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241.
The evolution of paleo-Changjiang incised-valley fills in relation to step-like, postglacial sea-level rises is presented, based on sedimentary facies analyses and 14C age dating on three sediment cores. Timing of rapid transgressions deduced from the succession of incised-valley fills correlate well with Barbados's very rapid, sea-level rise periods. By contrast, estuarine deposits aggraded actively, and the coastline did not retreat markedly during the Younger Dryas (YD) cooling event when the rising rate decelerated considerably relative to stages before and after the YD. 相似文献
242.
Paul J. Harrison Frank A. Whitney Atsushi Tsuda Hiroaki Saito Kazuaki Tadokoro 《Journal of Oceanography》2004,60(1):93-117
The western subarctic gyre (WSG) and the eastern Alaska Grye (AG) on each side of the subarctic North Pacific, have many similarities.
In both gyres, macronutrients are generally high and chl is low, and hence both gyres are High Nitrate, Low Chlorophyll (HNLC)
regions. Despite the general similarities between these two gyres, there are many important differences. The time series station
established at Stn KNOT on the southwest edge of the WSG and two in situ mesoscale iron enrichment experiments at each of
the gyres has provided more information on iron concentrations, the dual role of iron and silicate limitation and seasonal
cycles in the gyres. There is more seasonality in many parameters at Stn KNOT than at Stn P. There is an increase in Chl and
primary productivity at Stn KNOT in May followed by increased iron limitation in summer. Low DIC:NO3 ratios and high Si:NO3 ratios in the WSG, indicate lower calcification and higher diatom production than at Stn P. The sources of iron for these
areas are still not clear, but horizontal transport of iron rich coastal water and vertical transport could be important sources
at certain times of the year in addition to dust input. Satellite images show that chl-rich coastal waters occasionally extend
to the vicinity of Stn KNOT and therefore Stn KNOT may not always represent conditions in the main part of the WSG. This review
focuses mainly on a comparison of Stn KNOT and Stn P, two time series stations on the edge of two very large gyres. At present,
we have a limited understanding of the temporal and spatial variability within each of these large gyres.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
243.
From the viewpoint of dynamical topology, planetary magnetospheres are classified into three: Types 1, 2 and 3. When the rotation vector and dipole moment of a planet and the velocity vector of the solar wind are denoted as Ω, M, and V, respectively, the planetary magnetosphere with Ω∥M⊥V is called Type 1. The magnetospheres of the present Earth, Jupiter, and Uranus at its equinoctial points belong to this type. The magnetosphere with Ω∥M∥V is called Type 2, which includes the Uranian magnetosphere at its solstitial points. The magnetosphere with Ω⊥M and Ω⊥V is called Type 3. The Earth's palaeomagnetosphere is considered to have experienced Type 3 during excursions and transition stages of palaeomagnetic polarity reversals. In the Type 3 magnetosphere, drastic diurnal variations are expected in configurations of the dayside cusps, tail axis, neutral sheet, polar caps, and so on. A possible relation between the Type 3 palaeomagnetosphere and palaeoclimate of the Earth during polarity reversals and geomagnetic excursions is suggested. It is also suggested that the heliomagnetosphere during polarity reversals of the general field of the Sun exhibits a drastic configuration change similar to the Type 3 palaeomagnetosphere of the Earth. A relation between the perpendicular condition Ω⊥M and magnetic variable stars and pulsars is briefly discussed. 相似文献
244.
The auroragraph is a device for the analysis of any movements of patterns on movie films. Its application to the PPI record from an auroral radar is described, and examples from Syowa Station, Antarctica are given. The radar auroragraph has advantages over other more conventional methods of deriving the speed and direction of movement of auroral radar echoes in space. 相似文献
245.
Sotaro Takano Makoto Ito Takanori Nakano Keiji Horikawa Yuzuru Nakamura Takahiro Saito 《Sedimentary Geology》2004,170(3-4):189-206
Sequence-stratigraphic signatures of hemipelagic siltstones were investigated using profiles of the magnetic susceptibility and selected chemical composition of the Early Pleistocene deep-water successions of the Kiwada and Otadai Formations on the Boso Peninsula, Japan. In the context of an independently developed sequence-stratigraphic framework for the submarine-fan deposits of the Otadai Formation, the magnetic susceptibility and chemical composition, such as the concentrations of TiO2, MgO and Fe2O3, show that the lowstand systems tract deposits have higher values of these parameters than the transgressive and highstand systems tract deposits. In contrast, the CaO contents have inverse relationships with the magnetic susceptibility and are higher in the transgressive and highstand systems tract deposits. The positions of sequence boundaries largely coincide with the horizons from which the magnetic susceptibility and the contents of mafic component increase abruptly. The sequence-stratigraphic variations in the magnetic susceptibility and chemical composition of the submarine-fan hemipelagic siltstones are due to increases in the input of fine-grained, terrigenous clastic sediments from midwater flow suspension, in addition to the direct fluvial supply of relatively unmodified terrigenous clastic sediments during relative sea-level lowstands, although grain size of hemipelagic siltstones does not exhibit any distinct variation through depositional sequences. The Kiwada Formation is characterized by siltstone-dominated basin-plain deposits and its sequence-stratigraphic classification has been difficult when using just lithofacies features. Nevertheless, the profiles of the magnetic susceptibility and chemical composition of the basin-plain deposits are similar to those of the submarine-fan deposits with duration largely equivalent to the 41,000-years obliquity cycle of the Early Pleistocene oxygen isotope sea-level index. This finding indicates that the profiles of the magnetic susceptibility and chemical composition of hemipelagic siltstones reflect sequence-stratigraphic variation in the input of fine-grained terrigenous clastic sediments to the deep-water environments and are crucial for the recognition of cryptic sequence boundaries in hemipelagic successions. 相似文献
246.
247.
Moe Kyaw Thu Kensaku Tamaki Shin-Ichi Kuramoto Ryuji Tada Saneatsu Saito 《Island Arc》2002,11(1):61-78
Abstract High-resolution seismic stratigraphy of the Yamato Basin, Japan Sea, was successfully established using core-log-seismic data integration. The construction of synthetic seismograms by the combination of physical properties and well-log data from the Ocean Drilling Program (ODP) Site 797 was the key to accomplishing the high-resolution seismic stratigraphy. To achieve resolution comparable with well-log data and core lithology, single channel seismic reflection data taken from ODP underway geophysics were reprocessed, and then carefully compared with synthetic seismogram, core and well log profiles to identify seismic units. Ten seismic stratigraphic units were identified at the site, and seismic stratigraphic interpretation was successfully extended from the site to the nearby area along the Yamato Basin margin. The opal-A/opal-CT (biogenic silica/metastable diagenetic silica) boundary has different appearances at places from strong to weak, and mostly discontinuous. One of the significant results achieved from this study is clear distinction of the opal-A/CT boundary from a very strong reflector, which appears at 22 m below the opal-A/CT boundary. Through well-log and physical properties characterization of the different units, resistivity was found to be the best indicator of diatom content and with gamma-ray it also is an indicator of chert layers in the opal-CT zone. Velocity is not greatly effected by diatom ooze in the opal-A zone, however, it shows strong peaks and has an indirect relationship with gamma-ray in the opal-CT zone. Finally, successful correlation of Gamma-ray Attenuation Porosity Evaluator density and resistivity peaks with strong seismic reflectors from upper and lower stratified layers may provide new information on the late Neogene paleoceanography of the Japan Sea in high-resolution scale. 相似文献
248.
Ichiro Sunagawa Junji Takahashi Kazutoshi Aonuma Minoru Takahashi 《Physics and Chemistry of Minerals》1979,5(1):53-63
The flattened or elongated morphology often observed in contact twinned crystals has been referred to the so-called re-entrant corner effect at twin junctions. To re-investigate the validity of this mechanism, natural quartz crystals twinned after Japan Law have been subjected to re-growth in a commercial synthetic quartz autoclave, and the change in their morphology and surface microtopography by re-growth studied. It is found that although twin re-entrant corners may play a role of preferential growth sites, this role can be weakened considerably and in fact can become almost negligible when crystals grow under high supersaturation condition. Preferential growth at the re-entrant corner of a twin junction is probably due to clusters of dislocations concentrated in the composition plane, and not due to the so-called re-entrant corner effect in its original sense. 相似文献
249.
Hiroaki Tatebe Ichiro Yasuda Hiroaki Saito Yugo Shimizu 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(3):409-419
The horizontal transport of calanoid copepod Neocalanus flemingeri, N. plumchrus and N. cristatus in the subarctic North Pacific has been investigated by particle tracking experiments using an ocean circulation model. In our physical numerical model, the current and frontal systems in the subarctic Pacific are reproduced realistically, and fine-resolved (not smoothed) and vertically sheared western boundary currents in the model enable us to assess the differences in horizontal transports among Neocalanus species. In the experiments, seasonal vertical migration and life cycle of Neocalanus species is included, and this attempt is a novel approach in examining the transports of the zooplanktons. The maximal depths of the vertical migrations and the lengths of the surface and mesopelagic dwelling duration are the essential factors in characterizing the trajectory of the horizontal transport. Both small and large forms of N. flemingeri (hereafter NF-SF and NF-LF) whose mesopelagic-inhabited depths are the shallowest among the three Neocalanus species are transported to more distant regions from initial positions compared with the others. The longest transport distance is over 5000 km for NF-SF. On the other hand, the transport distance of the deepest inhabitant N. cristatus (hereafter NC) is the shortest. The differences in the transport distance are due to the current speed of the western boundary currents at the inhabited depth at which they spend most of their lifetime (ca. 3/4 of their lifetime). More than 82% of NF-LF that originated from the Okhotsk Sea completes its life cycle in the Okhotsk Sea, and all the animals out to the Pacific are transported to the south of the subarctic front where their survivals are unexpected due to high temperatures. This is consistent with the observed limited distribution of NF-LF in the Okhotsk Sea and its surrounding waters. Geographical genetic variations of Neocalanus species are reported as very low. This implies frequent genetic exchange all over the Pacific and its adjacent seas. Being consistent with the above, the present study suggests that the trans-Pacific transport of Neocalanus species can be accomplished within a few generations. 相似文献
250.