The chemical speciation of iron in the north-east Atlantic Ocean

Boyé, Marie; Aldrich, Annette; Berg, Constant M.G. van den; Jong, Jeroen de; Nirmaier, Hans; Veldhuis, Marcel J.W.; Timmermans, Klaas R.; Baar, H. J. W. de

doi:10.1016/j.dsr.2005.12.015

Cited by 58 publications

(54 citation statements)

References 76 publications

(118 reference statements)

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“…Between titrations the cups were rinsed briefly with Milli-Q. The iron complexing capacity determination of deep Pacific water (1000 m) was not affected by interference from the Fe-HS because of its low concentration and was measured onboard ship, as before (Van Den Berg 2006).…”

Section: Methodsmentioning

confidence: 99%

“…The bromate stock solution contained 0.4 mol L 21 bromate (AnalaR, BDH). Contaminating iron in the bromate and buffer solutions was removed by adsorption on MnO 2 and filtration (Van Den Berg 2006).…”

Section: Methodsmentioning

confidence: 99%

“…Iron complexation with marine HS in seawater has not been determined. Iron is known to occur organically complexed in seawater (Gledhill and Van Den Berg 1994;Rue and Bruland 1995;Boye et al 2006), but the identity of the ligand has not been established.…”

mentioning

confidence: 99%

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Evidence for geochemical control of iron by humic substances in seawater

Laglera

Berg

2009

Limnology & Oceanography

261

308

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A new method, based on the direct detection of iron-humic substance (HS) species by cathodic stripping voltammetry (CSV), is used to determine the iron binding capacity and complex stability of fulvic acid (FA), humic acid (HA), and the natural HS in the seawater. The FA binds 16.7 6 2.0 nmol iron (Fe) (mg FA) 21 , whereas the HA and the marine HS bind 32 6 2.2 nmol Fe (mg FA) 21 . The complex stabilities are (log K9 Fe9HS values) 10.6 for FA and 11.1 for HA and coastal HS. Measurements of coastal waters (Irish Sea) show that the HS occur in a widespread fashion, the HS concentration decreasing with increasing salinity and occurring at levels of 400 (at salinity 30) to 70 (at salinity 34) mg L 21 . A sample from the deep Pacific was found to contain 36 mg HS L 21 , amounting to 4% of the dissolved organic matter. Comparative measurement of the total iron complexing capacity by CSV with competitive ligand exchange showed that the natural HS can account for the entire ligand concentration in the shallow coastal and deep ocean waters tested. Measurements of the iron solubility showed that FA added to seawater and the HS in coastal waters maintain iron in solution at a level just below the iron binding capacity. The preliminary data for the open ocean indicate that the same may be true for HS in deep ocean waters. The data are consistent with a mechanism by which iron is transported from land to sea, associated with land-derived HS.Humic substances (HS) are ubiquitous hydrophobic components of the natural organic matter present in soil and aquatic environments that consist predominantly of polyphenols and benzoic/carboxylic acids (Buffle 1990). HS are operationally divided into humic acids (HAs) and fulvic acids ( Previous work has shown that HS in seawater can be determined at good sensitivity by cathodic stripping voltammetry (CSV), which takes advantage of adsorption of the complex on the mercury drop electrode as a concentration step prior to the CSV scan; bromate is added to enhance the sensitivity through a catalytic effect (Laglera et al. 2007). A very similar procedure (Obata and Van Den Berg 2001) is used to determine iron in seawater by means of CSV in the presence of a specific adsorptive ligand (2,3-dihydroxynaphthalene; DHN). The iron (Fe)-HS peak occurs at ,20.6 V, at nearly the same potential as the peak for Fe-DHN. The CSV response for FA (Suwannee River FA) and HA (SRHA) standards in ultraviolet (UV)-digested seawater in the presence of bromate was found to be the same as that for HS in natural waters (fresh, estuarine, and coastal waters), indicating that FA and HA are good model compounds for the natural HS.HS and iron are known to co-precipitate at the lowsalinity end of estuaries (Sholkovitz and Copland 1981), removing more than 99% of the dissolved iron and lowering its concentration from 0.5-10 mmol L 21 , which is typical for freshwaters (Nagai et al. 2007), to the 1-20 nmol L 21 range found in end-estuarine and coastal waters (Sanudo-Wilhelmy et al. 1996;Buck and Bruland 2007). The...

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Evidence for geochemical control of iron by humic substances in seawater

Laglera

Berg

2009

Limnology & Oceanography

261

308

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“…In the deep ocean, about half of the dissolved iron is colloidal, with a generally greater fraction in the surface layer. This is the essential paradox presented by iron -it behaves like a micronutrient yet has a very short oceanic residence time because of Reproduced from data published by Wu et al [88] (c) Vertical profile of strong ligand L 1 concentrations determined by Boye et al [89] at their station 10, 37.00.54 • N, 22.59.55 • W in the North-eastern Atlantic.…”

Section: The Provenance Of Ligandsmentioning

confidence: 99%

“…For example, Fig. 2c shows the vertical distribution of strong Fe-binding ligand L 1 in the North-eastern Atlantic determined by electrochemical titrations by Boye et al [89] This would seem to make it unlikely that L 1 can represent siderophore-like compounds, which have relatively low molecular mass (300-1000 Da), [72] even though the apparent stability complexes of the L 1 ligands, and siderophores, are very similar. However, these contradictory observations can be resolved if the siderophores, upon release into seawater by microbes, become strongly associated with organic colloids, as recently suggested by Buck et al [90] Again, we will return to this important point later on.…”

Section: The Provenance Of Ligandsmentioning

confidence: 99%

Iron-binding ligands and their role in the ocean biogeochemistry of iron

2007

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Environmental context. It is now well accepted that iron is an essential micronutrient for phytoplankton growth in many areas of the global ocean, even though this element is present in seawater in extremely low abundance. It is also known that most of the iron in seawater is present as complexes formed with ligands of natural organic matter whose nature and origin remain largely unknown. Here we consider how these iron-complexing ligands might have evolved during geological time, what factors may have given rise to their presence and the possible roles that they play in iron biogeochemistry.Abstract. Current knowledge about the role of iron-binding organic ligands in the ocean and their role in determining the biogeochemistry of this biologically active element has been summarised. Some electrochemical measurements suggest the presence of at least two ligand types, a strong binding ligand L 1 found mainly in the mixed layer and a weaker ligand L 2 found mainly in deep water. Speciation of Fe III is dominated by L 1 in the mixed layer and L 2 in the deep ocean. There is some evidence that L 1 is siderophore-like and is specifically generated by marine microbes (i.e. heterotropic bacteria and cyanobacteria). We suggest that this is a specific biological mechanism for sequestering iron in the mixed layer that developed early in the ocean's history (Archaean period, 2500-3500 million years BP), whereas the more ubiquitous L 2 ligand only arose at the close of the Proterozoic (500-2500 million years BP) when eukaryotic organisms evolved to switch on the ocean's biological pump, allowing L 2 ligands to form from the oxidation of sinking biological particles. This development coincided with the complete oxygenation of the ocean's interior which removed the iron-binding sulfide ion and allowed maintenance of the ocean's iron inventory. These speculations are accompanied by various suggestions about avenues for future research to better understand iron biogeochemistry.

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Humic substances may control dissolved iron distributions in the global ocean: Implications from numerical simulations

Misumi

Lindsay

Moore³

et al. 2013

Global Biogeochemical Cycles

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[1] This study used an ocean general circulation model to simulate the marine iron cycle in an investigation of how simulated distributions of weak iron-binding ligands would be expected to control dissolved iron concentrations in the ocean, with a particular focus on deep ocean waters. The distribution of apparent oxygen utilization was used as a proxy for humic substances that have recently been hypothesized to account for the bulk of weak iron-binding ligands in seawater. Compared to simulations using a conventional approach with homogeneous ligand distributions, the simulations that incorporated spatially variable ligand concentrations exhibited substantial improvement in the simulation of global dissolved iron distributions as revealed by comparisons with available field data. The improved skill of the simulations resulted largely because the spatially variable ligand distributions led to a more reasonable basin-scale variation of the residence time of iron when present at high concentrations. The model results, in conjunction with evidence from recent field studies, suggest that humic substances play an important role in the iron cycle in the ocean.

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The chemical speciation of iron in the north-east Atlantic Ocean

Cited by 58 publications

References 76 publications

Evidence for geochemical control of iron by humic substances in seawater

Evidence for geochemical control of iron by humic substances in seawater

Iron-binding ligands and their role in the ocean biogeochemistry of iron

Humic substances may control dissolved iron distributions in the global ocean: Implications from numerical simulations

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