A call for refining the role of humic-like substances in the oceanic iron cycle

Whitby, Hannah; Planquette, Hélène; Cassar, Nicolas; Bucciarelli, Eva; Osburn, Christopher L.; Janssen, David J.; Cullen, Jay T.; González, Aridane G.; Völker, Christoph; Sarthou, Géraldine

doi:10.1038/s41598-020-62266-7

Cited by 52 publications

(67 citation statements)

References 85 publications

(134 reference statements)

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“…Changes in planktonic community composition affect net primary production and overall carbon drawdown, which lead to further alteration of the food web and carbon cycling (Schofield et al, 2017;Joy-Warren et al, 2019;Arrigo et al, 1999;Alderkamp et al, 2012). These and other ongoing changes in the food web will also affect production of dissolved organic carbon (DOC) and thus ligands as they form a fraction of the DOC pool (Gledhill and Buck, 2012;Whitby et al, 2020). Generally, one expects that increased DOC production would lead to more ligands, but the binding strength depends on which molecules are formed (Gledhill and Buck, 2012;Hassler et al, 2017).…”

Section: Implications For Primary Productivitymentioning

confidence: 99%

“…Although EPS are relatively labile macromolecules, they can be present in up to micromolar concentrations in seawater, showing the potential to outcompete stronger binding siderophores (Hassler et al, 2017). In addition, humic substances (HS) or HS-like substances from various origins constitute another type of ligand (Krachler et al, 2015;Laglera et al, 2019a;Whitby et al, 2020). Typically, HS are derived from remineralization and degradation of organic matter (Burkhardt et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

“…HS-like substances have also shown to be part of Fe binding ligands in biologically refractory deep ocean dissolved organic matter (rDOM) with low Fe-bioavailability. However, photodegradation of rDOM was shown to increase the Fe bioavailability making Fe bound to such substances an important source in HNLC areas where upwelling plays a role (Hassler et al, 2020;Lauderdale et al, 2020;Whitby et al, 2020;Laglera et al, 2019a).…”

Section: Introductionmentioning

confidence: 99%

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Sources of Fe-binding organic ligands in surface waters of the western Antarctic Peninsula

Ardiningsih

Seyitmuhammedov

Sander

et al. 2020

Preprint

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Abstract. Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high nutrient low chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) was applied. Our results indicated that organic ligands in surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea-ice. Organic ligands in deeper shelf water are supplied via resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([Lt]) were between 1.2 nM eq. Fe and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentration (excess ligand concentration, [L'] = 0.8–5.0 nM eq. Fe). The [L'] made up to 80 % of [Lt], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe (αFe'L; the product of [L'] and conditional binding strength of ligands, KFe'Lcond). Since Fe is also supplied by shelf sediments and glacial discharge, the high complexation capacity over the shelf can keep Fe dissolved and available for local primary productivity later in the season, upon sea ice melting.

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Section: Implications For Primary Productivitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Sources of Fe-binding organic ligands in surface waters of the western Antarctic Peninsula

Ardiningsih

Seyitmuhammedov

Sander

et al. 2020

Preprint

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“…Useful qualitative information about the DOM pool in the aquatic environment (e.g., average aromaticity degree, molecular weight, and occurrence of humic-like, fulvic-like, and protein-like substances) can be gained indirectly via UV/Vis and fluorescence spectroscopic studies of its optically active fractions (colored and fluorescent dissolved organic matter, CDOM and FDOM) ( Yamashita et al, 2011 ; Osburn et al, 2012 ; Lee et al, 2018 ; Galletti et al, 2019 ; Marcinek et al, 2020 ). Including this information in speciation studies could improve our understanding of the sources and composition of metal-binding organic ligands ( Sanchez-Marin et al, 2010 ; Slagter et al, 2017 ; Watanabe et al, 2018 ; Wong et al, 2019 ; Whitby et al, 2020 ). However, these methods cannot characterize the binding sites or give information about nonfluorescent substances in DOM.…”

Section: Introductionmentioning

confidence: 99%

Organic Copper Speciation by Anodic Stripping Voltammetry in Estuarine Waters With High Dissolved Organic Matter

et al. 2021

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The determination of copper (Cu) speciation and its bioavailability in natural waters is an important issue due to its specific role as an essential micronutrient but also a toxic element at elevated concentrations. Here, we report an improved anodic stripping voltammetry (ASV) method for organic Cu speciation, intended to eliminate the important problem of surface-active substances (SAS) interference on the voltammetric signal, hindering measurements in samples with high organic matter concentration. The method relies on the addition of nonionic surfactant Triton-X-100 (T-X-100) at a concentration of 1 mg L−1. T-X-100 competitively inhibits the adsorption of SAS on the Hg electrode, consequently 1) diminishing SAS influence during the deposition step and 2) strongly improving the shape of the stripping Cu peak by eliminating the high background current due to the adsorbed SAS, making the extraction of Cu peak intensities much more convenient. Performed tests revealed that the addition of T-X-100, in the concentration used here, does not have any influence on the determination of Cu complexation parameters and thus is considered "interference-free." The method was tested using fulvic acid as a model of natural organic matter and applied for the determination of Cu speciation in samples collected in the Arno River estuary (Italy) (in spring and summer), characterized by a high dissolved organic carbon (DOC) concentration (up to 5.2 mgC L−1) and anthropogenic Cu input during the tourist season (up to 48 nM of total dissolved Cu). In all the samples, two classes of ligands (denoted as L1 and L2) were determined in concentrations ranging from 3.5 ± 2.9 to 63 ± 4 nM eq Cu for L1 and 17 ± 4 to 104 ± 7 nM eq Cu for L2, with stability constants logKCu,1 = 9.6 ± 0.2–10.8 ± 0.6 and logKCu,2 = 8.2 ± 0.3–9.0 ± 0.3. Different linear relationships between DOC and total ligand concentrations between the two seasons suggest a higher abundance of organic ligands in the DOM pool in spring, which is linked to a higher input of terrestrial humic substances into the estuary. This implies that terrestrial humic substances represent a significant pool of Cu-binding ligands in the Arno River estuary.

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“…Despite their importance, not much is known about the origin, loss and residence time of these organic substances (Gledhill and Buck, 2012;Gerringa et al, 2015;Hassler et al, 2017). Whilst more information is becoming available on specific molecules that bind Fe (Mawji et al, 2011;Boiteau et al, 2016) and the acid-base properties of marine dissolved organic matter (Lodeiro et al, 2020), the bulk of the ligands is of unknown identity and is described in terms of broad groups such as siderophores, humic acids and polysaccharides (Laglera et al, 2011;Gledhill and Buck, 2012;Bundy et al, 2016;Hassler et al, 2017;Dulaquais et al, 2018;Laglera et al, 2019a;Whitby et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Iron Speciation in Fram Strait and Over the Northeast Greenland Shelf: An Inter-Comparison Study of Voltammetric Methods

et al. 2021

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Competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV) is a widely used technique to determine dissolved iron (Fe) speciation in seawater, and involves competition for Fe of a known added ligand (AL) with natural organic ligands. Three different ALs were used, 2-(2-thiazolylazo)-p-cresol (TAC), salicylaldoxime (SA) and 1-nitroso-2-napthol (NN). The total ligand concentrations ([Lt]) and conditional stability constants (log K′Fe’L) obtained using the different ALs are compared. The comparison was done on seawater samples from Fram Strait and northeast Greenland shelf region, including the Norske Trough, Nioghalvfjerdsfjorden (79N) Glacier front and Westwind Trough. Data interpretation using a one-ligand model resulted in [Lt]SA (2.72 ± 0.99 nM eq Fe) > [Lt]TAC (1.77 ± 0.57 nM eq Fe) > [Lt]NN (1.57 ± 0.58 nM eq Fe); with the mean of log K′Fe’L being the highest for TAC (log ′KFe’L(TAC) = 12.8 ± 0.5), followed by SA (log K′Fe’L(SA) = 10.9 ± 0.4) and NN (log K′Fe’L(NN) = 10.1 ± 0.6). These differences are only partly explained by the detection windows employed, and are probably due to uncertainties propagated from the calibration and the heterogeneity of the natural organic ligands. An almost constant ratio of [Lt]TAC/[Lt]SA = 0.5 – 0.6 was obtained in samples over the shelf, potentially related to contributions of humic acid-type ligands. In contrast, in Fram Strait [Lt]TAC/[Lt]SA varied considerably from 0.6 to 1, indicating the influence of other ligand types, which seemed to be detected to a different extent by the TAC and SA methods. Our results show that even though the SA, TAC and NN methods have different detection windows, the results of the one ligand model captured a similar trend in [Lt], increasing from Fram Strait to the Norske Trough to the Westwind Trough. Application of a two-ligand model confirms a previous suggestion that in Polar Surface Water and in water masses over the shelf, two ligand groups existed, a relatively strong and relatively weak ligand group. The relatively weak ligand group contributed less to the total complexation capacity, hence it could only keep part of Fe released from the 79N Glacier in the dissolved phase.

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A call for refining the role of humic-like substances in the oceanic iron cycle

Cited by 52 publications

References 85 publications

Sources of Fe-binding organic ligands in surface waters of the western Antarctic Peninsula

Sources of Fe-binding organic ligands in surface waters of the western Antarctic Peninsula

Organic Copper Speciation by Anodic Stripping Voltammetry in Estuarine Waters With High Dissolved Organic Matter

Iron Speciation in Fram Strait and Over the Northeast Greenland Shelf: An Inter-Comparison Study of Voltammetric Methods

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