The mineral magnetic record of magnetofossils in recent lake sediments of Lake Ely, PA

Magnetic properties of uncultivated magnetotactic bacteria and their contribution to a stratified estuary iron cycle

“…This result is significant for three reasons. First, prior associations of BS-BM and BH-BI with magnetofossils remains speculative because numerical inversion of magnetization curves through which they were originally conceived 19 and continuously presumed 16,[48][49][50][51] has non-unique solutions. In addition, the coercivity distributions (characterized by skewness, median coercivity and dispersion factor) of diverse MTB types found in nature are poorly constrained.…”

“…Third, the skewed coercivity distributions that characterize uncultivated MTB point to the importance of modelling them as such, rather than symmetric distributions, so as to avoid the addition of coercivity distribution components that are not physically meaningful when quantifying the amount of magnetofossils. Both approaches are widely used 19,[50][51][52][53] .…”

“…There are also many known contemporary MTB strains that produce magnetite magnetosomes with aspect ratio o0.4, including all of the strains in the Nitrospirae phylum 35 . Moreover, coercivity component BH-BI have been detected in sediment samples containing putative elongated magnetite magnetosomes 50,51 . These magnetosomes have enhanced shape anisotropy and therefore a higher coercivity 57,58 .…”

Diagenetic Fate of Biogenic Soft and Hard Magnetite in Chemically Stratified Sedimentary Environments of Mamanguá Ría, Brazil

“…Overall, our results provide valuable insights into the stability of biogenic magnetite under reducing conditions and are consistent with a well‐known broader framework for mineral magnetic changes that occur in sediments during progressive diagenesis from oxic through to methanic conditions (e.g., Roberts, ). The relative stabilities of the frequently identified BS and BH components of Egli (, , ) have been discussed frequently in relation to varying diagenetic conditions (e.g., Chang et al, , ; Egli, , , ; Kodama et al, ; Usui et al, ; Yamazaki, ; Yamazaki & Shimono, ). However, inferences about the stability of these magnetite phases is based in all cases on diagenetic zonations based on magnetic properties with none of these studies including downcore pore water chemistry profiles.…”

“…Environmental magnetic studies can be a rapid and reliable way to track the spatial distribution of MTB, which have the potential to enable reconstruction of oxygen gradients in natural environments (Chang et al, ), where other proxies or methods of study are less readily applicable. For example, previous studies have suggested that the frequently identified biogenic soft (BS) and biogenic hard (BH) magnetite types are associated with equant and more elongated morphologies, respectively, and that their abundance varies in accordance with sedimentary oxygen content, where MTB that produce the BH component live in less oxygenated environments (Chang et al, , ; Egli, , , ; Kodama et al, ; Usui et al, ; Yamazaki, ; Yamazaki & Shimono, ). Despite the potential value of such proxy information, magnetic proxies for BS and BH magnetite have not been assessed adequately in relation to direct pore water determinations of sedimentary oxygenation.…”