Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains

• Published in: Journal of Geophysical Research: Solid Earth
• Main Authors: Chang, L., Winklhofer, M., Roberts, A. P., Heslop, D., Florindo, F., Dekkers, M. J., Krijgsman, W., Kodama, K., Yamamoto, Y.
• Other Authors: Chang, L.; Paleomagnetic Laboratory “Fort Hoofddijk,” Department of Earth Sciences, Utrecht University, Utrecht, Netherlands, Winklhofer, M.; Department of Earth and Environmental Sciences, Ludwig-Maximilians University, Munich, Germany, Roberts, A. P.; Research School of Earth Sciences, The Australian National University, Canberra, Australia, Heslop, D.; Research School of Earth Sciences, The Australian National University, Canberra, Australia, Florindo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia, Dekkers, M. J.; Paleomagnetic Laboratory “Fort Hoofddijk,” Department of Earth Sciences, Utrecht University, Utrecht, Netherlands, Krijgsman, W.; Paleomagnetic Laboratory “Fort Hoofddijk,” Department of Earth Sciences, Utrecht University, Utrecht, Netherlands, Kodama, K.; Center for Advanced Marine Core Research, Kochi University, Nankoku, Kochi, Japan, Yamamoto, Y.; Center for Advanced Marine Core Research, Kochi University, Nankoku, Kochi, Japan, Paleomagnetic Laboratory “Fort Hoofddijk,” Department of Earth Sciences, Utrecht University, Utrecht, Netherlands, Department of Earth and Environmental Sciences, Ludwig-Maximilians University, Munich, Germany, Research School of Earth Sciences, The Australian National University, Canberra, Australia, Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia, Center for Advanced Marine Core Research, Kochi University, Nankoku, Kochi, Japan
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2013
• Subjects: pelagic carbonates; biogenic magnetite; rock magnetism; environmental magnetism; ODP; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating; processes; transport; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism; Southern Ocean
• Online Access: http://hdl.handle.net/2122/8881; https://doi.org/10.1002/2013JB010381

Pelagic marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic “hard” component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial. Published 6049–6065 2.2. Laboratorio di paleomagnetismo JCR Journal restricted