Bedforms produced by the Kuroshio Current passing over the northern Izu Ridge     

Yu'suke?KuboEmail author  Wonn?Soh  Hideaki?Machiyama  Hidekazu?Tokuyama 《Geo-Marine Letters》2004,24(1):1-7

Current-generated bedforms were found on sandy seafloor at water depths of 200–400 m on the northern Izu Ridge, where the Kuroshio Current encounters and passes over the ridge. The observed bedforms include large dunes and sand ribbons and are interpreted to be products of present-day oceanographic conditions and to indicate intensive flow activity controlled by local topography. A comparison between the surface flow velocity estimated from empirical relationships for dune formation and the observed flow velocity suggests that the dunes are generated when the main axis of the meandering Kuroshio Current passes through this area, and that subsequent current velocities are sufficiently high to maintain the dunes up to the next event.  相似文献   

Three-year investigations into sperm whale-fall ecosystems in Japan   总被引：2，自引：0，他引：2  

Yoshihiro Fujiwara  Masaru Kawato  Tomoko Yamamoto  Toshiro Yamanaka  Waka Sato-Okoshi  Chikayo Noda  Shinji Tsuchida  Tomoyuki Komai  Sherine Sonia Cubelio  Takenori Sasaki  Karen Jacobsen  Kaoru Kubokawa  Katsunori Fujikura  Tadashi Maruyama  Yasuo Furushima  Kenji Okoshi  Hiroshi Miyake  Masayuki Miyazaki  Yuichi Nogi  Akiko Yatabe  & Takashi Okutani 《Marine Ecology》2007,28(1):219-232

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.  相似文献   

Geomorphology, sedimentary processes and development of the Zenisu deep-sea channel, northern Philippine Sea     

Shiguo Wu  Narumi Takahashi  Hidekazu Tokuyama  How Kin Wong 《Geo-Marine Letters》2005,25(4):230-240

The Zenisu deep-sea channel originates on the Izu-Ogasawara island arc, and disappears in the Shikoku Basin of the Philippine Sea. The geomorphology, sedimentary processes, and the development of the Zenisu deep-sea channel were investigated on the basis of swath bathymetry, side-scan sonar imagery, submersible observations, and seismic data. The deep-sea channel can be divided into three segments according to the downslope gradient and channel orientation. They are the Zenisu Canyon, the E–W fan channel, and the trough-axis channel. The sediment fill is characterized by turbidite and debrite deposition and blocky–hummocky avalanche deposits on the flanks of the Zenisu Ridge. In the Zenisu Canyon and the Zenisu deep-sea channel, sediment transport by turbidity currents generates sediment waves (dunes) observed during the Shinkai 6500 dive 371. The development of the Zenisu Canyon is controlled by a N–S shear fault, whereas the trough-axis channel is controlled by basin subsidence associated with the Zenisu Ridge. The E–W fan channel was probably affected by the E–W fault and the basement morphology.  相似文献   

Prediction of slope water intrusion into the Kii channel in summer     

Toshinori Takashi  Tateki Fujiwara  Toshiaki Sumitomo  Wataru Sakamoto 《Journal of Oceanography》2006,62(1):105-113

Intrusions of the warm, oligotrophic surface slope water (SSW) and the cold, nutrient-rich bottom slope water (BSW) from the continental slope influence the annual variations in water temperature and nutrient concentrations in the Kii Channel in August. In order to evaluate the relationships between both these intrusions and the distance of the Kuroshio axis from Cape Shionomisaki (Kuroshio distance), a Distance-Intrusion-Diagram (DID) for temperature, which can reproduce the vertical temperature profile of the channel, was constructed by analyzing the temperature and Kuroshio distance records in August for 1967–2001. DIDs for nutrients (nitrate and phosphate) are also constructed by using the relationship between the nutrient concentration and water temperature. The only explanatory variable in the DIDs is the Kuroshio distance. The DID for temperature predicts that the SSW occupies almost the entire water column when the Kuroshio approaches Cape Shionomisaki (Kuroshio distance = 18.5 km). When the Kuroshio distance lies in the range 18.5–74 km, the BSW thickness increases proportionally to the Kuroshio distance increment while the SSW thickness decreases. The BSW occupies the largest portion of the channel when the Kuroshio distance is 74 km. Further, beyond 74 km, the BSW thickness reduces gradually. Yearly variations in the temperature and concentrations of nitrate and phosphate were hindcast with the DIDs. The results revealed that the Kuroshio distance contributes 70%, 35%, and 30% of the variances in temperature, nitrate concentration, and phosphate concentration, respectively.  相似文献   

Structure of the strong tidal jet in the naruto strait     

Yoshio Takasugi  Tateki Fujiwara  Takehiko Higo 《Journal of Oceanography》1990,46(3):69-83

In order to clarify the structure of the strong tidal current at the Naruto Strait in the Seto Inland Sea of Japan, the sea-level values were observed in the strait and the current measurements were made with an Acoustic Doppler Current Profiler (ADCP).The tidal volume transports for M₂ and S₂ tides were about 74×10³ and 26×10³ m³ sec^–1, respectively. The horizontal profile of the velocity at the phase of the strong tidal current compares favorably with a theoretical profile of the two-dimensional steady turbulent jet except for the side parts of the profile. Moreover, the entrainment rate of the surrounding water into the strong tidal jet was estimated from the difference of mass flux between two cross-sections at the strait, the entrainment rate and entrainment constant for both the northward and southward flows being about 1.3–2.5×10^–4m^–1 and about 0.03–0.05, respectively.  相似文献   

Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3     

Kazuo Kobayashi  Jean-Paul Cadet  Jean Aubouin  Jacques Boulgue  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kin-ichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2–4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V “Jean Charcot” as a part of the Kaiko I cruise, Leg 3, in July–August 1984 under the auspices of the French-Japanese scientific cooperative program.  相似文献   

Microcracks induced in granite spheres by projectile impact at velocities ranging from 2.3 to 3.6 km/s     

S. Kawakami  Y. Kanaori  A. Fujiwara 《Rock Mechanics and Rock Engineering》1990,23(1):39-51

Summary Projectiles were impacted against granite spheres having a diameter of 15 cm at velocities ranging from 2.3 to 3.6 km/s. One target was fractured into a large core fragment and many shell-like fragments. Major cracks which divide the core fragment and many small shell-like fragments were formed along the caustic surface of the reflected shock waves that originated on the target surface. The shape of the caustic surfaces formed in spherical targets is called a cardioid. The other targets suffered impact cratering. They exhibit planar craters with no consicuous raised rim or depression. Microcrack distributions and microscopic effects of impact loading were observed on these targets. The site of extension fractures corresponds to grain boundaries, cleavage planes of biotite and feldspars, and along pre-existing microcracks. Kink bands of biotite were formed at the restricted regions beneath the center of the craters.  相似文献   

Tsunami ascending in rivers as an undular bore     

Yoshinobu Tsuji  Takashi Yanuma  Isao Murata  Chizuru Fujiwara 《Natural Hazards》1991,4(2-3):257-266

At time of the 1983 Japan Sea tsunami, waves in the form of a bore ascended many rivers. In some cases, bores had the form of one initial wave with a train of smaller waves, and in other cases, such a wave train did not appear and only a step with a flat water surface behind was observed. In the present study, it is clarified that both undular-type and nonundular-type bores can be recognized as solutions of the KdV-Burger's equation which was introduced by Johnson in 1972. Numerically obtained analytical solutions and results of laboratory experiments are compared.  相似文献   

Destruction of basaltic bodies by high-velocity impact     

Akira Fujiwara  Goro Kamimoto  Akimasa Tsukamoto 《Icarus》1977,31(2):277-288

As a simulation of collisional processes among solid bodies of various sizes in the solar system, polycarbonate projectiles of mass 0.37 g were impacted against cubic basaltic rocks of about 2 to 10 cm and larger with a velocity of 2.6 km/sec. The corresponding energy imparted per unit mass of target ranges from about 10⁶ to 10⁹ ergs/g. The phenomena are classified into four categories with increasing target size: (1) complete destruction, (2) remaining core, (3) transition region, and (4) crater formation. Empirical formulas for the cumulative mass of the fragments and the mass of the maximum fragment are given. The similarity of these formulas is briefly discussed. The experimental results are applied to the examination of the hypothesis that a single Martian satellite was once ruptured by impact, leaving the present two satellites. It is suggested that the radius of the parent satellite was larger than about 30 km.  相似文献   

Short‐term microscale topographic changes of coastal bedrock on shore platforms     

Wayne J. Stephenson  Anna J. Taylor  Maree A. Hemmingsen  Hidekazu Tsujimoto  Robert M. Kirk 《地球表面变化过程与地形》2004,29(13):1663-1673

We report a series of short‐term (diurnal) rock surface monitoring studies on inter‐ and supra‐tidal shore platforms using a traversing micro‐erosion meter at two sites, Kaikoura Peninsula, New Zealand, and Apollo Bay, Victoria, Australia. Statistically signi?cant day‐to‐day changes were measured. Surface rise and lowering occurred at rates above instrument error, with a maximum range of 3·378 mm between 1·697 mm (lowering) and ‐1·681 mm (rise). Individual measurements showed rises greater than 2 mm. These daily variations reveal that surface lowering and rise occur at a much shorter time scale than previously reported from other studies. The patterns observed suggest wetting and drying is the most likely process causing surface changes at these temporal scales. We argue that traversing micro‐erosion meter studies operating at a short‐term time scale of day‐to‐day provide meaningful results that open new opportunities for studying rock weathering and erosion in a coastal environment. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献