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61.
62.
Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies. 相似文献
63.
Three marine sediment cores from Osaka Bay were analyzed for 210Pb geochronology, heavy metal concentrations (Zn, Cu, and Pb) and stable lead isotope ratios (206Pb/207Pb) in order to reconstruct high-resolution heavy metal pollution history from 1900–2006. Anthropogenic metal accumulation in sediments peaked in 1970 in agreement with the high economic growth period in Japan. The comparison of temporal patterns of 206Pb/207Pb ratio with other areas of Japan suggested that the heavy metals, imported from several different countries during the periods of economic growth (1955 to 1973), are the main pollution source for the country. For the period 1970–2006, the sediment data reflect the result of stricter environmental regulations applied after the late 1960s. However, heavy metal concentrations in the surface sediments are still elevated to levels several times higher than the levels at the bottoms of the cores. Additionally, the lead isotope ratio does not show significant change after the 1980s. Secondary heavy metal pollution through the mixing of deeper polluted sediment appears to be the likely reason for the deterioration of present time submarine sediment environments. In conclusion, this study has demonstrated that it is difficult to recover over a period of several years the benthic quality of a bay, once it is heavily polluted. 相似文献
64.
H.Shirai Y.Kamide E.A.Kihn B.Hausman M.Shinohara H.Nakata M.Isowa T.K.Takada Y.Watanabe S.Masuda 《中国天文和天体物理学报》2003,3(4):375-380
This paper presents the recent progress in our project of estimating near real-time electric fields and currents in the ionosphere through our computer system called the Geospace Environment Data Analysis System (GEDAS). We show a new technique in which data from ground magnetometers are collected by the system and used as input for the KRM and AMIE programs to calculate the distribution of ionospheric electric fields and currents, as well as of other ionospheric parameters, such as electric potential patterns. One of the goals of this project is to specify ionospheric processes. Examples of the near real-time calculation and the data flow of our scheme are presented. 相似文献
65.
T. Noguchi M. Kimura T. Hashimoto M. Konno T. Nakamura M. E. Zolensky A. Tsuchiyama T. Matsumoto J. Matsuno R. Okazaki M. Uesugi Y. Karouji T. Yada Y. Ishibashi K. Shirai M. Abe T. Okada 《Meteoritics & planetary science》2014,49(7):1305-1314
We observed cross sectional ultra‐thin sections near the surface of 12 particles recovered from the S‐type asteroid Itokawa by the Hayabusa spacecraft in 2010, using spherical aberration–corrected STEM and conventional TEM. Although their mineralogy is almost identical to the equilibrated LL chondrites and therefore basically anhydrous, micrometer‐to‐submicrometer‐sized sylvite was identified on the surface of Itokawa particle RA‐QD02‐0034. Separately, micrometer‐sized halite was also identified on the surface of Itokawa particle RA‐QD02‐0129. Detailed inspection of the sample processing procedures at the JAXA's Planetary Materials Sample Curation Facility and textural observation of the sylvite and halite indicate that they were clearly present on two Itokawa particles before they were removed from Clean Chamber #2 at JAXA. However, there is no direct evidence for their extraterrestrial origin at present. If the sylvite and halite are extraterrestrial, their presence suggests that they may be more abundant on the surface of S‐type asteroids than previously thought. 相似文献
66.
Since observed precise data on the fluxes of the neutrinos from the Sun have recently become available from the Super-Kamiokande experiment, it has become possible, by using these data, to find out whether these fluxes vary periodically or aperiodically. Here we discuss the time variation of the solar neutrino fluxes from the data and suggest that the neutrino fluxes may vary with about a 30-month period. 相似文献
67.
Heavy oil exposure induces high moralities in virus carrier Japanese flounder Paralichthys olivaceus
The relationship between chemical exposure and disease outbreak in fish has not been fully defined due to the limitations of experimental systems (model fish and pathogens). Therefore, we constructed a system using the Japanese flounder, Paralichthys olivaceus, and viral haemorrhagic septicemia virus (VHSV), and evaluated it by heavy oil (HO) exposure. The fish were exposed to HO at 0.3, 0.03, 0.003, and 0 g/L following VHSV infection at doses of 10(2.5) or 10(3.5) tissue culture infectious dose (TCID)50/fish. As a result, groups given the dual stressors showed more than 90% mortality. Although VHSV infection at 10(2.5) and 10(3.5) TCID50/fish without HO exposure also induced high mortality, at 68.8% and 81.3%, respectively, HO exposure induced faster and higher mortality in the virus carrier fish, indicating that chemical stressors raise the risk of disease outbreak in fish. The experimental system established in this study could be useful for chemical risk assessment. 相似文献
68.
Yasuhiro Kuwayama Kei Hirose Nagayoshi Sata Yasuo Ohishi 《Physics and Chemistry of Minerals》2011,38(8):591-597
The equation of state and pressure-induced structural evolution of pyrite-type SiO2 have been investigated based on synchrotron X-ray diffraction measurements in a diamond-anvil cell. The Rietveld refinement
revealed that the oxygen coordinate x of pyrite-type SiO2 increases with increasing pressure. The SiO6 coordination polyhedra of pyrite-type SiO2 is less compressible than the unit cell, and the increase in x induces a rotation of the SiO6 coordination polyhedra to fill the blank space in the unit cell. Thus, the volume reduction in pyrite-type SiO2 is achieved mainly by the rotation of the SiO6 polyhedra, rather than by the compression of the SiO6 polyhedra. In addition, the increase in x with increasing pressure enhances a distortion of the coordination polyhedra of pyrite-type SiO2, implying that pyrite-type SiO2 is not likely to transform into a fluorite-type structure at higher pressures. 相似文献
69.
Lidong Dai Yuki Kudo Kei Hirose Motohiko Murakami Yuki Asahara Haruka Ozawa Yasuo Ohishi Naohisa Hirao 《Physics and Chemistry of Minerals》2013,40(3):195-201
The sound velocities of two aluminum-rich phases in the lower mantle, hexagonal new Al-rich phase (NAL) and its corresponding high-pressure polymorph orthorhombic Ca-ferrite-type phase (CF), were determined with the Brillouin scattering method in a pressure range from 9 to 73 GPa at room temperature. Both NAL and CF samples have identical chemical composition of Na0.4Mg0.6Al1.6Si0.4O4 (40 % NaAlSiO4–60 % MgAl2O4). Infrared laser annealing in the diamond anvil cell was performed to minimize the stress state of the sample and obtain the high-quality Brillouin spectra. The results show shear modulus at zero pressure G 0 = 121.960 ± 0.087 GPa and its pressure derivative G’ = 1.961 ± 0.009 for the NAL phase, and G 0 = 129.653 ± 0.059 GPa and G’ = 2.340 ± 0.004 for the CF phase. The zero-pressure shear velocities of the NAL and CF phases are obtained to be 5.601 ± 0.005 km/sec and 5.741 ± 0.001 km/sec, respectively. We also found that shear velocity increases by 2.5 % upon phase transition from NAL to CF at around 40 GPa. 相似文献
70.
Pablo Ortega Didier Swingedouw Valérie Masson-Delmotte Camille Risi Bo Vinther Pascal Yiou Robert Vautard Kei Yoshimura 《Climate Dynamics》2014,43(9-10):2585-2605
Greenland ice cores offer seasonal to annual records of δ18O, a proxy for precipitation-weighted temperature, over the last few centuries to millennia. Here, we investigate the regional footprints of the North Atlantic weather regimes on Greenland isotope and climate variability, using a compilation of 22 different shallow ice-cores and the atmospheric pressure conditions from the twentieth century reanalysis (20CR). As a first step we have verified that the leading modes of winter and annual δ18O are well correlated with oceanic (Atlantic multidecadal oscillation) and atmospheric [North Atlantic oscillation (NAO)] indices respectively, and also marginally with external forcings, thus confirming earlier studies. The link between weather regimes and Greenland precipitation, precipitation-weighted temperature and δ18O is further explored by using an isotope simulation from the LMDZ-iso model, where the 3-dimensional wind fields are nudged to those of 20CR. In winter, the NAO+ and NAO? regimes in LMDZ-iso produce the largest isotopic changes over the entire Greenland region, with maximum anomalies in the South. Likewise, the Scandinavian blocking and the Atlantic ridge also show remarkable imprints on isotopic composition over the region. To assess the robustness and model dependency of our findings, a second isotope simulation from the isotopic model is also explored. The percentage of Greenland δ18O variance explained by the ensemble of weather regimes is increased by a factor near two in both LMDZ-iso and IsoGSM when compared to the contribution of the NAO index only. Similarly, weather regimes provide a net gain in the δ18O variance explained of similar magnitude for the whole set of ice core records. Greenland δ18O also appears to be locally affected by the low-frequency variations in the centres of action of the weather regimes, with clearer imprints in the LMDZ-iso simulation. This study opens the possibility for reconstructing past changes in the frequencies of occurrence of the weather regimes, which would rely on the sensitive regions identified here, and the use of additional proxies over the North Atlantic region. 相似文献