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排序方式: 共有334条查询结果,搜索用时 15 毫秒
1.
Masayuki Takahashi Sooji Shimura Yukuya Yamaguchi Yoshihiko Fujita 《Journal of Oceanography》1971,27(2):43-50
The photo-inhibition of phytoplankton photosynthesis at higher intensities was examined with a cultured marine diatom,Phaeodactylum tricornutum, and natural samples. The question was to determine whether photo-inhibition results from excretion of photosynthetic products from cell or from an actual decrease in photosynthetic rate.
P. tricornutum cultured at 15 klux showed very little photo-inhibition up to 70 klux, and, in the sample cultured at 1 klux, most marked photo-inhibition was observed in 3 hours experiment. Extracellular release was less than 30% of particulate fixation, and did not show any extreme increase to supplement photosynthesis depression at higher light intensities. When the photosynthesis was measured during 10 minutes, both samples showed no photo-inhibition. The photosynthesis by low light sample lost the linearity of time-course with prolonged exposure at high light intensity. Observed photo-inhibition, therefore, we explained with the actual decrease in photosynthetic rate. Similar photo-inhibition could be seen in marine phytoplankton samples concentrated by filtration. 相似文献
2.
Photographic observations were carried out at depths of the shelf edge at the mouth of Uchiura Inlet, Suruga Bay, central Japan in order to clarify the life style of the isocrinid stalked crinoid,Metacrinus rotundus (Echinodermata). The distribution of the species was found to be restricted to a narrow area where boulders and rock outcrops were locally present. Mean density of the crinoid was 0.05 m–2, and this value was an order of magnitude smaller than that of the deeper isocrinid,Diplocrinus wyvillethomsoni, reported from the Bay of Biscay.Metacrinus rotundus formed a parabolic filtration fan with its arms recurved into the bottom current, and was thought to be a passive suspension feeder elevating the fan into the water column by its stalk. The distal half of the stalk lay along the hard substratum and about ten groups of cirri grasped the substratum. This mode of attachment was similar to that ofCenocrinus rather than that ofDiplocrinus. Metacrinus rotundus collect food at the layer between 10 and 50 cm above the sea floor, and do not utilize a higher layer even when this layer could be utilized by climbing over a larger boulder. Resuspended benthic materials are thought to be important as a food source forM. rotundus, and the crinoids seek not only locations of stronger currents but also the position where much resuspended matter is available. 相似文献
3.
Evidence for the applicability of GEK (Geomagnetic Electrokinetography) measurements to shallow water regions is provided
from observations in the shelf region of the East China Sea. The reason for the effectiveness of GEK measurements in this
case is investigated theoretically, and it is shown to be attributable to the existence of a thick conductive sedimentary
layer. In addition, it is shown that low conductive basement rock can be regarded as a good conductor for GEK measurements
if the current width is broad enough and if the ratio of current width to water depth is larger than the resistivity ratio
of basement rock to sea water. This implies that barotropic tidal currents can be measured with GEK in any ocean on the earth
if they have significant magnitudes. 相似文献
4.
Density,biomass and community structure of demersal fishes off the Pacific coast of northeastern Japan 总被引:8,自引:0,他引:8
Demersal fish communities were studied on the lower continental shelf and the upper continental slope along the Pacific coast of northeastern Japan. Species composition, number and weight of each species were examined based on otter trawl samples at 45 stations. Mean density and biomass of demersal fishes were 131 ha–1 and 21 kg ha–1, respectively. The ten most abundant species comprised of about 95% of total number and weight of overall catch indicating simple species composition. Gadiform fishesTheragra chalcogramma, Gadus macrocephalus andPhysiculus maximowiczi were the most important species by number, weight and frequency of occurrences, and three main community types represented by the three key species were recognized.Theragra-dominant community showed higher density and biomass, and lower diversity thanPhysiculus-dominant community did. Species diversity of demersal fish community was negatively correlated to density and biomass. Density and biomass of demersal fish community were high on the uppermost slope, and the high abundance resulted from low-diversity communities dominated byT. chalcogramma andG. macrocephalus. 相似文献
5.
Thermal and chemical evolution of the terrestrial magma ocean 总被引:8,自引:0,他引:8
Yutaka Abe 《Physics of the Earth and Planetary Interiors》1997,100(1-4):27-39
The Earth is likely to have experienced a magma ocean stage during accretion. Thermal and chemical evolution of magma ocean is investigated based on a one-dimensional two-phase-flow heat and mass transfer model. Differentiation at lower mantle pressure depends on the type of magma ocean and surrounding atmosphere. If the magma ocean is formed by the blanketing effect of a solar-type proto-atmosphere, extensive differentiation proceeds at lower mantle pressure. If the magma ocean is formed by the blanketing effect of an impact-induced steam atmosphere, no differentiation at lower mantle pressure is likely. If a very deep magma ocean is formed by a giant impact, whether differentiation proceeds at lower mantle pressure or not depends on grain size, viscosity of melt and/or properties of a transient atmosphere. On the contrary, chemical differentiation likely proceeds at upper mantle pressure irrespective of magma ocean type. A shallow magma ocean can remain for 100 200 My without any heating processes. 相似文献
6.
Sliding of natural and artificial slopes generally occurs during or following strong earthquakes. Such sliding is greatly affected by a combination of geological conditions and earthquake loading. Earthquake-induced landslides often cause more damage to infrastructure and human lives than the earthquake itself. Pseudo-static analysis is widely implemented as one of several design methods used in engineering practice to assess the seismic stability of natural and artificial slopes. However, the most important issue of pseudo-static analysis is to select the most appropriate method for measuring seismic coefficient. In order to investigate this, back analysis was conducted for surficial slides subjected to strong ground motion during the 2004 Mid-Niigata prefecture earthquake in Japan. This paper surveyed the stochastic properties of earthquake-induced surficial slides and clearly showed that the obtained results were applicable to back analysis of shear strength and seismic coefficient. In back analysis, soil properties such as soil strength and density and sliding depth were assumed as random variables owing to their uncertainties. Seismic coefficient is also assumed to be a random variable and varies with distance from the epicenter fault line. The analysis of 4504 recorded surficial slides clearly shows a unique relationship of landslide occurrence ratio with slope angle and distance from the epicenter fault line. This study’s results enhance the calculation of the shear strength of weathered soil covering slopes and the horizontal seismic coefficient through back analysis procedure. By considering possible stochastic properties of variables, some case studies were implemented in the back analysis. 相似文献
7.
Molecular and isotopic characteristics of gas hydrate-bound hydrocarbons in southern and central Lake Baikal 总被引:4,自引:4,他引:0
Akihiro Hachikubo Oleg Khlystov Alexey Krylov Hirotoshi Sakagami Hirotsugu Minami Yutaka Nunokawa Satoshi Yamashita Nobuo Takahashi Hitoshi Shoji Shin’ya Nishio Masato Kida Takao Ebinuma Gennadiy Kalmychkov Jeffrey Poort 《Geo-Marine Letters》2010,30(3-4):321-329
We investigated the molecular composition (methane, ethane, and propane) and stable isotope composition (methane and ethane) of hydrate-bound gas in sediments of Lake Baikal. Hydrate-bearing sediment cores were retrieved from eight gas seep sites, located in the southern and central Baikal basins. Empirical classification of the methane stable isotopes (δ13C and δD) for all the seep sites indicated the dominant microbial origin of methane via methyl-type fermentation; however, a mixture of thermogenic and microbial gases resulted in relatively high methane δ13C signatures at two sites where ethane δ13C indicated a typical thermogenic origin. At one of the sites in the southern Baikal basin, we found gas hydrates of enclathrated microbial ethane in which 13C and deuterium were both highly depleted (mean δ13C and δD of –61.6‰ V-PDB and –285.4‰ V-SMOW, respectively). To the best of our knowledge, this is the first report of C2 δ13C–δD classification for hydrate-bound gas in either freshwater or marine environments. 相似文献
8.
Yutaka Yoshikawa Akira Masuda Kenichi Marubayashi Michiyoshi Ishibashi 《Journal of Oceanography》2010,66(2):223-232
Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface
currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the
large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern
and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore
currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible
for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven
flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection
angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven
flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the
surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the
surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector
empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima
and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed
primarily by the incoming Tsushima Warm Current. 相似文献
9.
We describe a least-squares inversion approach to estimating the subsurface resistivity structure from cross-hole or borehole-to-surface electromagnetic data. It is assumed that the resistivity distribution is symmetric about the axis of a borehole and that vertical magnetic dipoles are located on the borehole axis. The receivers are placed either in another borehole or on the earth's surface. The inversion scheme uses the finite-element and smoothness-constrained least-squares methods. The computational effort required to obtain partial derivatives is reduced considerably by using the reciprocity principle. Numerical simulations show that the reconstructions are generally in good agreement with the true structures when the assumption of an axisymmetric earth structure holds. An example involving the breakdown of this assumption, which can be obtained by interchanging the source and receiver boreholes, suggests that the inversion result may also be useful for locating a general 3D anomaly although artifacts are present. 相似文献
10.
Naomi AOTA Yutaka MIYAMOTO Sakae KOSANDA Yasuji OURA Koh SAKAMOTO 《Geostandards and Geoanalytical Research》1994,18(1):65-84
Fifteen rock reference samples "Igneous rock series" issued by the Geological Survey of Japan were analysed for up to 31 elements by neutron activation analysis (NAA); 14 MeV-NAA for Si and Al, fission track method for U, radiochemical and instrumental NAA for rare-earth elements, and instrumental NAA for the remaining elements, with reactor neutrons for the latter three. The present results are compared with published values. 相似文献