Dynamics of natural organic Fe-binding ligands in the western North Pacific and its impact on Fe cycle

Research summary

  Iron (Fe) is well known as a key resource for primary productivity and material cycles in the ocean. Fe distribution and its bioavailability in seawater depend on the sources, sinks, and chemical speciation.  The chemical speciation of Fe is controlled by temperature, pH, redox status and complexation with natural organic ligands. Therefore, it is important to understand Fe speciation to shed light on its distribution and bioavailability.  In oxygenated seawater, the thermodynamically favored oxidation state of Fe is Fe(III).  Fe(III) is strongly hydrolyzed and its removal is mainly constrained by the formation of strong complex with natural organic ligands.  Indeed, it has been demonstrated that most dissolved Fe in seawater is complexed with natural organic ligands.  Humic substances, siderophores, cell breakdown products of phytoplankton via zooplankton grazing and virus cell lysis and exopolysaccharides are thought to act as natural organic ligands.  In seawater, these natural organic ligands are expected to exist as a mixture.  There are only a few reports about distribution of Fe-binding organic ligands in the western North Pacific, so the implication between Fe and organic ligands behaviors is not clear. In this study, the distribution of organic Fe-binding ligands is going to be investigated in the western subarctic North Pacific and its adjacent areas to clarify the impact of organic Fe-binding ligands on Fe cycle in the ocean.

Principle investigator:

Yoshiko Kondo (Nagasaki University ⋅ Graduate School of Fisheries and Environmental Sciences ⋅ Associate Professor ⋅ Chemical Oceanography)

Collaborator: Jun Nishioka (Hokkaido University ⋅ Institute of Low Temperature Science ⋅ Associate Professor ⋅ Chemical Oceanography)

Collaborator: Hajime Obata (The University of Tokyo ⋅ Atmosphere and Ocean Research Institute ⋅ Professor ⋅ Marine Geochemistry)

Collaborator: Shigenobu Takeda (Nagasaki University ⋅ Graduate School of Fisheries and Environmental Sciences ⋅ Professor ⋅ Biological Oceanography)