Possibility of recent changes in vertical distribution and size composition of chlorophyll-a in the western North Pacific region     

Hiroshi Ishida  Yutaka W. Watanabe  Joji Ishizaka  Toshiya Nakano  Naoki Nagai  Yuji Watanabe  Akifumi Shimamoto  Nobuhiro Maeda  Michimasa Magi 《Journal of Oceanography》2009,65(2):179-186

Our analysis of the last three decades of retrospective data of vertical distributions and size composition of chlorophyll-a (Chl-a) over the western North Pacific has revealed significant changes of three indices related to Chl-a during summer season, as follows: (1) decreasing linear trend of the proportion of Chl-a in surface layer to that of the whole water column by 0.4 and 2.3% year⁻¹ in the subtropical area along 137°E (STA₁₃₇) during 1972 to 1997 and in the Kuroshio Extension area along 175°E (KEA₁₇₅) during 1990 to 2001; (2) increasing linear trend of the depth of subsurface Chl-a maximum (DCM) by 0.4 and 2.6 m year⁻¹ in STA₁₃₇ and KEA₁₇₅; and (3) decreasing linear trend of larger-size Chl-a (>3 μm) by 0.1 and 2.5% year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. Water density (σ _θ ) at 75 m depth had also decreased by 0.006 and 0.05 year⁻¹ in STA₁₃₇ and KEA₁₇₅, respectively. The ratio of biogenic opal to biogenic CaCO₃ in the sinking flux decreased by 0.015 year⁻¹ in the subtropical region from 1997 to 2005. These findings may indicate that the subsurface chlorophyll maximum is deepening and larger phytoplankton such as diatoms has been decreasing during the past decade, associated with the decreasing density of surface water caused by warming in the western North Pacific, especially in the summer.  相似文献   

Observations of the North Equatorial Current,Mindanao Current,and Kuroshio current system during the 2006/07 El Niño and 2007/08 La Niña   总被引：1，自引：0，他引：1  

Yuji Kashino  Norievill España  Fadli Syamsudin  Kelvin J. Richards  Tommy Jensen  Pierre Dutrieux  Akio Ishida 《Journal of Oceanography》2009,65(3):325-333

Two onboard observation campaigns were carried out in the western boundary region of the Philippine Sea in December 2006 and January 2008 during the 2006/07 El Niño and the 2007/08 La Niña to observe the North Equatorial Current (NEC), Mindanao Current (MC), and Kuroshio current system. The NEC and MC measured in late 2006 under El Niño conditions were stronger than those measured during early 2008 under La Niña conditions. The opposite was true for the current speed of the Kuroshio, which was stronger in early 2008 than in late 2006. The increase in dynamic height around 8°N, 130°E from December 2006 to January 2008 resulted in a weakening of the NEC and MC. Local wind variability in this region did not appear to contribute to changes in the current system.  相似文献   

ESR dating of palaeolithic calcite: A comparison between powder and monocrystal spectra with thermal annealing     

Yuji Yokoyama  Roland Bibron  Concle Leger 《Quaternary Science Reviews》1988,7(3-4)

Evolution of ESR spectra with thermal annealing at different temperatures is studied for a monocrystal calcite taken in the Orgnac III site. Up to 20 ESR lines are recognized from the angular dependence of these lines. These lines are compared with the ESR lines observed for powder and rotating monocrystal calcites.The h1 line (g = 2.0057) and h3 line (g = 2.0007) are isotropic or nearly isotropic and are due to the electrons trapped in the amorphous region formed by fission tracks or alpha-ray recoil nuclei. The h2 line (g = 2.0021) is a composite of several different lines.  相似文献   

Space-time distribution patterns of destructive earthquakes in the inner belt of central Japan: Activity intervals and locations of earthquakes     

Yuji Kanaori  Shin-ichi Kawakami  Kenji Yairi 《Engineering Geology》1991,31(3-4):209-230

Based on a block structure model of the inner belt of central Japan, an examination was conducted of the space-time distribution patterns of destructiv magnitudes M 6.4 or greater (M =Japan Meteorological Agency Scale). The distribution patterns revealed a periodicity in earthquake activit seismic gaps. Major NW—SE trending left-lateral active faults divide the inner belt of central Japan into four blocks, 20–80 km wide. The occurrenc A.D. with M ≥ 6.4, which have caused significant damage, were documented in the inner belt of central Japan. The epicenters of these earthquakes close to the block boundaries.

Using the relationship between the magnitude of earthquakes which occurred in the Japanese Islands and the active length of faults that generated them, movement is calculated for each historical earthquake. Space—time distributions of earthquakes were obtained from the calculated lengths, the latitud of generation. When an active period begins, a portion or segment of the block boundary creates an earthquake, which in turn appears on the ground surf active period ends when the block boundary generates earthquakes over the entire length of the block boundary without overlapping.

Five seismic gaps with fault lengths of 20 km or longer can be found in the inner belt of central Japan. It is predicted that the gaps will generate ea magnitudes of 7.0. These data are of significance for estimating a regional earthquake risk over central Japan in the design of large earthquake resist

The time sequences of earthquakes on the block boundaries reveal a similar tendency, with alternating active periods with seismic activity and quiet pe activity. The inner belt of central Japan is now in the last stage of an active period. The next active period is predicted to occur around 2500 A.D.  相似文献   

Displaced dolomites in radiolarian cherts of the Chichibu Belt on Shikoku Island,Southwest Japan     

Hiroyoshi Sano 《Sedimentary Geology》1984,37(3):203-223

The northern tract of the Chichibu Belt on Shikoku Island, Southwest Japan, in places contains dolomites of Late Carboniferous age displaced into radiolarian cherts. The sections here examined are along the Niyodo gorge, central Shikoku. The sequence begins with thinly interbedded dolomitized radiolarian cherts and dolomites with a small amount of dolomitized radiolarian claystone and calcisiltite beds. These rocks, 5–10 m thick, are succeeded by a thick section of bedded and massive dolomites, commonly 40–50 m thick, which have thin intercalations of radiolarian claystone in the upper part. This dolomite sequence is depositionally overlain by a sequence, up to 50 m thick, comprising thinly interbedded radiolarian cherts and claystones, which, in turn, contain lenticular bodies of dolomite.Thin-section examination reveals that most of dolomites of the area have an arenitic or lithic texture, and should be termed doloarenite and dololithite. This means that dolomites are detrital. All lines of evidence suggest that the dolomites were not formed in the same depositional site in which the radiolarian cherts were being accumulated, but formed instead as allochthonous bodies which were displaced into a deep oceanic basin of chert deposition.The following sequence of events is postulated: (1) deposition of shallow-water calcareous sediments in a subtidal area; (2) dolomitization in a very shallow-water to supratidal environment; (3) displacement of dolomitized sediments, possibly mainly as debris flows into a deep-water, truely pelagic realm, in which siliceous radiolarian sediments were accumulating; (4) continued accumulation of siliceous sediments after the major influx of dolomitized sediments; and (5) minor influxes of dolomitized sediments during the continuous accumulation of siliceous sediments.  相似文献   

The observation of crack development around an underground rock chamber by borehole television system     

Yuji Kanaori 《Rock Mechanics and Rock Engineering》1983,16(2):133-142

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Sea navigation, challenges and potentials in South East Asia: an assessment of suitable sites for a shipping canal in the South Thai Isthmus     

Rajesh B. Thapa  Michiro Kusanagi  Akira Kitazumi  Yuji Murayama 《GeoJournal》2007,70(2-3):161-172

This paper discusses the situation of sea navigation in south East Asia focusing on the Strait of Malacca. The strait links the Indian and Pacific oceans, which is considered one of the busiest in several narrow channels around the world. The paper highlights the significance of the strait to global maritime trade, volume of traffic, and rising environmental and social consequences in the strait. A feasibility study of constructing a new shipping canal in the South Thai Kra Isthmus as an alternative option of Malacca route had been studied since 19th century. The paper explores suitable sites for a potential shipping canal in the Kra Isthmus using physiographic spatial data i.e., elevation, sea charts, geology, soils and river systems. Each spatial data was considered as a separate decision variable for site evaluation. Separate evaluation criterions were prepared for each variable based on shipping canal requirements. Overlaying the maps in GIS environment, the variables were carefully evaluated, and five geographic sites for the canal were derived. The length of the shipping canal over sea and land was computed for each site. Site B located in south of Ranong and Chumphon provinces, was the shortest one, whereas site C in Surat Thani, Pangnna and Krabi provinces was the longest. However, each site consisted of benefits and constraints.  相似文献   

Triassic mid-oceanic sedimentation in Panthalassa Ocean: Sambosan accretionary complex, Japan     

Tetsuji  Onoue  Hiroyoshi  Sano 《Island Arc》2007,16(1):173-190

Abstract   The Sambosan accretionary complex of southwest Japan was formed during the uppermost Jurassic to lowermost Cretaceous and consists of basaltic rocks, carbonates and siliceous rocks. The Sambosan oceanic rocks were grouped into four stratigraphic successions: (i) Middle Upper Triassic basaltic rock; (ii) Upper Triassic shallow-water limestone; (iii) limestone breccia; and (iv) Middle Middle Triassic to lower Upper Jurassic siliceous rock successions. The basaltic rocks have a geochemical affinity with oceanic island basalt of a normal hotspot origin. The shallow-water limestone, limestone breccia, and siliceous rock successions are interpreted to be sediments on the seamount-top, upper seamount-flank and surrounding ocean floor, respectively. Deposition of the radiolarian chert of the siliceous rock succession took place on the ocean floor in Late Anisian and continued until Middle Jurassic. Oceanic island basalt was erupted to form a seamount by an intraplate volcanism in Late Carnian. Late Triassic shallow-water carbonate sedimentation occurred at the top of this seamount. Accumulation of the radiolarian chert was temporally replaced by Late Carnian to Early Norian deep-water pelagic carbonate sedimentation. Biotic association and lithologic properties of the pelagic carbonates suggest that an enormous production and accumulation of calcareous planktonic biotas occurred in an open-ocean realm of the Panthalassa Ocean in Late Carnian through Early Norian. Upper Norian ribbon chert of the siliceous rock succession contains thin beds of limestone breccia displaced from the shallow-water buildup resting upon the seamount. The shallow-water limestone and siliceous rock successions are nearly coeval with one another and are laterally linked by displaced carbonates in the siliceous rock succession.  相似文献   

ACTIVE system for monitoring volcanic activity: A case study of the Izu-Oshima Volcano,Central Japan     

Hisashi Utada  Yuji Takahashi  Yuichi Morita  Takao Koyama  Tsuneomi Kagiyama 《Journal of Volcanology and Geothermal Research》2007

A system is proposed for the monitoring of changes in the underground structure of an active volcano over time by applying a transient electromagnetic method. The monitoring system is named ACTIVE, which stands for Array of Controlled Transient-electromagnetics for Imaging Volcano Edifice. The system consists of a transmitter dipole used to generate a controlled transient electromagnetic (EM) field and an array of receivers used to measure the vertical component of the transient magnetic field at various distances, with automatic operation of both units. In order to verify the performance of the proposed system, numerical and field experiments were carried out by application of the system to the Izu-Oshima volcano, where a remarkable change in the apparent DC resistivity over time had been detected in association with the eruption in 1986.  相似文献   

Wide-Field Camera for Gravitational Microlensing Survey: MOA-cam2     

Toshifumi Yanagisawa  Yasushi Muraki  Yutaka Matsubara  Fumio Abe  Kimiaki Masuda  Sachiyo Noda  Takahiro Sumi  Yuji Kato  Mitsuaki Fujimoto  Shuji Sato  Ian Bond  Nicholas Rattenbury  Philip Yock  Pam Kilmartin  John Hearnshaw  Micheal Reid  Denis Sullivan  Brian Carter  Richard Dodd  Garry Nankivell  Noiman Rumsey  Morihiro Honda  Maki Sekiguchi  Masanori Yoshizawa  Takashi Nakamura  Humitaka Sato  Seiji Kabe  Makoto Kobayashi  Yoshiyuki Watase  Jun Jugaku  Toshiharu Saito  Barbel Koribalsky 《Experimental Astronomy》2000,10(4):519-535

We have constructed a large, mosaic CCD camera called MOA-cam2 which has 4096 × 6144-pixelsto search for gravitational microlensing events. MOA-cam2 has three4096 × 2048-pixel SITe CCD chips, which have a very high quantum efficiency (nearly 80% in the wave region 500 to 800 nm),and three buttable sides. We have placed the threechips side by side with 100 m dead space. MOA-cam2 has been installed on the 61 cm Boller and Chivens telescope of the MOA collaboration at the Mt. John University Observatory (MJUO) in NewZealand since July 1998. The field coverage is 0.92° × 1.38° per exposure. The technical details of MOA-cam2 and the first images obtained with the Boller and Chivens telescope are presented. MOA-cam2 introduces a second phase of research on gravitational microlensing by the MOA collaboration.  相似文献