Sulfate reduction and sulfide deposition in deep-sea sediments from the southwestern Japan Sea     

Toshiyuki Masuzawa  Yasushi Kitano 《Journal of Oceanography》1983,39(5):251-258

Vertical profiles of total sulfur and organic carbon have been measured in two deep-sea piston cores from the southwestern Japan Sea where sulfate reduction is proceeding within the sediments. The content of total sulfur, most of which is present as pyrite, increases gradually with increasing depth, showing several peaks. The amount of diagenetically deposited sulfide-sulfur is estimated using a steady-state model that considers vertical change in the diffusion coefficient. It is suggested that two-thirds to three-fourths of the observed total sulfur content has been deposited diagenetically.  相似文献   

The effects of the reed,Phragmites australis (Trin.), on substratum grain-size distribution in a salt marsh   总被引：1，自引：0，他引：1  

Satoshi Takeda  Yasushi Kurihara 《Journal of Oceanography》1988,44(3):103-112

The effects of the reed,Phragmites australis (Trin.), growing in a brackish water lagoon, were studied in relation to the grain-size distribution of the substratum. At the salt marshes near the lagoon, the upper soils from the surface to a depth of 20 cm contained much silt-clay. These fine particles were found to be transferred from the river and fish ponds near the lagoon, and to be deposited when the tidal rhythm changed, that is, when the water current stopped. In addition, the fine particles, which were deposited on the bottom of the lagoon adjacent to the marshes, became resuspended as a result of wind-caused wave action, and then were transported and redeposited in the salt marshes at the flood tide. Since the reeds further reduced the water current caused by the waves and tide, the reeds were thought to promote redeposition of the resuspended matter. In other words, the reeds were considered to protect deposited and redeposited particles such as silt and clay from resuspension as a result of wave action by reducing the effects of waves and wind. These processes suggested that silt-clay will become abundant in the substratum of the salt marsh adjacent to the lagoon.  相似文献   

Degradation of lubricating oils by marine bacteria observed by quantitative mass spectrometry     

Yasushi Kawakami  Hajime Nishimura 《Journal of Oceanography》1981,37(1):1-7

Bacterial degradation of the hydrocarbons of lubricating oils was investigated by mass spectrometric analysis which gives both total amount and the composition of hydrocarbon types of residual oil. An unused lubricating oil, which mainly consisted of hydrocarbon types with only a small percentage ofn-alkanes, was degraded by marineBacillus sp. andPseudomonas sp. with 55 % and 25 % decreases in 10 days, respectively. Susceptibility of respective hydrocarbon types to biodegradation was in the following order: alkanes > non-condensed cycloalkanes, mono-aromatics > condensed cycloalkanes. A used lubricating oil of different brand showed a larger decrease than the unused oil. Both species of bacteria degraded large portions of alkane fraction of Arabian light crude oil.  相似文献   

Fluoride contents of saline and interstitial waters in the inlets of the Juneau Glacier Area,Alaska     

Yasushi Kitano  Yukihiro Furukawa 《Journal of Oceanography》1972,28(4):176-179

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Simultaneous multifrequency observations of an eruptive prominence at millimeter wavelengths     

Yoshihisa Irimajiri  Toshiaki Takano  Hiroshi Nakajima  Kiyoto Shibasaki  Yoichiro Hanaoka  Kiyoshi Ichimoto 《Solar physics》1995,156(2):363-375

Radio images and spectra of an eruptive prominence were obtained from simultaneous multifrequency observations at 36 GHz, 89 GHz, and 110 GHz on May 28, 1991 with the 45-m radio telescope at Nobeyama Radio Observatory (NRO), the National Astronomical Observatory, Japan (NAOJ). The radio spectra indicated that the optical depth is rather thick at 36 GHz whereas it is thin at 89 and 110 GHz. The H data, taken at Norikura Solar Observatory, NAOJ, suggest that the eruption of an active region filament was triggered by an H flare. The shape and position of the radio prominence generally coincided with those of H images. The radio emission is explained with an isothermal cool thread model. A lower limit for the electron temperature of the cool threads is estimated to be 6100 K. The range of the surface filling factors of the cool threads is 0.3–1.0 after the H flare, and 0.2–0.5 in the descending phase of the eruptive prominence. The column emission measure and the electron number density are estimated to be of the order of 10²⁸ cm^–5 and 10¹⁰ cm^–3, respectively. The physical parameters of a quiescent prominence are also estimated from the observations. The filling factors of the eruptive prominence are smaller than those of the quiescent prominence, whereas the emission measures and the electron densities are similar. These facts imply that each cool thread of the prominence did not expand after the eruption, while the total volume of the prominence increased.  相似文献   

Finite-element Simulation of Seismic Ground Motion with a Voxel Mesh     

Kazuki Koketsu  Hiroyuki Fujiwara  Yasushi Ikegami 《Pure and Applied Geophysics》2004,161(11-12):2183-2198

— Accurate simulation of seismic ground motion for three-dimensionally complex topography and structures is one of the most important goals of strong motion seismology. The finite-element method (FEM) is well suited for this kind of simulation, since traction-free conditions are already included in the formulation, and the Courant condition is less strict than for the finite-difference method (FDM). However, the FEM usually requires both large memory and computation time. These limitations can be overcome by using a mesh consisting of voxels (rectangular prisms) with isotropy built into the explicit formulation of the dynamic matrix equation. Since operators in the voxel FEM are the combinations of ordinary FDM operators and additional terms, the method keeps accuracy of the same order as FDM and the terms relax the Courant condition. The voxel FEM requires a similar amount of memory and only takes 1.2～1.4 times longer computation time. The voxel mesh can be generated considerably faster than the popular tetrahedral mesh. Both ground motions and static displacements due to a point or line source can be calculated using the voxel FEM approach. Comparisons with the reflectivity method and theoretical solutions demonstrate the successful implementation of the method, which is then applied to more complex problems.  相似文献   

Deep structure of the northeastern Japan arc and its implications for crustal deformation and shallow seismic activity   总被引：7，自引：1，他引：7  

Akira Hasegawa  Junichi Nakajima  Norihito Umino  Satoshi Miura 《Tectonophysics》2005,403(1-4):59-75

Seismic tomography studies in the northeastern Japan arc have revealed the existence of an inclined sheet-like seismic low-velocity and high-attenuation zone in the mantle wedge at depths shallower than about 150 km. This sheet-like low-velocity, high-attenuation zone is oriented sub-parallel to the subducted slab, and is considered to correspond to the upwelling flow portion of the subduction-induced convection. The low-velocity, high-attenuation zone reaches the Moho immediately beneath the volcanic front (or the Ou Backbone Range) running through the middle of the arc nearly parallel to the trench axis, which suggests that the volcanic front is formed by this hot upwelling flow. Aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the Backbone Range where they are expelled from solidified magma and migrate further upward. The existence of aqueous fluids may weaken the surrounding crustal rocks, resulting in local contractive deformation and uplift along the Backbone Range under the compressional stress field of the volcanic arc. A strain-rate distribution map generated from GPS data reveals a notable concentration of east–west contraction along the Backbone Range, consistent with this interpretation. Shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone. Based on these observations, a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern Japan arc.  相似文献   

Population genetic diversity and structure of a dominant tropical seagrass,Cymodocea rotundata,in the Western Pacific region          下载免费PDF全文

Dan M. Arriesgado  Hiroyuki Kurokochi  Yuichi Nakajima  Yu Matsuki  Wilfredo H. Uy  Miguel D. Fortes  Wilfredo L. Campos  Kazuo Nadaoka  Chunlan Lian 《Marine Ecology》2016,37(4):786-800

Cymodocea rotundata is an ecologically important tropical pioneer seagrass species distributed in the Indo‐Pacific region. The population genetic diversity and structure of this species were analysed at 46 sites spanning the Philippines, Ryukyu Islands (northern limit) and Hainan Island, by using microsatellite simple sequence repeat (SSR) markers. Analyses revealed the persistence of C. rotundata likely relies on local population dynamics and fitness influenced by environmental gradients, with sexual reproduction prevalent in the Philippines while the Ryukyu and Hainan populations were predominantly established by clonal spread. Analysis of molecular variance showed significant genetic differentiation (P < 0.001) among three geographic regions: the Philippines, Ryukyu and Hainan. Furthermore, the mean fixation index value was very high (F_ST = 0.36), indicating poor dispersal potential or limited gene flow. Allelic richness and heterozygosity of C. rotundata was comparable in the Philippines and Ryukyu Islands populations. More private alleles were found in the Philippines and excess heterozygotes in the Ryukyu Islands. STRUCTURE analysis revealed that the Ryukyu and Hainan populations were mosaics of admixed alleles of individuals from the Philippines. An assignment test suggested that recruitment occurs from the Northeast Philippines to Ryukyu Islands. These results suggest that the Philippine populations are tropical seagrass hotspots and perhaps the origin of the populations in the Ryukyu and Hainan Islands. This scenario is most likely driven by the Kuroshio Current and island integration events during plate tectonic activities. The Philippine Archipelago is considered of high importance for conservation objectives and management plan of seagrasses. Likewise, the Ryukyu Islands are also important in terms of conserving regional diversity because locally adapted genotypes have important evolutionary potential in the face of environmental change.  相似文献   

Texture and structural interpretation of the alteration of pyroxene to other biopyriboles     

Yoshiharu Nakajima  Paul H. Ribbe 《Contributions to Mineralogy and Petrology》1982,78(3):230-239

In a metamorphosed gabbro from Hokkaido, Japan, augite containing exsolved orthohypersthene and minor pigeonite has been altered to a variety of biopyriboles. High resolution transmission electron microscopy of slightly altered augite shows only narrow (010) lamellae of clinoamphibole which always contain even numbers of double chains. In more highly altered regions, all three pyroxenes are changed to double-, triple- and more highly polymerized multiple-chain biopyriboles, with chlorite d ₀₀₁ 14.5 Å) found only in orthopyroxene. Several (010) lamellae containing only one double chain have been observed, and their textural relationship to the surrounding single-chain host may explain how the rotated domains of biopyribole initially attain their orientation in the host pyroxene.A structural model is proposed for the polymerization of single chains in the tetrahedral layers of pyroxene which involves small movements of oxygens and tetrahedral atoms (Si, Al) with a minimum of bond breaking and re-forming, concommitant with hydroxylization of certain oxygens and the diffusion of Mg, Fe and/or Ca along the rift in the octahedral layer.  相似文献   

The formation of large mudwaves by turbidity currents on the levees of the Toyama deep-sea channel, Japan Sea   总被引：5，自引：0，他引：5  

Takeshi Nakajima  & Mikio Satoh 《Sedimentology》2001,48(2):435-463

The development of mudwaves on the levees of the modern Toyama deep‐sea channel has been studied using gravity core samples combined with 3·5‐kHz echosounder data and airgun seismic reflection profiles. The mudwaves have developed on the overbank flanks of a clockwise bend of the channel in the Yamato Basin, Japan Sea, and the mudwave field covers an area of 4000 km². Mudwave lengths range from 0·2 to 3·6 km and heights vary from 2 to 44 m, and the pattern of mudwave aggradation indicates an upslope migration direction. Sediment cores show that the mudwaves consist of an alternation of fine‐grained turbidites and hemipelagites whereas contourites are absent. Core samples demonstrate that the sedimentation rate ranged from 10 to 14 cm ka^?1 on the lee sides to 17–40 cm ka^?1 on the stoss sides. A layer‐by‐layer correlation of the deposits across the mudwaves shows that the individual turbidite beds are up to 20 times thicker on the stoss side than on the lee side, whereas hemipelagite thicknesses are uniform. This differential accretion of turbidites is thought to have resulted in the pattern of upcurrent climbing mudwave crests, which supports the notion that the mudwaves have been formed by spillover turbidity currents. The mudwaves are interpreted to have been instigated by pre‐existing large sand dunes that are up to 30 m thick and were created by high‐velocity (10°ms^?1), thick (c. 500 m) turbidity currents spilling over the channel banks at the time of the maximum uplift of the Northern Japan Alps during the latest Pliocene to Early Pleistocene. Draping of the dunes by the subsequent, lower‐velocity (10^?1ms^?1), mud‐laden turbidity currents is thought to have resulted in the formation of the accretionary mudwaves and the pattern of upflow climbing. The dune stoss slopes are argued to have acted as obstacles to the flow, causing localized loss of flow strength and leading to differential draping by the muddy turbidites, with greater accretion occurring on the stoss side than on the lee slope. The two overbank flanks of the clockwise channel bend show some interesting differences in mudwave development. The mudwaves have a mean height of 9·8 m on the outer‐bank levee and 6·2 m on the inner bank. The turbidites accreted on the stoss sides of the mudwaves are 4–6 times thicker on the outer‐bank levee than their counterparts on the inner‐bank levee. These differences are attributed to the greater flow volume (thickness) and sediment flux of the outer‐bank spillover flow due to the more intense stripping of the turbidity currents at the outer bank of the channel bend. Differential development of mudwave fields may therefore be a useful indicator in the reconstruction of deep‐sea channels and their flow hydraulics.  相似文献