Molybdenum evidence for expansive sulfidic water masses in ~750Ma oceans

Dahl, Tais W.; Canfield, Donald E.; Rosing, Minik T.; Gordon, Gwyneth W.; Knoll, Andrew H.; Anbar, Ariel D.

doi:10.1016/j.epsl.2011.09.016

Cited by 106 publications

(66 citation statements)

References 71 publications

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“…In the modern oceans, the balance between oxic and anoxic removal pathways yields a seawater δ 98/95 Mo value of 2.3‰, the highest known in Earth history. Lower δ 98/95 Mo values will be expected with more euxinic removal down to values of between 0.4‰ to 0.7‰, representing the range between the crustal average (0.4‰) and modern river water input to the ocean (0.7‰,) (46,48). In Gabon, enrichments in Mo concentration are found in both of the well established anoxic intervals (Fig.…”

Section: Relative Oxygenmentioning

confidence: 92%

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Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Canfield

Ngombi-Pemba

Hammarlund

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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123

139

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The oxygen content of Earth's atmosphere has varied greatly through time, progressing from exceptionally low levels before about 2.3 billion years ago, to much higher levels afterward. In the absence of better information, we usually view the progress in Earth's oxygenation as a series of steps followed by periods of relative stasis. In contrast to this view, and as reported here, a dynamic evolution of Earth's oxygenation is recorded in ancient sediments from the Republic of Gabon from between about 2,150 and 2,080 million years ago. The oldest sediments in this sequence were deposited in well-oxygenated deep waters whereas the youngest were deposited in euxinic waters, which were globally extensive. These fluctuations in oxygenation were likely driven by the comings and goings of the Lomagundi carbon isotope excursion, the longest-lived positive δ 13 C excursion in Earth history, generating a huge oxygen source to the atmosphere. As the Lomagundi event waned, the oxygen source became a net oxygen sink as Lomagundi organic matter became oxidized, driving oxygen to low levels; this state may have persisted for 200 million years.GOE | Paleoproterozoic | marine chemistry | Mo isotope | trace metal

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Section: Relative Oxygenmentioning

confidence: 92%

“…Therefore, the heaviest δ 98/95 Mo values are usually assumed to best reflect the seawater composition (45)(46)(47). In the modern oceans, the balance between oxic and anoxic removal pathways yields a seawater δ 98/95 Mo value of 2.3‰, the highest known in Earth history.…”

Section: Relative Oxygenmentioning

confidence: 99%

Oxygen dynamics in the aftermath of the Great Oxidation of Earth’s atmosphere

Canfield

Ngombi-Pemba

Hammarlund

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

123

139

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“…In this equation, k is a reaction coefficient that relates the burial flux to the seawater concentration. For a strictly first-order model, (36), this kind of first-order mass balance approach to specifying removal fluxes is a specific variant of the more generalized case:…”

Section: Interpreting the Enrichment Record: Model For Global Mass Bamentioning

confidence: 99%

Proterozoic ocean redox and biogeochemical stasis

Reinhard

Planavsky

Robbins

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

447

407

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The partial pressure of oxygen in Earth's atmosphere has increased dramatically through time, and this increase is thought to have occurred in two rapid steps at both ends of the Proterozoic Eon (∼2.5-0.543 Ga). However, the trajectory and mechanisms of Earth's oxygenation are still poorly constrained, and little is known regarding attendant changes in ocean ventilation and seafloor redox. We have a particularly poor understanding of ocean chemistry during the mid-Proterozoic (∼1.8-0.8 Ga). Given the coupling between redoxsensitive trace element cycles and planktonic productivity, various models for mid-Proterozoic ocean chemistry imply different effects on the biogeochemical cycling of major and trace nutrients, with potential ecological constraints on emerging eukaryotic life. Here, we exploit the differing redox behavior of molybdenum and chromium to provide constraints on seafloor redox evolution by coupling a large database of sedimentary metal enrichments to a mass balance model that includes spatially variant metal burial rates. We find that the metal enrichment record implies a Proterozoic deep ocean characterized by pervasive anoxia relative to the Phanerozoic (at least ∼30-40% of modern seafloor area) but a relatively small extent of euxinic (anoxic and sulfidic) seafloor (less than ∼1-10% of modern seafloor area). Our model suggests that the oceanic Mo reservoir is extremely sensitive to perturbations in the extent of sulfidic seafloor and that the record of Mo and chromium enrichments through time is consistent with the possibility of a Mo-N colimited marine biosphere during many periods of Earth's history.paleoceanography | geobiology

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“…The trace element molybdenum, preserved in black shales, can be a useful redox proxy of the ancient ocean (Algeo and Maynard, 2004;Dahl et al, 2011;Scott et al, 2008;Scott and Lyons, 2012;Tribovillard et al, 2006). In the modern oxygenated ocean, Mo is the most abundant transition metal (∼105 nM) (Collier, 1985;Lyons et al, 2009) and exists primarily as molybdate (MoO 4 2− ), with a residence time of ∼0.8 Myr (Emerson and Huested, 1991;Morford and Emerson, 1999).…”

Section: Molybdenum Geochemistrymentioning

confidence: 99%