[1] To understand the impact of dust deposition on ocean primary productivity, the evaluation of dust input is not sufficient, and the soluble iron supply is also needed. Measurements of iron in aerosols suggest a much higher solubility than in soil, implying substantial atmospheric processing of chemical or physical nature. Here, we have investigated the effect of the mineralogy on iron solubility. We have measured iron solubility from some minerals commonly found in dust (clay, feldspar and iron (hydr-)oxides). Firstly, we observe a greater solubility of iron resulting from clays (~4%) in comparison to iron (hydr-)oxides (<1%), independently of specific surface of minerals. Secondly, by considering amount of dissolved iron and the mineralogical composition of dust, our results indicate that dissolved iron fraction mainly comes from clay dissolution in contrast to that assumed in some biogeochemical models. In consequence, it appears that iron solubility is closely linked to the mineralogical composition of aerosol. Citation: Journet, E., K. V.

This paper presents data on elemental and mineralogical composition of mineral dust from various source regions of Africa collected during the African Monsoon Multidisciplinary Analyses (AMMA) SOP0/DABEX and Dust Ouflow and Deposition to the Ocean (DODO) DODO1 experiments (January–February 2006), and the DODO2 campaign (August 2006). Bulk filter samples were collected at the AMMA supersite of Banizoumbou, Niger, as well as on board the Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft. Both mineral dust and biomass burning in external mixing occurred in surface and elevated layers during the winter field phase of the campaign. However, mineral dust was overwhelming, accounting for 72% of the estimated aerosol mass in aged elevated biomass burning layers and up to 93% in plumes of mineral dust, which generally occurred in the boundary layer. A number of well‐defined episodes of advection of mineral dust could be identified both at the ground and on the aircraft. The elemental and mineralogical composition varied depending on source region. This variability could be well traced by the calcium content, which is enhanced in dust from North Africa but depleted in dust from the Sahel. Iron oxides in the form of hematite and goethite are enriched in dust emitted within Sahel and in Mauritania, whereas dust from the Bodélé depression is iron‐oxide depleted. Iron oxides represented between 2.4% and 4.5% of the total estimated dust oxide mass. This regional variability will have to be taken into account in estimating the optical properties of absorption of mineral dust from western Africa.