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   

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   

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   

Long-term variability of shelf water intrusion and its influence on hydrographic and biogeochemical properties of the Seto Inland Sea, Japan   总被引：1，自引：0，他引：1  

Shiho Kobayashi  Tateki Fujiwara 《Journal of Oceanography》2008,64(4):595-603

The variability of the pathway of the Kuroshio is known to control that of the intensity of upwelling of the cold and nutrient-rich deep shelf water at the shelf-break point. This study has investigated the influences of the long-term variability of the hydrographical and biogeochemical conditions at the shelf-break point on those in the inner Seto Inland Sea. Results from observations conducted since 1972 by prefectural fisheries observatories showed a temporary decrease of temperature in the lower layer of the entrance of Kii Channel in summertime in the specific years when the Kuroshio pathway favored deep shelf water intrusion. A corresponding change in temperature was also found in the inner shelf sea, such as western Osaka Bay and Harima-Nada. The model developed in this study covers a 30-year period and well reproduces the temporal change in temperature. It also shows sufficient reproducibility in both seasonal behavior of hydrographical and biogeochemical properties and the inter-annual variability of hydrographical properties throughout the eastern Seto Inland Sea. It was found that the inter-annual variations of annual total flux through the section at the entrance to Kii Channel affect the inter-annual variation of the observed concentration of Dissolved Inorganic Nitrogen (DIN) in Harima Nada, but the effect was smaller than those of river input and other parameters.  相似文献   

Evaluation of spatial resolution and estimation error of seafloor displacement observation from vessel-based bathymetric survey by use of AUV-based bathymetric data     

Toshiya Fujiwara  Yuka Masaki  Fujio Yamamoto 《Marine Geophysical Researches》2015,36(1):45-60

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On the mechanism of catastrophic destruction of minor planets by high-velocity impact     

Akira Fujiwara 《Icarus》1980,41(3):356-364

For the study of the collisional breakup of minor planets, semiquantitative interpretations of the catastrophic destruction of cubic rock targets by high-velocity impact reported by A. Fujiwara, G. Kamimoto, and A. Tsukamoto (1977, Icarus31, 277–288) are attempted. The conditions for transition and core-type destruction are derived from consideration of the side surface spallation, or central spallation, and the back surface spallation caused by the rarefaction pulses. In the derivation, the strengths of the original P-pulse at the crater rim and the bottom are given by application of the failure criterion. As the condition for complete destruction, an empirical rule is proposed. It is found that the critical sizes for these destructions vary as E^0.40 and the previously reported $\text{E}\text{M}\text{-}\text{scaling}$ is only an approximate rule (E, impact energy; M, target mass). The possibilities of extending of these results to larger bodies of any other shape are discussed.  相似文献   

Real-time geophysical measurements on the deep seafloor usingsubmarine cable in the southern Kurile subduction zone     

Hirata  K. Aoyagi  M. Mikada  H. Kawaguchi  K. Kaiho  Y. Iwase  R. Morita  S. Fujisawa  I. Sugioka  H. Mitsuzawa  K. Suyehiro  K. Kinoshita  H. Fujiwara  N. 《Oceanic Engineering, IEEE Journal of》2002,27(2):170-181

A permanent real-time geophysical observatory using a submarine cable was developed and deployed to monitor seismicity, tsunamis, and other geophysical phenomena in the southern Kurile subduction zone. The geophysical observatory comprises six bottom sensor units, two branching units, a main electro-optical cable with a length of 240 km and two land stations. The bottom sensor units are: 1) three ocean bottom broadband seismometers with hydrophone; 2) two pressure gauges (PGs); 3) a cable end station with environmental measurement sensors. Real-time data from all the undersea sensors are transmitted through the main electro-optical cable to the land station. The geophysical observatory was installed on the continental slope of the southern Kurile trench, southeast Hokkaido, Japan in July 1999. Examples of observed data are presented. Sensor noises and resolution are mentioned for the ocean bottom broadband seismometers and the PGs, respectively. An adaptable observation system including very broadband seismometers is scheduled to be connected to the branching unit in late 2001. The real-time geophysical observatory is expected to greatly advance the understanding of geophysical phenomena in the southern Kurile subduction zone  相似文献   

Windowed f-k spectra of a three-dimensional wavefield excited by a point source in a two-dimensional multilayered elastic medium     

Hiroyuki Fujiwara 《Geophysical Journal International》1997,128(3):571-584

When full 3-D modelling is too costly or cumbersome, computations of 3-D elastic wave propagation in laterally heterogeneous, multilayered 2-D geological structures may enhance considerably our ability to predict strong ground motion for seismological and engineering purposes. Towards this goal, we extend the method based on the combination of the thin-layer finite-element and boundary-element methods (TLFE-BEM) and calculate windowend f - k spectra of the 3-D wavefield. The windowed f - k spectra are spatially localized spectra from which the local properties of the wavefield can be extracted. The TLFE-BEM is particularly suited for calculating the complete wavefield where surface waves are dominant in multilayered media. The computations are performed in the frequency domain, providing the f - k spectra directly. From the results for the 3-D wavefield excited by a point source in a 2-D multilayered, sloped structure, it can be said that the phase velocity of the fundamental-mode Rayleigh wave in a laterally heterogeneous multilayered medium, estimated from the windowed f - k spectra, varies with the location of the point source. For the model calculated in this article, the phase velocity varies between the value for the flat layered structure of the thick-layer side and that for the structure just under the centre of the window. The exact subsurface structure just under the centre of an array in a laterally heterogeneous medium cannot be obtained if we use the f - k spectral analysis assuming a flat layered structure.  相似文献   

Fortnightly shifts of intrusion depth of oceanic water into Ise Bay     

Akihide?KasaiEmail author  Tateki?Fujiwara  Takuma?Kimura  Hirokatsu?Yamada 《Journal of Oceanography》2004,60(5):817-824

To clarify the time change in water exchanges between Ise Bay and the adjacent ocean, repeated hydrographic observations were conducted along the longitudinal section in Ise Bay. The results show that the mixing condition at the bay mouth (Irago Strait) changed fortnightly in summer. During the spring tides, the strait water below the pycnocline was well-mixed and nearly homogeneous. By contrast, it was weakly stratified during the neap tide. There is a strong negative correlation between the tidal range and the density difference between the upper and lower layers at the strait. In summer, the intrusion depth of oceanic water into the bay and consequent hydrographic conditions inside the bay changed frequently according to the tidal strength. During the spring tides a prominent bottom front was created at the bay mouth, indicating that the strait water, which is a mixture of oceanic and bay waters, intruded through the middle layer. On the other hand, during the neaps, cold and saline oceanic water intruded through the bottom layer into the bay. The intrusion depth is significantly correlated with the tidal range. It is considered that the wellmixed strait water, which has a density equivalent to the middle layer inside the bay, is lighter than the bottom bay water and thus intrudes through the middle layer during the spring tides, while insufficient mixing makes the bottom water at the strait heavier than the bay water, leading to the bottom intrusion during the neap tides.  相似文献   

Temporal variation of the partial pressure of CO2 in surface seawater of Iyo Nada in the Seto Inland Sea,Japan     

Yu-ichiro Kumamoto  Kitao Fujiwara  Hiroyuki Tsubota 《Journal of Oceanography》1995,51(6):681-697

The temporal variation of the partial pressure of carbon dioxide in surface seawater of Iyo Nada in the western Seto Inland Sea was measured by infrared absorption of carbon dioxide (CO₂) in air equilibrated with seawater. The variation of from January to late May in 1994 was relatively small (from 270 to 340 atm). on the contrary, the measured in September 1993 ranged from 200 to 450 atm. It seems that the relative high observed in the north and the south of Iyo Nada in September were caused by destruction of a stratification owing to tidal currents at straits between Hiroshima Bay and Iyo Nada and Hayasui Straits, respectively. The low observed in the central Iyo Nada in September was ascribed to a tidal front where high concentrations of chlorophyll-a and a relation between and chlorophyll-a in negative sense were found. Except the observation in the north of Iyo Nada in September, the in the surface seawater of Iyo Nada were lowe than the atmospheric (about 367 atm). The results obtained by this work and Kimotoet al. (1993) lead to the conclusion that Iyo Nada acts as a sink of the atmospheric CO₂ on the average.  相似文献