Humic substances influence on the distribution of dissolved iron in seawater: A review of electrochemical methods and other techniques

Abstract

Iron (Fe) is an essential trace element for the growth of phytoplankton in the ocean. Humic substances (HSs) are key components of dissolved Fe-binding organic ligands (Lt). Both Lt and HSs are widely accepted to regulate the distribution of dissolved iron (DFe) and influence its availability to marine phytoplankton and other organisms. This paper provides a concise overview of the historical progression of DFe determination and its speciation, including Lt and HSs, using electrochemical methods. It also reviews applications of these methods in examining the effects of HSs on DFe, drawing from spectroscopy, chromatography, and mass spectrometry data. Electrochemical techniques can measure the concentrations of HSs and the binding capacity of DFe, offering valuable insights into the role of HSs on DFe in marine settings. Spectroscopy, chromatography, and mass spectrometry allow for detailed characterization of the structure, properties, and types of organic ligands and HSs. These methodologies have enhanced our understanding of Lt and HSs, whether of marine or terrestrial origin, as significant ligands for DFe, influencing its concentration, distribution, and circulation. Future research should delve deeper into the mechanisms and chemical properties of Fe complexation with organic matter. Additionally, the impact of various factors on HSs complexes in relation to DFe warrants further exploration, benefiting from synchronous analysis using multiple detection methods. Such advancements would offer crucial insights into the biogeochemical cycling of Fe and enhance various research domains.