Preferred orientation of the trace fossil Entradichnus meniscus in eolian dune strata (Djadokhta Formation) at Tugrikiin Shiree,southern Mongolia and its paleoecological implications     

Koji Seike  Hitoshi Hasegawa  Niiden Ichinnorov 《Island Arc》2010,19(4):622-627

Eolian sand dune deposits of the Upper Cretaceous Djadokhta Formation at Tugrikiin Shiree, southern Mongolia, yield not only dinosaur skeletal remains but also numerous trace fossils produced by invertebrates. This paper describes the trace fossil Entradichnus meniscus, a long unlined and unbranched trail that is filled with meniscate laminae and occurs characteristically in positive epirelief. The trail is straight to gently meandering, parallel to the foreset laminae of the eolian dunes, and exhibits a significant preferred orientation parallel to the depositional dip of the cross‐stratification laminae. In addition, almost all the crescentic internal laminae of the trail show concave down‐dips. These features indicate that the trails were produced beneath the slipface of eolian dunes by the downward burrowing of the trace‐makers. This occurrence mode of E. meniscus of the Mongolian Cretaceous is very similar to that described from the Jurassic eolian dune deposits in North America. Hence, the downward burrowing of the E. meniscus animal might be a common feature in arid eolian dune deposits at least during the Jurassic and Cretaceous, and possibly reflecting a behavioral response to the morphology of large sand dunes under an arid climate.  相似文献   

Tsunami Observations in Rivers from a Perspective of Tsunami Interaction with Tide and Riverine Flow     

Elena Tolkova  Hitoshi Tanaka  Min Roh 《Pure and Applied Geophysics》2015,172(3-4):953-968

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Dominant sea-surface temperature anomaly patterns in summer over the North Pacific ocean     

Nanase Motokawa  Noriyuki Matsuo  Naoto Iwasaka 《Journal of Oceanography》2010,66(4):581-590

We investigated the structure and persistency of the dominant sea-surface temperature (SST) anomaly pattern in summer over the North Pacific from 1960 to 2004, which has been attracting less attention than those in winter. The leading empirical orthogonal functions (EOFs) for August and September, which can be treated as the summer patterns, rather resemble each other in both spatial structure and time variations but are quite different from those of the other months. A lag correlation analysis indicates that the summer patterns do not show significant persistency in the following winter and the summer of the next year. An inappropriate definition of the summer season might obscure the characteristics of the dominant summer SST anomaly pattern in the North Pacific.  相似文献   

Isotopic composition of dissolved inorganic carbon in subsurface sediments of gas hydrate-bearing mud volcanoes, Lake Baikal: implications for methane and carbonate origin   总被引：1，自引：1，他引：0  

Alexey A. Krylov  Oleg M. Khlystov  Akihiro Hachikubo  Hirotsugu Minami  Yutaka Nunokawa  Hitoshi Shoji  Tamara I. Zemskaya  Lieven Naudts  Tatyana V. Pogodaeva  Masato Kida  Gennady V. Kalmychkov  Jeffrey Poort 《Geo-Marine Letters》2010,30(3-4):427-437

We report on the isotopic composition of dissolved inorganic carbon (DIC) in pore-water samples recovered by gravity coring from near-bottom sediments at gas hydrate-bearing mud volcanoes/gas flares (Malenky, Peschanka, Peschanka 2, Goloustnoe, and Irkutsk) in the Southern Basin of Lake Baikal. The δ¹³C values of DIC become heavier with increasing subbottom depth, and vary between ?9.5 and +21.4‰ PDB. Enrichment of DIC in ¹³C indicates active methane generation in anaerobic environments near the lake bottom. These data confirm our previous assumption that crystallization of carbonates (siderites) in subsurface sediments is a result of methane generation. Types of methanogenesis (microbial methyl-type fermentation versus CO₂-reduction) were revealed by determining the offset of δ¹³C between dissolved CH₄ and CO₂, and also by using δ¹³C and δD values of dissolved methane present in the pore waters. Results show that both mechanisms are most likely responsible for methane generation at the investigated locations.  相似文献   

V-5 A study on the matching between the air turbine and phase control for the OWC wave power generator     

Hitoshi Hotta 《Ocean Engineering》1985,12(6):585-586

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Foreword     

S. Aramaki  S. Matsuo  O. Oshima  T. Tiba  Y. Sawada 《Bulletin of Volcanology》1992,54(Z1):1-6

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Modification of the damping function in the k–ε model to analyse oscillatory boundary layers     

Ahmad Sana  Abdul Razzaq Ghumman  Hitoshi Tanaka   《Ocean Engineering》2007,34(2):320-326

A simple relationship has been developed between the wall coordinate y⁺ and Kolmogorov's length scale using direct numerical simulation (DNS) data for a steady boundary layer. This relationship is then utilized to modify two popular versions of low Reynolds number k–ε model. The modified models are used to analyse a transitional oscillatory boundary layer. A detailed comparison has been made by virtue of velocity profile, turbulent kinetic energy, Reynolds stress and wall shear stress with the available DNS data. It is observed that the low Reynolds number models used in the present study can predict the boundary layer properties in an excellent manner.  相似文献   

Decomposition of Phytoplankton in Seawater. Part I: Kinetic Analysis of the Effect of Organic Matter Concentration     

Minoru Fujii  Shinichiro Murashige  Yuka Ohnishi  Atushi Yuzawa  Hitoshi Miyasaka  Yoshimi Suzuki  Hiroshi Komiyama 《Journal of Oceanography》2002,58(3):438-443

Decomposition experiments were conducted on cultured phytoplankton (Skeletonema costatum) in seawater containing decomposer and consumer of size less than 500 μm. We determined the decomposition rates of bulk particulate organic matter (POM), the ratio of labile to semi-refractory fractions in the POM, and the POM carbon/ nitrogen (C/N) ratio during decomposition. To identify the kinetic mechanisms involved in the reactions of different order (e.g., first- and second-order), we studied the sensitivity of reaction rates to the initial concentration of POM, ranging from 2.4 to 71 mg-C L⁻¹. The results showed that decomposition consists of two first-order reactions: decomposition of labile and of semi-refractory particulate organic carbon (POC). The decomposition rate constants found for labile (0.13 day⁻¹ at 20°C), and semi-refractory POC (0.008 day⁻¹ at 20°C), and the carbon weight ratio of semi-refractory POC (13% at 20°C), were insensitive to the initial organic matter concentration. The time-dependence of the C/N ratio was also independent of this initial concentration. The decomposition rate constants and the content of semi-refractory POC did not change, regardless of the absence or presence of 25–500 μm organisms in natural seawater. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Importance of feeding on regenerable parts of prey for juvenile stone flounder Platichthys bicoloratus in estuarine habitats   总被引：3，自引：0，他引：3  

Takeshi Tomiyama  Satoshi Katayama  Michio Omori  Hitoshi Honda 《Journal of Sea Research》2005,53(4):297-308

Prey availability is one of the most important factors affecting the quality of nursery grounds. Estuaries play an important role as nursery grounds for juvenile stone flounder, but the mechanism behind the consistently high availability of prey has never been examined. This study investigates which prey is mainly selected by juvenile stone flounder (15–55 mm standard length) in the estuary of the Natori River, northern Japan. In a cage experiment, juveniles showed positive selection for the palps of the spionid polychaete Pseudopolydora kempi in March, and for the siphons of the bivalve Nuttallia olivacea in April, May and June in both sandy and muddy-sand habitats. This selective predation showed that sublethal predation on regenerable parts of invertebrates is important for stone flounder. Nuttallia olivacea, the dominant bivalve in the estuary, was more abundant and in better somatic condition in the sandy area in spite of the stronger siphon-cropping pressure by juvenile stone flounder. These results confirm that sublethal predation on highly abundant benthos plays an important role in forming estuarine habitats into areas of high prey availability for juvenile stone flounder, which leads to their high growth rate.  相似文献   

Mesoscale eddy effects on temporal variability of surface chlorophyll a in the Kuroshio Extension     

Shinya Kouketsu  Hitoshi Kaneko  Takeshi Okunishi  Kosei Sasaoka  Sachihiko Itoh  Ryuichiro Inoue  Hiromichi Ueno 《Journal of Oceanography》2016,72(3):439-451

We investigated the relationship between chlorophyll a (Chl-a) concentrations estimated from satellite observations and the activity of eddies in the Kuroshio Extension region. High (low) area-averaged Chl-a concentrations were frequently observed in the core of cyclonic (anticyclonic) eddies. Such relationships between Chl-a concentrations and eddy cores were not frequently observed in the southern part of the recirculation gyre, and advection of background meridional gradient of Chl-a by eddy-edge currents accounted for Chl-a spatial variability. Decadal-scale changes of Chl-a concentrations around the Kuroshio Extension were strongly affected by eddy activity and transport but not by large-scale near-surface isopycnal heaving. We also found that decadal changes of nutrient concentrations near the main stream could affect Chl-a concentrations in the southern part of the recirculation gyre via southward transport of eddies and mean flow.  相似文献