Chemical Speciation Of Iron Research Articles

Distribution and chemical speciation of iron on the outer edge of the Changjiang diluted water plume of the East China Sea

In this study, we investigated the distribution of dissolved iron (DFe) and organic iron-binding ligands (LFe) in the area of contact between the Changjiang diluted water (CDW) plume and the branch of the Kuroshio Current during the early summer. Our objective was to evaluate how the interaction of these water masses affects the iron chemistry in this region. The upper 20 m of the stations on the northwestern sides was characterized by water of relatively low salinity (<33), which was influenced by the CDW. The northward branch of the Kuroshio Current likely flowed below this low-salinity water, at approximately 30–40 m. On the East China Sea continental shelf, low-oxygen water developed in the bottom water and advected horizontally towards the shelf slope on the isopycnic surface. The surface water, influenced by the CDW, contained relatively high concentrations of DFe and humic-like substances of riverine origin. However, the concentration of LFe in this water mass was not significantly different from that in the surrounding water masses. In low-oxygen water, the DFe concentration was high, and the concentration of humic-like substances was lower than that in the water from the upper layers. In addition to the LFe found in the oxygenated water, LFe with weaker affinities for ferric ions were also detected in this low-oxygen water, and the total concentration of LFe (>2 nM) was significantly higher than that in the other water masses. These results suggest that LFe released through biological decomposition of organic matter is more important for iron complexation in this area than humic-like substances. Therefore, it is essential to quantify diapycnal mixing with deep water on the continental shelf and shelf edge to evaluate the Kuroshio branch as a transporter of iron and LFe to the Sea of Japan.

Influence of pH and Dissolved Organic Matter on Iron Speciation and Apparent Iron Solubility in the Peruvian Shelf and Slope Region.

The chemical speciation of iron (Fe) in oceans is influenced by ambient pH, dissolved oxygen, and the concentrations and strengths of the binding sites of dissolved organic matter (DOM). Here, we derived new nonideal competitive adsorption (NICA) constants for Fe(III) binding to marine DOM via pH-Fe titrations. We used the constants to calculate Fe(III) speciation and derive the apparent Fe(III) solubility (SFe(III)app) in the ambient water column across the Peruvian shelf and slope region. We define SFe(III)app as the sum of aqueous inorganic Fe(III) species and Fe(III) bound to DOM at a free Fe (Fe3+) concentration equal to the limiting solubility of Fe hydroxide (Fe(OH)3(s)). A ca. twofold increase in SFe(III)app in the oxygen minimum zone (OMZ) compared to surface waters is predicted. The increase results from a one order of magnitude decrease in H+ concentration which impacts both Fe(III) hydroxide solubility and organic complexation. A correlation matrix suggests that changes in pH have a larger impact on SFe(III)app and Fe(III) speciation than DOM in this region. Using Fe(II) measurements, we calculated ambient DFe(III) and compared the value with the predicted SFe(III)app. The underlying distribution of ambient DFe(III) largely reflected the predicted SFe(III)app, indicating that decreased pH as a result of OMZ intensification and ocean acidification may increase SFe(III)app with potential impacts on surface DFe inventories.

Chemical speciation of iron in the euphotic zone along the Kuroshio Current

The distributions of dissolved iron (DFe) and organic iron-binding ligands (LFe) in the Kuroshio Current and its neighboring waters were elucidated from four cross-sectional surveys from the eastern coast of Taiwan to Sagami Bay. The Kuroshio surface water was characterized by a high salinity, low concentration of DFe, high concentration of LFe, and low fluorescence of humic-like substances, in comparison to the neighboring waters. The neighboring waters of the Kuroshio can be categorized into two types: the East China Sea water and coastal water. The East China Sea water was found near the Okinawa Trough, and characterized by a steep vertical gradient of DFe concentration, almost as low as that in the Kuroshio within the surface mixed layer, but reached ~0.5 nM below the mixed layer. Coastal water was observed on the southern coast of Japan, and its DFe concentration was high throughout the upper 200 m. The concentration of LFe in the Kuroshio water was significantly higher at 10-m depth than in the deeper layers. This suggests that humic-like substances, which are a major component of LFe in estuarine and deep waters, play a relatively minor role in the Kuroshio surface waters. Mixing with coastal waters can increase the concentration of bioavailable inorganic ferric ions in the Kuroshio surface water in two ways, by increasing the DFe concentration and decreasing the LFe concentration.

Electrode-electrolyte interactions in choline chloride ethylene glycol based solvents and their effect on the electrodeposition of iron

Although deep eutectic solvents (DES) and ethylene glycol (EG) electrolytes are gaining ground as media for the electrodeposition of metals, the influence of these electrolytes on the electrode and electrodeposits has not been elaborated before. In this work, we investigate how choline chloride: ethylene glycol based (ChCl:EG) electrolytes interact with the glassy carbon (GC) working surface at different potentials and, how these interactions change during the electrodeposition of iron from 1:2 and 1:4 ChCl:EG electrolytes. GC substrates are exposed to both electrolytes in absence of iron in order to study the pure electrolyte-substrate interactions. Linear sweep voltammetry was used to determine the potential range in which the different reactions occur, while time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to detect and identify the molecules adsorbed on the surface. In all systems, there is an accumulation of either choline or its derivatives on the electrode surface, with 1:4 ChCl:EG electrolytes showing different decomposition products from 1:2 ChCl:EG electrolytes. Choline accumulation and decomposition was also found on iron electrodeposits. The electrolyte composition has a major impact on the chemical speciation of iron, and on the deposit's adherence to the substrate. These are two crucial characteristics that define the efficiency of iron deposition from DES.

Effects of resuspension on the mobility and chemical speciation of zinc in contaminated sediments.

Identifying and quantifying the processes governing the mobilization of metals during resuspension events is key to assessing long-term metals efflux from sediments and associated ecological impacts. We investigated the effects of sediment resuspension on the mobilization and chemical speciation of zinc in two-week-long batch experiments using metal-contaminated sediments from Lake DePue (IL, USA). Measurements of dissolved zinc and sulfate allowed us to characterize the kinetics of metal sulfide dissolution and the resulting net release of zinc to the aqueous phase. X-ray absorption spectroscopy (XAS) provided direct insights into the chemical speciation of iron and zinc and their dynamic transformations during resuspension. While ZnS rapidly oxidized during resuspension, dissolved zinc increased only after two days of resuspension. We proposed a kinetic model to explain changes in the chemical speciation of zinc during these experiments as constrained by the dissolved species concentrations and chemical speciation as informed by XAS. Only 15% of the zinc mobilized was released to the aqueous phase while the remaining fraction repartitioned the solid phase either as a carbonate precipitate or as a sorbed species. Our results show that zinc sorption onto particle surfaces and reprecipitation of zinc minerals limit zinc solubility during resuspension of metal-sulfide sediments.

Alternate use of sulphur rich coals as solar photo-Fenton agent for degradation of toxic azo dyes

Abstract Low grade coals with high sulphur contents are not suitable as fuels in thermal power plants due to generation of high ash content and emission of toxic sulphur oxide gases. Here we have demonstrated an alternate use of pyrite rich coal as a source for sustainable generation of hydrogen peroxide and hydroxyl radicals in aqueous medium via solar light induced photo-Fenton process which were utilized for degradation of toxic azo-dyes. The textural, compositional and morphological features of pristine pyritic coals with varying sulphur concentrations are studied by an array of characterization techniques. The dye degradation capacities of pyrite rich coal are studied using model dye solutions e.g., Basic Blue 41 containing single azo group per unit and Trypan Blue containing two azo groups per unit. The rate of degradation (k) is faster for Basic Blue-41 (0.0192 min−1, ∼99% degradation) at optimized solar radiation exposure time, pH 6 and dose of 1 g/L pyritic coal. The dye degradation is presented as a measure of solar radiation accumulation energy per unit volume, and it is attributed to in-situ generation of hydrogen peroxide and hydroxyl radicals, and re-confirmed from scavenging studies. The dye degradation mechanism by pyritic coal is discussed in the light of solar photo-Fenton mechanism with respect to (1) qualitative identification of trace quantities of degradation products by gas chromatography-mass spectrometry technique; (2) leaching of 2700 mg/L iron in the reaction medium, estimated by inductive coupled plasma optical emission spectrometry, and (3) and changes in the chemical speciation of iron, sulphur and oxygen in the used coal by X-ray photoelectron spectroscopy.

Tumor-induced disorder of iron metabolism in major organs: a new insight from chemical speciation of iron.

ObjectiveTo investigate the evolution of iron speciation in major organs of tumor-bearing mice and its role in cancer formation and cancer-associated complications.MethodsThe concentration and chemical speciation of iron in the spleen, liver, lung, kidney, heart, blood, muscle, and tumor tissue of healthy mice and tumor-bearing mice were studied by synchrotron radiation-based total reflection X-ray fluorescence spectrometry (SR-TXRF) coupled with X-ray absorption spectroscopy (XAS).ResultsThe TXRF and XAS results showed that the iron content, especially the ferritin content, significantly decreased in the blood and spleen but significantly increased in the liver, lung, and muscle of mice after tumor implantation. The chemical speciation of iron in the tumor mainly comprised ferrous-sulfide-like iron and ferritin.ConclusionThe tumors disturbed the iron metabolism in major organs, and the evolution of iron may be involved in iron deficiency anemia, cancer growth, and immunity. Additionally, iron speciation-based markers may be further developed as clinical indicators for cancer and cancer-associated complications.

Chemical speciation of iron in sediments from the Changjiang Estuary and East China Sea: Iron cycle and paleoenvironmental implications

Chemical speciation of iron (Fe) in sediment offers a better understanding on iron cycle, early diagenesis, paleoredox condition and paleoclimatic changes. This study reports the Fe chemical speciation (total concentration FeT, highly reactive FeHR, poorly reactive FePR and unreactive FeU) in the surface sediments from the Changjiang (Yangtze River) Estuary and the East China Sea shelf. The FeHR concentrations in the estuarine and shelf sediments are much lower than those from the Changjiang and other rivers in the world, confirming the previous observations on geochemical fractionation effect in estuarine and shelf sediments. The high correlations of FeHR with FeT and Al concentrations and sediment surface area, suggest the dominance of clay minerals on FeHR composition in the sediments. The apparent enrichments of FeHR, total organic carbon and surface area in the hypoxia zone off the Changjiang Estuary are primarily caused by the local hydrodynamics and sedimentary processes. Despite the wide application of FeHR/FeT ratio for redox condition, its spatial distribution from the Changjiang river mouth to open shelf reveals no obvious enrichment in the hypoxia zone. This suggests that the episodic occurrence of hypoxia off the Changjiang Estuary (mostly in August) is hardly imprinted in particulate iron speciation. The distributions of Fe chemical speciation along the “river-estuary-open shelf” transect suggest the complex controls of particulate iron “shuttle transport” and deposition in the continental margin where fluvial input dominates and intense anthropogenic impact exists. Our study sheds new light on the source-to-sink process of particulate iron in the estuary and open shelf, and also provides important constraints of Fe speciation in modern and ancient archives from various depositional environments.

Chemical speciation of iron in seawater using catalytic cathodic stripping voltammetry with ligand competition against salicylaldoxime

The chemical speciation of iron in seawater is typically determined by cathodic stripping voltammetry (CSV) making use of ligand competition between an electroactive ligand added to obtain the CSV signal and the natural ligand to determine the complex stability of the natural species. Different procedures differ in the added ligand that is selected. Recent findings have suggested that several of these procedures suffer from interference by humic substances, which are now known to be ubiquitous in coastal and ocean waters. We re-optimise here CSV of iron speciation using salicylaldoxime (SA) in seawater, finding differences with the pre-existing method, and a different interpretation for the electroactive species. The main findings are that optimum sensitivity is obtained at ~5 × less SA, that the complex responsible for adsorption on the electrode is FeSA, that the FeSA2 species does not adsorb, and that the sensitivity of the method is much improved in the presence of dissolved oxygen (DO) through a catalytic effect (FeII acts as catalyst for the reduction of DO). The complex stability for complexes of Fe′ with SA (FeSA and FeSA2), in pH8 seawater, is calibrated over a range of SA concentrations between 1 and 40μM SA against EDTA and between 1 and 100μM SA without EDTA. Data fitting of the EDTA data gave log K′Fe′SA=6.50±0.04 and log B′Fe′SA2=10.85±0.08. The data fits agree with the formation of an electroactive species FeSA which is superseded by a non-electroactive FeSA2 at [SA]>5μM. Independent calibration of these stability constants on the basis of the formation of FeSA in competition only with the hydroxide species of FeIII, between 1 and 100μM SA, without EDTA, gave values of log K′Fe′SA=6.52±0.01 and log B′Fe′SA2=10.72±0.03. These are the values we propose for the constants as they are independent of any uncertainties in the speciation with EDTA. The similarity of these constants to those determined via calibration against EDTA shows that the speciation of Fe with SA and EDTA is well understood. The re-optimised method is applied to a mixed depth Celtic Sea sample, and two GEOTRACES samples from the Atlantic, at a SA concentration of 5μM. Ligand concentrations were 1.47 and 1.49 nM in the GEOTRACES water (log K′Fe′L values of 11.1 and 11.9) and 2.53 nM in the Celtic Sea water (log K′Fe′L=11.5). Application of the method to ligands added to seawater gave log K′Fe′L values of 11.6±0.1 for humic acid (Suwannee River) and 12.2±0.3 for a siderophore (desferrioxamine B). Measurement of the rate of dissociation of the complex of Fe with the natural ligand in Celtic seawater gave a value of kFeL=0.00133±0.0002s−1. The half-life of this reaction is 8.7minutes. This means that a reaction time of 1h is required after the addition of SA prior to analysis.

Effects of nitrogen on the distribution and chemical speciation of iron and zinc in pearling fractions of wheat grain.

Increasing nitrogen supply can increase Fe and Zn concentrations in wheat grain, but the underlying mechanisms remain unclear. Size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry was used to determine Fe and Zn speciation in the soluble extracts of grain pearling fractions of two wheat cultivars grown at two N rates (100 and 350 kg of N ha(-1)). Increasing N supply increased the concentrations of total Fe and Zn and the portions of Fe and Zn unextractable with a Tris-HCl buffer and decreased the concentrations of Tris-HCl-extractable (soluble) Fe and Zn. Within the soluble fraction, Fe and Zn bound to low molecular weight compounds, likely to be Fe-nicotianamine and Fe-deoxymugineic acid or Zn-nicotianamine, were decreased by 5-12% and 4-37%, respectively, by the high N treatment, whereas Fe and Zn bound to soluble high molecular weight or soluble phytate fractions were less affected. The positive effect of N on grain Fe and Zn concentrations was attributed to an increased sink in the grain, probably in the form of water-insoluble proteins.

Chemical speciation of iron in Antarctic waters surrounding free-drifting icebergs

Free-drifting icebergs in the Southern Ocean may serve as an important source of iron (Fe) to surrounding waters. We studied the chemical speciation of Fe in the waters around several Antarctic icebergs during cruises to the Scotia and Weddell Seas in June 2008 and March 2009. Iron(II) was measured by flow injection chemiluminescence, and Fe-binding ligands were determined following the cruises via competitive ligand equilibrium–cathodic stripping voltammetry. Iron(II) concentrations were significantly higher within 1 km of the nearest iceberg (146 ± 11 pM; 12 ± 0.8% of total dissolved Fe (DFe)) compared to farther stations (66 ± 12 pM; 4 ± 1% of DFe). Iron(II) concentrations were significantly positively correlated with incident light levels, indicating a photochemical source. However spatial Fe(II) gradients were statistically significant even after accounting for light effects and were stronger than gradients in DFe or phytoplankton biomass. Iron(II) was also higher at deeper depths along the iceberg face, suggesting Fe(II) is directly released from ice-rafted minerals. Total Fe-binding ligand concentrations were significantly higher closer to icebergs in the fall but not in the winter, when plankton biomass and grazing activity were substantially lower. Ligands were always present in excess of DFe, but ligands were more fully titrated with DFe in the fall. Ligand/DFe ratios were relatively low (1.2–1.7) compared to other Southern Ocean studies, suggesting that ligands were mostly titrated and additional Fe inputs would be prone to scavenging. Conditional stability constants of ligands (K′, with respect to Fe′) ranged from 10 11.9 to 10 12.9. Macrozooplankton grazing pressure was also elevated near icebergs and may have served as a source of Fe(II) and ligands. Icebergs appear to affect, directly and indirectly, the speciation of Fe in surrounding waters with potential implications for bioavailability and scavenging behavior.

Chemical Speciation and Dissolved Iron in the Pore Water of Patos Lagoon Sediments - Brazil

Sediments can sink or deliver elements to water column. Iron is considered an essential element for the development of cyanobacteria and a limitant to phytoplankton growth. Studies on the chemical speciation of iron in seawater have been conducted, but there is no information about its chemical speciation in pore water, as reported here. This paper presents a voltammetric method to analyze dissolved iron and its chemical speciation in sediment pore water, using adsorptive cathodic stripping voltammetry (AdCSV) and the technique of competitive ligand exchange (CLE-AdCSV), respectively. The limit of detection (LOD = 0.30 10 �6 mol L �1 ), the quantification (LOQ = 0.90×10 �6 mol L �1 ), precision (RSD = 4.9%) and accuracy (98%), were calculated from experiments using certified reference material SLRS-4 (National Research Council Canada). The chemical speciation of pore water from sediment samples collected during April 2009, in the Patos Lagoon Estuary (RS, Brazil), was analyzed for the first time, revealing that the ratio (labile iron to dissolved iron) is significantly lower in pore water extracted from sediments of the upper layer (0 to �5 cm), than from the overlaying water or of the pore water extracted from sediments of the lower layer (�15 to �20 cm).

Iron transformations during combustion of Pittsburgh no. 8 coal

The chemical speciation of iron in combustion-derived ash is an important factor in determining the likelihood of ash deposit formation and buildup. In this study, the transformation of iron were examined in ash produced by the combustion of a beneficiated Pittsburgh no. 8 bituminous coal under a range of oxygen concentration ranging from 0% to 100% O 2 in a drop tube furnace. The speciation of iron was found to be strongly dependent upon ash particle size, with the lowest fraction of glassy state iron found in the largest ash particles. Both the fraction of iron in a glassy state and the ratio of Fe +++(glass)/Fe ++(glass) increased with increasing O 2 concentration in the furnace. For the submicron ash particles, about 10% of the iron is formed by direct disintegration of pyrite and pyrrhotite during combustion. Most of the iron is however, present as Fe +++(glass), which results from the vaporization, recondensation, and coagulation of iron and silicates. For ash particles with size between 1 and 9 microns, most of the ash derives from mineral coalescence within the reacting char, with additional contribution from extraneous minerals. The fraction of glassy iron in those particles is high because of the high contact probability between iron melt and silicates. For the coarsest ash particles with size greater than 9 microns, extraneous pyrite is changed into hematite, and iron in the core of the char is changed into a glassy state.

Occurrence, properties and pollution potential of environmental minerals in acid mine drainage

This paper describes the occurrences, the mineralogical assemblages and the environmental relevance of the AMD-precipitates from the abandoned mine of Valdarcas, Northern Portugal. At this mining site, these precipitates are particularly related with the chemical speciation of iron, which is in according to the abundance of mine wastes enriched in pyrrhotite and pyrite. The more relevant supergene mineralogical assemblages include the following environmental minerals: soluble metal-salts, mainly sulphates, revealing seasonal behaviour, iron-hydroxysulphates and iron-oxyhydroxides, both forming ochre precipitates of poorly and well-crystalline minerals. Pollution potential of the most highly water soluble salts was analysed in order to evaluate the environmental effect of their dissolution by rainfall. Laboratory experiments, carried out with iron and aluminium sulphates, demonstrated the facility to release metals, sulphate and acidity upon dissolution. Regarding the ochre precipitates, composed by several less soluble iron (III)-minerals, the spatial distribution on the nearby aqueous system as well as the proportion of Jarosite, Schwertmannite and Goethite in the mixtures gave information about the halo's contamination promoted by the AMD emerging from the waste-dumps.

Iron speciation in fault gouge from the Ushikubi fault zone central Japan

Chemical species of iron and sulfur were measured using 57Fe Mossbauer spectroscopy and X-ray near edge structure, respectively, for the fault gouge samples collected from two sites along the ENE-WSW trending Ushikubi fault zone in central Japan. These gouge samples have distinguishable variations in their physical properties such as surface color and structure and these features are also reflected by the chemical speciation of iron and sulfur. Newly formed minerals, including calcite, dolomite, siderite, iron sulfide and pyrite, have close relation to the colors of fault gouge and respective to the geochemical environment within the fault zone. In addition, the variations in iron and sulfur species may have significance to evaluate the redox conditions in the fractures and furthermore to estimate the history and activity of the faults. Generally there is observacious enrichment of reducing species of iron and sulfur as well as chlorite in the relatively younger fracture, indicating favorable connection pathway with deep position and the fault zone is active. On the other hand, the stable fracture with a longer history is relatively enriched in ferric iron species and almost no sulfur in the gouge. These results from iron and sulfur speciation have a good agreement with evidence indicated by 14C dating from this fault zone.

Leaching of Arsenic from Granular Ferric Hydroxide Residuals under Mature Landfill Conditions

Most arsenic bearing solid residuals (ABSR) from water treatment will be disposed in nonhazardous landfills. The lack of an appropriate leaching test to predict arsenic mobilization from ABSR creates a need to evaluate the magnitude and mechanisms of arsenic release under landfill conditions. This work studies the leaching of arsenic and iron from a common ABSR, granular ferric hydroxide, in a laboratory-scale column that simulates the biological and physicochemical conditions of a mature, mixed solid waste landfill. The column operated for approximately 900 days and the mode of transport as well as chemical speciation of iron and arsenic changed with column age. Both iron and arsenic were readily mobilized under the anaerobic, reducing conditions. During the early stages of operation, most arsenic and iron leaching (80% and 65%, respectively) was associated with suspended particulate matter, and iron was lost proportionately faster than arsenic. In later stages, while the rate of iron leaching declined, the arsenic leaching rate increased greater than 7-fold. The final phase was characterized by dissolved species leaching. Future work on the development of standard batch leaching tests should take into account the dominant mobilization mechanisms identified in this work: solid associated transport, reductive sorbent dissolution, and microbially mediated arsenic reduction.

The chemical speciation of iron in the north-east Atlantic Ocean

The distribution of dissolved iron and its chemical speciation (organic complexation and redox speciation) were studied in the northeastern Atlantic Ocean along 23°W between 37 and 42°N at depths between 0 and 2000 m, and in the upper-water column (upper 200 m) at two stations further east at 45°N10°W and 40°N17°W in the early spring of 1998. The iron speciation data are here combined with phytoplankton data to suggest cyanobacteria as a possible source for the iron binding ligands. The organic Fe-binding ligand concentrations were greater than that of dissolved iron by a factor of 1.5–5, thus maintaining iron in solution at levels well above it solubility. The water column distribution of the organic ligand indicates in-situ production of organic ligands by the plankton (consisting mainly of the cyanobacteria Synechococcus sp.) in the euphotic layer and a remineralisation from sinking biogenic particles in deeper waters. Fe(II) concentrations varied from below the detection limit (<0.1 nM) up to 0.55 nM but represented only a minor fraction of 0% to occasionally 35% of the dissolved iron throughout the water column. The water column distribution of the Fe(II) suggests biologically mediated production in the deep waters and photochemical production in the euphotic layer. Although there was no evidence of iron limitation in these waters, the aeolian iron input probably contributed to a shift in the phytoplankton assemblage towards increased Synechococcus growth.

Chemical Speciation of Iron in Seawater by Cathodic Stripping Voltammetry with Dihydroxynaphthalene

The chemical speciation of iron in seawater is determined by cathodic stripping voltammetry using 2,3-dihydroxynaphthalene (DHN) as adsorptive and competing ligand. The optimized conditions include a DHN concentration of 0.5-1 microM, seawater at its original pH of 8, and equilibration overnight. The alpha-coefficient for DHN (=[FeDHN]/[Fe']) was calibrated against EDTA giving values of 166 for 0.5 microM DHN and 366 at 1 microM DHN and a value of 8.51 +/- 0.07 for log K'(Fe'DHN). The dissociation of the natural iron species FeL was found to have a characteristic reaction time of 50 min, indicating that titrations should be equilibrated overnight rather than the shorter periods sometimes used onboard ship. The method was applied to samples from the Pacific giving ligand concentrations of 1.1 and 1.6 nM for deep and surface waters, respectively, with an average value for log K'(FeL) of 11.9 +/- 0.3 compared to a value of 11.5 for the siderophore deferoxamine. The results are similar to those obtained previously for similar samples, but the new method has much greater sensitivity for iron than previous methods, leading to lower limits of detection and shorter analysis time.

The distribution and speciation of iron along 6°E in the Southern Ocean

Abstract The distribution and speciation of iron was determined along a transect in the eastern Atlantic sector (6°E) of the Southern Ocean during a collaborative Scandinavian/South African Antarctic cruise conducted in late austral summer (December 1997/January 1998). Elevated concentrations of dissolved iron (>0.4 nM) were found at 60°S in the vicinity of the Spring Ice Edge (SIE) in tandem with a phytoplankton bloom, chiefly dominated by Phaeocystis sp. This bloom had developed rapidly after the loss of the seasonal sea ice cover. The iron that fuelled this bloom was mostly likely derived from sea ice melt. In the Winter Ice Edge (WIE), around 55°S, dissolved iron concentrations were low ( 0.2 nM ) and corresponded to lower biological productivity, biomass. In the Antarctic Polar Front, at approximately 50°S, a vertical profile of dissolved iron showed low concentrations ( 0.2 nM ); however, a surface survey showed higher concentrations (1–3 nM), and considerable patchiness in this dynamic frontal region. The chemical speciation of iron was dominated by organic complexation throughout the study region. Organic iron-complexing ligands ([L]) ranged from 0.9 to 3.0 nM Fe equivalents, with complex stability log K Fe L ′ = 21.4 – 23.5 . Estimated concentrations of inorganic iron (Fe′) ranged from 0.03 to 0.79 pM, with the highest values found in the Phaeocystis bloom in the SIE. A vertical profile of iron-complexing ligands in the WIE showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition. This work further confirms the role iron that has in the Southern Ocean in limiting primary productivity.

The level of iron enrichment required to initiate diatom blooms in HNLC waters

The chemical speciation of iron in seawater is controlled by complexation with organic ligands, the character of which likely regulates which phytoplankton groups can readily access this resource. Evidence from the IronEx II mesoscale iron enrichment experiment provides some insight to this regulation. Dissolved iron (<0.4 μm) in the enriched surface waters during IronEx II was partitioned into colloidal (>1 kDa–0.4 μm) and soluble (<1 kDa) size fractions using cross flow filtration to better delineate iron dynamics with respect to phytoplankton growth. While dissolved concentrations in the patch increased by two orders of magnitude to ∼2 nM Fe, soluble concentrations only roughly doubled to ∼35 pM Fe, and this change occurred only during the first few days of the experiment. The subsequent decrease in soluble iron to ambient levels coincided with a dramatic increase in chlorophyll a, indicating that biological demand was responsible for the disappearance of soluble iron. This decrease also coincided with preferential drawdown of silicic acid over nitrate in the patch, indicating that diatoms were experiencing iron stress even as the bloom developed. Even so, calculations of the diffusional flux and iron uptake kinetics at the cellular level reveal that the concentrations of soluble iron during the later stages of the bloom were above that required to support continued rapid growth of the long, narrow pennate diatoms. This observation implies that the bulk of the organically bound soluble and colloidal iron was unavailable to meet the diatom growth requirements, and further that the measured increase in concentrations of strong Fe(III) complexing ligands impaired iron acquisition by diatoms. These findings indicate that excess macronutrients in HNLC waters might not be fully converted into diatom biomass even with repeated infusions of iron.