Integrated field spectroscopy of E+A (post-starburst) galaxies with the Kyoto tridimensional spectrograph II     

Tomotsugu Goto  Atsushi Kawai  Atsushi Shimono  Hajime Sugai  Masafumi Yagi  Takashi Hattori 《Monthly notices of the Royal Astronomical Society》2008,386(3):1355-1365

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Horizontal structure of planetary-scale waves at the cloud top of Venus deduced from Galileo SSI images with an improved cloud-tracking technique     

Toru Kouyama  Takeshi Imamura  Masato Nakamura  Takehiko Satoh  Yoshihumi Futaana 《Planetary and Space Science》2012,60(1):207-216

An improved cloud tracking method for deriving wind velocities from successive planetary images was developed. The new method incorporates into the traditional cross-correlation method an algorithm that corrects for erroneous cloud motion vectors by re-determining the most plausible correlation peak among all of the local maxima on the correlation surface by comparing each vector with its neighboring vectors. The newly developed method was applied to the Venusian violet images obtained by the Solid State Imaging system (SSI) onboard the Galileo spacecraft during its Venus flyby. Although the results may be biased by the choice of spatial scale of atmospheric features, the cloud tracking is the most practical mean of estimating the wind velocities with extensive spatial and temporal coverage. The two-dimensional distribution of the horizontal wind vector field over 5 days was obtained. It was found from these wind maps that the solar-fixed component in 1990 was similar to that in 1982 obtained by the Pioneer Venus orbiter. The deviation of the instantaneous zonal wind field from the solar-fixed component shows a distinct wavenumber-1 structure in the equatorial region. On the assumption that this structure is a manifestation of an equatorial Kelvin wave, the phase relationship between the zonal wind and the cloud brightness suggests a short photochemical lifetime of the violet absorber. The momentum deposition by this Kelvin wave, which is subject to radiative damping, would induce a westward mean-wind acceleration of ～0.3 m s^?1 per Earth day.  相似文献   

Modelling exposure of oceanic higher trophic-level consumers to polychlorinated biphenyls: Pollution ‘hotspots’ in relation to mass mortality events of marine mammals     

Itsuki C. Handoh  Toru Kawai 《Marine pollution bulletin》2014

Marine mammals in the past mass mortality events may have been susceptible to infection because their immune systems were suppressed through the bioaccumulation of environmental pollutants such as polychlorinated biphenyls (PCBs). We compiled mortality event data sets of 33 marine mammal species, and employed a Finely-Advanced Transboundary Environmental model (FATE) to model the exposure of the global fish community to PCB congeners, in order to define critical exposure levels (CELs) of PCBs above which mass mortality events are likely to occur. Our modelling approach enabled us to describe the mass mortality events in the context of exposure of higher-trophic consumers to PCBs and to identify marine pollution ‘hotspots’ such as the Mediterranean Sea and north-western European coasts. We demonstrated that the CELs can be applied to quantify a chemical pollution Planetary Boundary, under which a safe operating space for marine mammals and humanity can exist.  相似文献   

Application of Magnetotelluric (MT) Resistivity to Imaging of Regional Three-Dimensional Geologic Structures and Groundwater Systems     

Hisafumi Asaue  Taiki Kubo  Toru Yoshinaga  Katsuaki Koike 《Natural Resources Research》2012,21(3):383-393

Widespread definition of a groundwater system in three dimensions is necessary for the management and maintenance of groundwater resources. A magnetotelluric (MT) survey can be an effective geophysical prospecting method for imaging regional geological structures by measuring both shallow and deep resistivity. To demonstrate the capability of an MT survey to characterize a groundwater system, the Kumamoto area of central Kyushu in southwestern Japan was selected as a case study site because of its rich groundwater resources. Three-dimensional (3D) MT resistivity structure to a depth of 5?km was modeled by 1D inversion analysis of raw MT data and 3D interpolation of the resultant resistivity column data by the optimization principle method. Consequently, both deep and shallow aquifers were detected. A high-resistivity zone appears at depths between 500 and 2,000?m between the Futagawa?CHinagu faults and the Usuki?CYatsushiro tectonic line, which supports the existence of an aquiclude under the aquifer. The most important characteristic inferred from the 3D resistivity model is that the deep groundwater system below a depth of 1,000?m has two main flow paths. One path is likely to be through porous rocks because the low resistivity zone is regarded as tuff with sand and gravel, and the other flow path is interpreted to be through fractured zones along the Hinagu faults. Hence, the path and direction of the groundwater flows are probably controlled by geologic structures and the configuration of the active faults. These findings support the effectiveness of the MT method for investigating groundwater systems.  相似文献   

Intra-annual perturbations of stable isotopes in tufas: Effects of hydrological processes   总被引：1，自引：0，他引：1  

M. Hori  T. Kawai  A. Kano 《Geochimica et cosmochimica acta》2009,73(6):1684-1695

Tufas, which are freshwater carbonates, are potential archives of terrestrial paleoclimate. Time series of stable isotopic compositions commonly show regular seasonal patterns controlled by temperature-dependent processes, and some perturbation intrinsic to the locality. We examined three tufa-depositing sites in southwestern Japan with similar temperate climates, to understand the origin of local characteristics in the isotopic records. Seasonal change in the oxygen isotope is principally reflected by temperature-dependent fractionation between water and calcite but was perturbed after heavy rainfalls overwhelming the stability of the δ¹⁸O value of the groundwater at one site. Isotopic mass balance indicates an undersaturated and relatively small aquifer at this locality. Water δ¹⁸O values at the other two sites were stable, reflecting a regular seasonal change in the δ¹⁸O value of tufa. Perturbation of the δ¹³C values in tufa is largely due to CO₂ degassing from the stream, which significantly increases the δ¹³C values of dissolved inorganic carbon (DIC). At a site with remarkably high pCO₂ in springwater and a sensitive response of flow rate to rainfall, the amount of CO₂ degassing changed distinctly with flow rate. In contrast, the other two sites having low pCO₂ springwater reflect a regular seasonal pattern of δ¹³C in DIC and tufa specimens.  相似文献   

Productivity cycles in Lake Hovsgol, NW Mongolia, during the last 1 Ma and the age model of the HDP-04 drill core record     

A.A. Prokopenko  G.K. Khursevich  M.I. Kuzmin  T. Kawai 《Quaternary International》2009,205(1-2):111

Repetitive patterns in the records of total organic carbon (TOC), total nitrogen (TN) and δ¹³C_org observed in the Lake Hovsgol sediment section from HDP-04 drill core reflect past changes in productivity of Lake Hovsgol and in the isotopic composition of the lake's carbon pool. Lake Hovsgol productivity proxy signals are interpreted to represent the response of the Hovsgol lacustrine system to glacial–interglacial cycles of the Pleistocene. This interpretation is supported by the apparent orbitally-forced pattern in the TOC, TN and δ¹³C_org records of the past 250 ka in the BDP-96-2 drill core from neighboring Lake Baikal.The intervals with independent age control, such as the radiocarbon-dated last glacial–interglacial transition and the paleomagnetic reversals, make it evident that productivity proxy signals are reliable indicators of past cold-to-warm and warm-to-cold climate transitions, as seen from the agreement with the pattern of global climate change in marine δ¹⁸O records. The Brunhes/Matuyama reversal during the MIS 19 interglacial coincides with a distinct peak of TOC and TN in the Hovsgol record, similar to the signal during the Holocene interglacial. By contrast, the upper Jaramillo reversal in the Lake Hovsgol record occurs in a diatom-free calcareous interval characterized by minima in TOC, TN and by a ‘glacial’-type range of δ¹³C_org values. In both Lake Baikal and Lake Hovsgol records, peaks in TOC and TN contents help distinguishing past interglacials and interstadials, and isotopically-heaviest δ¹³C_org values help identify past glacial intervals.An age model for the HDP-04 drill core section is proposed based on recognizing the repetitive patterns in Lake Hovsgol productivity and lithologic records as regional paleoclimate cycles of middle to late Pleistocene. Absolute dates and diatom biostratigraphic correlation ties to the Lake Baikal record are used as key controls. In the proposed age model, the interval 81–24 m in the HDP-04 sediment section below the major unconformity is correlated to MIS 27 through late MIS 13, whereas the upper 24 m of the HDP-04 section is suggested to have recovered the sedimentary record of late MIS 7 to MIS 1.  相似文献   

Tomographic imaging of hydrated crust and mantle in the subducting Pacific slab beneath Hokkaido, Japan: Evidence for dehydration embrittlement as a cause of intraslab earthquakes   总被引：4，自引：3，他引：1  

Junichi Nakajima  Yusuke Tsuji  Akira Hasegawa  Saeko Kita  Tomomi Okada  Toru Matsuzawa 《Gondwana Research》2009,16(3-4):470-481

We estimate detailed three-dimensional seismic velocity structures in the subducting Pacific slab beneath Hokkaido, Japan, using a large number of arrival-time data from 6902 local earthquakes. A remarkable low-velocity layer with a thickness of ~ 10 km is imaged at the uppermost part of the slab and is interpreted as hydrated oceanic crust. The layer gradually disappears at depths of 70–80 km, suggesting the breakdown of hydrous minerals there. We find prominent low-velocity anomalies along the lower plane of the double seismic zone and above the aftershock area of the 1993 Kushiro-oki earthquake (M7.8). Since seismic velocities of unmetamorphosed peridotite are much higher than the observations, hydrous minerals are expected to exist in the lower plane as well as the hypocentral area of the 1993 earthquake. On the other hand, regions between the upper and lower planes, where seismic activity is not so high compared to the both planes, show relatively high velocities comparable to those of unmetamorphosed peridotite. Our observations suggest that intermediate-depth earthquakes occur mainly in regions with hydrous minerals, which support dehydration embrittlement hypothesis as a cause of earthquake in the subducting slab.  相似文献   

Quasi-static slip on the plate boundary associated with the 2003 M8.0 Tokachi-oki and 2004 M7.1 off-Kushiro earthquakes, Japan     

Naoki Uchida  Satoshi Yui  Satoshi Miura  Toru Matsuzawa  Akira Hasegawa  Yoshinobu Motoya  Minoru Kasahara 《Gondwana Research》2009,16(3-4):527-533

We analyzed small repeating earthquakes recorded over a 13-year period and GPS data recorded over an 8-month period to estimate interplate quasi-static slip associated with the 2003 Tokachi-oki earthquake (M8.0) and the 2004 off-Kushiro earthquake (M7.1). The repeating-earthquake analysis revealed that the slip rate near the source region of the Tokachi-oki earthquake was relatively low (< 5 cm/year) prior to the earthquake; however, in the last 3 years leading up to the event, a minor acceleration in slip occurred upon the deeper extension of the coseismic slip area of the earthquake. Repeating-earthquake and GPS data indicate that large amounts of afterslip occurred around the rupture area following the earthquake; the afterslip mainly propagated to the east of the coseismic slip area. We also infer that the occurrence of the 2004 off-Kushiro earthquake, located about 100 km northeast of the epicenter of the Tokachi-oki earthquake, was advanced by the afterslip associated with the Tokachi-oki earthquake.  相似文献   

The dynamics of big mantle wedge, magma factory, and metamorphic–metasomatic factory in subduction zones   总被引：1，自引：1，他引：0  

S. Maruyama  A. Hasegawa  M. Santosh  T. Kogiso  S. Omori  H. Nakamura  K. Kawai  D. Zhao 《Gondwana Research》2009,16(3-4):414-430

The East Asian continental margin is underlain by stagnant slabs resulting from subduction of the Pacific plate from the east and the Philippine Sea plate from the south. We classify the upper mantle in this region into three major domains: (a) metasomatic–metamorphic factory (MMF), subduction zone magma factory (SZMF), and the ‘big mantle wedge’ (BMW). Whereas the convection pattern is anticlockwise in the MMF domain, it is predominantly clockwise in the SZMF and BMW, along a cross section from the south. Here we define the MMF as a small wedge corner which is driven by the subducting Pacific plate and dominated by H₂O-rich fluids derived by dehydration reactions, and enriched in large ion lithophile elements (LILE) which cause the metasomatism. The SZMF is a zone intermediate between MMF and BMW domains and constitutes the main region of continental crust production by partial melting through wedge counter-corner flow. Large hydrous plume generated at about 200 km depth causes extensive reduction in viscosity and the smaller scale hydrous plumes between 60 km and 200 km also bring about an overall reduction in the viscosity of SZMF. More fertile and high temperature peridotites are supplied from the entrance to this domain. The domain extends obliquely to the volcanic front and then swings back to the deep mantle together with the subducting slab. The BMW occupies the major portion of upper mantle in the western Pacific and convects largely with a clockwise sense removing the eastern trench oceanward. Sporadic formation of hydrous plume at the depth of around 410 km and the curtain flow adjacent to the trench cause back arc spreading. We envisage that the heat source in BMW could be the accumulated TTG (tonalite–trondhjemite–granodiorite) crust on the bottom of the mantle transition zone. The ongoing process of transportation of granitic crust into the mantle transition zone is evident from the deep subduction of five intra-oceanic arcs on the subducting Philippine Sea plate from the south, in addition to the sediment trapped subduction by the Pacific plate and Philippine Sea plate. The dynamics of MMF, SZMF and BMW domains are controlled by the angle of subduction; a wide zone of MMF in SW Japan is caused by shallow angle subduction of the Philippine Sea plate and the markedly small MMF domain in the Mariana trench is due to the high angle subduction of Pacific plate. The domains in NE Japan and Kyushu region are intermediate between these two. During the Tertiary, a series of marginal basins were formed because of the nearly 2000 km northward shift of the subduction zone along the southern margin of Tethyan Asia, which may be related to the collision of India with Asia and the indentation. The volume of upper mantle under Asia was reduced extensively on the southern margin with a resultant oceanward trench retreat along the eastern margin of Asia, leading to the formation of a series of marginal basins. The western Pacific domain in general is characterized by double-sided subduction; from the east by the oldest Pacific plate and from the south by the oldest Indo-Australian plate. The old plates are hence hydrated extensively even in their central domains and therefore of low temperature. The cracks have allowed the transport of water into the deeper portions of the slab and these domains supply hydrous fluids even to the bottom of the upper mantle. Thus, a fluid dominated upper mantle in the western Pacific drives a number of microplates and promote the plate boundary processes.  相似文献   

A Study Of The Atmospheric Boundary Layer Using Radon And Air Pollutants As Tracers     

Toshio Kataoka  Eiji Yunoki  Mitsuo Shimizu  Tadashige Mori  Osamu Tsukamoto  Yukitaka Ohashi  Ken Sahashi  Toshihiko Maitani  Koh’ichi Miyashita  Toru Iwata  Yoko Fujikawa  Akira Kudo  Roger H. Shaw 《Boundary-Layer Meteorology》2001,101(2):131-156

Concentrations of radon ²²²Rn andair pollutants, meteorological parametersnear the surface and vertical profiles of meteorological elements were measured atUchio (Okayama City, Okayama Prefecture, Japan) 12 km north from the coast ofthe Inland Sea of Japan. In the nighttime, the ²²²Rn concentration increased in the case of weak winds, but did not increase as much in the case of moderate or strong winds, as had been expected. In the daytime, the ²²²Rn concentrationheld at a slightly higher than average level for the period from sunrise to about 1100 JST. It is considered that this phenomenon is due to a period of morning calm, that is, a transition period from land breeze to sea breeze.NO, which is sensitive to traffic volume,brought information concerning advection.Oxidant concentrations,which reflect the availability of sunlight,acted in the reverse manner to ²²²Rnconcentrations. Thus, a set of ²²²Rn and air pollutants could provide useful information regarding the local conditions of the atmospheric boundary layer.  相似文献