Solubilities of Al, Pb, Cu, and Zn in rain sampled in the marine environment over the North Atlantic Ocean and Mediterranean Sea

Abstract

Chemical processes controlling the dissolved and particulate phase distribution of crustal (Al) and noncrustal metals (Pb, Cu, and Zn) appear to differ in marine precipitation sampled over the North Atlantic Ocean and Mediterranean Sea. Dissolved Al appears to be in equilibrium with a trivalent Al salt at rainwater pH < 5.1, whereas dissolved Pb, Cu, and Zn concentrations are probably controlled by adsorption/desorption processes in which rainwater particulates provide surface‐active sorption sites. In both processes, rainwater pH is a critical parameter. Results suggest that in marine precipitation with pH < 5, > 80% of the total Pb, Cu, and Zn concentrations are delivered to the surface oceans in the dissolved form. For a corresponding pH range, Al solubility varies from <5% to >60%. Over the wider observed pH range (of 3.5 to 6.9), the solubilities of Pb, Cu, Zn, and Al are highly variable. The use of mean trace metal solubilities for the assessment of dissolved atmospheric trace metal wet deposition fluxes, and their effects on surface ocean biogeochemistry should be constrained by taking into account rainwater pH in future estimates in global models.