Iron Isotope Research Articles

I2S-LWR Activation Analysis of Heat Exchangers Using Hybrid Shielding Methodology With SCALE6.1

The Integral Inherently Safe Light Water Reactor (I2S-LWR) concept developed by a team lead by Georgia Tech is a novel PWR reactor delivering electric power of 1000 MWe while implementing inherent safety features typically reserved for Generation III+ small modular reactors. The main safety feature is based on an integral primary circuit configuration, bringing together a compact core design with 121 fuel assemblies (FA), control rod drive mechanism (CRDM), 8 primary heat exchangers (PHE), 4 passive decay heat removal systems (DHRS), 8 pumps, and other integral components. A high power density core based on uranium silicide fuel (U3Si2) is selected to achieve high thermal power which is extracted with PHEs placed in the annular region between the barrel and the vessel. The compact and integrated design of I2S-LWR leads to activation of integral components, mainly made from stainless steel, so accurate and precise Monte Carlo (MC) simulations are needed to quantify potential dose rates to personnel during routine maintenance operation. This shielding problem is therefore very challenging, posing a non-trivial neutron flux solution in a phase space. This paper presents the performance of the hybrid shielding methodologies CADIS/FW-CADIS implemented in the MAVRIC sequence of the SCALE6.1 code package. The main objective was to develop a detailed MC shielding model of the I2S-LWR reactor along with effective variance reduction (VR) parameters and to calculate neutron fluence rates inside PHEs. Such results are then utilized to find the neutron activation rate distribution via 60Co generation inside of a stack of microchannel heat exchangers (MCHX), which will be periodically withdrawn for the maintenance. 59Co impurities are the main cause of (n,γ) radiative gamma dose to personnel via neutron activation since 60Co has half-life of 5.27 years and is emitting high energy gamma rays (1.17 MeV and 1.33 MeV). The developed MC model was successfully used to find converged fluxes inside all 8 stacks of PHEs with respect to MC statistics using the FW-CADIS methodology. For that purpose the SN module Denovo, based on forward-adjoint transport theory, was used to find VR parameters (importance map and biased source) to effectively bias MC simulation. Further research is required to account for other activation pathways, i.e. isotopes of iron which may generate 59Co through neutron activation and beta decay.

Geochemical and Seasonal Characteristics of Dissolved Iron Isotopes in the Mun River, Northeast Thailand

Dissolved iron (Fe) isotopes in river water have a pivotal role in understanding the Fe cycle in the surficial environment. A total of 13 samples of river water were collected from the Mun River to analyze the Fe isotopes and their controlling factors in river water, such as dissolved organic carbon (DOC) and different supply sources. The results showed that dissolved Fe (DFe) concentrations ranged from 21.49 μg/L to 232.34 μg/L in the dry season and ranged from 10.48 μg/L to 135.27 μg/L in the wet season, which might be ascribed to the dilution effect. The δ56Fe of the dry season (−0.34 to 0.57‰, with an average 0.09‰) was lower than that of the wet season (−0.15 to 0.48‰, with an average 0.14‰). Combined with the δ56Fe and DFe/DAl ratios, the end-members of DFe were identified, including rock weathering (high δ56Fe and low DFe/DAl ratio), anthropogenic inputs (high δ56Fe and high DFe/DAl ratio) and groundwater inputs (low δ56Fe and low DFe/DAl ratio). The relationship between δ56Fe and DOC concentrations suggested that the chelation of organic matter with heavy Fe isotopes was one of the important sources of heavy Fe isotopes in river water.

Iron isotope systematics during igneous differentiation in lavas from Kīlauea and Mauna Loa, Hawai'i

The Big Island of Hawai'i is currently the most active site of magmatic activity in the Hawaiian chain of volcanoes that are associated with a mantle plume in the Pacific Ocean. Mantle source variability and magmatic processes have both been proposed to significantly affect lava chemistry on the Big Island, which is most prominently illustrated in a radiogenic isotope dichotomy of the so-called ‘Kea’ and ‘Loa’ trends. Here, we present stable Fe isotopes (δ57Fe), complemented by radiogenic 176Hf/177Hf, in lavas from the Puʻu ʻŌʻō vent on the East Rift Zone of Kīlauea (Kea trend) and from the Southwest Rift Zone from Mauna Loa (Loa trend). In Hf isotopic space, lavas range from εHf = +8 to +13, with Puʻu ʻŌʻō samples aligning with published values of lavas from the ‘Kea-trend’ in SrHf isotope space, whereas Mauna Loa basalts and picrites presented here coincide with values of the Loa-trend. The Puʻu ʻŌʻō lavas have average δ57Fe of +0.15 ‰ and an average of MgO ~ 7 wt%. Mauna Loa basalts and picrites show on average lighter δ57Fe of +0.06 ‰ but higher MgO ~ 16 wt%. Combined, in a global OIB comparison, the Hawaiian samples have among the lowest δ57Fe reported to date. Both Puʻu ʻŌʻō and Mauna Loa lavas lie on a trend of decreasing δ57Fe with increasing MgO that is ascribed to olivine fractionation and accumulation. Geochemical indices of partial melting (e.g., (Gd/Yb)PM, TiO2) do not align with Fe isotopic signatures, whether corrected for crystal fractionation or not, and can thus not explain the heavy Fe isotopic signatures observed here. Likewise, a lack of co-variations of radiogenic isotopes with Fe isotopes do not support source inheritance from enriched, crustal-like plume components as the dominant process to explain the Fe isotopic signatures. On a three‑iron isotope plot, it appears that kinetic in combination or in exchange with equilibrium fractionation of stable isotopes can account for Fe isotopes lighter than δ57Fe < +0.15 ‰. An inherently heavy Fe isotope signature (> 0.15 ‰) is required to explain some of the high values measured here for which no geochemical proxy can be identified. Assuming fast recharge into the plumbing systems feeding Puʻu ʻŌʻō and Mauna Loa lavas with no presumed homogenisation in subsurface magma chambers, we surmise that the Hawaiian samples are reflecting lavas that experienced a combination of kinetic and equilibrium processes, which ultimately lead to a seemingly random distribution of Fe isotopes. The exposure to different magmatic processes, e.g., re-charging events, and the missing covariation between MgO vs δ57Fe argue for an open magma chamber underneath Puʻu ʻŌʻō and Mauna Loa, masking processes that influence Fe isotopes, i.e., source inheritance or melting degree. From our new stable Fe isotope data, we show that lavas, which travel through a plumbing system, can undergo multiple fractionation processes.

A one-million-year isotope record from siderites formed in modern ferruginous sediments

Abstract Ancient iron formations hold important records of environmental conditions during the Precambrian eons. Reconstructions of past oceanic systems require investigation of modern ferruginous analogs to disentangle water column and diagenetic signals recorded in iron-bearing minerals. We analyzed oxygen, iron, and carbon isotopes in siderite, a ferrous carbonate phase commonly used as an environmental proxy, from a 100-m-long record spanning a 1 Ma depositional history in ferruginous Lake Towuti, Indonesia. Combining bulk sediment and pore water geochemistry, we traced processes controlling siderite isotope signatures. We show that siderite oxygen isotope compositions (δ18O) reflect in-lake hydrological and depositional conditions. Low iron isotope values (δ56Fe) record water column oxygenation events over geological timescales, with minor diagenetic partitioning of Fe isotopes by microbial iron reduction after deposition. The carbon isotope compositions (δ13C) reflect the incorporation of biogenic HCO3–, which is consistent with sediment organic matter remineralization lasting over ca. 200 ka after burial. Positive δ13C excursions indicate an increased production of biogenic methane that escaped the sediment during low lake levels. Diffusion across the sediment–water interface during initial formation of siderites tends to align the isotope signatures of bottom waters to those of pore waters. As microbial reduction of ferric iron and oxidation of organic matter proceed and saturate pore water conditions with respect to siderite, overgrowth on nuclei partially mutes the environmental signal inherited from past bottom waters over ca. 1 Ma. Because high depositional fluxes of ferric iron and organic matter in early oceans would have promoted similar microbial processes in ferruginous deposits prior to lithification, the environmental record contained in siderite grains can successively integrate depositional and early diagenetic signals over short geological timescales.

Magnetite geochemistry and iron isotope signature of disseminated and massive mineralization in the Kalatongke magmatic Cu[sbnd]Ni sulfide deposit, northwest China

Magnetite is a common accessory mineral and an indicator to magma evolution and sulfide fractional crystallization in magmatic NiCu sulfide deposits. The Kalatongke magmatic sulfide deposit at the southern margin of the Central Asian Orogenic Belt is composed of 11 mafic intrusions. The sulfide orebodies (Y1, Y1 deep, and Y2) are hosted by three small mafic intrusions, and magnetite is common in all mineralized samples. Based on ilmenite exsolution texture, composition, and type of mineralization, three types of magnetite are identified, (1) primary Fe-rich magma-related magnetite (type 1), (2) sulfide liquid-related magnetite (type 2), and (3) hydrothermal magnetite (type 3). We speculate that Fe isotope equilibrium fractionation between early or co-crystallized light 54Fe-enriched sulfide and magnetite may account for the ultra-high magnetite δ56Fe value (0.70‰ to 1.35 ‰) in the magmatic magnetite (types 1 and 2). Enriched compatible elements in type 1 magnetite (TiO2 = 1.52 wt% to 7.89 wt%, V = 775 ppm to 2420 ppm, Cr = 2697 ppm to 14,658 ppm, and Ni contents = 478 ppm to 1256 ppm), reflect the characteristics of primary Fe-rich magmatic magnetite crystallized at relatively high temperature and low oxygen fugacity. Type 2 magnetite in massive ores has Ni (762 ppm to 1769 ppm) and δ56Fe (0.89 ‰ to 1.10 ‰) values similar to type 1 magnetite, but significantly lower TiO2, V and Cr contents (TiO2 = 0.07 to 3.72 wt%, V = 61 to 2314 ppm, Cr = 5 to 2937 ppm), indicating co-crystallization with an evolved sulfide liquid across a wide span of temperature and oxygen fugacity. Type 3 magnetite is of hydrothermal fluid origin, with low δ56Fe (0.29 ‰ to 0.41 ‰) and Ni (177 ppm to 377 ppm).Magnetite composition and Fe isotope signatures at the Kalatongke magmatic sulfide deposit can reveal the genesis of magnetite and the evolution of the melt and sulfide. The Y1 orebody was completely crystallized over a short period of time, while the Y1 deep and Y2 east orebodies underwent a protracted evolution during which magnetite co-crystallized from primitive Fe-rich melt, Fe-rich evolved melt and Cu-rich intermediate sulfide solution. Magnetite and sulfide in the Y2 west massive orebody likely formed last. The compatibility of both lithophile and chalcophile elements, combined with Fe isotopes in magnetite, makes magnetite a good indicator of silicate and sulfide melt evolution.

Refining the early Cambrian marine redox profile by using pyrite sulfur and iron isotopes

It is widely accepted that the emergence of metazoans in the Ediacaran-Cambrian transition might be triggered by oxygenation of the atmosphere-ocean system. However, some Ediacaran and early Cambrian macroscopic fossils (such as multicellular algae) were preserved under sulfidic conditions, challenging the conventional view of the prohibition of eukaryotes in the presence of H2S. It was proposed that organisms might have lived in some episodic non-sulfidic intervals although the ocean was predominantly sulfidic. However, the hypothesized short-lived non-sulfidic intervals were hardly identified by traditional bulk sample analyses, which cannot provide sufficiently high temporal resolution to resolve the short-term oxygenation events. In this study, we analyzed pyritized sponge spicules and disseminated pyrites from black shales of the early Cambrian Shuijingtuo Formation in South China. We conducted in situ pyrite sulfur (δ34Spy) and iron (δ56Fepy) isotopes as well as bulk sample pyrite sulfur isotope analyses. The intra-crystal or intra-spicule δ34Spy variations reflect the evolution of seawater and porewater geochemistry during pyrite formation, providing a higher temporal resolution of redox fluctuation in the early Cambrian ocean. Our study indicates: (1) The bulk sample pyrite sulfur isotope and pyrite content data suggest diagenetic pyrite precipitation in sediment porewater with H2S diffusion from the overlying sulfidic seawater; (2) Limited intra-crystal and intra-spicule δ34Spy variations imply that both spicule and disseminate pyrites had a homogenous S source from sulfidic seawater, and dissimilatory sulfate reduction (DSR) in sediment porewater was negligible; (3) The in situ iron isotope analyses indicate active dissimilatory iron reduction (DIR) in sediment that generated excessive ferrous iron (Fe2+) to compensate for Fe2+ consumption by pyrite precipitation, allowing Fe2+ to accumulate in ferruginous porewater. Therefore, the early Cambrian ocean was characterized by active DSR in sulfidic seawater and DIR in ferruginous sediment porewater. In addition, our study demonstrates that the seawater might be persistently sulfidic, and does not support the presence of intermittent non-sulfidic intervals for the survival of organisms. If correct, it is hypothesized that some primitive sponges might have survived in sulfidic seawater, although the seawater H2S concentration remains unknown.

Iron and sulfur isotope fractionation during pyrite dissolution-reprecipitation revealed by in-situ isotopic analyses in the Muping gold deposit (Jiaodong, China)

Pyrite is an excellent archive for understanding geochemical behaviors of elements and isotopes in the course of ore formation. Here we present a combined textural-geochemical characterization of gold-related pyrites from the Muping deposit of Jiaodong gold province. Element mapping reveals core-rim texture, with the core being enriched in Pb, Ag, Cu, and Sn, whereas the rims in Au and As. Electron backscattered diffraction analysis shows consistent crystallographic orientation for both core and rim in pyrite. Simultaneous in-situ isotopic measurements unravel a coupled variation in Fe-S isotopes during pyrite growth and modification. We interpret the core-rim texture as an indication of coupled dissolution-reprecipitation, where the cores precipitated from an initial fluid, and then dissolved and overgrown in response to cooling and oxidizing conditions. During this process, Pb, Ag, Cu, and Sn migrated out from the rims. Instead, Au were locked in the rims with the aid of As in the fluids. It is supposed that a variation of temperature and oxygen fugacity led to the disparity of Fe-S isotope of pyrite cores. Kinetic fractionation might account for the dispersion of Fe-S isotopic compositions of rims. The rims have relatively homogeneous S isotope composition. However, the variation of the Fe isotope of the rims was derived from different degrees of isotope exchange, suggesting that Fe isotope did not equilibrate with the mineralizing fluid. The different fractionation behavior of Fe-S isotopes in pyrite during fluid modification has a significant implication for reconstructing precipitation environment and tracing sources of ore-forming fluid and mineralization process.

Constant iron isotope composition of the upper continental crust over the past 3 Gyr

Constant iron isotope composition of the upper continental crust over the past 3 Gyr

Quantitating Iron Transport across the Mouse Placenta In Vivo using Nonradioactive Iron Isotopes.

Iron is essential for maternal and fetal health during pregnancy, with approximately 1 g of iron needed in humans to sustain a healthy pregnancy. Fetal iron endowment is entirely dependent on iron transfer across the placenta, and perturbations of this transfer can lead to adverse pregnancy outcomes. In mice, measurement of iron fluxes across the placenta traditionally relied on radioactive iron isotopes, a highly sensitive but burdensome approach. Stable iron isotopes (57Fe and 58Fe) offer a nonradioactive alternative for use in human pregnancy studies. Under physiological conditions, transferrin-bound iron is the predominant form of iron taken up by the placenta. Thus, 58Fe-transferrin was prepared and injected intravenously in pregnant dams to directly assess placental iron transport and bypass maternal intestinal iron absorption as a confounding variable. Isotopic iron was quantitated in the placenta and mouse embryonic tissues by inductively coupled plasma mass spectrometry (ICP-MS). These methods can also be employed in other animal model systems of physiology or disease to quantify in vivo iron dynamics.

Iron isotope compositions of subduction-derived rocks: Insights from eclogites and metasediments of the Münchberg Massif (Germany)

The Fe isotope systematics of subducted lithologies are crucial for the understanding of redox-dependent mass transfer in subducting slabs, with consequences for the compositions of arc magmas and of the deep mantle. We investigated eclogites, metagabbros, and paragneisses from the Variscan Münchberg Massif to unravel whether their Fe isotope compositions are dominated by the igneous/sedimentary protolith signature, by low-temperature seawater alteration, or by later fluid-rock interactions during the subduction-exhumation cycle. Although the eclogites are thought to be derived from a continental rather than oceanic setting (possibly a rift-drift transition stage), they have mid-ocean ridge basalt (MORB)-like major and trace element compositions. They are often moderately oxidized compared to MORB (Fe3+/ΣFe = 0.06 to 0.30). Their δ56Fe values (+0.00 to +0.17‰; mean + 0.08 ± 0.01‰) mostly resemble those of MORB (+0.07 to +0.17‰). The metagabbros, which are derived from a more enriched mantle source than the eclogites, yielded heavier δ56Fe values (+0.09 to +0.22‰) similar to ocean island basalts, whereas those of the paragneisses (+0.03 to +0.10‰) are typical for pelitic sediments.It appears that the Fe isotope compositions of the igneous protoliths are largely preserved and little if any Fe was mobilized during the diverse fluid-rock interaction stages. The parental magma of the eclogites was probably somewhat isotopically lighter than similarly differentiated MORB magmas, perhaps due to the presence of metasomatized, isotopically light peridotites in the subcontinental lithospheric mantle (SCLM) source. Although it is possible that δ56Fe values were slightly modified during seawater alteration and/or metamorphic fluid-rock interactions in some of the eclogites, the impact of fluid-rock interactions on the major element compositions of the eclogites appears to be small. Furthermore, the scarcity of metamorphic veins in the Münchberg Massif argues against significant Fe mobilization in the slab. We suggest that continental eclogites tend to retain their magmatic δ56Fe values throughout the subduction-exhumation cycle, whereas δ56Fe values of oceanic eclogites may often be dominated by seafloor alteration with potential local modifications in the slab close to fluid channels. The remarkable robustness of the Fe isotope compositions of continental eclogites suggests that they may be used to reconstruct protolith mantle source properties despite the complex post-magmatic history.

Investigation of the Scorodite Formation Mechanism in As(V) Solution Containing Fe(II) with Hematite Addition Using a Stable Iron Isotope

Investigation of the Scorodite Formation Mechanism in As(V) Solution Containing Fe(II) with Hematite Addition Using a Stable Iron Isotope

Fetal iron uptake from recent maternal diet and the maternal RBC iron pool

During pregnancy iron can be obtained from the diet, body iron stores, or iron released from RBC catabolism. Little is known about the relative use of these sources to support fetal iron acquisition. To describe longitudinal change in iron absorption and enrichment across gestation and partitioning of RBC iron to the fetus. Fifteen pregnant women ingested an oral stable iron isotope (57Fe) in the second trimester (T2) of pregnancy (weeks 14-16) to label the RBC pool, and a second oral stable isotope (58Fe) in the third trimester (T3) (weeks 32-35). Absorption was measured at T2 and T3. Change in RBC 57Fe enrichment was monitored (18.8-26.6 wk) to quantify net iron loss from this pool. Iron transfer to the fetus was determined based on RBC 57Fe and 58Fe enrichment in umbilical cord blood at delivery. Iron absorption averaged 9% at T2 and increased significantly to 20% (P=0.01) by T3. The net increase in iron absorption from T2 to T3 was strongly associated with net loss in maternal total body iron (TBI) from T2 to T3 (P=0.01). Mean time for the labeled RBC 57Fe turnover based on change in RBC enrichment was 94.9 d (95% CI: 43.5, 207.1 d), and a greater decrease in RBC 57Fe enrichment was associated with higher iron absorption in T2 (P=0.001). Women with a greater decrease in RBC 57Fe enrichment transferred more RBC-derived iron to their fetus (P<0.05). Iron absorption doubled from T2 to T3 as maternal TBI declined. Women with low TBI had a greater decrease in RBC iron enrichment and transferred more RBC-derived iron to their neonate. These findings suggest maternal RBC iron serves as a significant source of iron for the fetus, particularly in women with depleted body iron stores.

Laboratory study of iron isotope fractionation during dissolution of mineral dust and industrial ash in simulated cloud water

Atmospheric deposition is a key mode of iron (Fe) input to ocean regions where low concentrations of this micronutrient limit marine primary production. Various natural particles (e.g., mineral dust, volcanic ash) and anthropogenic particles (e.g., from industrial processes, biomass burning) can deliver Fe to the ocean, and assessment of their relative importance in supplying Fe to seawater requires knowledge of both their deposition flux and their Fe solubility (a proxy for Fe bioavailability). Iron isotope (54Fe, 56Fe, 57Fe, 58Fe) analysis is a potential tool for tracing natural and anthropogenic Fe inputs to the ocean. However, it remains uncertain how the distinct Fe isotopic signatures (δ56Fe) of these particles may be modified by physicochemical processes (e.g., acidification, photochemistry, condensation-evaporation cycles) that are known to enhance Fe solubility during atmospheric transport. In this experimental study, we measure changes over time in both Fe solubility and δ56Fe of a Tunisian soil dust and an Fe–Mn alloy factory industrial ash exposed under irradiation to a pH 2 solution containing oxalic acid, the most widespread organic complexing agent in cloud- and rainwater. The Fe released per unit surface area of the ash (∼1460 μg Fe m−2) is ∼40 times higher than that released by the dust after 60 min in solution. Isotopic fractionation is also observed, to a greater extent in the dust than the ash, in parallel with dissolution of the solid particles and driven by preferential release of 54Fe into solution. After the initial release of 54Fe, the re-adsorption of A-type Fe-oxalate ternary complexes on the most stable surface sites of the solid particles seems to impair the release of the heavier Fe isotopes, maintaining a relative enrichment in the light Fe isotope in solution over time. These findings provide new insights on Fe mobilisation and isotopic fractionation in mineral dust and industrial ash during atmospheric processing, with potential implications for ultimately improving the tracing of natural versus anthropogenic contributions of soluble Fe to the ocean.

Characterization of achondritic cosmic spherules from the Widerøefjellet micrometeorite collection (Sør Rondane Mountains, East Antarctica)

Achondritic micrometeorites represent one of the rarest (ca. 0.5–2.1%) particle types among Antarctic micrometeorite collections. Here, we present major, trace element and oxygen isotope compositions on five vitreous, achondritic cosmic spherules (341–526 µm in size) recovered from the Widerøefjellet sedimentary trap in the Sør Rondane Mountains (SRMs) of East Antarctica. We also present the first iron isotope data for four of these achondritic cosmic spherules. The particles were initially identified based on the atomic concentrations of Fe-Mg-Mn and their distribution in Fe/Mg versus Fe/Mn space, spanning a relatively wide range in Fe/Mg ratios (ca. 0.48–1.72). The Fe/Mn ratios cover a more restricted range (22.4–31.7), comparable to or slightly below the values measured for howardite-eucrite-diogenite (HED) and martian meteorites. One particle (WF1801-AC3) displays an elevated Fe/Mn ratio of ∼78, comparable to the values determined for lunar rocks. The negative correlation observed between the CaO + Al2O3 contents and the Fe/Si ratios of achondritic spherules reflects both the mineralogy of the precursor materials, as well as the extent of volatilization experienced during atmospheric entry heating. This trend suggests that the primary mineralogy of precursor materials may have been compositionally similar to basaltic achondrites. Based on their distribution in Ca/Si versus Al/Si space, we argue that the majority of achondritic cosmic spherules predominantly sample pyroxene- and/or plagioclase-rich (i.e., basaltic) precursor bodies. Such precursor mineralogy is also inferred from their rare earth element (REE) patterns, which show resemblances to fine-grained basaltic eucrites or Type 1 achondritic spherules (n = 3 – av. REEN = 11.2–15.5, (La/Yb)N = 0.93–1.21), pigeonite-rich equilibrated eucrite precursors or Type 2 achondritic spherules (n = 1 – av. REEN = 27.9, (La/Yb)N = 0.10), and possibly Ca-phosphates from (primitive) achondritic bodies (n = 1 – av. REEN = 58.8, (La/Yb)N = 1.59). This is clearly demonstrated for particle WF1801AC-1, which was likely inherited from a fine-grained eucritic precursor body. The pre-atmospheric oxygen isotope composition was reconstructed through compensation of mass-dependent fractionation processes as well as mixing with atmospheric oxygen, using iron isotope data. Two particles (WF1801AC-2, WF1801-AC4) display corrected oxygen isotope compositions (δ18O = 3.7–4.4‰) largely consistent with HED meteorites and may thus originate from HED-like parent bodies. The corrected oxygen isotope compositions (δ18O = 12.6–12.8‰) of the remaining particles (WF1801-AC3, WF1801-AC5) do not correspond to known meteorite fields and may represent two distinct types of unknown achondritic parent bodies or residual atmospheric entry effects. Finally, the abundance (ca. 0.5%) of achondritic cosmic spherules within the Widerøefjellet sedimentary trap is comparable to that observed in the South Pole Water Well (SPWW – ca. 0.5%), Novaya Zemlya glacier (ca. 0.45%) and Transantarctic Mountain (TAM) (ca. 2.1%) collections, confirming their overall rarity in micrometeorite collections. Unambiguous evidence for micrometeorites from the Moon or Mars remains absent from collections to date.

Evolution of low-lying M1 modes in germanium isotopes

Magnetic dipole strength functions are determined for the series of germanium isotopes from $N=Z=32$ to $N$ = 48 on the basis of a large number of transition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the $1{g}_{9/2}$ orbital is analyzed. A bimodal structure comprising an enhancement toward low transition energy and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled $1{g}_{9/2}$ orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and prove the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature.

The effect of a natural polyphenol supplement on iron absorption in adults with hereditary hemochromatosis

ObjectivesWe developed a natural polyphenol supplement that strongly chelates iron in vitro and assessed its effect on non-heme iron absorption in patients with hereditary hemochromatosis (HH).MethodsWe performed in vitro iron digestion experiments to determine iron precipitation by 12 polyphenol-rich dietary sources, and formulated a polyphenol supplement (PPS) containing black tea powder, cocoa powder and grape juice extract. In a multi-center, single-blind, placebo-controlled cross-over study, we assessed the effect of the PPS on iron absorption from an extrinsically labelled test meal and test drink in patients (n = 14) with HH homozygous for the p.C282Y variant in the HFE gene. We measured fractional iron absorption (FIA) as stable iron isotope incorporation into erythrocytes.ResultsBlack tea powder, cocoa powder and grape juice extract most effectively precipitated iron in vitro. A PPS mixture of these three extracts precipitated ~ 80% of iron when 2 g was added to a 500 g iron solution containing 20 µg Fe/g. In the iron absorption study, the PPS reduced FIA by ~ 40%: FIA from the meal consumed with the PPS was lower (3.01% (1.60, 5.64)) than with placebo (5.21% (3.92, 6.92)) (p = 0.026)), and FIA from the test drink with the PPS was lower (10.3% (7.29 14.6)) than with placebo (16.9% (12.8 22.2)) (p = 0.002).ConclusionOur results indicate that when taken with meals, this natural PPS can decrease dietary iron absorption, and might thereby reduce body iron accumulation and the frequency of phlebotomy in patients with HH.Trial registry: clinicaltrials.gov (registration date: 9.6.2019, NCT03990181).

Large iron isotope fractionation during mantle wedge serpentinization: Implications for iron isotopes of arc magmas

Arc magmas are usually more oxidized than lavas from intraplate settings and spreading ridges. However, iron isotopes of arc magmas are generally lighter, and the mechanism is still controversial. The mantle wedge serpentinite provides new insights to resolve this issue. Here we show that mantle wedge serpentinites/serpentinized peridotites from the Mariana forearc mantle wedge have both heavy Fe isotopes (δ56Fe=−0.01–0.15‰) and high Fe3+/ΣFe values (0.50–0.88), which are positively correlated. This indicates coupled iron oxidation and iron isotope fractionation induced by serpentinization in the mantle wedge. The high Fe3+/ΣFe values and high SO3 contents of the mature serpentinites further suggest that the forearc mantle wedge is highly oxidized. Here we present a new mechanism for iron isotope fractionation and iron oxidation during mantle wedge serpentinization. Because iron solubility is low in the resultant high-pH fluids at the early stage of serpentinization, ferrous iron liberated during olivine serpentinization preferentially precipitates as serpentine, Fe-rich brucite, and magnetite in the serpentinite. After the full consumption of olivine during the late-stage serpentinization, ferrous iron becomes soluble and mobile in low-pH chlorine/sulfate-rich penetrating fluids, and is therefore released to the fluid with light Fe isotopes during progressive serpentinization, leaving the residual serpentinite with heavy iron isotopes. This suggests that mature serpentinites at the base of mantle wedge can act as a filter that sequesters ferric iron with heavy iron isotopes and liberates ferrous iron with light iron isotopes to the penetrating slab fluid, which migrate up to the above mantle wedge and even the mantle melting zone. The highly oxidized forearc mantle wedge serpentinites can also be dragged down to the subarc depth, releasing oxidizing fluids by dehydration. These processes may oxidize the arc mantle wedge coupled with light Fe isotopes, the fluxed partial melting of which consequently produces oxidized arc magmas with light Fe isotopes.

The absence of an effect of nickel on iron isotope fractionation during core formation

The Fe isotopic compositions of mantles of differentiated inner solar system bodies are similar to, or heavier than those of chondritic meteorites. Core–mantle differentiation is a potential contributor to planetary isotopic fractionation. However, previous metal–silicate experiments provide only equivocal evidence for such fractionation, and have been used to argue that the Ni content of core-forming metal influences the extent of Fe isotopic fractionation. Here, we complement existing data with twenty-two novel metal–silicate equilibrium experiments with varying Ni content to better quantify the effect of Ni on the vector and magnitude of Fe isotopic fractionation during core formation. We find no statistically resolvable effect of the Ni content in the metallic phase on the metal–silicate Fe isotopic fractionation factor over a wide range of Ni concentrations (0–70 wt.% in the metal). In particular, the Fe isotopic composition of alloys from two experiments performed with 70 wt.% of Ni (δ56Femetal = 0.27 ± 0.04‰ and 0.32 ± 0.03‰, 2 standard deviations σ) are identical to the bulk experimental starting material (δ56Febulk = 0.27 ± 0.10‰, 2σ). Our data across all experiments yield an average isotopic fractionation factor Δ56Femet–sil = 0.05 ± 0.22‰ (2σ) at 1873 K and 1–2 GPa, suggesting that little to no isotopic fractionation of Fe is expected to occur during core formation at low pressures. As such, our data does not support core formation as the main mechanism causing the observed variability in Fe isotope ratios between the silicate Earth, Moon, Vesta and other differentiated asteroids. A combination of multiple accretion-related processes—including condensation from the solar nebula, volatile-depleting events such as giant impacts, and the disproportionation of ferrous iron to ferric iron and iron metal in larger bodies—as well as deep mantle and recycling processes could explain the heavier-than-chondritic signatures in the silicate Earth and Moon. Furthermore, our results support the ideality of mixing among Fe–Ni alloys, as previously demonstrated for physical properties but less conclusively evidenced for chemical properties.

Oxygen production and rapid iron oxidation in stromatolites immediately predating the Great Oxidation Event

Earth's surface became permanently oxygenated during the Great Oxidation Episode, a geochemical transition between ∼2.43 and 2.22 billion years ago, but shallow-water cyanobacterial oases with molecular oxygen production likely existed for hundreds of millions of years before, in the otherwise anoxic and iron-rich oceans. Despite abundant geochemical evidence for elevated ambient oxygen in the Archean upper ocean, sites of active microbial oxygen production have not been geochemically characterized. We report geochemical and iron isotopic data for a horizon of iron-rich stromatolites in the 2.46–2.43 Ga Griquatown Iron Formation in South Africa deposited on the margin of an anoxic ferruginous basin. Bulk-rock and micro-sampled iron isotope data for the stromatolites indicate quantitative oxidation of iron delivered by deep upwelling currents, which is most readily explained by cyanobacterial communities inhabiting the stromatolites and producing local oxygen enrichments near the fair-weather wave-base. Modest enrichments in Mn and Ce indicate high oxidation potential in this stromatolitic setting. The iron-rich nature of the stromatolites indicates that upwelling iron sources in the early Paleoproterozoic oceans overwhelmed established iron-precipitation mechanisms in deeper basins that had generally maintained iron-poor conditions in shallow-marine peritidal zone during the Neoarchean.

Iron from nanostructured ferric phosphate: absorption and biodistribution in mice and bioavailability in iron deficient anemic women

Food fortification with iron nanoparticles (NPs) could help prevent iron deficiency anemia, but the absorption pathway and biodistribution of iron-NPs and their bioavailability in humans is unclear. Dietary non-heme iron is physiologically absorbed via the divalent metal transporter-1 (DMT1) pathway. Using radio- iron isotope labelling in mice with a partial knockdown of intestine-specific DMT1, we assessed oral absorption and tissue biodistribution of nanostructured ferric phosphate (FePO4-NP; specific surface area [SSA] 98 m2g-1) compared to to ferrous sulfate (FeSO4), the reference compound. We show that absorption of iron from FePO4-NP appears to be largely DMT1 dependent and that its biodistribution after absorption is similar to that from FeSO4, without abnormal deposition of iron in the reticuloendothelial system. Furthermore, we demonstrate high bioavailability from iron NPs in iron deficient anemic women in a randomized, cross-over study using stable-isotope labelling: absorption and subsequent erythrocyte iron utilization from two 57Fe-labeled FePO4-NP with SSAs of 98 m2g−1 and 188 m2g−1 was 2.8-fold and 5.4-fold higher than from bulk FePO4 with an SSA of 25 m2g−1 (P < 0.001) when added to a rice and vegetable meal consumed by iron deficient anemic women. The FePO4-NP 188 m2g-1 achieved 72% relative bioavailability compared to FeSO4. These data suggest FePO4-NPs may be useful for nutritional applications.