title: Control of Earth-like magnetic fields on the transformation of ferrihydrite to hematite and goethite.
abstract: Hematite and goethite are the two most abundant iron oxides in natural environments. Their formation is controlled by multiple environmental factors; therefore, their relative concentration has been used widely to indicate climatic variations. In this study, we aimed to test whether hematite and goethite growth is influenced by ambient magnetic fields of Earth-like values. Ferrihydrite was aged at 95 °C in magnetic fields ranging from ~0 to ~100 μT. Our results indicate a large influence of the applied magnetic field on hematite and goethite growth from ferrihydrite. The synthesized products are a mixture of hematite and goethite for field intensities <~60 μT. Higher fields favour hematite formation by accelerating ferrimagnetic ferrihydrite aggregation. Additionally, hematite particles growing in a controlled magnetic field of ~100 μT appear to be arranged in chains, which may be reduced to magnetite keeping its original configuration, therefore, the presence of magnetic particles in chains in natural sediments cannot be used as an exclusive indicator of biogenic magnetite. Hematite vs. goethite formation in our experiments is influenced by field intensity values within the range of geomagnetic field variability. Thus, geomagnetic field intensity could be a source of variation when using iron (oxyhydr-)oxide concentrations in environmental magnetism.
authors.affiliation: State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, P.R. China.|Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Marine Science and Technology, Qingdao, P.R. China.
authors.forename: Zhaoxia
authors.initials: Z
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, P.R. China.|Laboratory for Marine Geology, Qingdao National Oceanography Laboratory for Marine Science and Technology, Qingdao, P.R. China.
authors.forename: Qingsong
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Earth Sciences, Paleomagnetic Laboratory 'Fort Hoofddijk', Faculty of Geosciences, Utrecht University, Budapestlaan 17, 3584 CD Utrecht, The Netherlands.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Dekkers
authors.affiliation: Departamento de Agronomía, Universidad de Córdoba, Edificio C4, Campus de Rabanales, 14071 Córdoba, Spain.
authors.forename: Vidal
authors.initials: V
authors.lastname: Barrón
authors.affiliation: Departamento de Agronomía, Universidad de Córdoba, Edificio C4, Campus de Rabanales, 14071 Córdoba, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Torrent
authors.affiliation: Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Roberts