Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula,Japan     

Makoto Ito  Kazuaki Ishikawa  Naohisa Nishida 《Sedimentology》2014,61(7):2042-2062

The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.  相似文献   

Rapid Alkalization in Lake Inawashiro, Fukushima, Japan: Implications for Future Changes in the Carbonate System of Terrestrial Waters     

Takuya Manaka  Hiroyuki Ushie  Daisuke Araoka  Akihiko Inamura  Atsushi Suzuki  Hodaka Kawahata 《Aquatic Geochemistry》2013,19(4):281-302

The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO₂ exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO₂ had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO₂ exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land.  相似文献   

Characteristics of evapotranspiration from a permafrost black spruce forest in interior Alaska   总被引：1，自引：1，他引：0  

Taro Nakai  Yongwon Kim  Robert C. Busey  Rikie Suzuki  Shin Nagai  Hideki Kobayashi  Hotaek Park  Konosuke Sugiura  Akihiko Ito 《Polar Science》2013,7(2):136-148

Here, the year 2011 characteristics of evapotranspiration and the energy budget of a black spruce forest underlain by permafrost in interior Alaska were explored. Energy balance was nearly closed during summer, and the mean value of the daily energy balance ratio (the ratio of turbulent energy fluxes to available energy) from June to August was 1.00, though a large energy balance deficit was observed in the spring. Such a deficit was explained partly by the energy consumed by snowmelt. Ground heat flux played an important role in the energy balance, explaining 26.5% of net radiation during summer. The mean daily evapotranspiration of this forest during summer was 1.37 mm day^?1 – considered typical for boreal forests. The annual evapotranspiration and sublimation yielded 207.3 mm year^?1, a value much smaller than the annual precipitation. Sublimation accounted for 8.8% (18.2 mm year^?1) of the annual evapotranspiration and sublimation; thus, the sublimation is not negligible in the annual water balance in boreal forests. The daytime average decoupling coefficient was very small, and the mean value was 0.05 during summer. Thus, evapotranspiration from this forest was mostly explained by the component from the dryness of the air, resulting from the aerodynamically rough surface of this forest.  相似文献   

Dynamic analysis of ground with rigorous use of strain dependency and its application to seismic microzonation of alluvial plane   总被引：1，自引：1，他引：0  

Takaharu Ito  Ikuo Towhata 《Natural Hazards》2012,64(2):1079-1104

Seismic microzonation is one of the most important measures to mitigate earthquake hazards in urban areas. Because the ground motion varies significantly with the subsurface geology, it is needed for microzonation to account as much as possible for the local soil conditions. Noteworthy is that nonlinear deformation properties of soil play essential roles in amplification of strong ground motion. It is desired furthermore to focus on the expected damage extent in addition to the calculated maximum acceleration and/or velocity. The present study first developed a computer code for one-dimensional response analysis of ground that reasonably takes into account nonlinear dynamic soil properties. Second, correlations between the calculated ground motion and damage extent were obtained by examining seismic damages during the past earthquakes. By combining these two issues, seismic microzonation was carried out, and detailed damage distribution was assessed. The product of this study covers not only the damage caused by ground shaking but also liquefaction problem and lifeline damage.  相似文献   

Structural changes of synthetic opal by heat treatment   总被引：1，自引：0，他引：1  

Akane Arasuna  Masayuki Okuno  Hiroki Okudera  Tomoyuki Mizukami  Shoji Arai  Shin’ichi Katayama  Mikio Koyano  Nobuaki Ito 《Physics and Chemistry of Minerals》2013,40(9):747-755

The structural changes of synthetic opal by heat treatment up to 1,400 °C were investigated using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared and Raman spectroscopies. The results indicate that the dehydration and condensation of silanol in opal are very important factors in the structural evolution of heat-treated synthetic opal. Synthetic opal releases water molecules and silanols by heat treatment up to 400 °C, where the dehydration of silanol may lead to the condensation of a new Si–O–Si network comprising a four-membered ring structure of SiO₄ tetrahedra, even at 400 °C. Above 600 °C, water molecules are lost and the opal surface and internal silanol molecules are completely dehydrated by heat effect, and the medium-temperature range structure of opal may begin to thermally reconstruct to six-membered rings of SiO₄ tetrahedra. Above 1,000 °C, the opal structure almost approaches that of silica glass with an average structure of six-membered rings. Above 1,200 °C, the opal changes to low-cristobalite; however, minor evidence of low-tridymite stacking was evident after heat treatment at 1,400 °C.  相似文献   

Geologic Core Holder with a CFR PEEK Body for the X-ray CT-Based Numerical Analysis of Fracture Flow Under Confining Pressure   总被引：1，自引：0，他引：1  

Noriaki Watanabe  Takuya Ishibashi  Noriyoshi Tsuchiya  Yutaka Ohsaki  Tetsuya Tamagawa  Yoshihiro Tsuchiya  Hiroshi Okabe  Hisao Ito 《Rock Mechanics and Rock Engineering》2013,46(2):413-418

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Age, geology, geophysics, and geochemistry of Mahukona Volcano, Hawai`i     

Michael O. Garcia  Diane Hanano  Ashton Flinders  Dominique Weis  Garrett Ito  Mark D. Kurz 《Bulletin of Volcanology》2012,74(6):1445-1463

The size, shape, and magmatic history of the most recently discovered shield volcano in the Hawaiian Islands, Mahukona, have been controversial. Mahukona corresponds to what was thought to be a gap in the paired sequence (Loa and Kea trends) of younger Hawaiian volcanoes (<4?Ma). Here, we present the results of marine expeditions to Mahukona where new bathymetry, sidescan sonar, gravity data, and lava samples were collected to address these controversies. Modeling of bathymetric and gravity data indicate that Mahukona is one of the smallest Hawaiian volcanoes (～6,000?km³) and that its magmatic system was not focused in a long-lived central reservoir like most other Hawaiian volcanoes. This lack of a long-lived magmatic reservoir is reflected by the absence of a central residual gravity high and the random distribution of cones on Mahukona Volcano. Our reconstructed subsidence history for Mahukona suggests it grew to at least ～270?m below sea level but probably did not form an island. New ⁴⁰Ar–³⁹Ar plateau ages range from 350 to 654?ka providing temporal constraints for Mahukona’s post-shield and shield stages of volcanism, which ended prematurely. Mahukona post-shield lavas have high ³He/⁴He ratios (16–21?Ra), which have not been observed in post-shield lavas from other Hawaiian volcanoes. Lava compositions range widely at Mahukona, including Pb isotopic values that straddle the boundary between Kea and Loa sequences of volcanoes. The compositional diversity of Mahukona lavas may be related to its relatively small size (less extensive melting) and the absence of a central magma reservoir where magmas would have been homogenized.  相似文献   

Potential of Oil Palm Trunk Sap as a Novel Inexpensive Renewable Carbon Feedstock for Polyhydroxyalkanoate Biosynthesis and as a Bacterial Growth Medium     

Bhadravathi Eswara Lokesh  Zubaidah Aimi Abdul Hamid  Takamitsu Arai  Akihiko Kosugi  Yoshinori Murata  Rokiah Hashim  Othman Sulaiman  Yutaka Mori  Kumar Sudesh 《洁净——土壤、空气、水》2012,40(3):310-317

Utilization of cheap renewable carbon feedstock for polyhydroxyalkanoate (PHA) production not only brings down its production cost but also ensures sustainability. The scope of this study was to evaluate the potential of sap extracted from felled oil palm trunk (OPT) as a novel inexpensive renewable carbon source for PHA production. OPT sap was found to be nutritionally rich and contained various fermentable sugars (5.5% w/v) as its major constituent. Termite gut isolate, Bacillus megaterium MC1 grew profoundly in mineral medium with OPT sap as carbon source and a cell density of 10.9 g/L was attained after 16 h of cultivation in shake flask cultures. A maximum poly‐3‐hydroxybutyrate [P(3HB)] content (% cell dry weight; CDW) of 30 wt% and a P(3HB) concentration of 3.28 g/L was recorded. Additionally, OPT sap extracted from younger tree trunks with prolonged storage had higher sugar content (10.8% w/v) and, when used as a growth medium without the addition of any nutrients, supported bacterial growth comparable to commercially available media.  相似文献   

Production of P(3HB‐co‐3HHx) with Controlled Compositions by Recombinant Cupriavidus necator Re2058/pCB113 from Renewable Resources          下载免费PDF全文

Paramasivam Murugan  Pragya Chhajer  Akihiko Kosugi  Takamitsu Arai  Christopher J. Brigham  Kumar Sudesh 《洁净——土壤、空气、水》2016,44(9):1234-1241

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Availability of an equation to evaluate error by optical path discretization in radiative transfer computation based on the successive order of scattering method   总被引：1，自引：0，他引：1  

Akihiko Tanaka  Masahiko Fujii  Tomohiko Oishi 《Journal of Oceanography》2012,68(1):215-218

The availability of an equation to evaluate the influence of multiple scattering in the single scattering process corresponding to a layer of arbitrary optical thickness was established. In order to confirm the validity of this equation, the radiance distribution in this layer was computed using a plane–parallel layer model based on the successive order of scattering method. The relative errors in a radiance distribution computed were evaluated as a function of optical thickness by the derived equation. It was shown that this equation provides a theoretical background for determining layer thickness using the plane–parallel layer model.  相似文献