Trace element behaviour in seawater during Etna's pyroclastic activity in 2001: Concurrent effects of nutrients and formation of alteration minerals

The eruption of Etna in Sicily on 13 July 2001 marked the most intense activity of the volcano in the last 300 years. The eruption occurred while the oceanographic cruise ANSIC 01 was being conducted to the east of Sicily, presenting a unique opportunity for the investigation of the chemical effects on the marine system during a period of significant (∼ 1 g m−2) ash deposition. Comparison of trace element data with measured concentrations from the oceanographic cruise JUVENILE 99, carried out two years before, indicates large enrichments of V, Cr, Mn, Fe, Co, Cu and Pb. We attribute this behaviour to leaching of freshly-erupted volcanic ash, according to trace element concentrations measured in suspended particulate matter (SPM). The exception is Pb, which is likely to be influenced by another, possibly anthropogenic, source. Trace element behaviour in the water column and during leaching experiments suggests that trace element distributions are driven by the occurrence of alteration minerals on glass surfaces, given that the main trace element source in seawater appears to come from the soluble-ash fraction. Trace element solubility is likely to be increased by organic complexation, which accelerates the alteration of ash particles. Organic substances suitable for complex trace elements are probably formed during the lysis of phytoplankton cells, produced during an increase in marine primary productivity associated with the volcanic fertilisation of surface waters.