A Generation Mechanism for Mesoscale Eddies in the Kuril Basin of the Okhotsk Sea: Baroclinic Instability Caused by Enhanced Tidal Mixing     

Kay?I.?OhshimaEmail author  Yasushi?Fukamachi  Takeshi?Mutoh  Masaaki?Wakatsuchi 《Journal of Oceanography》2005,61(2):247-260

Mesoscale eddies, particularly anticyclonic ones, are dominant features in the Kuril Basin of the Okhotsk Sea. In 1999, both surface drifter and hydrographic observations caught the same anticyclonic eddy northwest of Bussol’ Strait, which has a diameter of ∼100 km, typical surface velocity of 0.2–0.3 m s⁻¹, and less dense core extending to a depth of ∼1200 m. Based on an idea that the generation of mesoscale eddies is caused by strong tidal mixing in and around Kuril Straits, we have conducted a series of three-dimensional numerical model experiments, in which strong tidal mixing is simply parameterized by increasing coefficients of vertical eddy viscosity and diffusivity along the eastern boundary. Initially, a regular series of disturbances with a wavelength of ∼70 km starts to develop. The disturbances can be clearly explained by a linear instability theory and regarded as the baroclinic instability associated with the near-surface front formed in the region between the enhanced mixing and offshore regions. In the mature phase, the disturbances grow large enough that some eddies pinch off and advect offshore (westward), with the scale of disturbances increasing gradually. Typical eddy scale and its westward propagation speed are ∼100 km and ∼0.6 km day⁻¹, respectively, which are consistent with the observations by satellites. The westward propagation can be explained partly due to nonlinear effect of self-offshore advection and partly due to the β-effect. With the inclusion of the upper ocean restoring, the dominance of anticyclonic eddy, extending from surface to a depth of ∼1200 m, can be reproduced.  相似文献   

A new expression for the production rate of sea water droplets on the sea surface     

Noriko Iida  Yoshiaki Toba  Masaaki Chaen 《Journal of Oceanography》1992,48(4):439-460

A new set of empirical formulas for the production rate and the number concentration of sea-water droplets on the sea surface are proposed, synthesizing past observation data of sea-salt particles in the sea and water droplets in wind-wave tanks. A new levelz _c is introduced as the effective wind-sea surface where seawater droplets are produced. The new formulas are expressed in linear functions in logarithmic scales ofu*²/v _p , a parameter to describe overall conditions of airsea boundary processes, whereu _* is the friction velocity of air,v the kinematic viscosity of air and _p the peak angular frequency of wind-wave part of wave spectra. A model of coexistence of spray droplets and suspended particles near the sea surface is proposed. As for the independent parameter, a comparison between the uses ofu*²/v _p and ofu _* ³ which was the traditional way of parameterization excluding wave measure, shows that the advantage of usingu*²/v _p is statistically significant with a confidence limit 89% in F-test.  相似文献   

Recognizing cryptic environmental changes by using paleoecology and taphonomy of Pleistocene bivalve assemblages in the Oga Peninsula,northern Japan     

Tomoki Chiba  Masaaki Shirai  Shin'ichi Sato 《Quaternary Research》2014

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.  相似文献   

Contents of hepatic and renal metallothioneins in Hyposarcus pardalis: for construction of biomarker for heavy metal contamination in environments     

Shun Yukawa  Yustiawati  M. Suhaemi Syawal  Kenichi Kobayashi  Toshiyuki Hosokawa  Takeshi Saito  Shunitz Tanaka  Masaaki Kurasaki 《Environmental Earth Sciences》2014,71(4):1945-1952

The pollution of water by heavy metals is one of the most serious problems in the developing countries, where watercourses play important roles in transport and economic activities. The aim of this study was to examine whether Hyposarcus pardalis, a fish species widespread in the freshwater environment in Indonesia, could be used as a biomarker for environmental pollution by metals. To this effect, the concentrations of metallothioneins and metals in the livers and kidneys of H. pardalis were measured. In addition, to clarify the relationship between metallothionein concentrations and metal exposure, the concentrations of metallothioneins and metals were determined in the liver and the kidney of fish exposed to 50 and 500 ppb Cu and 500 ppb Mn, compared with those kept in clean water. Sufficient concentrations of metallothionein were detected in fish captured from Lake Rawakalong located in an industrial area in the suburbs of Jakarta. The results of exposure experiments suggested that H. pardalis retained a history of pollution in its organs for a long duration, and the metals bound to metallothioneins in the liver and kidney could be replaced with Cu following exposure. In conclusion, the hepatic and renal metallothioneins in H. pardalis are a useful candidate biomarker for monitoring heavy metal contamination.  相似文献   

Development of the core‐suspended isolation system     

Yutaka Nakamura  Masaaki Saruta  Akira Wada  Toru Takeuchi  Shigeru Hikone  Teiichi Takahashi 《地震工程与结构动力学》2011,40(4):429-447

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Isochemical breakdown of garnet in orogenic garnet peridotite and its implication to reaction kinetics     

Masaaki Obata  Kazuhito Ozawa  Kosuke Naemura  Akira Miyake 《Mineralogy and Petrology》2013,107(6):881-895

An isochemical kelyphite (orthopyroxene+spinel+plagioclase) that has nearly the same bulk chemical composition as the precursor garnet was found within a matrix of ordinary kelyphites (orthopyroxene+clinopyroxene+spinel±amphibole) in garnet peridotites from the Czech part of the Moldanubian Zone. It was shown that the kelyphitization of garnet took place in three stages: (1) the garnet-olivine reaction, accompanied by a long-range material transfer across the reaction zone, and (2) the isochemical breakdown of garnet, essentially in a chemically-closed system, and finally, (3) an open-system hydration reaction producing a thin hydrous zone (amphibole+spinel+plagioclase), which is located between the isochemical kelyphite and relict garnet. The presence of relict garnet suggests that this breakdown reaction of the second stage did not proceed to a completion probably being hindered by the formation of the hydrous zone at the reaction front. It was found by electron back-scattered diffraction method that orthopyroxene and spinel do not show any topotaxic relationship in the first type of kelyphite; whereas they show locally topotaxic relationship in the isochemical kelyphite. The transition from the first type to the second type of kelyphite is discussed on the basis of the detailed observations in the transition zone between the two kelyphites. More widespread occurrence of isochemical kelyphite is expected to occur in orogenic peridotites as well as from xenoliths brought by volcanics.  相似文献   

Missing ophiolitic rocks along the Mae Yuam Fault as the Gondwana–Tethys divide in north-west Thailand     

Ken-ichiro Hisada  Masaaki Sugiyama  Katsumi Ueno  Punya Charusiri  Shoji Arai 《Island Arc》2004,13(1):119-127

Abstract Thailand comprises two continental blocks: Sibumasu and Indochina. The clastic rocks of the Triassic Mae Sariang Group are distributed in the Mae Hong Son–Mae Sariang area, north‐west Thailand, which corresponds to the central part of Sibumasu. The clastic rocks yield abundant detrital chromian spinels, indicating a source of ultramafic/mafic rocks. The chemistry of the detrital chromian spinels suggests that they were derived from three different rock types: ocean‐floor peridotite, chromitite and intraplate basalt, and that ophiolitic rocks were exposed in the area, where there are no outcrops of them at present. Exposition of an ophiolitic complex denotes a suture zone or other tectonic boundary. The discovery of chromian spinels suggests that the Gondwana–Tethys divide is located along the Mae Yuam Fault zone. Both paleontological and tectonic aspects support this conclusion.  相似文献   

Geochemical and tectonic evolution of arc-backarc hydrothermal systems: implication for the origin of Kuroko and epithermal vein-type mineralizations and the global geochemical cycle, by Naotatsu Shikazono, Developments in Geochemistry 8, 463 pp., Elsevier, 2003, EUR 160. ISBN 0-444-51150-4     

Masaaki Shimizu 《Mineralium Deposita》2005,39(8):992-992

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The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western pacific ocean     

T. Okita  M. Okuda  K. Murano  T. Itoh  I. Kanazawa  M. Hirota  H. Hara  Y. Hashimoto  S. Tsunogai  S. Ohta  Y. Ikebe 《Journal of Atmospheric Chemistry》1986,4(3):343-358

During the winters of 1981 and 1982, measurements were taken on two Japanese islands of the aerosol and gaseous species which had been carried by northwesterly monsoons over the Pacific Ocean. The aerosols were characterized as sea-salt particles; soil particles, and as particles of sulfate, nitrate, organics and elemental carbon. At Chichi-jima island, which is about 800 km away from the main islands of Japan, it was found that the level of the anthropogenic components of the aerosols was considerably higher than their background level. The mean concentrations of the species on the islands are given in tabular forms. According to a survey made on board a ferry boat, the aerosol and gaseous species were fairly uniformly distributed along the southern coast of the main Japanese islands.  相似文献   

A Study of Tsunami Wave Fission in an Undistorted Experiment     

Masafumi Matsuyama  Masaaki Ikeno  Tsutomu Sakakiyama  Tomoyoshi Takeda 《Pure and Applied Geophysics》2007,164(2-3):617-631

To study tsunami soliton fission and split wave-breaking, an undistorted experiment was carried out which investigated tsunami shoaling on a continental shelf. Three models of the continental shelf were set up in a 205-m long 2-dimensional flume. Each shelf model was 100 m, long with slopes of either 1/100, 1/150, or 1/200. Water surface elevations were measured across the flume, including a dense cluster of wave gages installed around the point of wave-breaking. We propose new methods for calculating wave velocity and the wave-breaking criterion based on our interpretation of time series data of water surface elevation. At the point of wave-breaking, the maximum slope of water surface is between 20 to 50 deg., while the ratio of surface water particle horizontal velocity to wave velocity is from 0.5 to 1.2. The values determined by our study are larger than what has been reported by other researchers.  相似文献