Fe Isotope Research Articles

Novel bioanalytical strategy using isotope pattern deconvolution and ICP-QMS for the study of iron incorporation in erythrocytes: An insight to better assessment

Iron is an essential element for human life and its nutritional status in the human body is directly linked to human health. More than 1015 atoms of iron per second are necessary for the maintenance of haemoglobin formation. To predict iron bioavailability three approaches are normally employed: (a) faecal recovery; (b) plasma appearance; and (c) erythrocyte incorporation (the most used). Isotope Pattern Deconvolution (IPD) is a mathematical tool that allows the isolation of distinct isotope signatures from mixtures of natural abundance and enriched tracers. In this work we propose a novel strategy to assess erythrocyte iron incorporation, based on the use of an iron stable isotope (57Fe) and the IPD concept. This strategy allows direct calculation of the exogenous concentration of 57Fe incorporated into RBCs after supplementation. In this way, to determine the mass of iron incorporated into erythrocytes, the unique prediction that must be made is the blood volume, estimate to reproduce the natural dilution of the tracer (57Fe) in the blood. This novel bioanalytical approach was applied for the measurements of iron incorporation and further iron absorption studies in humans, using a group of twelve healthy participants, that should be further evaluated for the assessment of other chemical elements that could be of health concerns and directly impact society.

Iron mobility in subduction zone fluids at forearc depths and implications for mantle redox heterogeneity

The mobility of redox sensitive elements such as iron, carbon and sulfur in subduction zone fluids is important for redox transfer between the subducting slab and mantle wedge. However, the speciation of Fe during its mobility in subduction zone fluids at forearc depths is still unclear. Here, we studied the Fe isotope compositions of high-pressure (HP) fluid-metasomatized rocks (Mg-rich leucophyllite and gneiss, which is mineralogically transitional between leucophyllite and metagranite) from the Eastern Alps and found evidence for two distinct types of Fe species during Fe mobility in subduction zone fluids. The protolith of both types of rocks is metagranite, which shows δ56Fe values of 0.12–0.25‰. Compared to the metagranite, the transitional gneiss shows slightly higher Fe2O3t contents, lower Fe3+/∑Fe ratios and significantly lower δ56Fe values of −0.03–0.16‰, whereas the leucophyllite exhibits much lower Fe2O3t contents, comparable or slightly lower Fe3+/∑Fe ratios and generally higher δ56Fe values of up to 0.55‰. These observations indicate that the granitic protolith has experienced two types of fluid metasomatism. Combined with previous results, we infer the mobility of Fe in subduction zone fluids at forearc depths via two kinds of Fe species, Fe2+-(CO3), and Fe2+-(HS) or Fe2+-Cl. The Fe mobility was dominant in the form of the Fe2+-(CO3) complex in a carbonate-rich fluid during the formation of transitional gneiss, consistent with reported radiogenic Sr and isotopically light Mg isotope compositions, whereas Fe loss in the form of Fe2+-(HS) or Fe2+-Cl complexes via dissolution of biotite and phlogopite can account for the formation of leucophyllites. According to the tectonic evolution of the Eastern Alps, both types of fluids possibly originated from the dehydration of the sediment-serpentinite mélange produced by the subducting oceanic slab of the Alpine Penninic unit. The diversity of ferrous iron species in the subduction zone fluids at forearc depths probably reflects the variation in the redox properties of fluids derived from carbonate-rich sediment and serpentinite under such conditions. Our results provide an excellent example of tracing Fe mobility with distinct Fe species in subduction zone fluids.

The Iron Chaperone Poly C Binding Protein 1 Regulates Iron Efflux through Intestinal Ferroportin in Mice

Iron is an essential nutrient required by all cells but used primarily for red blood cell production. Because humans have no effective mechanism for ridding the body of excess iron, the absorption of dietary iron must be precisely regulated. The critical site of regulation is the transfer of iron from the absorptive enterocyte to the portal circulation via the sole iron efflux transporter, ferroportin (FPN). Here we report that poly(rC)-binding protein 1 (PCBP1), the major cytosolic iron chaperone, is necessary for the regulation of iron flux through FPN in the intestine of mice. PCBP1 binds iron-glutathione complexes in the cytosol of cells and delivers the iron to ferritin, the iron storage protein, to iron centers in enzymes, and to iron-sulfur cluster chaperones. PCBP1 also limits the chemical reactivity of iron, thereby limiting iron-catalyzed oxidative damage in cells. To explore the role of PCBP1 in dietary iron absorption, we developed mice with an inducible, enterocyte-specific deletion of PCBP1. Mice lacking PCBP1 in the intestinal epithelium exhibit low levels of enterocyte iron, poor retention of dietary iron in enterocyte ferritin, and excess efflux of iron through FPN. Kinetic studies of iron transport using a stable isotope ( 57Fe) coupled with a mini-hepcidin that blocks FPN activity demonstrated that PCBP1 deletion had no effect of intestinal iron uptake but caused high rates of iron efflux through FPN. Surprisingly, excess iron efflux occurred despite lower levels of FPN protein in enterocytes and upregulation of the iron regulatory hormone hepcidin. PCBP1 deletion and the resulting unregulated dietary iron absorption led to poor growth, severe anemia on a low iron diet and liver oxidative stress with iron loading on a high iron diet. To investigate the roles of PCBP1 more precisely in enterocytes, we developed 3-D organoid cultures from intestinal epithelium which functionally expressed the major iron trafficking proteins: divalent metal transporter 1, PCBP1, ferritin, transferrin receptor 1 and FPN. Ex vivo culture of wild-type and PCBP1-depleted enteroids demonstrated normal patterns of FPN expression and hepcidin-mediated turnover. However, fluorescence measurements of kinetically labile iron pools in enteroids competent or blocked for FPN iron efflux indicated that PCBP1 dramatically altered efflux activity. PCBP1 functioned as a cytosolic buffer for iron, binding and retaining iron and thereby keeping “free” iron at very low levels. This low concentration of free iron limited its availability for FPN-mediated efflux and allowed hepcidin-mediated changes in FPN levels to regulate the amount of iron exported from the enterocyte. Thus, by binding enterocyte iron, PCBP1 reduces the concentration of unchaperoned, “free” iron to a low level. This low level of cytosolic free iron is necessary for hepcidin-mediated regulation of FPN activity.

Iron isotope evidence in continental intraplate basalts for mantle lithosphere imprint on heterogenous asthenospheric melts

Iron isotope studies on ocean island basalts (OIBs) and mid-ocean ridge basalts (MORBs) have disclosed the contribution of pyroxenite lithologies in the generation of basaltic magmas. Whether Fe isotopic compositions of continental intraplate basalts can be applied to trace lithological heterogeneity within the mantle source regions remains poorly investigated. To explore the systematics of stable Fe isotopes as a potential probe of lithological heterogeneity in the source of continental intraplate basalts, we present twenty-four Fe isotope data on a suite of well-characterized Cenozoic basalts from SE China. The samples show a large range of Fe isotope values (δ56Fe = +0.09‰ to +0.20‰), which correlate with SiO2, CaO/Al2O3, Ti/Eu, Hf/Hf*, Zr/Nb, Dy/Yb, La/Yb, Nb/Y, K/La, Sr/Ce, δ66Zn and estimated equilibrium pressures. The samples with the highest δ56Fe values represent early-stage low-silica basalts with moderately enriched Sr-Nd isotope ratios and high δ66Zn values, while the late-stage high-silica basalts display a broad δ56Fe decrease with increasing 87Sr/86Sr and with decreasing εNd and δ66Zn. We demonstrate that the heaviest Fe isotope signatures cannot be derived from a pure peridotite source and require a pyroxenite component in the source. Combined with other geochemical proxies, we show that the heaviest basalt compositions are consistent with low-degree melts produced by the adiabatic decompression of a carbonated pyroxenite-bearing asthenospheric mantle. Mixing of these hybrid melts with melt produced from in-situ melting of the subduction-modified sub-continental lithospheric mantle (SCLM) reproduces the Fe-isotope variability of the late-stage basalts. Our results demonstrate the significance of lithological heterogeneity in the mantle source of continental intraplate basalts and highlight the subsequent imprint of mantle lithosphere in the evolution of their Fe isotope compositions. Finally, this study exemplifies the potential of the Fe-Zn stable isotope pair for mantle geochemistry; coupled with traditional radiogenic isotopes and major and trace element concentrations, they formed an efficient tool to trace the nature and contribution of the mantle source components in the formation of intraplate basalts.

New Potential Sulfide Reference Materials for Microbeam S‐Fe‐Cu Isotope Measurements

S‐Fe‐Cu isotope systems are powerful tracers for revealing geochemical processes. However, the microanalysis of S‐Fe‐Cu isotopes is critically limited by the lack of suitable reference materials. Herein, we present three potential reference materials Ll‐Cpy (chalcopyrite), Ll‐Po (pyrrhotite) and Ll‐Sp (sphalerite) for in situ S‐Fe‐Cu isotope measurements. Numerous in situ S‐Fe‐Cu isotope measurements were performed over two years to assess isotopic homogeneity. The bulk S isotopic compositions were determined independently in seven laboratories by isotope ratio mass spectrometry (IRMS); the preferred δ34SV‐CDT for Ll‐Cpy, Ll‐Po, Ll‐Sp are 6.13 ± 0.37‰ (2s), 6.42 ± 0.37‰ (2s) and 6.28 ± 0.38‰ (2s), respectively. The bulk Fe isotope ratios in Fe‐bearing Ll‐Cpy and Ll‐Po were determined using solution nebulisation multi‐collector inductively coupled plasma‐mass spectrometry, and the obtained δ56FeIRMM‐014 values are 0.57 ± 0.07‰ (2s) and ‐0.62 ± 0.07‰ (2s), respectively. The mean bulk δ65CuNIST SRM 976 value of Ll‐Cpy is 0.57 ± 0.06‰ (2s). All the bulk values are in good agreement with the long‐term statistical results of laser ablation‐MC‐ICP‐MS and proposed as the recommended values. These sulfides are well characterised and isotopically homogeneous (at 30–40 μm spatial resolution), and can be used as potential calibration materials for in situ S‐Fe‐Cu isotope measurements.

Fractionation of iron and chromium isotopes in hydrothermal plumes from the northern Mid-Atlantic Ridge

Hydrothermal venting impacts the global-scale biogeochemical cycles of many trace metals and their isotopes. Processes in hydrothermal plumes regulate the dispersal of vent-derived metals and may vary in response to differences in the geologic setting of vent fields and/or the geochemistry of the overlying ocean water. Here we present results of analyses of dissolved Fe and Cr concentrations, and dissolved Fe isotope (δ56Fe) and Cr isotope (δ53Cr) distributions, in seawater samples collected from above TAG and Rainbow vent sites on the Mid-Atlantic Ridge during the GEOTRACES GA13 cruise. We show that profiles of dissolved Fe and Cr isotopes through the near-field hydrothermal plumes are the mirror image of each other. Oxidation of Fe(II) and precipitation of Fe-(oxyhydr)oxides account for the low δ56Fe values of dissolved Fe, as low as −1.83 ‰ at TAG and −6.94 ‰ at Rainbow. Plume samples with low δ56Fe values are associated with elevated δ53Cr values of dissolved Cr compared to background seawater (by up to +0.14 ‰ and +0.69 ‰ at TAG and Rainbow, respectively), while particulate Cr is characterised by relatively low δ53Cr values (−1.02 to −1.22 ‰). This striking result suggests that seawater Cr(VI) is reduced to Cr(III) and precipitates on the surface of Fe(III) particles within the hydrothermal plume. Reduction of Cr(VI) and scavenging of Cr(III) by plume Fe-(oxyhydr)oxide particles mean that high-temperature hydrothermal systems are likely a net sink for seawater Cr at Rainbow (and also at TAG). As the removal flux of Cr is related to the flux of hydrothermal Fe(II) and the rate of Fe(II) oxidation in the hydrothermal plume, it may (i) vary across vent sites at a global scale and (ii) change over glacial-interglacial cycles.

Mantle Oxidation Induced by Recycled Carbonate: Insights From Mg‐Zn‐Fe‐Cu Isotopic Systematics of Intraplate Basalts

AbstractMantle oxidation plays an essential role in volatile cycling between Earth’s interior and exterior. However, the conceivable oxidizer remains enigmatic and needs to be explored by geochemical tools. Here, we examine the potential of recycled carbonates in inducing redox changes of the deep mantle through combined isotopic studies of Mg (δ26Mg), Zn (δ66Zn), Fe (δ56Fe), and Cu (δ65Cu) on a suite of intraplate alkaline basalts proposed to have originated from the mantle transition zone (∼440–660 km). Compared with mid‐ocean ridge basalts (MORB), these basalts have variably lower δ26Mg and higher δ66Zn, the typical features of marine carbonates, indicating the presence of various amounts of deeply recycled carbonates in their sources. As the estimated amounts of recycled carbonates in sources increase (i.e., lower δ26Mg and higher δ66Zn), the basalts have higher δ56Fe and lower δ65Cu compared with MORB. These correlations cannot be explained alone by binary mixing between recycled carbonates and the pristine mantle because of the much lower Fe and Cu contents of marine carbonates than those of the mantle and instead require redox‐driven isotope fractionation induced by mantle carbonate metasomatism. During partial melting of an oxidized mantle source, isotopically heavy ferric iron and isotopically light sulfide were preferentially incorporated/dissolved into the melts that are enriched in heavy Fe and light Cu isotopes. These observations highlight that recycled carbonates serve as an important oxidizer for the deep mantle and facilitate the extraction of mantle sulfides, which can be effectively tracked by Fe and Cu isotopic systematics of intraplate basalts.

Biogeochemistry of iron in coastal Antarctica: isotopic insights for external sources and biological uptake in the Amundsen Sea polynyas

Seasonal phytoplankton blooms in the Antarctic Amundsen Sea Polynyas are thought to be supported by an external supply of iron (Fe) from circumpolar deep waters, benthic sediments, and/or ice shelf meltwaters. However, largely due to the limited amount of Fe data reported for the Amundsen Sea Polynyas, understanding of the sources and processes that affect the biogeochemistry of Fe in this region (notably within the ice shelf system) remains limited. Here, we present the first investigation of dissolved Fe isotope distributions (δ56Fe) along the conveyer belt of waters into and through the Amundsen Sea, via the Dotson Ice Shelf, from samples collected during austral summer (2017–2018). Our dataset allows us to characterize and compare the dissolved δ56Fe signatures of incoming modified Circumpolar Deep Water (mCDW) and of sedimentary sources on the continental shelf. The range in dissolved δ56Fe (–1 to +0.1 ‰) observed in the Amundsen Sea close to the seafloor, coupled with elevated dissolved Fe concentrations (up to 1.6 nmol/L), suggests that Fe is released from shelf sediments via a combination of reductive and non-reductive processes, with non-reductive dissolution input being relatively more important (20–56 %) than reductive dissolution (4–12 %). Near the Dotson Ice Shelf, the δ56Fe in the mCDW inflow (–0.70 ‰) was lower than the mCDW outflow (–0.23 ‰), whereas any change in dissolved Fe concentrations was negligible. We speculate that this shift in dissolved δ56Fe underneath the ice shelf is driven by a combination of enhanced preservation (and addition) of lithogenic colloidal Fe(III) and/or complexation with Fe-binding ligands, together with a differential loss of Fe2+. We also found distinct δ56Fe signatures in surface waters of the polynya, with apparent preferential uptake of isotopically light Fe in a bloom dominated by diatoms leading to a relatively heavy remnant dissolved δ56Fe signature of +1.06 ‰, compared to a bloom dominated by haptophytes where more modest and variable isotope fractionation was observed. The different isotopic composition between the two regions could be related to the dominance of different species, but this remains speculative. Despite prominent biological uptake, we suggest that other factors such as rapid recycling (e.g., adsorption and regeneration), bacterial regeneration, and complexation with organic ligands, together with the supply of lithogenic particles also play important roles in setting surface dissolved δ56Fe in the Amundsen Sea Polynyas. Overall, this study provides a further understanding of the external Fe sources and the biogeochemical processes in the Amundsen Sea and thus a baseline on how changing conditions in Antarctica can affect Fe cycling in the Southern Ocean and beyond.

Iron dynamics and isotope fractionation in soil and rice during 2000 years of rice cultivation

Abstract Background and aims Paddy management results in frequent redox cycles of the soil and thus changes in the terrestrial iron (Fe) cycle. We intended to test that the increasing duration of paddy management and the increasing frequency of soil redox cycles leave their fingerprint on Fe isotope composition of paddy systems, which could subsequently be used to deduce the origin of rice plants as related to the extent of past soil paddy management. Methods We sampled soil and rice plants of a paddy chronosequence in China with rice cultivation history up to 2000 years and determined the changes of soil Fe pools and Fe isotope composition of the soil and rice plants. Results Prolonged paddy management reduced Fe concentrations in submerged topsoil leading to an enrichment of heavy Fe isotopes, with the δ56Fe values 0.12‰ heavier than the parent material after 2000 years. Particularly, Fe oxides were lost quickly, while exchangeable and organic-associated Fe continuously accumulated during paddy management and played an increasing role in the plant-available Fe pool in the topsoil. The Fe content in rice also increased with paddy age, while its Fe isotope composition did not reflect that of paddy soil but resembled that of the Fe plaques on the roots. Conclusion Prolonged rice cropping altered the biological contribution in the terrestrial Fe cycle. However, while soil Fe pools that are closely linked with biological activities were affected rather quickly, the changes in the whole soil Fe system were detectable only after a millennium of paddy management.

Enrichment of cobalt in the Xiarihamu Ni-Co sulfide deposit in the East Kunlun orogenic belt, Western China: Constraints from distribution of cobalt in sulfides and Fe and S isotopes of sulfides

The Xiarihamu Ni-Co sulfide deposit in the East Kunlun orogenic belt (EKOB), western China, is the largest magmatic Ni-Cu-(Co) sulfide deposit found in the orogenic belts worldwide. The geochemical behavior of Co during the evolution of sulfide melt is key to understand the enrichment process of Co in the Xiarihamu deposit, however remains unclear. In this study, the Co contents of sulfide inclusions enclosed within olivine and pyroxene and those of the sulfides interstitial to olivine and pyroxene in the Xiarihamu deposit were examinated by the Scanning Electron Microscopy (SEM) -Energy Dispersive Spectroscopy (EDS) and Electron Probe Microanalyzer (EPMA). The Fe and S isotopic compositions of the sulfides were measured in situ by LA-MC-ICPMS. The results show that Co contents increase from silicate to sulfide and arsenide minerals, and from chalcopyrite to pyrrhotite and pentlandite in the sulfides. High Co contents in pentlandite of pyroxenite (av. 2.79 %) and gabbro (av. 7.34 %) indicate that Co is enriched in the pentlandite of pyroxenite in different stage of magma. The pyrrhotite and pentlandite show positive correlation of Co with Fe and Ni, and suggested isomorphic substitution of Co for Fe and Ni. The δ56Fe values increase from pyrrhotite to pentlandite due to kinetic fractionation of Fe isotopes of Fe valent and bond length/strength, because pyrrhotite has longer bond and weaker bond strength of Fe-S than pentlandite, and display lighter Fe isotopic compositions. The δ56Fe values of pentlandite increase substantially from host peridotite to pyroxenite, which could be related to subsolidus fractional crystallization processes of monosulfide solid solution (MSS). The sulfide segregated and crystallized early from the MSS is richen in light Fe isotope. The sulfides in gabbro have high δ34S values, similar to δ34S of the sulfides in the country rocks of Proterozoic granitic gneiss, indicating a continuous addition of external sulfur into magma chamber. The δ34S and δ56Fe values of the sulfides approximately increase with increasing Co contents. Higher δ56Fe and δ34S values and Co contents of pentlandite in the pyroxenite suggest that the Co enrichment is mainly associated with sulfide saturation of magmas by crustal contamination.

Isotopic dependence of (n,α) reaction cross sections for Fe and Sn nuclei

The (n,α) reactions play an important role for the energy generation and the synthesis of chemical elements in the stars, as well as for nuclear engineering and medical applications. The aim of this study is to explore the evolution of (n,α) reactions in Fe and Sn isotope chains in order to assess the cross section properties with the increase of neutron number in target nucleus, and to make a comparison with other relevant neutron induced reactions. The cross section calculations are based on the statistical Hauser-Feshbach and exciton models in TALYS nuclear reaction code, using global optical model potential that is additionally adjusted by the (n,α) cross section data for 54Fe and 118Sn. The calculations of (n,α) reactions in Fe and Sn isotopes provide the insight into their isotopic dependence and properties over the complete relevant range of neutron energies. The cross sections result in pronounced maxima at lower-mass isotopes, and rather strong decrease for neutron-rich nuclei consistent with the reduction of the reaction Q-value and increased contributions from other exit channels from compound nucleus. The analysis of the Maxwellian averaged cross sections at temperatures in stellar environment shows that the (n,α) reactions have significant contributions for low-mass Fe isotopes, that is opposite than for Sn isotopes. For both neutron rich isotopes γ and neutron emissions dominate, with their interplay depending on the temperature involved.

Tracking Initial Fe(II)-Driven Ferrihydrite Transformations: A Mössbauer Spectroscopy and Isotope Investigation.

Transformation of nanocrystalline ferrihydrite to more stable microcrystalline Fe(III) oxides is rapidly accelerated under reducing conditions with aqueous Fe(II) present. While the major steps of Fe(II)-catalyzed ferrihydrite transformation are known, processes in the initial phase that lead to nucleation and the growth of product minerals remain unclear. To track ferrihydrite-Fe(II) interactions during this initial phase, we used Fe isotopes, Mössbauer spectroscopy, and extractions to monitor the structural, magnetic, and isotope composition changes of ferrihydrite within ∼30 min of Fe(II) exposure. We observed rapid isotope mixing between aqueous Fe(II) and ferrihydrite during this initial lag phase. Our findings from Mössbauer spectroscopy indicate that a more magnetically ordered Fe(III) phase initially forms that is distinct from ferrihydrite and bulk crystalline transformation products. The signature of this phase is consistent with the early stage emergence of lepidocrocite-like lamellae observed in previous transmission electron microscopy studies. Its signature is furthermore removed by xylenol extraction of Fe(III), the same approach used to identify a chemically labile form of Fe(III) resulting from Fe(II) contact that is correlated to the ultimate emergence of crystalline product phases detectable by X-ray diffraction. Our work indicates that the mineralogical changes in the initial lag phase of Fh transformation initiated by Fe(II)-Fh electron transfer are critical to understanding ferrihydrite behavior in soils and sediments, particularly with regard to metal uptake and release.

Iron isotopes reveal seasonal variations in the mechanisms for iron-bearing particle and colloid formation in the Lena River catchment, NE Siberia

Large Arctic rivers are an important source of iron (Fe) to the Arctic Ocean, though seasonal variations in the terrestrial source and supply of Fe to the ocean are unknown. To constrain the seasonal variability, we present Fe concentrations and isotopic compositions (δ56Fe) for particulate (>0.22 µm) and colloidal (<0.22 µm–1 kDa) Fe from the Lena River, NE Russia. Samples were collected every month during winter baseflow (September 2012–March 2013) and every 2–3 days before, during and after river ice break-up (May 2015).Iron in particles have isotope ratios lower than crustal values during winter (e.g., δ56FePart = −0.37 ± 0.16‰), and crustal-like values during river ice break-up and spring flood (e.g., δ56FePart = 0.07 ± 0.08‰), indicating a change in the source of particulate Fe between winter and spring flood. Low isotope values are indicative of mineral dissolution, transport of reduced Fe in sub-oxic, ice-covered sub-permafrost groundwaters and near-quantitative precipitation of Fe as particles. Crustal-like isotopic compositions result from the increased supply of detrital particles from riverbank and soil erosion during river ice break-up and flooding. Iron colloids (<0.22 μm) have δ56Fe values that are comparable to or lower than crustal values during winter (e.g., δ56FeCol = −0.08 ± 0.05‰) but similar to or higher than crustal values during spring flood (e.g., δ56FeCol = +0.24 ± 0.11‰). Low δ56Fe ratios for colloidal Fe during winter are consistent with precipitation from isotopically light Fe(II)aq transported in sub-permafrost groundwaters. Higher colloidal δ56Fe ratios during the spring flood indicate that these colloids are supplied from surface soils, where Fe is fractionated via oxidation or organic carbon complexation, similar to during summer. Approximately half of the annual colloidal Fe flux occurs during spring flood while most of the remaining colloidal Fe is supplied during summer months. The total amount of colloidal Fe transported during winter was relatively low. The seasonal variation in colloidal Fe isotope values may be a useful tool to trace the source of colloidal Fe to the Arctic Ocean and monitor future changes in the sources and supply of Fe from the permafrost landscape to the Lena River basin.

Iron isotope heterogeneity in magmas of subduction zones and its origin

Iron isotope heterogeneity of subduction-related primitive magmas was traditionally thought to be predominantly attributed to the addition of slab-derived components. However, the specific subducted material responsible for inducing Fe isotope heterogeneity in the subarc-backarc mantle remains poorly constrained. Here we report Fe isotopic compositions of a series of backarc basin basalts (BABBs) from the Woodlark Basin (an intra-arc rift basin), Vate Trough (a nascent rear-rift basin), and Lau Basin (a relatively mature basin) in the southwestern Pacific. Even though these BABBs have various geochemical compositions ranging from mid-ocean ridge basalts (MORB)-like to arc-like, which should be affected by various amounts of the slab-derived fluids and/or sediment melts, their δ56Fe values (0.05–0.18‰) are within the range of global MORB (0.05–0.17‰). After correction for crystal fractionation, the primitive δ56Fe values (δ56Fe-prim) displayed no co-variation with indicators of subduction contributions (e.g., Ce/Pb, Nb/U, Ba/La, and Th/Yb) or source redox conditions caused by slab inputs (e.g., V/Yb, V/Ti), suggesting that the δ56Fe-prim values of these BABBs are rarely affected by subduction metasomatism and the change in oxygen fugacity caused by subducted input. Therefore, we proposed that the MORB-like δ56Fe values of the studied BABBs were primarily caused by mantle melting processes. Furthermore, we presented a compilation of available Fe isotopic data for BABBs and island arc basalts (IABs) and used these data to evaluate Fe isotope heterogeneity in subduction settings. In particular, compared with δ56Fe-prim of MORB, the δ56Fe-prim of BABBs from the Central Lau Spreading Centre in the Lau Basin and the IABs have lower values, whereas BABBs from the Rochambeau Ridges in the Lau Basin have higher δ56Fe-prim values. By comprehensively considering the factors affecting the variation in Fe isotopic compositions in magmatic rocks in subduction zones (e.g., crystal fractionation, partial melting of the mantle, redox conditions, and subduction-related metasomatism), we proposed that the varied Fe isotopic compositions in subduction settings could reflect their heterogeneous sources, which may be related to plate subduction. Specifically, during plate subduction, a melt-depleted refractory forearc mantle peridotite (with low δ56Fe values) could be dragged by subducted slab into subarc or backarc depths, resulting in light Fe isotopic enrichment in island arc magmas or BABBs; additionally, serpentinites (both in the slab and mantle wedge) can generate light Fe isotopic enrichment in island arc magmas. High δ56Fe values in the BABB (e.g., from the Rochambeau Ridges in the Lau Basin) may result from the toroidal influx of nearby upwelling plume components or the assimilation of hydrothermally altered oceanic crust.

Low-δ56Fe fluid released from serpentinite as recorded by iron isotopes of Myanmar jadeitites

Melt extraction and subduction zone fluid infiltration can produce light Fe isotope compositions of arc lavas relative to the MORBs. However, the Fe isotope signature of subduction zone fluid is poorly constrained, which has hampered our understanding of Fe cycling in the subduction zone. Jadeitite veins in forearc serpentinite provide a unique record for the characteristics of subduction zone fluids. Here we report Fe isotope data for Myanmar jadeitites and associated rocks to constrain the Fe isotope signature of subduction zone fluids. Two types of jadeitites from Myanmar display distinct δ56Fe much lower than typical igneous rocks. White jadeitites, directly precipitated from fluids, have variable δ56Fe from −0.60‰ to −0.04‰, while green jadeitites, formed by fluid-chromite interaction, have δ56Fe (−0.44‰ to −0.19‰) similar to the associated amphibole-rich blackwalls (−0.47‰ to −0.23‰). The light Fe isotope signature of the jadeitites is not induced by weathering, kinetic fractionation, dissolution of Fe-rich carbonate, or mineral dissolution-reprecipitation process. Instead, it most likely reflects the Fe isotope variation of serpentinite-derived fluids. Correlations of δ56Fe with REEs, Sb, and U in white jadeitites suggest that the jadeitite-forming fluid is a mixture of serpentinite-derived and sediment-derived fluids. In contrast, correlations of δ56Fe with Si, Al, and Cr in green jadeitites record the interaction of low-δ56Fe fluids with chromite. Considering the abundance of the serpentinite-derived fluid, it can effectively influence the Fe isotope compositions of the ambient mantle and arc lavas.

Iron isotope fractionation of redox and geochemical cycling in the typical Gleysols in Mun River Basin, Northeast Thailand

Iron (Fe) isotope is a potential tool for tracking redox process and geochemical cycling in terrestrial environment. In this study, Fe concentration and its isotopic composition (δ56Fe) in two typical Gleysol profiles (M1 and M2) were investigated to distinguish the processes which influence the variation of Fe isotopic composition during redox regimes in the Mun River Basin (MRB). Under oxidizing condition, Fe(II) was oxidized and re-precipitated to form Fe(III) (hydr)oxides zone (Fe nodule-containing zone) in two Gleysol profiles, leading to extremely light Fe isotopes in these zones. The results revealed that the lowest δ56Fe value in Fe(III) (hydr)oxides zone was derived from the migration of light Fe isotopes in upper zone, and Fe(II) was retained and oxidized to Fe(III) (hydr)oxides. Proton-promoted dissolution and leaching were two critical factors leading to a decrease in Fe concentration, which were accompanied by the accumulation of heavy Fe isotopes in the upper zone of M1 profile. In M2 profile, light Fe induced by soil organic matter was accumulated in the topsoil with abundant organic matter. These findings provide comprehensive information of Fe isotopic fractionation and Fe cycling in soil profiles, which would contribute to the understanding of biogeochemical elemental cycling in terrestrial ecosystems.

Iron Isotope Constraints on the Structure of the Early Solar System

The recent advent of nontraditional isotopic systems has revealed that meteorites display a fundamental isotopic dichotomy between noncarbonaceous (NC) and carbonaceous (C) groups, which represent material from the inner and outer solar system, respectively. On the basis of iron isotope anomalies, this view has recently been challenged in favor of a circumsolar disk structured into three distinct reservoirs (the so-called isotopic trichotomy). In this scenario, the CI chondrites—a rare type of carbonaceous chondrites with chemical composition similar to that of the Sun’s photosphere—would sample a distinct source region than other carbonaceous chondrites, located beyond Saturn’s orbit. Here, we report a model based on the available data for both mass-dependent fractionation of Te stable isotopes and mass-independent Fe nucleosynthetic anomalies. On the basis of the Te–Fe isotopic correlation defined by all carbonaceous chondrites including CIs, we show that the NC-CC dichotomy extends to Fe isotopes. Our finding thus supports (i) the existence of only two reservoirs in the early solar system and (ii) the ubiquitous presence of CI-like dust throughout the carbonaceous reservoir. Our approach also reveals that the carrier phase of 54Fe anomalies corresponds to Fe–Ni metal beads mostly located within chondrules. Finally, we propose that the CC chondrule component records a constant mix of refractory inclusions and NC-like dust.

Energy rates due to Fe isotopes during presupernova evolution of massive stars

This work presents the microscopic calculation of energy rates (γ-ray heating and (anti)neutrino cooling rates) due to weak decay of selected Fe Isotopes. The isotopes have astrophysical significance during the presupernova evolution of massive stars. The energy rates are calculated using the pn-QRPA model and compared with the independent particle model (IPM), large scale shell model (LSSM) and recent shell model calculation (GXPF1J). The reported (anti)neutrino cooling rates are smaller by up to two orders of magnitude at low core temperature values than the IPM rates. The two calculations compare well at T = 30 GK. The comparison of cooling rates with the LSSM is interesting. The pn-QRPA cooling rates due to even-even Fe isotopes are smaller (up to 2 orders of magnitude). For the odd-A isotopes, the reported rates are bigger up to an order of magnitude. The pn-QRPA computed cooling rates are, up to 2 orders of magnitude, bigger when compared with the GXPF1J calculation. The γ-ray heating rates due to electron capture rates rise with the temperature and density values of the stellar core. On the other hand, the γ-ray heating due to β-decay increases with the core temperature values but decreases by orders of magnitude when the stellar core stiffens. The pn-QRPA computed γ heating rates are bigger (up to 3 orders of magnitude) at high temperatures and densities (for the case of 55,56Fe) when compared with the recent shell model results. Owing to the importance of energy rates, this study may contribute to a realistic simulation of presupernova evolution of massive stars.

Contribution of natural and agricultural activities on Fe dynamics: Insights from Fe isotope in soils under different land-use types

Evaluating the contribution of natural and agricultural factors on Fe dynamics in soils is crucial to the study of material cycling in critical zone observation. Five soil profiles under cultivated land, abandoned cultivated land, grassland, shrub land, and secondary forest from Puding karst catchment in Guizhou Province, China, were analyzed to identify natural and agricultural contributions to Fe processes. Vertical distribution changes of Fe content and Fe isotopic compositions (δ56Fe) were investigated. The results presented that natural chemical weathering accompanied by soil erosion occurs primarily in the upper layer, leading to the loss of Fe from the surface to the bottom during the eluviation-illuviation process. Fe isotopic fractionation occurred in soils rich in natural organic matter (i.e., secondary forest and shrub land), resulting in the accumulation of lighter Fe isotopes. Soil impacted by anthropogenic activity have higher Fe content (e.g., cultivated land or abandoned cultivated land). The reduction of Fe is the principal cause of light Fe isotopes in the upper layer, which is caused by periodic artificial irrigation on cultivated land. Compared to worldwide soils, Puding soils are impacted by natural organic matter, eluviation-illuviation, and agricultural activities, which tend to modify Fe isotopic signatures on a local scale within soil profiles. Fe isotopic fractionations in bulk soils among different land-use soils are very limited. This study provides insightful analysis based on Fe isotopic to recognize natural and anthropogenic activities on Fe dynamic, and offers information on material cycling in the Puding karst catchment.

Origins of magmatism in the Okinawa Trough: Fe–Sr–Nd–Pb–Hf isotopic constraints

ABSTRACT The Okinawa Trough is an incipient back-arc basin formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate and is a natural laboratory for studying basin evolution, magmatism, and crust-mantle interactions during the early stages of back-arc spreading. Back-arc spreading and recent magmatism are occurring mainly in the Middle Okinawa Trough (MOT) and Southern Okinawa Trough (SOT). In order to investigate the magmatism in the Okinawa Trough, volcanic rock samples from the MOT and SOT were analysed for Fe – Sr – Nd – Pb – Hf isotopic compositions. The Fe isotopic compositions of basaltic andesite samples from the SOT are similar to or lower than MORBs. The fluid/melt derived from the subducted slab, especially the fluid dehydrated from slab serpentinites and sediment-derived melts, entered the overlying depleted mantle wedge and participated in magma generation, which resulted in the low δ56Fe values of the SOT basaltic magmas. The δ56Fe values of volcanic rocks from the MOT increase with increasing SiO2 contents, suggesting a gradual enrichment of heavy Fe isotopes during the evolution of the magma as it ascended to the surface. While the Sr – Nd – Pb – Hf isotopic compositions do not vary significantly, suggesting that the different samples are the products of different degrees of crystal fractionation of comagma. The fractional crystallization of olivine, pyroxene, and ilmenite minerals, which enrich in light Fe isotopes, resulted in the gradual increase in Fe isotopic values of magma during its evolution. The dacites and rhyolites from the southernmost Okinawa Trough have the similar δ56Fe values with the basaltic andesite and the basalt from the SOT and MOT, accompanied by significantly lower Nd and Hf isotope ratios relative to basalts, reflecting that the contamination of crustal materials would not change the magma in Fe isotope compositions evidently. Compared with the MOT, the volcanic rocks from the SOT was more affected by subduction components on their underlying mantle, and those from the southernmost experienced more contamination by crustal materials in the evolving magma.