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81.
82.
Itsuro Kita Yoshitada Asakawa Tsutomu Yuri Mitsuhiro Yasui Yoichi Shimoike Masatsugu Yamamoto Hidenao Hasegawa Sachihiro Taguchi Hirochika Sumino 《Bulletin of Volcanology》2012,74(5):1121-1139
The tectonic environment of Kyushu, Japan is affected both by the subduction of the Philippine Sea plate and by the extensional tectonics related to rifting of Okinawa Trough at the eastern margin of the Eurasia Plate. We found that the Sendai fault zone acts as a channel for concurrent eruption of oceanic island basalt (OIB)-type and island arc (IA)-type basaltic rocks, propagating west to east in the Sendai region of southern Kyushu. The location of the Sendai fault zone is likely to correspond to the left-lateral shear zone in southern Kyushu as inferred by GPS Earth Observation Network. A similar magmatic association is present in the Beppu–Shimabara (BS) graben system in central Kyushu. The associate magmas of OIB-type rocks in Kyushu can be classified into typical, EM II-like and their intermediate OIB-type magmas in addition to MORB-like OIB-type magma in 87Sr/86Sr–Nb/Y systematics. Typical OIB-type and intermediate OIB-type magmas are erupted within the Sendai fault zone and BS graben system, respectively. The former is characterized by highest Nb/Y but low 87Sr/86Sr similar to MORB-like OIB-type magma erupted in northern Kyushu and the latter has intermediate Nb/Y and 87Sr/86Sr between typical and EM II-like OIB-type magmas. Almost all the IA-type rocks within the Sendai fault zone are generated from parental IA-type magma in Kyushu and characterized by weak crustal assimilation, having the lowest 87Sr/86Sr similar to typical OIB-type magma but the highest 143Nd/144Nd of arc magmas in Kyushu. The ages of both types of basaltic rocks within the Sendai fault zone range from 1.6 to <0.01?Ma clearly younger than those of andesitic rocks on northern and southern outsides of the fault zone and become younger from west to east. Initial formation of the fault zone has been induced by the counterclockwise rotation of southern Kyushu during the last 2?Ma as well as the BS graben system. Kyushu has continued to be split into three parts by the Sendai fault zone and BS graben during the Quaternary; northern, central, and southern zones. Their initial formation ages are likely to be linked to the initial rifting age of the middle Okinawa Trough back-arc basin. 相似文献
83.
Atsushi Yamaguchi Yuji Watanabe Hiroshi Ishida Takashi Harimoto Kazushi Furusawa Shinya Suzuki Joji Ishizaka Tsutomu Ikeda Masayuki Mac Takahashi 《Journal of Oceanography》2004,60(4):773-787
As part of the research program WEST-COSMIC Phase I (1997–2001), vertical profiles down to the greater depths (0–2000 m or
5800 m) of the plankton community structure composed of heterotrophic bacteria, phytoplankton, protozooplankton and metazooplankton
were studied at one station in each subarctic (44°N) and in transitional region (39°N), and two stations in subtropical region
(30°N and 25°N); all in 137–155°E in the western North Pacific Ocean. The biomass of all four taxonomic groups decreased rapidly
with increasing depths at all stations, although the magnitude of depth-related decrease differed among the groups. As plankton
community structure, metazooplankton biomass and bacterial biomass occupied >50% of the total in 0–2000 and 2000–4000 or 5000
m strata, respectively, at subarctic and transitional stations, while bacterial biomass contributed to >50% of the total consistently
from 0 through 4800 or 5800 m at subtropical stations. Metazooplankton biomass integrated over the greater depths exhibited
a clear latitudinal pattern (high north and low south), but this was not the case for those of the other taxonomic groups.
As a component of metazooplankton, an appreciable contribution of diapausing copepods to the metazooplankton was noted at
subarctic and transitional stations, but they were few or nil at subtropical stations. As protozooplankton assemblages, heterotrophic
microflagellates (HMF) and dinoflagellates were two major components at subarctic and transitional stations, but were only
HMF predominated at subtropical stations. From biomass ratios between heterotrophic bacteria, HMF and dinoflagellates, “sinking
POC-DOC-heterotrophic bacteria-HMF-heterotrophic dinoflagellates” link was proposed as a microbial food chain operative in
the deep layer of the western North Pacific. All results are discussed in the light of latitudinal differences in the structure
and functioning of plankton community contributing to the ‘biological pump’ in the western North Pacific Ocean.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
84.
Yuji Watanabe Atsushi Yamaguchi Hiroshi Ishida Takashi Harimoto Shinya Suzuki Yoshio Sekido Tsutomu Ikeda Yoshihisa Shirayama Masayuki Mac Takahashi Takashi Ohsumi Joji Ishizaka 《Journal of Oceanography》2006,62(2):185-196
The first CO2 exposure experiments on several species of pelagic copepods inhabiting surface and deep layers in the western North Pacific
were conducted. Living organisms were collected from two layers between the surface and 1,500 m between latitudes of 11 and
44°N, and they were exposed aboard ship to various pCO2 up to about 98,000 μatm. Mortality of copepods from both shallow and deep layers in subarctic to subtropical regions increased with increasing
pCO2 and exposure time. Deep-living copepods showed higher tolerance to pCO2 than shallow-living copepods. Furthermore, deep-living copepods from subarctic and transitional regions had higher tolerances
than the subtropical copepods. The higher tolerances of the deep-living copepods from subarctic and transitional regions may
be due to the adaptation to the natural pCO2 conditions in the subarctic ocean. 相似文献
85.
Tsutomu Nakazawa Akira Nishimura Yasufumi Iryu Tsutomu Yamada Hiroshi Shibasaki Satoshi Shiokawa 《Marine Geology》2008,247(1-2):35-45
Carbonate rock cores drilled on the Kikai Seamount, northern Philippine Sea are examined for better understanding of tectonic history of the northern Philippine Sea. The Kikai Seamount, the summit of which is at 1960 m water depth, is an isolated high on the northwestern part of the Amami Plateau formed by subduction-related arc volcanism, and is situated close to the axis of the Ryukyu Trench in front of the Ryukyu Arc, SW Japan. The seamount is capped with shallow-water carbonates such as coral rudstone. Detailed examinations of lithology, larger foraminiferal assemblages, and Sr isotope composition reveal that the core material comprises Miocene carbonates unconformably overlain by Early Pleistocene carbonates. It indicates rapid subsidence of the Kikai Seamount since the Early Pleistocene. The most probable cause of rapid subsidence is collision and subduction of the Amami Plateau laden with the Kikai Seamount. The rapid subsidence may have started when the western corner of the plateau reached the Ryukyu Trench and began subduction beneath the Ryukyu Arc. The onset of the subsidence is likely to be controlled by a motion change in the Philippine Sea Plate. The latest change in subduction direction from north to northwestward into northwestward to west has been believed to have occurred at 1-2 Ma during latest Pliocene to Early Pleistocene time. The change of direction resulted in the shift from oblique into right-angle subduction of the plate beneath the Ryukyu Arc and also the onset of the collision and subduction of the Amami Plateau. 相似文献
86.
Tsutomu Ikeda 《Journal of Oceanography》2011,67(6):785-790
This study demonstrates reduced electron transfer system (ETS) activity of mixed copepods collected from 5,000 to 7,000 m
depths [3.21 ± 1.25 μl O2 (mg protein)−1 h−1 at 10°C] as compared with mixed copepods from 0 to 200 m depths [5.93 ± 1.66 μl O2 (mg protein)−1 h−1 at 10°C] of the western subarctic Pacific. At the in situ temperature of 1.5°C, the 5,000–7,000 m ETS data, in terms of wet
mass (WM)-specific respiration rates (R), is equivalent to [0.052 ± 0.021 μl O2 (mg WM)−1 h−1] which is similar to or greater than those reported for selected copepods or mixed mesozooplankton from <5,000 m depth by
previous workers. 相似文献
87.
Hiroyuki Hirashita Takaya Nozawa Tsutomu T. Takeuchi Takashi Kozasa 《Monthly notices of the Royal Astronomical Society》2008,384(4):1725-1732
We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). Since at high redshift ( z > 5), low-mass stars cannot be dominant sources for dust grains, SNe II and PISNe, whose progenitors are massive stars with short lifetimes, should govern the dust production. Here, we theoretically investigate the extinction curves of dust produced by SNe II and PISNe, taking into account reverse shock destruction induced by collision with ambient interstellar medium. We find that the extinction curve is sensitive to the ambient gas density around a SN, since the efficiency of reverse shock destruction strongly depends on it. The destruction is particularly efficient for small-sized grains, leading to a flat extinction curve in the optical and ultraviolet wavelengths. Such a large ambient density as n H ≳ 1 cm−3 produces too flat an extinction curve to be consistent with the observed extinction curve for SDSS J1048+4637 at z = 6.2. Although the extinction curve is highly sensitive to the ambient density, the hypothesis that the dust is predominantly formed by SNe at z ∼ 6 is still allowed by the current observational constraints. For further quantification, the ambient density should be obtained by some other methods. Finally, we also discuss the importance of our results for observations of high- z galaxies, stressing a possibility of flat extinction curves. 相似文献
88.
The moment magnitude (M w) 9.0 Tohoku-Oki Earthquake occurred on March 11, 2011, generating an unusually large tsunami. The seismic shocks and tsunami inundation severely damaged the Fukushima Daiichi Nuclear Power Plant. Radionuclide emission due to reactor breakdown contaminated wide areas of Fukushima and its surroundings. Heavy rainfall causes runoff across surface soil, and fine soil particles are susceptible to uptake by the flowing water. The high radioactivity of grains suspended in floodwater indicates that radioactive fallout was streamed into rivers in particulate form and transported downstream under high-flow conditions. Here, we investigated the diachronic mode of 134Cs and 137Cs in central Fukushima, through which the contaminated air mass drifted and caused wet deposition of radionuclides. Stratigraphic measurements of radioactivity in sediment cores is the method employed in this study to determine the basin-wide movement of 134Cs and 137Cs, to evaluate the significance of the erosion–transportation–accumulation processes on natural decontamination in terrain characterized by steep slopes and high precipitation. Stratigraphic results illustrate the process of fluvial sediment discharge, and the massive deposition of radiocaesium suggests basin-wide movement of fallout during concentrated rainfall. Grain suspension in torrential currents is an important pathway for transportation of radionuclides from land to sea, and the appearance of hotspots on floodplains and the offshore sea floor is the consequence of erosion and transportation under seasonal heavy precipitation. Radioactive horizons occur in offshore sediment columns and thus radiocaesium discharged from the estuary will persist forever under the sea floor if no artificial disturbance occurs. 相似文献
89.
Masafumi Matsuyama Masaaki Ikeno Tsutomu Sakakiyama Tomoyoshi Takeda 《Pure and Applied Geophysics》2007,164(2-3):617-631
To study tsunami soliton fission and split wave-breaking, an undistorted experiment was carried out which investigated tsunami
shoaling on a continental shelf. Three models of the continental shelf were set up in a 205-m long 2-dimensional flume. Each
shelf model was 100 m, long with slopes of either 1/100, 1/150, or 1/200. Water surface elevations were measured across the
flume, including a dense cluster of wave gages installed around the point of wave-breaking. We propose new methods for calculating
wave velocity and the wave-breaking criterion based on our interpretation of time series data of water surface elevation.
At the point of wave-breaking, the maximum slope of water surface is between 20 to 50 deg., while the ratio of surface water
particle horizontal velocity to wave velocity is from 0.5 to 1.2. The values determined by our study are larger than what
has been reported by other researchers. 相似文献
90.
Masao Ohno Hirochika Sumino Pedro A. Hernandez Tsutomu Sato Keisuke Nagao 《Journal of Volcanology and Geothermal Research》2011,199(1-2):118-126
The relation of magma and crustal activity has been studied from spatial distribution of 3He/4He ratios of gas and/or water samples over the Izu Peninsula, where significant crustal deformation associated with seismic swarm activities has been observed since 1970s. The air-corrected values of 3He/4He ratios ranged from 3.5 to 8.2 RA, where RA is the atmospheric 3He/4He ratio = 1.4 × 10? 6, indicating that helium is mostly of magmatic origin. Among the three pressure sources proposed to explain the crustal deformation, two inflation sources beneath the inland of northeast and the mid east coast of the Izu Peninsula locate in the broad distribution of high 3He/4He ratios, which supports relation of magma to the crustal uplift. In contrast, the distribution of 3He/4He ratios around the tensile fault assumed in the area of seismic swarms appears not to indicate existence of significant amount of magma below the tensile fault. Alternatively, the results suggest magma below a point several kilometers south of the tensile fault. The seismic swarms are explained either by fluid pressurization of thermal water heated by this magma or by intrusion of magma to the tensile fault moved obliquely from the deep magma reservoir. 相似文献