Solubility of aerosol trace elements: sources and deposition fluxes in the Canary Region

Abstract

African dust inputs have important effects on the climate and marine biogeochemistry of the subtropical North Atlantic Ocean. The impact of dust inputs on oceanic carbon uptake and climate is dependent on total dust deposition fluxes as well as the bioavailability of nutrients and metals in the dust. In this work, the solubility of trace metals (Fe, Al, Mn, Co and Cu) and ions (Ca, sulphate, nitrate and phosphate) has been estimated from the analysis of a long-time series of 109 samples collected over a 3-year period in the Canary Islands. Solubility is primarily a function of aerosol origin, with higher solubility values corresponding to aerosols with more anthropogenic influence. Using soluble fractions of trace elements measured in this work, atmospheric deposition fluxes of soluble metals and nutrients have been calculated. Inputs of dissolved nutrients (P, N and Fe) have been estimated for the mixed layer. Considering that P is the limiting factor when ratios of these elements are compared with phytoplankton requirements, an increase of 0.58 nM of P in the mixed layer (similar to 150 m depth) and in a year can be estimated, which can support an increase of 0.02 mu g Chla L-1 y(-1). These atmospheric inputs of trace metals and nutrients appear to be significant relative to the concentrations reported in this region, especially during the summer months when the water column is more stratified and deep-water nutrient inputs are reduced.