Long-term (36-year) observations on the dynamics of the fish-killing raphidophyte Chattonella in Harima-Nada,eastern Seto Inland Sea,Japan     

Tetsuya Nishikawa  Yutaka Hori  Satoshi Nagai  Kazutaka Miyahara  Yukinobu Nakamura  Kazuhiro Harada  Kuninao Tada  Ichiro Imai 《Journal of Oceanography》2014,70(2):153-164

Long-term changes of the fish-killing raphidophyte Chattonella spp. (Chattonella antiqua, Chattonella marina and Chattonella ovata) were examined in relation to environmental factors at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan, for 36 years from 1973 to 2008. Long-term trends in the dynamics of Chattonella populations were considered to relate to environmental factors such as nutrient concentrations and water temperature. High nutrient levels during the period from the 1970s to the early 1980s have contributed to the high cell density and large-scale red tides of Chattonella spp. in Harima-Nada. However, nutrient levels exhibited a decreasing trend thereafter, and it is thought that Chattonella spp. cannot form large-scale blooms under the present conditions. After the mid-1990s, the occurrence period of vegetative cells of Chattonella spp. has been several weeks or 1 month earlier than that of the 1970s and early 1980s, and the appearance frequency of Chattonella spp. has increased in the northern coastal area, although the cell density and the spatial scale of the distribution have become lower and smaller than those in the previous decades. It is suggested that the timing of germination of Chattonella cysts has become earlier as a result of the increase in water temperature, and the chances of vegetative growth have also increased, especially at the northern coast where most of large rivers discharge into the Harima-Nada. In addition, the present results revealed that fewer diatoms were also one of the significant factors for the high abundance of Chattonella spp. in Harima-Nada.  相似文献   

Millennial-scale oscillations of the westerly jet path during the last glacial period   总被引：1，自引：0，他引：1  

Kana Nagashima  Ryuji Tada  Atsushi Tani  Youbin Sun  Yuko Isozaki  Shin Toyoda  Hitoshi Hasegawa 《Journal of Asian Earth Sciences》2011,40(6):239-1220

It has been established that East Asian summer monsoon intensity varies with Dansgaard–Oeschger cycles, suggesting a connection between the climates of East Asia and the North Atlantic on a millennial timescale. However, the dynamics of such a connection are still unsolved. Here we demonstrate that temporal changes in the provenance of aeolian dust in Japan Sea sediments, which we interpret to reflect changes in the westerly jet path over East Asia, exhibit variations in harmony with Dansgaard–Oeschger cycles. The dominance of dust with a Mongolian Gobi provenance during stadials suggests a westerly jet axis located to the south of the Himalaya–Tibetan Plateau throughout most of the year, whereas the co-dominance of dust from both the Taklimakan Desert and the Mongolian Gobi during interstadials suggests that the westerly jet axis jumped to the north of the Tibetan Plateau at latest in summer. As the shift of the westerly jet axis to the north of the Tibetan Plateau is closely related to the onset of the East Asian summer monsoon, changes of the westerly jet path apparently critically affect the teleconnection between the climates of Asia and North Atlantic on a millennial timescale.  相似文献   

Effect of solid to solution ratio on biogenic silica determination in coastal sediments     

Nattapong Loassachan  Kuninao Tada 《Journal of Oceanography》2008,64(5):657-662

The method of DeMaster (1981) for measuring biogenic silica (BSi) in marine sediments was modified. We found a considerable effect of the solid to solution (S/S) ratio on BSi determination in coastal sediments. The BSi contents determined by DeMaster’s method were overestimated due to the contribution of clay mineral-derived extractable Si at a low S/S ratio (<1 g l⁻¹), and incomplete recovery of BSi was observed due to incomplete extraction when using a high S/S ratio (>2 g l⁻¹). For BSi analysis of coastal sediment samples, the BSi content of representative samples must be measured using various S/S ratios to determine the appropriate S/S ratio in order to minimize the contribution of extractable Si derived from clay minerals and to obtain sufficiently efficient extraction with 1% Na₂CO₃ before actual sample measurement. One way to determine the appropriate S/S ratio is to use artificial sediment which has a theoretical Si and clay mineral content similar to the sediment sample composition. Using artificial sediment, the S/S ratio of 2 g l⁻¹ seems appropriate for measuring the BSi content of the coastal sediments investigated in this study, because 99.6% recovery can be achieved.  相似文献   

Comparison of Chlorophyll a Concentrations Obtained with 90% Acetone and N,N-dimethylformamide Extraction in Coastal Seawater     

Kuninao Tada  Hitomi Yamaguchi  Shigeru Montani 《Journal of Oceanography》2004,60(2):259-261

Determinations of Chlorophyll a (Chl a) in eutrophic coastal marine waters were compared using N, N-dimethylformamide (DMF) and 90% acetone techniques. Measured Chl a concentrations ranged from 0.89 to 10.65 μg l₋₁ for 90% acetone extracts and from 0.97 to 12.92 μg l⁻¹ for DMF extracts, respectively, for 24 surface water samples from the Harima-nada, Seto Inland Sea, Japan. Chl a concentrations using DMF as a solvent were consistently higher than those found using 90% acetone (p < 0.001, n= 24). Chl a is thus likely to be underestimated (by 13%) when 90% acetone is used for eutrophic waters. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A generic formulation for microtremor exploration methods using three-component records from a circular array   总被引：1，自引：0，他引：1  

Ikuo Cho  Taku Tada  Yuzo Shinozaki 《Geophysical Journal International》2006,165(1):236-258

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Continuous GPS Array and Present-day Crustal Deformation of Japan   总被引：1，自引：0，他引：1  

T. Sagiya  S. Miyazaki  T. Tada 《Pure and Applied Geophysics》2000,157(11-12):2303-2322

—A GPS array with about 1,000 permanent stations is under operation in Japan. The GPS array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the Japanese islands. Based on daily coordinate data of the GPS stations, strain rate distribution is estimated. Most regions with a large strain rate are related to plate boundaries and active volcanoes. In addition, the Niigata-Kobe Tectonic Zone (NKTZ) is recognized as a region of large strain rate along the Japan Sea coast and in the northern Chubu and Kinki districts. This newly found tectonic zone may be related to a hypothetical boundary between the Eurasian (or Amurian) and the Okhotsk (or North America) plates. Precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities. Appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations.  相似文献   

Large earthquakes initiate by the acceleration of slips on the downward extensions of seismogenic faults     

Yoshihisa Iio  Yoji KobayashiTakashi Tada 《Earth and Planetary Science Letters》2002,202(2):337-343

In order to examine the relationship between anomalous crustal deformations and subsequent large earthquakes, we compiled and examined data on preseismic anomalous crustal deformations for two earthquakes that occurred in and around the Japanese Islands in recent years. We found that the slip on a downward extension of a seismogenic fault accelerates before the main shock and that the average slip velocity is inversely proportional to the time remaining until the main shock occurs.  相似文献   

Non-hypersingular boundary integral equations for two-dimensional non-planar crack analysis     

Taku Tada  Teruo Yamashita 《Geophysical Journal International》1997,130(2):269-282

We derive a set of non-hypersingular boundary integral equations, both elastodynamic and elastostatic, for the analysis of arbitrarily shaped 2-D anti-plane and in-plane cracks located in an infinite homogeneous isotropic medium, rendered in a unified nomenclature for all cases. The hypersingularities that appear in the usual formulations for the dynamic cases, existent both at the source point and at the wavefront, are removed by way of a regularization technique based on integration by parts. The equations for the in-plane cases are presented in terms of a local Cartesian coordinate system, one of the axes of which is always held locally tangential to the crack trace. The expressions for the elastic field at any point on the model plane are also given.
Our formulations are shown to yield accurate numerical results, as long as appropriate stabilization measures are taken in the numerical scheme. The numerical applicability of our method to non-planar crack problems is illustrated by simulations of dynamic growth of a hackly crack which has small off-plane side-branches. The results imply that the branching of a crack brings about a significant decrease in the crack-tip stress concentration level and consequently may play an essential role in the arrest of earthquake rupturing.  相似文献   

Elastic stress and strain in jointed rock masses by means of crack tensor analysis   总被引：7，自引：0，他引：7  

Prof. M. Oda  T. Yamabe  Y. Ishizuka  H. Kumasaka  H. Tada  K. Kimura 《Rock Mechanics and Rock Engineering》1993,26(2):89-112

Summary An elastic stress-strain relation is formulated in terms of crack tensors which makes it possible to take into account explicitly the effect of joints on elastic behavior of rock masses. The present study is to discuss some related topics which may be encountered in its practical application. Two problems are solved by incorporating the elastic stress-strain relation into a program for three-dimensional finite element analyses; i. e., stress concentration by surface loading and displacement by excavation of an intersecting tunnel. Validity of the results is checked by comparing them with a laboratory model test and a field test, with the following conclusions: The overall distribution of stress definitely depends on a joint stiffness ratio (i. e., normal stiffness to shear stiffness). If the ratio is chosen as unity, the stress concentration occurs mainly in the direction parallel to major joints. If the ratio is high, say 10, then the stress concentrates along the perpendicular as well as the parallel directions to major joints. It can be said, on the basis of the fairly good agreement of the calculations using the high stiffness ratio with the field and laboratory measurements, that the elastic solution by crack tensors provides a practical tool for estimating the stress and strain in strongly jointed rock masses.  相似文献   

Crustal deformations associated with the 1986 fissure eruption of Izu-Oshima volcano, Japan, and their tectonic significance     

Manabu Hashimoto  Takashi Tada 《Physics of the Earth and Planetary Interiors》1990,60(1-4):324-338

We have investigated crustal deformations associated with the 1986 eruption of Izu-Oshima volcano, Japan, which was accompanied by an intensive fissure eruption. Two fissure crater chains, with NW-SE trend were created in the northern part of the caldera and on its northwestern flank. Their trend is consistent with the direction of compressive stress in this region. Depression of > 30 cm in the central zone including the caldera, and in the northwestern and southeastern parts in the island, was detected by precise leveling. On the other hand, uplifts up to 20 cm in the northeastern and southwestern parts were observed. Tide observations revealed that the Okada tide station, the leveling datum in Izu-Oshima, may have subsided by 5 cm after the eruption. An 1 m opening of fissure craters was detected by distance measurements of the baselines which cross fissure craters. Horizontal displacements obtained by reoccupation of control points showed a symmetrical pattern which was consistent with the opening of fissure craters. Anomalous strain changes were also observed in the surrounding regions—contractions were observed in the Boso and the Miura peninsula, northeast of Izu-Oshima, and extensions in the Izu peninsula.

To interpret these crustal deformations, a model which consists of a nearly vertical tensile fault and a deflation source is presented. The tensile fault lies parallel to the fissures and is divided into two parts according to depth. The deeper part of the tensile fault is 12 km long, 10 km wide, and has 2 km burial depth and 2.7 m opening displacement. The shallower part, which may represent the fissure craters, is 4 km long, 2 km wide, and the amount of opening is estimated to be 1 m. However, the deflation source may be located at a depth of 10 km beneath the northwestern flank of the caldera and depression just above the source is estimated to be 30 cm. A deflation source is required to explain the subsidence at the Okada tide station and the extension in the Izu peninsula. This model suggests that the eruption might have released tensile stresses in and around the Izu region which result from bending of the subducting Philippine Sea plate.  相似文献