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Iron cycle

The iron cycle, commonly referred to as the ferrous wheel, is the biogeochemical process governing the transformation, mobility, and exchange of iron between its primary oxidation states—ferrous (Fe²⁺) and ferric (Fe³⁺)—across Earth's atmosphere, hydrosphere, biosphere, and lithosphere through abiotic reactions and microbial metabolism.^[1]^[2] Iron enters ecosystems primarily via rock weathering, releasing soluble Fe²⁺ that oxidizes to insoluble Fe³⁺ precipitates under oxic conditions, while microbial dissimilatory reduction solubilizes Fe³⁺ minerals using organic matter or inorganics like hydrogen as electron donors.^[2]^[3] This cycle profoundly influences environmental dynamics, as iron functions as a critical cofactor in enzymes for respiration, photosynthesis, and nitrogen fixation, yet its low bioavailability—due to Fe³⁺ hydrolysis and precipitation—limits primary productivity in vast high-nutrient, low-chlorophyll (HNLC) ocean regions, constraining phytoplankton blooms and subsequent carbon export to sediments.^[2]^[4] Oceanic iron inputs derive from aeolian dust (e.g., from arid regions like the Sahara), hydrothermal vents, riverine sediments, and glacial melt, with biological recycling amplifying availability through rapid uptake and remineralization by microbes and grazers, often turning over surface soluble iron pools weekly.^[5]^[6] On land, iron cycling modulates soil redox gradients, pollutant mobility (e.g., arsenic sorption to Fe oxides), and greenhouse gas emissions via coupled processes like denitrification or methane oxidation linked to Fe³⁺ reduction.^[2]^[3] Emerging research underscores "cryptic" iron cycling—simultaneous oxidation and reduction in microenvironments—and novel microbial linkages, such as nitrate-dependent Fe²⁺ oxidation or anaerobic ammonium oxidation tied to Fe³⁺, challenging prior views of iron as a unidirectional sink and highlighting its dynamic feedback on carbon, nitrogen, and sulfur cycles across geological timescales.^[2]^[7] These processes, intensified by anthropogenic dust mobilization and climate-driven redox shifts, underscore iron's outsized role in regulating ecosystem resilience and global element fluxes, though quantification remains complicated by nanoscale mineral transformations and microbial electron transfer via nanowires or cytochromes.^[3]^[8]

Geological and Evolutionary Context

Precambrian Iron Dynamics

During the Archean and early Proterozoic eons of the Precambrian, spanning approximately 4.0 to 1.8 billion years ago (Ga), oceanic iron dynamics were dominated by a ferruginous (iron-rich and anoxic) chemistry, with dissolved ferrous iron (Fe²⁺) concentrations orders of magnitude higher than modern levels, often exceeding 10-100 μM in deep waters. This state arose from abundant hydrothermal vent inputs of Fe²⁺—estimated to be several orders of magnitude greater than today due to higher mantle heat flux and seafloor spreading rates—and continental weathering under a reducing atmosphere lacking free oxygen, which kept iron soluble and prevented widespread precipitation. Suboxic surface waters occasionally allowed partial oxidation via photochemical reactions or early microbial activity, but bulk ocean transport occurred as dissolved Fe²⁺, with residence times lengthening from ~0.2 million years (Ma) around 2.52 Ga to ~2.3 Ma by 2.39 Ga, indicating expansive dissolved inventories buffered against removal.^[9]^[10]^[11] Banded iron formations (BIFs), the hallmark archives of Precambrian iron cycling, accumulated primarily between 3.8 and 1.8 Ga, with peak deposition near 2.5 Ga coinciding with the rise of oxygenic photosynthesis by cyanobacteria. These chemical sediments feature rhythmic laminations of iron oxides (e.g., hematite, magnetite) and chert (silica), formed when upwelling Fe²⁺-rich deep waters encountered transiently oxygenated shallow zones, rapidly oxidizing Fe²⁺ to insoluble ferric iron (Fe³⁺) that precipitated as nanoparticles aggregating into bands; seasonal or episodic oxygen pulses from cyanobacterial blooms likely drove the banding via Fe³⁺ reduction and reoxidation cycles mediated by dissimilatory iron-reducing bacteria or anoxygenic phototrophs using Fe³⁺ as an electron acceptor. Biologically recycled continental iron, derived from microbial weathering of basaltic crust, contributed substantially to BIF iron budgets, with isotopic evidence showing up to 50% of Fe sourced from subaerially altered landmasses rather than solely hydrothermal vents.^[12]^[13]^[14] Iron-silicate precipitation, such as greenalite formation, also played a role in early diagenetic iron removal under variable pH conditions in anoxic sediments, where Fe²⁺ reacted with biogenic silica; this process was kinetically enhanced in Precambrian oceans lacking eukaryotic silica biomineralizers, promoting authigenic mineral growth without skeletal influence. The cessation of major BIF deposition after ~1.8 Ga reflected progressive ocean oxygenation during and post-Great Oxidation Event (~2.4 Ga), which scoured dissolved Fe²⁺ via oxidation and burial as sulfides or oxides, shifting iron cycling toward lower oceanic inventories and establishing a more modern, low-Fe state. Minor Neoproterozoic BIFs (~0.8-0.6 Ga) suggest transient ferruginous regressions amid "boring billion" stability, but overall, Precambrian dynamics underscore iron's role as a key electron shuttle in pre-oxygenic biogeochemistry, buffering early biospheres against oxygen toxicity.^[9]^[12]

Post-Oxygenation Evolution

The Great Oxidation Event (GOE), occurring between approximately 2.46 and 2.06 billion years ago, marked a pivotal shift in Earth's iron biogeochemistry by elevating atmospheric oxygen levels, which oxidized abundant dissolved ferrous iron (Fe²⁺) to insoluble ferric iron (Fe³⁺) oxyhydroxides.^[15] This oxidation drastically reduced the solubility and bioavailability of iron in surface oceans and terrestrial environments, transitioning global waters from predominantly ferruginous (Fe²⁺-rich, anoxic) conditions to more oxygenated states where iron precipitated rapidly upon contact with O₂.^[16] Post-GOE marine Fe²⁺ concentrations became highly sensitive to atmospheric pO₂ fluctuations, with models indicating that even modest oxygen increases could drive near-quantitative removal of dissolved iron via scavenging onto particles or direct precipitation, fundamentally altering iron transport and sinks.^[17] Geological records reflect this evolution through the decline of banded iron formations (BIFs) after about 1.85 billion years ago, as oxidative sinks dominated over reductive hydrothermal inputs that had sustained high Fe²⁺ fluxes in pre-GOE oceans.^[18] Instead, iron began accumulating in continental margins and sediments as Fe³⁺-rich phases, with expanded aerobic cycling evident in Archean-Proterozoic shelf environments where partial Fe²⁺ oxidation persisted amid lingering anoxia in deeper waters.^[19] This period also saw the stabilization of iron oxyhydroxides as major sinks, influencing coupled nutrient cycles like phosphorus, where iron-bound P release decreased under oxygenated conditions, potentially exacerbating phosphorus limitation for early life.^[16] Biologically, the post-GOE iron scarcity—exacerbated by Fe³⁺ insolubility in oxic settings—drove evolutionary innovations in iron acquisition. Microorganisms, facing chronic low bioavailability, convergently developed high-affinity systems, including siderophores (low-molecular-weight chelators that solubilize Fe³⁺) and ATP-binding cassette (ABC) transporters for ferric uptake, adaptations that likely emerged after 2.3 billion years ago to enable assimilation in oxidative environments.^[20] Iron oxidation pathways diversified independently across lineages, with aerobic neutrophilic oxidizers exploiting Fe²⁺ gradients for energy, while reductive dissolution by dissimilatory iron-reducing bacteria (e.g., via Geobacter-like mechanisms) facilitated iron remobilization in anoxic microzones.^[21] These adaptations expanded the aerobic iron cycle, linking iron redox transformations to oxygen production and organic matter degradation, and set the stage for iron's role in later eukaryotic evolution despite competition from alternative metals like copper.^[22]

Terrestrial Iron Cycling

Weathering and Pedogenic Processes

Weathering of primary iron-bearing minerals in bedrock, such as biotite, olivine, and pyroxenes, initiates the release of iron into the terrestrial environment through physical disintegration and chemical alteration during soil formation.^[23] Chemical weathering predominates in mobilizing iron, involving hydrolysis of silicates and oxidation of Fe²⁺ to Fe³⁺, which reduces mineral stability and promotes dissolution under surface conditions of oxygen and water.^[24] This process results in significant iron efflux from continents, as evidenced by isotopic studies of Early Carboniferous paleosols showing up to 50% iron loss relative to parent material in some profiles.^[25] In pedogenic environments, released iron undergoes transformation into secondary oxides and hydroxides, forming minerals like ferrihydrite, lepidocrocite, goethite, and hematite through precipitation and aging sequences driven by pH, redox potential, and organic matter interactions.^[26] Amorphous ferrihydrite initially precipitates under oxidizing conditions and crystallizes over time, with organic acids from decomposing matter enhancing solubility and influencing oxide morphology during early pedogenesis.^[27] These pedogenic iron oxides coat soil particles, imparting red or brown hues characteristic of well-drained soils, and serve as indicators of weathering intensity, with dithionite-extractable iron fractions increasing in advanced soil profiles derived from basalt or granite.^[28]^[29] Biological processes amplify iron cycling in weathering zones, where epilithic microorganisms and mycorrhizal fungi produce siderophores and low-molecular-weight organic acids that chelate and solubilize iron from recalcitrant minerals, facilitating its translocation and incorporation into soil aggregates.^[30]^[31] Redox oscillations in seasonally flooded soils promote microbial dissimilatory iron reduction, mobilizing Fe²⁺ for groundwater transport, followed by reoxidation and precipitation as mottles or concretions upon drainage, which structures soil horizons and influences permeability.^[32] Pedogenic iron dynamics thus link weathering to soil functionality, with oxide stability controlling phosphorus sorption and carbon stabilization, as higher pedogenic Fe-to-clay ratios correlate with enhanced organic carbon retention in mineral-associated forms.^[33]

Bioavailability in Soils and Vegetation

Iron bioavailability in soils is constrained despite total concentrations often ranging from 20,000 to 550,000 mg/kg dry weight, as iron predominantly exists as insoluble ferric (Fe³⁺) oxides such as goethite and hematite under aerobic conditions.^[34] Solubility of Fe³⁺ plummets with rising pH, decreasing from roughly 10⁻⁸ M at pH 4 to 10⁻²⁰ M at pH 8, severely limiting availability in neutral to alkaline soils common in calcareous regions.^[34] Ferrous (Fe²⁺) forms, more soluble and bioavailable, prevail in acidic or reducing environments, such as waterlogged paddy fields, where redox potentials favor reduction.^[35] Organic matter and microbial activity can enhance solubility via chelation, but high bicarbonate levels in alkaline soils further precipitate iron, exacerbating deficiency risks.^[36] Plants regulate iron uptake to maintain tissue levels of 50–100 mg/kg dry weight, essential for chlorophyll synthesis, electron transport, and enzymatic functions.^[34] Non-grass species (Strategy I) respond to deficiency by acidifying the rhizosphere through H⁺-ATPase extrusion (e.g., AHA2 in Arabidopsis), reducing Fe³⁺ to Fe²⁺ via root ferric chelate reductases (e.g., FRO2), and importing Fe²⁺ through transporters like IRT1, though this also risks co-uptake of toxic metals such as Cd and Zn.^[35] Grass species (Strategy II) secrete phytosiderophores, including mugineic acid, to chelate soil Fe³⁺, forming soluble complexes transported by yellow stripe-like (YSL) proteins (e.g., YS1 in maize); this approach is less pH-dependent and effective in calcareous soils.^[35] Some crops like rice employ both strategies, combining phytosiderophore release with direct Fe²⁺ uptake under flooded conditions.^[35] Vegetation growth is particularly vulnerable in alkaline soils, affecting approximately 30% of global croplands and causing interveinal chlorosis due to impaired photosynthesis.^[35] Root exudates, including organic acids, and associations with iron-solubilizing rhizobacteria (e.g., via bacterial siderophores) amplify bioavailability, with microbial interactions enabling up to several-fold increases in soluble iron pools.^[37] Deficiency remediation often involves soil acidification or foliar Fe applications, but genetic enhancements, such as introducing Strategy II genes into Strategy I plants, have boosted rice yields by up to 7.9-fold on high-pH soils.^[38] These dynamics underscore iron's role as a limiting micronutrient, influencing vegetation distribution and productivity in iron-poor pedogenic environments.^[36]

Aquatic Iron Cycling

Oceanic Sources, Transport, and Limitation

Oceanic iron primarily enters the marine environment through atmospheric dust deposition, which supplies bioavailable dissolved iron (dFe) via aeolian transport from arid regions such as the Sahara Desert, contributing significantly to surface waters in the Atlantic and Pacific Oceans.^[39] Hydrothermal vents at mid-ocean ridges release substantial quantities of reduced iron into deep waters, with plumes dispersing dFe over thousands of kilometers via deep circulation, particularly influencing iron availability in the Southern Ocean where it supports phytoplankton productivity distant from vents.^[40] Continental margin sediments and benthic fluxes provide boundary sources of iron through reductive dissolution, while riverine inputs deliver particulate and colloidal iron from terrestrial weathering, though much is sequestered in estuaries.^[41] Anthropogenic aerosols, including from industrial emissions, represent an underappreciated soluble iron source, potentially enhancing deposition to high-nutrient regions by factors exceeding prior estimates.^[42] Transport of oceanic iron occurs predominantly as dFe, where over 99% complexes with strong organic ligands such as siderophores produced by microbes, preventing precipitation and scavenging in oxic waters and enabling persistence over basin scales.^[43] Particulate iron, including lithogenic dust and biogenic particles, undergoes remineralization during sinking, releasing dFe that can be re-complexed or transported laterally by currents, with slowly sinking aggregates facilitating cross-basin transfer in the upper ocean.^[44] Ligand-mediated partitioning governs reversible exchanges between dissolved and colloidal/particulate phases, modulating bioavailability; for instance, weaker ligands in hydrothermal plumes initially lose iron to particles before stabilization.^[45] Iron limitation prevails in high-nutrient, low-chlorophyll (HNLC) regions covering approximately 25-40% of the ocean surface, including the Southern Ocean, subarctic Pacific, and equatorial upwelling zones, where low dFe concentrations (<0.1 nM) constrain phytoplankton growth despite abundant macronutrients like nitrate and phosphate.^[46] This scarcity arises from iron's low solubility in oxygenated seawater (precipitating as Fe(III) oxyhydroxides) and rapid removal via particle scavenging, rendering external inputs episodic and insufficient for full primary production potential.^[47] In HNLC areas, iron stress alters phytoplankton community structure, favoring efficient taxa like diatoms under chronic limitation, and co-limitation with light or other trace metals can exacerbate productivity deficits, influencing global carbon export.^[48] Experimental iron additions, such as those in SOIREE and SOFeX, confirm relief of limitation, stimulating blooms and demonstrating iron's role as the proximate control on biomass in these regions.^[49]

Freshwater and Estuarine Dynamics

In freshwater systems, iron inputs derive mainly from soil weathering, groundwater discharge, and atmospheric deposition, with speciation dominated by low-solubility ferric (Fe(III)) oxyhydroxides under oxic, near-neutral pH conditions that limit dissolved concentrations to trace levels. Dissolved iron levels vary geographically, typically ranging from <1 μg/L in oligotrophic streams to 8–135 μg/L in temperate rivers and up to 2,500 μg/L in seasonally stratified or humic-laden boreal waters where organic complexation stabilizes Fe(II) or colloidal forms. In anoxic sediments or hypoxic zones, dissimilatory iron-reducing prokaryotes such as Geobacter and Shewanella species reduce Fe(III) minerals to soluble ferrous (Fe(II)), promoting remobilization and export during low-oxygen events, while microaerophilic iron oxidizers like Gallionella and Leptothrix precipitate Fe(III) at oxic-anoxic interfaces, forming characteristic stalks or sheaths that contribute to particulate flux. Riverine transport favors colloidal and organically bound iron over truly dissolved (<0.2 μm) fractions, with photochemical oxidation and biological uptake further constraining bioavailability in sunlit surface waters; however, acidification or high dissolved organic carbon enhances persistence, as observed in peatland-draining systems where fluxes can exceed 10–100 μmol m⁻² d⁻¹ seasonally. Estuarine dynamics impose a pronounced "iron trap" through salinity-driven processes: mixing with seawater elevates ionic strength, inducing rapid flocculation and coagulation of Fe(III) hydroxides and colloids, which settle as aggregates and remove ~90% of incoming dissolved riverine iron via sedimentation before oceanic export. This non-conservative behavior is amplified in turbid, macrotidal estuaries, where tidal pumping and resuspension recycle iron within the system but limit net marine delivery, with removal efficiencies modulated by particle size, organic coatings, and pH gradients. In estuarine marshes and sediments, seasonal anoxia fosters microbial Fe(III) reduction coupled to organic matter decomposition, enhancing porewater Fe(II) diffusion and potential reflux to overlying waters, though sulfide precipitation as iron monosulfides sequesters it during sulfidogenic conditions; vegetation in tidal zones further influences cycling by oxygenating rhizospheres, promoting localized Fe(III) precipitation and limiting export. These processes collectively position estuaries as net sinks, buffering oceanic iron limitation while sustaining local redox gradients critical for nutrient transformations.

Biological Processes in Iron Cycling

Prokaryotic Mechanisms

Prokaryotes mediate key transformations in the iron cycle through dissimilatory reduction and oxidation of iron oxyhydroxides, influencing iron solubility and bioavailability across redox gradients.^[50] Dissimilatory iron-reducing microorganisms (DIRMs), including bacteria such as Geobacter and Shewanella species, utilize Fe(III) as a terminal electron acceptor during anaerobic respiration, coupling the oxidation of organic substrates or hydrogen to the reduction of insoluble Fe(III) minerals like ferrihydrite or goethite to soluble Fe(II).^[51] This process generates energy via electron transport chains involving c-type cytochromes and multi-heme proteins on the outer membrane, enabling direct electron transfer to mineral surfaces, while indirect mechanisms employ exogenous electron shuttles such as humic substances or endogenously produced quinones.^[50] Iron oxidation by prokaryotes occurs primarily through chemolithotrophic pathways, where neutrophilic and acidophilic bacteria derive energy from the oxidation of Fe(II) to Fe(III). Neutrophilic iron oxidizers, such as Gallionella ferruginea and Leptothrix ochracea, thrive in circumneutral pH environments like freshwater sediments and wetlands, precipitating Fe(III) oxyhydroxides as stalks or sheaths that facilitate iron immobilization and influence sediment geochemistry.^[52] Acidophilic species like Acidithiobacillus ferrooxidans dominate in low-pH settings such as acid mine drainages, accelerating Fe(II) oxidation via enzymatic systems including cytochrome c and rusticyanin, which enhance iron cycling rates and contribute to secondary mineral formation.^[53] Under iron-limited conditions, prokaryotes employ siderophores—high-affinity Fe(III)-chelating compounds—to solubilize and acquire iron from the environment. These non-ribosomal peptide or polyketide-derived molecules, exemplified by enterobactin in Escherichia coli and pyoverdine in Pseudomonas species, form stable complexes with Fe(III) that are recognized by specific outer membrane receptors and transported into the cell via TonB-dependent systems.^[54] Siderophore-mediated acquisition not only supports microbial growth but also alters iron speciation in soils and aquatic systems, promoting reductive dissolution of Fe(III) minerals and enhancing overall iron mobility in biogeochemical cycles.^[55]

Eukaryotic and Multicellular Roles

Eukaryotic microorganisms, particularly marine phytoplankton, drive significant iron uptake in ocean surface waters to support photosynthesis, electron transport, and nitrogen fixation. These organisms employ reductive mechanisms to assimilate ferric iron, reducing it to ferrous form via plasma membrane reductases, followed by high-affinity transporters. Siderophore-bound iron is also utilized, with some species like diatoms expressing receptors for ferrioxamine complexes prevalent in seawater. In high-nutrient, low-chlorophyll regions, phytoplankton iron demand can deplete dissolved iron stocks, limiting primary production until recycled through grazing or vertical mixing.^[56]^[57] Terrestrial eukaryotic fungi enhance iron bioavailability in soils through siderophore production, forming complexes that solubilize iron for uptake by mycorrhizal partner plants. Arbuscular and ectomycorrhizal fungi secrete hydroxamate or carboxylate siderophores, which chelate Fe(III) under low-pH, iron-poor conditions, enabling efficient transfer to plant roots via strategy I (reduction) or strategy II (chelation) pathways. This symbiotic iron mobilization prevents chlorosis in crops and forests, recycling iron from organic matter decomposition back into bioavailable forms. Fungal siderophores also compete with bacterial ones, influencing community dynamics in rhizospheres.^[58]^[59] Multicellular eukaryotes, including plants and marine animals, mediate iron transport and export in biogeochemical cycles. Land plants accumulate iron in leaves and roots, with subsequent litterfall and root turnover returning it to soils via mineralization, though much is retained in recalcitrant biomass. In pelagic systems, zooplankton graze iron-laden phytoplankton, assimilating ~20-50% of ingested iron while egesting the rest in fecal pellets that sink rapidly, exporting iron to depths beyond 100 meters and alleviating surface limitation in the Southern Ocean. Larger animals amplify this: Antarctic krill recycle ~10-20% of regional iron inputs through molting and excretion, sustaining phytoplankton blooms; sperm whales contribute ~50 tonnes of iron annually via defecation, enhancing carbon sequestration; and penguin guano deposits ~521 tonnes yearly from Chinstrap populations alone, fertilizing coastal waters. These processes underscore multicellular roles in vertical iron flux, countering aeolian inputs' short residence times (~days).30988-5)^[60]^[61]^[62]

Interactions with Other Biogeochemical Cycles

Carbon and Primary Productivity Linkages

Iron availability exerts a primary control on marine primary productivity in regions where macronutrients abound but phytoplankton biomass remains low, such as high-nutrient, low-chlorophyll (HNLC) areas encompassing approximately 20-40% of the global ocean surface, including the Southern Ocean and equatorial Pacific.^[63] In these zones, iron limitation curtails phytoplankton growth, reducing carbon fixation rates and the efficiency of the biological carbon pump, which exports organic carbon to the deep ocean and sequesters atmospheric CO₂ on timescales of centuries to millennia. Phytoplankton demand iron for essential metalloproteins, including cytochromes in electron transport chains, ferredoxin in photosynthesis, and nitrogenase in diazotrophs, with optimal cellular Fe:C ratios ranging from 10 to 100 μmol Fe per mol C under replete conditions.^[64] Iron deficiency impairs photosystem II assembly and rubisco activase function, directly diminishing CO₂ assimilation.^[65] Field experiments adding dissolved iron to HNLC waters have consistently induced phytoplankton blooms, elevating primary production by factors of 10-20 and increasing particulate organic carbon export. For instance, the 2004 Crozet natural iron fertilization event, driven by island-derived inputs, resulted in enhanced downward carbon fluxes of 0.1-0.4 mol C m⁻² yr⁻¹, with roughly 30% of new production contributing to sequestration below 100 m depth. Similarly, artificial enrichments like SOFeX (2002) demonstrated that iron-stimulated diatoms can drive carbon export efficiencies up to 25% of total primary production, though remineralization in surface layers often limits net sequestration.^[66] These linkages underscore iron's role in modulating the ocean's capacity to draw down ~10-15 Gt C yr⁻¹ via the biological pump under current conditions.^[63] Internal dynamics of the iron cycle, including organic ligand complexation that enhances solubility and microbial remineralization of particulate iron, generate feedbacks that influence carbon cycling independent of external supplies. Modeling studies indicate these processes can decouple oceanic CO₂ uptake from atmospheric forcing during deglaciation events, where iron recycling amplified productivity and carbon storage by up to 20-50 ppm in atmospheric CO₂ reductions.^[67] In contrast, terrestrial iron cycling linkages to primary productivity are mediated through soil pedogenesis and plant uptake, where bioavailable Fe³⁺ reduction to Fe²⁺ facilitates root absorption and chlorophyll synthesis, but global carbon flux impacts are secondary to oceanic effects given land's ~50% share of net primary production yet lower iron sensitivity.^[1] Climate-driven changes, such as acidification reducing iron speciation or dust deposition variations, could alter these balances, potentially shifting ~1-5% of global carbon sequestration efficiency.^[68]

Nitrogen, Sulfur, and Phosphorus Couplings

Iron bioavailability modulates biological nitrogen fixation in marine systems, where the nitrogenase enzyme requires iron as a cofactor, leading to iron limitation of diazotrophs in high-nutrient, low-chlorophyll (HNLC) regions of the open ocean. Changes in atmospheric iron deposition can perturb the marine nitrogen cycle, with model simulations indicating up to 70% increases in water-column denitrification and 15% rises in nitrogen fixation under altered iron fluxes. In soils, iron redox transformations influence nitrogen cycling; for instance, ferric iron reduction under anoxic conditions can enhance denitrification rates, while abiotic reactions involving ferrous iron (Fe(II)) facilitate nitrate reduction, thereby linking iron oxidation to nitrogen loss. Microorganisms further couple these cycles through nitrate-dependent anaerobic iron oxidation, where bacteria such as Pseudomonas and Acidovorax species oxidize Fe(II) using nitrate as an electron acceptor, conserving energy and producing nitrite or dinitrogen gas.^[69]^[70]^[71] Sulfur-iron interactions predominantly occur in anoxic sediments, where dissolved sulfide produced by microbial sulfate reduction reacts with iron oxides or dissolved Fe(II) to form iron sulfides like pyrite (FeS₂), effectively sequestering both elements and preventing sulfide toxicity to benthic organisms. This process contributes to a "cryptic" sulfur cycle, where much of the reduced sulfur is reoxidized without escaping to overlying waters, modulated by iron availability; in iron-rich sediments, up to 90% of sulfide can be trapped as Fe-S minerals. In marine oxygen minimum zones, sulfur cycling intersects with iron through microbial consortia that couple sulfate reduction to iron reduction, influencing trace metal speciation and carbon remineralization. Bistable redox states in sediments and oceans arise from iron-sulfur feedbacks, where high iron inputs favor pyrite formation and low iron promotes free sulfide accumulation, altering ecosystem redox dynamics over geological timescales.^[72]^[73]^[74] Phosphorus cycling is tightly coupled to iron through adsorption and coprecipitation, with ferric iron oxides (e.g., ferrihydrite) binding phosphate strongly in oxic soils and sediments, reducing phosphorus bioavailability and mitigating eutrophication risks. Under anoxic conditions, dissimilatory iron reduction by microbes releases bound phosphorus, increasing its mobility; for example, in lake sediments, seasonal iron reduction can elevate porewater phosphate by 50-100% during stratification. Iron-based amendments, such as ferrous salts, are applied to immobilize phosphorus in eutrophic waters, enhancing sorption capacity and reducing internal loading by up to 80% in treated systems. In coastal sediments, phosphorus remobilization is linked to coupled iron-sulfur transformations, where sulfide-induced iron dissolution liberates phosphate, with kinetic models showing release rates tied to Fe:S ratios below 1:15. Microbially, phosphorus-iron associations influence nutrient stoichiometry, as iron nanoparticles can decrease phosphorus bioavailability by 30-50% in freshwater systems through aggregation and settling.^[75]^[76]^[77]

Anthropogenic Modifications

Industrial Emissions and Pollution

Industrial activities, particularly iron and steel production, constitute the primary anthropogenic sources of iron emissions to the atmosphere, accounting for 59-63% of total anthropogenic iron releases globally.^[78] These emissions arise from processes such as smelting, coke production, and fossil fuel combustion in blast furnaces, releasing iron-containing particulates and aerosols that undergo atmospheric transport and deposition.^[79] Other contributors include coal and oil combustion, which elevate soluble iron fractions through interactions with sulfuric and nitric acids in polluted air, enhancing bioavailability compared to natural dust sources.^[80]^[81] Atmospheric deposition from these industrial emissions perturbs the natural iron cycle by increasing inputs of bioavailable iron to remote ocean regions, where iron limitation constrains primary productivity. In the Northwest Pacific, anthropogenic sources contribute approximately 31% of total aerosol iron and 87% of its soluble fraction, demonstrating the outsized role of pollution in altering iron speciation and solubility.^[82] Studies indicate that such inputs have invaded surface oceans, supplementing traditional mineral dust supplies and potentially shifting phytoplankton community dynamics, as evidenced by altered spring blooms in regions like the Southern Ocean.^[83]^[84] Globally, trends from 1980 to 2015 show increasing anthropogenic iron emissions, contrasting with declines in dust-derived iron, thereby amplifying human influence on marine iron cycling.^[85] Beyond atmospheric pathways, industrial pollution introduces iron to aquatic and terrestrial systems via wastewater discharge and mining runoff, leading to elevated concentrations that disrupt local biogeochemical balances. Iron ore mining generates acid mine drainage rich in dissolved iron, which oxidizes and precipitates in receiving waters, smothering benthic habitats and altering sediment redox conditions critical to the iron cycle.^[86] In urban-industrial areas, such as those near steelworks, atmospheric deposition correlates with heightened soil and water iron levels, influencing microbial iron reduction and oxidation processes.^[87] While iron's essentiality tempers direct toxicity, excess anthropogenic loading can induce oxidative stress in organisms and catalyze unwanted redox reactions, underscoring the need for emission controls to mitigate cycle perturbations.^[88]^[89]

Intentional Interventions and Experiments

Ocean iron fertilization experiments represent the primary intentional interventions aimed at manipulating the marine iron cycle to alleviate iron limitation in high-nutrient, low-chlorophyll (HNLC) waters, thereby stimulating phytoplankton blooms and testing potential for enhanced carbon sequestration through biological pump amplification. These experiments, conducted between 1990 and 2009, involved targeted additions of dissolved iron, typically as ferrous sulfate (FeSO₄), at concentrations of 0.5–2 nM over patches ranging from kilometers to tens of kilometers in scale. Thirteen major artificial ocean iron fertilization (aOIF) trials confirmed iron's role in constraining primary production, with additions consistently inducing phytoplankton biomass increases of 10- to 30-fold and elevated net primary production, though iron retention in surface waters was short-lived due to scavenging and oxidation processes.^[90]^[91] Early experiments, such as IronEx I in 1993 (equatorial Pacific) and IronEx II in 1995, demonstrated rapid chlorophyll enhancement and community shifts toward larger diatoms, with IronEx II achieving a sustained bloom over 15 days following 1.2 tons of iron addition. Subsequent Southern Ocean trials like SOIREE (1999, ~61°S, 140°E) added ~1 ton of iron, producing a coherent bloom patch with CO₂ drawdown of ~25–50 µmol kg⁻¹, though export was limited by shallow remineralization; mixing enhanced uptake in SOIREE compared to EisenEx (2001, ~21°S, 17°E), where stronger winds facilitated fourfold greater atmospheric CO₂ absorption despite similar iron inputs of ~13 tons. SOFeX (2002) and SERIES (2002, subarctic Pacific) further showed diatom-dominated responses and modest particulate organic carbon flux to 100 m depths, but deep-ocean (>1000 m) sequestration remained inefficient, often <1% of stimulated production.^[90]^[92] The LOHAFEX experiment (January–March 2009, Southern Atlantic, 47–49°S, 14–16°W) released ~6 tons of iron in two pulses to target 0.3–1.5 nM concentrations, inducing a ~300 km² bloom dominated by nanoflagellates (e.g., Phaeocystis antarctica-like), with chlorophyll a rising from 0.5 to 1.25 µg L⁻¹; however, intense protozoan grazing and microbial remineralization prevented significant carbon export below the mixed layer, releasing fixed carbon back as CO₂. Across all trials, only one (SOFeX-S) documented verifiable deep carbon accumulation, highlighting systemic limitations including rapid Fe(II) oxidation to particulate forms, zooplankton-mediated recycling, and incomplete particle sinking. Empirical data indicate aOIF yields modest sequestration potential, equivalent to ~10% atmospheric CO₂ offset in modeled large-scale applications, insufficient for meaningful climate mitigation without unmanageable ecological risks like altered food webs or dimethyl sulfide emissions.^[93]^[94]^[90] Regulatory responses curtailed further large-scale efforts; the 2010 London Protocol amendment imposed a moratorium on non-scientific ocean fertilization, citing uncertainties in long-term efficacy and side effects, though small-scale research persists under strict oversight. Proposed variants, such as nanoparticle or dust-derived iron, remain untested at scale and face similar bioavailability and dispersion challenges observed in sulfate-based additions.^[94]

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Precambrian BIFs were formed mainly in two periods: Archean to Paleoproterozoic (3.8~1.8 Ga) and Late Neoproterozoic (0.8~0.6 Ga) [3,4,5,6]. The peak of BIFs ...
[13]
The Biology Behind Banded Iron Formations - NASA Astrobiology
Mar 4, 2013 · These rock formations likely formed when Fe(II)-rich hydrothermal fluid wells up into shallow water. Fe(II) then undergoes oxidation.
[14]
Biologically recycled continental iron is a major component ... - PNAS
Banded iron formations (BIFs) are Precambrian chemical marine sedimentary rocks that represent the major source of Fe used in today's society. Early studies ...<|separator|>
[15]
Oxygen dynamics in the aftermath of the Great Oxidation of Earth's ...
The Great Oxidation of Earth's atmosphere about 2.3 billion years ago began a series of geochemical events leading to elevated oxygen levels for the next 200 ...
[16]
Evolution of iron and oxygen biogeochemical cycles during the ...
Aug 25, 2023 · Here, we develop a biogeochemical model to investigate the coupled biogeochemical evolution of Fe-O2 -P-C cycles across the GOE. Our model ...
[17]
Evolution of iron and oxygen biogeochemical cycles during the ...
Aug 25, 2023 · Here, we develop a biogeochemical model to investigate the coupled biogeochemical evolution of Fe–O 2 –P–C cycles across the GOE.
[18]
Triple iron isotope constraints on the role of ocean iron sinks in early ...
Oct 23, 2020 · The role that iron played in the oxygenation of Earth's surface is equivocal. Iron could have consumed molecular oxygen when Fe3+-oxyhydroxides ...
[19]
Expansion of the aerobic iron biogeochemical cycle during ... - Nature
Feb 15, 2025 · The latter reflects complete oxidation and quantitative removal of dissolved iron from seawater, followed by complete reduction of oxidized iron ...
[20]
Temporal variation of planetary iron as a driver of evolution - PNAS
Dec 6, 2021 · Cells need to assimilate iron and post-GOE, increasingly would need to do so in oxidative conditions where iron is insoluble. Siderophores ...
[21]
Insight into the evolution of the iron oxidation pathways - ScienceDirect
Based on what is known today about Fe(II) oxidation pathways, we propose that they arose independently more than once in evolution and evolved convergently.
[22]
Iron: Life's primeval transition metal - PNAS
Sep 9, 2024 · While iron can be an excellent redox-active metal in oxidizing environments, its post-GOE shortage likely required life to expand to other metal ...
[23]
The role of iron-bearing minerals for the deep weathering of a ...
Aug 20, 2022 · Our study shows that the transformation of iron-bearing silicates (especially biotite) to Fe(III) (oxyhydr)oxides and clay minerals is the dominant weathering- ...
[24]
5.2 Chemical Weathering – Physical Geology - BC Open Textbooks
Chemical weathering results from chemical changes to minerals that become unstable when they are exposed to surface conditions.
[25]
Iron Loss During Continental Weathering in the Early Carboniferous ...
Mar 22, 2023 · Significant iron (Fe) loss can occur during continental weathering and efflux to the ocean via runoff, historically affecting global Fe cycling and marine ...
[26]
(PDF) Iron Compounds as Indicators of Pedogenic Processes
Dec 2, 2015 · This Chapter is concerned with the distribution, occurrence, and properties of Fe compounds as characteristics of soils in selected parts of ...
[27]
Organic matter governs weathering rates and microstructure ...
Jan 1, 2023 · Our experiments show that this combination of processes fractionates OM and sustains iron mobility already at the early stage of pedogenesis.
[28]
Clay and Fe (oxyhydr)oxide mineralogy in the basalt weathering ...
Jul 26, 2024 · Clay and Fe (oxyhydr)oxide mineralogy in the basalt weathering profile in Hainan (southern China): implications for pedogenesis process ...
[29]
[PDF] pedogenic or soil forming processes - Rama University
The iron released during weathering is oxidized to form FeO, Fe2O 3 and coats clay, silt or sand particles imparting characteristic red color to soils. The ...
[30]
Biogenic Weathering: Solubilization of Iron from Minerals by Epilithic ...
In this environment, biogenic weathering is most likely caused by the chelating effects of LMWOA generated during the citric acid cycle (Krebs cycle). This ...
[31]
Ectomycorrhizal fungi integrate nitrogen mobilisation and mineral ...
Sep 11, 2023 · Ectomycorrhizal fungi have been postulated to play an important part in weathering, and even in pedogenesis (Leake & Read, 2017), but there are ...
[32]
Effects of human activities on pedogenesis and iron dynamics in ...
Iron (Fe) isotopes can effectively unveil the Fe cycle mechanisms under redox and biological conditions during the weathering and pedogenic processes. Fe ...
[33]
Iron oxides and aluminous clays selectively control soil carbon ...
Mar 3, 2021 · We found that the ratio of pedogenic Fe to aluminous clay is more consequential for OC storage and stabilization than their individual contents.
[34]
[PDF] Ecological Soil Screening Level for Iron
In various soils and especially at low pH, iron oxides can precipitate on clay surfaces. These coatings, once formed, are stable at higher pHs. The coatings ...Missing: pedogenic | Show results with:pedogenic
[35]
Iron uptake and transport in plants: The good, the bad, and the ionome
Fe availability is dictated by the soil redox potential and pH. In soils that are aerobic or of higher pH, Fe is readily oxidized, and is predominately in the ...Missing: vegetation | Show results with:vegetation
[36]
Plant strategies to mine iron from alkaline substrates | Plant and Soil
Nov 29, 2022 · In concert with oxygen, soil alkalinity strongly restricts the availability of iron, an essential nutrient with a multitude of functions in ...Missing: bioavailability | Show results with:bioavailability
[37]
Research progress on iron absorption, transport, and molecular ...
Jul 3, 2023 · Plants absorb iron from soil by interacting with microorganisms. When the content of reducing iron in soil is insufficient, plants will ...Missing: vegetation | Show results with:vegetation
[38]
https://pmc.ncbi.nlm.nih.gov/articles/PMC2764373
[39]
GEOTRACES: Ironing Out the Details of the Oceanic Iron Sources?
May 24, 2024 · Elevated dFe concentrations are found near boundary sources (dust, sediments, hydrothermal vents) and also in some cases at remarkably long ...
[40]
More to hydrothermal iron input than meets the eye - PNAS
Until less than 10 y ago, hydrothermal vents were disregarded as important sources of Fe to the wider ocean as the Fe supplied was assumed to fall out in ...
[41]
The stabilisation and transportation of dissolved iron from high ...
Aug 1, 2013 · The supply of Fe to the world's oceans is poorly constrained, with atmospheric dust, rivers, sediments and remineralisation of sinking particles ...
[42]
The underappreciated role of anthropogenic sources in atmospheric ...
Apr 13, 2022 · Atmospheric deposition to the open oceans is a major source of new soluble iron, commonly used as a proxy for iron that is bioavailable for ...<|separator|>
[43]
The Organic Complexation of Iron in the Marine Environment
The organic complexation of Fe, with typically >99.9% of dFe complexed by ligands in the marine environment, is a nearly ubiquitous feature of dFe speciation in ...
[44]
Slowly Sinking Particles Underlie Dissolved Iron Transport Across ...
Mar 29, 2021 · Such organic ligands may contribute to the transfer of Fe to the particulate phase by binding Fe and then aggregating into larger particles ...
[45]
Organic iron-binding ligands mediate dissolved-particulate ...
May 20, 2025 · Organic iron-binding ligands mediate iron exchange in hydrothermal plumes. Initially, weaker ligands and iron are lost to particulate phase, ...
[46]
From the Ocean to the Lab—Assessing Iron Limitation in ...
Iron is growth-limiting for phytoplankton in 25%–30% of the world's oceans [1,2]. Since the discovery of high nutrient-low chlorophyll (HNLC) zones in the ...
[47]
What controls dissolved iron concentrations in the world ocean?
The dissolved iron source in the ocean interior is remineralization from sinking particulate organic matter. Scavenging removes dissolved iron only at ...
[48]
Roles of Iron Limitation in Phytoplankton Dynamics in the Western ...
The subarctic Pacific is one of the major high-nitrate, low-chlorophyll (HNLC) regions where marine productivity is greatly limited by the supply of iron ...Abstract · Introduction · Results · Discussion
[49]
Phytoplankton and light limitation in the Southern Ocean: Learning ...
Feb 27, 2010 · The widespread iron limitation leads to generally low chlorophyll a (chl a) concentrations [Moore et al., 1999], so the area (Figure 1), along ...
[50]
Dissimilatory Fe(III) and Mn(IV) reduction - PMC - NIH
With Fe(III) or Mn(IV) as the sole electron acceptor, these organisms can completely oxidize fatty acids, hydrogen, or a variety of monoaromatic compounds. This ...
[51]
Application of dissimilatory iron-reducing bacteria for the ...
Shewanella and Geobacter are two common DIRB, that are capable of anaerobic respiration by reducing Fe(III) to Fe(II) (Shi et al., 2016). Geobacter is a genus ...
[52]
Neutrophilic lithotrophic iron-oxidizing prokaryotes and their role in ...
May 9, 2014 · Occurrence of iron oxidizers in freshwater and marine ecosystems, thermal springs, areas of hydrothermal activity, and underwater volcanic areas ...
[53]
https://www.microbiologyresearch.org/content/journal/micro/10.1099/mic.0.045344-0
[54]
Siderophore-Based Iron Acquisition and Pathogen Control - PMC
For the utilization of siderophores, microorganisms have to tightly regulate enzymes and transport systems that allow concerted siderophore biosynthesis, ...
[55]
Iron metabolism and biochemical cycling mediated by microorganisms
Mar 5, 2024 · This Research Topic aims to provide an overview of new insights into iron metabolism and biogeochemical cycling. The goal is to expand knowledge ...
[56]
Iron Uptake Mechanisms in Marine Phytoplankton - PubMed Central
Dark/light cycles may also be involved in regulating iron uptake systems in phytoplankton species, because the photoreductive dissociation of natural ferric ...
[57]
Molecular Mechanisms for Iron Uptake and Homeostasis in Marine ...
The micronutrient iron is essential for phytoplankton growth due to its central role in a wide variety of key metabolic processes including photosynthesis ...<|separator|>
[58]
Mechanisms of iron acquisition from siderophores by ...
Plants that use microbial siderophores may also be more Fe efficient by virtue of their ability to use a variety of Fe sources under different soil conditions.
[59]
(PDF) Mechanisms of iron acquisition from siderophores by ...
Aug 6, 2025 · The research on the ecology of fungal siderophores has been focused on the role of the fungal siderophores in the acquisition of iron by plants.<|separator|>
[60]
Iron defecation by sperm whales stimulates carbon export in the ...
Jun 16, 2010 · We estimate that Southern Ocean sperm whales defecate 50 tonnes of iron into the photic zone each year. Molar ratios of Cexport ∶Feadded ...Missing: marine animals
[61]
The contribution of penguin guano to the Southern Ocean iron pool
Apr 11, 2023 · With an average guano concentration of 3 mg iron g−1, we estimate that the Chinstrap penguin population is recycling 521 tonnes iron yr−1, ...
[62]
Pelagic Iron Recycling in the Southern Ocean - Frontiers
Mar 28, 2018 · Recent studies suggest that recycling of iron by animals in the surface layer could enhance primary productivity in the Southern Ocean.
[63]
The Biological Productivity of the Ocean | Learn Science at Scitable
Productivity fuels life in the ocean, drives its chemical cycles, and lowers atmospheric carbon dioxide. Nutrient uptake and export interact with circulation to ...
[64]
Iron–Nutrient Interactions within Phytoplankton - PMC
Aug 18, 2016 · A lack in both Fe and light (e.g., high latitude HNLC regions) results in the dual limitation of photosynthesis.
[65]
High iron requirement for growth, photosynthesis, and low-light ...
Iron limits carbon fixation in much of the modern ocean due to the very low solubility of ferric iron in oxygenated ocean waters.
[66]
Ocean Islands Fuel Productivity and Carbon Sequestration Through ...
Jan 29, 2009 · The team showed that this natural iron fertilization enhanced phytoplankton growth and productivity and the amount of carbon exported from the ...<|separator|>
[67]
Ocean iron cycle feedbacks decouple atmospheric CO2 ... - Nature
Jul 8, 2024 · This first-order response suggests iron cycle feedbacks may be a critical driver of the ocean's response to climate changes, independent of external iron ...
[68]
Acclimation of Phytoplankton Fe:C Ratios Dampens the ...
Apr 10, 2023 · The link between iron availability and carbon export is strongly dependent on the phytoplankton iron quotas or cellular Fe:C ratios.
[69]
Impact of Changes to the Atmospheric Soluble Iron Deposition Flux ...
Feb 20, 2020 · Changes in iron deposition cause large perturbations to the marine nitrogen cycle, up to 70% increase in denitrification and 15% increase in ...
[70]
Interactions of Iron with the Nitrogen Cycle - University of Kentucky
Abiotic denitrification by naturally occurring Fe(II) could playa significant role in coupling the redox cycles ofN and Fe in soil environments, yet there is ...
[71]
Microbially Mediated Coupling of Fe and N Cycles by Nitrate ... - NIH
Jan 2, 2018 · The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations.
[72]
Iron and sulfur speciation and cycling in the sediments of marine ...
Aug 20, 2021 · This will prevent the formation of pyrite and result in a 'cryptic' sulfur cycle. We studied the cycling of iron and sulfur in deep water (>800 ...Abstract · Methods · Discussion · Conclusions
[73]
The Biogeochemical Sulfur Cycle of Marine Sediments - PMC
Manganese and iron reduction are focused toward the surface sediment, but Fe(III) is also buried and acts as an oxidant for sulfide in the deeper sediment ...
[74]
Bistability in the redox chemistry of sediments and oceans - PNAS
Dec 14, 2020 · We show that both sedimentary and aquatic systems display intrinsic iron–sulfur bistability, which is tightly linked to the formation of reduced iron–sulfide ...
[75]
Impact of iron addition on phosphorus dynamics in sediments of a ...
Jan 1, 2024 · Addition of iron (Fe) salts has been used to enhance P retention in lake sediments. However, its effects on sediment geochemistry are poorly studied.
[76]
Kinetic Exchange of Remobilized Phosphorus Related to ...
Nov 23, 2019 · Phosphorus (P) cycling in coastal sediment can be strongly coupled to iron (Fe) and sulfur (S) geochemical transformations.
[77]
Regulation of phosphorus bioavailability by iron nanoparticles in a ...
Dec 10, 2018 · This study addresses the coupling of P with dispersed iron nanoparticles in lakes, an interaction that may fundamentally alter the bioavailability of P to ...
[78]
Atmospheric outflow of anthropogenic iron and its deposition to ...
Jan 1, 2021 · Iron and steel industry are the dominant sources of Fe, accounting for 59–63% of the total anthropogenic Fe emissions. Geotropically ...
[79]
Aerosol Iron from Metal Production as a Secondary Source of ...
Feb 28, 2023 · Iron-containing particles co-emitted with sulfur dioxide from metal production substantially contribute to atmospheric bioaccessible iron fluxes ...
[80]
Anthropogenic combustion iron as a complex climate forcer - Nature
Apr 23, 2018 · Iron emitted by anthropogenic (fossil fuel) combustion is a source of soluble iron that is currently considered less important than other ...
[81]
Air pollution causes high iron solubility in anthropogenic aerosols ...
May 2, 2019 · It was confirmed that anthropogenic iron in aerosols from air pollution is dissolved more quickly in water than natural iron during atmospheric ...<|separator|>
[82]
Quantifying anthropogenic emission of iron in marine aerosol in the ...
Feb 20, 2024 · Anthropogenic source contributed 31 % of total Fe and 87 % of soluble Fe in aerosol in the Northwest Pacific. •. Anthropogenic Fe resolved by ...
[83]
Anthropogenic Iron Invasion into the Ocean: Results from the East ...
Jul 25, 2023 · Traditionally, atmospheric input of natural mineral dust has been considered as a main source of Fe in the surface ocean.
[84]
Anthropogenic iron alters the spring phytoplankton bloom in ... - PNAS
Jun 2, 2025 · Industrial emissions now add to the natural iron supply, but ecosystem impacts from anthropogenic iron input have not yet been demonstrated.
[85]
Recent (1980 to 2015) Trends and Variability in Daily‐to ...
Aug 30, 2020 · Statistically significant emission trends exist: dust iron decreases, fire iron slightly increases, and anthropogenic iron increases.
[86]
Environmental Impacts of Iron Ore Mining | UKGBC
Land use change driven by mining is a major environmental concern, affecting ecology and local populations via habitat destruction, water use, and pollution.
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(PDF) Influence of Iron and Steel Industry on Selected Elements of ...
Oct 17, 2025 · The total atmospheric deposition (AD) was sampled in the urban and industrial area with iron and steel works and other urban sources of ...
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Air Pollution Aspects of Iron and its Compounds - epa nepis
Iron and its compounds present as pollutants in the atmosphere can cause deleterious effects to humans, animals/ and materials.
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Constraining Present‐Day Anthropogenic Total Iron Emissions ...
Aug 28, 2024 · Iron emissions from human activities, such as oil combustion and smelting, affect the Earth's climate and marine ecosystems.
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BG - Reviews and syntheses: Ocean iron fertilization experiments
We introduce the scientific aOIF experimental design guidelines for a future Korean Iron Fertilization Experiment in the Southern Ocean (KIFES).
[91]
The past, present, and future of artificial ocean iron fertilization ...
Jan 23, 2019 · A review paper published in Biogeosciences on aOIF experiments provides a thorough overview of 13 scientific artificial OIF experiments conducted in HNLC ...Missing: peer- | Show results with:peer-
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[PDF] Oceanography
The success of IronEx II paved the way for considering a mesoscale enrichment experiment in the challenging environ- ment of the Southern Ocean (Frost,. 1996), ...
[93]
Microbial Community Response during the Iron Fertilization ... - NIH
In two fertilization steps, an acidified iron(II) sulfate solution was released into the water at days 0 (27 January 2009) and 18 (14 February 2009) of the ...Missing: outcomes | Show results with:outcomes<|separator|>
[94]
Next steps for assessing ocean iron fertilization for marine carbon ...
The efficiency of iron fertilization for previous mesoscale OIF experiments has generally been low, with estimates suggesting that only ≈1% of added iron was ...