The chemical speciation of iron in the north-east Atlantic Ocean

The distribution of dissolved iron and its chemical speciation (organic complexation and redox speciation) were studied in the northeastern Atlantic Ocean along 23°W between 37 and 42°N at depths between 0 and 2000 m, and in the upper-water column (upper 200 m) at two stations further east at 45°N10°W and 40°N17°W in the early spring of 1998. The iron speciation data are here combined with phytoplankton data to suggest cyanobacteria as a possible source for the iron binding ligands. The organic Fe-binding ligand concentrations were greater than that of dissolved iron by a factor of 1.5–5, thus maintaining iron in solution at levels well above it solubility. The water column distribution of the organic ligand indicates in-situ production of organic ligands by the plankton (consisting mainly of the cyanobacteria Synechococcus sp.) in the euphotic layer and a remineralisation from sinking biogenic particles in deeper waters. Fe(II) concentrations varied from below the detection limit ( Synechococcus growth.