Oxygen Isotope Signatures of Phosphate in Wildfire Ash

Abstract

Atmospheric aerosol deposition is a significant source of phosphorus (P) in many terrestrial and marine ecosystems worldwide, influencing their biogeochemistry and primary production. Particles emitted from wildfires (hereafter, ash) are the second most important source of atmospheric P after airborne dust. In this study, we aim to identify the signature of ash oxygen isotopes in phosphate. This will enable the use of this signature for the separation of ash from other atmospheric P sources. We measured P concentrations and δ18OP in ash from natural and experimental fires and also from ash heated at different temperatures. The HCl and resin P concentrations (average ± SE) were 3.15 ± 0.35 and 1 ± 0.1 mg g–1, respectively. The HCl and resin δ18OP were 15.5 ± 0.4 and 14.7 ± 0.4‰ (average ± SE), respectively. Based on previous studies, we suggest possible isotope exchange reactions during the combustion process, between oxygen in phosphate and oxygen from other probable sources (i.e., the atmosphere, and CaC...