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121.
Daisuke Nagaoka Masahito Shigemitsu Masao Minagawa Shinichiro Noriki 《Journal of Oceanography》2010,66(1):117-132
We have investigated Pb concentrations and isotopic compositions in settling particles collected by sediment traps experiments
over a period of two years, from May 2005 to April 2007, at two depths, 770 and 5100 m, at station KNOT in the Northwestern
Pacific Ocean (44°N, 155°E). To the identify provenances of Pb, the samples were separated into two fractions by chemical
leaching techniques, with the leachate expected to contain Pb of anthropogenic origin. Isotopic compositions of Pb and concentrations
of Pb, Sc, Mn, La, Yb, and Th were measured by quadrupole ICP-MS. The isotope ratios of leachable Pb in settling particles
were 207Pb/206Pb = 0.860 ± 0.001; 208Pb/206Pb = 2.116 ± 0.002 (mean ± 95% confidence intervals), which are similar to those of aerosols in China that are greatly affected
by pollution from coal combustion. We estimated the mean contribution from anthropogenic Pb sources to the Pb in settling
particles, using the conventional binary (anthropogenic and natural Pb) mixing equation for Pb isotopes, as 90% in the upper
trap and 78% in the lower trap. Furthermore, we found a significant negative correlation between the isotope ratios of Pb
and concentrations of leachable Mn, normalized to those of leachable Pb, suggesting that manganese oxides play an important
role in transporting Pb from the upper layers of the ocean to the deeper layers. Our results support the speculation published
in a previous study that Pb might be scavenged by Mn oxides in the Northwestern Pacific Ocean. 相似文献
122.
Daisuke Nakashima Keisuke Nagao Anthony J. Irving 《Meteoritics & planetary science》2018,53(5):952-972
Noble gases in the five angrites Northwest Africa (NWA) 1296, 2999, 4590, 4801, and 4931 were analyzed with total melting and stepwise heating methods. The noble gases consist of in situ components: spallogenic, radiogenic, nucleogenic, and fission. Cosmic-ray exposure ages of the angrites (including literature data) spread uniformly from <0.2 to 56 Ma, and coarse-grained angrites have longer exposure ages than fine-grained angrites. It is implied that the parent bodies from which the two subgroups of angrites were ejected are different and have distinct orbital elements. The 244Pu-136Xe relative ages of the angrites obtained by using 244Pu/150Nd ratios are as old as that of Angra dos Reis, reflecting their early formation. On the other hand, another method to obtain 244Pu-136Xe relative ages, using fission 136Xe, spallogenic 126Xe, and Ba/REE ratios, yields systematically older 244Pu-136Xe ages than those obtained by using 244Pu/150Nd ratios, which is explained by apparently high Ba/REE ratios caused by Ba contamination during terrestrial weathering. The 244Pu/238U ratio at 4.56 Ga of angrites is estimated as 0.0061 ± 0.0028, which is consistent with those for chondrules, chondrites, achondrites, and a terrestrial zircon. It is suggested that initial 244Pu/238U ratio has been spatially homogeneous at least in the inner part of the early solar system. 相似文献
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126.
Nicolas C.M. Marty Jordi Cama Daisuke Chino Angelina Razafitianamaharavo Jocelyne Brendlé Josep M. Soler Christophe Tournassat 《Geochimica et cosmochimica acta》2011,75(20):5849-5864
The effect of pH and Gibbs energy on the dissolution rate of a synthetic Na-montmorillonite was investigated by means of flow-through experiments at 25 and 80 °C at pH of 7 and 9. The dissolution reaction took place stoichiometrically at 80 °C, whereas at 25 °C preferential release of Mg over Si and Al was observed. The TEM-EDX analyses (transmission electronic microscopy with quantitative chemical analysis) of the dissolved synthetic phase at 25 °C showed the presence of newly formed Si-rich phases, which accounts for the Si deficit. At low temperature, depletion of Si concentration was attributed to incongruent clay dissolution with the formation of detached Si tetrahedral sheets (i.e., alteration product) whereas the Al behaviour remains uncertain (e.g., possible incorporation into Al-rich phases). Hence, steady-state rates were based on the release of Mg. Ex situ AFM measurements were used to investigate the variations in reactive surface area. Accordingly, steady-state rates were normalized to the initial edge surface area (11.2 m2 g−1) and used to propose the dissolution rate law for the dissolution reactions as a function of ΔGr at 25 °C and pH∼9:
127.
Daisuke Hasegawa Jinyu Sheng David A. Greenberg Keith R. Thompson 《Ocean Dynamics》2011,61(11):1845-1868
The Bay of Fundy in eastern Canada has the highest tides in the world. Harnessing the tidal energy in the region has long
been considered. In this study, the effects of tidal in-stream energy extraction in the Minas Passage on the three-dimensional
(3D) tidal circulation in the Bay of Fundy (BoF) and the Gulf of Maine (GoM) are examined using a nested-grid coastal ocean
circulation model based on the Princeton Ocean Model (POM). The nested-grid model consists of a coarse-resolution (~4.5 km)
parent sub-model for the GoM and a high-resolution (~1.5 km) child sub-model for the BoF. The tidal in-stream energy extraction
in the model is parameterized in terms of nonlinear Rayleigh friction in the momentum equation. A suite of numerical experiments
are conducted to determine the ranges of extractable tidal in-stream energy and resulting effects on the 3D tidal circulation
over the Bay of Fundy and the Gulf of Maine (BoF-GoM) in terms of the Rayleigh friction coefficients. The 3D model results
suggest that the maximum energy extraction in the Minas Passage increases tidal elevations and tidal currents throughout the
GoM and reduces tidal elevations and circulation in the upper BoF, especially in the Minas Basin. The far-field effect of
tidal energy extraction in the Passage on the 3D tidal circulation in the BoF-GoM is examined in two cases of harnessing tidal
in-stream energy from (a) the entire water column and (b) the lower water column within 20 m above the bottom in the Passage.
The 3D model results demonstrate that tidal in-stream energy extraction from the lower water column has less impact on the
tidal elevations and circulation in the BoF-GoM than the energy extraction from the whole water column in the Minas Passage. 相似文献
128.
Tomoko Sato Hiroto Takada Takehiko Yagi Hirotada Gotou Taku Okada Daisuke Wakabayashi Nobumasa Funamori 《Physics and Chemistry of Minerals》2013,40(1):3-10
We have investigated the high-pressure behavior of cristobalite in helium by powder X-ray diffraction. Cristobalite transformed to a new phase at about 8 GPa. This phase is supposed to have a molar volume of about 30 % larger than cristobalite, suggesting the dissolution of helium atoms in its interstitial voids. On further compression, the new phase transformed to a different phase which showed an X-ray diffraction pattern similar to cristobalite X-I at about 21 GPa. On the other hand, when the new phase was decompressed, it transformed to another new phase at about 7 GPa, which is also supposed to have a molar volume of about 25 % larger than cristobalite. On further decompression, the second new phase transformed to cristobalite II at about 2 GPa. In contrast to cristobalite, quartz did not show anomalous behavior in helium. The behavior of cristobalite in helium was also consistent with that in other mediums up to about 8 GPa, where the volume of cristobalite became close to that of quartz. These results suggest that dissolution of helium may be controlled not only by the density (amount of voids) but also by the network structure of SiO4 tetrahedra (topology of voids). 相似文献
129.
The knowledge from the compression behavior of densified SiO2 glass suggests that SiO2 melt may behave as a single phase having a densified network structure (intermediate-range order) at the pressure condition of the Earth’s deep upper mantle, including the transition zone. A simple and easy-to-use equation of state of silicate melts which is applicable to a wide range of chemical composition at the pressure condition of the deep upper mantle is proposed based on the assumption that SiO2 component is in its densified state (or phase). The equation of state proposed in this study is consistent with all the available density data of silicate melts with an SiO2 content of about 35–55 mol% measured with large-volume presses at pressures between 8 and 22 GPa. The equations of state in previous studies differ considerably from each other. The main reason for the discrepancies seems to be that the compression behavior of multiple states (or phases) of silicate melts has been described in most cases with a single equation of state. It is necessary to consider that silicate melts are in their densified states (or phases) in the deep upper mantle. 相似文献
130.
Taketo Shimano Takeshi Nishimura Nobuyuki Chiga Yoshinobu Shibasaki Masato Iguchi Daisuke Miki Akihiko Yokoo 《Bulletin of Volcanology》2013,75(12):1-7
We develop an automatic system for the sampling of ash fall particles, to be used for continuous monitoring of magma ascent and eruptive dynamics at active volcanoes. The system consists of a sampling apparatus and cameras to monitor surface phenomena during eruptions. The Sampling Apparatus for Time Series Unmanned Monitoring of Ash (SATSUMA-I and SATSUMA-II) is less than 10 kg in weight and works automatically for more than a month with a 10-kg lead battery to obtain a total of 30 to 36 samples in one cycle of operation. The time range covered in one cycle varies from less than an hour to several months, depending on the aims of observation, allowing researchers to target minute-scale fluctuations in a single eruptive event, as well as daily to weekly trends in persistent volcanic activity. The latest version, SATSUMA-II, also enables control of sampling parameters remotely by e-mail commands. Durability of the apparatus is high: our prototypes worked for several months, in rainy and typhoon seasons, at windy and humid locations, and under strong sunlight. We have been successful in collecting ash samples emitted from Showa crater almost everyday for more than 4 years (2008–2012) at Sakurajima volcano in southwest Japan. 相似文献