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 CaCO3 and CaO
formed in the ash). The unique isotopic signature in the ash, ranging
from 11.5 to 19.4‰ in the HCl and resin P fractions, is different
from that of other atmospheric P sources such as airborne tree pollen,
which has δ18OP values between 19.2‰
and 29.6‰, and Saharan-dust samples collected in Israel, which
have δ18OP values ranging from 20.7‰
to 22.6‰. Thus, the δ18OP can be
used as a marker for identifying atmospheric P from wildfires and
for estimating its importance to the global P cycle.