A precise bathymetric map of the world’s deepest seafloor,Challenger Deep in the Mariana Trench   总被引：2，自引：0，他引：2  

Masao Nakanishi  Jun Hashimoto 《Marine Geophysical Researches》2011,32(4):455-463

Data from three bathymetric surveys by R/V Kairei using a 12-kHz multibeam echosounder and differential GPS were used to create an improved topographic model of the Challenger Deep in the southwestern part of the Mariana Trench, which is known as the deepest seafloor in the world. The strike of most of the elongated structures related to plate bending accompanied by subduction of the Pacific plate is N70°E and is not parallel to the trench axis. The bending-related structures were formed by reactivation of seafloor spreading fabric. Challenger Deep consists of three en echelon depressions along the trench axis, each of which is 6–10 km long, about 2 km wide, and deeper than 10,850 m. The eastern depression is the deepest, with a depth of 10,920 ± 5 m.  相似文献   

Active spreading and hydrothermalism in North Fiji Basin (SW Pacific). Results of Japanese French Cruise Kaiyo 87     

Jean-Marie Auzende  Eiichi Honza  Xavier Boespflug  Satendra Deo  Jean-Philippe Eissen  Jun Hashimoto  Philippe Huchon  Junichiro Ishibashi  Yo Iwabuchi  Philip Jarvis  Masato Joshima  Kiyoyuki Kisimoto  Yasuto Kuwahara  Yves Lafoy  Tsuyoshi Matsumoto  Jean-Pierre Maze  Kiyohiko Mitsuzawa  Hiroyasu Monma  Takeshi Naganuma  Yukihiro Nojiri  Suguru Ohta  Kiyoshi Otsuka  Yoshihisa Okuda  Hélène Ondreas  Akira Otsuki  Etienne Ruellan  Myriam Sibuet  Manabu Tanahashi  Takeo Tanaka  Tetsuro Urabe 《Marine Geophysical Researches》1990,12(4):269-283

The aim of the Japanese-French Kaiyo 87 cruise was the study of the spreading axis in the North Fiji Basin (SW Pacific). A Seabeam and geophysical survey allowed us to define the detailed structure of the active NS spreading axis between 16° and 22° S and its relationships with the left lateral motion of the North Fiji Fracture Zone. Between 21° S and 18°10′ S, the spreading axis trends NS. From 18°10 S to 16°40 S the orientation of the spreading axis changes from NS to 015°. North of 16°40′ S the spreading axis trends 160°. These two 015° and 160° branches converge with the left lateral North Fiji fracture zone around 16°40′ S to define an RRFZ triple junction. Water sampling, dredging and photo TV deep towing give new information concerning the hydrothermal activity along the spreading axis. The discovery of hydrothermal deposits associated with living communities confirms this activity.  相似文献   

Life habit of vesicomyid clam,Calyptogena soyoae,and hydrogen sulfide concentration in interstitial waters in Sagami Bay,Japan     

Jun Hashimoto  Suguru Ohta  Katsunori Fujikura  Yoshihiro Fujiwara  Shunji Sukizaki 《Journal of Oceanography》1995,51(3):341-350

In and around the beds of vesicomyid clam (Calytogena soyoae) located off Hatsushima Island in Sagami Bay, central Japan, hydrogen sulfide concentration in bottom water and interstitial water was measured every 10 cm from just above seafloor to 40 cm deep usingin situ separative dialysis bags. While hydrogen sulfide over 0.01 mmol/kg was not measured from the seawater just above the dense clam beds, the concentration of hydrogen sulfide increased rapidly below 10 cm deep. The results indicate that the habit of the clam is correlated with high concentration of hydrogen sulfide contained in pore waters of sediments between depths of 10 and 20 cm from the bottom surface. Concentrations of hydrogen sulfide ranging from approximately 0.05 mmol/kg to 0.6 mmol/kg might be suitable requirement for the habitat ofC. soyoae.  相似文献   

Variations in turbulent energy dissipation and water column stratification at the entrance of a tidally energetic strait     

Shiho Kobayashi  Eisuke Hashimoto  Masayuki Nagao  Yoshio Takasugi 《Journal of Oceanography》2009,65(5):657-664

We observed tidal currents, turbulent energy dissipation and water column stratification at the entrance of a narrow strait (Neko Seto) in the Seto Inland Sea, Japan, using a free-falling turbulent microstructure profiler (TurboMAP) and acoustic Doppler current profiler (ADCP). The variation in turbulent energy dissipation at the entrance of the strait was not at quarter-diurnal frequency but at semi-diurnal frequency; turbulent energy dissipation was enhanced during the ebb tide, although it was moderate during the flood tide. This result is consistent with the results of Takasugi (1993), which showed the asymmetry of tidal energy loss during a semidiurnal tidal cycle using control volume analysis. It is suggested that significant turbulent energy dissipation is generated in the strait, which influences the properties of water outside the strait when tidal currents flow out from the strait.  相似文献   

Influence of cluster environments on X-ray cluster morphology     

Yasuhiro Hashimoto  J. Patrick Henry  Hans Böhringer 《Monthly notices of the Royal Astronomical Society》2007,380(2):835-838

We investigated the influence of environment on cluster morphology by examining the alignment of the cluster position angle with respect to the nearest neighbour cluster. The cluster position angle and ellipticity were measured using high spatial resolution X-ray data taken from the Chandra archive, while the nearest neighbour sample was extracted from the Abell cluster catalogue. We found high confidence for an alignment when neighbour distance (Dn) was less than  70  h ⁻¹  Mpc, while we found no significant variations of the confidence level at various values of Dn less than  70  h ⁻¹  Mpc.  相似文献   

Analysis of primary production in the Seto Inland Sea, Japan, using a simple ecosystem model     

Toshiya Hashimoto  Hidetaka Takeoka 《Journal of Oceanography》1998,54(2):123-132

A simple model of lower trophic level ecosystem has been created to analyze possible environmental control of primary production in eight sub-areas of the Seto Inland Sea. The primary production rates observed by Hashimotoet al. (1997a) in these sub-areas are well reproduced by the model, including horizontal processes such as horizontal transport of nutrients and vertical processes such as vertical mixing, light intensity and sinking of particulate matter. Without taking account of horizontal processes the model also successfully reproduces the observed primary production rates in some areas, but if fails to reproduce those in the others. This shows that the relative importance of the horizontal transport on the primary production differs are by area. Two time scales,T _z andT _H, are introduced to explain this difference.T _z is a vertical cycling time of material, which is defined as the time during which the stock of the material in the water column is utilized for primary production;T _H is the horizontal transit time of the material. The relative importance of the horizontal process is well explained by theT _H/T _z ratio; that is, the horizontal transport process is important in the areas where this ratio is small. Further the possible mechanisms of nutrient supply for the primary production in each sub-area are investigated using this model.  相似文献   

Spatial changes in a macrozoobenthic community along environmental gradients in a shallow brackish lagoon facing Sendai Bay, Japan   总被引：3，自引：0，他引：3  

Gen Kanaya  Eisuke Kikuchi   《Estuarine, Coastal and Shelf Science》2008,78(4):674-684

The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat.  相似文献   

Bathymetry and Canyons of the western Solomon Sea     

H. L. Davies  J. B. Keene  K. Hashimoto  M. Joshima  J. E. Stuart  D. L. Tiffin 《Geo-Marine Letters》1987,6(4):181-191

The floor of the western Solomon Sea (for new bathymetric map see inside back cover of this issue) is dominated by the arched and ridged basement of the Solomon Sea Basin, the partly-sediment-filled New Britain Trench, and a more completely filled trench, the Trobriand Trough. There is a deep basin where the trenches join (149° Embayment), and a silled basin west of the New Britain Trench (Finsch Deep). Submarine canyons descend from the west and south to the 149° Embayment. Abyssal fans and plains are structurally defined and locally disturbed by young faults. Probable submerged pinnacle reefs stand in water depths as great as 1,200 m.  相似文献   

Characteristics and implication of clay minerals in the northern and southern parts of the Chelung-pu fault, Taiwan   总被引：1，自引：0，他引：1  

Y. Hashimoto  K. Ujiie  A. Sakaguchi  H. Tanaka 《Tectonophysics》2007,443(3-4):233

In this study, we report the characteristics of clay minerals present in the Chelung-pu fault in Taiwan. In the 1999 Chi-Chi earthquake, different slip motions were recorded along the Chelung-pu fault in the northern and southern parts of the fault. The characteristics of clay minerals present in the fault zones can be attributed to the differences in motion. We analyzed the shallow drill core samples obtained from the northern and southern sites penetrating the fault. The clay minerals identified in most of the samples from both the sites are smectite, illite, and chlorite. There are illite–smectite mixed layers with a high illite content and no chlorite–smectite mixed layer. In some samples, no smectite is detected. We also examined the iron content and symmetry of iron and magnesium in the silicate and hydroxide layers in chlorite. At the northern site, the total iron content in chlorite of gouge is larger than that of the host rocks. On the other hand, at the southern site, the total iron content varies widely. It is hypothesized that the smectite consumption and differences in the characteristics of chlorite may be controlled by the differences in the lithology, fluid chemistry, fluid temperature, or fault activities (heating or breakage) between the northern and southern sites.  相似文献   

Stratigraphy and optically stimulated luminescence (OSL) dating of a Quaternary sequence along the Dong Nai River, southern Vietnam   总被引：1，自引：0，他引：1  

Toshiyuki Kitazawa  Takahiro Nakagawa  Tetsuo Hashimoto  Masaaki Tateishi 《Journal of Asian Earth Sciences》2006,27(6):788-804

The pre-Holocene Cenozoic sequence outcrops in the terrestrial part of the eastern margin of the Mekong Basin. However, the stratigraphy of the sequence is still unclear. Its detailed stratigraphy and chronology were therefore studied along the Dong Nai River, southern Vietnam, and the lithofacies and the relations among the formations were investigated from the outcrops. The ages of the deposits were determined by using optically stimulated luminescence (OSL) dating.The Ba Mieu Formation was deposited about 176±52 ka during marine isotope stage (MIS) 7–6. The Thu Duc Formation was deposited about 97±27 ka during MIS 5. Both the Ba Mieu and Thu Duc formations are composed of fluvial and tidally influenced coastal deposits. The newly proposed Nhon Trach Formation was originally an eolian (blanket) deposit, but it has been partly reworked by fluvial processes. The Nhon Trach Formation was deposited about 10.9±4.7 ka, in the last part of the Pleistocene to the beginning of the Holocene. The OSL ages for the Ba Mieu, Thu Duc, and Nhon Trach formations are younger than the ages previously assigned to these formations.  相似文献