Role of biogenic silica in the removal of iron from the Antarctic seas

Ingall, Ellery D.; Diaz, Julia M.; Longo, Amelia F.; Oakes, Michelle; Finney, Lydia; Vogt, Stefan; Lai, Barry; Yager, Patricia L.; Twining, Benjamin S.; Brandes, Jay

doi:10.1038/ncomms2981

Cited by 65 publications

(37 citation statements)

References 35 publications

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“…38-39,42 This possible distortion in the 1 s →3 d pre-edge transitions during electron transfer (Fe(III) → Fe(II)) in the octahedral coordination environment, may explain the intensity gain observed for Fit_Fe(II&III) as a result of their quadrupolar character. 38,40-41 This finding corroborates the initial EPR observations. Furthermore, the Fe(III)CaM and Fit_Fe(II&III) spectra appear to align with the standard Fe(III) spectrum, both in the 1 s →4 s (main-edge) and in the 1 s →3 d (pre-edge) transition regions, demonstrating a 100% Fe(III) composition in the pre-phenol-dosed sample (Fe(III)CaM) with no distortion in the coordination environment.…”

Section: Resultssupporting

confidence: 90%

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Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

Nwosu

Roy

Cruz

et al. 2016

Environ. Sci.: Processes Impacts

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Environmentally persistent free radicals (EPFRs) have been found at a number of Superfund sites, with EPFRs being formed via a proposed redox process at ambient environmental conditions. The possibility of such a redox process taking place at ambient environmental conditions is studied utilizing a surrogate soil system of phenol and iron(III)-exchanged calcium montmorillonite clay, Fe(III)CaM. Sorption of phenol by the Fe(III)CaM is demonstrated by Fourier-transformed infra-red (FT-IR) spectroscopy, as evidenced by the peaks between 1345 cm−1 and 1595 cm−1, and at lower frequencies between 694 cm−1 and 806 cm−1, as well as X-ray diffraction (XRD) spectroscopy, as shown by an increase in interlayer spacing within Fe(III)CaM. The formation and characterization of the EPFRs is determined by electron paramagnetic resonance (EPR) spectroscopy, showing phenoxyl-type radical with a g-factor of 2.0034 and ΔHp-p of 6.1 G at an average concentration of 7.5 × 1017 spins/g. EPFRs lifetime data are indicative of oxygen and water molecules being responsible for EPFR decay. The change in the oxidation state of the iron redox center is studied by X-ray absorption near-edge structure (XANES) spectroscopy, showing that 23% of the Fe(III) is reduced to Fe(II). X-ray photoemission spectroscopy (XPS) results confirm the XANES results. These findings, when combined with the EPFR concentration data, demonstrate that the stoichiometry of the EPFR formation under the conditions of this study is 1.5 × 10−2 spins/Fe(II) atom.

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Section: Resultssupporting

confidence: 90%

“…38-42 A significant edge shift from 7125.5 eV to 7124.0 eV and 7122 eV to 7120 eV at the centre and the base of the K-edge towards the Fe(II) energy for the phenol-dosed sample (Fit_Fe(II&III)), when compared to the Fe(III) standard, provides further strong evidence of the change in oxidation state of iron from Fe(III) to Fe(II). 38-41 …”

Section: Resultsmentioning

confidence: 99%

Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

Nwosu

Roy

Cruz

et al. 2016

Environ. Sci.: Processes Impacts

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“…In this study, the database of mineral standards was run on the same beamline [63]. An iterative process was used to refine the standard database used to model the spectra.…”

Section: Data Reduction and Analysismentioning

confidence: 99%

Enhanced Iron Solubility at Low pH in Global Aerosols

et al. 2018

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Abstract:The composition and oxidation state of aerosol iron were examined using synchrotron-based iron near-edge X-ray absorption spectroscopy. By combining synchrotron-based techniques with water leachate analysis, impacts of oxidation state and mineralogy on aerosol iron solubility were assessed for samples taken from multiple locations in the Southern and the Atlantic Oceans; and also from Noida (India), Bermuda, and the Eastern Mediterranean (Crete). These sampling locations capture iron-containing aerosols from different source regions with varying marine, mineral dust, and anthropogenic influences. Across all locations, pH had the dominating influence on aerosol iron solubility. When aerosol samples were approximately neutral pH, iron solubility was on average 3.4%; when samples were below pH 4, the iron solubility increased to 35%. This observed aerosol iron solubility profile is consistent with thermodynamic predictions for the solubility of Fe(III) oxides, the major iron containing phase in the aerosol samples. Source regions and transport paths were also important factors affecting iron solubility, as samples originating from or passing over populated regions tended to contain more soluble iron. Although the acidity appears to affect aerosol iron solubility globally, a direct relationship for all samples is confounded by factors such as anthropogenic influence, aerosol buffer capacity, mineralogy and physical processes.

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“…Preliminary work by Emoto et al (2013) shows marine diatom BSi has elemental concentrations at levels close to the concentrations of the continental crust, which is much higher than expected. Cell-specific analysis using synchrotron radiation demonstrates that diatoms can accumulate excess quantities of the micronutrient Fe (Nuester et al 2012), and this productivity is key in removing Fe from surface waters of the Southern Ocean (Ingall et al 2013). Dillon and Evans (2001) and Nürnberg and Dillon (1993) present Fe budgets for a series of Canadian lakes draining the Cambrian shield where Fe retention seems to be important, hinting at a similar freshwater mechanism.…”

Section: Implications For Weathering Rate Calculationmentioning

confidence: 99%

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

et al. 2014

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Weathering of silicate minerals releases dissolved silicate (DSi) to the soil-vegetation system. Accumulation and recycling of this DSi by terrestrial ecosystems creates a pool of reactive Si on the continents that buffers DSi export to the ocean. Human perturbations to the functioning of the buffer have been a recent research focus, yet a common assumption is that the continental Si cycle is at steadystate. However, we have no good idea of the timescales of ecosystem Si pool equilibration with their environments. A review of modelling and geochemical considerations suggests the modern continental Si cycle is in fact characterised in the longterm by an active accumulation of reactive Si, at least partially attributable to lakes and reservoirs. These lentic systems accumulate Si via biological conversion of DSi to biogenic silica (BSi). An analysis of new and published data for nearly 700 systems is presented to assess their contribution to the accumulating continental pool. Surface sediment BSi concentrations (n = 692) vary between zero and [60 % SiO 2 by weight, apparently independently of lake size, location or water chemistry. Using sediment core BSi accumulation rates (n = 109), still no relationships are found with lake or catchment parameters. However, issues associated with single-core accumulation rates should in any case preclude their use in elemental accumulation calculations. Based on lake/reservoir mass-balances (n = 34), our best global-scale estimate of combined lake and reservoir Si retention is 1.53 TMol year -1 , or 21-27 % of river DSi export. Again, no scalable relationships are apparent, suggesting Si retention is a complex process that varies from catchment to catchment. The lake Si sink has implications for estimation of weathering flux generation from river chemistry. The size of the total continental Si pool is poorly constrained, as is its accumulation rate, but lakes clearly contribute substantially. A corollary to this emerging understanding is that the flux and isotopic composition of DSi delivered to the ocean has likely varied over time, partly mediated by a fluctuating continental pool, including in lakes.

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Role of biogenic silica in the removal of iron from the Antarctic seas

Cited by 65 publications

References 35 publications

Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

Formation of environmentally persistent free radical (EPFR) in iron(iii) cation-exchanged smectite clay

Enhanced Iron Solubility at Low pH in Global Aerosols

Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration

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