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排序方式: 共有619条查询结果,搜索用时 31 毫秒
491.
Water mass variability in the western North Pacific detected in a 15-year eddy resolving ocean reanalysis 总被引:2,自引:0,他引:2
492.
To assess differences in fish assemblage structures among microhabitats within the surf zone of an exposed sandy beach, three microhabitats (onshore current, rip current, and river adjacent sites) were sampled at Sanrimatsubara Beach, western Japan, in May, August, and November 2002 and 2003. Although several physical variables (e.g. wave height, current speed, turbidity, salinity, and sand particle size) and major prey abundances (calanoid copepods and mysids) differed among the sites, no significant differences were apparent in the numbers of fish species and individuals among the sites in any month in either year. In addition, species and individual numbers of two dominant feeding groups (zooplankton feeders, and epiphytic and benthic crustacean feeders) did not show any significant responses to among-site differences in prey abundance. Cluster and ordination analysis confirmed the similarity in fish species composition among the three sites. These results indicated that the surf zone fish assemblage structures were similar among the microhabitats in spite of there being microhabitat-related differences in abiotic and biotic environments. 相似文献
493.
Shingo Kato Kurt Hara Hiroko Kasai Takashi Teramura Michinari Sunamura Jun-ichiro Ishibashi Takeshi Kakegawa Toshiro Yamanaka Hiroyuki Kimura Katsumi Marumo Tetsuro Urabe Akihiko Yamagishi 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1844-1855
Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40 m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields. 相似文献
494.
Seasonal transition of hydrological processes in a slow‐moving landslide in a snowy region 下载免费PDF全文
Hikaru Osawa Yuki Matsushi Sumio Matsuura Takashi Okamoto Tatsuya Shibasaki Hiroyuki Hirashima 《水文研究》2018,32(17):2695-2707
A comprehensive understanding of seasonal hydrological dynamics is required to describe the influence of pore‐water pressure on the stability of landslides in snowy regions. This study reports on the results of continuous meteorological and hydrological observations over 2 years on a landslide body comprising Neogene sedimentary rocks in northern Japan, where a thick (3–5 m) seasonal snowpack covers the land surface. Monitoring of the volumetric water content in shallow unsaturated zones (<0.8 m depth) and pore‐water pressure in saturated bedrock at depths of 2.0 and 5.2 m revealed clear seasonality in hydrological responses to rainfall and meltwater supply. During snow‐free periods, both the shallow soil moisture and deep pore‐water pressure responded rapidly to intense rainwater infiltration. In contrast, during snowmelt, the deep pore pressure fluctuated in accordance with the daily cycle of meltwater input, without notable changes in shallow moisture conditions. During occasional foehn events that cause intense snow melting in midwinter, meltwater flows preferentially through the layered snowpack, converging to produce a localized water supply at the ground surface. This episodically triggers a significant rise in pore‐water pressure. The seasonal differences in hydrological responses were characterized by a set of newly proposed indices for the magnitude and quickness of increases in the pressure head near the sliding surface. Under snow‐covered conditions, the magnitude of the pressure increase tends to be suppressed, probably owing to a reduction in infiltration caused by a seasonal decrease in the permeability of surface soils, and effective pore‐water drainage through the highly conductive colluvial layer. Deep groundwater flow within bedrock remained in a steady upwelling state, enhanced by increasing moisture in shallow soils under snow cover, reflecting the convergence of subsurface water from surrounding hillslopes. 相似文献
495.
496.
Takashi Onaka 《Earth, Moon, and Planets》2009,104(1-4):337-348
AKARI, formerly known as ASTRO-F, is a satellite mission dedicated to infrared astronomy for the first time in Japan. It has a 685-mm aperture telescope with two focal-plane instruments cooled by liquid helium (LHe) and mechanical coolers on board for observations in the 2–180 μm infrared spectral range. AKARI was launched on 2006 February 21 (UT) into a sun-synchronous polar orbit and started observations in May, 2006. It carried 179 liter LHe that lasted for 550 days and observations with LHe were carried out for more than 15 months. During the LHe holding period, AKARI made all-sky survey observations with six bands from 9 to 160 μm, which surpass the IRAS all-sky survey data in the sensitivity, spatial resolution, and spectral coverage. Together with the all-sky observation, AKARI also made pointing observations for about 10 min at a given position of the sky to execute deep imaging and spectroscopy from near- to far-infrared. Both focal-plane instruments work successfully on orbit and more than 90% of the sky was observed in the all-sky survey. After LHe exhaustion, near-infrared observations are planned to continue. This paper reports the in-orbit performance of AKARI and its early observational results so far obtained. 相似文献
497.
Katherine H. Joy Channon Visscher Michael E. Zolensky Takashi Mikouchi Kenji Hagiya Kazumasa Ohsumi David A. Kring 《Meteoritics & planetary science》2015,50(7):1157-1172
Lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the Moon. Apollo 16 sample 60016 is an “ancient” feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 Ga. The breccia contains a small (70 × 50 μm) rock fragment composed dominantly of an Fe‐oxide phase with disseminated domains of troilite. Fragments of plagioclase (An95‐97), pyroxene (En74‐75, Fs21‐22,Wo3‐4), and olivine (Fo66‐67) are distributed in and adjacent to the Fe‐oxide. The silicate minerals have lunar compositions that are similar to anorthosites. Mineral chemistry, synchrotron X‐ray absorption near edge spectroscopy (XANES) and X‐ray diffraction (XRD) studies demonstrate that the oxide phase is magnetite with an estimated Fe3+/ΣFe ratio of ~0.45. The presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the Fe‐magnetite or wüstite–magnetite oxygen buffer. This discovery provides direct evidence for oxidized conditions on the Moon. Thermodynamic modeling shows that magnetite could have been formed from oxidization‐driven mineral replacement of Fe‐metal or desulphurisation from Fe‐sulfides (troilite) at low temperatures (<570 °C) in equilibrium with H2O steam/liquid or CO2 gas. Oxidizing conditions may have arisen from vapor transport during degassing of a magmatic source region, or from a hybrid endogenic–exogenic process when gases were released during an impacting asteroid or comet impact. 相似文献
498.
499.
An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC 总被引:1,自引:1,他引:0
Yoshimitsu Chikamoto Masahide Kimoto Masayoshi Ishii Takashi Mochizuki Takashi T. Sakamoto Hiroaki Tatebe Yoshiki Komuro Masahiro Watanabe Toru Nozawa Hideo Shiogama Masato Mori Sayaka Yasunaka Yukiko Imada 《Climate Dynamics》2013,40(5-6):1201-1222
Decadal climate predictability is examined in hindcast experiments by a multi-model ensemble using three versions of the coupled atmosphere-ocean model MIROC. In these hindcast experiments, initial conditions are obtained from an anomaly assimilation procedure using the observed oceanic temperature and salinity with prescribed natural and anthropogenic forcings on the basis of the historical data and future emission scenarios in the Intergovernmental Panel of Climate Change. Results of the multi-model ensemble in our hindcast experiments show that predictability of surface air temperature (SAT) anomalies on decadal timescales mostly originates from externally forced variability. Although the predictable component of internally generated variability has considerably smaller SAT variance than that of externally forced variability, ocean subsurface temperature variability has predictive skills over almost a decade, particularly in the North Pacific and the North Atlantic where dominant signals associated with Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) are observed. Initialization enhances the predictive skills of AMO and PDO indices and slightly improves those of global mean temperature anomalies. Improvement of these predictive skills in the multi-model ensemble is higher than that in a single-model ensemble. 相似文献
500.