Relationships Between Iron Oxides and Magnetic Properties in Intertidal Sediments of the Yangtze Estuary, China

Abstract

AbstractIron oxide analyses using DCB (Dithionite‐Citrate‐Carbonate) and AOD (Ammonium Oxalate in the Dark) extractions as well as magnetic measurements are conducted on intertidal sediments of the Yangtze Estuary, China. The results are used to explore the relationships between iron oxides and magnetic properties, to estimate different iron oxide pools semi‐quantitatively, and to investigate the impact of DCB extraction on the variations of magnetic properties. It is revealed that magnetic susceptibility and SIRM (Saturation Isothermal Remanent Magnetization) have significant correlations with DCB‐ and AOD‐extractable iron oxides. A semi‐quantitative estimation indicates a dominance of amorphous iron oxides, with magnetite occupies only 12 percent of the total iron oxides. The effect of DCB extraction on magnetic properties rely on the grain size and the content of magnetic minerals. DCB extraction removes a large fraction of fine‐grained iron oxides in the < 2µm particle size. Coarse magnetite can also be dissolved by DCB extraction. The differences between pre‐ and post‐DCB values of S–100 and HIRM suggest that anti‐ferromagnetic iron oxides are more abundant than magnetite in the clay (< 2µm) fraction.