Occurrence of juvenile Japanese flounder Paralichthys olivaceus in brackish estuaries     

Takeshi Tomiyama  Yoh Yamashita  Masaru Tanaka 《Estuarine, Coastal and Shelf Science》2009

Juvenile Japanese flounder Paralichthys olivaceus usually inhabit high salinity inshore sandy areas. In June–August 1997, 25 individuals of juvenile Japanese flounder (33–75 mm total length) were collected in the Natori and Nanakita River estuaries in Sendai Bay, Japan. This is the first record of this species being collected in brackish estuaries in which salinities fluctuate from 0 to 30 over a spring tidal cycle. Factors of rainfall, river flow, or year class strength of Japanese flounder were unable to explain the unusual occurrence of this species in the estuaries. The collected juvenile Japanese flounder were considered to have migrated into the estuaries around the time of the passage of an unusually early typhoon that affected this area, indicating the possibility that this species utilizes estuaries for refuge from strong disturbance in its usual habitats. The juveniles fed mainly upon mysids both in the estuaries and the sandy beach area, indicating that estuaries can be a substitute nursery habitat for this species.  相似文献   

Production and transport of long-chain alkenones and alkyl alkenoates in a sea water column in the northwestern Pacific off central Japan     

Ken Sawada  Nobuhiko Handa  Takeshi Nakatsuka 《Marine Chemistry》1998,59(3-4)

Sinking particles collected from year-long time-series sediment traps at 1674, 4180, 5687 and 8688 m depths, the underlying bottom sediment at 9200 m depth, and suspended particles from surface and subsurface waters in the northwestern North Pacific off Japan were analyzed for long-chain alkenones and alkyl alkenoates (A&A) which are derived mainly from Gephyrocapsacean algae, especially Emiliania huxleyi and Gephyrocapsa oceanica. Alkenone temperature records in sediment trap samples at 1674 m were almost similar to observed sea surface temperatures (SST) with a time delay of one half to one full month. However, alkenone temperatures in trap samples were about slightly lower than measured SST in late spring to early fall. The lowering might be caused by formation of the seasonal thermocline. Nevertheless, these temperature drops observed in trap samples were smaller than those actually observed in a subsurface layer off central Japan. Vertical profiles of A&A concentrations and alkenone temperatures in suspended particles collected from the subsurface waters in early fall indicated that these compounds were produced mostly in a surface mixed layer above the depth of the chlorophyll maximum even in warm seasons. These results suggested that alkenone temperatures strongly reflected SST rather than the temperatures of thermocline waters in these study areas even in such a warm season. Pronounced maxima in A&A fluxes found in sediment trap samples at 1674 m in late spring to summer showed that A&A productions were highest during the periods of spring bloom, according to a time delay between alkenone temperatures and observed SST. Seasonal patterns of alkenone records in trap samples at 4180 and 5687 m could also preserve SST signals well, suggesting that A&A in deep sea waters were mainly derived from primary products in the surface layer. A&A fluxes tended to decrease with water depth, and the ratios of A&A to particulate organic carbon (POC) rapidly decreased in underlying bottom sediment. This clearly indicates that A&A were decomposed and diluted by other refractory organic materials in either the water column or the sediment–water interface. However, A&A compositions were consistently uniform between the trap samples and the underlying bottom sediments, so that A&A could not qualitatively alter during early diagenetic processes.  相似文献   

    

Takeshi Arakaki  Alfonso Mucci 《Aquatic Geochemistry》1999,5(2):225

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Characteristics of crustal structures in the Yamato Basin,sea of Japan,deduced from seismic explorations     

Takeshi Sato  Tetsuo No  Shuichi Kodaira 《Island Arc》2023,32(1):e12474

Crustal structures around the Yamato Basin in the southeastern Sea of Japan, inferred from recent ocean bottom seismography (OBS) and active-source seismological studies, are reviewed to elucidate various stages of crustal modification involved from rifting in the crust of the surrounding continental arc to the production of oceanic crust in the Yamato Basin of the back-arc basin. The northern, central, and southern areas of the Yamato Basin have crustal thicknesses of approximately 12–16 km, and lowermost crusts with P-wave velocities greater than 7.2 km/s. Very few units have P-wave velocities in the range 5.4–6.0 km/s, which corresponds to the continental upper crust. These findings, combined with previous geochemical analysis of basalt samples, are interpreted to indicate that a thick oceanic crust has been formed in these areas of the basin, and that this oceanic crust has been underplated by mantle-derived magma. In the central Yamato Basin, the original continental crust has been fully breached and oceanic crust has been formed. Conversely, the presence of a unit corresponding to the continental upper crust and the absence of a high-velocity part in the lower crust implies that the southwestern edge of the Yamato Basin has a rifted crust without significant intrusion. The Oki Trough has a crust that is 17–19 km thick with a high-velocity lower crust and a unit corresponding to the continental upper crust. The formation of the Oki Trough resulted from rifting with magmatic intrusion and/or underplating. We interpret these variations in the crustal characteristics of the Yamato Basin area as reflecting various instances of crustal modification by thinning and magmatic intrusion due to back-arc extension, resulting in the production of a thick oceanic crust in the basin.  相似文献   

Mid- and far-infrared extinction coefficients of hydrous silicate minerals     

Chiyoe Koike  Hiroichi Hasegawa  Takeshi Hattori 《Astrophysics and Space Science》1982,88(1):89-98

Extinction coefficients were measured for three kind of hydrous silicate minerals, montmorillonite, chlorite and serpentine, from 7 to 140 m. The infrared extinction coefficients of these minerals show (1) a few broad bands in the mid-infrared region and (2) a less steep wavelength-dependence in the far-infrared region, in contrast to those of high-temperature magnesium silicates. In the far-infrared region, montmorillonite shows a ^–0.8±0.1 dependence (, the wavelength) without any band structure, chlorite has a double maxima structure around 80 m, and serpentine shows a rather steep dependence with a small peak at 77 m.The changes of mid-infrared spectra by heating were measured. Change in chlorite spectrum is the most significant. Many fine features appear by heating and then they disappear. Above 900°C one broad feature remains around 10 m. Fine features of the montmorillonite spectrum disappear by heating. For serpentine, many new peaks appear and the spectrum resembles the spectrum of olivin. In near-infrared a band around 2.72 m disappears by heating.Extinction coefficients at very low temperatures were measured in the far-infrared region. For montmorillonite and serpentine, the spectrum is the same as that at room temperature. The double peaks of chlorite around 80 m become higher.  相似文献   

Phase equilibria and the pressure-temperature path of the highest-grade Ryoke metamorphic rocks in the Yanai district, SW Japan     

Takeshi Ikeda 《Contributions to Mineralogy and Petrology》1998,132(4):321-335

The garnet-cordierite zone, the highest-grade zone of the Ryoke metamorphic rocks in the Yanai district, SW Japan, is defined by the coexistence of garnet and cordierite in pelitic rocks. Three assemblages in this zone are studied in detail, i.e. spinel + cordierite + biotite, garnet + cordierite + biotite and garnet + biotite, all of which contain quartz, K-feldspar and plagioclase. The Mg/(Fe + Mg) in the coexisting minerals decreases in the following order: cordierite, biotite, garnet and spinel. Two facts described below are inconsistent with the paragenetic relation in the K₂OFeOMgOAl₂O₃SiO₂H₂O (KFMASH) system in terms of an isophysical variation. First, garnet and biotite in the last assemblage have Mg/(Fe + Mg) higher than those in the second. Second, the first two assemblages are described by the reaction, while they occur in a single outcrop. The addition of MnO, ZnO and TiO₂ to the system can resolve the inconsistencies as follows. The assemblage garnet + biotite can consist of garnet and biotite higher in Mg/(Fe + Mg) than those in garnet + cordierite + biotite as long as they are enriched in spessartine and depleted in Al, respectively. The assemblage garnet + cordierite + biotite becomes stable relative to spinel + cordierite + biotite with increasing spessartine content or decreasing gahnite content and the Ti content of biotite. The constituent minerals of the assemblages, spinel + cordierite + biotite and garnet + cordierite + biotite, preserve several reaction microstructures indicative of prograde reactions, and together with retrograde reactions, and This suggests that the pressure-temperature path of the rocks includes an isobaric heating and an isobaric or decompressional cooling. The high-grade areas consisting of the K-feldspar-cordierite zone, sillimanite-K-feldspar zone and garnet-cordierite zone have prograde paths involving isobaric heating and show a southwards increase in pressure with a thermal maximum in the middle. These high-grade zones are closely associated with the gneissose granitic rocks, suggesting that the Ryoke metamorphism, one of the typical low-pressure type, is caused by the heat supply from the syn-tectonic granitic rocks that emplaced at the middle level of the crust. Received: 22 August 1997 / Accepted: 11 May 1998  相似文献   

Laboratory experiment and digital simulation of multiple fill-cut terrace formation     

Takeshi Mizutani 《Geomorphology》1998,24(4):353-361

The formation mechanism of multiple erosional terraces which develop in the dissection process of sedimentary valley fills was investigated by laboratory experiments and computer simulations. Sequences of unpaired terraces were produced on experimental fan-like deposits under conditions of constant water discharge, no base-level change, and no sediment supply. The terraces developed as a result of the repetition of lateral shifting and stillstand of the stream channel at each cross-section during continuous downcutting. This mode of channel migration was caused by meander growth during which amplitude and wavelength increased with time. The terrace formation process was well-reproduced by computer simulations using a meander model having a similar wave mode.  相似文献   

Influence of evaporation from the forest floor on evapotranspiration from the dry canopy     

Kenichi Daikoku  Shigeaki Hattori  Aiko Deguchi  Yu Aoki  Mari Miyashita  Kazuho Matsumoto  Junichi Akiyama  Shinichi Iida  Tae Toba  Yuji Fujita  Takeshi Ohta 《水文研究》2008,22(20):4083-4096

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Effects of the introduction of rice on evapotranspiration in seasonal wetlands          下载免费PDF全文

Tetsuji Suzuki  Takeshi Ohta  Tetsuya Hiyama  Yasuhiro Izumi  Osmund Mwandemele  Morio Iijima 《水文研究》2014,28(17):4780-4794

Land use changes in wetland areas can alter evapotranspiration, a major component of the water balance, which eventually affects the water cycle and ecosystem. This study assessed the effect of introduced rice‐cropping on evapotranspiration in seasonal wetlands of northern Namibia. By using the Bowen ratio–energy balance method, measurements of evapotranspiration were performed over a period of 2.5 years at two wetland sites—a rice field (RF) and a natural vegetation field (NVF)—and at one upland field (UF) devoid of surface water. The mean evapotranspiration rates of RF (1.9 mm daytime^?1) and NVF (1.8 mm daytime^?1) were greater than that in UF (1.0 mm daytime^?1). RF and NVF showed a slight difference in seasonal variations in evapotranspiration rates. During the dry season, RF evapotranspiration was less than the NVF evapotranspiration. The net radiation in RF was less in this period because of the higher albedo of the non‐vegetated surface after rice harvesting. In the early growth period of rice during the wet season, evapotranspiration in RF was higher than that in NVF, which was attributed to a difference in the evaporation efficiency and the transfer coefficient for latent heat that were both affected by leaf area index (LAI). Evapotranspiration sharply negatively responded to an increase in LAI when surface water is present according to sensitivity analysis, probably because a higher LAI over a surface suppresses evaporation. The control of LAI is therefore a key for reducing evaporation and conserving water. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Interannual variation of evapotranspiration in an eastern Siberian larch forest     

Bao‐Lin Xue  Hikaru Komatsu  Ayumi Kotani  Kyoichi Otsuki  Takeshi Ohta 《水文研究》2012,26(15):2360-2368

In a deciduous larch forest in eastern Siberia, the mean and standard deviation of the total evapotranspiration (E) during May to September (day of year (DOY) = 121–274) for 2003–2006 were 181.5 and 26.4 mm, respectively. The interannual variation (IAV) in the total E was caused by the IAV in E for the canopy‐foliated period (DOY = 164–253), not by the IAV in the dates of leaf expansion and leaf fall. For the years with higher total E, E in the canopy‐foliated period was consistently higher, which corresponded to the higher soil water content in these years. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献