Abstract Magnetotactic bacteria produce chains of magnetite crystals within a cell. Bacterial magnetites have characteristic morphologies and sizes under strict biological control. We examined morphologies of fossil bacterial magnetites (magnetofossils) preserved in Pacific deep-sea sediments and its relation to organic carbon fluxes (Fig.1). Isotropic crystals dominate magnetofossils in sediments in a relatively oxidized condition and anisotropic crystals in a more reduced condition. Our finding has important implications for biomineralization processes, and demonstrates the potential of magnetofossil morphology as a paleoenvironmental indicator.

Fig.1. Relation between organic carbon (Corg) flux and the ratio of isotropic, octahedral magnetofossils.