Sedimentary records of multidecadal-scale variability of diatom productivity in the Bungo Channel, Japan, associated with the Pacific Decadal Oscillation     

Michinobu Kuwae  Azumi Yamashita  Yuichi Hayami  Atsushi Kaneda  Takashige Sugimoto  Yoshio Inouchi  Atsuko Amano  Hidetaka Takeoka 《Journal of Oceanography》2006,62(5):657-666

In order to examine the responses of primary productivity in the southern coastal sea of Japan to the Pacific Decadal Oscillation (PDO) in the 20th century, sedimentary records of diatom productivity (diatom valve fluxes) were reconstructed using core samples from the Bungo Channel (BC) in southwest Japan. The record of the Thalassionema spp. flux—the best index of fall primary productivity in the BC—indicated a multidecadal-scale duration with a low flux (1943–1982) and those with a high flux (1913–1943 and 1982–2001); apparent shifts were recognized in 1943 and 1982. The shift in 1982 was also recognized in the flux records of other early summer to fall predominant genera in the BC and, previously, in the biogenic silica records from a broad region of the southeast BC. This indicates that in our records, this shift reflects a general trend in the primary production in the southeast BC. A comparison among the Thalassionema spp. flux records, meteorological data from an observatory adjacent to the core site, and the PDO index showed that the flux records were more similar to the PDO index than the other meteorological records, which suggests that the multidecadal-scale variability of the BC primary productivity may be associated with some marine-derived forcing. The bottom intrusions of nutrient-rich water that upwelled from the shelf slope into the BC, the axis movement or the transport of the Kuroshio Current off the BC, and a basin-scale wind stress in the North Pacific might play an important role in this forcing and mediate between the BC primary productivity and the PDO.  相似文献   

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   

Compaction and fragmentation of porous gypsum targets from low-velocity impacts     

Yuichi Fujii 《Icarus》2009,201(2):795-801

We performed low-velocity impact experiments of gypsum spheres with porosity ranging from 0 to 61% and diameter ranging from 25 to 83 mm. The impact velocity was from 0.2 to 22 m/s. The target was an iron plate. The outcome of gypsum spheres with porosity 31-61% was different from those of non-porous ice [Higa M., Arakawa, M., Maeno, N., 1996. Planet. Space Sci. 44, 917-925; Higa M., Arakawa, M., Maeno, N., 1998. Icarus 133, 310-320] and non-porous gypsum. In between the intact and fragmentation modes, the outcome of the non-porous ice and gypsum was crack growth at the impact point. However, the outcome of the porous gypsum was compaction. We found that the restitution coefficients of the porous gypsum spheres were all in a similar range, in spite of the difference of the porosity and size at impact velocities up to about 10 m/s where they begin to be fragmented in pieces. Moreover, there is not a large difference between the restitution coefficient of porous and non-porous gypsum. These results collectively indicate that restitution coefficient of gypsum spheres of cm-size is not strongly dependent upon the porosity and compaction process.  相似文献   

Simple monitoring method for precaution of landslides watching tilting and water contents on slopes surface   总被引：2，自引：2，他引：0  

Taro Uchimura  Ikuo Towhata  Trinh Thi Lan Anh  Jou Fukuda  Carlos J. B. Bautista  Lin Wang  Ichiro Seko  Taro Uchida  Akira Matsuoka  Yosuke Ito  Yuichi Onda  Sho Iwagami  Min-Seok Kim  Naoki Sakai 《Landslides》2010,7(3):351-357

A low-cost and simple monitoring method for early warning of landslides is proposed. To detect abnormal deformation of a slope, this method employs a tilt sensor in place of an extensometer on the slope surface. In order to examine the relevance of measuring rotation angle on a slope surface by tilt sensor, model tests were conducted, and rotation on the slope surface was observed together with slide displacement along the surface. The rotation data responded 30 min before failure in a model test, which could be useful as a signal for early warning. However, the behavior of rotation before failure varies from case to case, and thus, criteria to issue warning should be defined more carefully. For a model slope made of uniform loose sand, measurement of slide displacement along the slope surface is sensitive to failure at the toe, while the measurement of rotation on the slope surface is useful to detect the development of progressive failure upward along the slope. Wireless sensor units with microelectromechanical systems (MEMS) tilt sensor and volumetric water content sensor were also examined on a real slope in Kobe City, and a long-term monitoring was attempted. A simple but possible way to define the criteria of judgment to issue warning can be proposed based on combination of data obtained by the tilt sensors and volumetric water content sensors.  相似文献   

Tsunami deposits from the 1993 Southwest Hokkaido earthquake and the 1640 Hokkaido Komagatake eruption,northern Japan   总被引：1，自引：0，他引：1  

Yuichi Nishimura  Naomichi Miyaji 《Pure and Applied Geophysics》1995,144(3-4):719-733

The southwest Hokkaido tsunami of July 12th, 1993, left continuous onshore sand deposits along the west coast of Oshima Peninsuka, Hokkaido, northern Japan. We investigated spatial distribution and lithofacies of the new tsunami deposits for its identification of ancient tsunami deposits. An eyewitness acount and bent plants helped our interpretation of the onshore tsunami behavior. We regard the following properties as typical of the coastal tsunami sand deposits: (1) The deposits cover the surface almost continuously on gentle topography. (2) Deposit thicknesses and mean grain sizes descrease with distance from the sea. (3) Deposit thicknesses and lithofacies vary greatly across local surface undulation. (4) Graded bedding reflecting tsunami runup and backwash is present in thick deposits. (5) The deposits are widely distributed along the coast and extend inland several tens of meters to 100 m. We examined a candidate for the paleo-tsunami deposits associated with the 1640 Komagatake eruption, and confirmed that the similar patterns are typical of ancient tsunami deposits.  相似文献   

Caledonide development offshore–onshore Svalbard based on ocean bottom seismometer, conventional seismic, and potential field data     

Asbjrn Johan Breivik  Rolf Mjelde  Paul Grogan  Hideki Shimamura  Yoshio Murai  Yuichi Nishimura 《Tectonophysics》2005,401(1-2):79-117

The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sørkapp Basin, bordered by a 7 km deep basement high to the west, and 7–9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between 19°E and 20°E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the V_P, V_P/V_S ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10–50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles.  相似文献   

The effect of urbanization on sediment disasters     

Yuichi Maruyama  Masami Sugiura 《GeoJournal》1996,38(3):355-364

An aim of the study is to understand the effect of recent urbanization on the increase of sediment disasters. A case study was done in Nagasaki City and its vicinity, where a severe disaster had occurred in July 1982. The results of this study are summarized as follows: (1) The houses built in the first period locate on the relatively safe morphological units such as lower terrace and gentle foot slope. (2) The houses built in the second period intruded onto the rather risky morphological units; steep slope, valley floor and river bed. These units were not used as a residential area before. (3) The houses built in the last period are settled on the more risky area compared to older settled areas. However the demand for new housing land increased. Thus it was decided to develop the area risky to sediment disaster.  相似文献   

Suppressive Effects of Traditional Mulching Using Japanese Knotweed (Fallopia japonica) on Solanaceae Crop Diseases     

INAGAKI Hidehiro  KUBOTA Sakiko  HASEGAWA Kana  UNNO Nahoko  USUI Yukiko  TAKIKAWA Yuichi 《资源与生态学报(英文版)》2021,12(6):869-875

Poaceae plant species, such as silver grass, are commonly used in mulching activities Japan. In contrast, local farmers have traditionally used Japanese knotweed (Fallopia japonica) mulch in the cultivation of solanaceous crops in the Nishi-Awa area of Japan, which is a Globally Important Agricultural Heritage Systems site. We have previously evaluated the positive effects of Japanese knotweed mulching on solanaceous crops, such as eggplants, tomato, and potato. In the present study, we observed that the naturally occurring diseases in the solanaceous crops tended to decrease when the knotweed mulching system was adopted, in comparison to when Poaceae mulch was adopted. In eggplants, leaf mold and powdery mildew decreased under Japanese knotweed mulching. We further evaluated the effects of Japanese knotweed mulching by inoculating test plants with Pseudomonas cichorii. We observed suppression of bacterial disease and tomato mosaic virus under Japanese knotweed mulching and following spraying with Japanese knotweed extracts. In addition, disease-resistance genes were expressed at high levels in Arabidopsis thaliana, a model plant, following treatment with Japanese knotweed extracts. The results suggest that Japanese knotweed has potential applications in future sustainable agriculture activities.  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