A sulfidic driver for the end-Ordovician mass extinction

Emma U. Hammarlund, Tais Wittchen Dahl, David A.T. Harper, David P.G. Bond, Arne T. Nielsen, Christian J. Bjerrum, Niels H. Schovsbo, Hans P. Schoenlaub, Jan A. Zalasiewicz, Donald Eugene Canfield

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

Resumé

The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in S-34 in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats. (C) 2012 Elsevier B.V. All rights reserved.
OriginalsprogEngelsk
TidsskriftProceedings of the National Academy of Sciences of the United States of America
Vol/bind331–332
Sider (fra-til)128-139
ISSN0027-8424
DOI
StatusUdgivet - 2012

Fingeraftryk

mass extinction
Ordovician
Hirnantian
extinction
pyrite
continental shelf
sea level
oxygenation
sulfur isotope
ocean
habitat loss
nutrient cycling
molybdenum
transgression
glaciation
carbon isotope
deep water
water column
geochemistry
organic carbon

Citer dette

Hammarlund, Emma U. ; Dahl, Tais Wittchen ; Harper, David A.T. ; Bond, David P.G. ; Nielsen, Arne T. ; Bjerrum, Christian J. ; Schovsbo, Niels H. ; Schoenlaub, Hans P. ; Zalasiewicz, Jan A. ; Canfield, Donald Eugene. / A sulfidic driver for the end-Ordovician mass extinction. I: Proceedings of the National Academy of Sciences of the United States of America. 2012 ; Bind 331–332. s. 128-139.
@article{d20d0325f9144ad3bab9e6a81f7e1422,
title = "A sulfidic driver for the end-Ordovician mass extinction",
abstract = "The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in 34S in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats.",
author = "Hammarlund, {Emma U.} and Dahl, {Tais Wittchen} and Harper, {David A.T.} and Bond, {David P.G.} and Nielsen, {Arne T.} and Bjerrum, {Christian J.} and Schovsbo, {Niels H.} and Schoenlaub, {Hans P.} and Zalasiewicz, {Jan A.} and Canfield, {Donald Eugene}",
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doi = "10.1016/j.epsl.2012.02.024",
language = "English",
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pages = "128--139",
journal = "Proceedings of the National Academy of Sciences of the United States of America",
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Hammarlund, EU, Dahl, TW, Harper, DAT, Bond, DPG, Nielsen, AT, Bjerrum, CJ, Schovsbo, NH, Schoenlaub, HP, Zalasiewicz, JA & Canfield, DE 2012, 'A sulfidic driver for the end-Ordovician mass extinction', Proceedings of the National Academy of Sciences of the United States of America, bind 331–332, s. 128-139. https://doi.org/10.1016/j.epsl.2012.02.024

A sulfidic driver for the end-Ordovician mass extinction. / Hammarlund, Emma U.; Dahl, Tais Wittchen; Harper, David A.T.; Bond, David P.G.; Nielsen, Arne T.; Bjerrum, Christian J.; Schovsbo, Niels H.; Schoenlaub, Hans P.; Zalasiewicz, Jan A.; Canfield, Donald Eugene.

I: Proceedings of the National Academy of Sciences of the United States of America, Bind 331–332, 2012, s. 128-139.

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

TY - JOUR

T1 - A sulfidic driver for the end-Ordovician mass extinction

AU - Hammarlund, Emma U.

AU - Dahl, Tais Wittchen

AU - Harper, David A.T.

AU - Bond, David P.G.

AU - Nielsen, Arne T.

AU - Bjerrum, Christian J.

AU - Schovsbo, Niels H.

AU - Schoenlaub, Hans P.

AU - Zalasiewicz, Jan A.

AU - Canfield, Donald Eugene

PY - 2012

Y1 - 2012

N2 - The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in 34S in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats.

AB - The end-Ordovician extinction consisted of two discrete pulses, both linked, in various ways, to glaciation at the South Pole. The first phase, starting just below the Normalograptus extraordinarius Zone, particularly affected nektonic and planktonic species, while the second pulse, associated with the Normalograptus persculptus Zone, was less selective. Glacially induced cooling and oxygenation are two of many suggested kill mechanisms for the end-Ordovician extinction, but a general consensus is lacking. We have used geochemical redox indicators, such as iron speciation, molybdenum concentrations, pyrite framboid size distribution and sulfur isotopes to analyze the geochemistry in three key Hirnantian sections. These indicators reveal that reducing conditions were occasionally present at all three sites before the first pulse of the end-Ordovician extinction, and that these conditions expanded towards the second pulse. Even though the N. extraordinarius Zone appears to have been a time of oxygenated deposition, pyrite is significantly enriched in 34S in our sections as well as in sections reported from South China. This suggests a widespread reduction in marine sulfate concentrations, which we attribute to an increase in pyrite burial during the early Hirnantian. The S-isotope excursion coincides with a major positive carbon isotope excursion indicating elevated rates of organic carbon burial as well. We argue that euxinic conditions prevailed and intensified in the early Hirnantian oceans, and that a concomitant global sea level lowering pushed the chemocline deeper than the depositional setting of our sites. In the N. persculptus Zone, an interval associated with a major sea level rise, our redox indicators suggests that euxinic conditions, and ferruginous in some places, encroached onto the continental shelves. In our model, the expansion of euxinic conditions during the N. extraordinarius Zone was generated by a reorganization of nutrient cycling during sea level fall, and we argue, overall, that these dynamics in ocean chemistry played an important role for the end-Ordovician mass extinction. During the first pulse of the extinction, euxinia and a steepened oxygen gradient in the water column caused habitat loss for deep-water benthic and nektonic organisms. During the second pulse, the transgression of anoxic water onto the continental shelves caused extinction in shallower habitats.

U2 - 10.1016/j.epsl.2012.02.024

DO - 10.1016/j.epsl.2012.02.024

M3 - Journal article

VL - 331–332

SP - 128

EP - 139

JO - Proceedings of the National Academy of Sciences of the United States of America

JF - Proceedings of the National Academy of Sciences of the United States of America

SN - 0027-8424

ER -