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1. Seasonal iron fluxes and iron cycling in sandy bioirrigated sediments

   https://doi.org/10.3389/fmars.2023.1293893  

   Swenson Perger, Darci A.; Dwyer, Ian P.; Aller, Robert C.; Volkenborn, Nils; Heilbrun, Christina; Wehrmann, Laura M. (November 2023, Frontiers in Marine Science)

   Permeable sediments, which represent more than 50% of the continental shelves, have been largely neglected as a potential source of Fe in current global estimates of benthic dissolved iron Fed fluxes. There are open questions regarding the effects of a range of factors on Fed fluxes from these deposits, including seasonal dynamics and the role of bioirrigation. To address these gaps, we performed laboratory-based sediment incubation experiments with muddy sands during summer (21 °C) and winter (7 °C). We used bioirrigation mimics to inject overlying water into the permeable sediment with patterns resembling the bioirrigation activity of the prolific bioturbating polychaete,Clymenella torquata. Newly developed in-line Fe accumulators were used to estimate Fe fluxes with a recirculating set-up. We found high Fed fluxes from sandy sediments, especially in benthic chambers with simulated bioirrigation. In the winter fluxes reached 200 µmol Fed m-2 d-1 at the onset of irrigation and then decreased over the course of a 13-day experiment while in the summer fluxes from irrigated sediments reached 100 µmol Fed m-2 d-1 and remained high throughout a 7-day experiment. Despite different geochemical expressions of Fe-S cycling and resulting porewater Fed concentrations in winter and summer, large Fed fluxes were sustained during both seasons. Solid-phase and porewater concentration profiles showed that maximum concentrations of key constituents, including total solid-phase reactive Fe, and porewater Fed and ammonium, were located closer to the sediment water interface (SWI) in irrigated cores than in non-irrigated cores due to the upward advective transport of dissolved porewater constituents. This upward transport also facilitated Fed fluxes out of the sediments, especially during times of active pumping. Our study demonstrates the potential for large Fed fluxes from sandy sediments in both summer and winter, despite relatively low standing stocks of labile organic matter and porewater Fed. The primary driver of these high fluxes was advective porewater transport, in our study induced by the activity of infaunal organisms. These results suggest that permeable sediments, which dominate shelf regions, must be explicitly considered in global estimates of benthic Fed fluxes, and cannot be simply extrapolated from estimates based on muddy sediments. 

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2. Reduced expression of iron transport and homeostasis genes in Pseudomonas fluorescens during iron uptake from nanoscale iron

   https://doi.org/10.1016/j.impact.2018.08.009  

   Sinha, Sanjivni; Das, Tonoy K.; Bezbaruah, Achintya N.; Fortuna, Ann-Marie (October 2018, NanoImpact)
3. Free Iron and Iron-Reducing Microorganisms in Permafrost and Permafrost-Affected Soils of Northeastern Siberia

   https://doi.org/10.1134/S1064229320100166  

   Rivkina, E. M.; Fedorov-Davydov, D. G.; Zakharyuk, A. G.; Shcherbakova, V. A.; Vishnivetskaya, T. A. (October 2020, Eurasian Soil Science)

   null (Ed.)
4. Copper and iron uptake in continentalhydrothermal systems

   Andrade-Barahona, E; Cox, A. (July 2023, Goldschmidt Abstracts #13652)
5. Composition and Pressure Effects on Partitioning of Ferrous Iron in Iron-Rich Lower Mantle Heterogeneities

   https://doi.org/10.3390/min11050512  

   Dorfman, Susannah M.; Nabiei, Farhang; Boukaré, Charles-Edouard; Prakapenka, Vitali B.; Cantoni, Marco; Badro, James; Gillet, Philippe (May 2021, Minerals)

   Both seismic observations of dense low shear velocity regions and models of magma ocean crystallization and mantle dynamics support enrichment of iron in Earth’s lowermost mantle. Physical properties of iron-rich lower mantle heterogeneities in the modern Earth depend on distribution of iron between coexisting lower mantle phases (Mg,Fe)O magnesiowüstite, (Mg,Fe)SiO3 bridgmanite, and (Mg,Fe)SiO3 post-perovskite. The partitioning of iron between these phases was investigated in synthetic ferrous-iron-rich olivine compositions (Mg0.55Fe0.45)2SiO4 and (Mg0.28Fe0.72)2SiO4 at lower mantle conditions ranging from 33–128 GPa and 1900–3000 K in the laser-heated diamond anvil cell. The resulting phase assemblages were characterized by a combination of in situ X-ray diffraction and ex situ transmission electron microscopy. The exchange coefficient between bridgmanite and magnesiowüstite decreases with pressure and bulk Fe# and increases with temperature. Thermodynamic modeling determines that incorporation and partitioning of iron in bridgmanite are explained well by excess volume associated with Mg-Fe exchange. Partitioning results are used to model compositions and densities of mantle phase assemblages as a function of pressure, FeO-content and SiO2-content. Unlike average mantle compositions, iron-rich compositions in the mantle exhibit negative dependence of density on SiO2-content at all mantle depths, an important finding for interpretation of deep lower mantle structures. 

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