyzed δ18OP values of modern human teeth collected at 12 sites located at latitudes ranging from 4°N to 70°N together with the corresponding oxygen composition of tap waters (δ18OW) from these areas. In addition, the δ18O of some raw and boiled foods were determined and simple mass balance calculations were performed to investigate the impact of solid food consumption on the oxygen isotope composition of the total ingested water (drinking water + solid food water). The results, along with those from three, smaller published data sets, can be considered as random estimates of a unique δ18OW/δ18OP linear relationship: δ18OW = 1.54(±0.09) × δ18OP−33.72(±1.51) (R2 = 0.87: p [H0:R2 = 0] = 2 × 10−19). The δ18O of cooked food is higher than that of the drinking water. As a consequence, in a modern diet the δ18O of ingested water is +1.05 to 1.2‰ higher than that of drinking water in the area. In meat-dominated and cereal-free diets, which may have been the diets of some of our early ancestors, the shift is a little higher and the application of the regression equation would slightly overestimate δ18OW in these cases.