Determinations of dissolved and particulate iron and Fe(II) were carried out in the Baltic Sea. Results from the Gulf of Bothnia supported river runoff as one of the major iron sources. Downwards and upwards fluxes of iron corroborated that the Fe(II) pool below the redoxcline hardly could reach surface. Discrepancies between theoretical and empirical Fe(II) halftimes emphasize the role of photochemical processes and the presence of organic ligands. A potential biomass production based on Fe(II) values points toward a minor role of iron as a limiting factor for cyanobacteria blooms.
