Fractional solubility of aerosol iron : synthesis of a global-scale data set

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Aerosol deposition provides a major input of the essential micronutrient iron to the open ocean. A critical parameter with respect to bioavailability is the proportion of aerosol iron that enters the oceanic dissolved iron pool – the so-called fractional solubility of aerosol iron (%FeS). Here we present a global-scale compilation of total aerosol iron loading (FeT) and %FeS values for ~1100 samples collected over the open ocean, the coastal ocean, and some continental sites, including new data from the Atlantic Ocean. The global-scale compilation reveals a remarkably consistent trend in the fractional solubility of aerosol iron as a function of total aerosol iron loading, with the great bulk of the data falling along an inverse hyperbolic trend. The large dynamic range in %FeS (0-95%) varies with FeT in a manner similar to that identified for aerosols collected in the Sargasso Sea by Sedwick et al. (2007), who posit that the trend reflects near-conservative mixing between air masses that carry lithogenic mineral dust (with high FeT and low %FeS) and non-soil-dust aerosols such as anthropogenic combustion emissions (with low FeT and high %FeS), respectively. An increasing body of empirical evidence points to the importance of aerosol source and composition in determining the fractional solubility of aerosol iron, such that anthropogenic combustion emissions appear to play a critical role in determining this parameter in the bulk marine aerosol. The robust global-scale relationship between %FeS and FeT may provide a simple heuristic method for estimating aerosol iron solubility at the regional to global scale.
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