Effect of ocean warming and acidification on the Fe(II) oxidation rate in oligotrophic and eutrophic natural waters

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

doi:10.1007/s10533-016-0192-x

Cited by 20 publications

(16 citation statements)

References 81 publications

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Section: Kinetic Studiessupporting

confidence: 76%

“…The oxidation kinetics of Fe(II) in seawater are significantly faster in presence of high concentrations of silicate due to the role played by the Fe(II)-silicate complexes on the overall oxidation process (Samperio-Ramos et al, 2016). The results obtained in SWEN are close to those from other studies carried out with North Atlantic seawater enriched with nutrients Samperio-Ramos et al, 2016), confirming that the silicate affected the Fe(II) oxidation rate and the lifetime of Fe(II). This study also shows a lessening in the oxidation rate of Fe(II) due to the presence of the organic ligands released from the coccolitophorid E. huxleyi, proving that the organic matter exuded by phytoplankton can preserve Fe(II) for longer periods in oxygen rich waters, as a result of the formation of ferrous organic complexes (Rijkenberg et al, 2006;Roy et al, 2008;Breitbarth et al, 2009a;González et al, 2014).…”

Section: Kinetic Studiessupporting

confidence: 76%

“…Nevertheless, the oxidation rate of Fe(II) did not show a significant response to DUA additions. The uncomplexed inorganic Fe(II), the more labile species to form organic complexes, dominates the Fe(II) speciation at pH lower than 7.8 (Samperio-Ramos et al, 2016). The hydrolysis of metal, which prevents the coordination with the carboxylic moieties, increase under the pH conditions here studied (Millero et al, 2009).…”

Section: Kinetic Studiesmentioning

confidence: 83%

“…In line with previous studies (Samperio-Ramos et al, 2016), we have used a kinetic model to consider the Fe(II) oxidation process in seawater enriched with nutrients (SWEN) at 25 • C ( Table 1). The modeling approach also took into consideration the different pH/pCO 2 conditions fixed in the microcosms (Samperio-Ramos et al, 2017).…”

Section: Kinetic Model Considering Exudates Of E Huxleyi Produced Unmentioning

confidence: 99%

“…With levels of H 2 O 2 < 125 nM, oxygen saturated conditions and pH > 7.5, O 2 dominates the oxidation kinetics of inorganic species of Fe(II), since the k app by O 2 is proportional to [OH − ] 2 and the k app by H 2 O 2 is proportional to [OH − ] ( Moffett and Zika, 1987;González-Dávila et al, 2006). Nevertheless, our model also included the role played by H 2 O 2 and O − 2 in the oxidation process, including the individual rates for Fe(II) for both species (Santana-Casiano et al, 2005;Samperio-Ramos et al, 2016).…”

Section: The Kinetic Modeling Approachesmentioning

confidence: 99%

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Effect of Organic Fe-Ligands, Released by Emiliania huxleyi, on Fe(II) Oxidation Rate in Seawater Under Simulated Ocean Acidification Conditions: A Modeling Approach

2018

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The potential effect of ocean acidification on the exudation of organic matter by phytoplankton and, consequently, on the iron redox chemistry is largely unknown. In this study, the coccolithophorid Emiliania huxleyi was exposed to different pCO 2 conditions (225-900 µatm), in order to determine the role of natural organic ligands on the Fe(II) oxidation rate. Oxidation kinetics of Fe(II) were studied as a function of pH (7.75-8.25) and dissolved organic carbon levels produced (0-141.11 µmol C L −1 ) during the different growth stages. The Fe(II) oxidation rate always decreased in the presence of exudates as compared to that in the exudates-free seawater. The organic ligands present in the coccolithophorid exudates were responsible for this decrease. The oxidation of Fe(II) in artificial seawater was also investigated at nanomolar levels over a range of pH (7.75-8.25) at 25 • C in the presence of different glucuronic acid concentrations. Dissolved uronic acids (DUA) slightly increased the experimental rate compared to control artificial seawater (ASW) which can be ascribed to the stabilization of the oxidized form by chelation. This behavior was a function of the Fe(II):DUA ratio and was a pH dependent process. A kinetic model in ASW, with a single organic ligand, was applied for computing the equilibrium constant (log K FeCHO+ = 3.68 ± 0.81 M −1 ) and the oxidation rate (log k FeCHO+ = 3.28 ± 0.41 M −1 min −1 ) for the Fe(II)-DUA complex (FeCHO + ), providing an excellent description of data obtained over a wide range of DUA concentrations and pH conditions. Considering the Marcus theory the Fe(III) complexing constant with DUA was limited to between 10 13 and 10 16 . For the seawater enriched with exudates of E. huxleyi a second kinetic modeling approach was carried out for fitting the Fe(II) speciation, and the contribution of each Fe(II) species to the overall oxidation rate as a function of the pH/pCO 2 conditions. The influence of organic ligands in the Fe(II) speciation diminished as pH decreased in solution. During the stationary growth phase, the FeCHO + complex became the most important contributor to the overall oxidation rate when pH was lower than 7.95. Because CO 2 levels modify the composition of excreted organic ligands, the redox behavior of Fe in solution may be affected by future acidification conditions.

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Section: Kinetic Studiessupporting

confidence: 76%