Drainage Density and Relative Relief in Humid Steep Mountains with Frequent Slope Failure     

Takashi Oguchi 《地球表面变化过程与地形》1997,22(2):107-120

Previous studies in Japanese mountains have shown that drainage density (D) correlates negatively with relief (R) and the erosion rate (E), whereas elsewhere both R and E correlate positively with D. To investigate the inconsistency, this paper compares two types of D–R relations for eight mountain river basins in central Japan. R is computed from a digital elevation model for 1109 morphometric samples of area 0·5 km × 0·5 km. Drainage networks in these cells were first constructed by map criteria applied previously in Japan — deeply notched V-shaped contours with an angle <53°. The resulting D correlates negatively with R, confirming preceding studies. When drainage lines along shallower hollows were added, however, the calculated D essentially constant. These relations arise from active landsliding in high-relief terrains, which has eroded steep channel banks into gentle ones. The decline of channel banks with increasing R is accelerated in terrains underlain by soft rocks, because of rapid erosion. The constant D for all the drainage lines indicates a uniform frequency or spacing of ridges and hollows on hillslopes in rugged humid mountains. Because the D–R and D–E relations for Japan reflect a uniquely Japanese physiographic setting characterized by frequent landsliding, they differ from those relations for other regions where channelization by gullying predominates. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Intrusion events of the intermediate Oyashio Water into Sagami Bay, Japan     

Tomoharu Senjyu  Noriko Asano  Masaji Matsuyama  Takashi Ishimaru 《Journal of Oceanography》1998,54(1):29-44

Intermediate intrusion of low salinity water (LSW) into Sagami Bay was investigated on the basis of CTD data taken in Sagami Bay and off the Boso Peninsula in 1993–1994. In October 1993, water of low temperature (<7.0°C), low salinity (<34.20 psu) and high dissolved oxygen concentration (>3.5 ml I⁻¹) intruded along the isopycnal surface of {ie29-1} at depths of 320–500 m from the Oshima East Channel to the center of the bay. On the other hand, the LSW was absent in Sagami Bay in the period of September–November 1994, though it was always found to the south off the Boso Peninsula. Salinity and dissolved oxygen distributions on relevant isopycnal surfaces and water characteristics of LSW cores revealed that the LSW intruded from the south off the Boso Peninsula to Sagami Bay through the Oshima East Channel. The LSW cores were distributed on the continental slope along 500–1000 m isobaths and its onshore-offshore scales were two to three times the internal deformation radius. Initial phosphate concentrations in the LSW revealed its origin in the northern seas. These facts suggest that the observed LSW is the submerged Oyashio Water and it flows southwestward along the continental slope as a density current in the rotating fluid. The variation of the LSW near the center of Sagami Bay is closely related to the Kuroshio flow path. The duration of LSW in Sagami Bay is 0.5 to 1.5 months.  相似文献   

Planktonic ciliates as food for the scyphozoan <Emphasis Type="Italic">Aurelia coerulea</Emphasis>: feeding and growth responses of ephyra and metephyra stages     

Takashi Kamiyama 《Journal of Oceanography》2018,74(1):53-63

Blooms of the moon jellyfish, Aurelia coerulea, often occur in eutrophic embayments where microzooplankton are abundant. Hence, microzooplankton may play a role in A. coerulea population dynamics. In this study, feeding and growth responses of the ephyra and metephyra stages of A. coerulea were examined on a diet of planktonic ciliates, the main components of microzooplankton. Laboratory experiments indicated that ephyrae actively fed on ciliates and that the central disc diameter increased over the 5-day incubation period. Carbon-specific growth rates estimated from daily increases of central disc diameter increased with carbon-specific prey consumption rates until about 4 µg C ind day^?1 and then became saturated. By fitting these results to rectangular hyperbolic equations, the maximum specific growth rates were estimated to be 0.32 day^?1 for ciliate prey. However, the central disc diameter of the metephyrae did not increase on a diet of ciliates during the 5-day incubation, even though consumption of prey ciliates was observed. These results suggest that planktonic ciliates serve as a food source for growth at the ephyra stage of A. coerulea and then the contribution to growth decreases at and after the metephyra stage. This prey switch-dependency on the development stage of A. coerulea may be associated with the frequent occurrence of jellyfish blooms in eutrophic embayments.  相似文献   

Lagrangian observation of phytoplankton dynamics at an artificially enriched subsurface water in Sagami Bay,Japan     

Takako Masuda  Ken Furuya  Naoko Kohashi  Mitsuhide Sato  Shigenobu Takeda  Makoto Uchiyama  Naho Horimoto  Takashi Ishimaru 《Journal of Oceanography》2010,66(6):801-813

Phytoplankton dynamics in the lower euphotic zone were observed by tracking a subsurface water released at 20-m depth from Takumi, an artificial upwelling device. Takumi continually discharged seawater pumped up from a depth of 205 m: this water was mixed with 5-m depth water to adjust the density to that of 20-m depth water of Sagami Bay, Japan. The discharged water was pulse-labeled at Takumi with uranine and tracked for 63.9 h with a drifting buoy equipped with a drogue at 20-m depth. We present a simple model to estimate in situ phytoplankton net growth rates from temporal changes in phytoplankton abundance in the discharged water with correction for the influence of water exchange between the discharged water and neighboring layers. Lagrangian observation showed active growth of pico- and nanophytoplankton, especially cryptophytes and Synechococcus (Cyanobacteria), in the subsurface layer. In contrast, diatoms grew little in spite of micromolar concentrations of nutrients. The active growth of pico- and nanophytoplankton was in good agreement with shipboard serial dilution culture experiments. The low growth activity of diatoms was suggested to be related to low light availability in the subsurface layer.  相似文献   

Education for sustainable development for Tokyo Bay: Developing a practice framework of university-based coastal ESD     

Midori Kawabe  Hiroshi Kohno  Takashi IshimaruOsamu Baba  Naho HorimotoReiko Ikeda  Jota KandaTakafumi Kudo  Masaji MatsuyamaMasato Moteki  Yayoi OshimaTsuyoshi Sasaki 《Marine Policy》2009

This paper reviews the initial phase of a coastal education for sustainable development program for Edomae, the innermost reaches of Tokyo Bay. The program has been steered by a working group of Tokyo University of Marine Science and Technology faculty members from different academic backgrounds. Although the process began with conventional educational ideas, the ESD practice framework evolved to include more interactive activities. The overall goal is to pursue discussions of a plan for the sustainable use of Tokyo Bay in the coastal communities through a university–community partnership by developing Edomae ESD leaders in the coastal community.  相似文献   

Magnetic detection of heated soils at paleolithic sites in Japan     

Hayao Morinaga  Hiroo Inokuchi  Hideki Yamashita  Akira Ono  Takashi Inada 《Geoarchaeology》1999,14(5):377-399

We present a methodological approach to detect heated soil on ancient sites, using magnetic measurements. The method is based on changes in magnetic signals of soil by heating. The following three types of soil were used for testing the method: silty soil (SS), weathered volcanic ash (WVA, = loam) and fairly fresh volcanic ash (VA) called Odori tephra. On heating above 250–600°C, the magnetic susceptibility and remanent magnetization intensity increased for the SS and WVA samples, reflecting chemical alteration of magnetic minerals (from goethites to magnetites through hematites). The VA sample showed no susceptibility change suggesting the absence of goethites within it. On heating below 250°C, only the intensities of all the samples increased. This is possibly due to acquisition of thermal remanent magnetization. The largest change of the magnetic signals was identified for the SS sample and the smallest one was seen for the VA sample. Therefore, the in situ susceptibility measurement, which is the nondestructive and indirect method, seems to be effective to detect heated soil for sites of aqueous deposits as the SS. On the other hand, for sites of aeolian deposits as the WVA (loam) and VA, the intensity measurement of collected soils seems to be the most reliable method to detect evidence of heating. The degree of the magnetic stability (coercivity) against progressive alternating-field demagnetization was also an important parameter, indicating whether the investigated soils were heated or unheated. © 1999 John Wiley & Sons, Inc.  相似文献