Redox Changes Research Articles

Leaching and geochemical evaluation of oxyanion partitioning within an active coal ash management unit

Field monitoring combined with laboratory leaching characterization and geochemical speciation modeling were used to identify important geochemical parameters and controlling mechanisms for leaching of oxyanions from coal ash in a disposal site. The site consisted of dry stacked ash on top of a former surface impoundment. Constituents leached from the dry stacked ash served as sources for the soluble fractions of constituents in underlying impoundment ash. Weathering of field ash was evidenced by the identification of calcite and ettringite. Porewater concentrations of As, B, and V in the field pH range (9–11) and liquid-to-solid ratio (L/S) condition (∼0.6 L/kg-dry) were primarily controlled by Ca-bearing precipitates (Ca-arsenate, B-substituted carbonate solid solution, Ca-vanadate, and V-substituted ettringite solid solution). The leachable fraction of Mo as a function of pH was limited by the available content in the solid, with aqueous concentrations of Mo being a function of L/S. Leaching behavior of Cr and Se was sensitive to the redox changes (from suboxic to oxic conditions) during field ash collection and laboratory leaching tests, including oxidative dissolution of insoluble Cr(III)-oxides and conversion of Se(0) in the solid to dissolved Se(IV)/Se(VI). Oxidation resulted in increased Cr concentrations from < 0.00005 (in porewater) to 0.001–0.1 mg/L (in laboratory eluates). The identified geochemical parameters and leaching-controlling mechanisms provide the bases for understanding and estimating the partitioning of oxyanions in other disposal sites with alkaline and suboxic conditions. This case study also provides a typical example of laboratory test results interpretation and field leaching behavior estimation for other studies.

TMET-12. HYPERPOLARIZED Δ- [1-13C] GLUCONOLACTONE IMAGING VISUALIZES TERT-ASSOCIATED CHANGES IN DYNAMIC PENTOSE PHOSPHATE PATHWAY METABOLISM IN GLIOBLASTOMA

Abstract BACKGROUND TERT promoter mutations are a hallmark of glioblastoma (GBM). We recently reported that the expression of TERT and its upstream transcriptional factor, GABPB1, are strongly correlated with redox in GBM with TERT promoter mutations. However, further imaging biomarkers which visualize redox-associated metabolism and TERT expression are needed. Here we demonstrate that 13C magnetic resonance spectroscopy (MRS) of hyperpolarized δ-[1-13C] gluconolactone metabolism is a useful imaging tool to visualize changes in dynamic pentose phosphate pathway (PPP) metabolism that reflect TERT-associated changes in redox in GBM. METHODS U251 human GBM cells stably expressing shRNA targeting TERT or GABPB1 were compared to controls. Doxycyclin-inducible shTERT or shGABPB1 U251 cells were also examined. For in vivo studies, cells were injected into immunodeficient rat brains and tumors confirmed by T2-weighted MRI. δ-[1-13C] gluconolactone was polarized using a Hypersense DNP polarizer and injected into live cells or tumor-bearing rats. For cells 13C-MRS was acquired using a 500MHz Agilent spectrometer and analyzed using Mnova and Matlab software. For in vivo13C-MRS studies, spectra were acquired using a 3T Bruker scanner and a spectral spatial echo-planar spectroscopic imaging sequence. Spectral signal to noise was improved using Tensor denoising. Spectra were processed using a custom-written Matlab script. RESULTS Hyperpolarized 6-phosphogluconolactone (6PG), the metabolic product from δ-[1-13C] gluconolactone via the PPP, was significantly reduced in TERT or GABPB1 silenced cells compared to control cells in both U251 models. The positive correlation between TERT expression and 6PG level was confirmed by linear regression analysis. Hyperpolarized 6PG production in both tumor models was also significantly reduced in TERT or GABPB1-silenced tumors compared to controls. CONCLUSION We successfully visualized TERT-associated changes in dynamic PPP metabolism in a GBM model in cells and in vivo. Hyperpolarized δ-[1-13C] gluconolactone is a potential tool for monitoring TERT expression in GBM with TERT promoter mutations.

Redox state and the sirtuin deacetylases are major factors that regulate the acetylation status of the stress protein NQO1.

The stress induced protein NQO1 can participate in a wide range of biological pathways which are dependent upon the interaction of NQO1 with protein targets. Many of the protein-protein interactions involving NQO1 have been shown to be regulated by the pyridine nucleotide redox balance. NQO1 can modify its conformation as a result of redox changes in pyridine nucleotides and sites on the C-terminal and helix seven regions of NQO1 have been identified as potential areas that may be involved in redox-dependent protein-protein interactions. Since post-translational modifications can modify the functionality of proteins, we examined whether redox-dependent conformational changes induced in NQO1 would alter lysine acetylation. Recombinant NQO1 was incubated with and without NADH then acetylated non-enzymatically by acetic anhydride or S-acetylglutathione (Ac-GSH). NQO1 acetylation was determined by immunoblot and site-specific lysine acetylation was quantified by mass spectrometry (MS). NQO1 was readily acetylated by acetic anhydride and Ac-GSH. Interestingly, despite a large number of lysine residues (9%) in NQO1 only a small subset of lysines were acetylated and the majority of these were located in or near the functional C-terminal or helix seven regions. Reduction of NQO1 by NADH prior to acetylation resulted in almost complete protection of NQO1 from lysine acetylation as confirmed by immunoblot analysis and MS. Lysines located within the redox-active C-terminus and helix seven regions were readily acetylated when NQO1 was in an oxidized conformation but were protected from acetylation when NQO1 was in the reduced conformation. To investigate regulatory mechanisms of enzymatic deacetylation, NQO1 was acetylated by Ac-GSH then exposed to purified sirtuins (SIRT 1-3) or histone deacetylase 6 (HDAC6). NQO1 could be deacetylated by all sirtuin isoforms and quantitative MS analysis performed using SIRT2 revealed very robust deacetylation of NQO1, specifically at K262 and K271 in the C-terminal region. No deacetylation of NQO1 by HDAC6 was detected. These data demonstrate that the same subset of key lysine residues in the C-terminal and helix seven regions of NQO1 undergo redox dependent acetylation and are regulated by sirtuin-mediated deacetylation.

Dynamic ocean redox conditions during the end-Triassic mass extinction: Evidence from pyrite framboids

The end-Triassic (∼201 Mya) records one of the five largest mass extinction events of the Phanerozoic. Extinction losses were coincident with large igneous province volcanism in the form of the Central Atlantic Magmatic Province (CAMP) and major carbon isotope excursions (CIEs), suggesting a link between these phenomena. Marine anoxia has been implicated as a causal factor in the crisis, but there remains some uncertainty regarding the role of marine redox changes in marine extinction phases because both intensity and duration of marine anoxia are poorly constrained. We employ high resolution pyrite framboid size-frequency analysis at two Triassic-Jurassic (Tr-J) boundary sections: Kuhjoch in Austria (the Tr-J Global Boundary Stratotype Section and Point; GSSP) and St. Audrie's Bay in England (former GSSP candidate) in order to further evaluate the role of marine anoxia in the end-Triassic mass extinction (ETME). The St. Audrie's Bay section records predominantly anoxic conditions punctuated by weakly oxygenated (dysoxic) conditions through the Tr-J transition, even during shallow-water intervals. Kuhjoch experienced both anoxic and dysoxic conditions during the ETME but became better oxygenated near the Tr-J boundary. Marine anoxia is therefore implicated in the extinction at both locations. A similar redox history is known from the Central European Basin, Western Tethys and Panthalassa, where marine anoxia developed in the lead up to the ETME prior to reoxygenation around the Tr-J boundary. • High-resolution pyrite framboids size distribution from two European Triassic-Jurassic boundary sections. • Global dynamic ocean redox evolution through the Triassic-Jurassic boundary is reconstructed. • Oxygen restriction occurred in extremely shallow waters and was likely one of the key causes of the crisis.

Nanotherapy based on magneto-mechanochemical modulation of tumor redox state.

Magnetic nanoparticles (MNs) are typically used as contrast agents for magnetic resonance imaging or as drug carriers with a remotely controlled delivery to the tumor. However, they can also potentiate the action of anticancer drugs under the influence of applied constant magnetic (CMFs) and electromagnetic fields (EMFs). This review demonstrates the role of magneto-mechanochemical effects produced by MNs alone and loaded with anticancer agents (MNCs) in response to CMFs and EMFs for modulation of tumor redox state. The combined treatment is suggested to act by two mechanisms: spin-dependent electron transport propagates free radical chain reactions, while magnetomechanical interactions cause conformational changes in drug molecules loaded onto MNs and generate reactive oxygen species (ROS). By adjusting the parameters of CMFs and EMFs during the magneto-mechanochemical synthesis and subsequent treatment, it is possible to modulate ROS production and switch redox signaling involved in ERK1/2 and NF-κB pathways from initiation of tumor growth to inhibition. Observations of tumor volume in different animal models and treatment combinations reported a 6%-70% reduction as compared with conventional drugs. Despite these results, there is a general lack of research in magnetic nanotheranostics that link redox changes across multiple levels of organization in the tumor-bearing host. Further multidisciplinary studies with more focus on the relationship between the electron transport processes in biomolecules and their effects on the tumor-host interaction should accelerate the clinical translation of magnetic nanotheranostics. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Oxidation state-specific fluorescent copper sensors reveal oncogene-driven redox changes that regulate labile copper(II) pools

Copper is an essential metal nutrient for life that often relies on redox cycling between Cu(I) and Cu(II) oxidation states to fulfill its physiological roles, but alterations in cellular redox status can lead to imbalances in copper homeostasis that contribute to cancer and other metalloplasias with metal-dependent disease vulnerabilities. Copper-responsive fluorescent probes offer powerful tools to study labile copper pools, but most of these reagents target Cu(I), with limited methods for monitoring Cu(II) owing to its potent fluorescence quenching properties. Here, we report an activity-based sensing strategy for turn-on, oxidation state-specific detection of Cu(II) through metal-directed acyl imidazole chemistry. Cu(II) binding to a metal and oxidation state-specific receptor that accommodates the harder Lewis acidity of Cu(II) relative to Cu(I) activates the pendant dye for reaction with proximal biological nucleophiles and concomitant metal ion release, thus avoiding fluorescence quenching. Copper-directed acyl imidazole 649 for Cu(II) (CD649.2) provides foundational information on the existence and regulation of labile Cu(II) pools, including identifying divalent metal transporter 1 (DMT1) as a Cu(II) importer, labile Cu(II) increases in response to oxidative stress induced by depleting total glutathione levels, and reciprocal increases in labile Cu(II) accompanied by decreases in labile Cu(I) induced by oncogenic mutations that promote oxidative stress.

A toolbox of engineered mosquito lines to study salivary gland biology and malaria transmission.

Mosquito saliva is a vehicle for the transmission of vector borne pathogens such as Plasmodium parasites and different arboviruses. Despite the key role of the salivary glands in the process of disease transmission, knowledge of host-pathogen interactions taking place within this organ is very limited. To improve the experimental tractability of the salivary glands, we have generated fluorescent reporter lines in the African malaria mosquito Anopheles coluzzii using the salivary gland-specific promoters of the anopheline antiplatelet protein (AAPP), the triple functional domain protein (TRIO) and saglin (SAG) coding genes. Promoter activity was specifically observed in the distal-lateral lobes or in the median lobe of the salivary glands. Besides a comparison of the expression patterns of the selected promoters, the fluorescent probes allowed us to evaluate the inducibility of the selected promoters upon blood feeding and to measure intracellular redox changes. We also combined the aapp-DsRed fluorescent reporter line with a pigmentation-deficient yellow(-) mosquito mutant to assess the feasibility of in vivo microscopy of parasitized salivary glands. This combination allowed locating the salivary gland through the cuticle and imaging of individual sporozoites in vivo, which facilitates live imaging studies of salivary gland colonization by Plasmodium sporozoites.

CP12 fine-tunes the Calvin-Benson cycle and carbohydrate metabolism in cyanobacteria.

The regulatory protein CP12 can bind glyceraldehyde 3-phosphate dehydrogenase (GapDH) and phosphoribulokinase (PRK) in oxygenic phototrophs, thereby switching on and off the flux through the Calvin-Benson cycle (CBC) under light and dark conditions, respectively. However, it can be assumed that CP12 is also regulating CBC flux under further conditions associated with redox changes. To prove this hypothesis, the mutant Δcp12 of the model cyanobacterium Synechocystis sp. PCC 6803 was compared to wild type and different complementation strains. Fluorescence microscopy showed for the first time the in vivo kinetics of assembly and disassembly of the CP12-GapDH-PRK complex, which was absent in the mutant Δcp12. Metabolome analysis revealed differences in the contents of ribulose 1,5-bisphosphate and dihydroxyacetone phosphate, the products of the CP12-regulated enzymes GapDH and PRK, between wild type and mutant Δcp12 under changing CO2 conditions. Growth of Δcp12 was not affected at constant light under different inorganic carbon conditions, however, the addition of glucose inhibited growth in darkness as well as under diurnal conditions. The growth defect in the presence of glucose is associated with the inability of Δcp12 to utilize external glucose. These phenotypes could be complemented by ectopic expression of the native CP12 protein, however, expression of CP12 variants with missing redox-sensitive cysteine pairs only partly restored the growth with glucose. These experiments indicated that the loss of GapDH-inhibition via CP12 is more critical than PRK association. Measurements of the NAD(P)H oxidation revealed an impairment of light intensity-dependent redox state regulation in Δcp12. Collectively, our results indicate that CP12-dependent regulation of the CBC is crucial for metabolic adjustment under conditions leading to redox changes such as diurnal conditions, glucose addition, and different CO2 conditions in cyanobacteria.

Conversion Reactions and Redox Changes on the Surface of Lithium-Ion Battery Cathode Materials during Chemical Vapor Treatment for ALD

Atomic layer deposition (ALD) has emerged as a promising technology for applying ultrathin protective coatings on lithium-ion battery (LIB) cathode surfaces to improve their cycling stability. While there have been numerous reports evaluating the electrochemical performance of these surface-modified cathode materials, the chemical changes induced on the surface of the cathode materials by the ALD coatings and the individual ALD precursors are not fully studied. We performed a systematic investigation to understand the interfacial changes of 12 different cathode materials upon coating with aluminum oxide (Al2O3) using trimethyl aluminum (TMA) and H2O, and aluminum fluoride (AlF3) using TMA and hydrogen fluoride pyridine (HFPy). We also explored the effects of the individual TMA and HFPy precursors on the cathode surfaces. The surface composition and microstructure of these cathode materials, which range from simple transition metal oxides (e.g., NiO and MnO) to complex multi-element cathode materials (e.g., LiNixMn1-x-yCoyO2, NMC), were studied via X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). The XPS measurements reveal that the transition metals in the cathode materials undergo selective oxidation/reduction depending upon the nature of the precursor, the coating, and the cathode material. Furthermore, XPS and STEM measurements show the conversion of surface carbonate species to the corresponding metal fluorides upon HF exposure. This conversion reaction is self-limiting but extends hundreds of nanometers below the surface in the case of Li2CO3. ALD and chemical vapor treatment provide new avenues to systematically control the interface of the cathode materials in LIBs that are not possible by conventional coating methods.

Copper isotope fractionation in magmatic Ni–Cu mineralization systems associated with the variation of oxygen fugacity in silicate magmas

Significant variations of oxygen fugacity (fO2) in silicate magmas are widely suggested to play an important role in formation of magmatic Ni–Cu deposits in convergent margin settings. Copper isotopes have potential to track redox change of magmatic systems, but the linkage of silicate magma oxygen fugacity with Cu isotope fractionation in magmatic Ni–Cu mineralization systems is still uncertain. A combined study of Cu isotopes and estimated oxygen fugacities can provide novel and direct insights into this issue. In this study, four magmatic Ni–Cu deposits in Eastern Tianshan (NW China) were investigated in order to reveal the fO2 variations in silicate magmas as a function of redox-induced Cu isotope fractionation. The silicate magma fO2 of the four deposits widely varies from ∼QFM –2.2 to + 0.6, from ∼QFM –0.7 to 0.0, from ∼QFM –1.4 to –0.2, and from ∼QFM –1.2 to –0.6 for the Tulaergen, Huangshandong, Huangshannan, and Hulu deposits, respectively. Models using olivine compositions, Cu/Pd ratios, and estimated silicate magma fO2 suggest that the silicate magmas gradually became more oxidized as Ni–Cu mineralization proceeded. The closed-system R factor equation and the Rayleigh equation were used to model mineralization processes and related Cu isotope fractionation. Modelling using δ65Cu values and the estimated fO2 indicates that the evolved silicate magmas with high fO2 tend to incorporate heavier Cu isotopes. Our studies indicate that the fO2 variation of silicate magmas is the key factor governing Cu isotope fractionation in magmatic Ni–Cu mineralization systems in convergent tectonic settings, which is potentially applicable for other magmatic Ni–Cu deposits worldwide.

Marine redox variation and hydrographic restriction in the early Cambrian Nanhua Basin, South China

The early Cambrian Nanhua Basin is an important archive of information related to contemporaneous marine redox evolution and its relationship to the radiation of early animals. However, the nature of watermass conditions in the Nanhua Basin remains uncertain owing to conflicting redox signals. Here, we generated a redox proxy dataset comprising Fe speciation, redox-sensitive element (RSE), pyrite framboid size distributions, and molybdenum isotopic data (δ98Mo), in combination with proxies for hydrographic restriction (i.e., Co × Mn, Cd/Mo, and Mo/TOC), in order to evaluate environmental conditions in the basinal Yuanjia section. We then compared these data with previous results for outer-shelf (Jinsha, Zhongnancun, and Yangjiaping), slope (Daotuo, Songtao, and Longbizui), and basinal facies (Silikou) to develop an integrated picture of environmental (especially redox) changes in the early Cambrian Nanhua Basin. At Yuanjia, the lower member (LM, 0–28 m) is characterized by weakly euxinic conditions and an intense Fe-Mn shuttle, and the upper member (UM, 28–65 m) by moderately euxinic conditions and a weak Fe-Mn shuttle. Our integrated analysis demonstrates co-existence of oxic surface waters, euxinic mid-depth waters, and ferruginous deep waters in the Nanhua Basin, with euxinic conditions prevailing in shelf-slope facies of the Yangtze Block and basinal facies of the Cathaysia Block but declining in intensity from the LM to the UM. The Nanhua Basin changed from being moderately restricted with strong upwelling during the LM to relatively more restricted with weak upwelling during the UM. We infer that redox fluctuations in the early Cambrian Nanhua Basin were linked to hydrographic restriction, although global factors such as low seawater sulfate concentrations may have played a role also. Our study highlights the need for caution in assuming that redox variation in the early Cambrian Nanhua Basin was representative of contemporaneous global-ocean redox states.

Nitrogen Isotopes from the Neoproterozoic Liulaobei Formation, North China: Implications for Nitrogen Cycling and Eukaryotic Evolution

The nitrogen isotope compositions (δ15N) of sedimentary rocks can provide information about the nutrient N cycling and redox conditions that may have played important roles in biological evolution in Earth’s history. Although considerable δ15N data for the Precambrian have been published, there is a large gap during the early Neoproterozoic that restrains our understanding of the linkages among N cycling, ocean redox changes and biological evolution during this key period. Here, we report bulk δ15N and organic carbon isotope (δ13Corg) compositions as well as the total nitrogen (TN) and total organic carbon (TOC) contents from the Tonian fossiliferous Liulaobei Formation in the southern part of the North China Platform. The δ15N in the study section is dominated by very stable values centering around +4.3‰, which is moderately lower than in modern sediments (~ +6‰). These positive δ15N values were attributed to partial denitrification under low primary productivity (scenario 1) and/or denitrification coupled with dissimilatory nitrate reduction to ammonium (DNRA) (scenario 2). In either case, the availability of fixed nitrogen may have provided the nutrient N required to facilitate facilitated eukaryotic growth. Our study highlights the pivotal role of nutrient N in the evolution of eukaryotes.

Rice hull biochar enhances the mobilization and methylation of mercury in a soil under changing redox conditions: Implication for Hg risks management in paddy fields.

Biochar amendment to paddy soils was promising to mitigate mercury (Hg) accumulation in rice; thus, it was applied to reduce human Hg exposure via rice consumption. However, how biochar affects Hg mobilization and MeHg formation in soil under changed redox potential (Eh) conditions remained unknown. Here, we explored the change of dissolved total Hg (DTHg) and dissolved MeHg (DMeHg), and their controlling biogeochemical factors in a soil with(out) biochar amendment under changing Eh conditions using biogeochemical microcosm. Biochar amendment resulted in a widen Eh range (-300 to 400mV) compared to the control (-250 to 350mV), demonstrating that biochar promoted reduction-oxidization reactions in soil. Biochar amendment enhanced Hg mobilization by mediating reductive dissolution of Fe/Mn (hydr)oxides. Thus, the increased Hg availability promoted MeHg formation in the soils. Biochar amendment changed the soil organic matter (SOM) composition. Positive correlations between the relative abundance of LIPID (lipids, alkanes/alkenes), ALKYL (alkylaromatics), and suberin and MeHg concentrations indicate that these SOM groups might be related to MeHg formation. Biochar enhanced the releasing and methylation of Hg by promoting the mobilization of Fe(oxyhydr)oxides and alternation of carbon chemistry under dynamic Eh conditions. There is an unexpected environmental risk associated with biochar application to paddy soils under dynamic Eh condition, and one should be aware this risk when applying biochar aiming to minimize human Hg exposure health risks via rice consumption.

The understudied winter: Evidence of how precipitation differences affect stream metabolism in a headwater

Climate change is causing pronounced shifts during winter in the US, including shortening the snow season, reducing snowpack, and altering the timing and volume of snowmelt-related runoff. These changes in winter precipitation patterns affect in-stream freeze-thaw cycles, including ice and snow cover, and can trigger direct and indirect effects on in-stream physical, chemical, and biological processes in ~60% of river basins in the Northern Hemisphere. We used high-resolution, multi-parameter data collected in a headwater stream and its local environment (climate and soil) to determine interannual variability in physical, chemical, and biological signals in a montane stream during the winter of an El Niño and a La Niña year. We observed ~77% greater snow accumulation during the El Niño year, which caused the formation of an ice dam that shifted the system from a primarily lotic to a lentic environment. Water chemistry and stream metabolism parameters varied widely between years. They featured anoxic conditions lasting over a month, with no observable gross primary production (GPP) occurring under the ice and snow cover in the El Niño year. In contrast, dissolved oxygen and GPP remained relatively high during the winter months of the La Niña year. These redox and metabolic changes driven by changes in winter precipitation have significant implications for water chemistry and biological functioning beyond the winter. Our study suggests that as snow accumulation and hydrologic conditions shift during the winter due to climate change, hot-spots and hot-moments for biogeochemical processing may be reduced, with implications for the downstream movement of nutrients and transported materials.

From high‐pressure β‐V2O5 to κ‐NaxV2O5 (x = 0.4 − 0.55): A structural, chemical, and kinetic insight into a sodiated phase with a large interlayer space

AbstractVanadium pentoxide polymorphs are attracting much interest due to their remarkable electrochemical performance as positive electrodes for rechargeable metal‐ion batteries. High‐pressure β‐V2O5 is an interesting positive electrode material for Na‐ion batteries able to intercalate 1 Na+/formula unit delivering a capacity of 147 mAh g−1. The sodium intercalation of 0.4 Na+ has been described in the literature as a two‐phase domain involving an important structural rearrangement yielding NaxV2O5, but details about the structural changes upon sodium intercalation and structure of intercalated Na0.4V2O5 have not been elucidated so far. In this work, we performed operando synchrotron X‐ray diffraction measurements on sodium batteries on discharge. A full crystal structure determination for such phase, which we have called κ‐Na0.4V2O5, was carried out for the first time directly from operando measurements in monoclinic space group C2/m. Structural analysis was completed with bond valence sum calculations revealing the sites of intercalated sodium in κ‐NaxV2O5 and the structure was further optimized by means of density functional theory calculations. Operando X‐ray absorption spectroscopy and ex situ X‐ray photoelectron spectroscopy allowed to unveil the redox changes upon the phase transformation from β‐V2O5 into κ‐NaxV2O5, providing information about the reduction of vanadium from V5+ to V4+. The phase transformation also produced enhanced charge transfer and sodium diffusion processes, as deduced from both impedance and kinetic study.

Mesoproterozoic surface oxygenation accompanied major sedimentary manganese deposition at 1.4 and 1.1Ga.

Manganese (Mn) oxidation in marine environments requires oxygen (O2 ) or other reactive oxygen species in the water column, and widespread Mn oxide deposition in ancient sedimentary rocks has long been used as a proxy for oxidation. The oxygenation of Earth's atmosphere and oceans across the Archean-Proterozoic boundary are associated with massive Mn deposits, whereas the interval from 1.8-1.0Ga is generally believed to be a time of low atmospheric oxygen with an apparent hiatus in sedimentary Mn deposition. Here, we report geochemical and mineralogical analyses from 1.1Ga manganiferous marine-shelf siltstones from the Bangemall Supergroup, Western Australia, which underlie recently discovered economically significant manganese deposits. Layers bearing Mn carbonate microspheres, comparable with major global Mn deposits, reveal that intense periods of sedimentary Mn deposition occurred in the late Mesoproterozoic. Iron geochemical data suggest anoxic-ferruginous seafloor conditions at the onset of Mn deposition, followed by oxic conditions in the water column as Mn deposition persisted and eventually ceased. These data imply there was spatially widespread surface oxygenation ~1.1Ga with sufficiently oxic conditions in shelf environments to oxidize marine Mn(II). Comparable large stratiform Mn carbonate deposits also occur in ~1.4Ga marine siltstones hosted in underlying sedimentary units. These deposits are greater or at least commensurate in scale (tonnage) to those that followed the major oxygenation transitions from the Neoproterozoic. Such a period of sedimentary manganogenesis is inconsistent with a model of persistently low O2 throughout the entirety of the Mesoproterozoic and provides robust evidence for dynamic redox changes in the mid to late Mesoproterozoic.

Incipient reddening of Ordovician carbonates: The origin and geochemistry of yellow and pink colouration in limestones

Red colouring in marine red beds (MRB) is commonly attributed to deposition and early diagenesis under specific redox conditions. Therefore, the MRB can be considered time-specific facies. However, since red colouring is a subjective criterion, it is difficult to establish a colour limit for the MRB in the scale from grey to yellow, orange, pink to red. Using spectral reflectance, carbonate petrology, bulk-rock and in-situ geochemistry data from three sections of Ordovician orthoceratite carbonates of South China, we addressed the question whether the incipient reddening in the pink carbonates was associated with similar redox changes and palaeoceanographic conditions like in the MRB. The yellowish grey to greyish orange pink (Munsell Rock Colour Chart) carbonates with low concentrations of hematite (< 0.01 %) are transitional from goethite-bearing grey to hematite-enriched true MRB. The red-coloured skeletal interiors, microstromatolites, nodules and filamentous microborings suggest an extensive microbial activity which was accompanied by precipitation of authigenic aluminosilicates (clays). We hypothesize that the microbial clay precipitation is an important intermediate step in Fe transformation from its primary sources to hematite in the MRB. The carbonate deposition was followed by early diagenetic, shallow-subsurface REE fractionation, and FeMn (+Mo, U and V) redox cycling along microbially controlled redox microgradients. The geochemical redox signature of the pink carbonates is very similar to the MRBs of Devonian and Ordovician age. They were deposited under similar palaeoenvironmental conditions on a deeper shelf inhabited by skeletal heterotrophs, with reduced rates of organic matter burial and slow sedimentation rates. The sedimentation of the pink carbonates and MRBs seem to randomly coincide with the coeval global sea-level changes and δ13Ccarb fluctuations suggesting that the local controls of sediment colour override the global ones.

Southern Hemisphere Westerly Winds have modulated the formation of laminations in sediments in Lago Fagnano (Tierra del Fuego, Argentina) over the past 6.3 ka

Tierra del Fuego in Argentina is a unique location to examine past Holocene wind variability since it intersects the core of the Southern Hemisphere Westerly Winds (SHWW). The SHWW are the most powerful prevailing winds on Earth. Their variation plays a role in regulating atmospheric CO2 levels and rainfall amounts and distribution, both today and in the past. We obtained a piston core (LF06‐PC8) from Bahía Grande, a protected sub‐basin at the southern margin of Lago Fagnano, the largest lake in Tierra del Fuego. This article focuses on the uppermost 185 cm of this core, corresponding to laminated sediment from the last ~6.3 ka. Laminations consist of millimetre‐scale paired dark and light layers. Previous studies and new geochemical analysis show that the dark and light layers are characterized by differing concentrations of Mn and Fe. We attribute the distribution of Mn and Fe to episodic hypolimnic oxic–anoxic variations. The age model suggests an approximately bidecadal timescale for the formation of each layer pair. We propose a new model of these redox changes with the SHWW variations. The most likely phenomenon to produce complete water‐column mixing is thermobaric instability, which occurs in colder winters with low‐intensity SHWW (El Niño‐like conditions). In contrast, windier winters are characterized by higher temperatures and reduced mixing in the water column, facilitating a decline in oxygen concentration. Laminations, and the inferred presence of periodic hypolimnion redox changes, are common features of the past ~6.3 ka. Geochemical proxy variability is compatible with an intensification of El Niño/Southern Oscillation activity during the past ~2 ka.

Mercury, organic matter, iron, and sulfur co-cycling in a ferruginous meromictic lake

Mercury (Hg) speciation in natural waters is controlled by redox conditions and microbiological activity. Water columns of meromictic lakes have large and stable redox chemical and biological gradients that allow the investigation of many Hg chemical transformations. In this study, Hg speciation (elemental Hg = Hg0, methylated Hg = MeHg) and partitioning between truly dissolved (<3 kDa), colloidal (<0.45 μm and >3 kDa), and particulate (>0.45 μm) fractions, were determined throughout a high-resolution water column profile in the ferruginous meromictic Lake Pavin (Massif Central, France) in July 2018. Total Hg concentrations (THg) in water ranged between 0.4 and 8.8 pmol L−1. The particulate phase represented 10–70% of the THg, with a peak found in the mesolimnion associated with the particulate organic carbon maximum. In the mesolimnion, the colloidal fraction represented 12–68% of THg, and the highest value was found at the top of the sulfidic zone, whereas the truly dissolved Hg species (70 ± 9%) dominated in all the rest of the sulfidic zone. MeHg ranged from less than 10% of THg in the oxic mixolimnion to more than 90% in the anoxic monimolimnion. The Hg methylation was most active within the suboxic zone where iron and sulfate reduction are occurring. These results, associated with those of the partition of organic matter (OM), sulfur, and iron, in conjunction with thermodynamic calculations, allow us to present a conceptual scheme for the Hg cycle in the lake. Atmospheric Hg deposited onto surface waters of the lake is partially photo-reduced and returned to the air, another part is scavenged by biogenic particulate matter and conveyed at depth by settling organic material. Water stratification and redox changes create a sequence of reactions from oxic to ferruginous waters where Hg is successively (i) desorbed from particulate OM where mineralization occurs, (ii) adsorbed onto iron-oxy(hydr)oxides, (iii) desorbed where they dissolved, (iv) precipitate as HgS, (v) methylated, and (vi) reduced as Hg0 in the deepest part of the lake. In brief, the (micro)biological uptake, OM, iron and sulfur recycling, through associated microbial consortia, control the Hg cycling in the Pavin waters.

Available nitrogen and ammonia-oxidizing archaea in soil regulated N2O emissions regardless of rice planting under a double rice cropping-fallow system

Changing redox conditions in paddy fields due to more frequent events govern the soil biogeochemical processes that further affect the generation and emission of N2O from soil. However, studies on the effect of rice cropping on soil N2O emission under rice-growing seasons and relevant mechanisms are scarce. A double rice cropping-fallow (RF) field in central China, with rice cropping (RF-CC) and non-rice cropping (RF-NC) cultivation, were selected to investigate that effect of rice planting on soil N2O emissions and key functional genes related to N2O-production and consumption, such as the ammonia-monooxygenase gene derived from ammonia-oxidizing archaea (AOA-amoA) and ammonia-oxidizing bacteria (AOB-amoA) and nitrous oxide reductase gene (nosZ). The results of the static opaque chamber-gas chromatography technique showed that seasonal cumulative N2O emissions from RF-NC treatment during the first and second rice growing season were 1.02 ± 0.17 and 2.95 ± 0.12 kg N ha−1, respectively, and were comparable to those from RF-CC treatment (0.82 ± 0.09 and 2.97 ± 0.18 kg N ha−1, respectively), indicating rice cropping had no crucial effect on soil N2O emissions. No significant difference was found in the abundance of the aforementioned genes between two treatments. For both RF-CC and RF-NC treatments, N2O fluxes were positively correlated with the soil available nitrogen, such as dissolved inorganic N (DIN) and microbial biomass N (MBN), suggesting that soil available N was a key factor controlling N2O emissions. Increased transcripts of the AOA-amoA gene may facilitate N2O production and were confirmed by the positive linear relations between N2O fluxes and the abundance of AOA-amoA gene for both treatments. The structural equation model (SEM) indicated that both soil available N and AOA-amoA gene contributed more than 70% to their effects on N2O emission for both treatments. These results implied that soil N2O emissions during therice-growing period could be regulated by the interaction of soil parameters and related functional genes, rather than the effect of rice cropping under a RF system.