Jellyfish patch formation investigated by aerial photography and drifter experiment     

Shinya Magome  Tomohiro Yamashita  Takeshi Kohama  Atsushi Kaneda  Yuichi Hayami  Satoru Takahashi  Hidetaka Takeoka 《Journal of Oceanography》2007,63(5):761-773

Jellyfish patch formation is investigated by conducting a drifter experiment combined with aerial photography of a sustained patch of the moon jellyfish in Hokezu Bay, Japan. Jellyfish patches are aggregations of individuals that are caused by a combination of swimming (active influence) and advection by currents (passive influence). The drifter experiment involved the injection of 49 drifters around a distinct surface patch of jellyfish within an area of approximately 300 m × 300 m. The drifters’ motion, caused only by the passive influence, was recorded in a series of 38 aerial photographs taken over approximately 1 h. The ambient uniform current field larger than the patch scale was estimated from the movement of the centroid position of drifters, while the distribution of horizontal divergence and relative vorticity around the patch was estimated from the time-derivative in areas of triangles formed by the drifters. The centroid positions of both drifters and patches moved stably toward the bay head at different speeds. The difference vector between the patch and drifter centroids was directed to the sun, and was opposite to the ambient current. The distributions of vorticity and divergence around patches exhibited inhomogeneity within the patch scale, and the drifters in this nonuniform current field aggregated near the convergence area within 1 h. The results suggest that horizontal patch formation is predominantly influenced by passive factors at the surface of Hokezu Bay. Furthermore, the upward swimming against downwelling may make sustained patch in surface layer.  相似文献   

Life history ofEuphausia similis (crustacea,euphausiacea) in Sagami Bay,central Japan     

Yuichi Hirota  Takahisa Nemoto  Ryuzo Marumo 《Journal of Oceanography》1990,46(6):237-249

The life history ofEuphausia similis G.O. Sars in Sagami Bay, central Japan, has been studied by examining the abundance, size distribution, and occurrence of each growing stage from egg to adult. Three cohorts were laid within the period from July 1979 to July 1980. Individuals of cohort I of 1980 were laid in November and December 1979, and matured and spawned in March and April of the following year. Those of cohort II of 1980 laid in January and February 1980 should mature in November and spawn after December, by analogy with cohort II of 1979. Cohort III of 1980 was laid in April 1980, but decreased in number in July. Cohort II was the dominant cohort in Sagami Bay throughout the period studied. From December 1979 to April 1980 when the mixing layer was present, many eggs ofE. similis were in the epipelagic zone. It is suggested that the spawning season ofE. similis roughly coincided with the season of active feeding, indicated by high fullness of stomachs in individuals. The production of juveniles and adults was about 1.33 mg C m^–2 day^–1, and the production to bio mass (P/B) ratio was estimated to be 4.78 between July 1979 and July 1980.  相似文献   

Organizational Dynamics of the U.S. Logistics Industry: An Economic Geography Perspective*     

Yuko Aoyama  Samuel Ratick  Guido Schwarz 《The Professional geographer》2006,58(3):327-340

Although the logistics industry provides critical services to all sectors of the economy, few studies exist in economic geography that examine and explain the organizational dynamics of this industry. This article highlights the significance of the logistics industry in contemporary industrialization and argues that an enriched understanding of the interaction between technology and space can be achieved by examining the evolution of an industry that plays a central role in the contemporary economy. We focus on dimensions that are identified as particularly important: organizational, geographic, and risk and security.  相似文献   

The first absolute gravity measurements in Indonesia     

Yoichi Fukuda  Toshihiro Higashi  Shuzo Takemoto  Maiko Abe  Sjafra Dwipa  Dendi Surya Kusuma  Achmad Andan  Koichiro Doi  Yuichi Imanishi  Giuseppe Arduino 《Journal of Geodynamics》2004,38(3-5):489

For the purposes of the calibration of the superconducting gravimeter (SG) in Bandung and the establishment of the absolute gravity (AG) points, we carried out AG measurements for the first time in Indonesia in November 2002. The measurements in Bandung were conducted between November 15th and 20th by means of a FG5 (#210), and 14,520 effective drops were obtained. The gravity value newly determined at the AG point in Bandung is 977976701.2 μgal (1 μgal = 10⁻⁸ ms⁻²) and the scale factor for the SG is −52.22 μgal/V. We also established another AG point in Yogyakarta near Merapi volcano and carried out AG measurements in Yogyakarta between November 22nd and 26th. The gravity value determined for this station is 978203093.5 μgal.  相似文献   

Temperatures and Oxygen Isotopic Compositions of Hydrothermal Fluids for the Takatori Tungsten-copper Deposit, Japan     

Yasuhiro Shibue    Hitoshi Chiba    Minoru Kusakabe  Yuichi Morishita 《Resource Geology》2005,55(2):101-110

Abstract. Fluid inclusion and oxygen isotope studies are performed to obtain temperatures and oxygen isotopic compositions of hydrothermal fluids for the vein-type tungsten-copper deposit at Takatori in Ibaraki Prefecture, Japan. Temperatures of the hydrothermal fluids are calculated from fluid inclusion data. The calculation incorporates the effects of the salinity, gas concentration, and fluid pressure. The fluid temperatures range from 370 to 460C. For these calculations, this study obtains a density equation for H₂O-NaCl-CO₂ solution at the vapor-liquid two-phase boundary. Then the present study combines the obtained equation with the equation of state by Bowers and Helgeson (1983).
The fluid temperatures determined in this study are applied to the calculation of oxygen isotopic compositions of the hydrothermal fluids. The calculation of the oxygen isotopic compositions is based on the oxygen isotope analyses of vein quartz. The oxygen isotopic compositions of vein quartz range from +13.5 to +14.4 % relative to SMOW. Then, the oxygen isotopic compositions of the hydrothermal fluids in equilibrium with the vein quartz are calculated to be from +9.7 to +10.5 %. These δ¹⁸O_fluid values agree with those of magmatic fluids derived from the ilmenite-series granitic rock, which is related to the mineralization. Keywords: Takatori tungsten-copper deposit, fluid inclusion, oxygen isotope, vein quartz, H₂O-NaCl-CO₂ solution, density  相似文献   

Decadal-scale variation in COD and DIN dynamics during the summer in the inner area of the Ariake Sea,Japan     

Yuichi Hayami  Naoki Fujii 《Journal of Oceanography》2018,74(6):551-563

More than 30 years of chemical oxygen demand (COD) and dissolved inorganic nitrogen (DIN) data for the inner area of the Ariake Sea were analyzed with a box model to show the changes in the average seasonal budget and the decadal-scale variation during the summer. The COD peaked in August and March on average. This summertime peak can be explained by an enhanced riverine load and increased primary production. The peak in March suggested additional organic matter production. There were also two peaks in DIN concentration on average: a summertime peak that could be explained by an enhanced riverine load, and a peak in December that was more complicated to explain. From the 1970s to the early 1990s, the bottom water in this area became increasingly hypoxic due to increased COD during the summer, even though there were minimal increases in terrestrial COD and nutrient loads and there were tidal flats covering a widespread area during this period. The increase in COD was caused by increased net ecosystem production, which was due to enhanced primary production induced by an increased freshwater residence time and decreased bivalve grazing. There was a negative feedback control in which hypoxia progressively increased, leading to declines in bivalve biomass, which in turn decreased the grazing pressure limiting primary production, meaning that primary production increased and the area became even more hypoxic. The net DIN production decreased during the 1980s and the 1990s. This was consistent with the change in net ecosystem production according to the COD.  相似文献   

Population genetic diversity and structure of a dominant tropical seagrass,Cymodocea rotundata,in the Western Pacific region          下载免费PDF全文

Dan M. Arriesgado  Hiroyuki Kurokochi  Yuichi Nakajima  Yu Matsuki  Wilfredo H. Uy  Miguel D. Fortes  Wilfredo L. Campos  Kazuo Nadaoka  Chunlan Lian 《Marine Ecology》2016,37(4):786-800

Cymodocea rotundata is an ecologically important tropical pioneer seagrass species distributed in the Indo‐Pacific region. The population genetic diversity and structure of this species were analysed at 46 sites spanning the Philippines, Ryukyu Islands (northern limit) and Hainan Island, by using microsatellite simple sequence repeat (SSR) markers. Analyses revealed the persistence of C. rotundata likely relies on local population dynamics and fitness influenced by environmental gradients, with sexual reproduction prevalent in the Philippines while the Ryukyu and Hainan populations were predominantly established by clonal spread. Analysis of molecular variance showed significant genetic differentiation (P < 0.001) among three geographic regions: the Philippines, Ryukyu and Hainan. Furthermore, the mean fixation index value was very high (F_ST = 0.36), indicating poor dispersal potential or limited gene flow. Allelic richness and heterozygosity of C. rotundata was comparable in the Philippines and Ryukyu Islands populations. More private alleles were found in the Philippines and excess heterozygotes in the Ryukyu Islands. STRUCTURE analysis revealed that the Ryukyu and Hainan populations were mosaics of admixed alleles of individuals from the Philippines. An assignment test suggested that recruitment occurs from the Northeast Philippines to Ryukyu Islands. These results suggest that the Philippine populations are tropical seagrass hotspots and perhaps the origin of the populations in the Ryukyu and Hainan Islands. This scenario is most likely driven by the Kuroshio Current and island integration events during plate tectonic activities. The Philippine Archipelago is considered of high importance for conservation objectives and management plan of seagrasses. Likewise, the Ryukyu Islands are also important in terms of conserving regional diversity because locally adapted genotypes have important evolutionary potential in the face of environmental change.  相似文献   

Fossil worm tubes from the presumed cold-seep carbonates of the Miocene Hayama Group, Central Miura Peninsula, Japan     

Takeshi  Naganuma  Yuichi  Okayama  Mutsuo  Hattori Yasumitsu  Kanie 《Island Arc》1995,4(3):199-208

Abstract Fossil worm tubes were collected from the Hayama Group, Miura Peninsula, Japan, together with abundant fossils of Calyptogena-Acharax clams. The fossil worm tubes were well preserved and coated with milky white amorphous silica. Most of the tubes were 1-3 mm in diameter, and up to 10 cm in length. Worm tubes were found in siltstone and limestone, and formed network-like assemblages. Elemental mapping on the tube cross-sections revealed the localization of sulfur, zinc and iron at the worm tubes, which suggests that sulfur-related metabolism and deposition occurred in association with the worm tubes. High resolution analysis revealed the localization of zinc-sulfur (sphalerite, ZnS) on the tubes, while iron-sulfur (pyrite, FeS₂) was localized at the center of the tubes. The spatially separate sphaleritization and pyritization imply that epiphytic and endosymbiotic microorganisms perform different sulfur metabolisms, such as sulfate-reduction and sulfide-oxidation.  相似文献   

ACTIVE system for monitoring volcanic activity: A case study of the Izu-Oshima Volcano,Central Japan     

Hisashi Utada  Yuji Takahashi  Yuichi Morita  Takao Koyama  Tsuneomi Kagiyama 《Journal of Volcanology and Geothermal Research》2007

A system is proposed for the monitoring of changes in the underground structure of an active volcano over time by applying a transient electromagnetic method. The monitoring system is named ACTIVE, which stands for Array of Controlled Transient-electromagnetics for Imaging Volcano Edifice. The system consists of a transmitter dipole used to generate a controlled transient electromagnetic (EM) field and an array of receivers used to measure the vertical component of the transient magnetic field at various distances, with automatic operation of both units. In order to verify the performance of the proposed system, numerical and field experiments were carried out by application of the system to the Izu-Oshima volcano, where a remarkable change in the apparent DC resistivity over time had been detected in association with the eruption in 1986.  相似文献   

Groundwater-level Anomalies Associated with a Hypothetical Preslip Prior to the Anticipated Tokai Earthquake: Detectability Using the Groundwater Observation Network of the Geological Survey of Japan,AIST     

Norio Matsumoto  Yuichi Kitagawa  Naoji Koizumi 《Pure and Applied Geophysics》2007,164(12):2377-2396

We infer the groundwater-level anomalies associated with a hypothetical preslip prior to the anticipated M 8 Tokai earthquake, and evaluate the detectability of the anomalies using data from seven groundwater wells. We evaluate the detectability of the anomalies under the following assumptions: (1) an Mw 5.5–6.5 aseismic preslip event occurs at the plate boundary in and around the hypothetical focal zone of the Tokai earthquake; (2) the total amount of the strain step at each observation associated with the preslip can be calculated by tensile and shear faulting based on the dislocation model; (3) a normalized strain history associated with the preslip is defined from the results of numerical simulations based on rate- and state-dependent friction laws; and (4) the groundwater-level anomaly prior to the earthquake is proportional to the estimated history of the strain change associated with the preslip. We investigate the detection time of the anomaly at seven wells given an Mw 5.5, 6.0, or 6.5 aseismic preslip at one of the 272 grid points in and around the area of the hypothetical focal zone of the Tokai earthquake. As a result, over the time interval between 1 and 48 hours prior to the hypothetical Tokai earthquake, we are able to detect at each of the seven wells a hypothetical Mw 6.5 preslip at 10–86 of the 272 grid points, an Mw 6 preslip at 0–19 grid points, and an Mw 5.5 preslip at 0–5 grid points.  相似文献