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431.
Intrusion of less saline shelf water into the Kuroshio subsurface layer in the East China Sea 总被引:7,自引:0,他引:7
Atsuhiko?IsobeEmail author Eiji?Fujiwara Pil-Hun?Chang Koichi?Sugimatsu Manabu?Shimizu Takeshi?Matsuno Atsuyoshi?Manda 《Journal of Oceanography》2004,60(5):853-863
The possible origin and cause of the less saline shelf water detected in the Kuroshio subsurface layer around the shelf edge
of the East China Sea are investigated using observational results obtained in May 1998–2001 in conjunction with a dataset
archived by Japan Oceanographic Data Center and a numerical model. The observations show that subsurface intrusions of less
saline water are always detected in May in layers above 24.5σθ isopycnal surface, and that salinity inversions (i.e., areas
in which the less saline water lies beneath the saline water) are detected around the trough of the Kuroshio frontal eddy
(or wave). Analyses of the archived dataset reveal that the isopycnal surface of 24.5σθ is the deepest layer of the Kuroshio
pycnocline outcropping to the sea surface on the shallow shelf in early spring. Outcropping isopycnals above 24.5σθ encounter
a less saline water plume originating from the Changjiang, especially in the western East China Sea. Thereafter, the less
saline water moves along isopycnal layers and reaches the Kuroshio front around the shelf edge. Numerical models demonstrate
that, when the frontal wave captures the less saline water, the shelf water takes the form of a salinity inversion in the
trough because isohalines in the frontal wave have a phase lag between the upper and lower layers in consequence of the baroclinic
instability. 相似文献
432.
Takeshi Uji 《Journal of Oceanography》1984,40(4):303-313
An ocean wind-wave prediction model MRI-II is developed on the basis of the energy balance equation which contains five energy
transfer processes, namely, the input by the wind, the nonlinear transfer among the components of windsea by resonant wave-wave
interactions, wave breaking, frictional dissipation and the effect of opposing winds.
The nonlinear energy transfer is expressed implicitly together with the wind effect by Toba's one-parameter representation
of windsea, but neither swell-swell nor swell-windsea resonant interactions are considered.
Hypothetical assumptions are introduced to describe wave breaking effects. The numerical constant required in the assumptions
of wave breaking is determined through trial test runs for a hindcast performed on the North-western Pacific Ocean.
The significant wave height, one-dimensional wave spectrum and two-dimensional wave spectrum hindcasted by this new model
are in more reasonable agreement with observations than those obtained with our old model MRI. 相似文献
433.
Shigeaki Kojima Takanori Kobayashi Jun Hashimoto Suguru Ohta 《Journal of Oceanography》1995,51(2):257-259
Phylogenetic relationship among three species of deep-sea vesicomyid bivalvesCalyptogena, i.e.,C. soyoae, C. solidissima, C. fausta and an undescribed species of the Iheya Ridge, Okinawa Trough was analyzed on the basis of the RFLP analysis of the fragment (about 1 kbp) of cytochrome oxidase I. Both the two populations ofC. soyoae (off Hatsushima and Okinoyama Bank, Sagami Bay) consisted of two haplotypes, which could be discriminated by only one restriction site (1.7% sequence divergence).Calyptogena of the Iheya Ridge could not be distinguished from one of the two haplotypes ofC. soyoae. Nucleotide substitution rates between species were calculated and dendrograms were constructed. 相似文献
434.
Tatsuki Toda Tomoko Okashita Takeshi Maekawa Bin Abdul Adzis Kee Alfian Mohd Kushairi Mohd Rajuddin Ryota Nakajima Wenxi Chen Kunio T. Takahashi Bin Haji Ross Othman Makoto Terazaki 《Journal of Oceanography》2007,63(1):113-123
Coral community structures at eleven fringing reef sites were investigated along the coast of Peninsular Malaysia. Estimated
coverage of coral communities is examined by applying quantitative digital image analysis to the line transect method. Four
coral community types were characterized by dominant genera and lifeforms: Acropora branching community, Montipora-Acropora community, Porites massive community, and Heliopora community. Live coral coverage in all study sites ranged from 17.9% to 68.6%. Most reefs were in “fair” condition while some
reefs were shown to be in “poor” condition. Coral community structures among the study sites were divided into the west coast
of Peninsular Malaysia with a dominant Porites massive lifeform, and the east coast with a variety of lifeform categories of Montipora and Acropora. Physical effects such as the monsoon wind regime and sedimentation are likely to influence the formation of dominant coral
communities around Peninsular Malaysia. 相似文献
435.
The staggered grid finite-difference method is a powerful tool in seismology and is commonly used to study earthquake source
dynamics. In the staggered grid finite-difference method stress and particle velocity components are calculated at different
grid points, and a faulting problem is a mixed boundary problem, therefore different implementations of fault boundary conditions
have been proposed. Viriuex and Madariaga (1982) chose the shear stress grid as the fault surface, however, this method has
several problems: (1) Fault slip leakage outside the fault, and (2) the stress bump beyond the crack tip caused by S waves
is not well resolved. Madariaga et al. (1998) solved the latter problem via thick fault implementation, but the former problem remains and causes a new issue;
displacement discontinuity across the slip is not well modeled because of the artificial thickness of the fault. In the present
study we improve the implementation of the fault boundary conditions in the staggered grid finite-difference method by using
a fictitious surface to satisfy the fault boundary conditions. In our implementation, velocity (or displacement) grids are
set on the fault plane, stress grids are shifted half grid spacing from the fault and stress on the fictitious surface in
the rupture zone is given such that the interpolated stress on the fault is equal to the frictional stress. Within the area
which does not rupture, stress on the fictitious surface is given a condition of no discontinuity of the velocity (or displacement).
Fault normal displacement (or velocity) is given such that the normal stress on the fault is continuous across the fault.
Artificial viscous damping is introduced on the fault to avoid vibration caused by onset of the slip. Our implementation has
five advantages over previous versions: (1) No leakage of the slip prior to rupture and (2) a zero thickness fault, (3) stress
on the fault is reliably calculated, (4) our implementation is suitable for the study of fault constitutive laws, as slip
is defined as the difference between displacement on the plane of z = + 0 and that of z = − 0, and (5) cessation of slip is achieved correctly. 相似文献
436.
Masaaki Okuda Hiroomi Nakazato Norio Miyoshi Takeshi Nakagawa Hiroko Okazaki Saneatsu Saito Asahiko Taira 《Island Arc》2006,15(3):338-354
Abstract The 250-m Choshi core (CHOSHI-1), drilled from hemipelagic muds of the Inubo Group, has been physically, geochemically and tephrochronologically analyzed back to 1 Ma. We provide pollen results for the 19–169 m section of the core (400–780 ka) bracketed by the marker tephra Ty1 (equivalent to J4) and the Brunhes–Matuyama paleomagnetic boundary. The results show good agreement with the corresponding oxygen isotope (δ18 O) profile, with high δ18 O intervals dominated by boreal conifers Picea , Abies , Pinus (subgen. Haploxylon ) and Tsuga ( diversifolia ), whereas low δ18 O intervals are dominated by temperate conifers Cryptomeria , Taxaceae-Cephalotaxaceae-Cupressaceae and Sciadopitys . In order to confirm pollen-climate relations for the relevant taxa, a modern surface pollen dataset for the Japanese archipelago was consulted. In this analysis, the ratios of Cryptomeria / Picea and temperate/boreal conifers serve as proxies for the 100-kyr glacial/interglacial cycle during the Middle Pleistocene. Distinct signals for marine isotope stages (MIS) 11, 12, 13–15, 16, 17 and 18–19 are recognized in accordance with the tephrochronology and δ18 O of the same core. Application of the criteria to an independent pollen record from Lake Biwa provides an integrated pollen stratigraphy for mid-latitude Japan during the past 800 ky. Some degree of uncertainty remains in the chronology of the MIS13–15 interval, relating to the uncertainty in the eruption age of widespread tephra Ks11. 相似文献
437.
— The epicentral area of the 1998 Papua New Guinea Earthquake and Tsunami off Sissano Lagoon, northern coast of Papua New Guinea (M=7.1; 17 July, 1998) was surveyed by the Research Vessel Kairei in January 1999. Precise bathymetric survey by use of SEABEAM-2112 and other geophysical surveys (bottom reflectivity, sub-bottom profiling, surface ship gravity and geomagnetic surveys) were carried out and four piston core samples were collected during the nine days' survey. The area was also surveyed by use of the Japanese deep sea research ROV Dolphin-3K and research submersible Shinkai-2000 after the regional geophysical survey, in order to locate the possible seismic faults and/or underwater landslides as the source of tsunami and to study the process which took place off Sissano Lagoon and the driving force of the event. The study area is characterised by substantial fan sediment supply from Sissano Lagoon. Straight small-scale submarine canyons and valleys are eroding the shelf slope constructed by the fan sediment. Topographic features of arcuate slumps caused by landslides are recognised at numerous sites of the study area. Most of them are old and the most recent is located 25 km northeast off the Sissano Lagoon. Two major topographic depressions on the shelf were located off Sissano Lagoon. The western is a depression of about 10-km width and the eastern is a meandering deep-sea canyon. Amphitheatre topographic features with slumps caused by landslides that were discovered by Kairei's cruise were extensively surveyed in the study area. Six dives by Dolphin-3K and seven dives by Shinkai-2000 revealed that a fresh crack of about 15 km in total length is located along the slope of the amphitheatre. The crack is apparently the upper slope of a large-scale slumping on the amphitheatre, characterised by tensional stress on it. The easternmost part of the fresh crack is accompanied by living chemosynthetic organisms such as mussels and tube worms. The chemosynthetic community is apparently associated with cold seepage along the crack suggesting that the crack was constructed very recently. The areas other than the crack were rather old with bioturbation. 相似文献
438.
439.
440.
Volcanic explosion earthquakes accompanying explosive eruptions are viewed as representing an abrupt release of pressurized magma beneath a volcano through a vent. I examine the source mechanisms of explosion earthquakes assuming two extreme cases of magma property. When magma is assumed to be a perfect gas which migrates upward isentropically through a vent acting as a nozzle, the seismic source is expressed as a single force. On the other hand, when magma flow is assumed to be incompressible, an implosive source is dominant. Both source models predict that the seismic magnitude is proportional to the cross-sectional area of the vent. I investigate observed seismic magnitudes for different volcanoes based on data in published papers and reports. The results show that the seismic magnitude of the largest event for each volcano is essentially proportional to the cross-sectional area of the vent for vent radii ranging from 10 to 600 m. The consistency found between the theoretical prediction and the observed relation suggests that the vent area plays a substantial role in the magnitude of explosion earthquakes. I further estimate that initial pressures in the reservoir are of the order of a few MPa, with a one order of magnitude uncertainty based on the single force model. I also apply the implosive source model to the observed seismic magnitudes and estimate the product of bulk modulus of magma and flow velocity to be 1010–1011 J/m2 s. 相似文献