The determination of labile Fe in ferrihydrite by ascorbic acid extraction: Methodology, dissolution kinetics and loss of solubility with age and de-watering

Raiswell, R.; Vu, Hong Phuc; Brinza, Loredana; Benning, Liane G.

doi:10.1016/j.chemgeo.2010.09.002

Cited by 110 publications

(112 citation statements)

References 51 publications

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“…A similar inverse correlation between porewater dFe(II) and hydroxylamine-HCl leachable Fe has been observed in surface sediment from the North Sea, where the leachable Fe pool was also suggested to originate from sub-surface DIR (Henkel et al 2016). The ascorbic acid leach extracts easily reducible ferrihydrite, which is the first amorphous Fe oxyhydroxide phase precipitated due to Fe(II) oxidation (Raiswell et al 2010). The hydroxylamine-HCl leach extracts ferrihydrite as well as other reactive Fe phases that have been argued to be bioavailable (Berger et al 2008).…”

Section: Discussionsupporting

confidence: 65%

“…In order to examine phase associations of Fe and Mn in solid sediment phases, two leaching schemes were applied to one core per season: (i) an ascorbic acid leach (Raiswell et al 2010) was applied, to extract the easily reducible oxide phases, such as amorphous ferrihydrite, but not the more crystalline oxide phases, and (ii) an acetic acid-hydroxylamineHCl (H-HCl) leach (Berger et al 2008), that extracts other amorphous oxide phases as well as ferrihydrite. Fe and Mn in the leach solutions were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, iCAP6000 Series, Thermo Scientific).…”

Section: Methodsmentioning

confidence: 99%

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Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

et al. 2017

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Shelf sediments underlying temperate and oxic waters of the Celtic Sea (NW European Shelf) were found to have shallow oxygen penetrations depths from late spring to late summer (2.2-5.8 mm below seafloor) with the shallowest during/after the spring-bloom (mid-April to mid-May) when the organic carbon content was highest. Sediment porewater dissolved iron (dFe,\0.15 lm) mainly ([85%) consisted of Fe(II) and gradually increased from 0.4 to 15 lM at the sediment surface to *100-170 lM at about 6 cm depth. During the late spring this Fe(II) was found to be mainly present as soluble Fe(II) ([85% sFe, \0.02 lm). Sub-surface dFe(II) maxima were enriched in light isotopes (d 56 Fe -2.0 to -1.5%), which is attributed to dissimilatory iron reduction (DIR) during the bacterial decomposition of organic matter. As porewater Fe(II) was oxidised to insoluble Fe(III) in the surface sediment layer, residual Fe(II) was further enriched in light isotopes (down to -3.0%). Ferrozine-reactive Fe(II) was found in surface porewaters and in overlying core top waters, and was highest in the late spring period. Shipboard experiments showed that depletion of bottom water Responsible Editor: Martin Solan.Electronic supplementary material The online version of this article (doi:10.1007/s10533-017-0309-x) contains supplementary material, which is available to authorized users. 49-67 DOI 10.1007/s10533-017-0309-x oxygen in late spring can lead to a substantial release of Fe(II). Reoxygenation of bottom water caused this Fe(II) to be rapidly lost from solution, but residual dFe(II) and dFe(III) remained (12 and 33 nM) after [7 h. Iron(II) oxidation experiments in core top and bottom waters also showed removal from solution but at rates up to 5-times slower than predicted from theoretical reaction kinetics. These data imply the presence of ligands capable of complexing Fe(II) and supressing oxidation. The lower oxidation rate allows more time for the diffusion of Fe(II) from the sediments into the overlying water column. Modelling indicates significant diffusive fluxes of Fe(II) (on the order of 23-31 lmol m -2 day -1 ) are possible during late spring when oxygen penetration depths are shallow, and pore water Fe(II) concentrations are highest. In the water column this stabilised Fe(II) will gradually be oxidised and become part of the dFe(III) pool. Thus oxic continental shelves can supply dFe to the water column, which is enhanced during a small period of the year after phytoplankton bloom events when organic matter is transferred to the seafloor. This input is based on conservative assumptions for solute exchange (diffusion-reaction), whereas (bio)physical advection and resuspension events are likely to accelerate these solute exchanges in shelf-seas.

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Section: Discussionsupporting

confidence: 65%

Section: Methodsmentioning

confidence: 99%

Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

et al. 2017

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“…Whilst dried sediment exhibits a rapid decline in FeAsc wt. % (Raiswell et al, 2010), it is not clear how storage of ice or wet sediments affects FeAsc.…”

Section: Discussionmentioning

confidence: 99%

“…1) for comparative purposes. FeAsc leaches were conducted on wet sediment as per Raiswell et al (2010), with leached Fe determined by measuring absorbance (λ = 562 nm) before and after the addition of ferrozine (as detailed in Supplementary Information Methods).…”

Section: Methodsmentioning

confidence: 99%

The heterogeneous nature of Fe delivery from melting icebergs

Hopwood¹,

Cantoni²,

Clarke³

et al. 2017

Geochem. Persp. Let.

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The micronutrient iron (Fe) can be transported from marine terminating glaciers to the ocean by icebergs. There are however few observations of iceberg Fe content, and the flux of Fe from icebergs to the offshore surface ocean is poorly constrained. Here we report the dissolved Fe (DFe), total dissolvable Fe (TdFe) and ascorbic acid extractable Fe (FeAsc) sediment content of icebergs from Kongsfjorden, Svalbard. The concentrations of DFe (range 0.63 nM -536 nM, mean 37 nM, median 6.5 nM) and TdFe (range 46 nM -57 µM, mean 3.6 µM, median 144 nM) both demonstrated highly heterogeneous distributions and there was no significant correlation between these two fractions. FeAsc (range 0.0042 to 0.12 wt. %) was low compared to both previous measurements in Kongsfjorden and to current estimates of the global mean. FeAsc content per volume ice did however, as expected, show a significant relationship with sediment loading (which ranged from < 0.1 -234 g L -1 of meltwater). In the Arctic, icebergs lose their sediment load faster than ice volume due to the rapid loss of basal ice after calving. We therefore suggest that the loss of basal ice is a potent mechanism for the reduction of mean TdFe and FeAsc per volume of iceberg. Delivery of TdFe and FeAsc to the ocean is thereby biased towards coastal waters where, in Kongsfjorden, DFe (18 ± 17 nM) and TdFe (mean 8.1 µM, median 3.7 µM) concentrations were already elevated.

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“…Furthermore, it has been shown that 2-3 % of the Fe within glacial rock flour can be leached into the dissolved size fraction (< 0.2 µm) with ultrapure water; a large proportion of which should be bioavailable (Schroth et al, 2009). It is thought that this dFe is leached from nanoparticulate Fe (oxyhydr)oxides in glacial rock flour over time (Raiswell, 2011;Raiswell et al, 2010) following an exponential decay, so it is possible that this source could be excluded from the < 0.2 µm dissolved fraction, but included in the 1-53 µm particulate fraction presented here. This is especially true of nanoparticulate Fe that is attached to the surface of larger sediment grains as has been observed previously in glacial sediments (Shaw et al, 2011).…”

Section: What Are the Sources Of Particulate Trace Metals Over The Plmentioning

confidence: 99%

Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

et al. 2015

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Abstract. The KEOPS2 project aims to elucidate the role of natural Fe fertilisation on biogeochemical cycles and ecosystem functioning, including quantifying the sources and processes by which iron is delivered in the vicinity of the Kerguelen Archipelago, Southern Ocean. The KEOPS2 process study used an upstream high-nutrient, low-chlorophyll (HNLC), deep water (2500 m), reference station to compare with a shallow (500 m), strongly fertilised plateau station and continued the observations to a downstream, bathymetrically trapped recirculation of the Polar Front where eddies commonly form and persist for hundreds of kilometres into the Southern Ocean. Over the Kerguelen Plateau, mean particulate (1-53 µm) Fe and Al concentrations (pFe = 13.4 nM, pAl = 25.2 nM) were more than 20-fold higher than at an offshore (lower-productivity) reference station (pFe = 0.53 nM, pAl = 0.83 nM). In comparison, over the plateau dissolved Fe levels were only elevated by a factor of ∼ 2. Over the Kerguelen Plateau, ratios of pMn / pAl and pFe / pAl resemble basalt, likely originating from glacial/fluvial inputs into shallow coastal waters. In downstream, offshore deep-waters, higher pFe / pAl, and pMn / pAl ratios were observed, suggesting loss of lithogenic material accompanied by retention of pFe and pMn. Biological uptake of dissolved Fe and Mn and conversion into the biogenic particulate fraction or aggregation of particulate metals onto bioaggregates also increased these ratios further in surface waters as the bloom developed within the recirculation structure. While resuspension of shelf sediments is likely to be one of the important mechanisms of Fe fertilisation over the plateau, fluvial and glacial sources appear to be important to areas downstream of the island. Vertical profiles within an offshore recirculation feature associated with the Polar Front show pFe Published by Copernicus Publications on behalf of the European Geosciences Union. P. van der Merwe et al.: Kerguelen Plateau: particulate trace metal sourcesand pMn levels that were 6-fold and 3.5-fold lower, respectively, than over the plateau in surface waters, though still 3.6-fold and 1.7-fold higher respectively than the reference station. Within the recirculation feature, strong depletions of pFe and pMn were observed in the remnant winter water (temperature-minimum) layer near 175 m, with higher values above and below this depth. The correspondence between the pFe minima and the winter water temperature minima implies a seasonal cycle is involved in the supply of pFe into the fertilised region. This observed association is indicative of reduced supply in winter, which is counterintuitive if sediment resuspension and entrainment within the mixed layer is the primary fertilising mechanism to the downstream recirculation structure. Therefore, we hypothesise that lateral transport of pFe from shallow coastal waters is strong in spring, associated with snow melt and increased runoff due to rainfall, drawdown through summer and reduced supply in winter when snowfal...

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The determination of labile Fe in ferrihydrite by ascorbic acid extraction: Methodology, dissolution kinetics and loss of solubility with age and de-watering

Cited by 110 publications

References 51 publications

Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

Stability of dissolved and soluble Fe(II) in shelf sediment pore waters and release to an oxic water column

The heterogeneous nature of Fe delivery from melting icebergs

Sourcing the iron in the naturally fertilised bloom around the Kerguelen Plateau: particulate trace metal dynamics

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