An environmental magnetic analysis of the Osaka Bay sediments: Relationship with sea water conditions

We analyzed the sea water composition and the rock magnetic properties of the sediments from Osaka Bay for understanding the control of the sea water environment over dissolution of iron oxide and formation of iron sulfide. Formation of framboidal pyrite and greigite was recognized even at the center of the bay, where oxygen-rich water was observed at the sea bottom, as well as in the inner part of the bay, where water ventilation was poor due to the density stratification of the sea water. A large supply of organic matter may result in an anoxic condition within the sediment. The clear relationship between the sea bottom dissolved oxygen content and the concentration ratio of hematite suggests that selective dissolution of magnetic minerals controls the variation of magnetic properties in the Osaka Bay. S-ratio, the ratio of magnetization carried by hematite to total magnetization, is a possible proxy for the water environment in the Osaka Bay.