The Zealandia Volcanic Complex: Further evidence of a lower crustal “hot zone” beneath the Mariana Intra‐oceanic Arc,Western Pacific     

Robert J. Stern  Yoshihiko Tamura  Hiroshi Shukuno  Takashi Miyazaki 《Island Arc》2019,28(5)

This paper addresses formation of felsic magmas in an intra‐oceanic magmatic arc. New bathymetric, petrologic, geochemical, and isotopic data for Zealandia Bank and two related volcanoes in the south‐central Mariana arc is presented and interpreted. These three volcanoes are remnants of an older andesitic volcano that evolved for some time and became dormant long enough for a carbonate platform to grow on its summit before reawakening as a rhyodacitic volcano. Zealandia lavas are transitional between low‐ and medium‐K and tholeiitic and calc‐alkaline suites. They define a bimodal suite with a gap of 56–58 wt% SiO₂; this suggests that mafic and felsic magmas have different origins. The magmatic system is powered by mantle‐derived basalts having low Zr/Y and flat rare earth element patterns. Two‐pyroxene thermometry yields equilibration temperatures of 1000–1100 °C for andesites and 900–1000 °C for dacites. Porphyritic basalts and andesites show textures expected for fractionating magmas but mostly fine‐grained felsic lavas do not. All lavas show trace element signatures expected for mantle and crustal sources that were strongly melt‐depleted and enriched by subduction‐related fluids and sediment melts. Sr and Nd isotopic compositions fall in the normal range of Mariana arc lavas. Felsic lavas show petrographic evidence of mixing with mafic magma. Zealandia Bank felsic magmatism supports the idea that a large mid‐ to lower‐crustal felsic magma body exists beneath the south‐central Mariana arc, indicating that MASH (mixing, assimilation, storage, and homogenization) zones can form beneath intra‐oceanic as well as continental arcs.  相似文献   

A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 – I. Observation, data analysis and luminosity function     

Naoyuki Tamura †  Ray M. Sharples  Nobuo Arimoto  Masato Onodera  Kouji Ohta  Yoshihiko Yamada 《Monthly notices of the Royal Astronomical Society》2006,373(2):588-600

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Daily variations in the occurrences of pelagic fishes and zooplankton within a coastal fishing ground of the southwestern Japan Sea     

Yoshihiko Ogawa  Tamio Nakahara 《Journal of Oceanography》1981,36(6):275-285

This paper analyzes daily variations in the occurrences of pelagic fishes and zooplankters on a small regional scale. The data used are based on daily observations repeated at 24h intervals during 6 days from 16 to 21, September, 1971, in coastal waters close to Esaki, a fishing port in the southwestern part of the Japan Sea (Yamaguchi Prefecture). The observations comprised acoustic surveys of the fish population, zooplankton sampling with a net, and Secchi disc readings, for evaluating relationships between the abundances of pelagic fishes and their food, as well as alternations in water masses. No clear correlation between pelagic fishes and their food, copepods, within a short time period was observed; fish population continued to decrease with eastward movements of fish schools although the abundances of copepods remained at almost the same level during the observations. Patterns of changes in both settled volumes of plankton and transparencies evidently suggested the occurrence of alternations in water masses. Pelagic fish schools proved to move in company with the transition of water masses.  相似文献   

Topographic effect of a marine ridge on the spin-down of a cyclonic eddy with mean flow     

Yoshihiko Sekine 《Journal of Oceanography》1993,49(5):593-606

The topographic effect of a meridional marine ridge on the spin-down of a cyclonic eddy, which is embedded in a zonal mean flow, is examined by use of a two layer numerical model. It is shown that the cyclonic eddy initially given on the eastern flank of the marine ridge decays in a short time. This result is common to all cases with the different volume transports of the mean flow (3070 Sv) and of the cyclonic eddy (1535 Sv). During the decay process, the cyclonic eddy shifts mainly northward into the shallower region, which is different from the dominant westward shift of the isolated cyclonic eddy. If the mean flow across over the marine ridge at the more northern latitude, the cyclonic eddy spins down more rapidly. A mean flow shifts zonal or south-eastward over a western side of the ridge, while it deflects north-eastward over an eastern side. The deflection angle of mean flow over the ridge depends on the intensity of lower layer velocity and density stratification. It is suggested that the topographic effect of the meridional marine ridge on the cyclonic eddy with mean flow is influenced both by the global phenomena that controls the inclination of the mean flow from zonal direction and by the local phenomena that controls the intensity of the topographic effect of the marine ridge.  相似文献   

Hydrographic structure of the Kuroshio large meander-cold water mass region down to the deeper layers of the ocean     

Haruo Ishii  Yoshihiko Sekine  Yoshiaki Toba 《Journal of Oceanography》1983,39(5):240-250

The hydrographic structure of the region of large meander of the Kuroshio and the large cold water mass, which were formed in 1975, was observed down to the ocean bottom, during three cruises of the R/VHakuho Maru in September 1975, September 1976, and December 1977. The analysis of observed data indicates the following common features: the horizontal gradient of the specific volume anomaly exists down to a 3,500 db surface, corresponding to the existence of baroclinic geostrophic current down to this depth. These facts demonstrate that the current of the Kuroshio is not confined to the upper layer during periods of existence of the large meander. On a T-S diagram, the Kuroshio water and the water in the large cold water mass can be discriminated down to a 5°C surface, but there is evidence of mixing due to conspicuous interleaving between the two water masses, near the thermocline. Below the thermocline, water types defined by points on the T-S diagram can be traced from a deeper level in the Kuroshio water to a shallower level in the cold water mass, indicating that in the deeper layers the Kuroshio water continues to be uplifted toward the center of the cold water mass. The same inference is also obtained from the distribution of dissolved oxygen.  相似文献   

Influence of Kuroshio Flow on the Horizontal Distribution of North Pacific Intermediate Water in the Shikoku Basin     

Yoshihiko Sekine  Shingo Miyamoto 《Journal of Oceanography》2002,58(4):611-616

The influence of the Kuroshio flow on the horizontal distribution of North Pacific Intermediate Water (NPIW) in the Shikoku Basin is examined based upon observational data collected by the training vessel “Seisui-maru” of Mie University together with oceanographic data compiled by the Japan Oceanographic Data Center (JODC). Although it has been stated that the NPIW with salinity less than 34.2 psu had been confined to the south of the Kuroshio main axis along the PT (KJ) Line on the eastern side of the Izu Ridge, a similar tendency can be detected on the western side of the Izu Ridge. Namely, the NPIW on the southern side of the Kuroshio main axis in the Shihoku Basin does not indicate a tendency to go northward across the Kuroshio main axis without an increase in salinity of more than 34.2 psu. However, the JODC data show that less saline water (<34.2 psu) was present on the northern side of the Kuroshio main axis south of the Kii Peninsula in May 1992. Satellite observed sea surface temperature (SST) data suggested that the Kuroshio approaches the Kii Peninsula after forming a small meander off Kyushu and some intrusions of the NPIW into the northern coastal side of the Kuroshio main axis occurred in this period. It is concluded that intrusion of the NPIW with salinity less than 34.2 psu to the northern coastal side through the Kuroshio main axis occurred during the decay period of the small meander path in May 1992. Based on these observational results, the source of the salinity minimum water on the northern coastal side of the Kuroshio main axis is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Melting relations of peridotite and the density crossover in planetary mantles     

Eiji Ohtani  Yoshihiko Nagata  Akio Suzuki  Takumi Kato 《Chemical Geology》1995,120(3-4):207-221

Melting relations of primitive peridotite were studied up to 25 GPa. The change of the liquidus phase from olivine to majorite occurs at 16 GPa. We confirmed the density crossover of the FeO-rich peridotite melt and the equilibrium olivine (Fo₉₀) at 7 GPa. Sinking of equilibrium olivine (Fo₉₅) in the primitive peridotite melt was observed up to 10 GPa. The compression curves of FeO-rich peridotitic and komatiite melts reported in this and earlier work suggest that the density crossover in the Earth's mantle will be located at 11–12 GPa at 2000°C, consistent with an previous estimation by C.B. Agee and D. Walker.

The density crossover can play a key role in the Moon and the terrestrial planets, such as the Earth, Venus and Mars. Majorite and some fraction of melt could have separated from the ascending diapir and sunk downwards at the depths below the density crossover. This process could have produced a garnet-rich transition zone in the Earth's mantle. The density crossover may exist in the FeO-rich lunar mantle at around the center of the Moon. The density crossover which exists at the depth of 600 km in the Martian mantle plays a key role in producing a fractionated mantle, which is the source the parent magmas of the SNC meteorites.  相似文献   

Regeneration dynamics of iron and nutrients from bay sediment into bottom water of Funka Bay,Japan     

Nanako Hioki  Kenshi Kuma  Yuichiroh Morita  Daichi Miura  Atsushi Ooki  Seiji Tanaka  Hiroji Onishi  Tetsuya Takatsu  Naoto Kobayashi  Yoshihiko Kamei 《Journal of Oceanography》2015,71(6):703-714

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A Subaru/Suprime-Cam wide-field survey of globular cluster populations around M87 – II. Colour and spatial distribution     

Naoyuki Tamura †  Ray M. Sharples  Nobuo Arimoto  Masato Onodera  Kouji Ohta  Yoshihiko Yamada 《Monthly notices of the Royal Astronomical Society》2006,373(2):601-612

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Evaluation of Vector Winds Observed by NSCAT in the Seas around Japan     

Harunobu Masuko  Kohei Arai  Naoto Ebuchi  Masanori Konda  Masahisa Kubota  Kunio Kutsuwada  Teruko Manabe  Akira Mukaida  Tetsuo Nakazawa  Atsushi Nomura  Akira Shibata  Yoshihiko Tahara 《Journal of Oceanography》2000,56(5):495-505

In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms^–1, which satisfies the mission requirement of accuracy, 2 ms^–1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms^–1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ship's motion, such as pitching and rolling.  相似文献