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Published June 1986 | public
Journal Article

Magnetotactic bacteria and single-domain magnetite in hemipelagic sediments


Remanent magnetism in marine sediments has been used extensively over the past twenty years to calibrate the geological time-scale, study geomagnetic reversals and secular variation, and measure the rates of seafloor spreading. Although these sediments may contain different magnetic minerals, magnetite is the most commonly observed and magnetically stable phase, and its size, shape and post-depositional fate affect the magnetic remanence of the sediments. Biogenic magnetites are single-domain, with a high natural magnetic remanence (NRM), and have been suggested as a significant source of magnetic remanence in marine sediments. We have studied surface sediments from the Santa Barbara Basin and report the occurrence of living magnetotactic bacteria and the deposition of biogenic ultra-fine-grained, single-domain magnetite. Using a novel extraction technique, transmission electron microscopy and SQUID magnetometry, we show that these bacteria and the magnetite they produce are the major source of stable remanent magnetism in these sediments.

Additional Information

© 1986 Nature Publishing Group. We thank M. Kastner for providing the samples and H. Lowenstam and K. H. Nealson for helpful discussion. This work was supported by NSF grants EAR8407655 and EAR8351370 to J.L.K. and S.-B.R.C., and by an NRC Research Associateship Award to J.F.S. This is Caltech Division of Geological and Planetary Sciences contribution no. 4328

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August 22, 2023
October 20, 2023