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Aeolian dust is a significant source of phosphorus (P) in various ecosystems. The Saharan desert is the major dust source on earth and it contributes atmospheric P to terrestrial ecosystems which often depend on these inputs. Since estimations on the contribution of dust to the atmospheric P cycle vary between studies, accurate estimations on the aerosol-P inputs to ecosystems can be enhanced by an identification method for dust from the other atmospheric P sources. In the current study, we explored the use of the oxygen stable isotopes in phosphate, δ18O P , as a marker for desert dust P. To characterize the δ18O P in Saharan dust, we analyzed atmospheric particles sampled in Puerto Rico, which has good exposure in summer to African dust with little exposure to wildfires, local, or anthropogenic influence on atmospheric inputs. Additionally, to evaluate possible isotopic fractionations in desert dust sources, which could affect the soil δ18O P before transport, we analyzed the δ18O P in Israeli desert soils that served as an analog. Saharan dust storms sampled at Puerto Rico were found to have δ18O P values of 22.5 ± 0.3‰ in the resin fraction (which represents labile inorganic P), similar to previously reported values of Saharan dust sampled in Israel. The data from Israel desert soils demonstrated that biological activity in desert crusts can have a small effect (with a maximum difference of 3.3‰ between the topsoil and the subsoil) on the δ18O P of desert soils, mainly when developed soil crust is present, as a result of intracellular isotopic equilibration between oxygen in phosphate and soil water. However, biological crusts are not considered a major dust source. Additionally, Saharan dust sampled in Israel and in Puerto Rico had a δ18O P similar to apatite minerals derived from sedimentary phosphorites. Thus, we suggest the dust source had little or no biological activity. Furthermore, the δ18O P in Saharan dust was distinctive from other atmospheric P sources, such as pollen and wildfire ash, and as a result, the δ18O P can be used to distinguish between these atmospheric P main sources. • Atmospheric dust is an important source of P for many ecosystems. • We analyzed the δ18O P and P concentrations in Saharan dust, desert soils and crusts. • Biological processes in crusts affect the δ18O P of dust from desert origin slightly. • δ18O P can help distinguish between desert dust and other main atmospheric P sources. [ABSTRACT FROM AUTHOR]