Iron is an essential element in many key biochemical processes, including respiration, nitrogen fixation, nitrate reduction, and chlorophyll biosynthesis. Iron speciation measurements show that >99% of dissolved iron is complexed by organic ligands that form very strong ferri-organic complexes that help stabilize Fe(III) in seawater, increasing its concentration to levels that can sustain microbial growth. However, the composition of these ligands that play an important role in the marine iron cycle remains largely unknown. Scientists from Woods Hole Oceanographic Institution and the University of Southern California propose to characterize the naturally occurring iron-binding ligands. Specifically, the investigators plan to collect strong iron-binding ligands from very large volume (>104 L) samples and perform detailed spectral analysis (mass spectrometry and nuclear magnetic resonance spectroscopy) to determine ligand distributions, functional group characteristics, and ultimately the structures of major ligands. Preliminary results from the North Pacific Ocean show our collection protocol recovers 60% of Fe-ligand complexes and 25-30% of total ligands. Measured conditional stability constants of the ligand extract (Kcond L/Fe' 1012) and competitive isotopic (55Fe and Ga (III)) labeling in the presence of strong chelators (EDTA, DTPA, DFB) allows us to target only strong ligands for spectral analysis. Characterization of naturally occurring iron binding ligands would provide a better understanding of iron speciation in seawater, and complement on-going studies of Fe-ligand bioavailability in pure cultures and mixed assemblages of marine plankton.
As regards broader impacts, a Fulbright postdoctoral scholar would participate in the research. One graduate student from the University of Southern California would be supported and trained as part of this project. One high school student would also be supported and trained as part of this project at the Woods Hole Oceanographic Institution. In addition, it is anticipated that undergraduate students supported via the Woods Hole Oceanographic Institution summer student fellowship program would participate in the study.
