Persistent organochlorine residues in sediments from the Chukchi Sea, Bering Sea and Gulf of Alaska   总被引：14，自引：0，他引：14  

Hisato Iwata  Shinsuke Tanabe  Mari Aramoto  Norio Sakai  Ryo Tatsukawa 《Marine pollution bulletin》1994,28(12):746-753

Three surface sediments and two sediment cores were collected from the Gulf of Alaska, Bering Sea and Chukchi Sea, and analysed for persistent organochlorines (OCs). The geographical distributions of OCs showed different patterns according to their physicochemical properties. The concentrations of HCHs and HCB revealed rather uniform distribution, suggesting their more transportable nature in long-range atmospheric transport. On the other hand, DDTs and PCBs were predicted to be less transportable via the atmosphere due to the decreasing trends of residue levels in sediments from south to north. The OC profiles in the sediment core from the Gulf of Alaska which seemed to be preserved without turbation revealed the elevated residue levels from bottom to surface layers. This implies that the aerial inputs of OCs in the cold ocean are still continuing significantly. The accumulation rates of OCs into sediments were rather smaller than the atmospheric inputs, indicating that the residue levels in water bodies are unlikely to decrease rapidly in the near future.  相似文献   

Biological significance of effects of phytophagous fishes on phytoplankton     

T. Miura  K. Iwata  Zhang Zongshe 《中国海洋湖沼学报》1989,7(4):335-338

The effects of phytophagous fishes on phytoplankton primary productivity in a freshwater pond, the importance of recycling of algae in fish feces, and the species specific interaction with phytoplanktons were studied. Phaeopigment amounts in pond water and in feces of fish were compared. The reduction of chlorophylla into phaeopigments in the process of passing through the phytophagous fish intestines was analyzed, and used for a direct comparison of the production rates of phytoplanktons before and after intestinal passage.  相似文献   

Mechanical properties and stress–dilatancy relationships of unsaturated soil under various cyclic loading conditions     

Tun Tun  Win  Sato  Tomotaka  Saito  Hirotaka  Kohgo  Yuji 《Acta Geotechnica》2020,15(7):1799-1813

Acta Geotechnica - Most studies investigating the effect of cyclic loading on soil properties have been conducted for saturated soils. Embankments such as fill dams, roads and railways are usually...  相似文献   

Influence of fine sediment on the fluidity of debris flows     

Norifumi Hotta  Takahiro Kaneko  Tomoyuki Iwata  Haruo Nishimoto 《山地科学学报》2013,10(2):233-238

Debris flows include a great diversity of grain sizes with inherent features such as inverse grading, particle size segregation, and liquefaction of fine sediment. The liquefaction of fine sediment affects the fluidity of debris flows, although the behavior and influence of fine sediment in debris flows have not been examined sufficiently. This study used flume tests to detect the effect of fine sediment on the fluidity of laboratory debris flows consisting of particles with various diameters. From the experiments, the greatest sediment concentration and flow depth were observed in the debris flows mixed with fine sediment indicating increased flow resistance. The experimental friction coefficient was then compared with the theoretical friction coefficient derived by substituting the experimental values into the constitutive equations for debris flow. The theoretical friction coefficient was obtained from two models with different fine-sediment treatments: assuming that all of the fine sediments were solid particles or that the particles consisted of a fluid phase involving pore water liquefaction. From the comparison of the friction coefficients, a fully liquefaction state was detected for the fine particle mixture. When the mixing ratio and particle size of the fine sediment were different, some other cases were considered to be in a partially liquefied transition state. These results imply that the liquefaction of fine sediment in debris flows was induced not only by the geometric conditions such as particle sizes, but also by the flow conditions.  相似文献   

Dating of altered mafic intrusions by applying a zircon fission track thermochronometer to baked country rock,and implications for the timing of volcanic activity during the opening of the Japan Sea          下载免费PDF全文

Hiroyuki Hoshi  Hideki Iwano  Tohru Danhara  Naoyoshi Iwata 《Island Arc》2015,24(2):221-231

Once a mafic intrusive rock has become altered, it is generally difficult to obtain a reliable intrusion age using conventional isotopic dating methods. To overcome this problem, this study used zircon fission track (ZFT) thermochronometry to determine the timing of crystallization of altered mafic intrusions. ZFT dating was carried out on samples of baked granite country rock adjacent to dolerite dikes (5–10 m thick) in the Takato area of central Japan. Three granite samples collected within 8 mm of a dike contact yielded consistent ZFT ages of 17–16 Ma, with confined track lengths indicative of the complete annealing of pre‐existing tracks by reheating due to dike intrusion. An older ZFT age was obtained for one granite sample collected within 20 mm of the contact, but confined track length measurements indicate that this is an incompletely reset age that lies between the ZFT age of the unbaked granitic country rocks (ca. 55 Ma) and the emplacement age of the dike. Petrographic examinations suggest that post‐intrusion hydrothermal activity did not influence the ZFT ages. We conclude that the 17–16 Ma ZFT age represents the emplacement age of the dikes. Our results show that ZFT dating of baked country rock is an effective tool for dating altered mafic intrusions, for which other dating techniques are not applicable. In the eastern part of Southwest Japan, dispersed volcanic activity occurred in the late Early to early Middle Miocene (18–15 Ma), and the volcanic belt extended into the forearc. This pulse of activity was possibly related to the injection of asthenospheric material into the trench‐side mantle wedge beneath the Japan arc. We also present young apatite fission track ages (ca. 4 Ma) that may reflect a Middle Miocene or later thermal event associated with local magmatic activity near the Takato area.  相似文献   

Lunar gravity field determination using SELENE same-beam differential VLBI tracking data   总被引：2，自引：0，他引：2  

S. Goossens  K. Matsumoto  Q. Liu  F. Kikuchi  K. Sato  H. Hanada  Y. Ishihara  H. Noda  N. Kawano  N. Namiki  T. Iwata  F. G. Lemoine  D. D. Rowlands  Y. Harada  M. Chen 《Journal of Geodesy》2011,85(4):205-228

A lunar gravity field model up to degree and order 100 in spherical harmonics, named SGM100i, has been determined from SELENE and historical tracking data, with an emphasis on using same-beam S-band differential VLBI data obtained in the SELENE mission between January 2008 and February 2009. Orbit consistency throughout the entire mission period of SELENE as determined from orbit overlaps for the two sub-satellites of SELENE involved in the VLBI tracking improved consistently from several hundreds of metres to several tens of metres by including differential VLBI data. Through orbits that are better determined, the gravity field model is also improved by including these data. Orbit determination performance for the new model shows improvements over earlier 100th degree and order models, especially for edge-on orbits over the deep far side. Lunar Prospector orbit determination shows an improvement of orbit consistency from 1-day predictions for 2-day arcs of 6 m in a total sense, with most improvement in the along and cross-track directions. Data fit for the types and satellites involved is also improved. Formal errors for the lower degrees are smaller, and the new model also shows increased correlations with topography over the far side. The estimated value for the lunar GM for this model equals 4902.80080±0.0009 km³/s² (10 sigma). The lunar degree 2 potential Love number k ₂ was also estimated, and has a value of 0.0255 ± 0.0016 (10 sigma as well).  相似文献   

Geodynamics and Tectonics of Central Asia: Continental Growth in Vendian-Paleozoic Time     

M.M. Buslov  T. Watanabe  Y. Fujiwara  K. Iwata  Yu.I. Saphonova  O.T. Obut  Y. Sugai 《Gondwana Research》2001,4(4):587

  相似文献   

Basin and crustal velocity structure models for the simulation of strong ground motions in the Kinki area,Japan     

Tomotaka Iwata  Takao Kagawa  Anatoly Petukhin  Yoshihiro Ohnishi 《Journal of Seismology》2008,12(2):223-234

We constructed a prototype of the basin and crustal structure model for the Kinki area, southwest of Japan, for the simulation of strong ground motions of hypothetical crustal and subduction earthquakes. We collected results of the deep seismic velocity profiles obtained by the reflection experiments and seismic imaging results, which were conducted in the Kinki area. The obtained profiles give underground velocity structures of the crust, from the surface to the subducting slab. We also gather the basin velocity structure information of the Osaka, Kyoto, Nara, and Ohmi basins. To examine the applicability of the constructed velocity structure model to the ground motion simulation, we simulated waveforms of an intermediate size event occurred near the source area of the hypothetical subduction earthquakes. Simulated ground motions using the basin and crustal velocity structure model are fairly well reproducing the observations at most of stations, and the constructed basin and crustal velocity structure model is applicable for the long-period ground motion simulations.  相似文献   

Rip current spacing     

Noriyuki Iwata 《Journal of Oceanography》1976,32(1):1-10

Mass, momentum and energy conservation laws, including the radiation stress, are used to derive an equation of the eigenvalues of rip current spacing.A coastal region with linear bottom slope is divided into two parts: Offshore region and surfzone separated by the breaker line. Wave set-up, wave energy and mean current are assumed to be composed of basic state, which is a function of the distance from the coast to offshore only, and of superposed two-dimensional perturbations.In the case of normal incidence of waves, basic steady current system vanishes and perturbations are found to be of cellular shape. According to the boundary conditions at the coast, stream function of perturbed motion in the surfzone can be represented by the confluent hypergeometric function, while in the offshore zone it is approximated by the modified Bessel function.Interpolation of the stream functions in the surf and offshore regions enables us to obtain a characteristic relation which gives the eigenvalues of nondimensional alongshore spacing of rip current system as a function of a parameter determined by the bottom friction coefficient, width of the surfzone and breaker height.  相似文献   

Identification of aryl hydrocarbon receptor 2 in aquatic birds; cDNA cloning of AHR1 and AHR2 and characteristics of their amino acid sequences     

Yasui T  Kim EY  Iwata H  Tanabe S 《Marine environmental research》2004,58(2-5):113-118

The toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and its related planar halogenated aromatic hydrocarbons (PHAHs) are mediated by the aryl hydrocarbon receptor (AHR). To investigate the potential sensitivity to PHAHs and the evolutional diversity of AHR in aquatic birds, AHR cDNAs were initially cloned and sequenced from the livers of a black-footed albatross (Diomedea nigripes) and a common cormorant (Phalacrocorax carbo). In this study, we report the identification of two distinct AHR paralog genes in these species. The two full-length AHR cDNAs from albatross were highly divergent (33% overall amino acid identity, and 60% identity in the N-terminal half). Phylogenetic analysis showed that one of them belongs to the AHR1 clade and the other one to the AHR2 clade, which has been identified only from fishes, but not yet from mammals and birds. Albatross AHR1 encoded a 861-residue protein with a predicted molecular mass of 96.7 kDa, and in the case of albatross AHR2, 925 amino acids and 100.7 kDa. From cormorant liver, the full-length AHR1 cDNA and the partial AHR2 cDNA were cloned. This result strongly suggests that bird species also possess two distinct AHR genes (AHR1 and AHR2). To our knowledge, this is the first report on the presence of an AHR2-like isoform in bird species as well as in fish.  相似文献