Organic complexation and speciation of iron in the South and Equatorial Atlantic

Our investigation into the organic complexation and speciation of dissolved Fe in water column samples taken during the 1996 Intergovernmental Oceanog raphic Commission Baseline Expedition to the South and Equatorial Atlantic Ocean confirms the ubiquity of Fe-complexing ligands. In most samples Fe is greater than 99% organically complexed by a ligand with a conditional stab ility constant (K ' (FeL,Fe ')) between 10(12) and 10(14). The deep-water m asses exhibit no systematic differences with respect to ligand concentratio n or percent organic complexation. Greater than 2% of total dissolved Fe wa s present as inorganic Fe in some surface waters (1 m). The Amazon River do es not appear to be a major source of these Fe-complexing ligands to the op en ocean. Therefore, even in this area of relatively high atmospheric depos ition, the majority of dissolved Fe is organically complexed by a ligand of unknown origin, and phytoplankton could potentially be Fe-limited if they only respond only to inorganic Fe. (C) 2001 Elsevier Science Ltd. All right s reserved.