Kind, Jessica; Gehring, Andreas Ulrich; Winklhofer, Michael; Hirt, Ann Marie
Combined use of magnetometry and spectroscopy for identifying magnetofossils in sediments.
In: Geochemistry Geophysics Geosystems, Vol. 12
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Identification of the mineral remains of magnetotactic bacteria (MTB),known as magnetofossils, is of particular interest because theiroccurrence can be used for environmental and climatic reconstructions.Single-domain magnetite particles, which are biomineralized in the cellbody of MTB, have characteristic properties that can be used to detecttheir fossil remains. Acquisition of anhysteretic and isothermalremanent magnetization (ARM and IRM), first-order reversal curve (FORC)diagrams, and ferromagnetic resonance (FMR) spectra were used to detectthe magnetic mineral inventory in Holocene lake sediments. A comparativeanalysis in terms of the discriminatory power of these methods ispresented. The FORC diagrams contain two distinct features: a sharphorizontal ridge centered on the horizontal axis B-c and a feature withsymmetric spread along the vertical B-b axis. The coercivity spectraderived from the central ridge coincides with that derived from ARM andIRM acquisition curves and is compatible with the presence ofnoninteracting linear chains of single-domain magnetite. The secondfeature on FORC diagrams is indicative of interacting particles inclusters. In the FMR spectra from bulk sediment, two populations areseparated empirically based on the FORC information. An asymmetricsignal is taken to describe the population, which contains single-domainparticles in clusters. Empirical spectral separation of thiscontribution results in FMR spectra that are similar to those of intactMTB, which strongly suggests that a fraction of linear magnetosomechains is present. Combination of FMR and FORC results demonstrates thestrong potential of these methods for identifying magnetofossils, basedon alignment and interaction patterns of magnetic particles.