Iron and manganese shuttle has no effect on sedimentary thallium and vanadium isotope signatures in Black Sea sediments

Chen, Xinming; Li, Siqi; Newby, Sean M.; Lyons, Timothy W.; Wu, Fei; Owens, Jeremy D.

doi:10.1016/j.gca.2021.11.010

Cited by 16 publications

(8 citation statements)

References 97 publications

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“…modern upwelling zones), Mn oxides are unstable and thus inefficiently buried, hindering preservation of a large net positive Tl isotope fractionation effect (average offset of +2.1 epsilon units; Wang et al, 2022). Sediments forming in upwelling zones below bottom waters with especially low O 2 contents oftentimes exhibit no net isotope fractionation effect whatsoever, a phenomenon also observed in all sediments studied to date forming within and below the chemocline of modern anoxic basins (Chen et al, 2022;Fan et al, 2020;Ostrander et al, 2023;Owens et al, 2017).…”

Section: Re Sultsmentioning

confidence: 76%

“…Because the residence time of Tl in seawater today (~18,500 years; Nielsen et al, 2017) exceeds the ocean mixing time (~1000 years), ε 205 Tl SW today is globally homogenous. By contrast, authigenic Tl isotopic contributions (ε 205 Tl A ) leached from modern sediments formed under anoxic bottom waters (Chen et al, 2022; Fan et al, 2020; Ostrander et al, 2023; Owens et al, 2017), and even some sediments formed under O 2 ‐bearing bottom waters with reducing porewaters (Wang et al, 2022), do not fractionate Tl isotopes and thus capture ε 205 Tl SW . By analogy, sedimentary rocks deposited under anoxic conditions can be used to reconstruct variations in ε 205 Tl SW stemming from past changes in global Mn oxide burial (burial equating to long‐term preservation in sediments; evading dissolution on short timescales).…”

Section: Introductionmentioning

confidence: 99%

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Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion

et al. 2023

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Reconstructing the oxygenation history of Earth's oceans during the Ediacaran period (635 to 539 million years ago) has been challenging, and this has led to a polarizing debate about the environmental conditions that played host to the rise of animals. One focal point of this debate is the largest negative inorganic C‐isotope excursion recognized in the geologic record, the Shuram excursion, and whether this relic tracks the global‐scale oxygenation of Earth's deep oceans. To help inform this debate, we conducted a detailed geochemical investigation of two siliciclastic‐dominated successions from Oman deposited through the Shuram Formation. Iron speciation data from both successions indicate formation beneath an intermittently anoxic local water column. Authigenic thallium (Tl) isotopic compositions leached from both successions are indistinguishable from bulk upper continental crust (ε205TlA ≈ −2) and, by analogy with modern equivalents, likely representative of the ancient seawater ε205Tl value. A crustal seawater ε205Tl value requires limited manganese (Mn) oxide burial on the ancient seafloor, and by extension widely distributed anoxic sediment porewaters. This inference is supported by muted redox‐sensitive element enrichments (V, Mo, and U) and consistent with some combination of widespread (a) bottom water anoxia and (b) high sedimentary organic matter loading. Contrary to a classical hypothesis, our interpretations place the Shuram excursion, and any coeval animal evolutionary events, in a predominantly anoxic global ocean.

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Section: Re Sultsmentioning

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion

et al. 2023

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“…This Tl-rich phase was most likely pyrite-a notion that gains strong support from the correlation revealed between authigenic Tl abundances and shale pyrite Fe contents (R 2 = 0.84; Figure 7B). Second, sediments from the three anoxic settings studied thus far using Tl isotopes (Black Sea, Cariaco Basin, and Santa Barbara Basin) always capture the overlying seawater ε 205 Tl value (Owens et al, 2017;Fan et al, 2020;Chen et al, 2022). It is reasonable to assume that, by analogy, our shales deposited under comparable conditions also captured the overlying seawater ε 205 Tl value.…”

Section: Tl Isotope Datamentioning

confidence: 88%

“…By contrast, Fe oxide minerals are unlikely to fractionate Tl isotopes because the likely fractionation mechanism-oxidation of Tl(I) to Tl(III)-does not occur during sorption to Fe oxides (Peacock and Moon 2012). Moreover, neither of the two remaining primary marine Tl outputs today imparts a substantial isotopic fractionation effect; low-temperature oceanic crust alteration imparts only a slight negative isotope fractionation effect (average ε 205 Tl = -7.2; Nielsen et al, 2017), and no isotope fractionation is observed in Tl leached from pyrite from sediments deposited under anoxic bottom waters, presumably because of quantitative Tl transfer to pyrite in these settings (Owens et al, 2017;Fan et al, 2020;Chen et al, 2022).…”

Section: Tl Isotope Proxymentioning

confidence: 99%

Shale Heavy Metal Isotope Records of Low Environmental O2 Between Two Archean Oxidation Events

et al. 2022

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Evidence of molecular oxygen (O2) accumulation at Earth’s surface during the Archean (4.0–2.5 billion years ago, or Ga) seems to increase in its abundance and compelling nature toward the end of the eon, during the runup to the Great Oxidation Event. Yet, many details of this late-Archean O2 story remain under-constrained, such as the extent, tempo, and location of O2 accumulation. Here, we present a detailed Fe, Tl, and U isotope study of shales from a continuous sedimentary sequence deposited between ∼2.6 and ∼2.5 Ga and recovered from the Pilbara Craton of Western Australia (the Wittenoom and Mt. Sylvia formations preserved in drill core ABDP9). We find a progressive decrease in bulk-shale Fe isotope compositions moving up core (as low as δ56Fe = –0.78 ± 0.08‰; 2SD) accompanied by invariant authigenic Tl isotope compositions (average ε205TlA = –2.0 ± 0.6; 2SD) and bulk-shale U isotope compositions (average δ238U = –0.30 ± 0.05‰; 2SD) that are both not appreciably different from crustal rocks or bulk silicate Earth. While there are multiple possible interpretations of the decreasing δ56Fe values, many, to include the most compelling, invoke strictly anaerobic processes. The invariant and near-crustal ε205TlA and δ238U values point even more strongly to this interpretation, requiring reducing to only mildly oxidizing conditions over ten-million-year timescales in the late-Archean. For the atmosphere, our results permit either homogenous and low O2 partial pressures (between 10−6.3 and 10−6 present atmospheric level) or heterogeneous and spatially restricted O2 accumulation nearest the sites of O2 production. For the ocean, our results permit minimal penetration of O2 in marine sediments over large areas of the seafloor, at most sufficient for the burial of Fe oxide minerals but insufficient for the burial of Mn oxide minerals. The persistently low background O2 levels implied by our dataset between ∼2.6 and ∼2.5 Ga contrast with the timeframes immediately before and after, where strong evidence is presented for transient Archean Oxidation Events. Viewed in this broader context, our data support the emerging narrative that Earth’s initial oxygenation was a dynamic process that unfolded in fits-and-starts over many hundreds-of-millions of years.

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“…A possible explanation is that the slow diffusion of dissolved oxygen from the more oxidizing overlying waters and the upward diffusion of dissolved Mn (II) from the pore water of anoxic surface sediments to the sediment-water interface (Ozturk, 1995) cause the oxidation of dissolved Mn (II) and its precipitation as Mn (IV) oxides (Pohl and Hennings, 1999). The Mn enrichment in the surface layers of UN11 resembles concentrations in sediments from suboxic parts of the Black Sea (Kiratli and Ergin, 1996;Chen et al, 2022).…”

Section: Geochemical Findings and Element Interrelationsmentioning

confidence: 99%

Sediment quality assessment in an industrialized Greek coastal marine area (western Saronikos Gulf)

et al. 2023

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Abstract. Eight sediment cores from the coastal marine area of the western Saronikos Gulf have been analysed for grain size and geochemistry. The concentrations of eight metals (Al, Fe, Mn, Cu, Cr, Ni, Pb and Zn) were measured along with total organic carbon (TOC) and carbonate content. The cores are fairly homogeneous in terms of carbonates and the downcore variability of TOC percentage (% TOC) and are characterized by high surficial values that decrease with depth. Metal concentrations from both geological (Al, Mn, Cr, Ni) and anthropogenic origin (Cu, Pb, Zn) are higher in the muddy fraction than in the sand fraction of sediments. The spatial distribution of Al, Fe, Mn, Cu, Pb and Zn in surface sediments presents increasing concentrations from the northeast to the southwest part of the study area and from the shallow to the deeper parts in contrast to Cr and Ni, which are increased in the northern nearshore stations. Based on the vertical distributions, the metal to Al ratios of Cu, Pb and Zn show a constant decrease over depth along most cores, indicating the anthropogenic effects to surface sediments, while Fe/Al is constant. Spearman's correlation analysis performed among the fine-grain metal contents demonstrated a strong positive correlation (r>0.5, p<0.05) between Al, Fe, Mn, Cu, Pb and Zn. The calculated enrichment factors indicate minimal to moderate pollution. The concentrations of Cr at most surface sediments are higher than the “effects range low” (ERL) value (81 mg kg−1) but below the “effects range median” (ERM) value (370 mg kg−1), and the concentrations of Ni are always higher than the ERM value (51.6 mg kg−1). In contrast, the concentrations of Cu, Pb and Zn at most surface sediments are below ERL values. The mean effects range medium quotients (mERMq) of surface sediments, based on the overall metal concentrations, indicated that the surface sediments of most cores are moderately toxic. The levels of Cr, Ni, Mn and Zn at most stations are decreased in 2017, but the concentrations of Pb and Cu are increased in 2017, compared to a previous study of 2007. The concentrations of Cu, Pb and Zn in the surface sediments of the western Saronikos Gulf are lower than levels reported for the inner Saronikos Gulf, Elefsis Bay and other polluted hotspot areas in Greece, owing to a lower degree of urban and industrial development.

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Iron and manganese shuttle has no effect on sedimentary thallium and vanadium isotope signatures in Black Sea sediments

Cited by 16 publications

References 97 publications

Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion

Widespread seafloor anoxia during generation of the Ediacaran Shuram carbon isotope excursion

Shale Heavy Metal Isotope Records of Low Environmental O2 Between Two Archean Oxidation Events

Sediment quality assessment in an industrialized Greek coastal marine area (western Saronikos Gulf)

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