Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans
Anoxic and iron-rich oceanic conditions prevailed throughout most of the Archean and Proterozoic (4000 to c.540 million years ago, Ma), but the oceans are hypothesised to have become progressively oxygen-rich during the Ediacaran–Cambrian transition interval, coincident with the rise of animal life....
Published in: | Earth and Planetary Science Letters |
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2019
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Online Access: | https://risweb.st-andrews.ac.uk/portal/en/researchoutput/uranium-isotope-evidence-for-an-expansion-of-anoxia-in-terminal-ediacaran-oceans(6800cda3-85cc-4bce-a90b-15b457cb74d6).html https://doi.org/10.1016/j.epsl.2018.10.045 |
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ftunstandrewcris:oai:risweb.st-andrews.ac.uk:publications/6800cda3-85cc-4bce-a90b-15b457cb74d6 2023-05-15T18:43:56+02:00 Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans Tostevin, Rosalie Clarkson, Matthew O. Gangl, Sophie Shields, Graham A. Wood, Rachel A. Bowyer, Fred Penny, Amelia Stirling, Claudine H. 2019-01-15 https://risweb.st-andrews.ac.uk/portal/en/researchoutput/uranium-isotope-evidence-for-an-expansion-of-anoxia-in-terminal-ediacaran-oceans(6800cda3-85cc-4bce-a90b-15b457cb74d6).html https://doi.org/10.1016/j.epsl.2018.10.045 eng eng info:eu-repo/semantics/restrictedAccess Tostevin , R , Clarkson , M O , Gangl , S , Shields , G A , Wood , R A , Bowyer , F , Penny , A & Stirling , C H 2019 , ' Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans ' , Earth and Planetary Science Letters , vol. 506 , pp. 104-112 . https://doi.org/10.1016/j.epsl.2018.10.045 Redox Uranium Ediacaran Oxygen Animals article 2019 ftunstandrewcris https://doi.org/10.1016/j.epsl.2018.10.045 2022-06-02T07:52:22Z Anoxic and iron-rich oceanic conditions prevailed throughout most of the Archean and Proterozoic (4000 to c.540 million years ago, Ma), but the oceans are hypothesised to have become progressively oxygen-rich during the Ediacaran–Cambrian transition interval, coincident with the rise of animal life. We utilise the uranium isotope ratio of seawater ( 238 U/ 235 U; reformulated as δ 238 U), an effective tracer of oceanic redox conditions, as a proxy for changes in the global proportion of anoxic seafloor. We present a new δ 238 U dataset for carbonate rocks from the Lower Nama Group, Namibia, deposited in a shelf ramp succession during the terminal Neoproterozoic (∼550 to ∼547 Ma). These data capture a transition from δ 238 U similar to the modern ocean towards persistently low δ 238 U (average = −0.81 ± 0.06‰). Such low δ 238 U are consistent with enhanced U drawdown from the water column under anoxic conditions, and the preferential export of ‘heavy’ 238 U to sediments following U(VI)–U(IV) reduction. Placing our results into a steady state ocean box model suggests at least a third of the global seafloor was covered by anoxic bottom waters compared with only 0.3% in today's oxygenated oceans. Comparison with δ 238 U from older sediments deposited in other basins further supports an expansion of anoxic bottom waters towards the end of the Ediacaran. Our data are consistent with an emerging picture of a dominantly anoxic Ediacaran ocean punctuated by brief ocean oxygenation events. In the Nama Group, the transition towards globally widespread anoxic conditions post-dates the first appearance of both skeletal metazoans and soft-bodied fauna of the Nama Assemblage. This suggests that the global expansion of anoxia did not coincide with the decline of the Ediacaran biota, or drive the biotic turnover between the White Sea and Nama Assemblages. The impact of this global redox change on metazoan ecosystems is unclear, since the expansion of anoxia, if contained mainly within deeper waters, may not have impinged ... Article in Journal/Newspaper White Sea University of St Andrews: Research Portal White Sea Earth and Planetary Science Letters 506 104 112 |
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Open Polar |
collection |
University of St Andrews: Research Portal |
op_collection_id |
ftunstandrewcris |
language |
English |
topic |
Redox Uranium Ediacaran Oxygen Animals |
spellingShingle |
Redox Uranium Ediacaran Oxygen Animals Tostevin, Rosalie Clarkson, Matthew O. Gangl, Sophie Shields, Graham A. Wood, Rachel A. Bowyer, Fred Penny, Amelia Stirling, Claudine H. Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
topic_facet |
Redox Uranium Ediacaran Oxygen Animals |
description |
Anoxic and iron-rich oceanic conditions prevailed throughout most of the Archean and Proterozoic (4000 to c.540 million years ago, Ma), but the oceans are hypothesised to have become progressively oxygen-rich during the Ediacaran–Cambrian transition interval, coincident with the rise of animal life. We utilise the uranium isotope ratio of seawater ( 238 U/ 235 U; reformulated as δ 238 U), an effective tracer of oceanic redox conditions, as a proxy for changes in the global proportion of anoxic seafloor. We present a new δ 238 U dataset for carbonate rocks from the Lower Nama Group, Namibia, deposited in a shelf ramp succession during the terminal Neoproterozoic (∼550 to ∼547 Ma). These data capture a transition from δ 238 U similar to the modern ocean towards persistently low δ 238 U (average = −0.81 ± 0.06‰). Such low δ 238 U are consistent with enhanced U drawdown from the water column under anoxic conditions, and the preferential export of ‘heavy’ 238 U to sediments following U(VI)–U(IV) reduction. Placing our results into a steady state ocean box model suggests at least a third of the global seafloor was covered by anoxic bottom waters compared with only 0.3% in today's oxygenated oceans. Comparison with δ 238 U from older sediments deposited in other basins further supports an expansion of anoxic bottom waters towards the end of the Ediacaran. Our data are consistent with an emerging picture of a dominantly anoxic Ediacaran ocean punctuated by brief ocean oxygenation events. In the Nama Group, the transition towards globally widespread anoxic conditions post-dates the first appearance of both skeletal metazoans and soft-bodied fauna of the Nama Assemblage. This suggests that the global expansion of anoxia did not coincide with the decline of the Ediacaran biota, or drive the biotic turnover between the White Sea and Nama Assemblages. The impact of this global redox change on metazoan ecosystems is unclear, since the expansion of anoxia, if contained mainly within deeper waters, may not have impinged ... |
format |
Article in Journal/Newspaper |
author |
Tostevin, Rosalie Clarkson, Matthew O. Gangl, Sophie Shields, Graham A. Wood, Rachel A. Bowyer, Fred Penny, Amelia Stirling, Claudine H. |
author_facet |
Tostevin, Rosalie Clarkson, Matthew O. Gangl, Sophie Shields, Graham A. Wood, Rachel A. Bowyer, Fred Penny, Amelia Stirling, Claudine H. |
author_sort |
Tostevin, Rosalie |
title |
Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
title_short |
Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
title_full |
Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
title_fullStr |
Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
title_full_unstemmed |
Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans |
title_sort |
uranium isotope evidence for an expansion of anoxia in terminal ediacaran oceans |
publishDate |
2019 |
url |
https://risweb.st-andrews.ac.uk/portal/en/researchoutput/uranium-isotope-evidence-for-an-expansion-of-anoxia-in-terminal-ediacaran-oceans(6800cda3-85cc-4bce-a90b-15b457cb74d6).html https://doi.org/10.1016/j.epsl.2018.10.045 |
geographic |
White Sea |
geographic_facet |
White Sea |
genre |
White Sea |
genre_facet |
White Sea |
op_source |
Tostevin , R , Clarkson , M O , Gangl , S , Shields , G A , Wood , R A , Bowyer , F , Penny , A & Stirling , C H 2019 , ' Uranium isotope evidence for an expansion of anoxia in terminal Ediacaran oceans ' , Earth and Planetary Science Letters , vol. 506 , pp. 104-112 . https://doi.org/10.1016/j.epsl.2018.10.045 |
op_rights |
info:eu-repo/semantics/restrictedAccess |
op_doi |
https://doi.org/10.1016/j.epsl.2018.10.045 |
container_title |
Earth and Planetary Science Letters |
container_volume |
506 |
container_start_page |
104 |
op_container_end_page |
112 |
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1766234468849287168 |