Phase relations of iron–silicon alloys at high pressure and high temperature

The phase relations of Fe-6.4 wt% Si and Fe-9.9 wt% Si have been investigated up to 130 GPa and 2,600 K based on in situ synchrotron X-ray diffraction measurements in a laser-heated diamond-anvil cell along with chemical analysis of the quenched samples using a field-emission electron probe microanalyzer. We found that the maximum solubility of silicon in solid hcp-iron increases with increasing pressure. Linear extrapolation of the phase boundary between hcp + B2 and hcp phases for Fe-9.9 wt% Si suggests that the solid hcp-iron can include more than 9.9 wt% Si at the Earth’s inner-core conditions. If silicon is a major light element in the outer core, a substantial amount of silicon may be incorporated into the inner core during inner-core solidification.     

High-pressure transformations of ilmenite to perovskite, and lithium niobate to perovskite in zinc germanate

In-situ X-ray powder diffraction measurements conducted under high pressure confirmed the existence of an unquenchable orthorhombic perovskite in ZnGeO₃. ZnGeO₃ ilmenite transformed into perovskite at 30.0 GPa and 1300±150 K in a laser-heated diamond anvil cell. After releasing the pressure, the lithium niobate phase was recovered as a quenched product. The perovskite was also obtained by recompression of the lithium niobate phase at room temperature under a lower pressure than the equilibrium phase boundary of the ilmenite–perovskite transition. Bulk moduli of ilmenite, lithium niobate, and perovskite phases were calculated on the basis of the refined X-ray diffraction data. The structural relations among these phases are considered in terms of the rotation of GeO₆ octahedra. A slight rotation of the octahedra plays an important role for the transition from lithium niobate to perovskite at ambient temperature. On the other hand, high temperature is needed to rearrange GeO₆ octahedra in the ilmenite–perovskite transition. The correlation of quenchability with rotation angle of GeO₆ octahedra for other germanate perovskites is also discussed.     

Estrogen equivalent concentration of individual isomer-specific 4-nonylphenol in Ariake sea water, Japan

Concentrations of 4-nonylphenol (NP) were determined by isomer-specific quantification of individual NP isomers based on relative response factor (RRF) quantification with GC–MS in combination with steam distillation extraction. Concentrations of NP in the Ariake Sea decreased with distance from the river mouth (St.A; 49 ng NP/l) to offshore areas (St.C; 11 ng NP/l). Even the least concentration in water from St.C in Ariake Sea was sufficient to have adverse effects on barnacles. The isomers, NP1–NP14 were separated by GC–PFC and identified structurally with NMR. The isomers varied in estrogenic activity with NP7 exhibiting the greatest estrogenic activity with a potency that was approximately 1.9 × 10⁻³ that of 17β-estradiol (E2) in recombinant yeast screen system. The coefficient of variation (CV) of NP isomer’s concentrations among three samples at St.A, B and C were 4–75%. This suggests that NP isomers might be independently degraded in aquatic environmental samples. The predicted estrogenic activity of measured concentrations of NP in Ariake Sea was 2.7–3.0-fold greater than the measured estrogen agonist activity.     

Electrical conductivities of pyrolitic mantle and MORB materials up to the lowermost mantle conditions

The electrical conductivities of natural pyrolitic mantle and MORB materials were measured at high pressure and temperature covering the entire lower mantle conditions up to 133 GPa and 2650 K. In contrast to the previous laboratory-based models, our data demonstrate that the conductivity of pyrolite does not increase monotonically but varies dramatically with depth in the lower mantle; it drops due to high-spin to low-spin transition of iron in both perovskite and ferropericlase in the mid-lower mantle and increases sharply across the perovskite to post-perovskite phase transition at the D″ layer. We also found that the MORB exhibits much higher conductivity than pyrolite. The depth–conductivity profile measured for pyrolite does not match the geomagnetic field data below about 1500-km depth, possibly suggesting the existence of large quantities of subducted MORB crust in the deep lower mantle. The observations of geomagnetic jerks suggest that the electrical conductivity may be laterally heterogeneous in the lowermost mantle with high anomaly underneath Africa and the Pacific, the same regions as large low shear-wave velocity provinces. Such conductivity and shear-wave speed anomalies are also possibly caused by the deep subduction and accumulation of dense MORB crust above the core–mantle boundary.     

Comparison of four ensemble methods combining regional climate simulations over Asia

A number of uncertainties exist in climate simulation because the results of climate models are influenced by factors such as their dynamic framework, physical processes, initial and driving fields, and horizontal and vertical resolution. The uncertainties of the model results may be reduced, and the credibility can be improved by employing multi-model ensembles. In this paper, multi-model ensemble results using 10-year simulations of five regional climate models (RCMs) from December 1988 to November 1998 over Asia are presented and compared. The simulation results are derived from phase II of the Regional Climate Model Inter-comparison Project (RMIP) for Asia. Using the methods of the arithmetic mean, the weighted mean, multivariate linear regression, and singular value decomposition, the ensembles for temperature, precipitation, and sea level pressure are carried out. The results show that the multi-RCM ensembles outperform the single RCMs in many aspects. Among the four ensemble methods used, the multivariate linear regression, based on the minimization of the root mean square errors, significantly improved the ensemble results. With regard to the spatial distribution of the mean climate, the ensemble result for temperature was better than that for precipitation. With an increasing number of models used in the ensembles, the ensemble results were more accurate. Therefore, a multi-model ensemble is an efficient approach to improve the results of regional climate simulations.     

In situ X-ray diffraction measurements of the <Emphasis Type="Italic">fcc</Emphasis>–<Emphasis Type="Italic">hcp</Emphasis> phase transition boundary of an Fe–Ni alloy in an internally heated diamond anvil cell

The phase transition boundary between the face-centered cubic (fcc) structure and hexagonal close-packed (hcp) structure in an Fe–Ni alloy was determined at pressures from 25 to 107 GPa by using an internally resistive-heated diamond anvil cell (DAC), combined with in situ synchrotron X-ray diffraction measurements. The fcc–hcp phase transition boundary in Fe–9.7 wt% Ni is located at slightly lower temperatures than that in pure Fe, confirming the previous understanding that the addition of Ni expands the stability field of the fcc phase. The dP/dT slope of the boundary was determined to be 0.0426 GPa/K, which is slightly larger than that of pure Fe. The pressure interval of the two-phase region is about 6 GPa at a constant temperature, implying that the previous estimates by laser-heated DAC experiments of 10–20 GPa were overestimated. The two-phase region of fcc + hcp would be limited to a pressure of about 120 GPa even in Fe–15 wt%Ni, excluding the possibility of the existence of the fcc phase in the inner core if the simple linear extrapolation of the two-phase region is applied. The pressure and temperature dependences of the c/a axial ratio of the hcp phase in Fe–9.7 wt% Ni are generally consistent with those in pure Fe, suggesting that Ni has minor effects on the c/a ratio.     

Characteristics of the stream network composition of drainage basins in the Japanese Islands

This research is to analyze the composition of stream networks of drainage basins in Japan and to discuss the characteristics of drainage basins in the Japanese Islands. Study areas were selected for 180 drainage basins in the entire country. In this study, a topographic map with a scale of 1:50,000 was used and inserted into the valley line by V-shaped-contour methods in each drainage basin. The streams are ordered according to Strahler's system and measured by the stream number, stream length, stream slope, drainage area, and stream fall in each drainage basin. Horton's law of drainage network composition holds good in most drainage basins in Japan. The average values of the bifurcation ratio, stream length ratio, stream slope ratio, drainage area ratio, and stream fall ratio are 4.24, 1.91, 1.98, 4.52, and 1.04, respectively. The mean bifurcation ratio of drainage basins in Japan is 4.24, and this ratio is slightly greater than in other countries. It is also greater than the theoretical value of 4.0. This implies that the slope of drainage basins in Japan is so steep and the relief energy so large that excess streams have developed to a rather marked degree. The average stream fall ratio is 1.04 for drainage basins in Japan. It suggests that drainage basins are generally considered to be in a stage of maturity in stream channel development for the Japanese Islands. The stream fall ratio, however, is slightly greater than 1.0. Although, the stream beds are nearly in dynamic equilibrium in most cases, it tends to be in a slightly aggrading state.     

Peculiar dispersion of salt by wind-driven fluctuations in the stratified water near the coast

A peculiar dispersion of salt, which was found in a partially mixed estuary by long-term continuous measurements of current and salinity and directed outward in the upper layer and inward in the lower layer in summer, is reported and discussed. The cause is estimated to be salinity stratification and wind-driven fluctuations in water near the coast. The general formulation is presented and a great possibility of negative dispersion against the horizontal gradient is pointed out. Dispersion coefficients are also estimated.