Bundy, Randelle MResing, Joseph AMoore, Laura2024-02-122024-02-122024-02-122023Moore_washington_0250E_26310.pdfhttp://hdl.handle.net/1773/51229Thesis (Ph.D.)--University of Washington, 2023Iron (Fe) is an essential nutrient for life, but it is only present in low concentrations in the ocean. Dissolved Fe (dFe) is the most biologically labile fraction of Fe in seawater, the majority of which is bound to a heterogeneous pool of organic ligands. These organic ligands stabilize dFe against precipitative loss and mediate the bioavailability and biogeochemical cycling of this critical element. Characterizing the organic ligand pool is primarily done using one of two independent approaches. The first, competitive ligand exchange-adsorptive cathodic stripping voltammetry (CLE-ACSV), is an electrochemical technique used to measure the concentration and average Fe-binding strength of the total ligand pool. The second, liquid chromatography-mass spectrometry (LC-MS), is used to identify specific iron-binding ligands and most frequently targets a class of strongly Fe-binding molecules known as siderophores. My dissertation combines LC-MS and CLE-ACSV techniques in order to characterize Fe-binding ligands at multiple levels and examine ligand impact on the stabilization and transport of dissolved Fe. I identified the ubiquitous presence of siderophores in novel oceanographic environments, including within the Eastern Tropical North Pacific oxygen deficient zone and near diverse hydrothermal venting systems along the Southern East Pacific Rise. In both study regions, I explored the critical role of organic ligands and siderophores in stabilizing dFe and facilitating Fe transport into the ocean interior. This dissertation expands ligand characterization studies to environments near key Fe sources to the deep ocean, including continental margins and hydrothermal vents, and identifies siderophores across a much wider range of chemical and dFe gradients than has previously been observed. This dissertation presents some of the first combined LC-MS and CLE-ACSV ligand characterization studies and offers unprecedented insight into the dynamics of the organic ligand pool near critical Fe sources.application/pdfen-USnoneChemical speciationEastern tropical north PacificIron ligandsSiderophoresSouthern East Pacific RiseChemical oceanographyBiogeochemistryOceanographyThesis