Molybdenum(VI) speciation in sulfidic waters:

Erickson, Britt E.; Helz, George R.

doi:10.1016/s0016-7037(99)00423-8

Cited by 586 publications

(142 citation statements)

References 40 publications

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“…The sensitivity of sedimentary Mo content to redox fluctuations is due to the conversion of the relatively inert molybdate ion (MoO 2− 4 ) in seawater to a series of particlereactive thiomolybdates (MoO x S 4−x ) under exposure to hydrogen sulfide (H 2 S). Where the concentration of H 2 S aq exceeds ∼ 11 µM, the so-called sulfide switch is activated and a quantitative conversion to tetrathiomolybdate MoS 2− 4 may occur (Helz et al, 1996;Erickson and Helz, 2000), triggering effective fixation of Mo in association with Fe-S phases (Helz et al, 1996(Helz et al, , 2011O'Connor et al, 2015) and organic matter (Helz et al, 1996;Algeo and Lyons, 2006;Dahl et al, 2017). In addition, Mo is reduced from oxidation state (VI) to (IV) during burial in sediments (Dahl et al, 2013).…”

Section: Molybdenum Contentmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment. Here we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated the depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented and, in addition to gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. Alongside the anthropogenic nutrient input, the progressive deoxygenation since the beginning of the 1900s was fueled by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s. We find no evidence of similar anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality.

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Section: Molybdenum Contentmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

et al. 2018

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“…3 ) on the reaction pathway towards the formation of tetrathiomolybdate (MoS 2− 4 ). [42] It has also been proposed that this sulfidation does not follow first order kinetics and that a three-fold increase in H 2 S concentration may result in a 100-fold change in reaction rates. [42] Furthermore, the sulfidic forms have been shown to be more susceptible to scavenging.…”

Section: In Situ Profilesmentioning

confidence: 99%

“…[42] It has also been proposed that this sulfidation does not follow first order kinetics and that a three-fold increase in H 2 S concentration may result in a 100-fold change in reaction rates. [42] Furthermore, the sulfidic forms have been shown to be more susceptible to scavenging. [43] Recently, evidence for the analogous intermediates of (oxy)thioarsenates (AsO x S 3− 3−x , x = 0-3) has been presented.…”

Section: In Situ Profilesmentioning

confidence: 99%

High-resolution two-dimensional quantitative analysis of phosphorus, vanadium and arsenic, and qualitative analysis of sulfide, in a freshwater sediment

2008

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Environmental context. Chemical characterisation of sediment microniches can reveal diagenetic processes that may not be detected by larger-scale analysis. With the development of a new preparation method for a binding phase gel, the technique of diffusive gradients in thin films has been used to demonstrate links between the diagenesis of sulfide, phosphorus, vanadium and arsenic at microniches. Knowledge of these processes may improve predictions of past deposition climates where trace elements are considered as paleoredox proxies. Abstract.Recently introduced techniques that can provide two-dimensional images of solution concentrations in sediments for multiple analytes have revealed discrete sites of geochemical behaviour different from the average for that depth (microniches). We have developed a new preparation method for a binding phase, incorporated in a hydrogel, for the diffusive gradients in thin films (DGT) technique. It allows co-analysis of sulfide and the reactive forms of phosphorus, vanadium and arsenic in the porewaters at the surface of the device. This gel, when dried and analysed using laser ablation mass spectrometry, allows the acquisition of high-resolution sub-millimetre-scale data. The binding phase was deployed within a DGT device in a sediment core collected from a productive lake, Esthwaite Water (UK). Localised removal of phosphate and vanadium from the porewaters has been demonstrated at a microniche of local sulfide production. The possible removal processes, including bacterial uptake and reduction of vanadate to insoluble V III by sulfide, are discussed. Understanding processes occurring at this scale may allow improved prediction of pollutant fate and better prediction of past climates where trace metals are used as paleoredox proxies.

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“…Indeed, total sulfide concentrations of > 100 µM have been reported to prevail in the uppermost centimeters of the sediment column within the SMTZ in an analogous setting in the coastal Baltic Sea . Assuming a salinity and temperature of 5.6 and 9 ºC, respectively (Virtasalo et al, 10 2005) and a pH of 6.6 (our unpublished data) at the sediment-water interface, this total sulfide concentration corresponds to H2Saq concentration of > 70 µM (calculated with R package AquaEnv, Hoffmann et al, 2010), clearly exceeding the requirement of 11 µM H2Saq for the activation of the sulfide-switch (Helz, et al, 1996;Erickson and Helz, 2000). The annual accumulation rate of Mo is expected to be controlled by the duration of the late summer period when the SMTZ is located closest to the sediment surface (Adelson et al, 2001;Helz and Adelson, 2013).…”

Section: Progressive Intensification Of Hypoxia During the Modern Warmentioning

confidence: 68%

“…The sensitivity of sedimentary Mo content to redox fluctuations is due to the conversion of the relatively inert molybdate ion (MoO4 2-) in seawater to a series of particle-reactive thiomolybdates (MoOxS4-x) under exposure to hydrogen sulfide (H2S). Where the concentration of H2Saq exceeds ~ 11 µM, the so-called sulfide-switch is activated and a quantitative conversion to tetrathiomolybdate MoS4 2-5 may occur (Helz et al, 1996;Erickson and Helz, 2000), triggering effective fixation of Mo in association with Fe-S phases (Helz, et al, 1996(Helz, et al, , 2011O´Connor et al, 2015) and organic matter (Helz et al, 1996;Algeo and Lyons 2006;Dahl et al, 2017). In addition, Mo is reduced from oxidation state (VI) to (IV) during burial in sediments (Dahl et al, 2013).…”

Section: Molybdenum Contentmentioning

confidence: 99%

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century

Jokinen¹,

Virtasalo²,

Jilbert³

et al. 2018

Preprint

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Abstract. The anthropogenically forced expansion of coastal hypoxia is a major environmental problem affecting coastal ecosystems and biogeochemical cycles throughout the world. The Baltic Sea is a semi-enclosed shelf sea whose central deep basins have been highly prone to deoxygenation during its Holocene history, as shown previously by numerous paleoenvironmental studies. However, long-term data on past fluctuations in the intensity of hypoxia in the coastal zone of the Baltic Sea are largely lacking, despite the significant role of these areas in retaining nutrients derived from the catchment.Here 5 we present a 1500-year multiproxy record of near-bottom water redox changes from the coastal zone of the northern Baltic Sea, encompassing the climatic phases of the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA), and the Modern Warm Period (MoWP). Our reconstruction shows that although multicentennial climate variability has modulated depositional conditions and delivery of organic matter (OM) to the basin the modern aggravation of coastal hypoxia is unprecedented, and besides gradual changes in the basin configuration, it must have been forced by excess human-induced nutrient loading. The 10 progressive deoxygenation since the beginning of 1900s was originally triggered by the combined effects of gradual shoaling of the basin and warming climate, which amplified sediment focusing and increased the vulnerability to hypoxia. Importantly, the anthropogenic eutrophication of coastal waters in our study area began decades earlier than previously thought, leading to a marked aggravation of hypoxia in the 1950s through fueling primary productivity, while we find no evidence of anthropogenic forcing during the MCA. These results have implications for the assessment of reference conditions for coastal 15 water quality. Furthermore, this study highlights the need for combined use of sedimentological, ichnological, and geochemical proxies in order to robustly reconstruct subtle redox shifts especially in dynamic, non-euxinic coastal settings with strong seasonal contrasts in the bottom water quality. 25Biogeosciences Discuss., https://doi

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Molybdenum(VI) speciation in sulfidic waters:

Cited by 586 publications

References 40 publications

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

High-resolution two-dimensional quantitative analysis of phosphorus, vanadium and arsenic, and qualitative analysis of sulfide, in a freshwater sediment

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century

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Molybdenum(VI) speciation in sulfidic waters:

Cited by 586 publications

References 40 publications

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20th century

High-resolution two-dimensional quantitative analysis of phosphorus, vanadium and arsenic, and qualitative analysis of sulfide, in a freshwater sediment

A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20&lt;sup&gt;th&lt;/sup&gt; century

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A 1500-year multiproxy record of coastal hypoxia from the northern Baltic Sea indicates unprecedented deoxygenation over the 20<sup>th</sup> century