The Kellwasser events in the Upper Devonian Frasnian to Famennian transition in the Toc Tat Formation,northern Vietnam     

Toshifumi Komatsu  Ryota Urakawa  Toshitaka Inada  Kazuki Yamauchi  Takumi Maekawa  Reishi Takashima  Mark Williams  Phong D. Nguyen  Hung D. Doan  Minh T. Nguyen  Shuji Niko  Gengo Tanaka  Tatsuhiko Yamaguchi 《Island Arc》2019,28(1)

Upper Devonian carbonates of the Toc Tat Formation in the Si Phai Pass area of Dong Van District, northern Vietnam were deposited in carbonate platform, slope, and basin environments. These carbonates yield abundant conodonts indicative of the Palmatolepis nasuta, Pa. linguiformis and Pa. triangularis zones, the Frasnian–Famennian stage boundary being identified by the first occurrence of Pa. triangularis. Two positive carbon isotope excursions are recognized, the lower excursion peaking in the interval of the lower to middle Pa. nasuta Zone, whilst the upper excursion peaks just above the local Frasnian–Famennian boundary. Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. Locally, tentaculitoid taxa (Nowakia, Styliolina, Homoctenus, and Metastyliolina?) are abundant in the interval of the Pa. nasuta Zone, but show a drastic decline in abundance before the Lower Kellwasser Event, and only two taxa survived into the Famennian.  相似文献   

Research on the stabilization treatment of clay slope topsoil by organic polymer soil stabilizer     

Jin Liu  Bin Shi  Hongtao Jiang  He Huang  Gonghui Wang  Toshitaka Kamai 《Engineering Geology》2011,117(1-2):114-120

The topsoil of clayey slope is easy to erosion because it is weak in its strength, water stability and erosion resistance. A new organic polymer soil stabilizer, which was developed for the stabilization treatment of clay slope topsoil and was named as STW, was introduced in this study. In order to understand the effect of STW on the stabilization of clayey soil, laboratory tests on the unconfined compressive strength, shear strength, water stability and erosion resistance of untreated and treated soil specimens are performed, The results indicated that STW soil stabilizer can significantly increased the unconfined compression strength, shear strength, water stability and erosion resistance of clayey soil. The unconfined compression strength increased with the increasing of curing time and the variation mainly occurs in the first 24-hour. With the addition amounts of STW increasing, the strength, water stability and erosion resistance increased at the curing time being 48 h, but in the case of friction angle, no major change was observed. Based on the scanning electron microscopy (SEM) analysis of the stabilized soil, the stabilization mechanisms of STW soil stabilizer in the clayey soil were discussed. Finally, a field test of the stabilization treatment of clay slope topsoil with STW was carried out, and the results indicated that the STW soil stabilizer on the stabilization treatment of clay slope topsoil is effective for improving the erosion resistance of slope topsoil, reducing the soil loss and protecting the vegetation growth. Therefore, this technique is worth popularizing for the topsoil protection of clay slope.  相似文献   

Parallel Implementation of Dispersive Tsunami Wave Modeling with a Nesting Algorithm for the 2011 Tohoku Tsunami     

Toshitaka Baba  Narumi Takahashi  Yoshiyuki Kaneda  Kazuto Ando  Daisuke Matsuoka  Toshihiro Kato 《Pure and Applied Geophysics》2015,172(12):3455-3472

  相似文献   

In-situ survey of nanomolar manganese in seawater using an autonomous underwater vehicle around a volcanic crater at Teishi Knoll,Sagami Bay,Japan     

Takashi Doi  Michiaki Takano  Kei Okamura  Tamaki Ura  Toshitaka Gamo 《Journal of Oceanography》2008,64(3):471-477

We present the results of a chemical survey at a submarine volcano, Teishi Knoll, obtained using a submersible in-situ Mn analyzer (GAMOS) mounted on an autonomous underwater vehicle (AUV) platform. During this survey, high-resolution data of dissolved Mn were obtained in three dimensions in nearly real time. The AUV enabled continuous detailed observations along a preprogrammed pathway, which could not have been performed with conventional CTD hydrocasts. During this observation, anomalously high dissolved Mn concentrations were obtained within the crater, corresponding to high water temperatures. The anomalies might be a hydrothermal signature due to volcanic activity from the crater.  相似文献   

Silver in Tokyo Bay estuarine waters and Japanese rivers     

Yan Zhang  Hajime Obata  Toshitaka Gamo 《Journal of Oceanography》2008,64(2):259-265

Dissolved and particulate concentrations of silver in Tokyo Bay estuarine waters and Japanese rivers were determined in this study. The dissolved silver concentrations in the surface water of Tokyo Bay range from 5.9 to 15.1 pmol kg⁻¹, which is comparable to those in the surface water of the Japan Sea, but two or three times higher than those in the surface water of the open ocean. However, elevated concentrations of dissolved silver are not found in Tokyo Bay compared with those in other highly urbanized estuaries, such as San Francisco Bay (20∼243 pmol kg⁻¹). In the Tokyo Bay estuary, silver typically exhibits non-conservative mixing behavior, which is a common feature in the other estuaries reported previously. Dissolved silver concentrations decrease with salinity from the rivers to the mouth of Tokyo Bay. Silver is efficiently scavenged by suspended particulates, as evidenced by the high conditional distribution coefficients for silver throughout the estuary (log K_d > 5.0 ± 0.6). The silver fluxes into Tokyo Bay via inflowing rivers and atmospheric deposition were estimated as 83 kg y⁻¹ and 15 kg y⁻¹, respectively. A simple budget calculation shows that the silver supplied from rivers and atmosphere must be rapidly scavenged within the Tokyo Bay estuary.  相似文献   

Long-term bottom water warming in the north Ross Sea     

Hirokazu Ozaki  Hajime Obata  Mikio Naganobu  Toshitaka Gamo 《Journal of Oceanography》2009,65(2):235-244

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.  相似文献   

Families of periodic orbits in Hill’s problem with solar radiation pressure: application to Hayabusa 2     

Marco Giancotti  Stefano Campagnola  Yuichi Tsuda  Jun’ichiro Kawaguchi 《Celestial Mechanics and Dynamical Astronomy》2014,120(3):269-286

This work studies periodic solutions applicable, as an extended phase, to the JAXA asteroid rendezvous mission Hayabusa 2 when it is close to target asteroid 1999 JU3. The motion of a spacecraft close to a small asteroid can be approximated with the equations of Hill’s problem modified to account for the strong solar radiation pressure. The identification of families of periodic solutions in such systems is just starting and the field is largely unexplored. We find several periodic orbits using a grid search, then apply numerical continuation and bifurcation theory to a subset of these to explore the changes in the orbit families when the orbital energy is varied. This analysis gives information on their stability and bifurcations. We then compare the various families on the basis of the restrictions and requirements of the specific mission considered, such as the pointing of the solar panels and instruments. We also use information about their resilience against parameter errors and their ground tracks to identify one particularly promising type of solution.  相似文献   

Responses of phytoplankton and heterotrophic bacteria in the northwest subarctic Pacific to in situ iron fertilization as estimated by HPLC pigment analysis and flow cytometry   总被引：3，自引：0，他引：3  

Koji Suzuki  Akira Hinuma  Hiroaki Saito  Hiroshi Kiyosawa  Hongbin Liu  Toshiro Saino  Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):167

To verify the hypothesis that the growth of phytoplankton in the Western Subarctic Gyre (WSG), which is located in the northwest subarctic Pacific, is suppressed by low iron (Fe) availability, an in situ Fe fertilization experiment was carried out in the summer of 2001. Changes over time in the abundance and community structure of phytoplankton were examined inside and outside an Fe patch using phytoplankton pigment markers analyzed by high-performance liquid chromatography (HPLC) and flow cytometry (FCM). In addition, the abundance of heterotrophic bacteria was also investigated by FCM. The chlorophyll a concentration was initially ca. 0.9 μg l⁻¹ in the surface mixed layer where diatoms and chlorophyll b-containing green algae (prasinophytes and chlorophytes) were predominant in the chlorophyll biomass. After the iron enrichment, the chlorophyll a concentration increased up to 9.1 μg l⁻¹ in the upper 10 m inside the Fe patch on Day 13. At the same time, the concentration of fucoxanthin (a diatom marker) increased 45-fold in the Fe patch, and diatoms accounted for a maximum 69% of the chlorophyll biomass. This result was consistent with a microscopic observation showing that the diatom Chaetoceros debilis had bloomed inside the Fe patch. However, chlorophyllide a concentrations also increased in the Fe patch with time, and reached a maximum of 2.2 μg l⁻¹ at 5 m depth on Day 13, suggesting that a marked abundance of senescent algal cells existed at the end of the experiment. The concentration of peridinin (a dinoflagellate marker) also reached a maximum 24-fold, and dinoflagellates had contributed significantly (>15%) to the chlorophyll biomass inside the Fe patch by the end of the experiment. Concentrations of 19′-hexanoyloxyfucoxanthin (a prymnesiophyte marker), 19′-butanoyloxyfucoxanthin (a pelagophyte marker), and alloxanthin (a cryptophyte marker) were only incremented a few-fold increment inside the Fe patch. On the contrary, chlorophyll b concentration reduced to almost half of the initial level in the upper 10 m water column inside the Fe patch at the end of the experiment. A decrease with time in the abundance of eukaryotic ultraphytoplankton (<ca. 5 μm in size), in which chlorophyll b-containing green algae were possibly included was also observed by FCM. Overall, our results indicate that Fe supply can dramatically alter the abundance and community structure of phytoplankton in the WSG. On the other hand, cell density of heterotrophic bacteria inside the Fe patch was maximum at only ca. 1.5-fold higher than that outside the Fe patch. This indicates that heterotrophic bacteria abundance was little respondent to the Fe enrichment.  相似文献   

Relationship between atmospheric fluxes and concentrations of terrigenous materials in the surface air over the Japan Sea     

Suzuki  Toshitaka 《Journal of Oceanography》1994,50(2):173-178

Relationship between atmospheric deposition fluxes and concentrations of Si and²¹⁰Po in the surface air were examined through daily basis simultaneous observation at the coast of the Japan Sea. Both the Si and²¹⁰Po, the atmospheric fluxes were highly variable from day to day. According to correlation analysis, there was no significant correlation between flux and atmospheric concentration of these terrigenous materials in the surface air. On the other hand, flux of Si and²¹⁰Po significantly correlated to precipitation rate. These results indicate that the atmospheric flux of terrigenous material is not constantly proportional to atmospheric concentration in the surface air. This may be due to the deposition flux represents an integrated value throughout the air column of in-and below-cloud, while the air concentration represents only the environment of earth's surface.  相似文献   

Light scattering and size distribution of particles in the surface waters of the North Pacific Ocean   总被引：1，自引：0，他引：1  

Shigehiko Sugihara  Ryohei Tsuda 《Journal of Oceanography》1979,35(2):82-90

The volume scattering function and size distribution of suspended particles in the surface water were determined in the North Pacific. The relationship between the scattering coefficient estimated from observed volume scattering function and cross-section concentration of the particles greater than 2.4m in diameter was found to be linear in both northern and southern regions of central North Pacific. Difference in the constant of proportionality between two regions, however, was very great. Moreover the constant in the southern region was too large compared with the values obtained by the Mie theory. This is considered to be due to the fact that particles smaller than 2.4m which were not measureable by the Coulter Counter, were neglected in the calculation of cross-section concentration. If small particles are taken into consideration, total cross-section concentration and scattering coefficient in the two regions tend to follow a linear relation. From the correlation between the scattering coefficient computed from size distribution and the volume scattering function, the refractive index of particles was estimated to be 1.03–1.05. By the same procedure, the refractive index of particles in Tateyama Harbour where the water was very turbid, was estimated to be also 1.03–1.05. This is in contrast to the result for the refractive index of particles originating from the river which flows into the harbour. This index was found to be 1.10–1.20.  相似文献