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Yoshio Takahashi - One of the best experts on this subject based on the ideXlab platform.

  • Vanadium micro-XANES determination of oxygen fugacity in olivine-hosted glass inclusion and groundmass glasses of martian primitive shergottite Yamato 980459
    American Mineralogist, 2020
    Co-Authors: Ryoichi Nakada, Tomohiro Usui, Masashi Ushioda, Yoshio Takahashi
    Abstract:

    Abstract The Redox Condition of magma determines the stability and composition of crystallizing and volatile phases in martian meteorites, reflecting the evolution of the martian interior. In the current study, direct analyses on the oxidation states of V, Cr, and Fe were performed based on the X-ray absorption near-edge structure (XANES) measurements equipped with a micro-sized X-ray beam. We first applied the micro-XANES (μ-XANES) technique to the olivine-hosted glass inclusion and groundmass glass of martian meteorite Yamato 980459 (Y98), which is interpreted as representing a primary melt composition. Mass-balance calculations and XANES spectra comparisons indicated that, while chromite and pyroxene affected Cr and Fe K-edge XANES spectra, the contribution of these minerals was minimal for V. The pre-edge peak intensity of V K-edge XANES enabled the estimation of the oxygen fugacity for inclusion and groundmass glasses. The calculated oxygen fugacity (fO2) of the glass inclusions was near the Iron-Wüstite (IW) buffer (IW-0.07 ± 0.32) for the glass inclusion, whereas it was 0.9 log units more oxidized (IW+0.93 ± 0.56) for the groundmass glasses. This result suggests that the Redox Condition of the parent magma of Y98 evolved during magma ascent and emplacement. Since Y98 is interpreted to have evolved in a closed system, our finding suggests that fractional crystallization and/or ascent of magma potentially induces the fO2 increase. This study shows that the μ-XANES technique enables us to determine the fO2 by only measuring a single phase of glassy compounds, and thus, it is useful to discuss the Redox Condition of volcanic rocks even if they do not crystallize out several equilibrium phases of minerals.

  • application of arsenic in barite as a Redox indicator for suboxic anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Application of arsenic in barite as a Redox indicator for suboxic/anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Speciation of As in calcite by micro-XAFS: Implications for remediation of As contamination in groundwater
    Journal of Physics: Conference Series, 2013
    Co-Authors: Y Yokoyama, Yasuko Terada, Teruki Iwatsuki, Yoshio Takahashi
    Abstract:

    To evaluate the role of calcite as a host phase of arsenic (As) in As-contaminated groundwater, distribution behavior of Asbetween natural calcite and groundwater in deep underground was investigated based on As oxidation state. Speciation analyses of As in natural calcite by μ-XRF-XAFS analyses showed (i) preferentialarsenate uptake by calcite, and (ii) promptness of arsenate uptake by minor iron (Fe) carbonate minerals coprecipitated with calcite. These findings suggest that the effect of calcite on As remediation of the As-contamination systems stronglydepends on arsenite to arsenate ratio (i.e., Redox Condition) in groundwater, and maybe governed bythe amount of Fe coprecipitated with calcite.

  • Role of Fe speciation on arsenic solubility in flooded paddy soil
    2011
    Co-Authors: Noriko Yamaguchi, Tomoyuki Makino, Seigo Amachi, Yoshio Takahashi
    Abstract:

    Introduction Health risks associated with the chronic, low-dose uptake of arsenic (As) have been of great concern. In paddy soil, mobility of As is controlled by soil Redox Condition [1]. In addition, Fe speciation in soil is a determining factor in controlling As mobility. Fe (hydr)oxide undergoes reductive dissolution with the development of anaerobic Conditions and the adsorbed As is concomitantly released to solution due to loss of the adsorption phase. Nonetheless, Fe speciation in soil solid phase and its relation with As mobility has not been well understood. The purpose of this study was to evaluate the role of Fe speciation on As mobility.

Kohei Tokunaga - One of the best experts on this subject based on the ideXlab platform.

  • application of arsenic in barite as a Redox indicator for suboxic anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Application of arsenic in barite as a Redox indicator for suboxic/anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

Ronald D. Delaune - One of the best experts on this subject based on the ideXlab platform.

  • Crude Oil Effects on Redox Status of Salt Marsh Soil in Louisiana
    Soil Science Society of America Journal, 2017
    Co-Authors: Brian Michael Levine, Ronald D. Delaune, John R. White, Kanchan Maiti
    Abstract:

    In 2010, the Deepwater Horizon (DWH) oil spill triggered extensive research on crude oil impacts on flora and fauna of the Gulf of Mexico. Little research has investigated impact of spilled oil on Redox Condition of wetland soil. Redox Condition is an excellent proxy for oxygen levels, which control biogeochemical functions linked to valuable ecosystem services. The goal of this study was to quantify effects of crude oil on wetland soil Redox Conditions in cores collected from a salt marsh in Barataria Bay, LA. Treatments tested were nonoiled control, weathered crude oil at the soil surface, fresh crude oil at the soil surface, and a layer of buried weathered crude oil 5 cm beneath the soil surface to mimic the presence of buried oil found in marshes. No significant differences in Redox potentials were detected among treatments at any depth at the end of the 35-d flooded, anaerobic study. After drainage of the cores began, Redox was measured to the time to reach the aerobic threshold (+300 mV) within the rhizosphere. Mean Redox values for control cores reached +300 mV after 193 h. Both fresh and weathered crude oil surface treatments reached +300 mV after 316 h while the buried crude oil treatment reached the aerobic threshold after 370 h. These results suggest the presence and location of crude oil in the soil profile can impact soil Redox Conditions which could alter biogeochemical processes over the long term and induce oxygen stress on wetland vegetation and organisms in the soil.

  • Fungal and bacterial mediated denitrification in wetlands: influence of sediment Redox Condition.
    Water research, 2010
    Co-Authors: Dong-cheol Seo, Ronald D. Delaune
    Abstract:

    Fungal and bacterial denitrification rates were determined under a range of Redox Conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (−200, −100, 0, +100, +250 and +400 mV) ranging from strongly reducing to moderately oxidizing Conditions. Denitrification was determined using the substrate-induced respiration (SIR) inhibition and acetylene inhibition methods. Cycloheximide (C15H23NO4) was used as the fungal inhibitor and streptomycin (C21H39N7O12) as the bacterial inhibitor. At Eh values of +250 mV and +400 mV, denitrification rates by fungi and bacteria were 34.3–35.1% and 1.46–1.59% of total denitrification, respectively, indicating that fungi were responsible for most of the denitrification under aerobic or weakly reducing Conditions. On the other hand, at Eh −200 mV, denitrification rates of fungi and bacteria were 17.6% and 64.9% of total denitrification, respectively, indicating that bacteria were responsible for most of the denitrification under strongly reducing Conditions. Results show fungal denitrification was dominant under moderately reducing to weakly oxidizing Conditions (Eh > +250 mV), whereas bacterial denitrification was dominant under strongly reducing Condition (Eh 

  • Cadmium concentration in sea bottom sediment and its potential risk in the upper Gulf of Thailand.
    Journal of environmental science and health. Part A Toxic hazardous substances & environmental engineering, 2009
    Co-Authors: Zin Hnin Ei Tun, Ronald D. Delaune, Preeda Parkpian, Robert P. Gambrell, Aroon Jugsujinda
    Abstract:

    Untreated or partially treated waste water discharge from industrial and domestic sources entering the Upper Gulf of Thailand have been reported to increase cadmium concentration in bottom sediment. This study was directed at providing a better understanding of cadmium transformation in the sediment from the area. Sediment samples collected from Chao Phraya River mouth (CPY), Bang Pakong River mouth (BPK) and Klong Dan estuary (KD) located in the Upper Gulf of Thailand were analyzed for cadmium concentration in various sediment particle size fractions. Using laboratory microcosms, cadmium release from sediment as affected by salinity and sediment Redox Condition was studied. A higher concentration of cadmium (0.2–0.6 μ g/g dry weight) was measured in finer sediment particle size fractions (< 0.075 mm) as compared to courser fractions at all sampling stations. Cadmium release from the sediment to water was influenced by both salinity and Redox Condition. Sediment was spiked with 10 ppm cadmium which is the...

  • Emissions of Reduced Gaseous Sulfur Compounds from Wastewater Sludge: Redox Effects
    Environmental Engineering Science, 2000
    Co-Authors: Istvan Devai, Ronald D. Delaune
    Abstract:

    ABSTRACT Oxidation-reduction (Redox) Condition is an important parameter in the processing of organic carbon sources in wastewater treatment facilities. During the mineralization of organic wastes ...

  • Light hydrocarbon production in freshwater marsh soil as influenced by soil Redox Conditions
    Water Air and Soil Pollution, 1996
    Co-Authors: Istvan Devai, Ronald D. Delaune
    Abstract:

    The potential role of wetland soil Redox Condition to global atmospheric light hydrocarbon budget was evaluated. The effect of soil Redox Condition on gaseous hydrocarbon production in freshwater marsh soil was studied. Soil from a Mississippi River Deltaic plain freshwater marsh was equilibrated under controlled Redox levels ranging from +550 mV to −170 mV The production of methane, ethane, propane, butane, ethylene, propylene and isobutane as influenced by Redox Condition was quantified. The production of all hydrocarbon gases increased as soil Redox potential decreased. A soil Redox value of -100 mV was critical for methane production. Isobutane production was also sensitive to Redox potential, with emission occurring only at soil Redox levels below 0 mV Results show the significance of degree of soil reduction in production or emission of light hydrocarbons in wetland soil or sediment. In addition to methane significant amounts of non-methane hydrocarbons are produced in wetland soils.

Yasuko Terada - One of the best experts on this subject based on the ideXlab platform.

  • application of arsenic in barite as a Redox indicator for suboxic anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Application of arsenic in barite as a Redox indicator for suboxic/anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Speciation of As in calcite by micro-XAFS: Implications for remediation of As contamination in groundwater
    Journal of Physics: Conference Series, 2013
    Co-Authors: Y Yokoyama, Yasuko Terada, Teruki Iwatsuki, Yoshio Takahashi
    Abstract:

    To evaluate the role of calcite as a host phase of arsenic (As) in As-contaminated groundwater, distribution behavior of Asbetween natural calcite and groundwater in deep underground was investigated based on As oxidation state. Speciation analyses of As in natural calcite by μ-XRF-XAFS analyses showed (i) preferentialarsenate uptake by calcite, and (ii) promptness of arsenate uptake by minor iron (Fe) carbonate minerals coprecipitated with calcite. These findings suggest that the effect of calcite on As remediation of the As-contamination systems stronglydepends on arsenite to arsenate ratio (i.e., Redox Condition) in groundwater, and maybe governed bythe amount of Fe coprecipitated with calcite.

Shinsuke Kawagucci - One of the best experts on this subject based on the ideXlab platform.

  • application of arsenic in barite as a Redox indicator for suboxic anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.

  • Application of arsenic in barite as a Redox indicator for suboxic/anoxic Redox Condition
    Chemical Geology, 2016
    Co-Authors: Kohei Tokunaga, Tomoya Uruga, Kiyofumi Nitta, Yasuko Terada, Oki Sekizawa, Shinsuke Kawagucci, Yoshio Takahashi
    Abstract:

    Abstract Redox Condition is an important factor that controls the behavior of various elements in an aquatic environment. Incorporation of Redox-sensitive trace elements in minerals describes Redox Conditions in water and provides information about past environmental changes, unless it is dissolved or recrystallized during sediment burial. In the present study, we explore the application of arsenate/arsenite ratios (As(V)/As(III)) in barite as a new geochemical proxy for paleo-environmental reconstruction. Laboratory experiments showed that both As(III) and As(V) could be incorporated into barite as As(III)- and As(V)-coprecipitated barite, respectively, which could more or less retain the information of the As(V)/As(III) ratio in coexistent water, if under equilibrium in terms of the Redox reactions. Furthermore, the As(V)/As(III) ratios in natural barite collected in (i) Tamagawa Hot Spring and (ii) Okinawa hydrothermal vent were determined by micro-X-ray fluorescence and micro-X-ray absorption fine structure analysis to (a) evaluate the reliability of the As(V)/As(III) ratio in barite as a Redox indicator in natural system and (b) estimate the depositional Redox Condition in water whether barite precipitated below or above the Redox boundary of As(V)/As(III), or the suboxic/anoxic boundary. Our previous study showed that barite–selenium oxyanion system could also be used as a proxy for the oxic-suboxic boundary because the selenate/selenite [Se(VI)/Se(IV)] ratio in barite is primarily correlated with the ratio in water. Given that the Redox boundary of the Se(VI)/Se(IV) ratio has higher Redox potential than the As(V)/As(III) boundary, the combination of these two systems can extend the Redox Condition, which can be specified by the analysis of one single barite grain to a wide region. Thus, one barite particle can provide information on the As(V)/As(III) and Se(VI)/Se(IV) ratios in water, and whether barite precipitated under oxic, suboxic, or anoxic Redox environments.