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Magnetic enhancement of Baltic Sea sapropels by greigite magnetofossils

Reinholdsson, Maja LU ; Snowball, Ian LU ; Zillen, L.; Lenz, Conny LU and Conley, Daniel LU (2013) In Earth and Planetary Science Letters 366. p.137-150
Abstract
Magnetotactic bacteria (MTB) are known to biosynthesise single-domain magnetite (Fe3O4) for geomagnetic navigation and their relict magnetosomes (called magnetofossils) can control the magnetic properties of lake and marine sediments. Magnetotactic bacteria also produce greigite (Fe3S4) magnetosomes but, compared to those made of magnetite, relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles. We studied the magnetic properties of sediment cores from two basins (the North Central Baltic Proper and eastern Gotland Basin) that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels, which are a signal of past... (More)
Magnetotactic bacteria (MTB) are known to biosynthesise single-domain magnetite (Fe3O4) for geomagnetic navigation and their relict magnetosomes (called magnetofossils) can control the magnetic properties of lake and marine sediments. Magnetotactic bacteria also produce greigite (Fe3S4) magnetosomes but, compared to those made of magnetite, relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles. We studied the magnetic properties of sediment cores from two basins (the North Central Baltic Proper and eastern Gotland Basin) that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels, which are a signal of past occurrences of anoxia and hypoxia in the Baltic Sea. Magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive X-ray spectrometry and we identified only single-domain greigite (Fe3S4) particles with a mean size of 55 x 75 nm, which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane. The degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss-on-ignition data, which indicates a link between the production of greigite magnetosomes, organic matter supply and preservation and redox conditions. The coercive force of collections of non-interacting greigite magnetofossils is similar to 13 mT, which is considerably lower than the magnetite counterparts (similar to 30 mT) and strictly non-bacterial and larger greigite single-domain grains (similar to 60 mT). The values of the interparametric ratios of SIRM/chi, chi(ARm)/SIRM and chi(ARm)/chi that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite. The presence of bacterial greigite, which is easily detected by magnetic measurements, forms a proxy for hypoxia and anoxia, thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the Baltic Sea have changed over time. (C) 2013 Elsevier B.V. All rights reserved. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
greigite, magnetosomes, biomineralisation, sediment, hypoxia, Baltic Sea
in
Earth and Planetary Science Letters
volume
366
pages
137 - 150
publisher
Elsevier
external identifiers
  • wos:000319177100013
  • scopus:84875656996
ISSN
1385-013X
DOI
10.1016/j.epsl.2013.01.029
language
English
LU publication?
yes
id
44fbff8f-0197-4ed5-bff8-9797959b8da8 (old id 3935655)
date added to LUP
2013-07-15 10:27:11
date last changed
2019-05-14 01:07:50
@article{44fbff8f-0197-4ed5-bff8-9797959b8da8,
  abstract     = {Magnetotactic bacteria (MTB) are known to biosynthesise single-domain magnetite (Fe3O4) for geomagnetic navigation and their relict magnetosomes (called magnetofossils) can control the magnetic properties of lake and marine sediments. Magnetotactic bacteria also produce greigite (Fe3S4) magnetosomes but, compared to those made of magnetite, relatively little is known about the sedimentary environments where they are produced and the magnetic properties of the preserved particles. We studied the magnetic properties of sediment cores from two basins (the North Central Baltic Proper and eastern Gotland Basin) that currently experience hypoxia and we discovered the magnetic enhancement of older laminated sapropels, which are a signal of past occurrences of anoxia and hypoxia in the Baltic Sea. Magnetic concentrates extracted from the laminated sapropels were characterised by transmission electron microscopy and energy dispersive X-ray spectrometry and we identified only single-domain greigite (Fe3S4) particles with a mean size of 55 x 75 nm, which we interpret as magnetofossils due to diagnostic chains of individual particles separated by an intact dividing membrane. The degree of magnetic enhancement in the laminated sapropels has a positive relationship with loss-on-ignition data, which indicates a link between the production of greigite magnetosomes, organic matter supply and preservation and redox conditions. The coercive force of collections of non-interacting greigite magnetofossils is similar to 13 mT, which is considerably lower than the magnetite counterparts (similar to 30 mT) and strictly non-bacterial and larger greigite single-domain grains (similar to 60 mT). The values of the interparametric ratios of SIRM/chi, chi(ARm)/SIRM and chi(ARm)/chi that we obtain for our greigite magnetofossils overlap with those previously considered to be diagnostic of magnetosomal magnetite. The presence of bacterial greigite, which is easily detected by magnetic measurements, forms a proxy for hypoxia and anoxia, thus aiding the palaeoenvironmental interpretation of how oxygen conditions in the Baltic Sea have changed over time. (C) 2013 Elsevier B.V. All rights reserved.},
  author       = {Reinholdsson, Maja and Snowball, Ian and Zillen, L. and Lenz, Conny and Conley, Daniel},
  issn         = {1385-013X},
  keyword      = {greigite,magnetosomes,biomineralisation,sediment,hypoxia,Baltic Sea},
  language     = {eng},
  pages        = {137--150},
  publisher    = {Elsevier},
  series       = {Earth and Planetary Science Letters},
  title        = {Magnetic enhancement of Baltic Sea sapropels by greigite magnetofossils},
  url          = {http://dx.doi.org/10.1016/j.epsl.2013.01.029},
  volume       = {366},
  year         = {2013},
}