Shallow water anoxia in the Mesoproterozoic ocean: Evidence from the Bashkir Meganticlinorium, Southern Urals

Doyle, Katherine A.; Poulton, Simon W.; Newton, Robert J.; Подковыров, В. Н.; Bekker, Andrey

doi:10.1016/j.precamres.2018.09.001

Cited by 40 publications

(19 citation statements)

References 110 publications

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“…For example, the “Canfield ocean” featured anoxic and euxinic (sulfide‐rich) deep‐ocean conditions through the Proterozoic, relieved only by a relatively unidirectional rise in oxygen during the late Ediacaran (Canfield, ). Broader stratigraphic and geographic coverage, including onshore–offshore transects, as well as new redox proxies have provided a more nuanced view of Proterozoic redox with much less stability (Diamond & Lyons, ; Doyle, Poulton, Newton, Podkovyrov, & Bekker, ; He et al, ; Li, Cheng, et al, ; Li, Zhang, et al, ; Planavsky, Cole, et al, ; Planavsky, Slack, et al, ; Sperling et al, ; Tang, Shi, Wang, & Jiang, ). Any attempts to model Proterozoic redox conditions are similarly left with the conclusion that the marine redox landscape was patchy and complicated (Reinhard, Planavsky, Olson, Lyons, & Erwin, ).…”

Section: Myths About Oxygen and The Rise Of Animalsmentioning

confidence: 99%

On the co‐evolution of surface oxygen levels and animals

et al. 2020

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Few topics in geobiology have been as extensively debated as the role of Earth's oxygenation in controlling when and why animals emerged and diversified. All currently described animals require oxygen for at least a portion of their life cycle. Therefore, the transition to an oxygenated planet was a prerequisite for the emergence of animals. Yet, our understanding of Earth's oxygenation and the environmental requirements of animal habitability and ecological success is currently limited; estimates for the timing of the appearance of environments sufficiently oxygenated to support ecologically stable populations of animals span a wide range, from billions of years to only a few million years before animals appear in the fossil record. In this light, the extent to which oxygen played an important role in controlling when animals appeared remains a topic of debate. When animals originated and when they diversified are separate questions, meaning either one or both of these phenomena could have been decoupled from oxygenation. Here, we present views from across this interpretive spectrum—in a point–counterpoint format—regarding crucial aspects of the potential links between animals and surface oxygen levels. We highlight areas where the standard discourse on this topic requires a change of course and note that several traditional arguments in this “life versus environment” debate are poorly founded. We also identify a clear need for basic research across a range of fields to disentangle the relationships between oxygen availability and emergence and diversification of animal life.

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Section: Myths About Oxygen and The Rise Of Animalsmentioning

confidence: 99%

On the co‐evolution of surface oxygen levels and animals

et al. 2020

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“…Lake Cadagno is a shallow weakly euxinic system (Canfield et al, 2010), which may make it a reasonable analogue for past shallow-water systems (e.g. Doyle et al, 2018) where oxidised iron compounds from riverine runoff and atmospheric dust are deposited onto the upper ocean and sink to anoxic waters where phototrophic organisms reside.…”

Section: Comparison Of Water Column δ 56 Fe Profiles To Other Lake Systems and The Black Seamentioning

confidence: 99%

Iron isotope transformations in the meromictic Lake Cadagno

Ellwood

Hassler

Moisset

et al. 2019

Geochimica et Cosmochimica Acta

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The iron isotope composition of sedimentary deposits is a key tool for tracking changes in the biogeochemistry and redox conditions of modern and geologically ancient aquatic systems. The use of iron isotopes to reconstruct oxic, anoxic and redox conditions is based on iron isotope fractionation associated with the iron(II)-iron(III) redox reaction and the formation of various iron oxy, hydroxy and sulfur species. However, the degree of iron isotope fractionation varies within the sedimentary record, and the processes leading to isotope fractionation within aquatic systems also vary. Here we investigate iron isotope fractionation within the water column of Lake Cadagno, Switzerland. Lake Cadagno is a 21 m deep alpine meromictic lake that is permanently stratified. It has two chemically distinct water layers: an oxic mixolimnion separated by a narrow chemocline from an anoxic monimolimnion. The chemocline is located across a narrow band between 10 and 13.5 m and is defined by steep chemical gradients in dissolved oxygen, redox potential, nutrients (nitrite + nitrate, ammonia), dissolved and particulate trace metals (iron and manganese) and sulfur species. Iron isotope determination ( 56 Fe/ 54 Fe ratio; expressed as δ 56 Fe) of both dissolved (δ 56 Fedissolved) and particulate (δ 56 Feparticulate) iron reveals a sharp transition within the chemocline with a heavy δ 56 Fedissolved value (+0.75 ‰) at 11.5 m and light δ 56 Fedissolved value (-0.61 ‰) below at 12 m.The large shift in δ 56 Fedissolved occurs where anoxygenic phototrophic bacteria become abundant.Modelling of the dissolved iron isotope fractionation within the chemocline produced fractionation factors of -0.60 ‰ (kinetic model) and -1.52 ‰ (equilibrium model) assuming a two-step process involving iron oxidation followed by precipitation. Changes in the isotope composition of particulate iron with depth are subtler to that of dissolved iron, with slightly lighter values (-0.18 ‰) above the chemocline and slightly heavier values (+0.13 ‰) below. The production of reduced iron(II) within and below the chemocline is likely coupled to dissimilatory iron(III) reduction and dissolution reactions associated with sinking iron(III) oxy and hydroxy species. These processes lead to a peak in dissolved iron concentrations at 12.5 m. The decline in dissolved iron concentration below this depth and its change in isotope composition is consistent with the formation of iron sulphide species, e.g. mackinawite, under mildly euxinic conditions. Overall our results indicate that variations in δ 56 Fedissolved likely involve a combination of biotic and abiotic processes with biological mixing enhancing the rate at which iron(II) is transferred across the chemocline. The observed isotope transformation of dissolved iron across the chemocline of Lake Cadagno may make it a reasonable analogue to past shallow-water systems with mild euxinia.

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“…However, a compilation of iron speciation data from deeper Mesoproterozoic settings revealed dominantly ferruginous conditions (Planavsky et al, 2011)-a conclusion that has been confirmed by subsequent iron speciation studies (Sperling et al, 2015;Beghin et al, 2017;Doyle et al, 2018;Zhang et al, 2018). It seems, then, that the Mesoproterozoic oceans may have been weakly redoxbuffered with frequent fluctuation in space and time between euxinic and ferruginous conditions (Planavsky et al, 2018), with evidence for at least weakly and intermittently oxic conditions in the surface waters (e.g., Hardisty et al, 2017).…”

Section: Local Redox Conditionsmentioning

confidence: 87%

“…Despite potential linkages between oxygen and evolution, the redox state of Mesoproterozoic atmosphere and oceans remains poorly constrained. Previous iron speciation studies have reported mostly locally anoxic and iron-rich (ferruginous) conditions in subsurface waters (Planavsky et al, 2011;Sperling et al, 2015;Doyle et al, 2018;Zhang et al, 2018)-however, both oxic and sulfidic conditions have also been reported in epeiric sea, open shelf, and basinal settings (e.g., Shen et al, 2002;Gilleaudeau and Kah, 2013;Sperling et al, 2014;Cox et al, 2016). Predominantly low marine oxygen levels are also evidenced by muted enrichment of redox-sensitive trace metals in many Mesoproterozoic-aged shales (e.g., Scott et al, 2008), as well as by both molybdenum (Arnold et al, 2004;Kendall et al, 2011) and, potentially, uranium isotope (Gilleaudeau et al, 2019) data.…”

Section: Introductionmentioning

confidence: 99%