Atmospheric mineral dust has been considered as one of the major sources of Fe to the surface water in the western subarctic North Pacific.Natural Fe(III) complexing organic ligands can affect chemical speciation of Fe in seawater by formation of iron complex,and thus may determine the fate of Fe supplied from the atmosphere.Although source of these ligands in surface seawater was unclear,it has been reported that Fe addition may induce release of Fe(III) complexing ligands by phytoplankton.Field observations were conducted during a mesoscale Fe-enrichment experiment in the western subarctic North Pacific (SEEDS-II) to investigate the complexation of Fe(III) with natural organic ligands through development and decline of phytoplankton bloom induced by the artificial Fe supplies.