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211.
Abstract   Hydrogenetic ferromanganese crusts are widespread on the floor of the northwestern Pacific Ocean, south and east of the Japanese Islands, despite vigorous tectonic activity, such as subduction and back-arc spreading, since at least the Mid-Paleogene over the Philippine Sea Plate region and nearby. The crusts occur mainly at water depths shallower than 3000 m, but also at greater depths of up to 6000 m. Fine-scale 10Be/9Be dating was undertaken on several 5–10 cm thick hydrogenetic ferromanganese crusts sampled from different geological environments, including inactive submarine volcanoes, tectonic escarpments and abandoned rifts. The results indicate that the crusts have grown at relatively constant rates of 4–7 mm/my without any significant time breaks. These uniform and constant growth rates suggest that the basins have been exposed constantly to oxygenated bottom waters since their formation in the Middle Miocene ( ca 15 Ma) or earlier. Local geological or oceanographic environmental changes might have slowed or increased some of the growth rates resulting in correlation of some internal structures. The Philippine Sea Plate region could have economic potential in areas of thick hydrogenetic ferromanganese crusts over a wide range of water depths.  相似文献   
212.
The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320–450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 MPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160–260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20–80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress.  相似文献   
213.
An atomic level study of rhenium and radiogenic osmium in molybdenite   总被引:1,自引:0,他引:1  
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 LIII-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 LIII-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   
214.
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 (Ptotal ∼ 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   
215.
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   
216.
The 1995 Kobe earthquake caused unprecedented damage to buildings and civil infrastructures in the city of Kobe and its surrounding areas. In order to evaluate the structural damage in this area due to the earthquake, it is important to estimate the distribution of earthquake ground motion. However, since the number of strong ground motion records is not enough in the heavily damaged areas, it is necessary to estimate the distribution using other data sources. In this paper, the fragility curves for low‐rise residential buildings were constructed using the recorded motions and the building damage data from the intensive field survey by the AIJ and CPIJ group. The fragility curves obtained were then employed to estimate the strong motion distribution in the district level for Kobe and the surrounding areas during the earthquake. The results may be useful to investigate the various damages caused by the earthquake. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
217.
Multiple Tuned Mass Dampers (MTMD's) consisting of many tuned mass dampers (TMD's) with distributed natural frequencies are considered for suppressing effectively the harmonically forced single mode response of structures. The fundamental characteristics of MTMD's are investigated analytically with the parameters of the covering frequency range of MTMD's, the damping ratio of each TMD and the total number of TMD's. The effectiveness and the robustness of MTMD's are also discussed in comparison with those of the usual single TMD. It is found that there exists an optimum MTMD for the given total number of TMD's with the optimum frequency range and the optimum damping ratio and that the optimum MTMD is more effective than the optimum single TMD. As for the robustness, it is also clarified that a MTMD can be much more robust than a single TMD while keeping the same level of effectiveness as the optimum single TMD.  相似文献   
218.
Wang  S.  Fernando  H. J. S.  Dorman  C.  Creegan  E.  Krishnamurthy  R.  Wainwright  C.  Wagh  S.  Yamaguchi  R. 《Boundary-Layer Meteorology》2021,181(2-3):365-393

This work presents ship-based measurements of fog off St John’s, Newfoundland, on 13 September 2018 during the Coastal Fog field campaign. The measurements included cloud-particle spectra, cloud-base height and aerosol backscatter, radiation, turbulence, visibility, and sea-surface temperature. Radiosonde soundings were made at intervals of less than 2 h. Fog occurred in two episodes during the passage of an eastward-moving synoptic low-pressure system. The boundary-layer structure during the first fog episode consisted of three layers, separated by two saturated temperature inversions, and capped by a subsidence inversion. The lowest layer was fog, and the upper layers were cloud. The second fog episode consisted of one well-mixed fog layer capped by a subsidence inversion. Low wind speeds and stable stratification maintained low surface-layer turbulence during fog. Droplet size distributions had typical bimodal distributions. The visibility correlated with the droplet number concentration and liquid water content. The air temperature was higher than the sea-surface temperature for the first 30 min of the first fog episode but was lower than the sea for the remainder of all fog. The sensible heat flux was upward, from sea to air, for the first 62% of the first fog episode and then reversed to downward, from air to sea, for the remainder of the first fog episode and the second fog episode. The counter-gradient heat fluxes observed (i.e., opposite to what is expected from the instantaneous air–sea temperature difference) appear to be related to turbulence, entrainment, and stratification in the fog layer that overwhelmed the influence of the air–sea temperature difference. While the synoptic-scale dynamics preconditioned the area for fog formation, the final step of fog appearance in this case was nuanced by stratification–turbulence interactions, local advective processes, and microphysical environment.

  相似文献   
219.
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   
220.
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   
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