An atomic level study of rhenium and radiogenic osmium in molybdenite   总被引：1，自引：0，他引：1  

Yoshio Takahashi  Tomoya Uruga  Hajime Tanida  Keiko H. Hattori 《Geochimica et cosmochimica acta》2007,71(21):5180-5190

Local atomic structures of Re and radiogenic Os in molybdenite from the Onganja mine, Namibia, were examined using X-ray absorption fine structure (XAFS). Rhenium L_III-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) show that the oxidation state of Re, the interatomic distances between Re and the neighboring atoms, and the coordination number of Re to S are very similar to those of Mo in molybdenite. The results confirm that Re is present as Re(IV) in the Mo site in molybdenite.Measurement of L_III-edge XANES and EXAFS of a minor concentration (8.55 ppm) of radiogenic Os was accomplished in fluorescence mode by removing the interfering X-rays from Re and other elements using a crystal analyzer system. The data indicate that the oxidation state of radiogenic Os is Os(III) and Os(IV) and clearly different from Os(II) in natural sulfide minerals, such as OsS₂ (erlichmanite). XANES data also suggest that radiogenic Os does not form a secondary Os phase, such as OsS₂ or Os metal, in molybdenite.EXAFS of radiogenic Os was successfully simulated assuming that Os is present in the Mo site in molybdenite. The data are consistent with the XANES data; Os does not form Os phases in molybdenite. The EXAFS simulation showed that the interatomic distance between Os and S is 2.27 Å, which is 0.12 Å smaller than the distances of Re-S and Mo-S (2.39 Å) in molybdenite. Similar valences and ionic sizes of Re and Mo in molybdenite support the fact that large amounts of Re can be incorporated into the Mo site as has been observed in previous studies, whereas the different properties of Os compared to Mo and Re suggested here support much lower abundance of common Os in molybdenite. This makes molybdenite an ideal mineral for the Re-Os geochronometer as shown in many studies. However, the shorter distance between radiogenic Os and S compared to those of Re-S and Mo-S in molybdenite suggests that the radiogenic Os has a smaller ionic size than Re(IV) and Mo(IV). Furthermore, Os may be partly present as Os(III). Smaller and lower charge Os can diffuse faster than larger and higher charge Re in molybdenite at a given set of conditions. Hence, our study provides an atomic-level explanation for the high mobility of Os compared to Re, which has been suggested by earlier workers using laser ablation ICP-MS.  相似文献   

Solubilities of nitrogen and noble gases in silicate melts under various oxygen fugacities: implications for the origin and degassing history of nitrogen and noble gases in the earth     

Akiko Miyazaki  Hajime Hiyagon  Kei Hirose 《Geochimica et cosmochimica acta》2004,68(2):387-401

Solubility experiments for nitrogen and noble gases (Ar and Ne) in silicate melts were conducted using two experimental configurations: one was conducted at 1 atmospheric pressure, T =1300°C and oxygen fugacity (fO₂) of IW + 0.9 (i.e., 0.9 log units higher than the iron-wüstite buffer) and the other at high pressures (P_total ∼ 2 × 10⁸ Pa), 1500°C and fO₂ ∼ IW + 6. For the former experiment, isotopically labeled-nitrogen (¹⁵N¹⁵N-enriched) was used to distinguish dissolved nitrogen from contaminating atmospheric or organic nitrogen and to examine dissolution mechanisms of nitrogen in silicate melts. The results obtained for the two series of experiments are consistent with each other, suggesting that Henry's law is satisfied for fN₂ of up to ∼250 atm (2.5 × 10⁷ Pa). The results are also consistent with our earlier results (Miyazaki et al., 1995) obtained at highly oxidizing conditions (fO₂ ∼ IW + 10). All these results support physical dissolution of nitrogen as N₂ molecules in silicate melts for fO₂ from ∼IW + 10 down to ∼IW. The observed solubility (Henry's constant) of nitrogen (3-5 × 10⁻⁹ mol/g/atm) is comparable to that of Ar (2-4 × 10⁻⁹ mol/g/atm), and much lower than that of Ne (11-14 × 10⁻⁹ mol/g/atm) at 1300°C. A preliminary experiment was also performed for partitioning of nitrogen and noble gases between clinopyroxene (cpx) and basaltic melt using a piston cylinder-type apparatus at 1.5 GPa and at 1270 to 1350°C. The obtained cpx/melt partition coefficient of nitrogen is 0.06, slightly lower than those of noble gases (∼0.1 for Ne to Xe), suggesting that nitrogen is as incompatible as or even slightly more incompatible than noble gases. The present results imply that a large nitrogen/Ar fractionation would not be produced by magmatic processes. Therefore, the two orders of magnitude difference between the N₂/³⁶Ar ratios in the Earth's atmosphere (∼10⁴) and that in the mantle (∼10⁶) must be explained by some other processes, such as incomplete segregation of metal blobs into the core and their later oxidation.  相似文献   

Dissolved Al, In, and Ce in the eastern Indian Ocean and the Southeast Asian Seas in comparison with the radionuclides Pb and Po     

Hajime Obata  Yoshiyuki Nozaki  Yoshiyuki Yamamoto 《Geochimica et cosmochimica acta》2004,68(5):1035-1048

To carry out comparative geochemical investigation of refractory and reactive metals in different oceanic settings covering different θ-S characteristics, productivity, dissolved oxygen profiles, water and sediment discharge, etc., we have determined the vertical profiles of dissolved (<0.04 μm) Al, In and Ce, as well as ²¹⁰Pb and ²¹⁰Po in the eastern Indian Ocean (from 40°S in the Southern Ocean to 8°N in the Bay of Bengal) and the Southeast Asian Seas. In the Antarctic Circumpolar Region, the concentrations of these refractory metals are very low, presumably due to very low the atmospheric input and intensified scavenging. Resemblance in the vertical profiles of these metals is often seen in some other stations. However, there are also significant differences among their distributions, for example, in the magnitude of surface enrichment caused by the external input from eolian and fluvial-coastal sources. Comparison of Al distributions in surface waters with those of atmospherically derived ²¹⁰Pb suggests the relative importance of eolian input over fluvial-coastal sources. Fluvial and coastal input appears to be insignificant for dissolved In, but may be important for Ce. The mean residence time of Al in the surface mixed layer was estimated to be ∼2 years which is similar to that of ²¹⁰Pb.In the intermediate and deep waters, the concentrations of each element vary with depth and location. The range of variation is in the order of Al>Ce>In, depending upon particle reactivity. Although dissolved Al decreases along the water trajectory by particle scavenging, variations of dissolved In and Ce are relatively small which may be due to less scavenging for both elements. Compared with significantly high (>4 pM) dissolved Ce throughout the water column in the Bay of Bengal, dissolved Al concentration remains low, suggesting that it has higher affinity to particles and hence is scavenged by sinking particulate matter. This is consistent with the observation that the dissolved Al in the Antarctic Intermediate Water (AAIW) decreases from 4 to 6 nM in the 30°S Perth Basin to <0.7 nM in the 10°S West Australia Basin along its trajectory. Using the chlorofluorocarbons (CFCs) ventilation age of AAIW (Fine, 1993), the mean residence time of Al in the intermediate and deep waters in the eastern Indian Ocean is estimated to be <17 yr, approximately the same as that of ²¹⁰Pb (10-15 yr). In the semiclosed basins of Southeast Asia, the distributions of Al, In and Ce are also very unique. In the South China Sea, there is a strong sediment source for dissolved In and Ce during the deepwater passage through the Luzon Strait.  相似文献   

Biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean from 2004 to 2013     

Masahide Wakita  Makio C. Honda  Kazuhiko Matsumoto  Tetsuichi Fujiki  Hajime Kawakami  Sayaka Yasunaka  Yoshikazu Sasai  Chiho Sukigara  Mario Uchimiya  Minoru Kitamura  Toru Kobari  Yoshihisa Mino  Akira Nagano  Shuichi Watanabe  Toshiro Saino 《Journal of Oceanography》2016,72(5):665-685

The annual flux of biologically produced organic carbon from surface waters is equivalent to annual net community production (NCP) at a steady state and equals the export of particulate and dissolved organic carbon (POC and DOC, respectively) to the ocean interior. NCP was estimated from carbon budgets of salinity-normalized dissolved inorganic carbon (nDIC) inventories at two time-series stations in the western subarctic (K2) and subtropical (S1) North Pacific Ocean. By using quasi-monthly biogeochemical observations from 2004 to 2013, monthly mean nDIC inventories were integrated from the surface to the annual maximum mixed layer depth and corrected for changes due to net air–sea CO₂ exchange, net CaCO₃ production, vertical diffusion from the upper thermocline, and horizontal advection. The annual organic carbon flux at K2 (1.49 ± 0.42 mol m^?2 year^?1) was lower than S1 (2.81 ± 0.53 mol m^?2 year^?1) (p < 0.001 based on t test). These fluxes consist of three components: vertically exported POC fluxes (K2: 1.43 mol m^?2 year^?1; S1: 2.49 mol m^?2 year^?1), vertical diffusive DOC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.25 mol m^?2 year^?1), and suspended POC fluxes (K2: 0.03 mol m^?2 year^?1; S1: 0.07 mol m^?2 year^?1). The estimated POC export flux at K2 was comparable to the sum of the POC flux observed with drifting sediment traps and active carbon flux exported by migrating zooplankton. The export fluxes at both stations were higher than those reported at other time-series sites (ALOHA, the Bermuda Atlantic Time-series Study, and Ocean Station Papa).  相似文献   

Comparison of sinking particles in the upper 200 m between subarctic station K2 and subtropical station S1 based on drifting sediment trap experiments     

Makio C. Honda  Hajime Kawakami  Kazuhiko Matsumoto  Masahide Wakita  Tetsuichi Fujiki  Yoshihisa Mino  Chiho Sukigara  Toru Kobari  Mario Uchimiya  Ryo Kaneko  Toshiro Saino 《Journal of Oceanography》2016,72(3):373-386

Drifting sediment trap experiments were conducted during various seasons to elucidate the characteristics of particles sinking through the upper 200 m of the water column in the western Pacific at subarctic station K2 and subtropical station S1. The sinking particle flux increased when primary productivity was high at each station, during June–July at K2 and during February at S1. Biogenic opal (Opal) and CaCO₃ were the major components of the fluxes at K2 and S1, respectively. Contrary to the expectation of a high flux at the eutrophic station K2 and low flux at the oligotrophic station S1, the annual average organic carbon fluxes at 100 m were comparable at both stations: 62.7 mg C m^?2 day^?1 at K2 and 56.1 mg C m^?2 day^?1 at S1. The similarity of the fluxes was perhaps a reflection of the unexpectedly high primary production at S1. At K2, the organic carbon export ratio (organic carbon flux/primary productivity) was significantly and negatively correlated with primary production and tended to decrease with depth. The magnitude of the rate of attenuation of the organic carbon flux with depth was larger at S1 than at K2. This rate of attenuation tended to decrease and increase with primary production at K2 and S1, respectively. The explanation for these patterns may be that the flux of labile organic carbon at relatively shallow depths decreased with increasing primary production at K2, and zooplankton grazing pressure increased with increasing primary productivity at S1.  相似文献   

Crustal lineaments, distribution of lower crustal intrusives and structural evolution of the Vøring Margin, NE Atlantic; new insight from wide-angle seismic models     

R. Mjelde  H. Shimamura  T. Kanazawa  S. Kodaira  T. Raum  H. Shiobara   《Tectonophysics》2003,369(3-4):199-218

Five lineaments on the volcanic Vøring Margin, NE Atlantic, have been identified in crustal scale models derived from Ocean Bottom Seismograph (OBS) data. It is suggested that the Vøring Basin can be divided in four compartments bounded by the Jan Mayen Fracture Zone/Lineament, a new lineament defined from this study, the Gleipne Lineament, the Surt Lineament and the Bivrost Lineament. The NW–SE trending Jan Mayen-, Gleipne- and Bivrost lineaments probably represent old zones of weakness controlling the onset of the early Eocene seafloor spreading, whereas the Surt- and New lineaments, rotated ca. 30° symmetrically from the azimuth of the Gleipne Lineament, may represent adjustment features related to the early Cretaceous/early Tertiary rifting. The longest landward extent of a lower crustal high-velocity body, assumed to represent intrusions related to the last phase of rifting, is found between the New Lineament and the Gleipne Lineament, where the body extends across the Helland Hansen Arch. Northeastwards in the Vøring Basin, the landward limit of the body steps gradually seawards, closely related to the interpreted lineaments. Northeast of the Gleipne Lineament, the body terminates close to the Fles Fault Complex, north of the Surt Lineament, it extends across the Nyk High, and northeast of the Bivrost Lineament the intrusions terminate around the Vøring Escarpment. Evidence for an interplay between active and passive rifting components is found on regional and local scales on the margin. The active component is evident through the decrease in magmatism with increased distance from the Icelandic plume, and the passive component is documented through the fact that all found crustal lineaments to a certain degree acted as barriers to magma emplacement. The increased thickness of the continental crust on the seaward side of the Vøring Escarpment, the upwarping of Moho and thinning of the lower crustal high-velocity layer in the western part of the Vøring Basin, as well as a strong shallowing of the Moho observed in parts of the area between the Jan Mayen Fracture Zone/Lineament and the New Lineament, can be explained by lithospheric delamination models.  相似文献   

Benzo(a)pyrene in the sediment of Osaka Bay and Keihin Canal and its estimated sources     

Yasushi Kawakami  Hajime Nishimura 《Journal of Oceanography》1976,32(4):175-181

Benzo(a)pyrene (BP) in the sediment of Osaka Bay were determined. High concentration was found at two stations near the mouth of Shin-Yodo and off Kobe respectively (0.98g g^–1 dry mud basis, 1.1g g^–1). The concentration decreases regularly from the mouth of the river further into the bay. The other supplemental determination was carried on the sediment and the seawater of Keihin Canal. Notable BP concentration of 89g g^–1 was observed in the sediment beneath the effluent outlet of a gasworks. The BP in the sediment near the ironworks was also considerable, while the BP was relatively less in the sediment beneath the effluent outlet of refineries. These data suggest that coke plants working in gasworks or ironworks may be the larger sources of BP than refineries. The results of Osaka Bay coincide with this hypothesis.Cadmium, lead, copper, zinc, nickel, ignition loss and fine sand content were measured from the same sediment samples of Osaka Bay. Cd, Pb, Cu and ignition loss showed the regular distributions which resemble to BP and accordingly, good correlations with BP. No significant correlations were found between BP and Ni, Zn and fine sand content which showed no regular distributions.  相似文献   

Improvement of short-term sea ice forecast in the southern Okhotsk Sea     

Ayumi Fujisaki  Hajime Yamaguchi  Fengjun Duan  Genki Sagawa 《Journal of Oceanography》2007,63(5):775-790

In this study, a numerical model of 7-day forecast of sea ice produced by the Japan Meteorological Agency was improved by the following approaches. First, a new ice dynamic model was introduced: the distributed mass/discrete floe model. The model takes account of discrete characteristics of ice floes and well simulates the ice edge location at low computational cost. Secondly, the grid size was reduced to 5 × 5 km for the future high resolution forecasts. Next, the sea surface current data was examined because it significantly influences sea ice movement. We applied two new datasets of HINO and Okhotsk Ocean General Circulation Model (Okhotsk OGCM), which are estimated by numerical simulations, for the 7-day forecast of sea ice. Ice southward speed in January and the whorl formations in February and March were well reproduced with Okhotsk OGCM datasets. Finally, the ocean heat flux at the ice-ocean interface was refined. As a result, we achieved an ice edge error reduction from 30.8 km to 23.5 km.  相似文献   

A new method of evaluating the mineralization of particulate and dissolved photoassimilated organic matter     

Masanobu Ishikawa  Hajime Nishimura 《Journal of Oceanography》1983,39(2):29-42

A new method of evaluating the rate of mineralization of photoassimilated organic matter is described. This method enables us to compare the rate of direct mineralization of particulate organic carbon (POC) to CO₂ with the rate of solubilization of photoassimilated organic carbon followed by the mineralization of the resultant dissolved organic carbon (DOC) under the same conditions. The direct mineralization of photoassimilated carbon from POC to CO₂ is a more significant process compared with the mineralization of extracellular released organic carbon. The first-order rate coefficients range from 0.132 to 0.434 day^–1 for direct mineralization and 0.034 to 0.189 day^–1 for solubilization.  相似文献   

Spatial variations of rare earth elements in north pacific surface water     

Yayoi Hongo  Hajime Obata  Dia Sotto Alibo  Yoshiyuki Nozaki 《Journal of Oceanography》2006,62(4):441-455

The concentration of dissolved rare earth elements (REE) were determined at 47 stations in the North Pacific surface waters. Combining with other previous data, we present the surface REE distribution in the North Pacific and discuss the controlling factors. The surface concentrations increase toward the high latitude and continental margin (e.g. [Nd] > 10 pmol kg⁻¹) from the central North Pacific (e.g. [Nd] < 5 pmol kg⁻¹). The North Pacific Deep Water-normalized REE patterns are varied, indicating that two or more factors contribute to the REE distribution. We examined four factors making the regional variation of surface REE concentrations mainly; a) particle scavenging, b) atmospheric dust input, c) vertical mixing and d) lateral transport from the coastal region. Flux calculations for Nd showed that the influence of atmospheric dust was less significant than the vertical input even in the western upwelling zone. Moreover, the longitudinal and latitudinal transitions of surface REE seem to reflect the lateral supply from the coastal areas. We constructed the diagram of surface Er/Lu and Er/Yb molar ratios in order to assess the origin and the input processes of the surface REE. Both molar ratios showed increasing trend toward PEW (Er/Lu (>10.5) and Er/Yb (>1.4)) from PSUW (Er/Lu (>7) and Er/Yb (>1.2)). The high Er/Lu and Er/Yb ratios in PEW indicate that the lateral supply of terrestrial materials from the coastal area is possibly the important factor in PEW, because only weathering and dissolution of rocks can explain such high Er/Lu and Er/Yb ratios to our knowledge.  相似文献