Link between iron and sulphur cycles suggested by detection of Fe(n) in remote marine aerosols

Abstract

IRON is essential to the growth of organisms, and iron derived from the atmosphere may be the limiting nutrient for primary productivity in some oceanic regions^1–6. Aeolian mineral dust is the chief source of marine iron in many areas^1–3,5,7, but there is little information on the chemical form of the iron in this dust. Here we report that Fe(n) contributed 56±32% of the total iron in marine aerosol samples collected over the central North Pacific and 49 + 15% at Barbados. We suggest that the key reaction that produces Fe(n), and hence increases the solubility of marine aerosol iron in sea water, is [Fe(in)(OH)(H₂O)₅]²⁺ + H₂O^ [Fe(n)(H₂O)₆]²⁺ + OH- (refs 8–10). The presence of Fe(n) in remote marine aerosols suggests that the OH radical has been produced in these heterogeneous reactions. From consideration of both the marine biological production of dimethylsulphide and the subsequent oxidation of reduced forms of sulphur in the atmosphere, we propose that the iron and sulphur cycles in both the atmosphere and the ocean may be closely coupled.