Deep hydrographic structure along 12°N and 13°N in the Philippine Sea     

Katsuto Uehara  Keisuke Taira 《Journal of Oceanography》1990,46(4):167-176

Hydrographic casts down to the bottom along two zonal sections at 12°N and 13°N (from 144°E to 127°E) were made with a CTD. Their analysis verified the existence of cold and saline abyssal water between the Mariana Ridge and the Kyushu-Palau Ridge. This result provides evidence of flow into the Philippine Sea through the deep gap called the Yap-Mariana Junction. The properties of deep water are variable in the West Mariana basin but quite homogeneous in the Philippine Basin, indicating the transitional nature in the West Mariana Basin and the existence of older bottom water in the Philippine Basin. A close examination suggests that the bottom water is slightly colder in the western part of the Philippine Basin than in the eastern part of the basin. This slightly colder deep water with a hundred kilometer scale in the western Philippine Basin might be related to a broad western boundary current flowing equatorward along the eastern rise of the Philippine Trench.  相似文献   

Selective detection of Fe and Mn species at mineral surfaces in weathered granite by conversion electron yield X-ray absorption fine structure     

Takaaki Itai  Yoshio Takahashi  Tomoya Uruga  Hajime Tanida  Atsuo Iida 《Applied Geochemistry》2008

A new method for the speciation of Fe and Mn at mineral surfaces is proposed using X-ray absorption fine structure in conversion electron yield mode (CEY-XAFS). This method generally reflects information on the species at the sub-μm scale from the particle surface due to the limited escape depth of the inelastic Auger electron. The surface sensitivity of this method was assessed by experiments on two samples of granite showing different degrees of weathering. The XANES spectra of the Fe-K and Mn-K edge clearly gave different information for CEY and fluorescence (FL) modes. These XANES spectra of Fe and Mn show a good fit upon application of least-squares fitting using ferrihydrite/MnO₂ and biotite as the end members. The XANES spectra collected by CEY mode provided more selective information on the secondary phases which are probably present at the mineral surfaces. In particular, CEY-XANES spectra of Mn indicated the presence of Mn oxide in unweathered granite despite a very small contribution of Mn oxide being indicated by FL-XANES and selective chemical-extraction analyses. Manganese oxide could not be detected by micro-beam XANES (beam size: 5 × 5 μm²) in unweathered granite, suggesting that Mn oxide thinly and ubiquitously coats mineral surface at a sub-μm scale. This information is important, since Mn oxide can be the host for various trace elements. CEY-XAFS can prove to be a powerful tool as a highly sensitive surface speciation method. Combination of CEY and FL-XAFS will help identify minor phases that form at mineral surfaces, but identification of Fe and Mn oxides at mineral surfaces is critical to understand the migration of trace elements in water-rock interaction.  相似文献   

Arsenic release from biotite into a Holocene groundwater aquifer in Bangladesh   总被引：1，自引：0，他引：1  

Ashraf Ali Seddique  Harue Masuda  Muneki Mitamura  Keiji Shinoda  Toshiro Yamanaka  Takaaki Itai  Teruyuki Maruoka  Kenji Uesugi  Kazi Matin Ahmed  Dipak Kumar Biswas 《Applied Geochemistry》2008,23(8):2236-2248

Continuous core sediments (to a depth of 90.1 m) taken at a transitional area of Holocene and Pleistocene deposits in Sonargaon, Bangladesh were characterized for their mineralogy and chemistry. Among the sediments of the lower part of the Holocene aquifer (depth: 18–29 m), where most domestic wells are installed, As is mostly fixed in biotite and organic phases. A positive correlation of As concentration with those of Al and Fe but not that of total organic C clearly suggests that biotite is a primary source of As. Although microbial reduction–dissolution of As-containing Fe oxyhydroxides is thought to cause As-enriched groundwater in the Ganges–Brahmaputra–Meghna delta plain, the authors conclude that chemical weathering of biotite is the primary formation mechanism and prevailing reducing conditions contribute to the expansion of As-enriched groundwater in the study area.  相似文献   

Correction to: Transition metals in the transition zone: partitioning of Ni,Co, and Zn between olivine,wadsleyite, ringwoodite,and clinoenstatite     

Li?ZhangEmail author  Joseph?R.?Smyth  Takaaki?Kawazoe  Steven?D.?Jacobsen  Shan?Qin 《Contributions to Mineralogy and Petrology》2018,173(7):60

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Transition metals in the transition zone: partitioning of Ni,Co, and Zn between olivine,wadsleyite, ringwoodite,and clinoenstatite     

Li?ZhangEmail author  Joseph?R.?Smyth  Takaaki?Kawazoe  Steven?D.?Jacobsen  Shan?Qin 《Contributions to Mineralogy and Petrology》2018,173(7):52

Ni, Co, and Zn are widely distributed in the Earth’s mantle as significant minor elements that may offer insights into the chemistry of melting in the mantle. To better understand the distribution of Ni²⁺, Co²⁺, and Zn²⁺ in the most abundant silicate phases in the transition zone and the upper mantle, we have analyzed the crystal chemistry of wadsleyite (Mg₂SiO₄), ringwoodite (Mg₂SiO₄), forsterite (Mg₂SiO₄), and clinoenstatite (Mg₂Si₂O₆) synthesized at 12–20 GPa and 1200–1400 °C with 1.5–3 wt% of either NiO, CoO, or ZnO in starting materials. Single-crystal X-ray diffraction analyses demonstrate that significant amounts of Ni, Co, and Zn are incorporated in octahedral sites in wadsleyite (up to 7.1 at%), ringwoodite (up to 11.3 at%), olivine (up to 2.0 at%), and clinoenstatite (up to 3.2 at%). Crystal structure refinements indicate that crystal field stabilization energy (CFSE) controls both cation ordering and transition metal partitioning in coexisting minerals. According to electron microprobe analyses, Ni and Co partition preferentially into forsterite and wadsleyite relative to coexisting clinoenstatite. Ni strongly prefers ringwoodite over coexisting wadsleyite with \({D}_{\text{Ni}}^{\text{Rw}/\text{Wd}}\)?=?4.13. Due to decreasing metal–oxygen distances with rising pressure, crystal field effect on distribution of divalent metal ions in magnesium silicates is more critical in the transition zone relative to the upper mantle. Analyses of Ni partitioning between the major upper-mantle phases implies that Ni-rich olivine in ultramafic rocks can be indicative of near-primary magmas.  相似文献   

Mass dispersal and angular momentum transfer during collisions between rubble-pile asteroids     

Takaaki Takeda  Keiji Ohtsuki 《Icarus》2007,189(1):256-273

We perform N-body simulations of impacts between initially non-rotating rubble-pile asteroids, and investigate mass dispersal and angular momentum transfer during such collisions. We find that the fraction of the dispersed mass (Mdisp) is approximately proportional to , where Qimp is the impact kinetic energy; the power index α is about unity when the impactor is much smaller than the target, and 0.5?α<1 for impacts with a larger impactor. Mdisp is found to be smaller for more dissipative impacts with small values of the restitution coefficient of the constituent particles. We also find that the efficiency of transfer of orbital angular momentum to the rotation of the largest remnant depends on the degree of disruption. In the case of disruptive oblique impacts where the mass of the largest remnant is about half of the target mass, most of the orbital angular momentum is carried away by the escaping fragments and the efficiency becomes very low (<0.05), while the largest remnant acquires a significant amount of spin angular momentum in moderately disruptive impacts. These results suggest that collisions likely played an important role in rotational evolution of small asteroids, in addition to the recoil force of thermal re-radiation.  相似文献   

Effects of tidally induced eddies on sporadic Kuroshio-water intrusion (kyucho)     

Taira Nagai  Toshiyuki Hibiya 《Journal of Oceanography》2013,69(4):369-377

The sudden intrusion of Kuroshio warm water into the Bungo Channel (kyucho) occurs mainly at neap tides during summer, suggesting that tidal mixing is one of the essential factors regulating kyucho. In order to clarify the physical mechanisms responsible for the regulation of kyucho, we carry out non-hydrostatic three-dimensional numerical experiments allowing Kuroshio warm water to intrude into a strong tidal mixing region. It is shown that the Kuroshio warm water can (or cannot) pass through the tidal mixing regions off the east coast of the Bungo Channel during neap (or spring) tides. The analysis of the dynamic balance off the east coast of the Bungo Channel shows that tidal residual currents generated by tidal flow interaction with complicated land configurations off the east coast of the Bungo Channel can also play an important role in regulating kyucho. In order to assess separately the effects of tidal mixing and tidal residual currents on kyucho, we incorporate the parameterized vertical mixing and tidal stresses into the numerical model instead of tidal currents. It is demonstrated that tidal mixing cannot by itself block the northward intrusion of Kuroshio warm water, and that an additional effect induced by tidal residual eddies equivalent to horizontal mixing is needed to regulate kyucho. This strongly suggests that the basin–ocean water exchange processes in areas with complicated land configurations can only be reproduced by taking into account the effects of tidal residual eddies on a 1-km scale in addition to tidal mixing effects evaluated by microstructure measurements.  相似文献   

Numerical Investigations of Mean Winds Within Canopies of Regularly Arrayed Cubical Buildings Under Neutral Stability Conditions   总被引：2，自引：2，他引：0  

Takaaki Kono  Tetsuro Tamura  Yasunobu Ashie 《Boundary-Layer Meteorology》2010,134(1):131-155

Recently, several attempts have been made to model the wind velocity in an urban canopy in order to accurately predict the mixing and transport of momentum, heat, and pollutants within and above the canopy on an urban scale. For this purpose, unverified assumptions made by Macdonald (Boundary-Layer Meteorol 97:25–45, 2000) to develop a model for the profile of the mean wind velocity within an urban canopy have been used. In the present study, in order to provide foundations for improving the urban canopy models, the properties of the spatially-averaged mean quantities used to make these assumptions have been investigated by performing large-eddy simulations (LES) of the airflow around square and staggered arrays of cubical blocks with the following plan area densities: λ _p = 0.05, 0.11, 0.16, 0.20, 0.25, and 0.33. The LES results confirm that the discrepancy between the spatial average of wind velocity and Macdonald’s five-point average of wind velocity can be large in both types of arrays for large λ _p . It is also confirmed that Prandtl’s mixing length varies significantly with height within the canopy, contrary to Macdonald’s assumption for both types of arrays and for both small and large λ _p . On the other hand, in accordance with Macdonald’s assumption, the sectional drag coefficient is found to be almost constant with height except in the case of staggered arrays with high λ _p .  相似文献   

Mesoscale current fluctuations observed in the deep western North Pacific     

Shiro Imawaki  Keisuke Taira  Toshihiko Teramoto 《Journal of Oceanography》1984,40(1):39-45

A set of simultaneous long-term, deep current measurements was taken using a moored array in the mid-ocean of the western North Pacific near 30°N, 146°E. Five current meters at three stations provided good quality records over 84 days. Low-frequency current fluctuations with meridional dominance are clearly seen in the deep layer records. They are consistent with signals of a mesoscale current fluctuation which has a period of about 100 days, an east-west wave length of about 200 km, and a westward phase propagation with a speed of about 2 cm sec^–1. Bottom intensification of the east component of low-frequency current fluctuations is also observed.  相似文献   

Variability of Upper Ocean Heat Balance in the Shikoku Basin during the Ocean Mixed Layer Experiment (OMLET)     

Hirotaka Otobe  Keisuke Taira  Shoji Kitagawa  Tomio Asai  Kimio Hanawa 《Journal of Oceanography》2003,59(5):619-627

The heat balance of the surface layer in the vicinity of the former Ocean Weather Station “Tango” (OWS-T; 29°N, 135°E), where a large amount of heat is transported by the Kuroshio and transferred to the atmosphere, was studied by during Ocean Mixed Layer Experiment (OMLET) as an oceanographic component of the Japanese World Climate Research Program (1987–1991). Temperature and velocity in the upper ocean measured using a surface moored buoy system deployed by the Ocean Research Institute, the University of Tokyo, in total 668 days of four time series namely the periods of April 1988–November 1988 (OMELET-88), August 1989–February 1990 (OMLET-89), April 1990–September 1990 (OMLET-901) and September 1990–January 1991 (OMLET-902). We have analyzed the moored buoy data of the upper 100 m for the latter three time series (OMLET-89, -901 and -902) and here we discuss the heat balance of the upper 100 m, in combination with surface heat flux and oceanographic data provided by the Japan Meteorological Agency. A large fluctuation of oceanic heat convergence/divergence of 200–300 W/m² in amplitude with predominant period of 20–30 days occurred in the first half of OMLET-89 period, which was just the early stage in the formation process of a large meander path of the Kuroshio. A large amount of heat convergence of 71 and 79 W/m² on average was detected in observation period of OMLET-89 and -901, respectively. During OMLET-902, relatively small heat convergence of 13 W/m² was obtained. It is suggested that these variations of oceanic heat convergence in this region were closely related to the fluctuation of the Kuroshio axis to the south of Japan. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献