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283.
Yoko?YokouchiEmail author Takuya?Saito Hitoshi?Mukai 《Journal of Atmospheric Chemistry》2018,75(2):171-180
Dibromomethane (CH2Br2), a natural stratospheric ozone depleting substance, is mostly emitted from the ocean, but the relative importance of coastal (or macroalgae) and open ocean emissions is unknown. We made long-term high-frequency measurements of CH2Br2 concentrations at two remote coastal sites in Japan, on the subtropical Hateruma Island (poor in macroalgae) and at Cape Ochiishi (rich in macroalgae). CH2Br2 concentrations at Hateruma showed prominent seasonal variation, being lower in summer (around 0.94 ppt) than in winter (around 1.23 ppt). In contrast, CH2Br2 concentrations at Ochiishi were highly variable, often exceeding 2 ppt in the summer but with minimum baseline concentrations close to those from Hateruma; in the winter the concentrations were almost constant at about 1.3 ppt. Analysis of the data suggested that (1) emissions from macroalgae were not likely to extend offshore, but instead were localized near the shore, (2) strong macroalgal emissions of CH2Br2 were almost limited to the summer, but it was not reflected in the seasonality of the baseline concentrations of CH2Br2 in the atmosphere, and therefore (3) macroalgal or coastal emissions of CH2Br2 in the temperate zone might have a rather limited contribution to the global CH2Br2 sources. These findings are especially important for the understanding of the tropospheric and stratospheric bromine budget. 相似文献
284.
Hitoshi Tomaru Ryo Matsumoto Richard B. Coffin John W. Pohlman George D. Spence 《Journal of Geochemical Exploration》2007,95(1-3):40
The isotopic composition (δD and δ18O) and chloride concentration (Cl−) of pore waters from the northern Cascadia continental margin offshore Vancouver Island were measured to characterize the relations between the water flow regime and the distribution, formation and dissociation of gas hydrates. The δD values of pore waters in gas hydrate-bearing sediments are slightly higher ( 1‰) than those of seawater as the result of gas hydrate dissociation during core recovery and handling. Within the seismic blanking zone, the δD values were slightly lower (− 1‰) than values measured from sites outside the blanking area (0‰). We attribute these differences to 1) distillation of D-rich water during hydrate formation in the center of the blanking zone and 2) limited migration of pore water between inside and outside of the blanking zone due to different fluid fluxes. In contrast, the δ18O values and Cl− concentrations do not show significant spatial variation due to decreased isotopic fractionation of oxygen and small fraction of chloride relative to hydrogen isotope during gas hydrate formation. The δD value of pore water, therefore, appears to be a sensitive indicator of gas hydrate occurrence. We estimate that gas hydrate occupied at least 2.0 to 6.3% of sediment pore space using δD distribution in this area. 相似文献
285.
Philippe Blanc Hélène Gailhanou Jacques Rogez Georges Mikaelian Hitoshi Kawaji Fabienne Warmont Stéphane Gaboreau Sylvain Grangeon Jean-Marc Grenèche Philippe Vieillard Claire I. Fialips Eric Giffaut Eric C. Gaucher F. Claret 《Physics and Chemistry of Minerals》2014,41(8):603-615
In the context of the deep waste disposal, we have investigated the respective stabilities of two iron-bearing clay minerals: berthierine ISGS from Illinois [USA; (Al0.975FeIII0.182FeII1.422Mg0.157Li0.035Mn0.002)(Si1.332Al0.668)O5(OH)4] and chlorite CCa-2 from Flagstaff Hill, California [USA; (Si2.633Al1.367)(Al1.116FeIII0.215Mg2.952FeII1.712Mn0.012Ca0.011)O10(OH)8]. For berthierine, the complete thermodynamic dataset was determined at 1 bar and from 2 to 310 K, using calorimetric methods. The standard enthalpies of formation were obtained by solution-reaction calorimetry at 298.15 K, and the heat capacities were measured by heat-pulse calorimetry. For chlorite, the standard enthalpy of formation is measured by solution-reaction calorimetry at 298.15 K. This is completing the entropy and heat capacity obtained previously by Gailhanou et al. (Geochim Cosmochim Acta 73:4738–4749, 2009) between 2 and 520 K, by using low-temperature adiabatic calorimetry and differential scanning calorimetry. For both minerals, the standard entropies and the Gibbs free energies of formation at 298.15 K were then calculated. An assessment of the measured properties could be carried out with respect to literature data. Eventually, the thermodynamic dataset allowed realizing theoretical calculations concerning the berthierine to chlorite transition. The latter showed that, from a thermodynamic viewpoint, the main factor controlling this transition is probably the composition of the berthierine and chlorite minerals and the nature of the secondary minerals rather than temperature. 相似文献