Ferromagnetic Resonance of Magnetite Biominerals Traces Redox Changes ∗ Thomas M
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Earth and Planetary Science Letters 545 (2020) 116400 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Ferromagnetic resonance of magnetite biominerals traces redox changes ∗ Thomas M. Blattmann a,b, , Barbara Lesniak c, Inés García-Rubio d,e, Michalis Charilaou f, ∗∗ Martin Wessels g, Timothy I. Eglinton b, Andreas U. Gehring c, a Biogeochemistry Research Center, JAMSTEC, 237-0061 Yokosuka, Japan b Geological Institute, ETH Zurich, 8092 Zurich, Switzerland c Institute of Geophysics, ETH Zurich, 8092 Zurich, Switzerland d Laboratory of Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland e Centro Universitario de la Defensa, 50090 Zaragoza, Spain f Department of Physics, University of Louisiana at Lafayette, Lafayette, LA 70504, USA g Institut für Seenforschung, Landesanstalt für Umwelt Baden-Württemberg, 88085 Langenargen, Germany a r t i c l e i n f o a b s t r a c t Article history: Redox variations govern a multitude of key geochemical and microbiological processes within lacustrine Received 18 October 2019 and marine systems, yet the interpretation of these geological archives can be limited because redox- Received in revised form 12 May 2020 sensitive microorganisms leave behind sparse fossil evidence. Here, we assess a biologically controlled Accepted 5 June 2020 magnetic proxy through investigation of a well-constrained sedimentary record covering a perturbation Available online 16 June 2020 of redox-conditions driven by a complete trophic cycle in Lake Constance. Ferromagnetic resonance Editor: I. Halevy spectroscopy of sediments reveals strong uniaxial anisotropy, indicative of single-domain magnetite Keywords: particles in intact or fragmentary chain arrangements, which are an unambiguous trait of magnetotactic magnetotactic bacteria bacteria (MTB) and their magnetofossil remains. We show that biogenic magnetite formed intra-cellularly magnetofossil in MTB faithfully records changing redox-conditions at or close to the sediment water-interface. Biogenic anoxia magnetite within sedimentary records points to the proliferation of MTB parallel to a decline in water sediment column dissolved oxygen and the formation of sulfidic surface sediments in Lake Constance associated redox gradient with an episode of eutrophication (1955–1991). We conclude that magnetofossils may serve as a sensitive eutrophication geological proxy to reconstruct dynamic redox-changes along the sediment-water interface and bottom waters. © 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction existence in sediments in the form of magnetofossils (Hesse, 1994; Kind et al., 2012; Kodama et al., 2013; Kopp and Kirschvink, 2008; Understanding the impact of redox dynamics within aquatic Roberts et al., 2012). These intracellularly produced ferrimagnetic 2+ 3+ systems is important for reconstructing biogeochemical processes nanoparticles, generally composed of magnetite (Fe Fe2 O4), de- in marine and lacustrine sedimentary records. Changing redox con- noted magnetosomes, are characterized by genetically-determined, ditions can drive faunal changes, which in turn critically affect well-defined sizes (typically 35-120 nm) with narrow shape dis- fossil assemblages and molecular (biomarker) signatures preserved tributions in the single-domain (SD) magnetic state (Bazylinski et in the geological record (Gambacorta et al., 2016). Redox-sensitive al., 1988; Devouard et al., 1998). Magnetosomes are aligned in microorganisms such as magnetotactic bacteria (MTB), which are chains along a cytoskeletal filament that stabilizes their arrange- present in freshwater and marine settings, are of special interest ment and prevents clumping (Kopp et al., 2006; Scheffel et al., because they may play an appreciable role in the cycling of iron in 2006). This linear arrangement generates a magnetic dipole that is aquatic systems (Chen et al., 2014) and can leave evidence of their used by MTB as a compass to navigate along Earth’s magnetic field (i.e., magnetotaxis) toward favored habitats around the oxic-anoxic transition zone (OATZ) (e.g., Spormann and Wolfe, 1984). MTB and Corresponding author at: Biogeochemistry Research Center, JAMSTEC, 237-0061 * their remains have been reported from Quaternary deposits (Kind Yokosuka, Japan. et al., 2012; Kodama et al., 2013), but magnetofossil evidence ex- ** Corresponding author. E-mail addresses: [email protected] (T.M. Blattmann), [email protected] tends back to the Cretaceous (Kopp and Kirschvink, 2008), with (A.U. Gehring). genes associated with magnetosome formation originating in the https://doi.org/10.1016/j.epsl.2020.116400 0012-821X/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 2 T.M. Blattmann et al. / Earth and Planetary Science Letters 545 (2020) 116400 Archean (Lin et al., 2017). Paleomagnetic studies are increasingly considering and seeking to extract paleoenvironmental informa- tion (e.g., nutrient availability, dissolved iron availability, oxygen concentrations) from magnetofossils embedded within a complex matrix of magnetic minerals in sedimentary records (Larrasoaña et al., 2003; Passier et al., 2001; Roberts et al., 2011, 2012; Sa- vian et al., 2014; Suk, 2016). Given the OATZ habitat of MTB and the stability of magnetosomes, magnetofossils may serve as ideal redox-sensitive proxies in geological archives as postulated previ- ously (Chang et al., 2018; Hawthorne and McKenzie, 1993; Larra- soaña et al., 2014). In recent years, ferromagnetic resonance (FMR) spectroscopy has been established as a powerful tool to quanti- tatively analyze the magnetic traits of cultured MTB (Charilaou, 2017; Kopp et al., 2006), and this in turn opened the door to de- tect MTB and magnetofossils in geological samples (Gehring et al., 2011a). Moreover, the FMR spectral response allows the essential discrimination between biogenic and detrital magnetite character- ized by SD and multi-domain, respectively (e.g., Gehring et al., 2009; Griscom, 1980), paving the way for magnetofossil identifica- tion in sedimentary records and extracting environmental changes. Here, we present the FMR spectral evolution yielded from a his- torically chronicled redox perturbation recorded in a sediment core th st from Lake Constance spanning the mid-19 to early 21 Century as a testbed to decipher the response of MTB. The rise and fall of MTB as witnessed by their magnetofossil legacy in sediments is proposed as a proxy for past water column and sediment-water interface redox changes. Fig. 1. Lake Constance sediment profile with chronology, organic carbon content, total sulfur content, and normalized magnetic susceptibility. 2. Materials and methods 1966). In recent years, it has been successfully applied to quantita- 2.1. Study site and sampling tively analyze the magnetic properties of cultured MTB (Charilaou et al., 2011a, 2015) and to detect magnetofossils in sedimentary Lake Constance, bordering Switzerland, Austria, and Germany, deposits (Gehring et al., 2011a; Kind et al., 2012; Kopp et al., 2006; is the second largest peri-alpine lake in Central Europe and in- Roberts et al., 2011). In the following, we summarize the basic FMR cludes a shelf, margin, and abyssal plain similar to ocean basin principles to justify the concept of spectral analysis in our study. In bathymetry (IGKB, 2016; Müller, 1966b; Wessels, 1998a). The ◦ ◦ an FMR experiment, the sample is subjected to a DC external mag- study site (47.5997 N 9.3581 E) on the southern slope of the netic field and an orthogonal microwave field. The DC field drives lake at a water depth of 100 m and sedimentation rate of 1-2 the magnetic moment of the sample to a precession around the mm/y, is a reference locality for monitoring of lacustrine primary field axis at a frequency that increases linearly with the strength productivity (Blattmann et al., 2019; Fuentes et al., 2013; IGKB, of the external field, i.e., the Larmor frequency, ωL = gμB Beff/, 2009; Wessels et al., 1999) and is representative of environmen- where is the reduced Planck constant, g is the Landé spectro- tal changes since the Late Glacial period (Wessels, 1998b). For this scopic splitting factor, μB is the Bohr magneton, and Beff is the study, a ∼1m gravity core (BO12-111) was retrieved in December effective magnetic field in the sample, consisting of both internal 2012, extruded, split in sections based on color (Fig. 1) and trans- (exchange and anisotropy) and external fields (DC field and mi- ferred to polyethylene bags. Each sample was homogenized, frozen ◦ crowave field). Once the precession frequency matches that of the at −20 C, and freeze-dried prior to analysis. incident microwave radiation, i.e., ωL = ωmw , resonance occurs and the sample absorbs microwave radiation as the magnetic moments 2.2. Sedimentary sulfur and organic carbon precess at maximum amplitude. In a FMR spectrum, the resonance Carbon and sulfur contents were determined using an ele- event is recorded as the absorption of microwaves that results in a mental analyzer (including an acidification module and furnace) resonance field, as a function of the external magnetic field. When coupled to an infrared detector (Analytik Jena multiEA 4000). To- the resonance condition is fulfilled, the absorption exhibits a max- tal inorganic carbon content was quantified using an acidification