Seasonal Variations in the Sea off Sanriku Coast, Japan     

Sachiko Oguma  Toru Suzuki  Yutaka Nagata 《Journal of Oceanography》2002,58(6):825-835

The temperature and salinity data obtained by the Iwate Fisheries Technology Center for the 25-year period from 1971 to 1995 were analyzed to clarify the seasonal variations in the sea off Sanriku, Japan. The variations of three typical waters found in this region, the Tsugaru Current water, the Oyashio water, and the Kuroshio water are discussed in terms, of a T-S scatter diagram referring to the water mass classification proposed by Hanawa and Mitsudera (1986). The mean temperature and salinity fields averaged for each month show clear seasonal variation. Distributions of the Tsugaru Current water and the Oyashio water can barely be distinguished in the fields deeper than 200 m since the Tsugaru Current has a shallow structure; however, the fields at 100 m depth indicate remarkable seasonal variation in the area of the Tsugaru Current. At 100 m depth, the temperature and salinity fronts between the Tsugaru Current water and the Oyashio water gradually disappear in January through April, appear again in May, then become clearest in September. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Pelagic chaetognaths in Sagami Bay and Suruga Bay,Central Japan     

Ryuzo Marumo  Sachiko Nagasawa 《Journal of Oceanography》1973,29(6):267-275

Pelagic chaetognaths in Sagami Bay and Suruga Bay, Central Japan, were studied. Their community structure was very similar in both of these bays. Four genera and 26 species were identified. In Sagami Bay the habitat segregation by depths was clearly obtained. The population and species number of epipelagic (0–200 m) chaetognaths were larger in summer than in winter. The populations of meso- (200–500 m) and bathypelagic (500–1,000 m) species were smaller than that of epipelagic ones and fairly stable seasonally.  相似文献   

Bacterial invasion of chaetognaths under laboratory and natural conditions     

Sachiko Nagasawa  Usio Simidu  Takahisa Nemoto 《Journal of Oceanography》1984,40(5):327-333

Chaetognaths are an abundant component of the plankton and are usually the most important carnivores. Head or tail damage is often found in chaetognath specimens from the laboratory and the sea. Examination by light and scanning electron microscopy (SEM) of specimens with such damage has revealed that bacterial invasion occurs in chaetognaths under laboratory and natural conditions. Living chaetognaths which cease feeding are found to have large numbers of attached bacteria and some parts of their body become opaque. Once they are attacked in this manner the body appears to be a mass of bacteria. Examination of field samples has shown that similar bacterial attacks occur in the sea. Bacterial growth is common inside the muscle tissue of field specimens. Up to 13.3% of two dominant species of chaetognaths in Suruga Bay are attacked by bacteria.  相似文献   

Feeding of a pelagic chaetognath,Sagitta nagae Alvariño in Suruga Bay,Central Japan     

Sachiko Nagasawa  Ryuzo Marumo 《Journal of Oceanography》1972,28(5):181-186

The feeding ofSagitta nagae, the most predominant chaetognath species in Suruga Bay, was studied. Specimens were collected with ORI-100 net (1.0 mm in mesh aperture) and MTD net (0.35 mm in mesh aperture) and were fixed with neutralized formalin. The main food organisms ofSagitta nagae were the copepods,Candacia bipinnata, Calanus pacificus andPareuchaeta russelli. The food-containing ratio (P/T, %) was higher at night and lower in the daytime. Here, P is the number ofSagitta containing food organisms in the gut and T is the total number ofSagitta examined. P/T was almost constant vertically in the upper 100 m layer. P/T was generally influenced neither by food density nor by the copepod numbers perSagitta in this study.Sagitta nagae took food throughout life. Food ingested bySagitta per day was calculated as 37.6% ofSagitta in dry weight.  相似文献   

Inter-seasonal variability of internal tides in the western Bay of Bengal     

Himansu K. Pradhan  A. D. Rao  Sachiko Mohanty 《Natural Hazards》2016,84(2):809-820

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A review of the origins of endemic species in Lake Biwa with special reference to the goby fish,Chaenogobius isaza     

Sachiko Takahashi 《Journal of Paleolimnology》1988,1(4):279-292

The 1400 m deep drilling of Lake Biwa has revealed that the lake probably originated ca. 5 · 10⁶ yr ago. After a geographic shift to its present position, and by more than 3.10⁵ yr ago, it had become a large and deep lake. The considerable longevity, large size and high diversity of habitats of this lake are considered to have contributed to its high abundance of endemic taxa. These taxa fall into two categories: (1) relict species of the Asiatic continent, higher latitude or marine origin; (2) species differentiated in the lake from littoral-lacustrine species, and having adapted to habitats peculiar to Lake Biwa. I discuss some of these endemic organisms, briefly review recent in vestigations on fossil organisms of the lake, and more fully discuss the origin of a representative endemic species, the pelagic gobiid fish Chaenogobius isaza Tanaka. This species is regarded as having differentiated from some littoral Chaenogobius species, creating a novel niche in the open water area after Lake Biwa was established as a deep lake.This is the seventh of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series.  相似文献   

Effect of seasonal and cyclonic winds on internal tides over the Bay of Bengal     

Mohanty  Sachiko  Rao  A. D.  Pradhan  Himansu 《Natural Hazards》2017,87(2):1109-1124

The influence of seasonal and cyclonic winds is studied on the characteristics of internal waves (IWs) over the western Bay of Bengal (BoB) by using MITgcm model. As the BoB experiences reversal of seasonal winds and also tropical cyclones during pre-monsoon and post-monsoon months, its effect is seen through the computation of spectral estimates of the IWs. It is seen that the peak estimate is associated with the semidiurnal frequency at all the depths and is found higher in May compared to November. This is attributed to the presence of shallow mixed layer depth and deep thermocline due to the upwelling favorable winds. The computation of isopycnal displacement infers that the internal tides are present from 40 to 120 m depth in case of upwelling favorable winds of May, whereas, the presence of internal tides is restricted between 90 and 120 m for the downwelling favorable winds of November. During May, the available potential energy is also seen in a narrow coastal stretch, whilst it is absent in November. During the Hudhud cyclone period of October 7–14, 2014, it is noticed from the spectral estimates that the IWs of tidal frequency are replaced by inertial frequency with a periodicity of about 2 days as a consequence of strong cyclonic winds. The progressive vector diagram shows the mean current is initially westward up to October 17, 2014 and then northeastward with well-defined clockwise circulation. The maximum radius of inertial oscillation of 15 km is observed. After the cyclone ceases, the estimate associated with inertial frequency slowly diminishes and enhances the estimates related to internal tides. The simulations also suggest that the internal tides are absent for about 6 weeks as a response of the cyclonic winds.

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An attempt to characterize phase Q: Noble gas, Raman spectroscopy and transmission electron microscopy in residues prepared from the Allende meteorite     

Jun-ichi Matsuda  Kazuhiko Morishita  Chie Miyakawa  Sachiko Amari  Seiji Takeda 《Geochimica et cosmochimica acta》2010,74(18):5398-5409

We have prepared a HF-HCl residue and its oxidized residue of the Allende meteorite and have measured the elemental concentrations and the isotopic compositions of noble gases. In the HF-HCl reside, noble gases are enriched in colloidal fraction compared to the non-colloidal fraction by a factor of 2-4. The heavy noble gases were evidently lost after the oxidization, indicating that phase Q (carrier of planetary heavy noble gases) was removed by the oxidation. The Raman spectroscopic parameters show that the colloidal fraction of the HF-HCl residue is more amorphous compared to the non-colloidal fraction. As the ion irradiation converts carbon into a more amorphous form, our result indicates that the “plasma model” is more plausible than the “labyrinth model” as the origin of phase Q. TEM (Transmission Electron Microscope) observations also show such a trace of ion irradiation. While the TEM observations did not show any large difference between the HF-HCl residue and its oxidized residue, the Raman spectroscopic parameters changed discretely resulting from the oxidization. This observation indicates that the oxidization not only dissolved and removed oxidized carbon, but also changed the carbon structure itself to a more amorphous (disordered) state. The Raman spectroscopic results indicate the possibility that release of Q-gas during oxidation is not accompanied by mass loss and that the release of Q-gas simply resulted from rearrangement of carbon structure during oxidation.  相似文献   

Chemistry of Late Early Triassic Siliceous Claystone ('Toishi-type' Shale) from the Oritate Area, Sambosan Belt, Kyushu, Southwest Japan     

Kosei Komuro    Sachiko Agematsu  Katsuo Sashida 《Resource Geology》2006,56(4):447-455

Abstract. Inorganic chemical compositions are determined for late Early Triassic siliceous claystone ('Toishi-type' shale) and associated chert from Oritate area, Sambosan Belt, Kyushu, southwest Japan. The siliceous claystone is similar in chemical composition to Post-Archean Australian Shale (PAAS), but is depleted in Ca, Sr, Mn, and Fe and slightly enriched in Cu, Zn, P, and rare earth elements (REEs). The siliceous claystone and associated chert have flat REE patterns with positive Eu anomalies and no distinct Ce anomaly. The siliceous claystone and associated chert have largely constant Ti/Al, Th/Al, and Nb/Al ratios compared to the variable ratios found in siliceous shale and sandstone deposited close to land in a trench setting. This suggests that the claystone and chert were deposited in a deep-sea pelagic environment and were derived mainly from the suspended fraction, including eolian dust and material transported from distant lands, rather than from turbidity currents that occurred close to land. The low Ca contents of the analyzed rocks indicate deposition below the calcium-carbonate compensation depth. The depletion of Mn and Fe, and no distinct Ce anomaly in the Oritate siliceous claystone are also evident, being similar to those in samples from the Sasayama and Kinkazan sections in the Mino-Tanba Belt, where oceanic anoxia developed during the Late Permian to earliest Triassic. This might suggest that oceanic anoxia prevailed through to the late Early Triassic.  相似文献   

An attempt to separate Q from the Allende meteorite by physical methods     

Sachiko Amari  Shiho Zaizen  Jun-Ichi Matsuda 《Geochimica et cosmochimica acta》2003,67(24):4665-4677

In order to characterize the planetary noble gas carrier Q, we separated a Q-rich floating fraction from the Allende meteorite into ten fractions by a combination of colloidal and density separations. All five noble gases in the separated fractions were analyzed by pyrolysis in 600 and 1600°C temperature steps. Half of Q in the floating fraction is concentrated in the fraction C1-8D with the density of 1.65 ± 0.04 g/cm³. All the separated fractions show similar isotopic ratios except for ⁴⁰Ar/³⁶Ar ratios. C1-8D has the lowest ³⁸Ar/³⁶Ar and ⁴⁰Ar/³⁶Ar ratios (0.18784 ± 0.00020 and 4.36 ± 0.15, respectively) in the 1600°C fraction, confirming that the fraction is enriched in Q. Most grains in C1-8D are carbonaceous with small amounts of F and O. These results imply either that the density of Q is 1.65 ± 0.04 g/cm³ or that Q preferentially sticks to matter of that density. All the separates have similar Q to diamond ratios, indicating that Q and diamond are closely associated.  相似文献