Formation of sand banks due to tidal vortices around straits     

Yoshio Takasugi  Tateki Fujiwara  Takashige Sugimoto 《Journal of Oceanography》1994,50(1):81-98

Sand banks around straits are used as a commercial fishing ground. In order to clarify the mechanism of sand bank formation, the Lagrangian method was used to measure currents and turbidity around the banks in the Neko Seto Sea in the Seto Inland Sea of Japan. A neutrally buoyant float released in the Neko Seto Strait at the maximum tidal flow stage was engulfed in a pair of tidal vortices and moved around one of the sand banks. The vertical distribution of turbidity, which was measured by the vessel moving with the neutral float, showed an extremely high turbidity in the bottom layer of this bank area. According to the analysis of these observational data, the process of sand bank formation around straits is as follows. The tidal vortex transports water mass with suspended materials (including sand) which are whirled up at the bottom by the tidal jet. In the decaying stage of the vortex, the materials in the bottom layer are gathered in the central part of the vortex by the secondary convergent flow in the vortex. Among these materials, a large-size sand particle with a high critical erosion velocity accumulates at the bottom and forms banks. The distribution of bottom sediment and the thickness of alluvium support this result.  相似文献   

Effect of seasonal change in gas transfer coefficient on air–sea CO2 flux in the western North Pacific     

Xuanrui Xiong  Yoshio Masuda  Taketo Hashioka  Tsuneo Ono  Yasuhiro Yamanaka 《Journal of Oceanography》2015,71(6):685-701

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Reconstruction of pollution history of organic contaminants in the upper Gulf of Thailand by using sediment cores: first report from Tropical Asia Core (TACO) project   总被引：1，自引：0，他引：1  

Boonyatumanond R  Wattayakorn G  Amano A  Inouchi Y  Takada H 《Marine pollution bulletin》2007,54(5):554-565

This paper reports the first reconstruction of a pollution history in tropical Asia from sediment cores. Four sediment core samples were collected from an offshore transect in the upper Gulf of Thailand and were analyzed for organic micropollutants. The cores were dated by measurement of (137)Cs and geochronometric molecular markers (linear alkylbenzenes, LABs; and tetrapropylene-type alkylbenzenes, TABs). Polychlorinated biphenyl (PCB) concentrations showed a subsurface maximum in layers corresponding to the 1970s, indicating the effectiveness of regulation of PCBs in Thailand. LAB concentrations increased over time, indicating the increase in input of sewage into the Gulf during the last 30 years. Hopanes, biomarkers of petroleum pollution, also increased over time, indicating that the inputs of automobile-derived hydrocarbons to the coastal zone has been increasing owing to the increased number of cars in Thailand since the 1950s. Polycyclic aromatic hydrocarbons (PAHs) increased in the layers corresponding to the 1950s and 1960s, probably because of the increased inputs of automobile-derived PAHs. PAH concentrations in the upper layers corresponding to the 1970s and later remained constant or increased. The absence of a subsurface maximum of PAHs contrasts with results observed in industrialized countries. This can be explained by the facts that the Thai economy did not depend on coal as an energy source in the 1960s and that economic growth has continued since the 1970s to the present. The deposition flux of PAHs and hopanes showed a dramatic offshore decrease, whereas that of LABs was uniform.  相似文献   

Apparent downward CO2 flux observed with open-path eddy covariance over a non-vegetated surface     

K. Ono  A. Miyata  T. Yamada 《Theoretical and Applied Climatology》2008,92(3-4):195-208

Summary The open-path eddy covariance (EC) method often shows unlikely downward CO₂ fluxes in late winter and early spring over drained paddy fields with few active plants. To understand why, we carried out intensive measurements in a bare paddy field from 9 to 11 April 2003, simultaneously using open- and closed-path EC methods; aerodynamic and dynamic closed-chamber methods were also used. During this period, the open-path EC method showed downward daytime CO₂ fluxes ranging from 0 to −5.9 μmol m⁻² s⁻¹, even after application of the WPL correction (density correction) and ordinary quality control tests. Because the closed-path EC and aerodynamic methods showed upward CO₂ fluxes, the downward CO₂ fluxes observed with open-path EC appear not to represent true CO₂ transport. Diurnal variations in the downward daytime CO₂ fluxes appeared to be correlated with increases in solar radiation during the day, and also with increases in sensible heat flux in weak winds but not under strongly windy conditions. The daytime 10-Hz time series data of vertical wind and CO₂ mixing ratio demonstrated that updrafts were CO₂ depleted in the open-path system, whereas the same updrafts were CO₂ enriched in the closed-path system. Careful examination of the discrepancies between the open- and the closed-path EC measurements revealed that the amplitudes of the 10-Hz temperature signals from the sonic anemometer and the resultant sensible heat fluxes were too small to compensate for the discrepancies observed during the daytime. The open-path EC method with the conventional application of the WPL correction is not necessarily appropriate for measuring small magnitudes of CO₂ flux (≤5 μmol m⁻² s⁻¹) under such surface and atmospheric conditions that the magnitude of the WPL correction is as great as that of the uncorrected CO₂ flux itself. Author’s addresses: Keisuke Ono, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan; Akira Miyata, Tomoyasu Yamada, National Institute for Agro-Environmental Sciences, Tsukuba, Japan  相似文献   

Variations in the redox state of As and Fe measured by X-ray absorption spectroscopy in aquifers of Bangladesh and their effect on As adsorption     

Takaaki Itai  Yoshio Takahashi  Ashraf Ali Seddique  Teruyuki Maruoka  Muneki Mitamura 《Applied Geochemistry》2010

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Determination of the oxidation state of radiogenic Pb in natural zircon using X-ray absorption near-edge structure     

Kazuya Tanaka  Yoshio Takahashi  Kenji Horie  Hiroshi Shimizu  Takashi Murakami 《Physics and Chemistry of Minerals》2010,37(4):249-254

We examined the L_III-edge Pb X-ray absorption near-edge structure (XANES) of three natural zircon samples with different amounts of radiation doses (1.9 × 10¹⁵ to 6.8 × 10¹⁵ α-decay events/mg). The results suggest that the oxidation state of radiogenic Pb in the zircon sample with the highest radiation dose is divalent. The XANES spectra of the two other samples with lower radiation doses suggest that radiogenic Pb(II) is present, and further that some Pb may be tetravalent. This is the first work on the determination of the oxidation state of radiogenic Pb in natural zircon using XANES.  相似文献   

Thrust faulting at a lithospheric plate boundary the Portugal earthquake of 1969     

Yoshio Fukao 《Earth and Planetary Science Letters》1973,18(2):205-216

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Seismic moment of great deep shocks     

Muneyoshi Furumoto  Yoshio Fukao 《Physics of the Earth and Planetary Interiors》1976,11(4):352-357

The long-period Rayleigh waves were investigated for the largest four deep shocks in 1963–1973 to determine the seismic moment by the same technique as used for shallow earthquakes. The results could be used for a quantitative comparison of source parameters between shallow and deep events. Three of the four shocks occurred beneath the South American continent (the Colombia earthquake, 1970; the western Brazil earthquake, 1963; the Peru—Bolivia border earthquake, 1963) and the other beneath the Japan Sea (1973). The focal depths are 653, 576, 593 and 575 km, respectively. The largest value of seismic moment was obtained as 2.1 · 10²⁸ dyncm for the Colombia earthquake. This value is still about forty times smaller than that for the great Alaskan earthquake. A slight inconsistency was found between the first-motion diagram and the Rayleigh wave radiation pattern for the Colombia earthquake and the Peru—Bolivia border earthquake.  相似文献   

Phase and group velocities and Q of mantle Love and Rayleigh waves of the first two modes and their azimuthal dependences for the 1963 Kurile Islands earthquake     

Yoshio Fukao  Minoru Kobayashi 《Physics of the Earth and Planetary Interiors》1983,32(1):4-35

Phase and group velocities and Q of mantle Love and Rayleigh waves from the 1963 Kurile Islands earthquake (M_w = 8.5) were determined over 37 great circle paths by a time variable filtering technique, in a period range 100–500 s for the fundamental modes and 100–275 s for the first higher modes. The preliminary reference Earth model (PREM) explains reasonably well the average dispersion results for the fundamental Love and Rayleigh waves. There exists a small, but significant inconsistency between the observation and the model for the first higher Love and Rayleigh waves. The Q structure of PREM is inconsistent with the observation for the fundamental Love waves, but explains other observations reasonably well. The dispersion of each mode shows a clear azimuthal dependence from which the four azimuthal windows were established. The phase and group velocity measurements for each window were, in general, shown to be mutually consistent. The azimuthal variations are largest for the first higher Rayleigh waves, indicating strong lateral heterogeneity in the structure of the low velocity zone. The first of the four windows is characterized by the largest fraction of Precambrian shields and the second window by the largest fraction of normal oceans. A comparison of these two windows may give some insight into deep lateral heterogeneity between continents and oceans. The observed phase and group velocities of the first window are systematically higher than those of the second window for the fundamental Love and Rayleigh waves at periods up to 400 s, and for the first higher Love and Rayleigh waves up to 175 s. Their differences are greatest for the first higher Rayleigh waves and least for the fundamental Rayleigh waves. Although the fundamental Rayleigh waves show the least velocity differences, their persistence up to a period of longer than 300 s is in striking contrast with some of the pure path phase velocities derived earlier for continents and oceans. A set of models for continents and oceans. PEM-C and PEM-O are not consistent with our observation. The third azimuthal window is characterized by trench-marginal seas and the fourth window by mountainous areas, typically the Asian high plateaus from northern China to the Middle East through Tibet. A comparison of these two windows gives some information about deep structural differences between subduction zones and continental collision zones, both belonging to plate convergence zones. For the fundamental and the first higher Love waves, the phase and group velocities for the third window are markedly low, whereas those for the fourth window are somewhat comparable to those for the second window. Slow Rayleigh waves are evident for two windows, with the fourth window apparently being the slowest for the fundamental Rayleigh above 200 s and for the first higher Rayleigh. For the fundamental Rayleigh waves, the third window is very slow below 200 s, but becomes progressively fast as the period increases and tends to be the fastest window around 400 s, suggesting a deep seated high velocity anomaly beneath trench-marginal seas. The dispersion characteristics of the fourth window indicate a thick high velocity lid with an extensive low velocity zone beneath it. The shield-like lithosphere, coupled with an extensive low velocity zone, may be a characteristic feature of continental collision zones. The particle motion of the fundamental Love waves was found not to be purely transverse to a great-circle connecting the epicenter to a station. The departure from the purely transverse motion is systematic among different periods, different G arrivals (G₂, G₃,…) and different stations, which may be interpreted as being due to lateral refraction.  相似文献   

Elastic properties of garnet solid-solution series     

Vladislav Babuška  Jiří Fiala  Mineo Kumazawa  Ichiro Ohno  Yoshio Sumino 《Physics of the Earth and Planetary Interiors》1978,16(2):157-176

The elastic constants of sixteen garnet specimens of wide variety in chemical composition are accurately determined by means of the rectangular parallelpiped resonance method. The dependence of the elastic properties on chemical composition is analyzed using the present data and those for seven garnets investigated by other authors. The property X_i of a garnet solid solution i is given by a linear addition law in terms of the mole fraction n_ij of component j; X_i = Σn_ijX_j where the X_j's are the properties of the end-members j (j = pyrope, almandine, spessartine, grossular and andradite). The X_j's are determined for density ρ, bulk modulus K, and shear moduli C_s = (C₁₁ ? C₁₂)/2 and C₄₄. No systematic deviation is observed from the linear addition law for the elastic moduli nor for other quantities such as the elastic wave velocities. The extrapolated elastic moduli (Mbar) of the end-members are: