Coexisting bronzite and clinobronzite and the thermal evolution of the Steinbach meteorite     

Arch M. Reid  Richard J. Williams  Hiroshi Takeda 《Earth and Planetary Science Letters》1974,22(1):67-74

Steinbach is a stony-iron meteorite with approximately equal amounts of silicate and metal that shows Widmanstätten structure. The silicate portion contains tridymite, orthobronzite, and clinobronzite that formed by inversion from high-temperature protobronzite. The assemblage orthobronzite-protobronzite-tridymite-metallic iron indicates an equilibrium temperature of 1200°C and an ?o₂ of 10^?12 under a total pressure of less than 2 kbar. Preservation of the high-temperature phase relations implies much more rapid cooling in the 1200-700°C range than the rates that have been deduced for the development of Widmanstätten structure in the 700-500°C range.  相似文献   

Iron regeneration and organic iron(III)-binding ligand production during in situ zooplankton grazing experiment     

Mitsuhide Sato  Shigenobu Takeda  Ken Furuya 《Marine Chemistry》2007,106(3-4):471-488

To elucidate iron regeneration and organic iron(III)-binding ligand formation during microzooplankton and copepod grazing on phytoplankton, incubation experiments were conducted in the western subarctic Pacific. During 8 days of dark incubation of ambient water and that amended with plankton concentrate, dissolved iron and organic iron(III)-binding ligands accumulated, approximately proportionally to the decrease in chlorophyll a. The observed increases in dissolved iron concentration were much greater than those expected from the consumption of phytoplankton biomass and previously reported Fe:C value of cultured algal cells, suggesting resolution from colloidal or particulate iron adsorbed onto the algal cell surface. When copepods were added to the ambient water, organic iron(III)-binding ligands accumulated more rapidly than in the control receiving no copepod addition, although consumed phytoplankton biomass was comparable between the two treatments. Bioassay experiment using filtrates collected from the incubation experiment showed that organic ligands formed during microzooplankton grazing reduced the iron bioavailability to phytoplankton and suppressed their growth. Moreover, picoplankton Synechococcus sp. and Micromonas pusilla were more suppressed by the organic ligands than the diatom Thalassiosira weissflogii. In conclusion, through microzooplankton and copepod grazing on phytoplankton, organic iron(III)-binding ligands as well as regenerated iron are released into the ambient seawater. Because the ligands lower iron bioavailability to phytoplankton through complexation and the degree of availability reduction varies among phytoplankton species, grazing by zooplankton can shift phytoplankton community structure in iron-limited waters.  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   

Landward migration of inner bars     

Tsuguo Sunamura  Ichirou Takeda 《Marine Geology》1984,60(1-4):63-78

A field investigation was carried out to collect data of inner bar migration. Profiles were measured once or twice a week for a two-year period at Naka Beach, Ibaraki Prefecture, Japan. It was found that the onshore migration of inner bars could be described by two dimensionless quantities as: $\text{5D}\text{(H}{}_{\mathrm{<mtext>b</mtext>}}\text{)}{}_{\mathrm{<mtext>max</mtext>}}\text{<}\text{(H}{}_{\mathrm{<mtext>b</mtext>}}\text{)}{}_{\mathrm{<mtext>max</mtext>}}\text{gT}{}^2{}_{\mathrm{<mtext>max</mtext>}}\text{<}\text{20D}\text{(H}{}_{\mathrm{<mtext>b</mtext>}}\text{)}{}_{\mathrm{<mtext>max</mtext>}}$ where (H_b)_max is the maximum value of daily average breaker height during one interval between surveys, T_max is the average wave period of the day giving (H_b)_max, D is the mean size of the beach sediment, and g is the acceleration due to gravity. Analyses based on surfzone sediment dynamics yields $\text{v}\text{?}\text{(}\text{wD}\text{b}\text{)}\text{= 2 × 10}{}^{\mathrm{?11}}\text{(}\text{(}\text{H}\text{?}{}_{\mathrm{<mtext>b</mtext>}}\text{D}\text{)}{}^3$, where $\text{v}\text{?}$ is the average speed of onshore bar-migration, b is the bar height, $\text{H}\text{?}{}_{\mathrm{<mtext>b</mtext>}}$ is the average breaker height, and w is the fall velocity of the beach sediment. Nomographs for the speed of landward migrating bars are also presented.  相似文献   

A layered-crust model of a Howardite parent body     

Hiroshi Takeda 《Icarus》1979,40(3):455-470

A Howardite parent body is a Vesta-like hypothetical asteroid composed of diogenites, eucrites, and howardites (polymict breccias of various diogenites and eucrites). Combined single-crystal X-ray diffraction and microprobe studies of their pyroxenes indicate that their exsolution and inversion textures vary systematically with respect to their crystallization trend deduced from their Mg and Ca concentrations. Mg-Rich, early crystallized (presumably deep-seated) members revealed slowly cooled textures, except Mg-Rich pyroxene fragments in eucritic polymict breccias. Present study of such pyroxenes in Yamato-74450 and -75015 found in Antarctica confirmed that they were originally cores of the very rapidly cooled Pasamonte-like pigeonites. Based on these data, we reconstructed a layered-crust model from bottom to top as: (A) Mg-rich diogenite layer with orthopyroxenes with or without exsolution lamellae of augite with common (100) plane; (B) Fe-rich diogenite layer with inverted low-Ca pigeonites and orthopyroxenes; (C) cumulate eucrite layer with low-Ca inverted pigeonites with blebby augite inclusions with (100) in common generally, and plagioclase (Binda is the most Mg-rich member of this layer); (D) Moore County-like layer with partially inverted pigeonites with (001) augite lamellae and plagioclase; (E) common eucrite layer with the Juvinas-like pigeonites with fine (001) augite lamellae and plagiocalse; (F) surface eucrite layer with the Pasamonte-like pigeonites which are chemically zoned.  相似文献   

Correction to: The Iodide and Iodate Distribution in the Seto Inland Sea,Japan     

Kazuhiko Takeda  Kengo Yamane  Yuuta Horioka  Kazuaki Ito 《Aquatic Geochemistry》2018,24(2):163-164

  相似文献   

Spatio-temporal deposition profile of an experimentally produced turbidity current with a continuous suspension supply     

Shun Nomura  Giovanni De Cesare  Mikito Furuichi  Yasushi Takeda  Hide Sakaguchi 《国际泥沙研究》2022,37(3):299-306

A turbidity current is a turbulent, particle-laden gravity current that is driven by density differences resulting from the presence of suspended sediment particles. The current travels downslope, bearing a large amount of sediment over a great distance, and forms fluvial and submarine bedforms. Knowledge of the spatio-temporal deposition profile of turbidity-deposited sediment is important for a better understanding of sediment transport by turbidity currents. In the current study, the depositi...  相似文献   

Chemical factors controlling the solubility of uraninite and their significance in the genesis of unconformity-related uranium deposits     

S. Kojima  S. Takeda  S. Kogita 《Mineralium Deposita》1994,29(4):353-360

A quantitative evaluation of the solubility of uraninite (UO₂) in aqueous solutions under hydrothermal conditions was made using previously reported thermodynamic data, so as to inquire into the controlling factors for Canadian unconformity-type ore mineralization as observed in the Athabasca uranium field. The results of solubility calculations suggest that uranyl carbonate complexes, such as UO₂CO ₃ ^o , UO₂(CO₃) ₂ ^2- and UO₂(CO₃) ₃ ^4- , predominate under relatively oxidizing and slightly acidic-alkaline conditions and that the uranyl chloride complex, UO₂Cl⁺ is dominant under acidic conditions. These features are predicted at temperatures up to 200 °C over reasonable ranges of CO₂ pressure (Pco₂) and salinity. Consequently, the physico-chemical parameters, such as oxygen activity (ao₂), and pH are regarded as the most important factors controlling uraninite solubility. Judging from the paragenetic sequences observed in most unconformity-type uranium deposits in the Athabasca district, appreciable decreases in the above variables are postulated to have occurred in the stage of principal uranium deposition. Such changes would be due to fluid-mixing phenomenon accompanied by the diagenetic-hydrothermal activity (Hoeve and Quirt 1987).  相似文献   

Stress induced transformation of pigeonites from achondritic meteorites     

Hiroshi Mori  Hiroshi Takeda 《Physics and Chemistry of Minerals》1988,15(3):252-259

A transmission electron microscopic (TEM) study was conducted to investigate the stress-induced transformation mechanisms of pigeonites from two achondrites. In pigeonites from the Allan Hills 77257 ureilite, abundant lamellae of orthopyroxene-pigeonite intergrowth accompanied by minor amounts of blebby augite precipitates were observed. In pigeonites from the Juvinas eucrite, some stacking faults running through the (001) augite lamellae were observed although most of the stacking faults terminated at the host-lamella interface. High resolution TEM observation shows the fringe offset produced by the stacking fault in the Juvinas pigeonites. The magnitude of the mismatch parallel to [001] is approximately c/4, which is related to the formation of the partial edge dislocation near the host-lamella interface. The partial dislocation is imaged as an edge dislocation with an (002) extra-plane. Three partial dislocation mechanisms with distinct displacement vectors are proposed in order to explain the stress-induced transformation textures observed in the achondritic pyroxenes. Further study will be required to determine unequivocally the mechanism of atomic displacements during stress-induced transformation. However, regardless of the actual mechanism of transformation, it is not difficult to convert orthopyroxene to clinopyroxene or vice versa by this transformation from the structural point of view. Low-Ca pyroxenes are deformed without a stress-induced transformation by slip at high temperature and geologically reasonable strain rates. However, meteoritic pyroxenes can be deformed by stress-induced transformation even at high temperature because preterrestrial impact processes will produce a deformation condition with high strain rates. Deformation at high strain rates and high temperature is very important when we interpret the microtexture of meteoritic pyroxenes.  相似文献   

Lagrangian observation of phytoplankton dynamics at an artificially enriched subsurface water in Sagami Bay,Japan     

Takako Masuda  Ken Furuya  Naoko Kohashi  Mitsuhide Sato  Shigenobu Takeda  Makoto Uchiyama  Naho Horimoto  Takashi Ishimaru 《Journal of Oceanography》2010,66(6):801-813

Phytoplankton dynamics in the lower euphotic zone were observed by tracking a subsurface water released at 20-m depth from Takumi, an artificial upwelling device. Takumi continually discharged seawater pumped up from a depth of 205 m: this water was mixed with 5-m depth water to adjust the density to that of 20-m depth water of Sagami Bay, Japan. The discharged water was pulse-labeled at Takumi with uranine and tracked for 63.9 h with a drifting buoy equipped with a drogue at 20-m depth. We present a simple model to estimate in situ phytoplankton net growth rates from temporal changes in phytoplankton abundance in the discharged water with correction for the influence of water exchange between the discharged water and neighboring layers. Lagrangian observation showed active growth of pico- and nanophytoplankton, especially cryptophytes and Synechococcus (Cyanobacteria), in the subsurface layer. In contrast, diatoms grew little in spite of micromolar concentrations of nutrients. The active growth of pico- and nanophytoplankton was in good agreement with shipboard serial dilution culture experiments. The low growth activity of diatoms was suggested to be related to low light availability in the subsurface layer.  相似文献