The Origin and Nature of Magnetic Particles From Soils and Sediments Constrained by Hydrodynamics and Geochemistry Around a Tropical Lagoon System

Magnetic iron oxides are commonly enriched in soils and sediments on Earth's surface. Magnetic properties are widely employed in soil taxonomy, sediment tracing and paleoclimate reconstruction as indicators of associated pedogenic and depositional processes. However, in coastal regions, frequent shifts in pedogenesis and diagenesis accompanied by changes in hydrodynamic and geochemical conditions from land to sea can influence the formation and preservation of magnetic particles in sediment sequences. To discern the origin and nature of magnetic particles driven by these processes, we systematically examined soils and sediments around a tropical lagoon that has been closing for two hundred years. We found that the finest superparamagnetic particles are enriched along with hematite from inland soils with high-Fe and high-Al backgrounds, which was driven by pedogenesis. Single-domain ferrimagnetic particles are enriched along with amorphous iron oxides in the lagoon with high-Mg and high-Mn backgrounds, which was driven by early diagenesis in quiet and reducing depositional environments. Coarse titanomagnetite particles are strongly enriched in inshore sediments with high-Si and high-Ti backgrounds, which was driven by seawater elutriation. However, magnetic particles in barrier bar soils have mixed features depending on the neighboring environment. Identifying magnetic particles derived from different soils and sediments in tropical coastal regions can assist in tropical coastal paleoclimate and paleoenvironment reconstruction on the basis of magnetic properties along coastal sediment sequences.