Iron In Seawater Research Articles

Molecular Mechanisms for Iron Uptake and Homeostasis in Marine Eukaryotic Phytoplankton.

The micronutrient iron is essential for phytoplankton growth due to its central role in a wide variety of key metabolic processes including photosynthesis and nitrate assimilation. As a result of scarce bioavailable iron in seawater, marine primary productivity is often iron-limited with future iron supplies remaining uncertain. Although evolutionary constraints resulted in high cellular iron requirements, phytoplankton evolved diverse mechanisms that enable uptake of multiple forms of iron, storage of iron over short and long timescales, and modulation of their iron requirement under stress. Genomics continues to increase our understanding of iron-related proteins that are homologous to those characterized in other model organisms, while recently, molecular and cell biology is revealing unique genes and processes with connections to iron acquisition or use. Moreover, there are an increasing number of examples showing the interplay between iron uptake and extracellular processes such as boundary layer chemistry and microbial interactions.

Enduring effect mechanism of Co(Ni) layers on excellent microwave absorption performance of carbonyl iron in seawater

The microwave absorbing materials (MAMs) applied in marine environment are confronted with corrosion, therefore, in order to guarantee the long-term function, the MAMs need to possess excellent microwave absorption performance and seawater corrosion resistance simultaneously. Carbonyl iron powder (CIP) has the characteristic of broadband response caused by magnetic loss, playing an important role in practical application as an MAM. Herein, to avoid the deterioration of microwave absorption property of CIP by seawater corrosion, protective layers of electroless plating Co(Ni) are introduced with less influence on magnetic loss. The CIP coated with Co layer (CIP@Co) shows the RLmin of −57.93 dB and an effective absorption bandwidth (EAB) of 8.56 GHz, after a long-time continuous immersion in seawater, its RLmin and EAB is −71.11 dB and 8.00 GHz, respectively. The EAB of CIP@Ni after immersing in seawater is also preserved 94 %, illustrating the long-life stability of the microwave absorption performance in seawater. The little effect of Co layer on the magnetic loss of CIP and the additional anticorrosion ability of electroless plating layers are two guarantees for enduring the excellent microwave absorption performance of CIP@Co in seawater. This work provides a solution to obtain MAMs with long-life excellent microwave absorption in seawater.

Stress Corrosion Cracking of Austenitic Cast Iron in Chloride-Containing Waters

Austenitic cast iron has been used for many years for pump cases, column pipes, and valves in seawater systems, particularly in the Middle East. Since the 1970s, failures have occurred by stress corrosion cracking, and there have been a number of research efforts to understand the problem and suggest means of preventing it. Cracking failures have continued and further research has been undertaken to try and understand the problem more thoroughly. This paper reviews the data from the early research, and presents the results of previously unpublished work, and its implications for the further use of austenitic cast iron in seawater and alternative alloys.

Hydrothermal vents contribute to high concentrations of dissolved iron in seawater

Hydrothermal vents contribute to high concentrations of dissolved iron in seawater

Effect of titanium and chromium diffusion coatings on corrosion resistance of sintered iron

The authors have studied the effect of titanium and chromium diffusion coatings on corrosion resistance of sintered iron in solutions of acids and salts. The samples of 85% density were obtained from powdered iron by static pressing in press dies and sintering in vacuum. The diffusion coatings were applied in molten lead with titanium and chromium additives at the temperature of 1100°C and 2 hours exposure time. Microstructure of the samples was then explored by the optical metallography method. The content of elements in the coatings was measured using energy dispersive X-ray microanalysis. Studies of corrosion resistance of the samples in solutions of acids and salts were conducted by the gravimetric method. Corrosion resistance was also evaluated by time to the first corrosion foci emerging and the area of corrosion damage. Diffusion titanium and chromium coatings have ensured higher corrosion resistance of sintered iron in all the aggressive media studied. Chromizing is the most efficient for protecting sintered iron in solutions of sulphuric and nitric acids, as well as in media containing acetic acid and hydrogen peroxide. Meanwhile, titanizing is the most efficient for protecting sintered iron in sea water.

Iron Elution from Iron and Steel Slag Using Bacterial Complex Identified from the Seawater.

Iron and steel slag (ISS) is a byproduct of iron refining processes. The lack of iron in seawater can cause barren grounds where algae cannot grow. To improve the barren grounds of the sea, a supply of iron to the seawater is necessary. This study focused on bacteria interacting with ISS and promoting iron elution in seawater. Sulfitobacter sp. (TO1A) and Pseudomonas sp. (TO1B) were isolated from Tokyo Bay and Sagami Bay. The co-culture of both bacteria promoted more iron elution than individual cultures. After the incubation of both bacteria with ISS, quartz and vaterite appeared on the surface of the ISS. To maintain continuous iron elution from the ISS in the seawater, we also isolated Pseudoalteromonas sp. (TO7) that formed a yellow biofilm on the ISS. Iron was eluted by TO1A and TO1B, and biofilm was synthesized by TO7 continuously in the seawater. The present research is expected to contribute to the improvement of ISS usage as a material for the construction of seaweed forests.

Microbial feedbacks optimize ocean iron availability

Iron is the limiting factor for biological production over a large fraction of the surface ocean because free iron is rapidly scavenged or precipitated under aerobic conditions. Standing stocks of dissolved iron are maintained by association with organic molecules (ligands) produced by biological processes. We hypothesize a positive feedback between iron cycling, microbial activity, and ligand abundance: External iron input fuels microbial production, creating organic ligands that support more iron in seawater, leading to further macronutrient consumption until other microbial requirements such as macronutrients or light become limiting, and additional iron no longer increases productivity. This feedback emerges in numerical simulations of the coupled marine cycles of macronutrients and iron that resolve the dynamic microbial production and loss of iron-chelating ligands. The model solutions resemble modern nutrient distributions only over a finite range of prescribed ligand source/sink ratios where the model ocean is driven to global-scale colimitation by micronutrients and macronutrients and global production is maximized. We hypothesize that a global-scale selection for microbial ligand cycling may have occurred to maintain "just enough" iron in the ocean.

Traceable and accurate quantification of iron in seawater using isotope dilution calibration strategies by triple quadrupole ICP-MS/MS: Characterization measurements of iron in a candidate seawater CRM

Accurate quantification of iron is crucial for the characterization of a candidate seawater certified reference material. Isotope dilution mass spectrometry as a primary method is one of the option for this purpose. In this study, triethylamine (TEA) assisted Mg(OH)2 co-precipitation is developed and combined with isotope dilution mass spectrometry for the characterization of candidate certified reference material, UME CRM 1206. The analytical protocol of co-precipitation was optimized to achieve reproducible yields of ~100% Fe with high salt rejection (residual salinity ~0.003%). Three calibration strategies, single, double and triple isotope dilution mass spectrometry (IDMS) coupled with co-precipitation were investigated in terms of metrological aspects. The determination of Fe was carried out by ICP-MS with tandem configuration (ICP-MS/MS) using NH3/He cell gas which was optimized for the minimum background equivalence concentration to be able to measure highly accurate 56Fe/57Fe ratio with the highest possible sensitivity. The background corrected typical procedural blank levels and limit of detection calculated based on three times the standard deviation of blanks were found as 9 ng/kg (0.16 nM) and 11 ng/kg (0.20 nM) for single IDMS, respectively. Trueness of the developed analytical methods has been demonstrated using CASS-6 and NMIA MX014 with complete and very precise recoveries. SI-traceable values with combined uncertainty (k = 2) were obtained for single, double and triple IDMS as (12.70 ± 0.16) ng/g, (12.728 ± 0.084) ng/g and (12.732 ± 0.062) ng/g, respectively. The relative combined uncertainty for each approach was calculated as 0.64%, 0.33% and 0.24%, respectively.

The role of pyrite in fossilisation and its potential instability

Pyrite often forms in organic-rich marine sediments through bacterial action. Bacteria reduce organics to form bisulphide, which reacts in turn with dissolved iron in seawater to form pyrite. Consequently, it is frequently found in stratigraphic formations that consist of marine clays. Pyrite can be involved in fossilisation through a number of ways, including complete replacement, as infill in permineralised bone, or simply as microcrystals finely disseminated through the fossil and matrix. Replacement by pyrite can often be easily recognised: the fossil may have a gold or brassy metallic lustre. Infill is harder to recognise, and disseminated pyrite even more so. Pyrite in fossils may be stable or unstable- in its stable form, pyritised fossils will generally retain their shiny, metallic appearance. Pyrite preservation and stability can vary even within the same specimen. Fossils preserved in pyrite can be prone to oxidation, particularly at high relative humidities. There are a number of signs that indicate oxidation is occurring, depending on the severity of the condition. One or more of the following may be present: a sulphurous smell, white or yellow powdery crystals on the surface of the specimen, expansion cracks, as well as acid burns on associated labels, boxes and drawers. Such burns often have a characteristic ovoid appearance. If left unchecked, pyrite oxidation can completely destroy a specimen and its labels.

Exploring the Potential Role of Terrestrially Derived Humic Substances in the Marine Biogeochemistry of Iron

There is a widely recognised link between iron bioavailability and phytoplankton growth in large tracts of the World Ocean. Iron bioavailability is thus pivotal to the removal of atmospheric carbon via the ocean’s ‘biological pump’. To evaluate future scenarios of global climate change, we must therefore understand better how the bioavailability of iron in seawater is linked to processes controlling its supply, chemical speciation and removal from the water column. Much of the research on iron inputs to the open ocean has focused on atmospheric, benthic (shelf sediments) and hydrothermal (mid-ocean) sources of iron. The conventional wisdom has been that riverine iron sources are negligible because many of the major world rivers exhibit extensive removal of dissolved iron by flocculation processes during estuarine mixing. However, recent studies have revealed that a fraction of iron associated with peatland-derived humic and fulvic acids may survive aggregation processes in the freshwater-seawater mixing zone, and thus be exported offshore. This review is a synthesis of available data and information for and against the hypothesis that land-derived humic substances exert a significant control on the marine biogeochemical cycle of iron. From the outset, it is shown that this hypothesis can neither be verified nor disproved at present, in part due to analytical difficulties in characterising the all-important marine colloidal phase. Evidence is then presented on the likely chemical nature and structure of iron-binding humic ligands along with implications for the lateral transport of iron in surface waters and its participation in carbon stabilisation in marine sediments. This is followed by a discussion of photochemically and microbially mediated processes acting on terrestrial humic substances and a discussion of how terrestrial humic substances may influence the biological availability of iron. The review finishes with a presentation of measurement technologies and approaches that could be used to assess (i) how iron-binding ligands in seawater relate to land-derived humic substances and (ii) how terrestrial humics may influence the global carbon cycle indirectly by influencing the processes that control the supply and maintain the pool of ‘dissolved’ iron in the ocean.

Effect of stabilizer concentration on the cavitation erosion resistance characteristics of the electroless nickel plated gray cast iron in seawater

In this study, electroless nickel (EN) plating was performed with stabilizer concentration to improve cavitation erosion resistance of gray cast iron under marine environment. Cavitation erosion tests were carried out in natural seawater solution in accordance with modified ASTM G32. The change of stabilizer concentration affected the plating rate, P content, and average crystal size of EN coating. The decrease of the plating rate with the stabilizer concentration and the flake-shaped graphite exposed to the gray cast iron surface negatively affected the cavitation erosion and corrosion prevention. In particular, cavitation erosion damage of EN coating was accelerated due to combined galvanic corrosion when the EN coating was destroyed and the substrate was exposed under the cavitation erosion environment.

Determination of the contribution of humic substances to iron complexation in seawater by catalytic cathodic stripping voltammetry

Improving our understanding of iron cycling in ocean waters is one of the most challenging tasks in oceanographic studies and requires new analytical strategies. The low solubility of inorganic iron in oxygen saturated waters is increased by organic complexation with a variety of natural ligands, the nature of which is a topic of debate. Electrochemical methods are important for speciation studies since they allow direct measurement of iron complexes at limits of detection below iron concentrations in ocean waters. Most of the natural iron ligands do not form electrolabile iron complexes with working electrodes currently in use. Humic substances are the exception as their iron complexes can be detected by cathodic voltammetry if a strong oxidant such as bromate is added for a catalytic reoxidation of iron. Here we propose a rearrangement and extension of the original analytical protocol (Laglera et al., 2007) [1]. Firstly, the humic standard prepared in ultrapure water is carefully saturated with iron before use, preventing underestimation of the iron-humic complexes during calibration. Secondly, before starting the common voltammetric analysis under iron saturation, extra voltammograms are collected at the natural iron concentration. We demonstrate that this rearrangement permits the determination of the percentage of iron-binding groups of humic substances in the sample that were originally bound to iron. After calibration, the concentration of iron present in the sample as humic complexes can be quantified. This is the first analytical development leading to the quantification of the contribution of a determined type of natural ligands to the organic speciation of iron in seawater. As a proof of concept we measured the concentration of Fe-HS complexes in Arctic Ocean waters characterized by a high content in terrigenous organic matter. We corroborated the importance of humic substances in the lateral transport of high concentrations of iron from the Arctic Ocean into the North Atlantic Ocean.

Pelagic Iron Recycling in the Southern Ocean: Exploring the Contribution of Marine Animals

The availability of iron controls primary productivity in large areas of the Southern Ocean. Iron is largely supplied via atmospheric dust deposition, melting ice, the weathering of shelf sediments, upwelling, sediment resuspension, mixing (deep water, biogenic, and vertical mixing) and hydrothermal vents with varying degrees of temporal and spatial importance. However, large areas of the Southern Ocean are remote from these sources, leading to regions of low primary productivity. Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean. The aim of this review is to provide a quantitative and qualitative assessment of the current literature on pelagic iron recycling by marine animals in the Southern Ocean and highlight the next steps forward in quantifying the retention and recycling of iron by higher trophic levels in the Southern Ocean. Phytoplankton utilize the iron in seawater to meet their metabolic demand. Through grazing, pelagic herbivores transfer the iron in phytoplankton cells into their body tissues and organs. Herbivores can recycle iron through inefficient feeding behavior that release iron into the water before ingestion, and through the release of fecal pellets. The iron stored within herbivores is transferred to higher trophic levels when they are consumed. When predators consume iron beyond their metabolic demand it is either excreted or defecated. Waste products from pelagic vertebrates can thus contain high concentrations of iron which may be in a form that is available to phytoplankton. Bioavailability of fecal iron for phytoplankton growth is influenced by a combination of the size of the fecal particle, presence of organic ligands, the oxidation state of the iron, as well as biological (e.g., remineralization, coprochaly, coprorhexy, and coprophagy) and physical (e.g., dissolution, fragmentation) processes that lead to the degradation and release of fecal iron. The flux of dissolved iron from pelagic recycling is comparable to other sources in the region such as atmospheric dust, vertical diffusivity, vertical flux, lateral flux and upwelling, but lower than sea ice, icebergs, sediment resuspension, and deep winter mixing. The temporal and seasonal importance of these various factors requires further examination.

Iron Supply Capacity of Porous Concrete Using Steelmaking Slag Aggregate for Seaweed Beds or Fish Reef Blocks

The desertification of coastal regions is a worldwide problem. It is believed that one of the potential influences is a reduction in the concentration of dissolved iron in seawater. On the other hand, there is a high demand for the use of steelmaking slag generated from iron works. Steelmaking slag concrete, hereafter referred to as SSC, is made from the byproducts of steelmaking, such as steelmaking and ground granulated blast-furnace slags. It has been shown that although SSC releases iron, the dissolved iron is oxidized and precipitates promptly. In the present research, porous-type SSC (POSSC) using hot-metal pretreatment slag (HPS) as an aggregate was manufactured, with the purpose of increasing the amount of iron released from HPS. In addition, the influence of incorporating humus into the paste on the concentration of dissolved iron in artificial seawater and the compressive strength of POSSC was investigated. Two commercially available leaf mulches were used as the humus. The effects of the void ratio and the water-to-binder ratio of the paste were also examined. As a result, it was confirmed that the larger the measured void ratio of the POSSC, the higher the concentration of total iron released by the POSSC. It was also demonstrated that, although a humus fraction of 2% of the volume of the HPS caused an approximately 2 N/mm2 reduction in the compressive strength, the humus clearly stabilized the long-term presence of dissolved iron in the artificial seawater.

Mechanism of “Differential Flow Velocity Cell Corrosion” of Cast Iron in Seawater

Mechanism of “Differential Flow Velocity Cell Corrosion” of Cast Iron in Seawater

Cavitation erosion behavior in seawater of electroless Ni-P coating and process optimization using Taguchi method

In this paper, optimum process conditions of electroless Ni-P (EN) coating were identified by Taguchi method to minimize cavitation erosion damage of gray cast iron in seawater. The concentration of complexing agent (lactic acid) and concentration of reducing agent in EN coating process have the greatest influence on cavitation erosion characteristics. The EN coating characteristics for the optimal conditions were analyzed using a scanning electron microscope, an energy dispersive X-ray spectrometer, and X-ray diffraction. The EN coating showed the best cavitation erosion resistance characteristic when the P content was 5.37 wt.%, and it had amorphous-nanocrystalline composite structure. Also, cavitation erosion mechanism was investigated by surface analysis of EN coating after cavitation erosion test.

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

Abstract The kinetics of Fe redox transformations are of crucial importance in determining the bioavailability of iron, due to inorganic Fe(II) and Fe weakly organic complexes being the most easily assimilated species by phytoplankton. The role played by the natural organic ligands excreted by the cyanobacteria Synecococcus PCC 7002 on the iron redox chemistry was studied at different stages of growth, considering changes in the organic exudation of the cyanobacteria, associated with growth under two different scenarios of iron availability. The oxidation/reduction processes of iron were studied at nanomolar levels and under different physicochemical conditions of pH (7.2– 8.2), temperature (5– 35 °C) and salinity (10– 37). The presence of natural organic exudates of Synechococcus affected the redox behavior of iron. A pH-dependent and photo-induced Fe(III) reduction process was detected in the presence of exudates produced under Fe-Low conditions. Photolytic reactions also modified the reactivity of those exudates with respect to Fe(II), increasing its lifetime in seawater. Without light mediated processes, organic ligands excreted under iron deficient conditions intensified the Fe(II) oxidation at pH A kinetic modeling approach to describe the speciation and the contribution of individual Fe(II) species to the overall oxidation rate was applied, considering the experimental data and delimiting the equilibrium and redox constants between iron and the major ligands present in solution. Two organic type ligands for the exudates of Synechococcus PCC 7002, with different iron-chelation properties were included in the model. The Fe(II) speciation was radically affected when organic ligands were considered. The individual contributions to the overall Fe(II) oxidation rate demonstrated that these organic ligands played a key role in the oxidation process, although their contributions were dependent on the prescribed iron conditions. The study, therefore, suggests that the variability in the composition and nature of organic exudates released, due to iron availability conditions, might determine the redox behaviour of iron in seawater.

Isolation and screening of resistant bacteria of heavy metal (Fe) at ship dismantling

The activity of ship dismantling is one of the sources of metal pollutant that polluted the environment. The aims of this study were analyze the iron concentration from the ship dismantling area, to isolate the bacteria from those area, and to determine the bacteria resistant on iron. Samplings was conducted in three point sampling at sea water and soil coast, respectively. Isolation of bacteria was carried out using pour plate methods. All isolated bacteria in seawater and soil samples were inoculated on nutrient agar medium (NA) containing ferrous metals (Fe2+) with various concentrations (0; 1,000; 2,000; 3,000; 4,000; 5,000; and 6,000 μg/mL). Based on the results, sea water and soil indicated that those area have contaminated with iron. The concentration of iron in seawater was 1.03, 1.01 and 1.00 μg/mL, respectively. Meanwhile, the concentration of iron in soil was 962.0, 966.05, 981.00 mg/kg, respectively. The result of qualitative and quantitative analysis showed that the isolates of AT, AL and CL coded bacteria have high resistance to the effect of iron. It indicated with clear zone of 6.00-7.00 mm at 6,000 μg/mL. In conclusion, both of bacteria are potential to be used for bioremediation of the ferrous metal (Fe2+) in further investigation.

Dissolution mechanisms of steelmaking slags in sea water

ABSTRACTNew methods to further utilize steelmaking slag must be developed from the viewpoint of not only the stable consumption of steelmaking slag but also the establishment of sustainable and environmental friendly steelmaking process. It is well known that the lack of iron in sea water, which is an essential minor nutrient for seaweeds, is a major reason for the severe deterioration of coastal environment all over the world. The trial application of steelmaking slag as a material to supply such mineral nutrients has revealed the positive effects on the improvement of coastal ecological system. Dissolution mechanisms of various elements from steelmaking slag into sea water must be clarified in order to apply the rehabilitation technology to seriously damaged coasts. In the present paper, the dissolution behaviours of nutrient elements from steelmaking slag and steelmaking slag blended with dredged soil into sea water, or sea water containing gluconic acid which have been previously studied through laboratory-scale experiments by authors were summarized, and the dissolution mechanisms were reviewed.

Laboratory culture experiments to study the effect of lignite humic acid fractions on iron solubility and iron uptake rates in phytoplankton

The major fractions of dissolved iron in seawater exist as a complex with organic ligands. A high bioavailability of iron bound to humic acid (HA) compared to the other model ligands, such as desferrioxamine B or ferrichrome, has been reported, which implies the importance of HA to control the geochemical behavior and the transfer of Fe to marine phytoplankton, particularly in estuarine and coastal waters. In the current work, the effect of different HA fractions (>100, 100–30, 30–10, 10–5, and 5–3 kDa), which were extracted from lignite, on the comparative solubility of iron in seawater and the corresponding influence on iron uptake and growth rate of the phytoplankton Prymnesium parvum (Haptophyta) was studied using laboratory cultures. The lower-molecular-weight (MW) HA fractions, such as 30–10, 10–5, and 5–3 kDa, remained soluble in the simulated seawater medium for a longer time span compared to the higher MW fractions. The lower MW fractions facilitated higher iron solubility and assisted in achieving a better phytoplankton growth rate. However, a reciprocal impact on phytoplankton growth rates was observed when the HA concentration increased to a higher range (0.18 to 18 mg-C L−1). The highest intracellular Fe uptake in phytoplankton occurred with 30–10 kDa HA in seawater, and the extracellular dissolved Fe concentrations were higher for smaller-sized HA fractions. In summary, our study showed that the controlled addition of lower MW fractions of HA (up to 30–10 kDa) in estuarine waters could ensure the accelerated uptake of Fe in phytoplankton as well as a better growth rate.