Hitoshi Sakai

Bio: Hitoshi Sakai is an academic researcher from University of Tokyo. The author has contributed to research in topics: Sulfur & Sulfate. The author has an hindex of 39, co-authored 92 publications receiving 6172 citations. Previous affiliations of Hitoshi Sakai include Okayama University.

Thermal decomposition of barium sulfate-vanadium pentoxide-silica glass mixtures for preparation of sulfur dioxide in sulfur isotope ratio measurements

Abstract: A previously reported procedure for the thermal decomposition of BaSO/sub 4/-V/sub 2/O/sub 5/-SiO/sub 2/ for the preparation of SO/sub 2/ in sulfur isotope ratio measurements has been studied in detail, certain portions of the procedure have been modified, and certain aspects of the reaction mechanism have been defined. It was determined that the /sup 18/O//sup 16/O ratio of SO/sub 2/ must be kept constant in order to apply a consistent correction factor for the effect of overlap of the ion currents due to /sup 32/S/sup 16/O/sup 18/O/sup +/ and /sup 34/S/sup 16/O/sub 2//sup +/ in the mass spectrometric determination of S isotope ratio. X-ray diffraction studies of the solid reaction products indicated that the V/sub 2/O/sub 5/ is essential in lowering the decomposition temperature of BaSO/sub 4/. In moderate amounts, SiO/sub 2/ seemed to aid in the smooth and complete evolution of the SO/sub 2/; however, excessive SiO/sub 2/ lowered the SO/sub 2/ yield and probably prevented melting. Excess V/sub 2/O/sub 5/ also lowered SO/sub 2/ yields, probably because it boiled off the reaction mixture. A ratio of SiO/sub 2//V/sub 2/O/sub 5/ of 1 was considered to be the best for complete, smooth evolution of SO/sub 2/. SO/sub 2/ producedmore » by this method is pure enough to be directly analyzed by mass spectrometry.« less

Isotopic properties of sulfur compounds in hydrothermal processes

Abstract: The reduced partition function ratio predicts that among sulfide minerals in isotopic equilibria the heavy isotope (34S) is enriched in the following order: galena < chalcopyrite < sphalerite < pyrite. This order also exists among coexisting sulfides in natural deposits. The isotopic composition of pyrite at hydrothermal temperatures is estimated to be very close to that of gaseous hydrogen sulfide. The isotopic property of aqueous sulfide ions is determined by the relative concentrations of the three species H2S, HS-, and S2-, all of which have different reduced partition function ratios. Therefore, the pH of hydrothermal solution is as important a parameter as the temperature in determining the isotopic ratio of a sulfide mineral. δS* of pyrite, for instance, in isotopic equilibrium with a solution at 500°K having a δS of 0.0‰, would be +5.0‰ at pH 9.5, +2.0‰ at pH 8.0, and 0.0‰ at pH 4.0. Some natural examples are discussed which may indicate a change with time in the pH as well as in the isotopic raito of hydrothermal solutions during mineralization. The isotopic exchange reaction between sulfide and sulfate is also discussed.

Stable isotopes in ecosystem studies

Abstract: The use of stable isotopes to solve biogeochemical problems in ecosystem analysis is increasing rapidly because stable isotope data can contribute both source-sink (tracer) and process information: The elements C, N, S, H, and all have more than one isotope, and isotopic compositions of natural materials can be measured with great precision with a mass spectrometer. Isotopic compositions change in predictable ways as elements cycle through the biosphere. These changes have been exploited by geochemists to understand the global elemental cycles. Ecologists have not until quite recently employed these techniques. The reasons for this are, first, that most ecologists do not have the background in chemistry and geochemistry to be fully aware of the possibilities for exploiting the natural variations in stable isotopic compositions, and second, that stable isotope ratio measurements require equipment not normally available to ecologists. This is unfortunate because some of the more intractable problems in ecology can be profitably addressed using stable isotope measurements. Stable isotopes are ideally suited to increase our understanding of element cycles in ecosystems. This review is written for ecologists who would like to learn more about how stable isotope analyses have been and can be used in ecosystem studies. We begin with an explanation of isotope terminology and fractionation, then summarize isotopic distributions in the C, N, and S biogeochemical cycles, and conclude with five case studies that show how stable isotope measurements can provide crucial information for ecosystem analysis. We restrict this review to studies of natural variations in C, N, and S isotopic abundances, cxcluding from consideration ~5N enrichment studies and hydrogen and oxygen isotope studies. Our focus on C, N, and S derives in part from our

Observations: Oceanic Climate Change and Sea Level

Abstract: The oceans are warming. Over the period 1961 to 2003, global ocean temperature has risen by 0.10°C from the surface to a depth of 700 m. Consistent with the Third Assessment Report (TAR), global ocean heat content (0– 3,000 m) has increased during the same period, equivalent to absorbing energy at a rate of 0.21 ± 0.04 W m–2 globally averaged over the Earth’s surface. Two-thirds of this energy is absorbed between the surface and a depth of 700 m. Global ocean heat content observations show considerable interannual and inter-decadal variability superimposed on the longer-term trend. Relative to 1961 to 2003, the period 1993 to 2003 has high rates of warming but since 2003 there has been some cooling.

Proterozoic ocean chemistry and evolution: A bioinorganic bridge?

Abstract: Recent data imply that for much of the Proterozoic Eon (2500 to 543 million years ago), Earth's oceans were moderately oxic at the surface and sulfidic at depth. Under these conditions, biologically important trace metals would have been scarce in most marine environments, potentially restricting the nitrogen cycle, affecting primary productivity, and limiting the ecological distribution of eukaryotic algae. Oceanic redox conditions and their bioinorganic consequences may thus help to explain observed patterns of Proterozoic evolution.