Fe-Binding Dissolved Organic Ligands in the Oxic and Suboxic Waters of the Black Sea

Gerringa, Loes J. A.; Rijkenberg, Micha J.A.; Bown, J.; Margolin, Andrew R.; Laan, Patrick; Baar, H. J. W. de

doi:10.3389/fmars.2016.00084

Cited by 14 publications

(10 citation statements)

References 93 publications

(176 reference statements)

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“…Due to the high heterogeneity of E. huxleyi exudates, the oxidation rate, as well as the equilibrium and acidity constants, might represent an average value of the sum of the individual rates/constants weighted by the fraction of each species in solution (Rose and Waite, 2003). The theoretical range (10 17 -10 21 M −1 ) of the stability constant for the Fe(III)-L complex is in reasonable agreement with those found in the literature for ligands with bindings capacities lower than L 1 (Gledhill and Buck, 2012;Bundy et al, 2014;Gerringa et al, 2016), including those estimated by Boye and van den Berg (2000) in E. huxleyi cultures.…”

Section: The Kinetic Modeling Approachessupporting

confidence: 85%

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: The Kinetic Modeling Approachessupporting

confidence: 85%

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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“…There were concerns about the basin's large pH and Fe gradients, which are known to influence the optical properties of DOM. However, since the Black Sea's pH range of 7.3–8.2 is similar to the that found in the open ocean (Key et al ; Hiscock and Millero ), and dissolved Fe concentrations are no greater than ∼ 382 nM (Gerringa et al ; Rolison ), both pH and Fe concentrations should have negligible effects on the optical properties of DOM (Poulin et al ).…”

Section: Methodsmentioning

confidence: 58%

“…Anomalous DOC profile is at Sta. 6 in the Batumi Eddy, whichGerringa et al (2016) suggested to result from DOC removal being controlled by depth rather than r h , or perhaps resulting from the circulation within the Batumi Eddy. Note that three inflowing Sea of Marmara seawater samples from the Bosporus Strait station are excluded from (a) and (b).…”

mentioning

confidence: 98%

Black Sea dissolved organic matter dynamics: Insights from optical analyses

Margolin

Gonnelli

Hansell

et al. 2018

Limnology & Oceanography

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To obtain qualitative information on the Black Sea's dissolved organic matter (DOM) pool, the optical properties (absorption and fluorescence) were measured in 111 samples collected across the basin. Chromophoric dissolved organic matter (CDOM) was considered at three wavelengths (254 nm, 280 nm, and 325 nm), along with the spectral slope between 275 nm and 295 nm (S275–295) and the specific ultraviolet absorbance at 254 nm (SUVA254). Using parallel factor analysis, a five‐component model identified three humic‐like components, a protein‐like component, and a polycyclic aromatic hydrocarbon‐like component. In the basin's oxic layer (upper ∼ 100 m), protein‐like CDOM was elevated, likely due to the production of this labile material, while humic‐like material was low, suggesting its removal by photo‐oxidation. In the underlying waters, the protein‐like material decreased, perhaps due to the utilization of this nitrogen‐containing DOM, while humic‐like material increased, suggesting its production at depth. In the anoxic layer (lower ∼ 2000 m), dissolved organic carbon (DOC) varied by only ∼ 10% while CDOM increased with depth by a factor of approximately two; the optical properties correlated well with the H2S‐equivalence of mineralization, referred to here as apparent carbon mineralization (ACM), while DOC did not. The strong correlation between CDOM and ACM is similar to correlations previously identified in the open ocean that compared CDOM with apparent oxygen utilization, suggesting that CDOM accumulates as a function of mineralization, independently of the oxidizing agent (i.e., oxygen or sulfate).

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“…The valence, speciation, solubility, adsorption, organic complexation and rates of redox processes of transition metals are subject to influences by physicochemical conditions such as environmental pH, O 2 content and redox potentials ( Byrne et al, 1988 ; Banks et al, 2012 ; Sunda, 2012 ; Scholz et al, 2014 ). The properties of transition metals in marine environments are influenced by diverse biological factors as well ( Morel and Price, 2003 ; Gerringa et al, 2016 ). The recently proposed “Ferrojan Horse Hypothesis” highlights a newly discovered viral mechanism for the behaviors of Fe in marine environments ( Bonnain et al, 2016 ).…”

Section: Eco-energetic Responses Of Nitrogen-cycling Chemolithoautotrmentioning

confidence: 99%

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment

Dang

Chen

2017

Front. Microbiol.

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Transformation and mobilization of bioessential elements in the biosphere, lithosphere, atmosphere, and hydrosphere constitute the Earth's biogeochemical cycles, which are driven mainly by microorganisms through their energy and material metabolic processes. Without microbial energy harvesting from sources of light and inorganic chemical bonds for autotrophic fixation of inorganic carbon, there would not be sustainable ecosystems in the vast ocean. Although ecological energetics (eco-energetics) has been emphasized as a core aspect of ecosystem analyses and microorganisms largely control the flow of matter and energy in marine ecosystems, marine microbial communities are rarely studied from the eco-energetic perspective. The diverse bioenergetic pathways and eco-energetic strategies of the microorganisms are essentially the outcome of biosphere-geosphere interactions over evolutionary times. The biogeochemical cycles are intimately interconnected with energy fluxes across the biosphere and the capacity of the ocean to fix inorganic carbon is generally constrained by the availability of nutrients and energy. The understanding of how microbial eco-energetic processes influence the structure and function of marine ecosystems and how they interact with the changing environment is thus fundamental to a mechanistic and predictive understanding of the marine carbon and nitrogen cycles and the trends in global change. By using major groups of chemolithoautotrophic microorganisms that participate in the marine nitrogen cycle as examples, this article examines their eco-energetic strategies, contributions to carbon cycling, and putative responses to and impacts on the various global change processes associated with global warming, ocean acidification, eutrophication, deoxygenation, and pollution. We conclude that knowledge gaps remain despite decades of tremendous research efforts. The advent of new techniques may bring the dawn to scientific breakthroughs that necessitate the multidisciplinary combination of eco-energetic, biogeochemical and "omics" studies in this field.

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Fe-Binding Dissolved Organic Ligands in the Oxic and Suboxic Waters of the Black Sea

Cited by 14 publications

References 93 publications

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

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

Black Sea dissolved organic matter dynamics: Insights from optical analyses

Ecological Energetic Perspectives on Responses of Nitrogen-Transforming Chemolithoautotrophic Microbiota to Changes in the Marine Environment

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