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“Hypoxic” Silurian oceans suggest early animals thrived in a low-O2 world

Haxen, Emma R. LU ; Schovsbo, Niels H. ; Nielsen, Arne T. ; Richoz, Sylvain LU ; Loydell, David K. ; Posth, Nicole R. ; Canfield, Donald E. and Hammarlund, Emma U. LU (2023) In Earth and Planetary Science Letters 622.
Abstract

Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian... (More)

Atmospheric oxygen (O2) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O2. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian foreland basin. Indeed, even during times of relative oxygenation, ichnological observations indicate that conditions were, at most, very weakly oxic. The results suggest that dissolved O2 was generally scarce in the bottom waters of the extensive Silurian seaway between Baltica and Avalonia, even between Paleozoic “Anoxic Events”. In light of delayed oxygenation of the atmosphere–hydrosphere system, it may be time to consider that early animals were adapted to “hypoxia” and thrived through ∼100 million years of low-O2 conditions after the Cambrian.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
animal evolution, Baltic basin, caledonian foreland basin, ocean oxygenation, redox, Silurian
in
Earth and Planetary Science Letters
volume
622
article number
118416
publisher
Elsevier
external identifiers
  • scopus:85173480893
ISSN
0012-821X
DOI
10.1016/j.epsl.2023.118416
language
English
LU publication?
yes
id
a843aa91-362d-4b45-b4ab-eeee3b6fc5b1
date added to LUP
2023-11-30 15:04:10
date last changed
2023-11-30 15:05:57
@article{a843aa91-362d-4b45-b4ab-eeee3b6fc5b1,
  abstract     = {{<p>Atmospheric oxygen (O<sub>2</sub>) concentrations likely remained below modern levels until the Silurian–Devonian, as indicated by several recent studies. Yet, the background redox state of early Paleozoic oceans remains poorly constrained, hampering our understanding of the relationship between early animal evolution and O<sub>2</sub>. Here, we present a multi-proxy analysis of redox conditions in the Caledonian foreland basin to Baltica from the early to the mid-Silurian. Our results indicate that anoxic to severely hypoxic bottom waters dominated during deposition of the Silurian sediments cored in the Sommerodde-1 well (Bornholm, Denmark), and regional comparison suggests that these conditions persisted across the Baltoscandian foreland basin. Indeed, even during times of relative oxygenation, ichnological observations indicate that conditions were, at most, very weakly oxic. The results suggest that dissolved O<sub>2</sub> was generally scarce in the bottom waters of the extensive Silurian seaway between Baltica and Avalonia, even between Paleozoic “Anoxic Events”. In light of delayed oxygenation of the atmosphere–hydrosphere system, it may be time to consider that early animals were adapted to “hypoxia” and thrived through ∼100 million years of low-O<sub>2</sub> conditions after the Cambrian.</p>}},
  author       = {{Haxen, Emma R. and Schovsbo, Niels H. and Nielsen, Arne T. and Richoz, Sylvain and Loydell, David K. and Posth, Nicole R. and Canfield, Donald E. and Hammarlund, Emma U.}},
  issn         = {{0012-821X}},
  keywords     = {{animal evolution; Baltic basin; caledonian foreland basin; ocean oxygenation; redox; Silurian}},
  language     = {{eng}},
  month        = {{11}},
  publisher    = {{Elsevier}},
  series       = {{Earth and Planetary Science Letters}},
  title        = {{“Hypoxic” Silurian oceans suggest early animals thrived in a low-O<sub>2</sub> world}},
  url          = {{http://dx.doi.org/10.1016/j.epsl.2023.118416}},
  doi          = {{10.1016/j.epsl.2023.118416}},
  volume       = {{622}},
  year         = {{2023}},
}