The mechanism of bottom water DO variation in summer at the northern mouth of Isahaya Bay,Japan     

Sangyeob Kim  Yuichi Hayami  Akira Tai  Akihide Tada 《Journal of Oceanography》2018,74(6):595-605

Recently, bivalves have been massively killed by anoxia or hypoxia in summer at the northern part of Isahaya Bay, Japan, which constituted a major problem for fisheries. However, the mechanism behind the occurrence of hypoxic water masses is unclear. It is known that the bottom water dissolved oxygen (DO) in this area is affected by the inflow of seawater into the northern mouth of Isahaya Bay. To understand the mechanism of hypoxia, it is necessary to determine the physical processes that cause changes in the bottom DO concentrations in this area. This study shows that there is a neap-spring tidal variation in bottom DO due to a change in vertical tidal mixing, and it also suggests that the decrease in bottom DO was generated by a baroclinic flow, which is due to the internal tide, and a shear flow, which is induced by the external tide in the bottom boundary layer. In addition, our study suggests that the source of cold and hypoxic water that appears in the bottom layer at low tide is the inner area of the Ariake Sea.  相似文献   

Effect of canopy openness and meteorological factors on spatial variability of throughfall isotopic composition in a Japanese cypress plantation   总被引：1，自引：0，他引：1       下载免费PDF全文

Xinchao Sun  Yuichi Onda  Akiko Hirata  Hiroaki Kato  Takashi Gomi  Xueyan Liu 《水文研究》2018,32(8):1038-1049

Spatial variability of throughfall (TF) isotopic composition, used as tracer input, influences isotope hydrological applications in forested watersheds. Notwithstanding, identification of the dominant canopy factors and processes that affect the patterns of TF isotopic variability remains ambiguous. Here, we examined the spatio‐temporal variability of TF isotopic composition in a Japanese cypress plantation, in which intensive strip thinning was performed and investigated whether canopy structure at a fine resolution of canopy effect analysis is related to TF isotopic composition and how this is affected by meteorological factors. Canopy openness, as an index of canopy structure, was calculated from hemispherical photographs at different zenith angles. TF samples were collected in a 10 × 10 m experimental plot in both pre‐thinning (from July to November 2010) and post‐thinning (from May 2012 to March 2013) periods. Our results show that thinning resulted in a smaller alteration of input δ¹⁸O of gross precipitation, whereas the changes in deuterium excess varied in both directions. Despite the temporal stability of spatial patterns in TF amount, the spatial variability of TF isotopic composition was not temporally stable in both pre‐ and post‐thinning periods. Additionally, after thinning, the isotopic composition of TF was best related to canopy openness calculated at the zenith angle of 7°, exhibiting three different relationships, that is, significantly negative, significantly positive, and nonsignificant. Changes in meteorological factors (wind speed, rainfall intensity, and temperature) were found to affect the relationships between TF δ¹⁸O and canopy openness. The observed shifts in the relationships reveal different dominant factors (partial evaporation and the selection), and canopy water flowpaths control such differences. This study provides useful insights into the spatial variability of TF isotopic composition and improves our understanding of the physical processes of interception through canopy passage.  相似文献   

Morphological transitions for pore water and pore air during drying and wetting processes in partially saturated sand     

Kido  Ryunosuke  Higo  Yosuke  Takamura  Fukushi  Morishita  Ryoichi  Khaddour  Ghonwa  Salager  Simon 《Acta Geotechnica》2020,15(7):1745-1761

Acta Geotechnica - Water retention characteristics are important for modeling the mechanical and hydraulic behavior of partially saturated sand. It is well known that the soil water characteristic...  相似文献   

Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf,Japan     

Jessica E. Pilarczyk  Yuki Sawai  Dan Matsumoto  Yuichi Namegaya  Naohisa Nishida  Ken Ikehara  Osamu Fujiwara  Chris Gouramanis  Tina Dura  Benjamin P. Horton 《Sedimentology》2020,67(3):1373-1392

Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined.  相似文献   

Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: a short review   总被引：2，自引：0，他引：2  

Takuya Tsugawa  Nobuki Kotake  Yuichi Otsuka  Akinori Saito 《GPS Solutions》2007,11(2):139-144

Medium-scale traveling ionospheric disturbances (MSTID) are wave-like perturbations of the ionospheric plasma with wavelengths of several hundred kilometres and velocities of several hundred metres per second. MSTID is one of the most common ionospheric phenomena that generally induce the perturbations of ionospheric total electron content (TEC) by ∼10¹⁶ electron/m², which corresponds to ∼54 ns (16.2 cm) delay at GPS L1 signal. In the past decade, several new characteristics on MSTIDs have been revealed by the TEC observations using the dense GPS receiver network in Japan. In this paper, we provide a short review of these new observations and summarize the morphological characteristics of MSTIDs in Japan.  相似文献   

Strong Updraft at a Sea-Breeze Front and Associated Vertical Transport of Near-Surface Dense Aerosol Observed by Doppler Lidar and Ceilometer     

Hironori Iwai  Yasuhiro Murayama  Shoken Ishii  Kohei Mizutani  Yuichi Ohno  Taichiro Hashiguchi 《Boundary-Layer Meteorology》2011,141(1):117-142

To study the wind field within the atmospheric boundary layer over the Tokyo metropolitan area, Doppler lidar observations were made 45 km north of Sagami Bay and 30 km west of Tokyo Bay, from 14 May to 15 June 2008. Doppler lidar on 27 May 2008 observed the vertical and horizontal wind structure of a well-developed sea-breeze front (SBF) penetrating from Sagami Bay. At the SBF, a strong updraft (maximum w approximately equal to 5 m s⁻¹) was formed with a horizontal scale of about 500 m and vertical scale of 2 km. The spatial relationship between the strong updraft over the nose of the SBF and prefrontal thermal suggests that the strong updraft was triggered by interaction between the SBF and the thermal. After the updraft commenced, a collocated ceilometer observed an intense aerosol backscatter up to 2 km above ground level. The observational results suggest that the near-surface denser aerosols trapped in the head region of the SBF escaped from the nose of the SBF and were then vertically transported up to the mixing height by the strong updraft at the SBF. This implies that these phenomena occurred not continuously but intermittently. The interaction situations between the SBF and prefrontal thermal can affect the wind structure at the SBF and the regional air quality.  相似文献   

Galactic cosmic-ray anisotropy and its heliospheric modulation, inferred from the sidereal semidiurnal variations observed in the rigidity range 300–600 GV with multidirectional muon telescope at Sakashita underground station     

K. Nagashima  K. Fujimoto

I. Morishita 《Planetary and Space Science》1991,39(12):1637-1655

The existence of sidereal semidiurnal variation of cosmic-ray intensity in a rigidity region 10²-10³ GV has been reported by many researchers, but there is no consensus of opinion on its origin. In this paper, using the observed semidiurnal variations in a rigidity range (300–600 GV) with 10 directional muon telescopes at Sakashita underground station (geog. lat. = 36°, long. = 138°E, DEPTH = 80 m.w.e.), the authors determine the magnitudes (η₁, η₂) and directions (a₁, a₂) of the first- and second-order anisotropies in the following galactic cosmic-ray intensity distribution (j) , where P_nis the nth order spherical function and χ_n is the pitch angle of cosmic rays with respect to a_n. For the determination, the influence of cosmic-ray's heliomagnetospheric modulation, geomagnetic deflection and nuclear interaction with the terrestrial material and also of the geometric configuration of the telescopes are taken into account. Usually, the semidiurnal variation is produced by the second-order anisotropy. The present observation, however, requires also the first-order anisotropy which usually produces only the diurnal variation, but can produce also the semidiurnal variation as a result of the heliospheric modulation. The first- and second-order anisotropies are characterized with η₁) > 0 and η₂ < 0 have almost the same direction (a₁ a₂) specified by the right ascension ( 0.75 h) and declination (δ 50°S) and, therefore, they can be expressed, as a whole, by an axis-symmetric anisotropy of loss-cone type (i.e. deficit intensities in a cone). It is noteworthy that this anisotropy approximately coincides with that inferred from the air shower observation at Mt Norikura in the rigidity region 10⁴ GV.  相似文献   

Petrogenesis of ultramafic rocks and olivine-rich troctolites from the East Taiwan Ophiolite in the Lichi mélange     

Morishita  Tomoaki  Ghosh  Biswajit  Soda  Yusuke  Mizukami  Tomoyuki  Tani  Ken-ichiro  Ishizuka  Osamu  Tamura  Akihiro  Komaru  Chihiro  Aari  Shoji  Yang  Hsiao-Chin  Chen  Wen-Shan 《Mineralogy and Petrology》2018,112(4):521-534

Mineralogy and Petrology - We examine ultramafic and olivine-rich troctolite blocks of the East Taiwan Ophiolite (ETO) in the Lichi Mélange. Although ultramafic rocks are extensively...  相似文献   

Geochemistry of spinel-hosted amphibole inclusions in abyssal peridotite: insight into secondary melt formation in melt–peridotite reaction     

Akihiro?TamuraEmail author  Tomoaki?Morishita  Satoko?Ishimaru  Shoji?Arai 《Contributions to Mineralogy and Petrology》2014,167(3):974

Spinel-hosted hydrous silicate mineral inclusions are often observed in dunite and troctolite as well as chromitite. Their origin has been expected as products associated with melt–peridotite reaction, based on the host rock origin. However, the systematics in mineralogical and geochemical features are not yet investigated totally. In this study, we report geochemical variations of the spinel-hosted pargasite inclusions in reacted harzburgite and olivine-rich troctolite collected from Atlantis Massif, an oceanic core complex, in the Mid-Atlantic Ridge. The studied samples are a good example to examine geochemical variations in the inclusions because the origin and geological background of the host rocks have been well constrained, such as the reaction between MORB melt and depleted residual harzburgite beneath the mid-ocean ridge spreading center. The trace-element compositions of the pargasite inclusions are characterized by not only high abundance of incompatible elements but also the LREE and HFSE enrichments. Distinctive trace-element partitioning between the pargasite inclusion and the host-rock clinopyroxene supports that the secondary melt instantaneously formed by the reaction is trapped in spinel and produces inclusion minerals. While the pargasite geochemical features can be interpreted by modal change reaction of residual harzburgite, such as combination of orthopyroxene decomposition and olivine precipitation, degree of the LREE enrichment as well as variation of HREE abundance is controlled by melt/rock ratio in the reaction. The spinel-hosted hydrous inclusion could be embedded evidence indicating melt–peridotite reaction even if reaction signatures in the host rock were hidden by other consequent reactions.  相似文献   

Tsunami deposit associated with the 2011 Tohoku‐oki tsunami in the Hasunuma site of the Kujukuri coastal plain,Japan          下载免费PDF全文

Dan Matsumoto  Yuki Sawai  Koichiro Tanigawa  Osamu Fujiwara  Yuichi Namegaya  Masanobu Shishikura  Kyoko Kagohara  Haruo Kimura 《Island Arc》2016,25(5):369-385

We describe the detailed sedimentary characteristics of a tsunami deposit associated with the 2011 Tohoku‐oki tsunami in Hasunuma, a site on the Kujukuri coastal plain, Japan. The thick tsunami deposit was limited to within 350 m from the coastline whereas the inundation area extended about 1 km from the coastline. The tsunami deposit was sampled by excavation at 29 locations along three transects and studied using peels, soft‐X imaging and grain‐size analysis. The deposit covers the pre‐existing soil and reached a maximum measured thickness of 35 cm. It consists mainly of well‐sorted medium to fine sand. On the basis of sedimentary structures and changes in grain size, we divided the tsunami deposit into several sedimentary units, which may correspond to multiple inundation flows. The numbers of units and their sedimentary features vary among the three transects, despite the similar topography. This variation implies a considerable influence of local effects such as elevation, vegetation, microtopography, and distance from footpaths, on the tsunami‐related sedimentation.  相似文献