Biomass and production of bacterioplankton at the hydrothermal vent areas in the rift system of the North Fiji Basin     

Utsumi  Motoo  Kojima  Shigeaki  Nojiri  Yukihiro  Ohta  Suguru  Seki  Humitake 《Journal of Oceanography》1994,50(6):635-642

Mesoscale distribution of the density and productivity of bacterioplankton at representative geological locations in the rift ecosystem of the North Fiji Basin were clarified by sampling using a mannedShinkai 6500 submersible. The bacterioplankton density inside the hot and warm fluids of hydrothermal vents was one order magnitude greater than that in the deep water outside the vent plume. The bacterial production was highest inside the hot and warm vent fluids, and was higher just outside the hot and warm vent fluids than further outside in the deep water surrounding the vent plume, respectively. Productivity from outside to inside the vent fluid varied from 0.01 to 0.71 gC m^–3 day^–1.  相似文献   

Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific   总被引：1，自引：0，他引：1  

Neelam Ramaiah  Shigenobu Takeda  Ken Furuya  Takeshi Yoshimura  Jun Nishioka  Tatsuo Aono  Yukihiro Nojiri  Keiri Imai  Isao Kudo  Hiroaki Saito  Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):253

Dynamics of transparent exopolymer particles (TEP) was studied during the first in situ iron-enrichment experiment conducted in the western subarctic Pacific in July–August 2001, with the goal of evaluating the contribution of TEP to vertical flux as a result of increased primary production following iron enrichment in open ocean ecosystems. Subsequent to the enhancement of phytoplankton production, we observed increase in TEP concentration in the surface layer and sedimentation of organic matter beneath it. Vertical profiles of TEP, chlorophyll a (Chl a) and particulate organic carbon (POC) were obtained from six depths between 5 and 70 m, from a station each located inside and outside the enriched patch. TEP and total mass flux were estimated from the floating sediment traps deployed at 200 m depth. Chl a and TEP concentrations outside the patch varied from 0.2 to 1.9 μg L⁻¹ and 40–60 μg XG equiv. L⁻¹, respectively. Inside the patch, Chl a increased drastically from day 7 reaching the peak of 19.2 μg L⁻¹ on day 13, which coincided with the TEP peak of 189 μg XG equiv. L⁻¹. TEP flux in the sediment trap increased from 41 to 88 mg XG equiv. m⁻² d⁻¹, with 8–14% contribution of TEP to total mass flux. This forms the basic data set on ambient concentrations of TEP in the western subarctic Pacific, and evaluation of the effect of iron enrichment on TEP.  相似文献   

Oxygen and carbon isotope zonations of wall rocks around the Kamioka Pb---Zn skarn deposits, central Japan: application to prospecting     

Koh Naito  Yasumasa Fukahori  He Peiming  Wakaba Sakurai  Hidehiko Shimazaki  Yukihiro Matsuhisa 《Journal of Geochemical Exploration》1995,54(3)

Mapping of the oxygen and carbon isotopic composition of hydrothermally altered wall rocks was conducted during blind ore prospecting for Pb---Zn skarn deposits in the Kamioka mining district, central Japan. The wall rocks consist of heterogeneous rock units. Oxygen and carbon isotope ratios were determined for 35 limestones and 33 silicate rocks from the area around the Mozumi deposit (3 km × 3 km) in the Kamioka mining district. The results (δ¹⁸O_spsmow of − 1.1 to + 17.3% and δ¹³C_sppdb of − 5.0 to +4.8% for limestones, and δ¹⁸O_spsmow of −0.8 to + 12.5% for silicate rocks) show isotope zonations of the wall rocks, with lighter isotopic compositions toward the center of mineralization. The isotope zonations likely formed by interaction of thermal waters with the wall rocks during skarn mineralization. The isotopically light zone indicates a higher paleotemperature or higher water-to-rock ratios, and occurs in the footwall of the 7Gohi fault. This structure is spatially related to the distribution of orebodies, indicating that the fault was the main conduit of the ore-forming fluids. The oxygen and carbon isotopic compositions of limestones vary regularly across limestone bodies hosted by the silicate wall rocks, suggesting that the thermal waters were pervasive throughout the wall rocks at the time of mineralization.An isotopically light zone was also found in the southeastern corner of the study area, where significant mineralization had yet to be identified. This suggested an extension of the extinct hydrothermal system to this area, and the possibility of hidden orebodies underneath. Recent drilling in this area has intercepted a zone 45 m thick with a grade of 13.4% Zn, 0.03% Pb and 8 g per metric ton at about 380 m depth.  相似文献   

Lattice preferred orientation in CaIrO<Subscript>3</Subscript> perovskite and post-perovskite formed by plastic deformation under pressure     

Ken Niwa  Takehiko Yagi  Kenya Ohgushi  Sébastien Merkel  Nobuyoshi Miyajima  Takumi Kikegawa 《Physics and Chemistry of Minerals》2007,34(9):679-686

Lattice preferred orientations (LPO) developed in perovskite and post-perovskite structured CaIrO₃ were studied using the radial X-ray diffraction technique combined with a diamond anvil cell. Starting materials of each phase were deformed from 0.1 MPa to 6 GPa at room temperature. Only weak LPO was formed in the perovskite phase, whereas strong LPO was formed in the post-perovskite phase with an alignment of the (010) plane perpendicular to the compression axis. The present result suggests that the (010) is a dominant slip plane in the post-perovskite phase and it is in good agreement with the crystallographic prediction, dislocation observations via transmission electron microscopy, and a recent result of simple shear deformation experiment at 1 GPa–1,173 K. However, the present result contrasts markedly from the results on MgGeO₃ and (Mg,Fe)SiO₃, which suggested that the (100) or (110) is a dominant slip plane with respect to the post-perovskite structure. Therefore it is difficult to discuss the behavior of the post-perovskite phase in the Earth’s deep interior based on existing data of MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃. The possible sources of the differences between MgGeO₃, (Mg,Fe)SiO₃ and CaIrO₃ are discussed.  相似文献   

Effect of incorporation of iron and aluminum on the thermoelastic properties of magnesium silicate perovskite     

Norimasa Nishiyama  Takehiko Yagi  Shigeaki Ono  Hirotada Gotou  Tatsuhiko Harada  Takumi Kikegawa 《Physics and Chemistry of Minerals》2007,34(3):131-143

In situ X-ray diffraction measurements of Fe- and Al-bearing MgSiO₃-rich perovskite (FeAl-Pv), which was synthesized from a natural orthopyroxene, were performed at pressures of 19–32 GPa and temperatures of 300–1,500 K using a combination of a Kawai-type apparatus with eight sintered-diamond anvils and synchrotron radiation. Two runs were performed using a high-pressure cell with two sample chambers, and both MgSiO₃ perovskite (Mg-Pv) and FeAl-Pv were synthesized simultaneously in the same cell. Thus we were able to measure specific volumes (V/V ₀) of Mg-Pv and FeAl-Pv at the same P−T conditions. At all the measurement conditions, values of the specific volume of FeAl-Pv are consistent with those of Mg-Pv within 2 Standard Deviation, strongly suggesting that effect of incorporation of iron and aluminum on the thermoelastic properties of magnesium silicate perovskite is undetectable in this composition, pressure, and temperature range. Two additional runs were performed using a high-pressure cell that has one sample chamber and unit-cell volumes of FeAl-Pv were measured at pressures and temperatures up to 32 GPa and 1,500 K, respectively. All the unit-cell volume data of FeAl-Pv perovskite were fitted to the high temperature Birch–Murnaghan equation of state and a complete set of thermoelastic parameters of this perovskite was determined with an assumption of K′ _300,0 = 4. The determined parameters are K _300,0 = 243(3) GPa, (∂K _T,0/∂T) _P = −0.030(8) GPa/K, a ₀ = 2.78(18) × 10⁻⁵ K⁻¹, and b ₀ = 0.88(28) × 10⁻⁸ K⁻², where a ₀ and b ₀ are the coefficients of the following expression describing the zero-pressure thermal expansion: α _T,0 = a ₀ + b ₀ T. The equation-of-state parameters of FeAl-Pv are in good agreement with those of MgSiO₃ perovskite at the conditions corresponding to the uppermost part of the lower mantle.  相似文献   

The stability and compressibility of MgAl2O4 high-pressure polymorphs     

S. Ono  T. Kikegawa  Y. Ohishi 《Physics and Chemistry of Minerals》2006,33(3):200-206

High-pressure and high-temperature experiments using a laser-heated diamond anvil cell (LHDAC) and synchrotron X-ray diffraction have revealed a phase transition in MgAl₂O₄. CaTi₂O₄-type MgAl₂O₄ was found to be stable at pressures between 45 and at least 117 GPa. The transition pressure of CaTi₂O₄-type phase in MgAl₂O₄ is much lower than that in the natural N-type mid-oceanic ridge basalt composition. The Birch–Murnaghan equation of state for CaTi₂O₄-type MgAl₂O₄ was determined from the experimental unit cell parameters with K ₀=219(±6) GPa, K ₀′=4(constrained value), and V ₀=238.9(±9) ų. The observed compressibility was in agreement with the theoretical compressibility calculated in a previous study. ε-MgAl₂O₄ was observed at pressures between 40 and 45 GPa, which has not been reported in natural rock compositions. The gradient (dP/dT slope) of the transition from the ε-type to CaTi₂O₄-type MgAl₂O₄ had a positive value. These results should resolve the dispute regarding the stable high-pressure phase of MgAl₂O₄, which has been reported in earlier studies using both the multi-anvil press and the diamond anvil cell.  相似文献   

Scavenging of Insoluble Particles from the Marine Atmosphere over the Sub-Arctic North Pacific     

Mitsuo Uematsu  Katsumoto Kinoshita  Yukihiro Nojiri 《Journal of Atmospheric Chemistry》2000,35(2):151-163

Direct deposition measurements ofatmospheric insoluble particles over the sub-ArcticNorth Pacific indicate that the number of particles(6.4 ± 3.8) × 10⁴ cm^-2 per rain eventwas fairly constant compared with the large variationof the precipitation rate, which ranged from 0.16 to18 mm per event for 43 rain days during the period ofMarch–September (total 109 days) 1996. Thissuggests that insoluble particles larger than 0.4 min area equivalent diameter are primarilyremoved at the margin of the rainfall area by wetscavenging processes below clouds in the marineatmosphere in sub-Arctic regions. The frequency ofrain events controls the fate of the troposphericaerosols larger than sub-micrometer in diameter. Reflecting the seasonal long-range transport of Asiandust, mineral particles were dominant as insolubleparticles in the spring rains, but carbonaceousparticles were dominant in the summer rains. Theatmospheric deposition of insoluble particles could besignificant as a source of sediment particles over thesub-Arctic North Pacific.  相似文献   

Long-term changes in distribution and chemistry of middle Miocene to Quaternary volcanism in the Chokai-Kurikoma area across the Northeast Japan Arc   总被引：1，自引：0，他引：1  

Hirofumi Kondo  Kazuhiro Tanaka  Yukihiro Mizuochi  Atusi Ninomiya 《Island Arc》2004,13(1):18-46

Abstract To understand the characteristics of long‐term spatial and temporal variation in volcanism within a volcanic arc undergoing constant subduction since the cessation of back‐arc opening, a detailed investigation of middle Miocene to Quaternary volcanism was carried out within the Chokai‐Kurikoma area of the Northeast Japan Arc. This study involved a survey of available literature, with new K–Ar and fission track dating, and chemical analyses. Since 14 Ma, volcanism has occurred within the Chokai‐Kurikoma area in specific areas with a ‘branch‐like’ pattern, showing an east–west trend. This is in marked contrast to the widespread distribution of volcanism with a north–south trend in the 20–14 Ma period. The east–west‐ trending ‘branches’ are characterized by regular intervals (50–100 km) of magmatism along the arc. These branches since 14 Ma are remarkably discrepant to the general northwest–southeast or north‐northeast–south‐southwest direction of the crustal structures that have controlled Neogene to Quaternary tectonic movements in northeast Japan. In addition, evidence indicating clustering and focusing of volcanism into smaller regions since 14 Ma was verified. Comparison of the distribution and chemistry of volcanic rocks for three principal volcanic stages (11–8, 6–3 and 2–0 Ma) revealed that widely but sparsely distributed volcanic rocks had almost the same level of alkali and incompatible element concentrations throughout the area (with the exception of Zr) in the 11–8 Ma stage. However, through the 6–3 Ma stage to the 2–0 Ma stage, the concentration level in the back‐arc cluster increased, while that in the volcanic front cluster remained almost constant. Therefore, the degree of partial melting has decreased, most likely with a simultaneous increase in the depth of magma segregation within the back‐arc zone, whereas within the volcanic front zone, the conditions of magma generation have changed little over the three stages. In conclusion, the evolution of the thermal structure within the mantle wedge across the arc since 14 Ma has reduced the extent of ascending mantle diapirs into smaller fields. This has resulted in the tendency for the distribution of volcanism to become localized and concentrated into more specific areas in the form of clusters from the late Miocene to Quaternary.  相似文献   

Assessment of urban heat island effect for different land use–land cover from micrometeorological measurements and remote sensing data for megacity Delhi     

Manju Mohan  Yukihiro Kikegawa  B. R. Gurjar  Shweta Bhati  Narendra Reddy Kolli 《Theoretical and Applied Climatology》2013,112(3-4):647-658

Urban heat island intensities (UHI) have been assessed based on in situ measurements and satellite-derived observations for the megacity Delhi during a selected period in March 2010. A network of micrometeorological observational stations was set up across the city. Site selection for stations was based on dominant land use–land cover (LULC) classification. Observed UHI intensities could be classified into high, medium and low categories which overall correlated well with the LULC categories viz. dense built-up, medium dense built-up and green/open areas, respectively. Dense urban areas and highly commercial areas were observed to have highest UHI with maximum hourly magnitude peaking up to 10.7 °C and average daily maximum UHI reaching 8.3 °C. UHI obtained in the study was also compared with satellite-derived land surface temperatures (LST). UHI based on in situ ambient temperatures and satellite-derived land surface temperatures show reasonable comparison during nighttime in terms of UHI magnitude and hotspots. However, the relation was found to be poor during daytime. Further, MODIS-derived LSTs showed overestimation during daytime and underestimation during nighttime when compared with in situ skin temperature measurements. Impact of LULC was also reflected in the difference between ambient temperature and skin temperature at the observation stations as built-up canopies reported largest gradient between air and skin temperature. Also, a comparison of intra-city spatial temperature variations based UHI vis-à-vis a reference rural site temperature-based UHI indicated that UHI can be computed with respect to the station measuring lowest temperature within the urban area in the absence of a reference station in the rural area close to the study area. Comparison with maximum and average UHI of other cities of the world revealed that UHI in Delhi is comparable to other major cities of the world such as London, Tokyo and Beijing and calls for mitigation action plans.  相似文献   

Narrower grid structure of artificial reef enhances initial survival of in situ settled coral     

Suzuki G  Kai S  Yamashita H  Suzuki K  Iehisa Y  Hayashibara T 《Marine pollution bulletin》2011,62(12):2803-2812

The initial factors that cause a decline in the survival of in situ settled corals remain poorly understood. In this study, we demonstrated through field experiments that the design of artificial grid plates may influence the initial survival of Acropora corals, with narrower grids being the most effective. In fact, grid plates with a 2.5-cm mesh presented the highest recorded survival rate (14%) at 6 months after settlement (representing approximately 50 corals per 0.25 m² of plate). This is the first study where such high survival rates, matching those of cultures under aquarium conditions, were obtained in the field without using additional protective measures, such as guard nets against fish grazing after seeding. Therefore, our results provide a foundation for establishing new and effective coral restoration techniques for larval seeding, in parallel to clarifying the details of the early life stages of reef-building corals.  相似文献