Development of an operational coastal model of the Seto Inland Sea,Japan     

Kei Sakamoto  Goro Yamanaka  Hiroyuki Tsujino  Hideyuki Nakano  Shogo Urakawa  Norihisa Usui  Mikitoshi Hirabara  Koji Ogawa 《Ocean Dynamics》2016,66(1):77-97

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Na-bearing Ca-Al-rich inclusions in the Yamato-791717 CO carbonaceous chondrite     

Kazushige Tomeoka  Koji Nomura  Hiroshi Takeda 《Meteoritics & planetary science》1992,27(2):136-143

Abstract Ca-Al-rich inclusions (CAIs) in the Yamato-791717 CO carbonaceous chondrite contain 5 to 80 vol% of nepheline, along with minor sodalite, and thus are among the most nepheline-rich CAIs known. The primary phases in inclusions are mainly spinel, fassaite, aluminous diopside, perovskite, and hibonite. In contrast to many CO chondrites, melilite is rare. Spinel contains variable amounts of Fe (0 to 57 mol% FeAl₂O₄) and is commonly zoned. Texture suggests that nepheline is a secondary alteration product formed by replacing mainly melilite, fassaite, and spinel; melilite is the most susceptible to alteration of the primary phases, so most of it was probably already consumed to form nepheline. The majority of inclusions are single concentric objects or aggregates of concentric objects. Lightly altered inclusions have cores of spinel surrounded by bands of nepheline (replacing fassaite), fassaite, and diopside. In moderately altered inclusions, spinel cores are replaced by nepheline. In heavily altered inclusions, the major part of internal areas (50 to 80% in volume) are replaced by nepheline. In some moderately and heavily altered inclusions, only diopside rims remain unaltered. Textural relationships indicate that the resistance of primary phases to alteration increases in the order melilite, fassaite, spinel, diopside. The alteration probably proceeded with reaction of the primary phases with the low-temperature (≤ 1000 K) nebular gas rich in Na, Fe and CI. The degree of alteration in Y791717 CAIs appears to be much higher than those in CAIs in other reported meteorites.  相似文献   

Seismic evidence of divergent rifting and subsequent deformation in the southern Japan Sea, and a Cenozoic tectonic synthesis of the eastern Eurasian margin   总被引：1，自引：0，他引：1  

Yasuto Itoh  Koji Uno  Hiroyuki Arato 《Journal of Asian Earth Sciences》2006,27(6):933-942

Neogene rift system configuration for the back-arc of southwest Japan, southern rim of the Japan Sea, is argued on the basis of reflection seismic interpretation. Divergent rifting and subsequent contraction provoked by an arc–arc collisional event are manifested by the formation of faulted grabens and their inverted deformation, respectively. We identified the following four Cenozoic tectonic epochs as a decomposition process of the eastern Eurasian margin based on reliable paleomagnetic data: (1) Plate margin rearrangement on a regional left-lateral fault through southwest Japan and Sikhote Alin, which constituted a continuous geologic province before the early Tertiary differential motion; (2) Early Tertiary clockwise rotation (>20°) of the east Tan-Lu block relative to the North China block; (3) Oligocene to early Miocene divergent rifting and spreading of the Japan Sea, which divided southwest Japan from the east Tan-Lu block; (4) Middle Miocene bending and back-arc inversion of southwest Japan caused by collision with the Izu-Bonin arc. According to the estimation of relative motions during these events, a paleogeographic reconstruction is presented through Cenozoic time.  相似文献   

Minerals formed and mineral formation from volcanic ash by weathering   总被引：2，自引：0，他引：2  

Koji Wada 《Chemical Geology》1987,60(1-4):17-28

Weathering of volcanic ash and pumice is unique regarding minerals formed and mineral formation. These minerals include allophane, imogolite, opaline silica and some halloysites, and have distinctive structures and properties. Studies on the surface and subsurface weathering of various volcanic ashes in different settings are reviewed. This review illustrates that relatively rapid weathering of finely comminuted volcanic ash well reflects the effects of climate, vegetation and time, and produces various combinations of weathering products. The moisture regime, the nature and amount of organic matter incorporated, the deposition of volcanic ash as overburden, and the chemical and mineralogical composition of parent ash are important in controlling the mineral formation in weathered volcanic ash.  相似文献   

Light utilization efficiency of phytoplankton in the Western Subarctic Gyre of the North Pacific during summer     

Yuichi Nosaka  Tomonori Isada  Isao Kudo  Hiroaki Saito  Hiroshi Hattori  Atsushi Tsuda  Koji Suzuki 《Journal of Oceanography》2014,70(1):91-103

We investigated the water-column light utilization efficiency (Ψ) of phytoplankton photosynthesis in the Western Subarctic Gyre (WSG) of the North Pacific during summer 2008. The Ψ values (0.64–1.86 g C [g Chl a]^?1 [mol photon]^?1 m²) obtained were observed to increase significantly with decreasing daily photosynthetic available radiation (PAR) and were generally higher than those of previous studies, not only from the subarctic Pacific but also from the world’s oceans. To examine the effect of iron availability on Ψ in the WSG, Ψ values were estimated from the data of two in situ iron fertilization experiments: the Subarctic Pacific Iron Experiment for Ecosystem Dynamics Study I (SEEDS-I) and II (SEEDS-II). We found that iron availability did not affect Ψ values. Overall, this study revealed that Ψ values changed remarkably in the WSG during the summer, and that higher values were found at the stations where moderate PAR levels (ca. 10–30 mol photons m^?2 day^?1) were observed and where autotrophic flagellates predominated in the phytoplankton assemblages.  相似文献   

Basin-scale distribution of prokaryotic phylotypes in the epipelagic layer of the Central South Pacific Ocean during austral summer     

Yuya Tada  Takuhei Shiozaki  Hiroshi Ogawa  Koji Suzuki 《Journal of Oceanography》2017,73(2):145-158

In the present study, we used catalyzed reporter deposition-fluorescence in situ hybridization to quantify the abundance of five bacterial (Alphaproteobacteria, SAR11, Gammaproteobacteria, SAR86, and Bacteroidetes) and two archaeal (Crenarchaeota and Euryarchaeota) phylotypes in the epipelagic layer (0–200 m) of the Central South Pacific Ocean along 170°W from 0° to 40°S. We found that the distribution patterns of these phylotypes differed from each other. All phylotypes except Gammaproteobacteria were particularly abundant at the surface water of the equatorial region, whereas Gammaproteobacteria was relatively abundant in the area from the southern part of the South Pacific Ocean. SAR11, affiliated with Alphaproteobacteria was the dominant phylotype at all depths, throughout the study area. The abundance of SAR11 significantly increased with chlorophyll a concentration, suggesting that phytoplankton could affect their distribution pattern. There was a positive correlation between Bacteroidetes abundance and water temperature, suggesting that the temperature gradient could be a critical factor determining their distribution in the South Pacific Ocean. Crenarchaeota and Euryarchaeota were more abundant at the equatorial region than in other study areas. Euryarchaeota abundance significantly decreased with depth, and increased with chlorophyll a concentration. This suggests that there was ecological interaction between Euryarchaeota and phytoplankton in the equatorial surface. Our data indicate that distinct hydrographic properties such as seawater temperature, salinity, and the concentrations of chlorophyll a and nutrients can principally control the basin-scale distribution of different prokaryotic phylotypes in the epipelagic layer of the Central South Pacific Ocean.  相似文献   

Comparison of carbon cycle between the western Pacific subarctic and subtropical time-series stations: highlights of the K2S1 project     

Makio C. Honda  Masahide Wakita  Kazuhiko Matsumoto  Tetsuichi Fujiki  Eko Siswanto  Kosei Sasaoka  Hajime Kawakami  Yoshihisa Mino  Chiho Sukigara  Minoru Kitamura  Yoshikazu Sasai  Sherwood L. Smith  Taketo Hashioka  Chisato Yoshikawa  Katsunori Kimoto  Shuichi Watanabe  Toru Kobari  Toshi Nagata  Koji Hamasaki  Ryo Kaneko  Mario Uchimiya  Hideki Fukuda  Osamu Abe  Toshiro Saino 《Journal of Oceanography》2017,73(5):647-667

A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.  相似文献   

A derivation of the scaling law, the power law and the scaling relation for fetch-limited wind waves using the renormalization group theory     

Koji Ueno 《Journal of Oceanography》1998,54(6):641-649

A state of wind waves at a fetch is assumed to be transformed into another state of wind waves at a different fetch by the renormalization group transformation. The scaling laws for the covariance of water surface displacement and for the one-dimensional and two-dimensional spectrum and the power law for the growth relation are derived from the fact that the renormalization group transformation constitutes a semigroup. The scaling relation or the relation among the exponents of the power law is also derived, using the two assumptions that the renormalization group transformation is applicable to fetch-limited wind waves and that the saturated range exists, which implies that the directional distribution function of energy in the wave number region much larger than the peak wave number does not depend on wave number.  相似文献   

Rediscovering wood-laden debris flow studies: A perspective from Japan     

Kenta Koyanagi  Taku Yamada  Koji Ishida 《地球表面变化过程与地形》2023,48(1):104-118

Debris flow is one of the dominant processes distributing large wood (LW) within mountainous catchments. However, little has been reviewed on wood-laden debris flow (WLDF), presumably owing to limited reviewable works. This article, therefore, navigates the international readers through 40 years of WLDF studies, most of which have been published only in Japanese. Firstly, we reviewed the historical development of Japanese WLDF particularly focusing on the 1980s and the 1990s. A series of post-disaster fieldworks from the July 1982 Nagasaki flood to the July 1990 Kumamoto flood provided 32 catchment-scale wood budgeting data; empirical relationships among drainage area, dominant tree species, sediment yield, and wood loads associated with single debris flow disasters were illustrated. Secondly, the characteristics of WLDF were summarized based on relevant previous studies on the recruitment, transport, and deposition processes of LW during debris flows. Thirdly, we discussed the connectivity between those Japanese WLDF studies and international LW studies by relating/contrasting their research approaches and spatiotemporal scales. In contrast to global LW research trends, Japanese WLDF studies have almost exclusively regarded LW as hazardous materials (i.e., “driftwood” or “woody debris”) that need to be retained upstream of the inhabited areas. Those practice-oriented WLDF studies were concentrated on drainage areas of 10⁻² to 10⁰ km², representing 1–6 orders of magnitude smaller spatial scales than those generally covered by existing international LW studies. Strongly motivated by engineering requirements, “dynamic” interactions between debris flows and LW during floods have also been physically presented, mainly based on unique laboratory experiments involving steep flume (> 0.05) and mobile bed conditions. Finally, some future works for WLDF were briefly stated from practical and scientific perspectives. By “rediscovering” those WLDF studies domestically developed in Japanese debris flow channels since the 1980s, a more comprehensive understanding of LW dynamics in the river system may be achieved.  相似文献