Phosphorus-bearing Aerosol Particles From Volcanic Plumes

Particles rich in P or bulk geochemical data of volcanic aerosol particles showing high P contents are known from many volcanic plumes (Stanton, 1994; Obenholzner et al., 2003). FESEM/EDS analysis of individual particles obtained from the passively degassing plume of Popocatepetl volcano, Mx. (1997) and from the plume of Stromboli (May 2003) show P frequently. Even at the high resolution of the FESEM, euhedral apatite crystals could not be observed. At Popocatepetl (1997) spherical Ca-P-O particles are common. Fluffy, fractal or botryoidal particles also can contain EDS-detectable amounts of P. The EDS spectrum of such particles can comprise various elements. However most particles show P, S and Cl. P-S and P-S-metal species are known in chemistry but do they occur in volcanic plumes? Stoichiometric considerations had been made in the past suggesting the existence of P-S species in plumes (Stanton 1994), gas sampling and remote gas monitoring systems have not detected yet such molecules in plumes. The particle spectrum of the reawakened Popocateptel volcano might be related to accumulation of volatiles at the top of a magma chamber during the phase of dormancy. P-Fe rich, Ca-free aggregates are also known from the eruption of El Chichon 1982 (SEM/EDS by M. Sheridan, per. comm. 08-24-2003). Persistently active volcanoes (i.e. Stromboli) represent a different category according to continuous degassing and aerosol particle formation. A particle collector ( ca. 90 ml/min) accompanied a COSPEC helicopter flight at Stromboli (May 15, 2003) after one of the rare types of sub-plinian events on April 5 2003. P-bearing particles are very common. For instance, an Fe oxide grain (diam. = 2 æm) is partially covered by fluffy and euhedral P-bearing matter. The elements detected are P, Cl, Na, Mg, Al, Si, K, Ca, Ti and (Fe). The fluffy and the euhedral (rhombohedral?) matter show in SE-BSE-mix image almost identical grey colors. At Stromboli and Popocatepetl particles on which Mg chlorides are present had been detected. Mg and P are major elements of magmas and are not considered to be highly volatile. Can such particles of probably volcanic origin be the source for easy soluble P necessary for the crystallization of P-bearing bio-minerals, i.e. in teeth of Mammalia, phosphorite concretions within kidneys of certain bivalves, the digestive glands of gastropods and crustaceans (Gooday et al., 1995), the formation of DNA, ATP or ADP of living organisms? The solubility of naturally occurring apatite cannot support the needs of P to the biomass (Cox 1995), even if P from apatite accumulates throughout Earth`s history a process provided by the food chain. P is number 10 of the naturally occurring elements of the upper continental crust (665 ppm; Wedepohl, 1995). It remains unknown: what is the influence of a polluted atmosphere to the formation of analyzed particles. Cox, P.A., 1995. Oxford University Press. Gooday et al., 199.5 J. mar. Biol. Ass. U.K., 75, 469-481. Obenholzner, J.H., et al., 2003. In Volcanic Degassing (Oppenheimer, Pyle, Barclay eds.). Geol. Soc., London Stanton, R.L., 1994. Clarendon Press - Oxford. Wedepohl, K.H., 1995. Geochim. Cosmochim. Acta, 59, 7, 1217-1232.