Flux of low salinity water from Aniva Bay (Sakhalin Island) to the southern Okhotsk Sea     

Sachiko Oguma  Tsuneo Ono  Yutaka W. Watanabe  Hiromi Kasai  Shuichi Watanabe  Daiki Nomura  Humio Mitsudera 《Estuarine, Coastal and Shelf Science》2011

In this study, we examined the relationship between the low salinity water in the shelf region of the southern Okhotsk Sea which was seasonally sampled (0–200 m), and fluxes of low salinity water from Aniva Bay. To express the source of freshwater mixing in the surface layer, we applied normalized total alkalinity (NTA) and stable isotopes of seawater as chemical tracers. NTA-S diagrams indicate that NTA of low salinity water in the upper 30 m layer just off the Soya Warm Current is clearly higher than in the far offshore region in summer and autumn. Using NTA-S regression lines, we could deduce that the low salinity and high NTA water in the upper layer originates from Aniva Bay. For convenience, we defined this water as the Aniva Surface Water (ASW) with values S < 32, NTA > 2450 μmol kg⁻¹. Formation and transport processes of ASW are discussed using historical data. The interaction between the maximum core of high NTA water on the bottom slope of eastern Aniva Bay and an anticyclonic eddy at the mouth of Aniva Bay are concluded to control ASW formation. Upwelling of the Cold Water Belt water at the tip of Cape Krillion is considered to cause ASW outflow from Aniva Bay.  相似文献   

Marine active-source seismic studies in the Japan Trench: a seismogenic zone in an ocean-continent collision zone     

Shuichi Kodair  Yasuyuki Nakamur  Gou Fujie  Seiichi Miura 《《地质学报》英文版》2018,92(Z1):94-95

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Topo-stress based probabilistic model for shallow landslide susceptibility zonation in the Nepal Himalaya   总被引：1，自引：1，他引：0  

Ranjan Kumar Dahal  Netra Prakash Bhandary  Shuichi Hasegawa  Ryuichi Yatabe 《Environmental Earth Sciences》2014,71(9):3879-3892

While dealing with slope stability issues, determining the state of stress and the relation between driving force and resisting force are the fundamental deterministic steps. Gravitational stresses affect geologic processes and engineering operations in slopes. Considering this fact, a concept of topo-stress evaluation is developed in this research and used to produce a shallow landslide susceptibility map in a model area. The topo-stress introduced in this research refers to the shear stress induced by the gravitational forces on the planes parallel to the ground surface. Weight of the material on a slope and friction angle of the jointed rock mass are the two fundamental parameters that are considered to govern topo-stress in this study. Considering topo-stress as a main factor for initiating shallow landslides, a GIS-based probabilistic model is developed for shallow landslide susceptibility zonation. An ideal terrain in central Nepal is selected as the study area for this purpose. Two event-based shallow landslide inventories are used to predict accuracy of the model, which is found to be more than 78 % for the first event-landslides and more than 76 % for the second event-landslides. It is evident from these prediction rates that the probabilistic topo-stress model proposed in this work is quite acceptable when regional scale shallow landslide susceptibility mapping is practiced, such as in the Himalayan rocky slopes.  相似文献   

Regional extraction of flexural-toppled slopes in epicentral regions of subduction earthquakes along the Nankai Trough using DEMs     

Atsuko Nonomura  Shuichi Hasegawa 《Environmental Earth Sciences》2013,68(1):139-149

In the epicentral region of subduction earthquakes, large-scale landslides are triggered by strong shaking of slopes weakened by flexural toppling. The distribution of flexural-toppled slopes is the primary information for predicting and mitigating landslide damage beforehand. This study proposes and tests a simple algorithm for extracting flexural-toppled slopes on a regional basis from a 10-m resolution digital elevation model by windows of two sizes. Local relief is extracted with a large window (200 × 200 pixels), and microtopography is extracted with a small window (3 × 3 pixels). The algorithm was derived from the region of the Kanagi-kuzure landslide in Shikoku, and tested at Aka-kuzure landslide in Honshu in Japan. Both areas are underlain by strongly tilted sedimentary rocks in epicentral regions of subduction earthquakes along the Nankai Trough.  相似文献   

Distribution of nitrous oxide dissolved in water masses in the eastern subtropical North Pacific and its origin inferred from isotopomer analysis     

Ayako Fujii  Sakae Toyoda  Osamu Yoshida  Shuichi Watanabe  Ken’ichi Sasaki  Naohiro Yoshida 《Journal of Oceanography》2013,69(2):147-157

N₂O concentration and its isotopomer ratios were measured over a wide area from San Diego to Honolulu in the eastern subtropical North Pacific (ESNP). Waters in the study area had an N₂O maximum (38.2–50.5 nmol kg^?1) at 600–1000 m depth, which is similar to the profiles obtained previously in other areas in the North Pacific. We separated the seawater into five water masses (two for the surface layer, two for the middle layer, and one for the deep layer) and deduced N₂O production–consumption mechanisms in each water body by use of N₂O isotopomer ratios. The results showed that the mechanisms differ slightly among water masses. In the “coastal” surface layer, N₂O is produced by nitrification (NH₂OH oxidation). In the “open ocean” surface layer, it is produced mainly by nitrifier denitrification and to a lesser extent by nitrification under substrate-limited conditions. In both “upwelling” and “open ocean” middle layers it is produced mainly by denitrification and to a lesser extent by nitrifier denitrification. It is also partly reduced. In the deep layer, it is produced predominantly by denitrification with partial reduction. In this way, isotopomers aid elucidation of production–consumption mechanisms of N₂O in the sea even though the mechanisms cannot always be ascertained.  相似文献   

Glacial–interglacial productivity and environmental changes in Lake Biwa,Japan: A sediment core study of organic carbon,chlorins and biomarkers     

Ryoshi Ishiwatari  Koichi Negishi  Hiroyasu Yoshikawa  Shuichi Yamamoto 《Organic Geochemistry》2009,40(4):520-530

Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/N_org values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m^?2 yr^?1 in the Holocene, while it is ～60 g C m^?2 yr^?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C₂₇–C₃₁ alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C₂₉ sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake.  相似文献   

Characteristics of crustal structures in the Yamato Basin,sea of Japan,deduced from seismic explorations     

Takeshi Sato  Tetsuo No  Shuichi Kodaira 《Island Arc》2023,32(1):e12474

Crustal structures around the Yamato Basin in the southeastern Sea of Japan, inferred from recent ocean bottom seismography (OBS) and active-source seismological studies, are reviewed to elucidate various stages of crustal modification involved from rifting in the crust of the surrounding continental arc to the production of oceanic crust in the Yamato Basin of the back-arc basin. The northern, central, and southern areas of the Yamato Basin have crustal thicknesses of approximately 12–16 km, and lowermost crusts with P-wave velocities greater than 7.2 km/s. Very few units have P-wave velocities in the range 5.4–6.0 km/s, which corresponds to the continental upper crust. These findings, combined with previous geochemical analysis of basalt samples, are interpreted to indicate that a thick oceanic crust has been formed in these areas of the basin, and that this oceanic crust has been underplated by mantle-derived magma. In the central Yamato Basin, the original continental crust has been fully breached and oceanic crust has been formed. Conversely, the presence of a unit corresponding to the continental upper crust and the absence of a high-velocity part in the lower crust implies that the southwestern edge of the Yamato Basin has a rifted crust without significant intrusion. The Oki Trough has a crust that is 17–19 km thick with a high-velocity lower crust and a unit corresponding to the continental upper crust. The formation of the Oki Trough resulted from rifting with magmatic intrusion and/or underplating. We interpret these variations in the crustal characteristics of the Yamato Basin area as reflecting various instances of crustal modification by thinning and magmatic intrusion due to back-arc extension, resulting in the production of a thick oceanic crust in the basin.  相似文献   

Local structure of (Ca, Sr)2 (Mg, Co, Zn) Si2O7 melilite solid-solution with modulated structure     

Takuo Tamura  Akira Yoshiasa  Kazuaki Iishi  Setsuo Takeno  Hironobu Maeda  Shuichi Emura  Kichiro Koto 《Physics and Chemistry of Minerals》1996,23(2):81-88

The local structure around Co, Zn and Sr atoms in incommensurately modulated, melilite-type X₂T¹ T ₂ ² O₇ (X=Ca and Sr, T¹=Mg, Co and Zn, T²=Si) solid-solutions has been investigated by EXAFS analyses. The modulated structure was confirmed in Ca_2-xSr_xCoSi₂O₇ solid-solutions with X=0.0 to 0.6 and for both Ca₂Mg_1-YCo_YSi₂O₇ and Ca₂Mg_1-YZn_YSi₂O₇ solid-solutions over the whole compositional range at room temperature. The actual bond-distances determined by the EXAFS method for the T¹ site (Co-, Zn-O) in the modulated structure are longer than the mean bond-distances obtained from the X-ray diffraction method. This is attributable to the libration of the T¹ tetrahedra. In the Ca_1-XSr_XCoSi₂O₇ solid-solution both the Sr-O and Co-O distances by the EXAFS method for the X-site increase from Ca end-member to Sr end-member. These increases are respectively 0.8% and 0.6%. This means the local expansions of the tetrahedral sheets and of the XO polyhedra are well matched. In the modulated Ca₂Co_1-YMg_YSi₂O₇ and Ca₂Zn_1-YMg_YSi₂O₇ solid-solutions, the actual Co-O and Zn-O distances for the T¹-sites are nearly constant in the whole compositional range. The compositional variations of the local structure around the cations in the solid-solution are different for the X and T¹ sites. It is concluded that the local geometric restriction for the size of substituted cation in X site is larger than that in T¹ site. The dimension of the tetrahedral sheet puts restriction on the size of the cations situated at the interlayer X sites. In other words, the different behavior of the local geometric restriction between the X and T¹ sites is an important feature of the melilite structure and is also related to the modulated structure.  相似文献   

Optically thick accretion onto black holes     

Shuichi Tamazawa  Kiyotaka Toyama  Noboru Kaneko  Yôrô Ôno 《Astrophysics and Space Science》1975,32(2):403-421

Spherically symmetric, steady-state, optically thick accretion onto a nonrotating black hole with the mass of is studied. The gas accreting onto the black hole is assumed to be a fully ionized hydrogen plasma withn ₀=10⁸ cm^–3 andT ₀=10⁴ K far from the black hole, and a new approximate expression for the Eddington factor is introduced. The luminosity is estimated to beL=1.875×10³³ erg s^–1, which primarily arises from the optical surface (1) ofT10⁴ K. The accretion flow is characterized by 1 and (v/c)10. In the optically thin region, the flow remains isothermal, and the increase of temperature occurs at 1. The radiative equilibrium is strictly realized at (v/c)10.  相似文献   

Linear waves in a radiating and scattering grey medium     

Noboru Kaneko  Shuichi Tamazawa  Yôrô Ôno 《Astrophysics and Space Science》1976,42(2):441-461

The problem on linear waves in a radiating and scattering grey medium is studied using Whitham's method. Analysis of the basic equations distinguishes two limiting cases: the one is theequilibrium case in which the energy exchange between the gas and radiation plays an essential role, and the other is theScattering case in which the effect of energy exchange is negligible. A new type ofradiation acoustic wave with the speed is found in the scattering case. The governing equations for linearized one-dimensional flow are reduced to one equation of radiative acoustics valid to order 1/c, and the criterion for the two limiting cases is derived from studying this equation. The harmonic solution is analytically studied to show that theeffective optical depth corresponding to the wavelength of perturbation gives the measure of the interaction between the gas and radiation. When _eff1, the sound speeda _g ² =P _g / and the propagating speed of radiative disturbancea _f ² =fc ² appear as the modified classical and radiation-induced modes respectively, wheref is the Eddington factor. When _eff1, the isentropic sound speeda _s ² =(P _g +P _r / appears in the equilibrium case, and the radiation acoustic speeda _A ² appears in the scattering case. The dispersion relation of the harmonic solution is numerically calculated. The result shows that the wave pattern depends critically on the ratio=P _g /(P _g +P _r ). When , the speeda _S anda _A arise from the modified classical mode, and when , they originate from the radiation-induced mode.  相似文献