Evolution of West Rota Volcano, an extinct submarine volcano in the southern Mariana Arc: Evidence from sea floor morphology, remotely operated vehicle observations and ⁴⁰Ar–³⁹Ar geochronological studies     

Robert J.  Stern  Yoshihiko  Tamura  Robert W.  Embley  Osamu  Ishizuka  Susan G.  Merle  Neil K.  Basu  Hiroshi  Kawabata  Sherman H.  Bloomer 《Island Arc》2008,17(1):70-89

Abstract West Rota Volcano (WRV) is a recently discovered extinct submarine volcano in the southern Mariana Arc. It is large (25 km diameter base), shallow (up to 300 m below sealevel), and contains a large caldera (6 × 10 km, with up to 1 km relief). The WRV lies near the northern termination of a major NNE‐trending normal fault. This and a second, parallel fault just west of the volcano separate uplifted, thick frontal arc crust to the east from subsiding, thin back‐arc basin crust to the west. The WRV is distinct from other Mariana Arc volcanoes: (i) it consists of a lower, predominantly andesite section overlain by a bimodal rhyolite‐basalt layered sequence; (ii) andesitic rocks are locally intensely altered and mineralized; (iii) it has a large caldera; and (iv) WRV is built on a major fault. Submarine felsic calderas are common in the Izu and Kermadec Arcs but are otherwise unknown from the Marianas and other primitive, intraoceanic arcs. ⁴⁰Ar–³⁹Ar dating indicates that andesitic volcanism comprising the lower volcanic section occurred 0.33–0.55 my ago, whereas eruption of the upper rhyolites and basalts occurred 37–51 thousand years ago. Four sequences of rhyolite pyroclastics each are 20–75 m thick, unwelded and show reverse grading, indicating submarine eruption. The youngest unit consists of 1–2 m diameter spheroids of rhyolite pumice, interpreted as magmatic balloons, formed by relatively quiet effusion and inflation of rhyolite into the overlying seawater. Geochemical studies indicate that felsic magmas were generated by anatexis of amphibolite‐facies meta‐andesites, perhaps in the middle arc crust. The presence of a large felsic volcano and caldera in the southern Marianas might indicate interaction of large normal faults with a mid‐crustal magma body at depth, providing a way for viscous felsic melts to reach the surface.  相似文献   

Diel tuning of photosynthetic systems in ice algae at Saroma-ko Lagoon, Hokkaido, Japan   总被引：1，自引：0，他引：1  

Shimpei Aikawa  Hiroshi Hattori  Yasushi Gomi  Kentaro Watanabe  Sakae Kudoh  Yasuhiro Kashino  Kazuhiko Satoh 《Polar Science》2009,3(1):57-72

Ice algae are the major primary producers in seasonally ice-covered oceans during the cold season. Diurnal change in solar radiation is inevitable for ice algae, even beneath seasonal sea ice in lower-latitude regions. In this work, we focused on the photosynthetic response of ice algae under diurnally changing irradiance in Saroma-ko Lagoon, Japan. Photosynthetic properties were assessed by pulse-amplitude modulation (PAM) fluorometry. The species composition remained almost the same throughout the investigation. The maximum electron transport rate (rETR_max), which indicates the capacity of photosynthetic electron transport, increased from sunrise until around noon and decreased toward sunset, with no sign of the afternoon depression commonly observed in other photosynthetic organisms. The level of non-photochemical quenching, which indicates photoprotection activity by dissipating excess light energy via thermal processes, changed with diurnal variations in irradiance. The pigment composition appeared constant, except for xanthophyll cycle pigments, which changed irrespective of irradiance. These results indicate that ice algae tune their photosynthetic system harmonically to achieve efficient photosynthesis under diurnally changing irradiance, while avoiding damage to photosystems. This regulation system may be essential for productive photosynthesis in ice algae.  相似文献   

Characterizing heterogeneous soil water flow and solute transport using information measures   总被引：1，自引：0，他引：1  

Kang Wang  Renduo Zhang  Yasuda Hiroshi 《Journal of Hydrology》2009,370(1-4):109-121

Heterogeneous water flow and solute transport in soils are an important phenomenon and difficult to be characterized. The objectives of this study were to investigate the heterogeneity of solute transport related to heterogeneous soil water flow using dye infiltration experiments, and to characterize heterogeneous water flow and solute transport in soils using the information theory. Field experiments of dye infiltration were performed in four plots. Various information measures were applied to characterize information content and complexity of water flow and solute transport in soils. Information contents and complexities of the maximum and apparent infiltration depths, and the mean and standard deviation of concentrations in the vertical direction of the plots were calculated. More heterogeneous processes of soil water flow and transport result in higher information/complexity values. The probability distributions of mean concentration were similar to those of the corresponding apparent infiltration depths for the plots, indicating that heterogeneity of dye concentrations was closely related to that of soil water flow. However, the range of information entropy and complexity of the water flow sequences was much narrower than that of the sequences of the concentrations. The results suggested that the transport processes were more heterogeneous than the water flow processes. Compared with the probability distributions of flow parameters, the information measures appeared to be a more versatile tool to describe flow and transport heterogeneities in soils.  相似文献   

Summertime sea surface temperature fronts associated with upwelling around the Taiwan Bank     

Kuo-Wei Lan  Hiroshi Kawamura  Ming-An Lee  Yi Chang  Jui-Wen Chan  Cheng-Hsin Liao 《Continental Shelf Research》2009

It is well known that upwelling of subsurface water is dominant around the Taiwan Bank (TB) and the Penghu (PH) Islands in the southern Taiwan Strait in summertime. Sea surface temperature (SST) frontal features and related phenomena around the TB upwelling and the PH upwelling were investigated using long-term AVHRR (1996–2005) and SeaWiFS (1998–2005) data received at the station of National Taiwan Ocean University. SST and chlorophyll-a (Chl-a) images with a spatial resolution of 0.01° were generated and used for the monthly SST and Chl-a maps. SST fronts were extracted from each SST images and gradient magnitudes (GMs); the orientations were derived for the SST fronts. Monthly maps of cold fronts where the cooler SSTs were over a shallower bottom were produced from the orientation.  相似文献   

Large‐scale folding in the Asemi‐gawa region of the Sanbagawa Belt,southwest Japan     

Hiroshi Mori  Simon Wallis 《Island Arc》2010,19(2):357-370

The Sanbagawa Belt generally shows higher metamorphic grade at higher structural levels. This inversion can be interpreted as reflecting an original inverted thermal structure typical of subduction zone environments. However, repetitions in the distribution of the metamorphic zones seen in central Shikoku, Japan, clearly show the original thermal structure has been affected by deformation after the peak of metamorphism. This repetition has been attributed to both the action of tectonic discontinuities and regional folding. It is important to distinguish between these two interpretations to determine the extent to which the original subduction zone sequence is preserved. Analyses of lithological and structural data reveal the presence of a large‐scale post‐metamorphic fold in the central part of the highest grade region. This folding has an axis that coincides with the thermal axis implied by the distribution of the metamorphic zonation, suggesting the repetition of metamorphic zones in this area can be accounted for by folding without the need for major discontinuities.  相似文献   

A scheme to treat the singularity in global seismic wavefield simulation using pseudospectral method with staggered grids     

Hiroshi Takenaka 《地震学报(英文版)》2010,(2):121-127

The pseudospectral method has been applied to the simulation of seismic wave propagation in 2-D global Earth model.When a whole Earth model is considered,the center of the Earth is included in the model and then singularity arises at the center of the Earth where r=0 since the 1/r term appears in the wave equations.In this paper,we extended the global seismic wavefield simulation algorithm for regular grid mesh to staggered grid configuration and developed a scheme to solve the numerical problems associated with the above singularity for a 2-D global Earth model defined on staggered grid using pseudospectral method.This scheme uses a coordinate transformation at the center of the model,in which the field variables at the center are calculated in Cartesian coordinates from the values on the grids around the center.It allows wave propagation through the center and hence the wavefield at the center can be stably calculated.Validity and accuracy of the scheme was tested by compared with the discrete wavenumber method.This scheme could also be suitable for other numerical methods or models parameterized in cylindrical or spherical coordinates when singularity arises at the center of the model.  相似文献   

Characterization of rainfall generated by dripper‐type rainfall simulator using piezoelectric transducers and its impact on splash soil erosion     

Mohamed A. M. Abd Elbasit  Hiroshi Yasuda  Atte Salmi  Hisao Anyoji 《地球表面变化过程与地形》2010,35(4):466-475

Rainfall erosivity represents the primary driver for particle detachment in splash soil erosion. Several raindrop erosivity indices have been developed in order to quantify the potential of rainfall to cause soil erosion. Different types of rainfall simulators have been used to relate rainfall characteristics to soil detachment. However, rainfall produced by different rainfall simulators has different characteristics, specifically different relationships between rainfall intensity and rainfall erosivity. For this reason, the effect of rainfall characteristics produced by a dripper‐type rainfall simulator on splash soil erosion (D_s) has been investigated. The simulated rainfall kinetic energy (KE) and drop size distribution (DSD) were measured using piezoelectric transducers, modified from the Vaisala RAINCAP^® rain sensor. The soil splash was evaluated under various simulated rainfall intensities ranging from 10 to 100 mm h^?1 using the splash‐cup method. The simulated rainfall intensity (I) and kinetic energy relationship (I–KE) was found to be different from natural rainfall. The simulated rainfall intensity and splash soil erosion relationship (I–D_s) also followed this same trend. The I–KE relationship was found to follow the natural rainfall trend until the rainfall intensity reached 30 mm h^?1 and above this limit the KE started to decrease. This emphasizes the importance of the I–KE relationship in determining the I‐D_s relationship, which can differ from one rainfall simulator to another. D_s was found to be highly correlated with KE (r = 0·85, P < 0·001), when data produced by the rainfall intensity ranged from 10 to 100 mm h^?1. However, when the threshold rainfall intensity (30 mm h^?1) was considered, the correlation coefficient further improved (r = 0·89, P = 0·001). Accordingly, to improve the soil splash estimation of simulated rainfall under various rainfall intensities the I–KE characterization relationship for rainfall simulators has to be taken into account. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Depositional Age of a Fossil Whale Bone from São Paulo Ridge,South Atlantic Ocean,Based on Os Isotope Stratigraphy of a Ferromanganese Crust          下载免费PDF全文

Tatsuo Nozaki  Yutaro Takaya  Takashi Toyofuku  Ayaka Tokumaru  Kosuke T. Goto  Qing Chang  Jun‐ichi Kimura  Yasuhiro Kato  Katsuhiko Suzuki  Adolpho Herbert Augustin  Hiroshi Kitazato 《Resource Geology》2017,67(4):442-450

Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13–04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe–Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (¹⁸⁷Os/¹⁸⁸Os ratio) of the Fe–Mn crust. Major‐ and trace‐element compositions of the crust are similar to those of Fe–Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post‐Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe–Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. ¹⁸⁷Os/¹⁸⁸Os ratios of three Fe–Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0–3 mm depth in the crust) was identical to that of present‐day seawater within error (~1.06). The value of 0.904 from the basal slice (6–9 mm) equaled seawater values from ca. 4–5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe–Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale‐fall biotic community.  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   

Impacts of the Nakhodka heavy-oil spill on an intertidal ecosystem: an approach to impact evaluation using geographical information system     

Teruhisa K  Masahiro N  Hiroshi K  Tomoko Y  Kouichi O;Marine Life Research Group of Takeno 《Marine pollution bulletin》2003,47(1-6):99-104

A major heavy-oil spill from the Russian tanker Nakhodka occurred in the Sea of Japan on 2 January 1997. We investigated the impacts of this spill on a rocky intertidal ecosystem along the southern coast of the Sea of Japan. We selected Imago-Ura Cove as our study site to observe temporal changes along the oiled shore, because minimal cleaning effort was made in this area. Field surveys were conducted every autumn and spring from 1997 to 2000. We measured coverage by macroalgae in 1 x 1-m(2) quadrats and counted the animals in 5 x 5-m(2) quadrats along the intertidal zone. Changes in the ecosystem caused by the oil spill were analyzed by applying a geographical information system (GIS) to the Sea of Japan for the first time. The GIS showed that following the accident there were heavily oiled areas in sheltered regions, but these decreased over the three years. It also showed that coverage by macroalgae and the number of animals increased, although some species of algae with microscopic sporophyte generations, and some populations of perennial shellfish, remained stable or decreased during the study period. GIS was able to trace temporal changes in intertidal communities resulting from the impacts of heavy oil on flora and fauna at a spatial scale of 10-100 m. GIS is thus a practical tool for visualizing, analyzing, and monitoring changes in an ecosystem polluted by oil, taking into account topographic differences along the coastline.  相似文献