Eccentricity cycles shown by early Pleistocene planktonic foraminifers of the Omma Formation, Sea of Japan     

Akihisa Kitamura  Katsunori Kimoto 《Global and Planetary Change》2007,55(4):273-283

There is a continuous record of planktonic foraminifers for oxygen isotope stages 50 to 26 (ca. 1.5–1.0 Ma) in the early Pleistocene Omma Formation near Kanazawa City, Central Japan, on the Sea of Japan coast. The warm-water species Globigerinoides ruber entered the Sea of Japan with the Tsushima Current during all interglacial periods and went locally extinct in the succeeding glacial periods. This implies that the marine climate of the Sea of Japan varied predominantly with the 41,000-year period of Earth's orbital obliquity. However, the relative abundances of G. ruber in marine isotope stages 47, 43 and 31 are significantly higher than those in other interglacial stages. These stages correspond to periods when eccentricity-modulated precession extremes were aligned with obliquity maxima. The Tsushima Current is a branch of the warm Kuroshio Current which is the strong northwestern component of the subtropical North Pacific Ocean gyre. Our data imply that the early Pleistocene climate in the northwestern Pacific was influenced not only by obliquity cycles but also by eccentricity cycles. This study also supports the climate model regarding eccentricity's role in the origin of low-frequency climate changes before the late Pleistocene ice ages.  相似文献   

Analysis of long‐term water balance in the source area of the Yellow River basin     

Yoshinobu Sato  Xieyao Ma  Jianqing Xu  Masayuki Matsuoka  Hongxing Zheng  Changming Liu  Yoshihiro Fukushima 《水文研究》2008,22(11):1618-1629

To analyse the long‐term water balance of the Yellow River basin, a new hydrological model was developed and applied to the source area of the basin. The analysis involved 41 years (1960–2000) of daily observation data from 16 meteorological stations. The model is composed of the following three sub‐models: a heat balance model, a runoff formation model and a river‐routing network model. To understand the heat and water balances more precisely, the original model was modified as follows. First, the land surface was classified into five types (bare, grassland, forest, irrigation area and water surface) using a high‐resolution land‐use map. Potential evaporation was then calculated using land‐surface temperatures estimated by the heat balance model. The maximum evapotranspiration of each land surface was calculated from potential evaporation using functions of the leaf area index (LAI). Finally, actual evapotranspiration was estimated by regulating the maximum evapotranspiration using functions of soil moisture content. The river discharge estimated by the model agreed well with the observed data in most years. However, relatively large errors, which may have been caused by the overestimation of surface flow, appeared in some summer periods. The rapid decrease of river discharge in recent years in the source area of the Yellow River basin depended primarily on the decrease in precipitation. Furthermore, the results suggested that the long‐term water balance in the source area of the Yellow River basin is influenced by land‐use changes. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Oxygen isotopic anomaly and solar nebular photochemistry     

Y. Kitamura  M. Shimizu 《Earth, Moon, and Planets》1983,29(2):199-202

At the cool periphery of the solar nebula, oxygen could photochemically be formed from water. The mixing of¹⁷O and¹⁸O enriched by the self-shielding effect of¹⁶O₂ to the dust grain melted by the shock waves there would explain the oxygen isotopic anomaly in the high-temperature mineral of the carbonaceous meteorites.  相似文献   

Further investigation on distributions of tangential discontinuity in the solar wind     

Ousuke Saka  Tai-Ichi Kitamura 《Planetary and Space Science》1976,24(11):1043-1047

The frequency of the occurrence of the tangential discontinuity (TD) was investigated at thirteen interacting regions (the leading edges) of the solar wind, where each averaged value of the total pressure reaches very much higher values, ranging from 3 × 10^?10 to 12 × 10^?10 erg/m³, than the non-interacting regions (the troughs or the high velocity regions, ?2 × 10^?10 erg/cm³).The present result that the degree of the occurrence is considerably higher in the interacting region than in the non-interacting region was confirmed to be consistent with our previous result. It was discovered that the occurrence frequency at the interacting region increases when strong interaction has occurred.  相似文献   

Short-period noncontact binaries     

Atsuma Yamasaki  Akira Okazaki  Masatoshi Kitamura 《Astrophysics and Space Science》1986,118(1-2):279-282

Five short-period noncontact binaries (GR Tau, UU Lyn, BV Eri, RU Eri, and BW Eri) are studied. It is found from photometric and spectroscopic observations that (1) both components are noncontact to each other but are very close to the respective Roche lobes; (2) period change does not appear or it is very small; and (3) component stars of UU Lyn and RU Eri are normal main sequence stars while those of GR Tau and BV Eri are smaller and less massive components indicating in an advanced evolutionary state having experienced mass reversal.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.  相似文献   

Characteristics of Gold Mineralization at the Ciurug Vein, Pongkor Gold-Silver Deposit, West Java, Indonesia     

Syafrizal    Akira Imai    Yoshinobu Motomura  Koichiro Watanabe 《Resource Geology》2005,55(3):225-238

Abstract. The Pongkor Gold‐Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein‐system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic‐andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug area are typical of those formed from acid to near‐neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near‐neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate‐quartz, manganese carbonate‐quartz, banded‐massive quartz and gray sulfide‐quartz facies. The major metallic minerals are pyrite, sphalerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimon‐pearceite and polybasite. Most of the electrum occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of calcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230d?C and from low salinity fluids (predominantly lower than 0.2 wt% NaCl equiv.). Fluid inclusions occur with features of boiling.  相似文献   

Gold-bearing Quartz Veins and Hydrothermal Alteration of the Paleozoic Epithermal System in the Francis Creek Area, North Queensland, Australia     

Agung Harijoko    Koichiro Watanabe    Yoshinobu Motomura  Eiji Izawa 《Resource Geology》2002,52(4):353-358

Abstract. The Francis Creek area located at the Sybil graben in North Queensland, Australia, has some features of epithermal gold mineralization such as gold-bearing quartz vein and silica body hosted in rhyodacitic rocks of the Late Carboniferous Hells Gate Formation. In order to understand the nature of the paleo-hydrothermal activity in this area and to aid exploration for an economic gold deposit in this area, we carried out hydrothermal alteration mapping surrounding the veins and silica body, over an area of about 7 times 5 km².
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area.  相似文献   

Variability of the Sea Surface Salinity (SSS) in the Western Tropical Pacific: On the Ability of an OGCM to Simulate the SSS, and on the Sampling of an Operating Merchant Ship SSS Network     

Mansour Ioualalen  Yoshinobu Wakata  Yoshikazu Kawahara  Yves Gouriou  David Varillon 《Journal of Oceanography》2003,59(1):105-111

The sea surface salinity (SSS) derived from a network developed at Institut de Recherche pour le Développement (IRD/Nouméa) has been analyzed during the period 1995–1998 in the tropical western Pacific. The measurements were made with thermosalinographs installed on merchant ships selected for their regularity and routes. The western tropical Pacific was sampled mainly along three regular routes across the equator leading to an average of a one month frequency. We analyze here how such a network can be efficient in monitoring the SSS at time scales longer than one month. For this purpose we have used results derived from the Princeton Ocean Model (POM) which is forced by the surface flux of National Centers for Environmental Prediction (NCEP) reanalysis data. The interannual variability of the simulated SSS exhibits very similar features to (sub-sampled) observations despite its being weakly damped to a climatology in order to avoid biases. Even smaller time scale phenomena can be simulated, like the erosion/reconstruction of the region composed of low density waters lying within the Pacific warm pool. The agreement between the observational data and the simulations indicate that the network sampling is sufficient to monitor the SSS variability of the western tropical Pacific from three-month to interannual time scales. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Kelvin Waves Excited by Intraseasonal Wind Forcing     

Yoshinobu Wakata 《Journal of Oceanography》2001,57(6):693-707

The Kelvin wave excited by an intraseasonal wind forcing with a 40-day period over the western Pacific Ocean was simulated using an ocean general circulation model, and was investigated by the use of spectral analysis. The amplitude of the temperature has two peaks north and south of the equator at the depth of the thermocline, and the amplitude of zonal velocity also has two peaks on the equator above and below the thermocline. The phase shows the upward propagation of the wave. It was queried why this wave, which appears to be transient rather than modelike, is formed quickly and always propagates with a phase velocity of about 3 m/s. The vertical one-dimensional forcing problem was studied, where the external forcing of up and down motions moving eastward is imposed at the surface. The growth time is estimated from the resonant solution. The first mode can resonate quickly, but the second cannot. The response in the infinitely deep ocean was also studied to focus on the transiency, where the reflection from the bottom is inhibited. The wave response to the forcing with a speed of about 3 m/s has a large amplitude, i.e. quasi-resonance occurs. In this case, the thermocline plays the role of a reflector, and the upper ocean between the sea surface and the thermocline behaves as a duct. Here, the small resonant cavity explains why the wave is formed so quickly, and the special value of the wave velocity is interpreted as a resonance condition in the duct. The wave corresponding to the second baroclinic mode could not be excited easily by the short-lived forcing at the surface, since this mode is mainly structured under the thermocline. It was found that the wave damps in consequence of leaking energy downward, and the damping rate depends on the period of the wave. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

The tsunami of 3 February 1605     

Hisashi Miyoshi  Kaname Satoh  Yoshinobu Tsuji 《Journal of Oceanography》1989,45(3):174-180

Whether the origins of the tsunami of 3 February 1605 were separated ones or a joined one, is one of the most important problems for Japanese society. When the marine knowledge has not been popularized, it has been considered that the damage pattern on Hachijo Island (including Kojima) was an important key to solving this question.It resembles the situation that the reports concerning the tsunami of 1 April 1946 were introduced to Japanese society under an internal disturbance just after the war, and we overlooked the most important consideration on the combination of tsunami and storm waves caused by the trade wind, and received this tsunami as an extraordinarily huge one.We studied the statistics of recent wind directions around Hachijo Island in January and February 1973, 1974, 1977, 1983, 1984, 1985, 1986 and 1987. And we believed that the probability was high that we could explain well that the damage pattern on Hachijo Island in 1605 was due to the combination of tsunami and storm waves caused by the monsoon.We need not, therefore, look back the damage pattern on Hachijo Island when we consider the fact that the necrologies of many temples in Shizuoka Prefecture record no death on 3 February 1605, proves to be the key to infer that the origins were separated ones.  相似文献