Factors influencing the seawater solubility of aerosol associated trace metals
Recent recognition of the importance of trace metals in oceanic biogeochemical cycling and of the significance o f atmospheric trace metals inputs to marine waters, highlights the need to assess the dissolved trace metals inputs from atmospheric sources. Atmospheric inputs are important to the surface waters of the Eastern Mediterranean, due to the reduction of riverine inputs. High-volume aerosol samples were collected from Haifa, Israel and Erdemli, Turkey in 1996. These samples were characterised by air mass back trajectories, because contrasting aerosol sources (urban and crustal) are apparent in this region. Trace metal (Cu, Pb and Zn) seawater solubility studies were determined for selected samples, under carefully controlled conditions (seawater at pH 8.0 and 25.0 ± 1.0 °C; shaking rate 150 osc min"'). The average seawater solubilities o f Zn and Pb from the northern (predominantly European source) wind sector were statistically higher than the southern (mainly Sahartm and Arabian desert source) wind sector. The total dry deposition fluxes o f trace metals were estimated from the geometric air concentrations of both wind sectors, the wind sector weighting and assimiing a deposition velocity of 0.1 cm s'K Trace metal seawater soluble fluxes were calculated using mean seawater solubilities of the aerosols from the northern and southern wind sectors. The soluble trace metal fluxes, by dry deposition, to the Eastern Mediterranean were compared with soluble wet deposition and riverine fluxes. A novel experimental system was assembled and validated, in order to (i) enhance our knowledge of the physiochemical and biological factors that affect the seawater solubility of trace metals and (ii) to refine the soluble trace metal flux estimates. The experimental system was capable of monitoring trace metal desorption reactions at high temporal resolutions (> 45 s). It was initially applied to the measurement of the extent and rate of desorption of total dissolved and Mabile dissolved' Cu, Pb and Zn from Liverpool urban particulate material, then to the seawater solubility of trace metals associated with urban particulate standard reference material and Saharan dust. In order to increase our understanding of the fate of trace metals associated with aerosol particles after dry deposition into seawater, the effects of bacteria, proportional mbcing of end member aerosols, particle concentrations, mbcing rates, light and temperature on the desorption of aerosol associated trace metals were separately investigated. It was found that the presence of bacteria in seawater and seawater temperature enhanced the seawater solubility of Zn, Pb and Cu. In addition, natural light enhanced the solubility of Cu from Saharan dust. Conversely, increasing the particle concentrations and the mixing rate of the incubated seawater caused a decrease the observed seawater solubility of aerosol associated trace metals (the decrease was greater for Pb and Zn than Cd and Cu).