Fractionation of oxygen isotopes between mammalian bone-phosphate and environmental drinking water

The δ¹⁸O of mammalian bone-phosphate varies linearly with δ¹⁸O of environmental water, but is not in isotopic equilibrium with that water. This situation is explained by a model of δ¹⁸O in body water in which the important fluxes of exchangeable oxygen through the body are taken into account. Fractionation of oxygen isotopes between body and environmental drinking water is dependent on the rates of drinking and respiration. Isotopic fractionation can be estimated from physiological data and the estimates correlate very well with observed fractionation. Species whose water consumption is large relatively to its energy expenditure is sensitive to isotopic ratio changes in environmental water.