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1.
1 IntroductionAnicecoreobtainedfrom polarglaciersoricesheetsisoneofthemostimportantarchivestoreconstructpaleoclimaticandpaleoatmosphericcondition .Informationonpale o environmentcanbeextractedfromicecoresaschemicaland/orphysicalsignals.Amongthechemicalsignals,heavymetalsarenotedassignalsofterrestrialenvironmentalchangeandanthropogenicpollution (e.g .Murozumietal.1 969;NgandPatterson 1 981 ;Hongetal.1 994) .SinceconcentrationsofmostofthemetalsinpolarsnowincentralGreen landareatorbelowthepptl… 相似文献
2.
Jose A.P. Rodriguez Sho Sasaki James M. Dohm Hideaki Miyamoto Goro Komatsu Justin C. Ferris 《Icarus》2005,175(1):36-57
The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration. 相似文献
3.
Under the purely centrifugal approximation (gravity and pressure force are neglected), stellar magnetospheres are classified into three main types of different physical properties in the two-dimensional parameter space. They are characterized essentially by the strength of the magnetic field and the plasma density, at the base of the magnetosphere. Among the three types, the type II magnetosphere has moderate surface densities for a given field strength, and is expected to possess a centrifugal wind blowing across the magnetic field lines without affecting them appreciably. Such a situation may be realized through a modification of the electric field from that under the ideal-MHD condition, owing to the inertia of a plasma. In order to illustrate this mechanism, the type II magnetosphere is taken up for a numerical simulation. The effect of artificial viscosity is avoided by integrating the characteristic equations for both components of the plasma, instead of solving the fluid equations directly. Our model reproduces a disk-like outflow of the centrifugal wind across the magnetic field lines which are closed through the equatorial plane. 相似文献
4.
Yoshio Takasugi Akira Hoshika Hideaki Noguchi Terumi Tanimoto 《Journal of Oceanography》1994,50(1):65-80
The strong tidal current (tidal jet) in straits generates tidal vortices with a scale of several kilometers. The role of the vortices in material transport was investigated in the Neko Seto Sea, located in the western part of the Seto Inland Sea of Japan. A clockwise vortex with a diameter of about 0.8 km was observed in Nigata Bay (lying between two straits, the Neko Seto Strait and the Meneko Seto Strait). It was concluded that the clockwise vortex was the tidal vortex which was generated by the tidal jet in the Meneko Seto Strait. The vortex moved into the bay with the tide, but tended to stay on the sand bank in the bay. It was confirmed by current measurement with an ADCP and turbidity measurement that the secondary convergent flow was generated in the bottom layer of the vortex. This secondary flow seemed to contribute to the formation of the sand bank. It was suggested that tidal vortices may play an important role in the sediment transport and formation of topography in and around straits. 相似文献
5.
Joji Ishizaka Yasuhisa Kitaura Yasuharu Touke Hiroaki Sasaki Akihiko Tanaka Hiroshi Murakami Toshikazu Suzuki Kazumi Matsuoka Hideaki Nakata 《Journal of Oceanography》2006,62(1):37-45
High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment
known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which
damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted
to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll
peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed
that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly
longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement
to accurately estimate chlorophyll in highly turbid water and in red tide areas. 相似文献
6.
Akira Shibata Kouichi Ohwada Masakazu Tsuchiya Kazuhiro Kogure 《Journal of Oceanography》2006,62(1):91-97
Peptidoglycan (PG) is a biopolymer found exclusively in the cell wall of bacteria. Recent chemical analysis of particulate
organic matter suggests that a major amount of the muramic acid, an amino sugar present only in PG, could not be accounted
for in terms of bacterial cells (Benner and Kaiser, 2003); however, data on particulate PG is quite sparse. In the present
study, conducted in 1996, the PG was examined at 5 sampling sites in the northwestern Pacific Ocean, and in natural seawater
cultures. Particulate PG, which was concentrated using a 96-well filtration plate equipped with Durapore filters (pore size,
0.22 μm), was measured by the silkworm larvae plasma (SLP) assay. The PG concentration generally decreased with depth and
correlated significantly with bacterial abundance throughout the entire water column. However, the ratio of particulate PG
to bacterial abundance varied with depth. The average ratio was 0.61 ± 0.53 (average ± SD, n = 40) between 50 and 2000 m,
which agreed with the bacterial cellular PG content from 0.63 to 1.1 fg cell−1 obtained in seawater cultures. On the other hand, the ratios of PG to bacteria from the surface to 50 m (3.7 ± 2.6, n = 29)
and below 2,000 m (2.1 ± 1.7, n = 7) were significantly higher than that between 50 and 2,000 m. These results may suggest
that, in the surface and deep layers, a significant fraction of particulate PG was present in bacterial detritus, whereas
this fraction was reduced in the middle layer. 相似文献
7.
Japanese fisheries production in the Japan/East Sea between 1958 and 2003 increased to their peak (1.76 million tons) in the late 1980s and decreased abruptly with the collapse of Japanese sardine. Catch results for 58 fisheries and various environmental time-series data sets and community indices, including mean trophic level (MTL) and Simpson’s diversity index (DI), were used to investigate the impacts of fishing and climate changes on the structure of the fish community in the Tsushima warm current (TWC) region of the Japan/East Sea. The long-term trend in fisheries production was largely dependent on the Japanese sardine that, as a single species, contributed up to 60% of the total production in the Japanese waters of the Japan/East Sea during the late 1980s. Excluding Japanese sardine, production of the small pelagic species was higher during 1960s and 1990s but lower during 1970s and 1980s. This variation pattern generally corresponds with the trend in water temperature, warmer before early 1960s and after 1990s but colder during 1970s and 1980s. The warm-water, large predatory fishes and cold water demersal species show opposite responses to the water temperature in the TWC region, indicating the significant impact of oceanic conditions on fisheries production of the Japan/East Sea. Declines in demersal fishes and invertebrates during 1970s and 1980s suggested some impact of fishing. MTL and DI show a similar variation pattern: higher during 1960s and 1990s but lower during 1970s and 1980s. In particular, the sharp decline during the 1980s resulted from the abundant sardine catches, suggesting that dominant species have a large effect on the structure of the fish community in the Japan/East Sea. Principal component analysis for 58 time-series data sets of fisheries catches suggested that the fish community varied on inter-annual to inter-decadal scales; the abrupt changes that occurred in the mid-1970s and late 1980s seemed to correspond closely with the climatic regime shifts in the North Pacific. These results strongly suggest that the structure of the fish community in the Japan/East Sea was largely affected by climatic and oceanic regime shifts rather than by fishing. There is no evidence showing “fishing down food webs” in the Japan/East Sea. However, in addition to the impacts of abrupt shifts that occurred in the late 1980s, the large predatory and demersal fishes seem to be facing stronger fishing pressure with the collapse of the Japanese sardine. 相似文献
8.
Some numerical experiments by the barotropic nonlinear two dimensional models are performed to study the water circulations in Lake Biwa, especially to study the large anticlockwise gyre in the north basin. The wind fields used in the experiments have no rotational component. This gyre is induced by the southerly wind and is approximately on the geostrophic balance. The vorticity of this gyre is contributed from the vertical stretching of the vortex tube by the variable bottom topography and the inertia term. But the latter term does not become effective if the bottom profile of the basin is flat. Therefore the horizontal circulation in the barotropic closed basin is the “topographic gyres”. The bottom stress has a little contribution to the vorticity balance of the gyre. 相似文献
9.
Two numerical studies (Endoh, 1977;Harashima
et al., 1978) have been proposed on a front formed by a coupling effect of cooling of the sea surface and inflow of the fresh water in a vertical two-dimensional plane without the rotation of the earth. It is, however, not easy to interpret their numerical results. A simple interpretation will be proposed by an analytical study in this paper.It is found that local convection due to the density inversion, which is expressed by the convective adjustment of the vertical diffusion coefficient in the actual numerical calculations, plays an important role on the front formation.The characteristics of the front is also clarified in the case of steady state. Namely, simple functional dependences are obtained of the position and the width of the front, the horizontal and the vertical velocities and the distribution of the buoyancy and the salinity in the neighborhood of the front on the horizontal coordinate, the cooling rate, the eddy coefficients of diffusion and viscosity, the water depth and the vertically averaged horizontal fluxes of buoyancy and salinity. 相似文献
10.