Phosphorus associations in aerosols: What can they tell us about P bioavailability?

Phosphorus (P) in aerosols can originate from multiple sources (mineral dust, biomass burning, fuel emissions) and can be associated with multiple phases including various minerals, organic matter and P adsorbed on particle surfaces. These associations will greatly impact the solubility of P in an aerosol sample and thus determine the bioavailability of P from atmospheric deposition to oceanic ecosystems. Here we use a sequential leaching extraction to determine the distribution of P within different operationally defined fractions in aerosol samples reaching the Gulf of Aqaba from different air mass trajectories and at different seasons. We found that on average 40% of the P in aerosols is associated with the "authigenic" fraction (soluble in acetic acid) which is unlikely to dissolve in seawater and become bioavailable. Another 15% is associated with each the HCl-"detrital" and insoluble organic matter components that are also not readily bioavailable. Only 15-30% of P is associated with phases that are water soluble or that are relatively soluble oxide phases that may be bioavailable for organisms. We did not find a consistent relationship between the distribution of P in the various phases and air-mass back trajectory or season but a distinct and strong positive correlation was observed between metals associated with anthropogenic sources such as Zn and Ni and the extractable water soluble P fraction. This suggests that anthropogenic P sources are more soluble and bioavailable than mineral sources even though most of the P in aerosols in this region is in the mineral phase. These results have implications for determining how changes in atmospheric input of P to the ocean related to urban development and anthropogenic (wood and fuel burning) activities may impact marine ecosystems.