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101.
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
102.
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
103.
This study investigates the applicability of neural networks to predict whether impact wave force will act on the upright section of a composite breakwater. We employ a three-layered neural network whose units of input layer are h/L, H/h, d/h and BM/h (h: the total water depth; L: the wavelength; H: the wave height; d: the water depth above the mound; BM: the horizontal distance from the shoulder of mound to the caisson). Teach signals are 0.99 and 0.01 according to the cases of occurrence and absence of impact wave force, respectively. The neural network whose parameters are determined through self-learning can accurately predict whether impact wave force occurs. 相似文献
104.
Sensitivity study of the air–ice drag coefficient C Dai is presented with an ice–ocean coupled model for the Sea of Okhotsk. The C Dai?×?103 value is varied from 2 to 5 based on the direct measurements in the region. The maximum volume transport of the East Sakhalin Current and the mean sea ice velocity were intensified as C Dai increased. The sensitivity experiment with the ice–water drag coefficient C Diw showed that the East Sakhalin Current volume transport is hardly affected by C Diw but significantly intensified by C Dai. While the ice drift in the off-ice-edge direction was intensified by the increase in C Dai and the decrease in C Diw, the ice edge location was nearly unchanged. This was due to melting caused by the relatively warm water inflow from the North Pacific. That is, sea ice extent in the region is strongly influenced by melting caused by a large ice–ocean heat transfer. In the active melting regions, the ice–ocean heat transfer of more than 100 W/m2 occurred even in mid-winter. This is the same order as the cooling by air in winter, and a heat insulation capacity of sea ice is weakened in such regions. 相似文献
105.
Grade index (Gindex) is a dimensionless number given as the volume-in-unit-time ratio of subaerial allocation to both subaerial and subaqueous allocations of sediment supplied to a delta from upstream. It was originally proposed for understanding the effect of basin water depth on the morphodynamics of delta distributary channels under stationary relative sea level. We here examine how rising relative sea level modulates the Gindex, using geometrical reasoning and numerical simulations. We find that the grade index model can account for autoretreat of the deltaic shoreline, autodrowning of the whole system, and autobreak of the deltaic sedimentation, all of which are the consequences of autogenic nonequilibrium responses to steadily rising relative sea level. The regressive-to-transgressive threshold (i.e. the onset of autoretreat) is crossed when the delta plain's dimensionless basal area (At*) encounters a critical value that is expressed in terms of Gindex: regression and transgression are sustained when At* is below and above the threshold, respectively. The mode of transgression depends on the slope conditions. If the hinterland slope (γ) is steeper than the foreset slope (β), both At* and Gindex decrease as the relative sea-level rises. Eventually, the depositional system experiences autodrowning when At* = Gindex = 0. If γ < β; on the other hand, both At* and Gindex increase. This latter slope condition eventually causes autobreak of the deltaic sedimentation, afterward of which At* = Gindex = 1. The grade index model is useful for interpreting and predicting the stratigraphic responses of natural deltaic clinoforms in conditions of rising relative sea level. 相似文献
106.
Iron, manganese and aluminum in upper waters of the western South Pacific Ocean and its adjacent seas 总被引:1,自引:0,他引:1
Hajime Obata Kiminori Shitashima Kenji Isshiki Eiichiro Nakayama 《Journal of Oceanography》2008,64(2):233-245
Total dissolvable iron, manganese and aluminum distributions in upper waters were determined in the western South Pacific,
Solomon Sea, Coral Sea, and Tasman Sea. In these oceanic regions, the surface aluminum distributions well reflect the atmospheric
deposition pattern of mineral dust in the western South Pacific reported previously. Surface manganese distributions derive
mainly from lateral transportation from the coastal sediments of western tropical islands. Compared to Mn and Al, the Fe distributions
reflect the nutrient cycle in upper waters. Iron limitation over the vast South Pacific, as revealed by physiological features
of phytoplankton, seems to be caused by low atmospheric dust deposition and low Fe:N ratios in deep waters. In the western
South Pacific, with its unique geographic and oceanographic settings, the local sources of trace metals might considerably
affect their biogeochemical cycles. 相似文献
107.
108.
Implementation and evaluation of alternative wave breaking formulas in a coastal spectral wave model 总被引:2,自引:0,他引:2
This paper describes methods and results of research for incorporating four different parameterized wave breaking and dissipation formulas in a coastal wave prediction model. Two formulations assume the breaking energy dissipation to be limited by the Rayleigh distribution, whereas the other two represent the breaking wave energy by a bore model. These four formulations have been implemented in WABED, a directional spectral wave model based on the wave action balance equation with diffraction, reflection, and wave–current interaction capabilities. Four parameterized wave breaking formulations are evaluated in the present study using two high-quality laboratory data sets. The first data set is from a wave transformation experiment at an idealized inlet entrance, representing four incident irregular waves in a slack tide and two steady-state ebb current conditions. The second data set is from a laboratory study of wave propagation over a complex bathymetry with strong wave-induced currents. Numerical simulation results show that with a proper breaking formulation the wave model can reproduce laboratory data for waves propagating over idealized or complicated bathymetries with ambient currents. The extended Goda wave breaking formulation with a truncated Rayleigh distribution, and the Battjes and Janssen formulation with a bore model produced the best agreement between model and data. 相似文献
109.
Hajime Kawakami Makio C. Honda Kazuhiko Matsumoto Tetsuichi Fujiki Shuichi Watanabe 《Journal of Oceanography》2010,66(1):71-83
Observations of primary productivity, 234Th, and particulate organic carbon (POC) were made from west to east across the northern North Pacific Ocean (from station
K2 to Ocean Station Papa) during September–October 2005. Primary productivities in this region varied longitudinally from
approximately 236 to 444 mgC m−2d−1 and clearly indicate the West High East Low (WHEL) trend. We estimated east-west variations in the POC flux from the surface
layer (0–100 m) by using 234Th as a tracer. POC fluxes in the western region (44–53 mgC m−2d−1) were higher than those in the eastern region (21–34 mgC m−2d−1). However, the export ratios (e-ratios) ranged from approximately 8% to 16% and did not show the WHEL trend. Contrary to our expectation, no relation between
POC flux (or e-ratio) and diatom biomass (or dominance) was apparent in autumn in the northern North Pacific. 相似文献
110.
The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (?9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc. 相似文献