Sulfidic anoxia in the oceans during the Late Ordovician mass extinctions – insights from molybdenum and uranium isotopic global redox proxies
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Sulfidic anoxia in the oceans during the Late Ordovician mass extinctions – insights from molybdenum and uranium isotopic global redox proxies. / Dahl, Tais W.; Hammarlund, Emma U.; Rasmussen, Christian Mac Ørum; Bond, David P. G.; Canfield, Donald E.
In: Earth-Science Reviews, Vol. 220, 103748, 2021.Research output: Contribution to journal › Review › Research › peer-review
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T1 - Sulfidic anoxia in the oceans during the Late Ordovician mass extinctions – insights from molybdenum and uranium isotopic global redox proxies
AU - Dahl, Tais W.
AU - Hammarlund, Emma U.
AU - Rasmussen, Christian Mac Ørum
AU - Bond, David P. G.
AU - Canfield, Donald E.
N1 - Publisher Copyright: © 2021
PY - 2021
Y1 - 2021
N2 - The Late Ordovician Mass Extinction wiped out 85% of animal species in two phases (LOME1 and LOME2). The kill mechanisms for the extinction phases are debated, but deteriorating climate and the expansion of marine anoxia appear to have been important factors. Nevertheless, the spatial extent and intensity of marine anoxia and its temporal relationship with the extinctions are not well understood. Here, we review existing global paleoredox proxy data based on molybdenum (Mo) and uranium (U) isotopes from four paleocontinents combined with new Mo isotope data from Dob's Linn, Scotland. Individually, these sedimentary records demonstrate significant redox fluctuations, but our coupled dynamic oceanic mass balance model for the evolution of the marine Mo and U cycles reveals that globally expansive ocean anoxia is best constrained by δ238U in carbonates from Anticosti Island that record expansive anoxia during LOME2. In addition, we consider periodic sulfidic anoxia developing in well-ventilated parts of the shallow oceans (e.g. during warmer periods with greater solar insolation) to have produced temporarily high seawater δ98Mo values during LOME1 in accordance with trends to high values observed in the sedimentary records. In this view, oceanic oxygen loss had a causal role during both extinction phases in the Late Ordovician.
AB - The Late Ordovician Mass Extinction wiped out 85% of animal species in two phases (LOME1 and LOME2). The kill mechanisms for the extinction phases are debated, but deteriorating climate and the expansion of marine anoxia appear to have been important factors. Nevertheless, the spatial extent and intensity of marine anoxia and its temporal relationship with the extinctions are not well understood. Here, we review existing global paleoredox proxy data based on molybdenum (Mo) and uranium (U) isotopes from four paleocontinents combined with new Mo isotope data from Dob's Linn, Scotland. Individually, these sedimentary records demonstrate significant redox fluctuations, but our coupled dynamic oceanic mass balance model for the evolution of the marine Mo and U cycles reveals that globally expansive ocean anoxia is best constrained by δ238U in carbonates from Anticosti Island that record expansive anoxia during LOME2. In addition, we consider periodic sulfidic anoxia developing in well-ventilated parts of the shallow oceans (e.g. during warmer periods with greater solar insolation) to have produced temporarily high seawater δ98Mo values during LOME1 in accordance with trends to high values observed in the sedimentary records. In this view, oceanic oxygen loss had a causal role during both extinction phases in the Late Ordovician.
KW - Geochemistry
KW - Global redox proxies
KW - Hirnantian
KW - Paleoenvironment
KW - Stable isotope fractionation
U2 - 10.1016/j.earscirev.2021.103748
DO - 10.1016/j.earscirev.2021.103748
M3 - Review
AN - SCOPUS:85111490611
VL - 220
JO - Earth-Science Reviews
JF - Earth-Science Reviews
SN - 0012-8252
M1 - 103748
ER -
ID: 281282647