3-D internal architecture of methane hydrate-bearing turbidite channels in the eastern Nankai Trough, Japan     

Satoshi Noguchi  Naoyuki Shimoda  Osamu Takano  Nobutaka Oikawa  Takao Inamori  Tatsuo Saeki  Tetsuya Fujii 《Marine and Petroleum Geology》2011,28(10):1817-1828

The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels.  相似文献   

Importance of intracellular Fe pools on growth of marine diatoms by using unialgal cultures and on the Oyashio region phytoplankton community during spring     

Koji Sugie  Kenshi Kuma  Satoshi Fujita  Satomi Ushizaka  Koji Suzuki  Tsutomu Ikeda 《Journal of Oceanography》2011,67(2):183-196

We report on the ability for luxury Fe uptake and the potential for growth utilizing intracellular Fe pools for 4 coastal centric diatom isolates and in situ phytoplankton assemblages, mainly composed of diatoms. Iron uptake of the diatom isolates and natural phytoplankton assemblages in the Oyashio region during spring blooms were prevented by adding hydroxamate siderophore desferrioxamine B (DFB). After the addition of DFB, intracellular Fe in the diatom isolates supported 2.4–4.2 cell divisions with 1.2–2.6 Chl a doublings. The intracellular Fe was primarily used for cell generation rather than Chl a production, leading to a reduction in the Chl a cell quota in the Fe-starved cells with time. The metabolic properties of the Fe-starved cells with their cell morphologies were different among species or genera. An on-deck incubation experiment also exhibited 1.9 cell divisions and 0.81 Chl a doublings of phytoplankton after the addition of DFB, also indicating the preference of cell generation over Chl a production. A decrease in the level of cellular Chl a, a main light-harvesting pigment in Fe-starved diatoms, may become a superior survival strategy to protect the cells from high irradiance that can cause photo-oxidative damages through photosynthesis. Such relatively low-Fe with high-light conditions could often occur in surface waters of the Oyashio region from spring to summer.  相似文献   

Breaking pattern and critical breaking condition of Japanese pine trees on coastal sand dunes in huge tsunami caused by Great East Japan Earthquake     

Norio Tanaka  Junji Yagisawa  Satoshi Yasuda 《Natural Hazards》2013,65(1):423-442

Coastal vegetation is widely recognized to reduce tsunami damage to people and buildings, and it has been studied recently because it requires relatively little capital investment compared with artificial measures, provides human-friendly beach fronts, and enhances inter-relationships with other ecological systems. However, the tsunami caused by the Great East Japan Earthquake at 14:46 JST on March 11, 2011, with a magnitude of 9.0 and epicenter 129?km east of Sendai, broke most of the sea wall (tsunami gates, large embankments) and caused catastrophic damage to coastal forests in the Tohoku and Kanto districts of Japan. A field survey was conducted to elucidate the critical breaking condition of Japanese coastal pine trees. Tree-trunk breakage was observed when the sea embankment was washed out or when there was no sea embankment and the tree was under strong inertia force or impact force by debris. Even though the trunk bending and breaking phenomena are different, statistical analysis showed that the critical diameters for trunk bending and trunk breaking were not very different. The overturning phenomenon is a little more complex than trunk breaking because the resistive force is a function of the substrate and root anchorage. An equation to determine the critical diameters for trunk bending, trunk breaking, and overturning was derived as a function of tsunami water depth, soil-root strength, and the hydrodynamic parameter (H _D ) formulated by Froude number, drag coefficient, and the ratio of impact force to drag force considering the physical mechanisms to resist the tsunami. Trunk bending and breaking were closely related to tsunami water depth and the hydrodynamic parameter (H _D ), but tree overturning was found to be more site specific, and the root-soil strength greatly affected the critical value. The proposed critical diameter equation and its coefficient are useful for the design of an inland forest of pine trees that can trap large trees, cars, debris, etc., to its breaking limit. The trapping function should be utilized more in the future designs of inland forests, if possible, on embankments.  相似文献   

Suspended matter in surface waters of the eastern Gulf of Guinea     

Brian D. Bornhold  Jean R. Mascle  Kenichi Harada 《Marine Geology》1973,14(4):M21-M31

Suspended matter in the surface waters of the eastern Gulf of Guinea was studied in relation to the prevailing oceanic currents and the sediment composition and source. A confused current system arises from the confluence of the Guinea Current and the South Equatorial Current in this area. Sediment-laden water is transported to the south of Fernando Póo into the Gulf in a south-westerly direction. The southeasterly flowing Guinea Current along the western edge of the Niger delta and the enormous sediment loads of the distributaries in this area contribute to a major lobe of suspended matter off the southwestern nose of the delta. Sediment concentration is inversely related to salinity in the northeastern Gulf. Sediment is also swept northwestward from the continental shelf of Gabon and the Congo Republic into the Gulf. Diatoms are the most abundant constituents with lesser amounts of organic aggregates and two varieties of fecal pellets.  相似文献   

Origin of the difference in the distribution behavior of tellurium and selenium in a soil-water system   总被引：4，自引：0，他引：4  

Teppei Harada 《Geochimica et cosmochimica acta》2008,72(5):1281-1294

The distribution behavior of tellurium (Te) between soil and water in a synthetic soil-water system was studied coupled with the speciation of Te both in soil and water phases by using X-ray absorption fine structure (XAFS) spectroscopy and a high-performance liquid chromatography connected to an ICP-MS (HPLC-ICP-MS), respectively. The results were compared with a similar data set for Se, which was simultaneously obtained in this study. The oxidation states and host phases of Te and Se in the soil samples were given by XAFS, while the oxidation states in water were given by HPLC-ICP-MS. It was found that both Te and Se in soil are mainly associated with Fe(III) hydroxides under oxic conditions. From the EXAFS analyses, the outer-sphere complex is important for the Se(VI) sorbed on Fe(III) hydroxides in soils, while Se(IV), Te(IV), and Te(VI) form inner-sphere complexes. Under reducing condition, it was found that Te(0) and Se(0) species were formed and that Se was more readily reduced to Se(0) than Te, as is predicted from their Eh-pH diagrams. The reduction process from hexavalent to zerovalent species was different between Se and Te, that is, the direct reduction from Se(VI) to Se(0) was observed for Se, while Te was reduced stepwise from Te(VI) to Te(0) via Te(IV). In terms of the distribution between soil and water, Se distribution to water was much higher than that of Te under wide redox conditions. For Se, selenate is the predominant species in water even under reducing condition due to the much higher solubility of Se(VI) than Se(IV). Furthermore, a much smaller distribution of Te in water was primarily due to the larger affinities of Te(IV) and Te(VI) to Fe(III) hydroxides than Se(VI), which originates from the formation of the inner-sphere complexes of Te(IV) and Te(VI) to Fe(III) hydroxides.  相似文献   

Influences of channelization on discharge of suspended sediment and wetland vegetation in Kushiro Marsh, northern Japan     

Futoshi Nakamura  Tadashi Sudo  Satoshi Kameyama  Mieko Jitsu 《Geomorphology》1997,18(3-4)

The effects of wetlands on hydrology, water quality, and wildlife habitat are internationally recognized. Protecting the remaining wetlands is one of the most important environmental issues in many countries. However wetlands in Japan have been gradually shrinking due to agricultural development and urbanization, which generally lowers the groundwater level and introduces suspended sediment and sediment-associated nutrients into wetlands. We examined the influences of channelization on discharge of suspended sediment and wetland vegetation in Hokkaido, northern Japan. The impact of river channelization was confirmed not only by the sediment budgets but also by river aggradation or degradation after the channelization and by the resultant vegetational changes. The budgets of suspended sediment demonstrated that wash load was the predominant component accounting for 95% of the total suspended load delivered into the wetland. This suspended sediment was primarily transported into the wetland by flooding associated with heavy rainfall. Twenty-three percent of the wash load and 63% of the suspended bed material load were deposited in the channelized reach, which produced aggradation of about 2 m at the end of the reach. A shorting of the length of the channel, due to channelization of a meandering river, steepened the slope and enhanced the stream power to transport sediment. This steepening shifted the depositional zones of fine sediment 5 km downstream and aggraded the riverbed. Development of the watershed may increase not only the water discharge but also the amount of suspended sediments. The aggradation reduced the carrying capacity of the channel and caused sediment ladened water to flood over the wetlands. The fine sediment accumulated on the wetlands gradually altered the edaphic conditions and wetland vegetation. A low percentage (10 to 15%) of organic contents of wetlands' soil is more evidence indicating that the present condition is far different from normal. Original vegetation such as sedges and Alnus japonica were disappearing from the adjacent areas of the river channel and were being replaced by willow trees (Salix spp.).  相似文献   

High thallium content in Kuroko-type ore     

Satoshi Murao  Shiro Itoh 《Journal of Geochemical Exploration》1992,43(3)

Tl, Ga and Ge contents of Kuroko and other types of ore deposits were analysed semiquantitatively and quantitatively. The results show that Tl content is extremely high in Kuroko-type deposits compared to other types of mineralization. The T1 content is especially high in yellow ore and pyrite crystals; thus this element is considered to be incorporated in pyrite.  相似文献   

Case study of debris flow disaster scenario caused by torrential rain on Kiyomizu-dera,Kyoto, Japan - using Hyper KANAKO system     

Kana?NakataniEmail author  Satoshi?Hayami  Yoshifumi?Satofuka  Takahisa?Mizuyama 《山地科学学报》2016,13(2):193-202

This paper presents debris-flow numerical simulations using the Hyper KANAKO system, developed by the authors. The system uses the debris flow simulator KANAKO 2D equipped with a graphical user interface (GUI); hence, a user can easily produce appropriate landform data for simulations using standard laser profiler data, and visualize the results using a GIS. Hyper KANAKO was applied to the streams around Kiyomizu-dera in Kyoto, Japan. Kiyomizu-dera is a famous temple in Japan which is visited by numerous tourists throughout the year. We simulated a disaster scenario of debris flow caused by torrential rain. We set the hydrograph using rainfall intensity data, and set the landform data using information from the Geospatial Information Authority of Japan (GSI) and a digital elevation model (DEM). We evaluated different mesh sizes and also used a digital surface model (DSM) to consider the building heights. The simulation results showed that with small mesh size, the debris flow moved through the roads, which seems realistic for a disaster situation. When buildings were considered, the flow direction changed, and a 1-m flow depth, which was deeper than in other cases, appeared in the flow path. This may pose a dangerous situation for evacuations.  相似文献   

Age determination of marine sediments in the western North Pacific by as partic acid chronology     

Naomi Harada  Nobuhiko Handa  Tadamichi Oba  Hiromi Matsuoka  Katsunori Kimoto  Masashi Kusakabe 《Journal of Oceanography》1997,53(1):1-7

The ages of fossil planktonic foraminifera,Pulleniatina obliquiloculata, in sediments (core 3bPC) from the western North Pacific were determined by aspartic acid chronology, which uses the racemization reaction rate constant of aspartic acid (k_Asp). Aspartic acid racemization-based ages (Asp ages) ranged from 7,600 yrBP at the surface, to 307,000 yrBP at a depth of 352.9 cm in the sediments. This sediment core was also dated by the glacial-interglacial fluctuation of δ¹⁸O chronology, and the ages determined by both chronologies were compared. The ages derived from aspartic acid chronology and δ¹⁸O stratigraphy were more or less consistent, but there appeared to be some differences in age estimates between these two dating methods at some depths within the core. In the core top sediments, the likely cause for the age discrepancy could be the loss of the surface sediment during sampling of the core. At depths of 66.3 and 139 cm within the core, Asp ages indicated reduced sedimentation rates duringca. 60,000-80,000 yrBP andca. 140,000–190,000 yrBP. The maximum age differences in both chronologies are 33,000 yr and 46,600 yr during each of these periods. These anomalous reductions in sedimentation rates occurring during these periods could possibly be related to some geological events, such as an increased dissolution effect of the calcium carbonate in the western North Pacific. Another possible reason for these age differences could be the unreliability in δ¹⁸O ages of core 3bPC as they were estimated by δ¹⁸O ages of another core, 3aPC.  相似文献   

Simultaneous vertical measurements of in situ pH and CO2 in the sea using spectrophotometric profilers     

Yoshiyuki Nakano  Hideshi Kimoto  Shuichi Watanabe  Koh Harada  Yutaka W. Watanabe 《Journal of Oceanography》2006,62(1):71-81

We have developed new systems capable of profiling to >1000 m for measuring in situ pH and fugacity of CO₂ (fCO₂) in the ocean using spectrophotometric analysis (pH and CO₂ profilers). The in situ pH is determined by detecting the color change of the pH indicator (m-cresol purple). It can withstand ambient pressure to 1000 m depth. The CO₂ profiler analyzed in situ fCO₂ by detecting the change of pH in an inner solution, equilibrated with the seawater through a gas permeable membrane. It can be operated to 2500 m depth. We used an amorphous fluoropolymer tubing form of AF-2400 for the gas permeable membrane due to its high gas permeability coefficients. The inner solution was a mixture of 2 μM bromocresol purple (BCP) and 5 μM sodium hydroxide. This system gave us a response time of 1 minute, which is twice as fast as previous systems. The precisions of pH and CO₂ profilers were within 0.002 and 2.5% respectively. We have used these profilers to study the North Pacific, obtaining good agreement with the difference between the data from profilers and a discrete bottle of 0.002 ± 0.005 pH (SE, n = 25) and −0.4 ± 3 μatm (SE, n = 31).  相似文献