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   

Seasonal variations of the surface currents in the Tsushima Strait     

Yutaka Yoshikawa  Akira Masuda  Kenichi Marubayashi  Michiyoshi Ishibashi 《Journal of Oceanography》2010,66(2):223-232

Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed primarily by the incoming Tsushima Warm Current.  相似文献   

Nd and Sr isotopic variations in acidic rocks formed under a peculiar tectonic environment in Miocene Southwest Japan     

Yasutaka Terakado  Hiroshi Shimizu  Akimasa Masuda 《Contributions to Mineralogy and Petrology》1988,99(1):1-10

Initial Nd and Sr isotopic ratios were obtained for middle Miocene igneous rocks as well as for related rocks from the Outer Zone of Southwest Japan to investigate the petrogenesis of acidic magmas and their relation to a peculiar tectonic environment bearing on the back-arc spreading of the Japan Sea. On the _Nd- _Sr diagram, data points for the acidic rocks fall in the – _Nd, + _Sr quadrant occupying different positions from those for sedimentary and old crustal rocks, and seem to define several subparallel lines which extend towards the lower-righthand sedimentary field. The S-type acidic rocks occupy an intermediate position between I-type rocks and sedimentary ones, a fact suggesting mixing of an igneous component and a sedimentary one. The linear mixing trend observed on the _Nd- _Sr diagram can be attained in the restricted case that the igneous component has similar Sr/Nd concentration ratios to that of the sedimentary one, which implies an intermediate to acidic composition for the igneous component. Inconsistency between the elemental and isotopic variations observed may be reconciled by considering that mixing, probably in the relatively deep part of the crust, might have occured prior to chemical differentiation processes. The episodic igneous activity and the high heat energy required to melt such materials involving sedimentary rocks may be explained by a model in which a hot mantle region probably corresponding to the rising part of the mantle convection supplied the heating energy to the Outer Zone of Southwest Japan when passing beneath Southwest Japan in the course of movement of the hot rising part from the Shikoku basin areas to the Japan Sea area.  相似文献   

High time resolution monitoring of tropospheric temperature with a Radio Acoustic Sounding System (RASS)     

T. Tsuda  Y. Masuda  H. Inuki  K. Takahashi  T. Takami  T. Sato  S. Fukao  S. Kato 《Pure and Applied Geophysics》1989,130(2-3):497-507

We have observed the time-height variation of the temperature field in the upper troposphere using a Radio Acoustic Sounding System (RASS) which consists of the MU radar and a high-power acoustic transmitter. The fast beam steerability of the MU radar has made it possible to measure temperature profiles in a fairly wide height range in the upper troposphere (5–11 km), even under intense wind conditions. Observations were continued for about 32 hr on 24–26 December, 1986 with a time-height resolution of 30 min and 150 m. During the observation period, the tropospheric jet was so intense that the acoustic wavefronts were severely distorted. Using wind velocity profiles observed by the MU radar we have numerically estimated the propagation of acoustic wavefronts, and further determined favorable pointing directions for the MU radar to receive significant backscattering from refractive index fluctuations produced by the acoustic waves. Conventional radiosonde soundings were carried out every 6 hr, which showed a temperature decrease of 4 K/day in the upper troposphere during the observation period. Temperature profiles taken by RASS agree well with the radiosonde results.  相似文献   

Nuclide analyses of rare earth elements of the Oklo uranium ore samples: a new method to estimate the neutron fluence     

Hiroshi Hidaka  Akimasa Masuda 《Earth and Planetary Science Letters》1988,88(3-4)

Isotopic ratios and abundances of all REE in two Oklo ore samples have been measured. We have succeeded in developing a new method to estimate the neutron fluence, the conversion factor of uranium and the average neutron energy (or temperature) based on Gd and U isotopic ratios. This new calculation is found to be useful in evaluating those parameters for the natural nuclear reactors at Oklo. Comparison is made between the neutron fluence values evaluated by our new method employing Gd isotopes and a previous one [11] employing Sm and Nd isotopes. The relative agreement becomes better with the increase of fluence. A relationship between the abundances of fissiongenic nuclides of La, Ce, Nd, Sm, and Gd and their mass numbers is also presented.  相似文献   

中国东部新生代玄武岩的地球化学（Ⅱ）Sr、Nd、Ce同位素组成   总被引：28，自引：5，他引：28  

刘丛强  解广轰  增田彰正 《地球化学》1995,(3)

对有代表性的中国东部新生代玄武岩的Ｓｒ、Ｎｄ和Ｃｅ同位素组成进行了系统的研究，结合系统的微量元素研究结果，进一步阐明其地幔源区同位素组成的不均一性；利用Ｃｅ、Ｎｄ同位素地球化学给出的信息，探讨富集Ⅰ型（ＥＭⅠ）地幔端元的成因。  相似文献   

Relation between chemical composition and particle-size distribution of ores in the profile of nickeliferous laterite deposits of the Rio Tuba Mine, Philippines   总被引：1，自引：0，他引：1  

Yoshio Ogura  Katsuyuki Murata  Michio Iwai 《Chemical Geology》1987,60(1-4):259-271

Lateritic Ni ore mined in the Rio Tuba Mine, Philippines, derived from ultramafic rock by tropical intense weathering, is generally composed of two accumulated zones, an upper laterite zone and a lower saprolite zone. These two zones are very different in appearance, mineral assemblage, chemical composition, and in other ways. A transitional zone may be seen between the upper and lower zones, but it does not develop to any appreciable thickness. Although serpentine and goethite are still predominant in the constituent minerals, other clay minerals are increasing.

The transitional zone may be subdivided into three groups based on chemical composition. The behaviour of the chemical composition in this horizon indicates a complicated process of component transportation under the weathering process.

In the ore, chemical components are closely related in particle size of constituent minerals. In the laterite - transitional - saprolite sequence, a common variation range and tendency in chemical composition for each particle size can be seen. However, taking samples with the same particle size the chemical composition obviously differed, representing the characteristics of the components for each zone.

Concerning the correlation coefficient of the chemical components of each zone, a somewhat different inter-component relationship can be seen in these zones. These differences of correlation suggest the different complicated lateritized conditions under which they are formed.  相似文献   

Introduction: (Re)thinking the scales of lived experience     

Jeffrey R Masuda  Valorie A Crooks 《Area》2007,39(3):257-258

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Possible europium-normal rare-earth abundances estimated from the lunar samples,and the terrestrial analogue     

Akimasa Masuda  Tsuyoshi Tanaka 《Contributions to Mineralogy and Petrology》1972,34(4):336-342

From the mathematical analysis of the rare-earth data on some of the Apollo 12 samples studied by Hubbard et al. (1971), the possible europium-normal primitive rare-earth pattern, in which europium is normal with respect to the adjacent rare-earth elements, has been estimated. A fact that the igneous rocks (Japanese geosynclinal basalts) appearing to reflect the analogous effect occur locally on the earth enhances our interests in the pattern resulting from the above estimation.  相似文献   

Rare earth elements in metagabbros from the Mid-Atlantic Ridge and their possible implications for the genesis of alkali olivine basalts as well as the lizard peridotite     

Akimasa Masuda  Noboru Nakamura  Tsuyoshi Tanaka 《Contributions to Mineralogy and Petrology》1971,32(4):295-306

Two foliated metagabbros from the Mid-Atlantic Ridge near 30° N were analyzed for rare earth elements. The chondrite-normalized rare earth pattern for one of them is quite similar to those for abyssal tholeiites. The pattern for another sample, however, is somewhat different from the above one. A new set of bulk partition coefficients for rare earth elements has been estimated correspondingly. This set throws a new light on the interpretation that many alkali olivine basalts were produced by a zone melting or partial melting of primary-liquid-type material. Also the same partition coefficients lead us to an inference that the high-temperature peridotite intrusion in the Lizard area, Cornwall, England, is a secondary-solid-type material which was once in equilibrium with a primary-solid-type material, whereas the pyroxenite, Canyon Mountain, Oregon, is a primary-solid-type material.Both of the metagabbros studied show positive europium anomaly.  相似文献