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231.
T. Ito 《Journal of Atmospheric Chemistry》1985,3(1):69-91
Systematic year-round observations of submicron aerosols were carried out at Syowa Station (69°00'S, 39°35'E) in 1978. On the basis of the results of these observations, it is concluded that two types of aerosols originating from different sources are present in the Antarctic croposphere. With the intrusion of maritime air, mostly in the polar night months, sea salt particles and ammonium sulfate particles contained originally in the clean maritime air are dominant. The size distribution of such aerosols is monomodal, having a single mode at around 0.03 m in radii. On the other hand, in the sunlit months, sulfuric acid droplets are predominant and the size distribution is bimodal, having an additional mode at around 0.005 m in radii. Those sulfuric acid particles seem to be formed photochemically within a specific layer in the mid to lower troposphere over Antarctica. Most Antarctic submicron particles are of tropospheric origin, not of stratospheric nor anthropogenic origin. 相似文献
232.
Recent, fresh, volcanic rocks of the intra-oceanic Mariana and Volcano Arcs were analyzed for O and Sr isotopic compositions in order to determine the source of these magmas. Fresh, non-arc, volcanic rocks from the regions surrounding the Mariana-Volcano Arcs and some DSDP sediments were also analyzed for comparison. The oxygen isotopic ratios of the arc lavas (5.5–6.8‰) exhibited a small inter-island variation that cannot be entirely explained by fractional crystallization. The Sr isotopic composition of the arc lavas is remarkably uniform (0.70332–0.70394 for the Marianas). Three models are considered in order to explain the observed isotopic characteristics: (1) bulk mixing and melting of MORB-type mantle with (a) subducted sediments, and (b) subducted oceanic crust (excluding sediments); (2) melting of a mixture of sediment-derived fluids and MORB-type mantle; and (3) melting of a mixture of sediment-derived fluids and oceanic island or “hot-spot” type mantle. The last model fits the data best. The conclusion that very small, and variable, amounts of sediment-derived fluid ( 1%) are required to explain the observed inter-island O isotopic variation, is consistent with that of other workers who used different isotopic and trace element methods. The generation of magmas in the Mariana-Volcano Arcs involves very little sediment and the source region of Mariana lavas is isotopically indistinguishable from that of hot-spot basalts. 相似文献
233.
234.
Keisuke Ito 《Earth and Planetary Science Letters》1974,21(2):169-180
Petrological models of the oceanic lithosphere are tested to satisfy geophysical and geochemical constraints within the framework of plate tectonics. Quartz eclogite, olivine eclogite, peridotite and dunite are considered as the material of the lithosphere. The temperature at the base of the lithosphere is assumed to be the solidus temperature. This temperature, the thermal conductivity, and the heat flow and topography changes with age are used as the geophysical constraints. The compressional wave velocity-depth profile is used to select preferred models. Among geophysically successful models, high-temperature models are preferred to wet low-temperature models, because the low-temperature models have difficulties in explaining the mechanism of generation of oceanic basalt magmas. A preferred model is a two-layer model 70 km thick consisting of peridotite at the upper lithosphere and olivine eclogite at the lower lithosphere bounded at the base by the dry solidus. 相似文献
235.
Keisuke Ito 《Pure and Applied Geophysics》1992,138(4):531-548
Recent advances in the theory of fracture and fragmentation are reviewed. Empirical laws in seismology are interpreted from a fractal perspective, and earthquakes are viewed as a self-organized critical phenomenon (SOC). Earthquakes occur as an energy dissipation process in the earth's crust to which the tectonic energy is continuously input. The crust self-organizes into the critical state and the temporal and spatial fractal structure emerges naturally. Power-law relations known in seismology are the expression of the critical state of the crust. An SOC model for earthquakes, which explains the Gutenberg-Richter relation, the Omori's formula of aftershocks and the fractal distribution of hypocenters, is presented. A new view of earthquake phenomena shares a common standpoint with other disciplines to study natural complex phenomena with a unified theory. 相似文献
236.
Akihiko Ito Koki Ouchi Isamu Hisa Susumu Seki Yoshio Seto Shoji Kurashina 《Journal of Oceanography》1984,40(2):98-104
In the consideration of safety it is required that packages containing radioactive wastes when dumped at sea should keep their
integrity and retain their contents until they reach the seabed. Packages containing simulated radioactive wastes (non-radioactive)
were tested by a free-fall method at depthsca. 4,300 m in an area for dumping industrial waste off Shikoku Island. Since the weight of the largest package was 4,300 kg,
special attention was paid to the connection of a buoyancy system with mooring rope. Descent and ascent velocities of the
free-fall system were calculated prior to the experiment. A free-fall experiment with an extremely heavy object, heavier than
ever previously reported, was accomplished without trouble by using the free-fall system. Recovery of a camera, flash-light,
and other components was successful in each of the three experiments. Successive photographing of the package during descent
was made and its integrity was observed using the photographs taken by the recovered camera. The packages remained intact
during descent and at least for a short time after arrival on the seabed. 相似文献
237.
Water masses in the subsurface and the intermediate layer are actively formed due to strong winter convection in the Japan
Sea. It is probable that some fraction of pollution is carried into the layer below the sea surface together with these water
masses, so it is important to estimate the formation rate and turnover time of water masses to study the fate of pollutants.
The present study estimates the annual formation rate and the turnover time of water masses using a three-dimensional ocean
circulation model and a particle chasing method. The total annual formation rate of water masses below the sea surface amounted
to about 3.53 ± 0.55 Sv in the Japan Sea. Regarding representative intermediate water masses, the annual formation rate of
the Upper portion of the Japan Sea Proper Water (UJSPW) and the Japan Sea Intermediate Water (JSIW) were estimated to be about
0.38 ± 0.11 and 1.43 ± 0.16 Sv, respectively, although there was little evidence of the formation of deeper water masses below
a depth of about 1500 m in a numerical experiment. An estimate of turnover time shows that the UJSPW and the JSIW circulate
in the intermediate layer of the Japan Sea with timescales of about 22.1 and 2.2 years, respectively. 相似文献
238.
Isotopic evolution and climate paleorecords: modeling boundary effects in groundwater-dominated lakes 总被引:1,自引:0,他引:1
We used an isotopic mass-balance model to examine how the hydrogeologic setting of lakes influences isotopic response of evaporating
lake water to idealized hydroclimatic changes. The model uses a monthly water and isotope balance approach with simplified
water-column structure and groundwater exchanges. The framework for comparative simulations is provided by lakes in a region
of the Northern Rocky Mountains that display high interlake geochemical variability, thought to be controlled by groundwater
hydraulics. Our analysis highlights several isotopic effects of flow between aquifers and lakes, leading to possible divergence
of isotopic paleorecords formed under a common climate. Amplitude of isotopic variation resulting from simulated climate forcing
was greatly damped when high groundwater fluxes and/or low lake volume resulted in low lake fluid residence time. Differing
precipitation and evaporation scenarios that are equivalent in annual fluid balance (P−E) resulted in different isotopic signatures,
interpreted as a result of evaporation kinetics. Concentrating low-δ groundwater inflow during spring months raised springtime
lake δ values, a counterintuitive result of coincidence between times of high groundwater inflow and the evaporation season.
Transient effects of reduced fluid balance caused excursions opposite in sign from eventual steady-state isotopic shifts resulting
from enhanced groundwater inflow dominance. Lags in response between climate forcing and isotopic signals were shortened by
high groundwater fluxes and resulting short lake residence times. Groundwater-lake exchange exerts control over patterns of
lake isotopic response to evaporation through effects on lake residence time, inflow composition, and seasonal timing of inflow
and outflow. Sediments from groundwater-linked lakes, often used for paleoenvironmental analysis, should be expected to reflect
isotopic complexities of the type shown here.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
239.
David A. Lockner Hidemi Tanaka Hisao Ito Ryuji Ikeda Kentaro Omura Hisanobu Naka 《Pure and Applied Geophysics》2009,166(10-11):1649-1667
The 1995 Kobe (Hyogo-ken Nanbu) earthquake, M = 7.2, ruptured the Nojima fault in southwest Japan. We have studied core samples taken from two scientific drillholes that crossed the fault zone SW of the epicentral region on Awaji Island. The shallower hole, drilled by the Geological Survey of Japan (GSJ), was started 75 m to the SE of the surface trace of the Nojima fault and crossed the fault at a depth of 624 m. A deeper hole, drilled by the National Research Institute for Earth Science and Disaster Prevention (NIED) was started 302 m to the SE of the fault and crossed fault strands below a depth of 1140 m. We have measured strength and matrix permeability of core samples taken from these two drillholes. We find a strong correlation between permeability and proximity to the fault zone shear axes. The half-width of the high permeability zone (approximately 15 to 25 m) is in good agreement with the fault zone width inferred from trapped seismic wave analysis and other evidence. The fault zone core or shear axis contains clays with permeabilities of approximately 0.1 to 1 microdarcy at 50 MPa effective confining pressure (10 to 30 microdarcy at in situ pressures). Within a few meters of the fault zone core, the rock is highly fractured but has sustained little net shear. Matrix permeability of this zone is approximately 30 to 60 microdarcy at 50 MPa effective confining pressure (300 to 1000 microdarcy at in situ pressures). Outside this damage zone, matrix permeability drops below 0.01 microdarcy. The clay-rich core material has the lowest strength with a coefficient of friction of approximately 0.55. Shear strength increases with distance from the shear axis. These permeability and strength observations reveal a simple fault zone structure with a relatively weak fine-grained core surrounded by a damage zone of fractured rock. In this case, the damage zone will act as a high-permeability conduit for vertical and horizontal flow in the plane of the fault. The fine-grained core region, however, will impede fluid flow across the fault. 相似文献
240.
Holocene millennial-scale climate variations documented by multiple lake-level proxies in sediment cores from Hurleg Lake,Northwest China 总被引:2,自引:0,他引:2
Cheng Zhao Zicheng Yu Yan Zhao Emi Ito Kenneth P. Kodama Fahu Chen 《Journal of Paleolimnology》2010,44(4):995-1008
Millennial-scale climate variability has not been well documented in arid northwest China due to the scarcity of high-resolution,
well-dated paleoclimate records. Here we present multi-proxy records from sediment cores taken in freshwater Hurleg Lake on
the northeastern Tibetan Plateau, which reveal millennial-scale lake-level and climate variations over the past 8,000 years.
This high-elevation region is very sensitive to large-scale climate change, thus allowing us to better understand Holocene
climate variations in East Asia. The lake-level record, derived from lithology, magnetic mineralogy, carbonate isotopes, ostracode
shell isotopes and trace elements, X-ray fluorescence (XRF), and gray scale data, indicates a highly variable and generally
dry climate from 7.8 to 1 ka (1 ka = 1,000 cal year BP), and a relatively stable and wet climate after 1 ka. Superimposed
on this general trend, six dry intervals at 7.6–7.2 ka, 6.2–5.9 ka, 5.3–4.9 ka, 4.4–3.8 ka, 2.7–2.4 ka, and 1.7–1.1 ka were
detected from the high-resolution carbonate content and XRF data. The generally dry climate between 7.8 and 1 ka was almost
synchronous with the decrease of East Asian and Indian monsoon intensities shortly after 8 ka. The six dry intervals can be
correlated with weak monsoon events recorded in the East Asia and Indian monsoon regions, as well as the North Atlantic cold
events. Our data suggest that millennial-scale monsoon variations could cause highly variable climate conditions in arid northwest
China during the Holocene. These millennial-scale climate variations may reflect changes in solar variation and/or changes
in oceanic and atmospheric circulation. 相似文献