Correlated molybdenum and uranium isotope signatures in modern anoxic sediments: Implications for their use as paleo-redox proxy

Brüske, Annika; Weyer, Stefan; Zhao, Mingyu; Planavsky, Noah J.; Wegwerth, Antje; Neubert, Nadja; Dellwig, Olaf; Lau, Kimberly V.; Lyons, Timothy W.

doi:10.1016/j.gca.2019.11.031

Cited by 74 publications

(68 citation statements)

References 105 publications

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“…5; Brüske et al, 2020). In this model, U reduction rates are proportional to sulphate reduction rates (following Cochran and , and a reactive continuum organic matter remineralization scheme (see Brüske et al, 2020). This exercise illustrates that, even for a constant intrinsic fractionation factor (i.e., representing a single U reduction pathway), the isotopic offset between seawater and anoxic sediments can vary as a function of two factors: the organic matter flux and the sedimentation rate (Fig.…”

Section: The Marine U Isotope Budgetmentioning

confidence: 89%

“…Controls on the variability of ∆anox can be more fully explored using a sediment reactive transport model ( Fig. 5; Brüske et al, 2020). In this model, U reduction rates are proportional to sulphate reduction rates (following Cochran and , and a reactive continuum organic matter remineralization scheme (see Brüske et al, 2020).…”

Section: The Marine U Isotope Budgetmentioning

confidence: 99%

“…The next generation of mass balance models, which will have variable U removal rates and fractionation factors within different settings, is an obvious step forward. For example, reactive transport models predict that varying organic matter fluxes and sedimentation rate will affect the isotope fractionation factor (Brüske et al, 2020;Lau et al, 2020).…”

Section: Future Directionsmentioning

confidence: 99%

“…B. the relationship between the U isotopic composition in final buried sediments and net primary productivity (NPP), with the lines represent varying seawater U isotopic composition. SeeBrüske et al (2020) for the description of the model.…”

mentioning

confidence: 99%

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Uranium isotopes in marine carbonates as a global ocean paleoredox proxy: A critical review

Zhang

Lenton

Rey

et al. 2020

Geochimica et Cosmochimica Acta

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The protracted oxygenation of the ocean-atmosphere system is one of the most fundamental changes to the Earth system through its history. The uranium isotopic composition (238U/235U, denoted as δ238U) of marine carbonates has been developed as a proxy to quantitatively track the timing, duration, and extent of global marine redox chemistry changes. This proxy has been applied to many critical evolutionary intervals in the last decade, significantly advancing our understanding of how life on Earth and its environment have co-evolved through geological history. Successful application of the uranium isotope paleoredox proxy requires a thorough understanding of the marine uranium budget, the processes by which seawater U-isotope signatures are recorded in marine carbonates, and the potential for alteration of these primary signatures by syn-and post-depositional diagenetic processes. Here, we provide a critical review of the U isotope proxy in marine carbonates with a focus on the current problems and areas where future work is needed to further develop this proxy. We also use a recently developed global C-P-U cycle model to illustrate that when the carbon cycle is perturbed by volcanic carbon injections, the ensuing transient relationship between seafloor anoxic area and δ238U can be complex and sometimes counter-intuitive.

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Section: The Marine U Isotope Budgetmentioning

confidence: 89%

Section: The Marine U Isotope Budgetmentioning

confidence: 99%

Section: Future Directionsmentioning

confidence: 99%

mentioning

confidence: 99%

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Uranium isotopes in marine carbonates as a global ocean paleoredox proxy: A critical review

Zhang

Lenton

Rey

et al. 2020

Geochimica et Cosmochimica Acta

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“…The redox sensitive behaviour and associated isotope fractionations of molybdenum (Mo) and uranium (U) have led to a prominent role for their sedimentary and isotope geochemistry in the evaluation of ancient ocean redox conditions. Both elements can show strong authigenic (seawater-derived) enrichment in marine organic carbon-rich sediments, accompanied by distinctive isotope signatures (e.g., Asael et al, 2013;Kendall et al, 2015;Brüske et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Rapid onset of ocean anoxia shown by high U and low Mo isotope compositions of sapropel S1

Andersen¹,

Matthews²,

Bar‐Matthews³

et al. 2020

Geochem. Persp. Let.

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Authigenic uranium isotope compositions of Holocene sapropel S1 (δ 238 U auth = þ 0.10 to þ0.52 ‰; ODP core 967, 2550 mbsl) are significantly higher than the proposed upper boundary (þ0.2 ‰) associated with the transport-porewater diffusion model for sediment uranium uptake. It is shown that these high δ 238 U auth values are compatible with rapid initial slowdown of thermohaline overturning and the development of an anoxic water column. These conditions would favour U uptake in an organic-rich floccule layer overlying the sediment-water interface. The high δ 238 U auth values correlate with low δ 98 Mo auth values (þ0.02 to −0.88 ‰), interpreted to reflect weakly euxinic conditions controlled by thiomolybdate-molybdate solution equilibria. The S1 data contrast markedly with published data from last interglacial sapropel S5 from the same core, which show δ 238 U auth and δ 98 Mo auth characteristics compatible with a restricted euxinic basin due to progressive slowdown in the thermohaline circulation. The U-Mo isotope data for S1 are similar to a range of published palaeosettings. Sapropels are therefore shown to be useful templates for the unravelling of the interplay between productivity and deep water renewal times in ancient settings.

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Inverse Mo versus U isotope correlation of Early Cambrian highly metalliferous black shales in South China indicates synsedimentary metal enrichment from a near-modern ocean

Xu,

Lehmann,

Weyer

et al. 2023

Miner Deposita

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Correlated molybdenum and uranium isotope signatures in modern anoxic sediments: Implications for their use as paleo-redox proxy

Cited by 74 publications

References 105 publications

Uranium isotopes in marine carbonates as a global ocean paleoredox proxy: A critical review

Uranium isotopes in marine carbonates as a global ocean paleoredox proxy: A critical review

Rapid onset of ocean anoxia shown by high U and low Mo isotope compositions of sapropel S1

Inverse Mo versus U isotope correlation of Early Cambrian highly metalliferous black shales in South China indicates synsedimentary metal enrichment from a near-modern ocean

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