The domain of validity of the KdV-type solitary rossby waves in the shallow water β-plane model

The Domain, where the necessary and sufficient conditions for the existence of the KdV-type solitary Rossby waves are satisfied is defined in the shallow water β-plane model. The KdV-type solitary Rossby waves are the Rossby waves whose time-longitude dependence is determined by the KdV equation. As far as an appropriate amplitude and an appropriate ratio of the scales of the east-west and north-south directions are given, the KdV-type solitary Rossby waves can exist for every basic zonal flow. This result suggests the large validity of the soliton model in geophysical fluid dynamics. The KdV-type solitary Rossby waves are classified into four categories: (1) shear solitons studied by Long, Larsen, Benny, Redekop, and Hukuda, (2) β-divergent solitons studied by Clarke, Yamagata, and Nogami, (3) β-solitons found in the case of the strong stratification, and (4) divergent solitons which exist in the planetary-geostrophic-scale zonal flow. A remarkable result is that, in addition to the conventional east-west elongated solitons, the north-south elongated solitons can also exist for the case of the divergent solitons.     

Hydrological and climatological glaciers observation 20 years on Tanggula Pass of Tibetan Plateau: its significance and contribution

Two decades have passed since China and Japan jointly launched hydrological & climatological observations on the glaciers in Tanggula Pass, Tibetan Plateau. Although the research institutions involved have been either restructured or renamed, their work, between 1989 and 1993, was ground-breaking and remains significant even to this day. Some observation sites established at that time are still utilized for large-scaled projects sponsored by GAME/Tibet, NSFC (Natural Science Foundation of China) and the Major State Basic Research Development Program of China (973 Program). Recently, a glacier monitoring system has been established on the cap of Dongkemadi Glacier, and is expected to make further contributions to research on the change of the cryospheric and climatic environment in the area.     

Geochemistry of adakitic quartz diorite in the Yamizo Mountains, central Japan: Implications for Early Cretaceous adakitic magmatism in the inner zone of southwest Japan

Abstract   Small-volume plutons of Early to Late Cretaceous ages are widely distributed in the Yamizo Mountains, central Japan. These plutons consist predominantly of granitoids, classified into hornblende gabbro, quartz diorite, hornblende–biotite granodiorite and coarse-grained biotite granite. The quartz diorite (52–64 wt% of SiO₂) is characterized by a high Sr content (606–769 p.p.m.) associated with a low Y (13–27 p.p.m.) and heavy rare earth element content (Yb content of 1.19–2.13 p.p.m.). On the Sr/Y versus Y diagram, this rock type mainly plots in the adakite and Archean high-Al tonalite, trondhjemite and granodiorite (TTG) field. Together with its initial Sr isotopic ratios, which range from 0.7038 to 0.7046, these data suggest that quartz diorite originated as slab melts. However, geochemical calculations assuming either eclogite or garnet amphibolite as the source material do not support this suggestion. Instead, the chemical compositions of quartz diorite are better explained by the fractional crystallization of hornblende, plagioclase and biotite from a primitive, basaltic melt in a magma chamber. In this case, the formation of the associated hornblende gabbro can also be explained by the accumulation of hornblende and plagioclase. Adakitic rocks of Early Cretaceous ages have also been reported in the Tamba Belt of the inner zone of southwest Japan, located ca 500 km west of the Yamizo Mountains. These rocks can be correlated to the adakitic rocks in the Yamizo Mountains based on the geology, petrography, geochemistry and radiometric ages. Therefore, we propose the possibility that the Early Cretaceous adakitic rocks in the inner zone of southwest Japan were produced by fractional crystallization from basaltic arc magmas generated by a partial melting of metasomatized wedge mantle peridotite.     

239,240Pu and137Cs in the East China and the Yellow Seas

The distribution and inventory of artificial radionuclides,^239,240Pu and¹³⁷Cs were determined in the East China and the Yellow Seas in 1987. Almost all of^239,240Pu and 50 to 80% of¹³⁷Cs in the continental shelf area are retained in the sediment column.^239,240Pu sediment inventory in the sea area is larger than the fallout input and tends to increase southwardly. This excess^239,240Pu and the lateral distribution are attributable to the supply of^239,240Pu by the Yangtze River discharge. On the contrary,¹³⁷Cs sediment inventory shows a decrease to the south, and the fact can be accounted for by the southward dispersion of fine silt particles discharged from the Yellow River. Total¹³⁷Cs inventory is smaller than the estimated fallout input, and the fact seems to indicate dispersion of¹³⁷Cs out of the shelf region. Vertical profiles of^239,240Pu and¹³⁷Cs contents in sediments differ from that of natural²¹⁰Pb, implying the effect of varied accumulation rates of the artificial radionuclides over the sediment particle mixing by benthic organisms. Apparent maximum sediment particle mixing coefficient (D _B ) calculated from the excess²¹⁰Pb profiles in stations located between the inner and outer shelves ranged from 1.4 to 8.3 cm²y^–1. ThisD _B value is higher than that in the Okinawa Trough (1.0 cm²y^–1), but lower than previously estimatedD _B value (26 cm²y^–1) in the outer shelf mud.     

Equilibrium configuration of the magnetosphere of a star loaded with accreted magnetized mass

Equilibrium configuration of the magnetosphere of a star loaded by the gravitationally accreted plasma having its own magnetic field is investigated. Axisymmetry around the star’s magnetic axis is assumed for simplicity. It is seen that two distinct configurations appear for the cases of parallel and antiparallel magnetic field of the accreted plasma with respect to the star’s magnetic moment. If the external field is antiparallel to the star’s magnetic moment, the stellar magnetosphere is confined within a spherical region surrounded by the external field with a separatric surface between them. This is an extension of the case of the spherical accretion of non-magnetic plasma dealt with thus far in connection with the mass accretion by the degenerate stars in X-ray binaries. It is noticed that the mass slides down along the field lines to the point closest to the star and is stratified hydrostatically in equilibrium to form a disk in the equatorial plane. The mass loading compresses the sphere as a whole in this case. If, on the other hand, the external field is parallel to the star’s magnetic moment, there appears a ring of magnetic neutral point in the equatorial plane. Polar field is open and extends to infinity while the low-latitude field is closed and faces the external field of opposite polarity across the neutral point. The increase of the loaded mass in this case causes a shrink of the closed field region, and the open polar flux is increased. Therefore, the transition between equilibria with small and large amount of the loaded mass requires the reconnection of magnetic lines of force, and the reconnection of the flux through the magnetic neutral ring is proposed as the mechanism of the steady or the intermittent mass leakage like the ones postulated for some X-ray bursters. Visiting Scientist supported by the Japan Society for the Promotion of Sciences.     

Temporal Change of Dissolved Inorganic Carbon in the Subsurface Water at Station KNOT (44°N, 155°E) in the Western North Pacific Subpolar Region

The dissolved inorganic carbon (DIC) and related chemical species have been measured from 1992 to 2001 at Station KNOT (44°N, 155°E) in the western North Pacific subpolar region. DIC (1.3∼2.3 µ mol/kg/yr) and apparent oxygen utilization (AOU, 0.7∼1.8 µmol/kg/yr) have increased while total alkalinity remained constant in the intermediate water (26.9∼27.3σ_θ). The increases of DIC in the upper intermediate water (26.9∼27.1σ_θ) were higher than those in the lower one (27.2∼ 27.3σ_θ). The temporal change of DIC would be controlled by the increase of anthropogenic CO₂, the decomposition of organic matter and the non-anthropogenic CO₂ absorbed at the region of intermediate water formation. We estimated the increase of anthropogenic CO₂ to be only 0.5∼0.7 µmol/kg/yr under equilibrium with the atmospheric CO₂ content. The effect of decomposition was estimated to be 0.8 ± 0.7 µmol/kg/yr from AOU increase. The remainder of non-anthropogenic CO₂ had increased by 0.6 ± 1.1 µmol/kg/yr. We suggest that the non-anthropogenic CO₂ increase is controlled by the accumulation of CO₂ liberated back to atmosphere at the region of intermediate water formation due to the decrease of difference between DIC in the winter mixed layer and DIC under equilibrium with the atmospheric CO₂ content, and the reduction of diapycnal vertical water exchange between mixed layer and pycnocline waters. In future, more accurate and longer time series data will be required to confirm our results.     

Ba, Si, U, Al, Sc, La, Th, C and C/C in a sediment core in the western subarctic Pacific as proxies of past biological production

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C_org) as well as its isotopic ratio (δ¹³C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba_ex, showed the best correlation with the Vostok δD (r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba_ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba_ex in WSAP were similar to those of Ba_ex in the Okhotsk Sea and of other proxies (C_org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba_ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD (r = 0.46, p < 0.001) than Ba_ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba_ex. While both the C_org content and U_ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ¹³C and the Vostok δD (r = 0.42, p < 0.001), between δ¹³C and Ba_ex (r = 0.60, p < 0.001) and between δ¹³C and Opal (r = 0.36, p < 0.01) indicates that δ¹³C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba_ex in WSAP and Loess (r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.     

New SHRIMP U–Pb zircon ages of granitic rocks in the Hida Belt,Japan: Implications for tectonic correlation with Jiamushi massif

Granitoids in the Hida region of Japan encompass two main rock types: younger type‐1 granites and older type‐2 granites. Sensitive high mass‐resolution ion microprobe (SHRIMP) U–Pb zircon dating of older type‐2 granites collected from the Tateyama area show similar ages of 245 ± 2 Ma and 248 ± 5 Ma for two gneissose granites, while a significantly younger intrusion age of 197 ± 3 Ma was determined for the younger type‐1 granites collected from the Hayatsukigawa River which belongs to the Okumayama pluton. A felsic gneiss sample (07HI‐3) collected from the right bank of the Hayatsukigawa River yielded multiple complex ages at 330 ± 6 Ma, indicating the timing of the Hida regional tectono‐thermal events that formed the Hida gneisses; 243 ± 8 Ma, representing the timing of intrusion of the augen granite; and 220 Ma, indicating the timing of regional dextral ductile shearing that caused a repeated recrystallization of metamorphic rocks in the study area. Considering the geochronological data, the rock types and assemblages, basement, and Sr–Nd isotopic constraints, we propose that the Hida Belt separated from the Jiamushi massif, which is located in the eastern margin of the Central Asian Orogenic Belt.     

Shear wave velocity measurement during a standard penetration test

An experiment was carried out to develop a technique to measure shear wave velocity simultaneously with the standard penetration test popular in soil engineering. In the standard penetration test an impact at the bottom of a borehole is produced by weight dropping and may be expected to generate seismic waves. A three-component geophone was set on the ground surface near the borehole and the waves generated were recorded with a magnetic recorder at successive depths of the penetration test. The predominance of the SV wave obtained with this simple method was assured by measurement of the particle orbit. Signal amplitudes decrease with depth and become less than the noise level at a certain depth. Therefore records from deeper sources must be processed to disclose the shear waves. Since waveforms of SV events generated by blows of the penetration test at a given depth are very similar, the signal to noise ratio would be expected to be improved by a stack of wave trains. A paste-up of the radial component after stacking was compared with that before stacking and a refinement was clearly recognized. A vertical distribution of shear wave velocity was obtained by reading the onset time at each depth. Shear wave velocities thus obtained were compared with N values from the standard penetration test and specific resistivities from electrical logging in the same borehole. The data were mutually consistent. This experiment showed that a convenient, precise shear wave velocity measurement can be conducted during the routine work of a standard penetration test.