Influences of physical processes on the ecosystem of Jakarta Bay: a coupled physical-ecosystem model experiment     

Koropitan  Alan F.; Ikeda  Motoyoshi; Damar  Ario; Yamanaka  Yasuhiro 《ICES Journal of Marine Science》2009,66(2):336-348

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Electron density distribution of FeTiO<Subscript>3</Subscript> ilmenite under high pressure analyzed by MEM using single crystal diffraction intensities     

Takamitsu Yamanaka  Yutaka Komatsu  Hironori Nomori 《Physics and Chemistry of Minerals》2007,34(5):307-318

Many of ilmenites ABO₃ compounds bearing transition elements have semiconductive, ferroelectric and antiferromagnetic properties. The high-pressure diffraction studies of FeTiO₃ have been conducted up to 8.2 GPa using synchrotron radiation in KEK at Tsukuba with diamond anvil cell. The compression mechanism of FeTiO₃ ilmenite has been investigated by the structure refinements converged to the reliable factors R = 0.05. The deformations of the FeO₆ and TiO₆ octahedra were reduced with increasing pressure. In order to elucidate the electric conductivity change with pressure, electron density distribution of ilmenite have been executed by maximum entropy method (MEM) using single-crystal diffraction intensity data. MEM based on F _obs(hkl) of FeTiO₃ clearly shows electron density in comparison with the difference Fourier synthesis based on F _obs(hkl) − F _calc(hkl). The radial distribution of the electron density indicates electron localization around the cation positions. The bonding electron density found in bond Fe–O and Ti–O is lowered with pressure. The isotropic temperature factors B _iso become smaller with increasing pressure. Nevertheless the thermal vibration is considerably restrained by the compression, the electric conductivity is enhanced with pressure. Neither charge transfer nor electron hopping between Fe and Ti along the c axis in FeTiO₃ is plausible under high pressure. But the electric conductivity due to electron super-exchange in Fe–Fe and Ti–Ti has been clarified by the MEM electron density distribution. The anisotropy in the electric conductivity has been clarified.  相似文献   

Influence of vegetation factors on biological soil crust cover on rehabilitated grassland in the hilly Loess Plateau, China   总被引：1，自引：0，他引：1  

Jian Zhang  Guobin Liu  Mingxiang Xu  Ming Xu  Norikazu Yamanaka 《Environmental Earth Sciences》2013,68(4):1099-1105

Biological soil crusts (BSCs) perform essential ecosystem functions in arid and semi-arid ecosystems worldwide. The formation, development, and distribution of BSCs are influenced by changes in multiple environmental factors, including changes in the vascular plant community. The influence of changes in vegetation factors on BSC cover in 8-, 12-, and 16-year-old rehabilitated grasslands were studied in the hilly area of the Chinese Loess Plateau. The rate of degradation of BSCs underneath litter (P < 0.01) and the degradation cover of BSCs (P < 0.05) differed significantly between the 8- and 16-year-old successions. Stepwise multiple linear regression analysis showed that the main vegetation factors influencing the dynamics of BSC cover differed among the 8-, 12-, and 16-year-old rehabilitated grasslands. Basal cover, phytomass, and litter cover were the main vegetation factors influencing the dynamics of BSC cover on 8-year-old rehabilitated grassland. Phytomass, litter thickness, and litter cover were the main factors influencing the dynamics of BSC cover on 12-year-old rehabilitated grassland. On 16-year-old rehabilitated grassland, Pielou evenness index, litter thickness, and litter biomass were the main vegetation factors influencing degradation of BSC cover underneath litter, whereas basal cover, litter thickness, and litter biomass were the main vegetation factors influencing the degradation cover of BSCs. At particular stages of herbaceous succession, vegetation factors can have a large influence on changes in the community’s basal cover and litter, which are key factors influencing changes in BSC cover. The degradation of BSCs underneath litter may be a result of complicated eco-physiological processes.  相似文献   

An evaluation of 3-D velocity models of the Kanto basin for long-period ground motion simulations     

Yadab P. Dhakal  Hiroaki Yamanaka 《Journal of Seismology》2013,17(3):1073-1102

We performed three-dimensional (3-D) finite difference simulations of long-period ground motions (2–10 s) in the Kanto basin using the Japan Seismic Hazard Information Station (J-SHIS 2009), Yamada and Yamanaka (Exploration Geophysics 65(3):139–150, 2012) (YY), and Head Quarter for Earthquake Research Promotion (HERP 2012) velocity models for two intermediate depth (68–80 km) moderate earthquakes (Mw 5.8–5.9), which occurred beneath the Kanto basin. The models primarily differ in the basic data set used in the construction of the velocity models. The J-SHIS and HERP models are the results of integration of mainly geological, geophysical, and earthquake data. On the other hand, the YY model is oriented towards the microtremor-array-observation data. We obtained a goodness of fit between the observed and synthetic data based on three parameters, peak ground velocities (PGVs), smoothed Fourier spectra (FFT), and cross-correlations, using an algorithm proposed by Olsen and Mayhew (Seism Res Lett 81:715–723, 2010). We found that the three models reproduced the PGVs and FFT satisfactorily at most sites. However, the models performed poorly in terms of cross-correlations especially at the basin edges. We found that the synthetics using the YY model overestimate the observed waveforms at several sites located in the areas having V _s 0.3 km/s in the top layer; on the other hand, the J-SHIS and HERP models explain the waveforms better at the sites and perform similarly at most sites. We also found that the J-SHIS and HERP models consist of thick sediments beneath some sites, where the YY model is preferable. Thus, we have concluded that the models require revisions for the reliable prediction of long-period ground motions from future large earthquakes.  相似文献   

Along-coast shifts of plankton blooms driven by riverine inputs of nutrients and fresh water onto the coastal shelf: a model simulation     

Yasuhiro Hoshiba  Yasuhiro Yamanaka 《Journal of Oceanography》2013,69(6):753-767

Rivers transport nutrients and suspended sediment matter (SSM) as well as fresh water from land to coastal regions, where the biological productivity is high. In the coastal area, the buoyancy of fresh water leads to the formation of horizontal anticyclonic gyres and vertical circulations, which affect the variation of biological production such as plankton blooms. However, the primary production caused by the 3-D dynamics have not been quantitatively discussed, and observations can hardly capture the daily temporal variations of phytoplankton blooms. We developed an ocean general circulation model including a simple ecosystem model, to investigate the 3-D and temporal changes in phytoplankton blooms caused by riverine input such as flooding. The distribution patterns of nutrients and phytoplankton differ significantly from that of fresh water. The phytoplankton maxima shift from the downstream (right-hand side of the river mouth) to the upstream regions (left-hand side of the river mouth). The shift that occurs is categorized by the different nitrate origins: (1) river-originated nitrate is dominant in the downstream region; (2) subsurface-originated nitrate is dominant in the upstream region, and is transported by upwelling associated with vertical circulation and horizontal anticyclonic gyre; and (3) regenerated nitrate is dominant in the upstream region. The total primary production in phytoplankton blooms is maintained not only by river-originated nitrate but also by subsurface-originated nitrate that is 1.5 times larger than the river-originated. Several case studies (e.g., including SSM) were conducted in this study.  相似文献   

Ecological variations in diatom assemblages in the Paleo-Kathmandu Lake linked with global and Indian monsoon climate changes for the last 600,000 years     

Tatsuya Hayashi  Yoshihiro Tanimura  Yoshihiro Kuwahara  Masao Ohno  Mami Mampuku  Rie Fujii  Harutaka Sakai  Toshiro Yamanaka  Takeshi Maki  Masao Uchida  Wataru Yahagi  Hideo Sakai 《Quaternary Research》2009,72(3):377-387

Variations in fossil diatom assemblages and their relationship with global and Indian monsoon climate changes for the last 600,000 yr were investigated using a core of ancient lake (Paleo-Kathmandu Lake) sediments drilled at the Kathmandu Basin, Nepal Himalaya. Chronological scales of the core were constructed by tuning pollen wet and dry index records to the SPECMAP δ¹⁸O stack record. Examinations of biogenic silica contents and fossil diatom assemblages revealed that variations in productivity and compositions of diatom assemblages were closely linked with global and Indian monsoon climate changes on glacial and interglacial time scales. When summer monsoonal rainfall increased during interglacials (interstadials), diatom productivity increased because of increased inputs of terrestrial nutrients into the lake. When summer monsoonal rainfall reduced and/or winter monsoonal aridification enhanced during glacials (stadials), productivity of the diatoms decreased and lake-level falling brought about changes in compositions of diatom assemblages. Monospecific assemblages by unique Cyclotella kathmanduensis and Puncticulata versiformis appeared during about 590 to 390 ka. This might be attributed to evolutionary fine-tuning of diatom assemblages to specific lake environmental conditions. Additionally, low-amplitude precessional variations in monsoon climate and less lake-level changes may have also allowed both species to dominate over the long periods.  相似文献   

High-resolution terrestrial carbon isotope and planktic foraminiferal records of the Upper Cenomanian to the Lower Campanian in the Northwest Pacific     

Reishi Takashima  Hiroshi Nishi  Toshiro Yamanaka  Keiichi Hayashi  Amane Waseda  Akiko Obuse  Takashige Tomosugi  Naoki Deguchi  Sunao Mochizuki 《Earth and Planetary Science Letters》2010,289(3-4):570-582

Making Upper Cretaceous biostratigraphic correlations between the Northwest Pacific and Tethyan–Atlantic sections have been difficult because of rare frequencies of age-diagnostic macro- and microfossils in the sequences in the Northwest Pacific region. In order to correlate these sections precisely, an integrated planktic foraminiferal and bulk wood carbon-isotope stratigraphy from the upper Cenomanian to the lower Campanian succession (the middle–upper part of the Yezo Group) of Hokkaido, northern Japan is established with an average resolution of 50 k.y. The δ¹³C curves from bulk wood of the Yezo Group and from bulk carbonate of English Chalk show remarkably similar patterns of isotopic fluctuation, allowing the correlation of 22 carbon isotopic events between these sections. This high-resolution correlation greatly improves the previous micro- and macrofossil biostratigraphic schemes in the Northwest Pacific region, and reveals that global events, such as the oxygen depletion at the OAE 2 horizon, the constant decrease in pCO₂ during the Late Cretaceous, and the eustatic sea-level falls in the late middle Turonian, Santonian/Campanian Boundary and early Campanian, are recorded in the Upper Cretaceous sequence of the Northwest Pacific.  相似文献   

Relationship between sinking organic matter and minerals in the shallow zone of the western Subarctic Pacific     

Masahito Shigemitsu  Yutaka W. Watanabe  Yasuhiro Yamanaka  Hajime Kawakami  Makio C. Honda 《Journal of Oceanography》2010,66(5):697-708

We used time-series sediment trap data for four major components, organic matter and ballast minerals (CaCO₃, opal, and lithogenic matter) from 150, 540, and 1000 m in the western subarctic Pacific (WSAP), where opal is the predominant mineral in sinking particles, to develop four simple models for settling particles, including the “ballast model”. The ballast model is based on the concept that most of the organic matter “rain” in the deep sea is carried by the minerals. These four models are designed to simultaneously reproduce the flux of each major component of settling particles at 540 and 1000 m by using the data for each component at 150 m as initial values. Among the four models, the ballast model, which considers the sinking velocity increase with depth, was identified as the best using the Akaike information criterion as a measure of the model fit to data. This model successfully reproduced the flux of organic matter at 540 and 1000 m, indicating that the ballast model concept works well in the shallow zone of the WSAP on a seasonal timescale. This also suggests that ballast minerals not only physically protect the organic matter from degradation during the settling process but also enhance the sinking velocity and reduce the degree of decomposition.  相似文献   

Field-induced oscillation and rotation of diamagnetic oxide crystals     

Chiaki Uyeda  Akira Tsuchiyama  Takamitu Yamanaka  Muneyuki Date 《Physics and Chemistry of Minerals》1993,20(2):82-85

The harmonic oscillations of large diamagnetic mineral samples induced by a magnetic field is reported, for single crystals of quartz, corundum, and calcite. It was seen for the first time that the period of oscillation, , was proportional to the reciprocal of the magnetic field, H, where the restoring force of the string suspending the crystal became negligible in the high magnetic field. Accordingly, the value of diamagnetic anisotropy, , could be measured from the — H curve with a sensitivity of 5 × 10^–10 emu/cc. The values were 5.50 × 10^–9 emu/cc for quartz, 4.20 × 10^–9 emu/cc for corundum, 9.9 × 10^–8 emu/cc for calcite, and 8.8 × 10^–8 emu/cc for polycrystalline talc piled with the (001) planes aligned parallel. Significant field-induced rotations were observed for the suspended crystals. When the field was applied along the direction of the diamagnetic hard axis of the stationary crystal, the crystal gradually rotated with increasing field, so that the direction of the hard-axis was perpendicular to the applied field. The field-induced energy has a the maximum value when the field is applied along the diamagnetic hard axis. This reorientation of the crystal occurs because the torque due to the field-induced anisotropic energy exceeds that of the restoring force in high magnetic fields.  相似文献   

Simulated biogeochemical responses to iron enrichments in three high nutrient, low chlorophyll (HNLC) regions   总被引：1，自引：0，他引：1  

Masahiko Fujii  Naoki Yoshie  Yasuhiro Yamanaka  Fei Chai 《Progress in Oceanography》2005,64(2-4):307

To fill temporal gaps in iron-enrichment experimental data and gain further understanding of marine ecosystem responses to iron enrichments, we apply a fifteen-compartment ecosystem model to three iron-enrichment sites, namely SEEDS (the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study; 48.5°N, 165°E) in the western North Pacific, SOIREE (the Southern Ocean Iron RElease Experiment; 61°S, 140°E) in the Southern Ocean, and IronExII (the second mesoscale iron enrichment experiment; 3.5°S, 104°W) in the Equatorial Pacific. The ecological effects of iron in the model are represented by changing two photosynthetic parameters during the iron-enrichment period. The model results successfully reproduce the observed biogeochemical responses inside and outside the iron patch at each site, such as rapid increases in plankton biomass and biological productivity, and decreases in surface nutrients and pCO₂, inside the patch. However, the modeled timing and magnitude of changes differ among the sites because of differences in both physical environments and plankton species. After the iron enrichment, the diatom productivity is strongly controlled by light at SOIREE and by silicate at IronExII and SEEDS. Light limitation due to self-shading by the phytoplankton is significant during the bloom at all sites. Sensitivity analysis of the model results to duration of the iron enrichment reveals that long-term multiple infusions over more than a week would not be effective at SEEDS because of strong silicate limitation on diatom growth. Sensitivity of the model to water temperature shows that export production is higher at lower temperatures, because of slower recycling of particulate organic carbon. Therefore, the e-ratio (the ratio of export production to primary production) is inversely correlated with temperature, and the relationship can be described with a linear function. Through this study, we conclude that ecosystem modeling is a powerful tool to help design future iron-enrichment experiments and observational plans.  相似文献