The Organic Ties of Iron - Organic Iron speciation related to humic substances and microbial interactions

Marine primary production is dependent on dissolved iron in seawater, in addition to other nutrients. As iron does not readily dissolve in seawater, stabilisation by iron-binding organic ligands is essential in these processes. Iron-binding organic ligands are a diverse and non-specified part of the dissolved organic matter pool and their fate is generally unknown.

Major contributors to this pool of Iron-binding organic ligands are humic substances, microbial breakdown products generally introduced into ocean systems from terrestrial sources. Notably in the Arctic Ocean surface water we find that the contribution of humic substances to the solubility of iron is very large. Iron and organic material are transported via the Transpolar Drift (TPD), ultimately to the north Atlantic. This transport will be strongly influenced by climate change due to changes in the catchments of the major Arctic rivers feeding into the TPD.

Another potentially major source of Iron-binding organic ligands are microbiotic interactions in the upper water column. To study representative processes, we cultured two phytoplankters and matching monospecific viruses in consistent low-iron conditions. In our studies we found that viral infection of phytoplankton is negatively impacted by low iron concentrations. In addition, we found that - dependent on the phytoplankton host - viral lysis can increase ligand concentrations. Bacteria are found to modify parts of the ligand pool, which introduces a possible loss factor of Iron-binding organic ligands.