Impact on the Fe redox cycling of organic ligands released by Synechococcus PCC 7002, under different iron fertilization scenarios. Modeling approach

Samperio-Ramos, Guillermo; González‐Dávila, Melchor; Santana-Casiano, J. Magdalena

doi:10.1016/j.jmarsys.2018.01.009

Cited by 11 publications

(6 citation statements)

References 106 publications

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“…Microcystis aeruginosa (Lee et al, 2017), coccolithophore Emiliania huxleyi (Samperio-Ramos et al, 2018a), and diatoms Chaetoceros radicans (Lee et al, 2017) and Phaeodactylum tricornutum (Santana-Casiano et al, 2014) have all been found to retard Fe(II) oxidation rates. Furthermore, the effect of cellular exudates on the reaction constant appears to scale with increasing total organic carbon (Samperio-Ramos et al, 2018b). This is also consistent with the release of Fe(II)-binding agents resulting in the formation of Fe(II)-L species with slower oxidation rates than inorganic Fe(II) speciation under specified physical/chemical conditions.…”

Section: Fe(ii) Decay Experimentssupporting

confidence: 71%

Fe(II) stability in seawater

Hopwood

Santana-González

Gallego-Urrea

et al. 2018

Preprint

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Abstract. The speciation of dissolved iron (DFe) in the ocean is widely assumed to consist exclusively of Fe(III)-ligand complexes. Yet in most aqueous environments a poorly defined fraction of DFe also exists as Fe(II). Here we deploy flow injection analysis to measure in-situ Fe(II) concentrations during a series of mesocosm/microcosm experiments in coastal environments in addition to the decay rate of this Fe(II) when moved into the dark. During 5 mesocosm/microcosm experiments in Svalbard and Patagonia, where dissolved (0.2&#8201;&#181;m) Fe and Fe(II) were quantified simultaneously, Fe(II) constituted 24&#8211;65&#8201;% of DFe suggesting that Fe(II) was a large fraction of the DFe pool. When this Fe(II) was allowed to decay in the dark, the vast majority of measured oxidation rate constants were retarded relative to calculated constants derived from ambient temperature, salinity, pH and dissolved O2. The oxidation rates of Fe(II) spikes added to Atlantic seawater more closely matched calculated rate constants. The difference between observed and theoretical decay rates in Svalbard and Patagonia was most pronounced at Fe(II) concentrations <&#8201;2&#8201;nM and attributed to a stabilising effect of cellular exudates upon Fe(II). This enhanced stability of Fe(II) under post-bloom conditions, and the existence of such a high fraction of DFe as Fe(II), challenges the assumption that DFe speciation is dominated by ligand bound-Fe(III) species.

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Section: Fe(ii) Decay Experimentssupporting

confidence: 71%

Fe(II) stability in seawater

Hopwood

Santana-González

Gallego-Urrea

et al. 2018

Preprint

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“…Various degradation mechanisms connected to protonation/deprotonation processes as well as redox processes affect SAHLs in the open ocean. Fe(III)–SAHLs complexes are not only vulnerable to photoinduced ligand-to-metal charge transfer , but also to superoxide mediated reduction of the organically complexed Fe(III) ,− as well as to Fe(III) reduction in the presence of catechol or other Fe(III)-reducing DOM originating from phytoplankton exudates. − It is also possible that oxidation of the ligand by H 2 O 2 might have an impact. , H 2 O 2 is present in surface seawater primarily due to photochemical processes mediated by DOM with H 2 O 2 concentrations varying both with depth and with sunlight intensity . Some of the degradation processes occur not only in surface waters but also in deep waters.…”

Section: High Conditional Stability Constants In Seawater Of Iron(iii...mentioning

confidence: 99%

Northern High-Latitude Organic Soils As a Vital Source of River-Borne Dissolved Iron to the Ocean

Krachler

2021

Environ. Sci. Technol.

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Organic soils in the Arctic−boreal region produce small aquatic humic ligands (SAHLs), a category of naturally occurring complexing agents for iron. Every year, large amounts of SAHLsloaded with iron mobilized in river basinsreach the oceans via river runoff. Recent studies have shown that a fraction of SAHLs belong to the group of strong iron-binding ligands in the ocean. That means, their Fe(III) complexes withstand dissociation even under the conditions of extremely high dilution in the open ocean. Fe(III)-loaded SAHLs are prone to UV-photoinduced ligand-to-metal charge-transfer which leads to disintegration of the complex and, as a consequence, to enhanced concentrations of bioavailable dissolved Fe(II) in sunlit upper water layers. On the other hand, in water depths below the penetration depth of UV, the Fe(III)-loaded SAHLs are fairly resistant to degradation which makes them ideally suited as long-lived molecular transport vehicles for river-derived iron in ocean currents. At locations where SAHLs are present in excess, they can bind to iron originating from various sources. For example, SAHLs were proposed to contribute substantially to the stabilization of hydrothermal iron in deep North Atlantic waters. Recent discoveries have shown that SAHLs, supplied by the Arctic Great Rivers, greatly improve dissolved iron concentrations in the Arctic Ocean and the North Atlantic Ocean. In these regions, SAHLs play a critical role in relieving iron limitation of phytoplankton, thereby supporting the oceanic sink for anthropogenic CO 2 . The present Critical Review describes the most recent findings and highlights future research directions.

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“…In addition, a change in pH also affects the oxidation rate constants of Fe(II), which decreases with decreasing pH. The redox chemistry of Fe is also affected by the presence of organic ligands in seawater (Santana-Casiano et al, 2000, 2014Waite, 2002, 2003;Craig et al, 2009;Roy and Wells, 2011;Gonzaìlez et al, 2012;González et al, 2014;Lee et al, 2017;Samperio-Ramos et al, 2018;Arreguin et al, 2021). On other hand, recent investigations studied the effect of ocean acidification on the organic processes where iron is involved (Gledhill et al, 2015;Avendaño et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Ocean Acidification Effect on the Iron-Gallic Acid Redox Interaction in Seawater

et al. 2022

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Ocean acidification impacts the iron (Fe) biogeochemistry both by its redox and its complexation reactions. This has a direct effect on the ecosystems due to Fe being an essential micronutrient. Polyphenols exudated by marine microorganisms can complex Fe(III), modifying the Fe(II) oxidation rates as well as promoting the reduction of Fe(III) to Fe(II) in seawater. The effect of the polyphenol gallic acid (GA; 3,4,5-trihydroxy benzoic acid) on the oxidation and reduction of Fe was studied. The Fe(II) oxidation rate constant decreased, increasing the permanence of Fe(II) in solutions at nM levels. At pH = 8.0 and in the absence of gallic acid, 69.3% of the initial Fe(II) was oxidized after 10 min. With 100 nM of gallic acid (ratio 4:1 GA:Fe), and after 30 min, 37.5% of the initial Fe(II) was oxidized. Fe(III) is reduced to Fe(II) by gallic acid in a process that depends on the pH and composition of solution, being faster as pH decreases. At pH > 7.00, the Fe(III) reduction rate constant in seawater was lower than in NaCl solutions, being the difference at pH 8.0 of 1.577 × 10–5 s–1. Moreover, the change of the Fe(III) rate constant with pH, within the studied range, was higher in seawater (slope = 0.91) than in NaCl solutions (slope = 0.46). The Fe(III) reduction rate constant increased with increasing ligand concentration, being the effect higher at pH 7.0 [k′ = 1.078 × 10–4 s–1; (GA) = 250 nM] compared with that at pH 8.0 [k′ = 3.407 × 10–5 s–1; (GA) = 250 nM]. Accordingly, gallic acid reduces Fe(III) to Fe(II) in seawater, making possible the presence of Fe(II) for longer periods and favoring its bioavailability.

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Impact on the Fe redox cycling of organic ligands released by Synechococcus PCC 7002, under different iron fertilization scenarios. Modeling approach

Cited by 11 publications

References 106 publications

Fe(II) stability in seawater

Fe(II) stability in seawater

Northern High-Latitude Organic Soils As a Vital Source of River-Borne Dissolved Iron to the Ocean

Ocean Acidification Effect on the Iron-Gallic Acid Redox Interaction in Seawater

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