Non‐Chained, Non‐Interacting, Stable Single‐Domain Magnetite Octahedra in Deep‐Sea Red Clay: A New Type of Magnetofossil?

Abstract

Magnetofossils, fossils of bacterial magnetosomes preserved in sediments and sedimentary rocks, are potential environmental proxies. Their widespread occurrence and ferromagnetism offer particular advantages. Magnetic bacteria and magnetofossils have been found in environments where few other fossils exist

Understanding the Role of Biogenic Magnetite in Geomagnetic Paleointensity Recording: Insights From Ontong Java Plateau Sediments

“…The difference in these contributions is greater in the deeper part of the core, where biogenic magnetite in the high‐coercivity window contributes up to 40% of the total remanent magnetization. The relative proportion of biogenic magnetite that we calculated should be considered as a minimum estimate because magnetosomes in multistranded configurations and in bent or fold‐collapsed chains can yield vertical spreads that are nearly symmetrical around the central ridge in FORC diagrams (Amor et al., 2022; Berndt et al., 2020; Chang et al., 2019; Inoue et al., 2021; Li et al., 2012; Usui & Yamazaki, 2021), which is counted as the terrigenous component in our calculation. The relative contributions of biogenic magnetite to the remanent magnetization in both coercivity windows increase with depth, which is consistent with the downcore k ARM /SIRM increase, and indicates an increasing relative abundance of biogenic magnetite.…”

“…Terrigenous magnetic minerals have been recognized as paleointensity signal recorders in RPI investigations for decades. Recently, biogenic magnetite and silicate‐hosted magnetic inclusions have also been recognized as stable, single‐domain (SD) carriers of NRM, and their roles in RPI recording have been studied extensively (Amor et al., 2022; Chang et al., 2021; Chang, Roberts, et al., 2016; Chen et al., 2017; Hong et al., 2019; Ouyang et al., 2014; Paterson et al., 2013; Roberts et al., 2012; Usui & Yamazaki, 2021; Yamazaki, 2008, 2009; Yamazaki et al., 2013; Yamazaki & Solheid, 2011).…”

Influence of Magnetofossils on Paleointensity Estimations Inferred From Principal Component Analyses of First‐Order Reversal Curve Diagrams for Sediments From the Western Equatorial Pacific

“…In addition, the comparison of the reconstructed FORC diagrams at PC scores (0, 2,000) and (0, −2,000) suggests that the contributions of extremely low coercivity near the origin increase with lower PC2 scores. These might represent nonchained isolated magnetofossils (Usui & Yamazaki, 2021). On the other hand, the contributions of the broad background component are similar (Figure 8a), which may explain the absence of the correlation between the k ARM /SIRM ratio and the PC2 score (Figure 8b).…”

“…It is considered that the FORC-PCA method can reduce the ambiguity of magnetofossil proportion estimations compared with the k ARM /SIRM ratio. Furthermore, information on bending and/or collapse of biogenic magnetite chains in sediments and differences in the morphology of biogenic magnetite can also be obtained from FORC diagrams (Berndt et al, 2020;Chang et al, 2019;Usui & Yamazaki, 2021;Wagner et al, 2021;Yamazaki et al, 2020), which may also influence RPI estimations. In this study, we use three sediment cores taken from the western equatorial Pacific, in which large differences in the proportion of magnetofossils to terrigenous magnetic minerals are expected.…”

Metagenomic and Microscopic Analysis of Magnetotactic Bacteria in Tangyin Hydrothermal Field of Okinawa Trough

“…According to these two basic characteristics, combined with the size, crystallographic structure, and composition of the magnetosomes, TEM can be used to identify magnetofossils effectively (Kopp and Kirschvink, 2008;Li et al, 2020a). Previous studies found that biogenic magnetite was distributed widely in deep-sea sediments (Petersen et al, 1986;Yamazaki et al, 2019;He and Pan, 2020;Usui and Yamazaki, 2021), and the proportions of bulletshaped magnetofossils increased in relatively reductive and less oxic environments, while isotropic magnetofossils dominated in relatively oxic environments (Hesse, 1994;Yamazaki and Kawahata, 1998;Yamazaki and Shimono, 2013;He and Pan, 2020;Lu et al, 2021). Recently, the known extent of MTB diversity has undergone a significant expansion due to the identification of magnetosome gene cluster (MGC)-containing genomes and studies screening for sequences homologous to known MGC genes (Lin et al, 2020;Uzun et al, 2020).…”