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Giant magnetofossils and hyperthermal events

Giant magnetofossils and hyperthermal events
Giant magnetofossils and hyperthermal events
Magnetotactic bacteria biomineralize magnetic minerals with precisely controlled size, morphology, and stoichiometry. These cosmopolitan bacteria are widely observed in aquatic environments. If preserved after burial, the inorganic remains of magnetotactic bacteria act as magnetofossils that record ancient geomagnetic field variations. They also have potential to provide paleoenvironmental information. In contrast to conventional magnetofossils, giant magnetofossils (most likely produced by eukaryotic organisms) have only been reported once before from Paleocene-Eocene Thermal Maximum (PETM; 55.8 Ma) sediments on the New Jersey coastal plain. Here, using transmission electron microscopic observations, we present evidence for abundant giant magnetofossils, including previously reported elongated prisms and spindles, and new giant bullet-shaped magnetite crystals, in the Southern Ocean near Antarctica, not only during the PETM, but also shortly before and after the PETM. Moreover, we have discovered giant bullet-shaped magnetite crystals from the equatorial Indian Ocean during the Mid-Eocene Climatic Optimum (?40 Ma). Our results indicate a more widespread geographic, environmental, and temporal distribution of giant magnetofossils in the geological record with a link to “hyperthermal” events. Enhanced global weathering during hyperthermals, and expanded suboxic diagenetic environments, probably provided more bioavailable iron that enabled biomineralization of giant magnetofossils. Our micromagnetic modelling indicates the presence of magnetic multi-domain (i.e., not ideal for navigation) and single domain (i.e., ideal for navigation) structures in the giant magnetite particles depending on their size, morphology and spatial arrangement. Different giant magnetite crystal morphologies appear to have had different biological functions, including magnetotaxis and other non-navigational purposes. Our observations suggest that hyperthermals provided ideal conditions for giant magnetofossils, and that these organisms were globally distributed. Much more work is needed to understand the interplay between magnetofossil morphology, climate, nutrient availability, and environmental variability.
0012-821X
258-269
Chang, Liao
f526f675-e627-4666-b1c9-3e94029706ee
Roberts, Andrew P.
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Williams, Wyn
d8b0d6be-3729-4126-a3ec-628638b75292
Fitz Gerald, John D.
d3ce84a5-666c-4acc-821b-d3508b3a1af9
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c
Jovane, Luigi
7e165ffb-8e06-4ac1-9c47-d3edf3e0ddd8
Muxworthy, Adrian R.
7fa5c819-b5ca-4354-83df-f9481b16ed1e
Chang, Liao
f526f675-e627-4666-b1c9-3e94029706ee
Roberts, Andrew P.
4f062491-5408-4edb-8dd1-140c6a42e93f
Williams, Wyn
d8b0d6be-3729-4126-a3ec-628638b75292
Fitz Gerald, John D.
d3ce84a5-666c-4acc-821b-d3508b3a1af9
Larrasoaña, Juan C.
6bf2e75f-54a1-42b8-96e0-b80d2462de2c
Jovane, Luigi
7e165ffb-8e06-4ac1-9c47-d3edf3e0ddd8
Muxworthy, Adrian R.
7fa5c819-b5ca-4354-83df-f9481b16ed1e

Chang, Liao, Roberts, Andrew P., Williams, Wyn, Fitz Gerald, John D., Larrasoaña, Juan C., Jovane, Luigi and Muxworthy, Adrian R. (2012) Giant magnetofossils and hyperthermal events. Earth and Planetary Science Letters, 351-352, 258-269. (doi:10.1016/j.epsl.2012.07.031).

Record type: Article

Abstract

Magnetotactic bacteria biomineralize magnetic minerals with precisely controlled size, morphology, and stoichiometry. These cosmopolitan bacteria are widely observed in aquatic environments. If preserved after burial, the inorganic remains of magnetotactic bacteria act as magnetofossils that record ancient geomagnetic field variations. They also have potential to provide paleoenvironmental information. In contrast to conventional magnetofossils, giant magnetofossils (most likely produced by eukaryotic organisms) have only been reported once before from Paleocene-Eocene Thermal Maximum (PETM; 55.8 Ma) sediments on the New Jersey coastal plain. Here, using transmission electron microscopic observations, we present evidence for abundant giant magnetofossils, including previously reported elongated prisms and spindles, and new giant bullet-shaped magnetite crystals, in the Southern Ocean near Antarctica, not only during the PETM, but also shortly before and after the PETM. Moreover, we have discovered giant bullet-shaped magnetite crystals from the equatorial Indian Ocean during the Mid-Eocene Climatic Optimum (?40 Ma). Our results indicate a more widespread geographic, environmental, and temporal distribution of giant magnetofossils in the geological record with a link to “hyperthermal” events. Enhanced global weathering during hyperthermals, and expanded suboxic diagenetic environments, probably provided more bioavailable iron that enabled biomineralization of giant magnetofossils. Our micromagnetic modelling indicates the presence of magnetic multi-domain (i.e., not ideal for navigation) and single domain (i.e., ideal for navigation) structures in the giant magnetite particles depending on their size, morphology and spatial arrangement. Different giant magnetite crystal morphologies appear to have had different biological functions, including magnetotaxis and other non-navigational purposes. Our observations suggest that hyperthermals provided ideal conditions for giant magnetofossils, and that these organisms were globally distributed. Much more work is needed to understand the interplay between magnetofossil morphology, climate, nutrient availability, and environmental variability.

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More information

Published date: 2012
Organisations: Geology & Geophysics

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Local EPrints ID: 344656
URI: https://eprints.soton.ac.uk/id/eprint/344656
ISSN: 0012-821X
PURE UUID: 3e27eeb5-0df5-4f2f-a8d5-5412bbb5ce16

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Date deposited: 26 Oct 2012 09:28
Last modified: 16 Jul 2019 21:50

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Contributors

Author: Liao Chang
Author: Andrew P. Roberts
Author: Wyn Williams
Author: John D. Fitz Gerald
Author: Juan C. Larrasoaña
Author: Luigi Jovane
Author: Adrian R. Muxworthy

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