Seasonal and spatial variation in the denitrifying activity in estuarine and lagoonal sediments     

Yukiko Senga  Minoru Okumura  Yasushi Seike 《Journal of Oceanography》2010,66(1):155-160

We have elucidated the seasonal and spatial variation in the potential denitrifying activity in estuarine and coastal lagoonal sediments in Lakes Shinji and Nakaumi, Japan. The denitrifying activity increased from summer through autumn and was positively correlated with the temperature of the overlying water at all sites except one, where the bottom was always more reductive than at the other sites and there was no NO₃ ⁻ as a substrate for denitrification from spring to autumn. Moreover, the relationship between the denitrifying activity and the distance from the sea showed different trends in estuarine and lagoonal sediments. These spatial differences indicate that different factors regulate the denitrification in estuarine and lagoonal sediments. Denitrifying activity in estuarine sediment was regulated by the discharge of freshwater containing NO₃ ⁻ or organic matter, while in the lagoonal sediments the occurrence of nitrification via the intrusion of oxic seawater into the reductive sediment appears to be a key requirement for the process of denitrification. Therefore, the denitrifying activity in the lagoonal sediment appears to be greater near the sea. Water intrusion is one of the key factors controlling denitrification in coastal marine ecosystems by affecting the supply of substrate available for denitrification.  相似文献   

Implication of Apatite and Anhydrite for Formation of an Iron‐Oxide‐Apatite (IOA) Rare Earth Element Prospect,Benjamin River,Canada          下载免费PDF全文

Mihoko Hoshino  Yasushi Watanabe  Yoshiaki Kon 《Resource Geology》2017,67(4):361-383

The Benjamin River apatite prospect in northern New Brunswick, Canada, is hosted by the Late Silurian Dickie Brook plutonic complex, which is made up of intrusive units represented by monzogranite, diorite and gabbro. The IOA ores, composed mainly of apatite, augite, and magnetite at Benjamin River form pegmatitic pods and lenses in the host igneous rocks, the largest of which is 100 m long and 10–20 m wide in the diorite and gabbro units. In this study, 28 IOA ore and rock samples were collected from the diorite and gabbro units. Mineralogical observations show that the apatite–augite–magnetite ores are variable in the amounts of apatite, augite, and magnetite and are associated with minor amounts of epidote‐group minerals (allanite, REE‐rich epidote and epidte) and trace amounts of albite, titanite, ilmenite, titanomagnetite, pyrite, chlorite, calcite, and quartz. Apatite and augite grains contain small anhydrite inclusions. This suggests that the magma that crystallized apatite and augite had high oxygen fugacity. In back scattered electron (BSE) images, apatite grains in the ores have two zones of different appearance: (i) primary REE‐rich zone; and (ii) porous REE‐poor zone. The porous REE‐poor zones mainly appear in rims and/or inside of the apatite grains, in addition to the presence of apatite grains which totally consist of a porous REE‐poor apatite. This porous REE‐poor apatite is characterized by low REE (<0.84 wt%), Si (<0.28 wt%), and Cl (<0.17 wt%) contents. Epidote‐group minerals mainly occur in grain boundary between the porous REE‐poor apatite and augite. These indicate that REE leached from primary REE‐rich apatite crystallized as allanite and REE‐rich epidote. Magnetite in the ores often occurs as veinlets that cut apatite grains or as anhedral grains that replace a part of augite. These textures suggest that magnetite crystallized in the late stage. Pyrite veins occur in the ores, including a large amount of quartz and calcite veins. Pyrite veins mainly occur with quartz veins in augite. These textures indicate pyrite veins are the latest phase. Apatite–augite–magnetite ore, gabbro–quartz diorite and feldspar dike collected from the Benjamin River prospect contain dirty pure albite (Ab₉₈Or₂–Ab₁₀₀) under the microscope. The feldspar dikes mainly consist of dirty pure albite. Occurrences of the dirty pure albite suggest remarkable albitization (sodic alteration) of original plagioclase (An_25.3–An₆₀ in Pilote et al., 2012) associating with intrusion of monzogranite into gabbro and diorite. SO₄^2? bearing magma crystallized primary REE‐rich apatite, augite and anhydrite reacted with Fe in the sodic fluids, which result in oxidation of Fe²⁺ and release of S^2? into the sodic fluids. REE, Ca and Fe from primary REE‐rich apatite, augite and plagioclase altered by the sodic fluids were released into the fluids. Then Fe³⁺ in the sodic fluids precipitated as Fe oxides and epidote‐group minerals in apatite–augite–magnetite ores. Finally, residual S^2? in sodic fluids crystallized as latest pyrite veins. In conclusion, mineralization in Benjamin River IOA prospect are divided into four stages: (1) oxidized magmatic stage that crystallized apatite, augite and anhydrite; (2) sodic metasomatic stage accompanying alteration of magmatic minerals; (3) oxidized fluid stage (magnetite–epidote group minerals mineralization); and (4) reduced fluid stage (pyrite mineralization).  相似文献   

Estimation of snow ablation under a dust layer covering a wide range of albedo     

Sunil Adhikary  Yasushi Yamaguchi  Katsuro Ogawa 《水文研究》2002,16(14):2853-2865

Ablation processes of snow under a thin dust cover are complicated compared with those under a thick cover, mainly owing to the effects of aggregation (redistribution) of dust particles on the conditions of surface melting. Aggregation of dust particles causes the snow surface to brighten after the initial dust configuration, thus affecting the relationship between initial dust concentration and surface albedo. In order to estimate snow ablation rate under a thin dust cover, we used a composite energy balance model in which the surface albedo is taken as a measured input variable. The estimated results of snow ablation agreed reasonably well with the observation, considering the measurement errors inherited in the snow depressions. Comparison of the two cases, that is, one considering the aggregation of dust particles (observation: albedo variable) and the other without aggregation (assumption: albedo constant), showed that the ablation rates were noticeably lower on the former case. This suggests that the aggregation of dust particles induces a reduction of snow ablation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Degradation of lubricating oils by marine bacteria observed by quantitative mass spectrometry     

Yasushi Kawakami  Hajime Nishimura 《Journal of Oceanography》1981,37(1):1-7

Bacterial degradation of the hydrocarbons of lubricating oils was investigated by mass spectrometric analysis which gives both total amount and the composition of hydrocarbon types of residual oil. An unused lubricating oil, which mainly consisted of hydrocarbon types with only a small percentage ofn-alkanes, was degraded by marineBacillus sp. andPseudomonas sp. with 55 % and 25 % decreases in 10 days, respectively. Susceptibility of respective hydrocarbon types to biodegradation was in the following order: alkanes > non-condensed cycloalkanes, mono-aromatics > condensed cycloalkanes. A used lubricating oil of different brand showed a larger decrease than the unused oil. Both species of bacteria degraded large portions of alkane fraction of Arabian light crude oil.  相似文献   

Sulfate reduction and sulfide deposition in deep-sea sediments from the southwestern Japan Sea     

Toshiyuki Masuzawa  Yasushi Kitano 《Journal of Oceanography》1983,39(5):251-258

Vertical profiles of total sulfur and organic carbon have been measured in two deep-sea piston cores from the southwestern Japan Sea where sulfate reduction is proceeding within the sediments. The content of total sulfur, most of which is present as pyrite, increases gradually with increasing depth, showing several peaks. The amount of diagenetically deposited sulfide-sulfur is estimated using a steady-state model that considers vertical change in the diffusion coefficient. It is suggested that two-thirds to three-fourths of the observed total sulfur content has been deposited diagenetically.  相似文献   

The effects of the reed,Phragmites australis (Trin.), on substratum grain-size distribution in a salt marsh   总被引：1，自引：0，他引：1  

Satoshi Takeda  Yasushi Kurihara 《Journal of Oceanography》1988,44(3):103-112

The effects of the reed,Phragmites australis (Trin.), growing in a brackish water lagoon, were studied in relation to the grain-size distribution of the substratum. At the salt marshes near the lagoon, the upper soils from the surface to a depth of 20 cm contained much silt-clay. These fine particles were found to be transferred from the river and fish ponds near the lagoon, and to be deposited when the tidal rhythm changed, that is, when the water current stopped. In addition, the fine particles, which were deposited on the bottom of the lagoon adjacent to the marshes, became resuspended as a result of wind-caused wave action, and then were transported and redeposited in the salt marshes at the flood tide. Since the reeds further reduced the water current caused by the waves and tide, the reeds were thought to promote redeposition of the resuspended matter. In other words, the reeds were considered to protect deposited and redeposited particles such as silt and clay from resuspension as a result of wave action by reducing the effects of waves and wind. These processes suggested that silt-clay will become abundant in the substratum of the salt marsh adjacent to the lagoon.  相似文献   

Fluoride contents of saline and interstitial waters in the inlets of the Juneau Glacier Area,Alaska     

Yasushi Kitano  Yukihiro Furukawa 《Journal of Oceanography》1972,28(4):176-179

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Formation Process of Zircon Associated with REE‐Fluorocarbonate and Niobium Minerals in the Nechalacho REE Deposit,Thor Lake,Canada     

Mihoko Hoshino  Yasushi Watanabe  Hiroyasu Murakami  Yoshiaki Kon  Maiko Tsunematsu 《Resource Geology》2013,63(1):1-26

The two drill holes, which penetrated sub‐horizontal rare earth element (REE) ore units at the Nechalacho REE in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify the enrichment mechanism of the high‐field‐strength elements (HFSE: Zr, Nb and REE). The REE ore units occur in the albitized and potassic altered miaskitic syenite. Zircon is the most common REE mineral in the REE ore units, and is divided into five types as follows: Type‐1 zircon occurs as discrete grains in phlogopite, and has a chemical character similar to igneous zircon. Type‐2 zircon consists of a porous HREE‐rich core and LREE–Nb–F‐rich rim. Enrichment of F in the rim of type‐2 zircon suggests that F was related to the enrichment of HFSE. The core of type‐2 zircon is regarded to be magmatic and the rim to be hydrothermal in origin. Type‐3 zircon is characterized by euhedral to anhedral crystals, which occur in a complex intergrowth with REE fluorocarbonates. Type‐3 zircon has high REE, Nb and F contents. Type‐4 zircon consists of porous‐core and ‐rim, but their chemical compositions are similar to each other. This zircon is a subhedral crystal rimmed by fergusonite. Type‐5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircon grains are filled by fergusonite. Type‐4 and type‐5 zircon grains have low REE, Nb and F contents. Type‐1 zircon is only included in one unit, which is less hydrothermally altered and mineralized. Type‐2 and type‐3 zircon grains mainly occur in the shallow units, while those of type‐4 and type‐5 are found in the deep units. The deep units have high HFSE contents and strongly altered mineral textures (type‐4 and type‐5) compared to the shallow units. Occurrences of these five types of zircon are different according to the depth and degree of the hydrothermal alteration by solutions rich in F and CO₃, which permit a model for the evolution of the zircon crystallization in the Nechalacho REE deposit as follows: (i) type‐1 (discrete magmatic zircon) is formed in miaskitic syenite. (ii) LREE–Nb–F‐rich hydrothermal zircon formed around HREE‐rich magmatic zircon (type‐2). (iii) type‐3 zircon crystallized through the F and CO₃‐rich hydrothermal alteration of type‐2 zircon which formed the complex intergrowth with REE fluorocarbonates; (iv) the CO₃‐rich hydrothermal fluid corroded type‐3, forming REE–Nb‐poor zircon (type‐4). Niobium and REE were no longer stable in the zircon structure and crystallized as fergusonite around the REE–Nb‐leached zircon (type‐4); (v) type‐5 zircon is formed by the more CO₃‐rich hydrothermal alteration of type‐4 zircon, suggested by the fact that type‐4 and type‐5 zircon grains are often included in ankerite. Type‐3 to type‐5 zircon grains at the Nechalacho REE deposit were continuously formed by leaching and/or dissolution of type‐2 zircon in the presence of F‐ and/or CO₃‐rich hydrothermal fluid. These mineral associations indicate that three representative hydrothermal stages were present and related to HFSE enrichment in the Nechalacho REE deposit: (i) F‐rich hydrothermal stage caused the crystallization of REE–Nb‐rich zircon (type‐2 rim and type‐3), with abundant formation of phlogopite and fluorite; (ii) F‐ and CO₃‐rich hydrothermal stage led to the replacement of a part of REE–Nb–F‐rich zircon by REE fluorocarbonate; and (iii) CO₃‐rich hydrothermal stage resulted in crystallization of the REE–Nb–F‐poor zircon and fergusonite, with ankerite. REE and Nb in hydrothermal fluid at the Nechalacho REE deposit were finally concentrated into fergusonite by way of REE–Nb–F‐rich zircon in the hydrothermally altered units.  相似文献   

Spinifex-like textured metaperidotites from the Higo Metamorphic Rocks,Japan, a possible high-pressure dehydration product of antigorite serpentinite     

Tadao Nishiyama  Hibiki Eguchi  Dai Shiosaki  Akira Yoshiasa  Nobutatsu Mochizuki  Yasushi Mori  Kazumasa Sugiyama  Hiroshi Arima  Kunio Yubuta 《Island Arc》2021,30(1):e12382

Spinifex-like textured metaperidotites from the Higo Metamorphic Rocks (HMR), west-central Kyushu, Japan, may be formed by high-pressure dehydration of antigorite, and may indicate deep subduction of serpentinite reaching a pressure–temperature condition of 1.6 GPa and 740–750 °C. Three rock types have been identified based on mineral assemblage and rock texture: Type I (L) consisting of medium-grained (1–5 cm long) olivine + enstatite + chromite ±tremolite with secondary talc and anthophyllite that occurs in low-grade metamorphic rocks of the biotite zone, Type I (H) of coarse-grained (up to 10 cm long) olivine + enstatite (with clinoenstatite lamella) + chromite ±tremolite with secondary talc that occurs in high-grade metamorphic rocks of the garnet-cordierite zone, and Type II composed of Al-spinel + chlorite + olivine + apatite + ilmenite with minor sodic gedrite in the garnet-cordierite zone together with Type I (H). Olivines in all rock types are mostly serpentinized during exhumation. The chromite-olivine thermometer gives 560–690 °C for Type I (L) rocks, and the spinel-olivine thermometer gives 610–740 °C for Type II rocks. The peak metamorphic pressure will be higher than 1.6 GPa based on the location of the experimentally determined invariant point (P = 1.6 GPa and T = 670 °C) of antigorite + forsterite + enstatite + talc + H₂O. This estimate is consistent with the occurrence of chlorite in Type II rocks, which is stable up to 890 °C at 2.0 GPa. The spinifex-like textured metaperidotites occur as small bodies in the low P/T type gneisses, implying tectonic juxtaposition of them probably during exhumation of the HMR. Recent findings of medium pressure (0.9–1.2 GPa) granulites and gneisses from the HMR may indicate that the HMR has a deep root into the wedge mantle from which the spinifex-like textured metaperidotites have derived.  相似文献   

Finite-element Simulation of Seismic Ground Motion with a Voxel Mesh     

Kazuki Koketsu  Hiroyuki Fujiwara  Yasushi Ikegami 《Pure and Applied Geophysics》2004,161(11-12):2183-2198

— Accurate simulation of seismic ground motion for three-dimensionally complex topography and structures is one of the most important goals of strong motion seismology. The finite-element method (FEM) is well suited for this kind of simulation, since traction-free conditions are already included in the formulation, and the Courant condition is less strict than for the finite-difference method (FDM). However, the FEM usually requires both large memory and computation time. These limitations can be overcome by using a mesh consisting of voxels (rectangular prisms) with isotropy built into the explicit formulation of the dynamic matrix equation. Since operators in the voxel FEM are the combinations of ordinary FDM operators and additional terms, the method keeps accuracy of the same order as FDM and the terms relax the Courant condition. The voxel FEM requires a similar amount of memory and only takes 1.2～1.4 times longer computation time. The voxel mesh can be generated considerably faster than the popular tetrahedral mesh. Both ground motions and static displacements due to a point or line source can be calculated using the voxel FEM approach. Comparisons with the reflectivity method and theoretical solutions demonstrate the successful implementation of the method, which is then applied to more complex problems.  相似文献