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排序方式: 共有108条查询结果,搜索用时 31 毫秒
71.
Kazuhiro Tsukada Yuki Nakane Koshi Yamamoto Toshiyuki Kurihara Shigeru Otoh Kenji Kashiwagi Minjin Chuluun Sersmaa Gonchigdorj Manchuk Nuramkhaan Masakazu Niwa Tetsuya Tokiwa 《Island Arc》2013,22(2):227-241
We describe the mode of occurrence and geochemical characteristics of basalts, in the Khangai–Khentei belt in Mongolia, overlain by Middle Paleozoic radiolarian chert in an extensive accretionary complex. These basalts are greatly enriched in K, Ti, Fe, P, Rb, Ba, Th, and Nb in comparison to the composition of the mid‐ocean ridge basalts, indicative of within‐plate alkaline type. Ti/Y vs Nb/Y and MnO/TiO2/P2O5 ratios of the basalts also suggest within‐plate affinities. Considering the geochemical characteristics as well as the conformable relationship with the overlying radiolarian chert, the alkaline basalts were clearly not continental but formed a pelagic oceanic island. The mode of occurrence and geochemistry of the basalts show that the alkaline basaltic volcanic activity had taken place to form an oceanic island in the Paleozoic pelagic region sufficiently far from continents to allow radiolarian ooze accumulation. 相似文献
72.
J. N. Pattan Toshiyuki Masuzawa D. V. Borole G. Parthiban Pratima Jauhari Mineko Yamamoto 《Journal of Earth System Science》2005,114(1):63-74
A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth
5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements
(Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply.
The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites
of ∼ 770 ka.
Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon
content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water
environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower,
complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline.
However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment
supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher
prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their
burial to seafloor remained unaffected throughout the past ∼ 1100 ka. 相似文献
73.
Keiichi Tadokoro Kin'Ya Nishigami Masataka Ando Naoshi Hirata Takashi Iidaka Yukihiro Hashida Kunihiko Shimazaki Shiro Ohmi Yasuyuki Kano Makoto Koizumi Shigemitsu Matsuo Hiroo Wada 《Island Arc》2001,10(3-4):235-243
Abstract A water injection experiment was carried out by the scientific drilling program named the 'Nojima Fault Zone Probe' during the two periods 9–13 February and 16–25 March 1997. The pumping pressure at the surface was approximately 4 MPa. The total amount of injected water was 258 m3 . The injection was made between depths of 1480 m and 1670 m in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone. A seismic observation network was deployed to monitor seismic activity related to the water injections. Seismicity suddenly increased in the region not far from the injection hole 4 or 5 days after the beginning of each water injection. These earthquakes were likely to be induced by the water injections. Most of the earthquakes had magnitudes ranging from −2 to +1. Numerous earthquakes occurred during the first injection, but only one could be reliably located and it was approximately 2 km north of the injection site. Between the two injection periods, earthquakes concentrated in the region approximately 1 km northwest of the injection site. During and after the second injection experiment, earthquakes were located approximately 1.5 km west of the injection site. Those earthquakes were located approximately 3 km or 4 km from the injection point and between 2 km and 4 km in depth. Values of intrinsic permeability of 10−14 –10−15 m2 were estimated from the time lapse of the induced seismic activity. The coefficient of friction in the area where the induced earthquakes occurred was estimated to be less than 0.3. 相似文献
74.
Toyoda Takahiro Fujii Yosuke Kuragano Tsurane Kosugi Naohiro Sasano Daisuke Kamachi Masafumi Ishikawa Yoichi Masuda Shuhei Sato Kanako Awaji Toshiyuki Hernandez Fabrice Ferry Nicolas Guinehut Stéphanie Martin Matthew Andrew Peterson K. Good Simon A. Valdivieso Maria Haines Keith Storto Andrea Masina Simona Köhl Armin Yin Yonghong Shi Li Alves Oscar Smith Gregory Chang You-Soon Vernieres Guillaume Wang Xiaochun Forget Gael Heimbach Patrick Wang Ou Fukumori Ichiro Lee Tong Zuo Hao Balmaseda Magdalena 《Climate Dynamics》2017,49(3):891-907
Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an... 相似文献
75.
76.
Toshiyuki Hibiya 《Journal of Oceanography》2004,60(3):637-643
The generation process of internal waves by strong tidal flow over a continental shelf slope is reproduced using a multi-level
numerical model. On the basis of the numerical results, the crucial role of the tidal advection effect in the generation process
of internal waves is demonstrated. The close relation between the resulting internal waveform and the strength of the tidal
advection effect is also examined. The barotropic forcing on the internal wave actually works within a relatively small horizontal
scale over the top of the continental shelf slope. When the maximum internal Froude number at the shelf break (Frm) is less than about 0.6, the amplitude of the resulting internal wave is almost proportional to Frm. When Frm is more than about 0.6, however, the amplitude of the resulting internal wave becomes larger than predicted by linear theory.
In particular, when Frm is more than unity, the time period during which the shoreward propagating internal wave stays in the barotropic forcing
region becomes much longer. Consequently, the internal wave is significantly amplified with the horizontal scale approaching
that of the barotropic forcing, which concentrates in a relatively small region over the top of the continental shelf slope.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
77.
Vertical profiles of pH, Eh, and major and minor chemical constituents in interstitial waters have been studied in four piston cores from deep-sea basins of the Japan Sea. Sulfate concentration decreases remarkably with increasing depth in three cores, and hydrogen sulfide is observed in two cores although the overlying bottom water is highly aerated. Three types of interstitial waters are observed in the four cores: (1) alkalinity and manganese concentration increase gradually with increasing depth, and sulfate reduction is not appreciable, (2) alkalinity increases and sulfate concentration decreases remarkably, and hydrogen sulfide is not detected, and (3) alkalinity increases and sulfate concentration decreases remarkably, and hydrogen sulfide is observed. Factors controlling the chemical composition of interstitial waters are discussed. 相似文献
78.
Toshiyuki Masuzawa Tie LiYun Duan Mineko YamamotoYuriko Hibi Takeshi NakatsukaHiroshi Kitazato Yoshihisa Kato 《Progress in Oceanography》2003,57(1):59-75
Sinking particles were collected using time-series sediment traps deployed at 350 and 20 mab at Site SB (34° 58.5’N, 139° 20.9’E, 1544 m depth) near the center of Sagami Bay, off Japan with high time resolutions of 5-8 days (March 1997 to August 1998) and 3-4.5 days (March 1998 to August 1998), respectively. The major components (CaCO3, OM, opal, and clay) of these sinking particles and surface bottom sediments were determined using a stepwise leaching method combined with gravimetry. Average total mass fluxes were 1480, 5560 and 3068 mg/m2/year at 350 mab, at 20 mab, and in the surface sediments, respectively, indicating an enhanced collection of sinking particles at 20 mab. Clay was the dominant component and biogenic components (opal+OM+CaCO3) were dominated mainly by opal and secondly by OM. On average, opal and CaCO3 contents decreased gradually as clay content increased with increasing depth from 350 mab-20 mab and in the surface sediments, indicating dissolution of opal and CaCO3 through sinking, rebound, resuspension or sedimentation processes. Thirteen total mass flux peaks at 17--40-day intervals were observed at 350 mab during the period from March 1997 to August 1998 except for winter, while eight peaks were observed at 20 mab for the period from March 1998 to August 1998. Two types of total mass peaks can be distinguished: one with a clear increase in biogenic flux (opal+OM+CaCO3) and little or no increase in clay flux and termed a bloom type (B-type), and the other with a clear increase in clay flux, little increase in biogenic flux and termed a resuspension type (R-type). Some R-type peaks, but not all, coincided with total mass flux peaks observed at the mouth of Tokyo Bay and suggested the possibility of the effect of particulate materials transported from Tokyo Bay to site SB. The enormously large peak observed at 20 mab in late May 1998 and that at 350 mab in early June 1998 were considered to be due to some physical perturbations from an earthquake swarm near site SB during the period from April to June 1998. The 17--40-day periodicity was associated clearly with the change in biogenic flux dominated by opal flux and is thought to reflect the periodicity of biological productivity dominated by diatoms in the euphotic zone of Sagami Bay. 相似文献
79.
Masaji Matsuyama Suguru Ohta Toshiyuki Hibiya Haruya Yamada 《Journal of Oceanography》1993,49(6):683-696
Current measurements carried out at the depth of 4 m above the sea bottom near the northern edge of the Suruga Trough in the early fall of 1985 indicated the existence of strong semidiurnal tidal currents, which were considered to be associated with internal tides. In order to examine the spatial structure of the bottom intensified tidal flow, more detailed current observations were carried out at three or four depths at two stations along the main axis of the Suruga Trough during about 70 days from August to October 1988. We obtained the following results: (1) the variations of the current velocity caused by the semidiurnal and diurnal internal tides are evident in all of the records, and the orientation of the major axis of each tidal ellipse nearly coincides with that of the main axis of the trough; (2) the semidiurnal internal tide is dominant over the diurnal internal tide at 4 m above the sea bottom at both stations; (3) at the northern station the semidiurnal internal tide is dominant over the diurnal internal tide, whereas they are nearly equal at the southern station except at 4 m above the sea bottom; (4) the biharmonic internal tides with 1/3 day and 1/4 day periods, are found near the sea bottom and the major axis of the tidal ellipse is perpendicular to the orientation of the main axis of the Suruga Trough. 相似文献
80.
Assessment of turbulence closure models for resonant inertial response in the oceanic mixed layer using a large eddy simulation model 总被引:1,自引:0,他引:1
Large eddy simulation (LES) of the resonant inertial response of the upper ocean to strong wind forcing is carried out; the
results are used to evaluate the performance of each of the two second-order turbulence closure models presented by Mellor
and Yamada (Rev Geophys Space Phys 20:851–875, 1982) (MY) and by Nakanishi and Niino (J Meteorol Soc Jpn 87:895–912, 2009) (NN). The major difference between MY and NN is in the formulation of the stability functions and the turbulent length scale,
both strongly linked with turbulent fluxes; in particular, the turbulent length scale in NN, unlike that in MY, is allowed
to decrease with increasing density stratification. We find that MY underestimates and NN overestimates the development of
mixed layer features, for example, the strong entrainment at the base of the oceanic mixed layer and the accompanying decrease
of sea surface temperature. Considering that the stability functions in NN perform better than those in MY in reproducing
the vertical structure of turbulent heat flux, we slightly modify NN to find that the discrepancy between LES and NN can be
reduced by more strongly restricting the turbulent length scale with increasing density stratification. 相似文献