Dynamic Nature of Soil Iron Minerals: Recent Advances Using Iron Isotope Tracers and Mössbauer Spectroscopy

Iron plays a central role in defining the redox and surface chemical environment of soils and sediments, by mediating the behavior of nutrients, pollutants, and carbon compounds. However, the mechanisms that drive dynamic changes in Fe speciation and mineral composition can be difficult to trace. Over three decades, technical advances in spectroscopy and theoretical modeling techniques have revealed detailed mechanisms of Fe mineral recrystallization and transformation. Here, we provide a perspective on the application of iron isotopic tracers to the development of atomic-scale mechanistic understanding of Fe mineral dynamics. We review key milestones in the advancement of 57Fe tracers coupled with 57Fe Mössbauer spectroscopy and draw links between the understanding of Fe dynamics with 57Fe tracers and biogeochemical cycling of other elements in soils and sediments. Iron isotopes are increasingly used in Fe biogeochemistry research, and our analysis will point out unique opportunities offered by 57Fe tracers to unravel important questions in soil biogeochemistry today.