Chikyukagaku
Online ISSN : 2188-5923
Print ISSN : 0386-4073
ISSN-L : 0386-4073
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Volume 41, Issue 2
Displaying 1-3 of 3 articles from this issue
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Original paper
  • Behavior of hydrogen peroxide between atmosphere and coastal seawater around Okinawa Island
    Takemitsu ARAKAKI, Hirotsugu IKOTA, Kouichirou OKADA, Yukiko KUROKI, H ...
    2007 Volume 41 Issue 2 Pages 35-41
    Published: May 25, 2007
    Released on J-STAGE: January 29, 2017
    DOIhttps://doi.org/10.14934/chikyukagaku.41.35
    JOURNAL FREE ACCESS
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    We studied hydrogen peroxide (H2O2) concentrations in seawater to better understand contribution of air-to-seawater partitioning of gaseous H2O2 during clear-sky conditions. Hydrogen peroxide concentrations were determined by POHPAA dimmer technique with a flow injection system. We collected coastal seawater at Sesoko Island and Hama-gyokou fishing port in Okinawa Island. The seawater samples were exposed to solar radiation in three different conditions. First condition in natural seawater, named "Open seawater", which is influenced by all the natural conditions such as solar radiation, seawater mixing, tidal movement, and microbial and phytoplankton activities. Second condition is seawater kept in the plastic container, named "Closed seawater", which avoids influences of seawater mixing and tidal movement. Third condition is seawater kept in quartz test tubes, named "Test Tube seawater", which avoids influences of seawater movement and air-to-seawater partitioning of H2O2. Comparison between Open and Closed seawaters showed that H2O2 concentrations in Open seawater were almost always lower than that of Closed seawaters, indicating that H2O2 concentrations were strongly influenced by seawater mixing, tidal movement, and microbial and phytoplankton activities. Comparison between Closed and Test Tube seawaters showed little difference in H2O2 concentrations between the two conditions, indicating that air-to-seawater partitioning of H2O2 had little influence on H2O2 concentrations in seawater during clear-sky conditions, and that increase in H2O2 concentration was mainly due to in situ photochemical reactions.
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The Shibata Award
  • Tectonochemistry at depths
    Ryuichi SUGISAKI
    2007 Volume 41 Issue 2 Pages 43-62
    Published: May 25, 2007
    Released on J-STAGE: January 29, 2017
    DOIhttps://doi.org/10.14934/chikyukagaku.41.43
    JOURNAL FREE ACCESS
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    This is a review of the researches I have been conducting with my colleagues over the past 50 years. We examined geochemically behaviors of materials in several natural phenomena such as (1) groundwater movement under alluvial plains, (2) fault activities, (3) crustal movements including earthquakes, (4) geological development of the Japanese Islands relating to plate movement, (5) hydrocarbon distribution in the earth mantle, and (6) syntheses of organic materials by shock waves. For the phenomena (1), (2), (3), I have focused on the behavior of deep seated fluids such as He, Ar, H2, CO2, and CH4. For (4), I paid attention to Ti, Mn, several heavy metals, and carbonates in particularly siliceous and argillaceous sediments, and REEs in pre-Cenozoic volcanics. I pointed out the tectonochemical significance of manganese carbonate bands, manganese micronodules, hydrothermal cherts. For (5) and (6), I emphasized that existence of mantle hydrocarbons and abiological syntheses of organics have strong implication to astrochemistry and origin of life.
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The Geochemical Society of Japan Award for Young Researchers
  • Subduction-related fluid occurrence in mantle revealed by residual pressure and isotopic compositions of fluid inclusion
    Junji YAMAMOTO
    2007 Volume 41 Issue 2 Pages 63-75
    Published: May 25, 2007
    Released on J-STAGE: January 29, 2017
    DOIhttps://doi.org/10.14934/chikyukagaku.41.63
    JOURNAL FREE ACCESS
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    An active convergent plate boundary comprises dynamic material circulation system where materials risen up from descending oceanic plate partly go back to the Earth's surface. An evaluation of the material flux in this system is important to assess future view of the planet Earth. In the mantle wedge, fluids circulate in various forms; i.e., aqueous fluids released from the descending oceanic lithosphere trigger partial melting of the mantle wedge, and the melt ascends through the mantle wedge leading arc volcanism. Investigations of mantle-derived xenoliths sampled from the active margin of a continent or an island arc are effective for identifying mantle processes, including partial melting and material circulation, in the mantle wedge. For the mantle xenoliths, however, various technical difficulties lie in the estimation of the depth where the xenoliths entrained by host magma. Since internal pressure (density) of CO2 inclusions in a mantle xenolith reflects both conditions of temperature and pressure where the xenolith existed, CO2 density in a fluid inclusion was estimated by Micro-Raman spectroscopy to calculate the depth (pressure) of origin applying to the equation of state of CO2 and the equilibration temperature. This newly developed method can serve as a new depth probe. Combination of the geobarometry and various micro-analyzing technique reveals the occurrence of subduction-related fluid in the mantle wedge with high spatial resolution. Four-dimensional (latitude, longitude, depth and geologic age) mapping of the fluid migration in the mantle wedge is theoretically possible to apply my developed techniques to mantle-derived xenolith, which remains the ancient record of the mantle.
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