Geostrophic balance of the Kuroshio as inferred from surface current and sea level observations

Historical observations of the surface current and daily mean sea level during the period 1965–1985 are analyzed in order to examine the geostrophic balance of the Kuroshio current in the Tokara Strait and near the Izu Islands. The variation in the sea level difference across the Kuroshio is associated with a variation in surface current velocity as predicted by the theory of geostrophic balance. However, the slope of the linear relation between the current velocity and sea level difference is smaller than the theoretically predicted value by about 30%. This disagreement may be ascribed to the effects of the centrifugal force and the occasional rise in sea level due to storm surges.Absolute mean sea level differences between the tidal stations are estimated by making use of the empirical relationship between the surface current and sea level difference. Estimated differences are: 87.4±22.1 cm between Naze and Nishinoomote, 24.3±9.2 cm between Miyake and Minamiizu, 41.3±17.7 cm between Miyake and Mera and 45.1±8.8 cm between Hachijyo and Miyake. The absolute value of sea level difference between Miyake and Minamiizu and that between Miyake and Mera may be about 30 cm, since geodetic levelling tells us that the mean sea level at Minamiizu is nearly equal to that at Mera.     

Estimation of urban heat island intensity using biases in surface air temperature simulated by a nonhydrostatic regional climate model

This study demonstrates that urban heat island (UHI) intensity can be estimated by comparing observational data and the outputs of a well-developed high-resolution regional climate model. Such an estimate is possible because the observations include the effects of UHI, whereas the model used does not include urban effects. Therefore, the errors in the simulated surface air temperature, defined as the difference between simulated and observed temperatures (simulated minus observed), are negative in urban areas but 0 in rural areas. UHI intensity is estimated by calculating the difference in temperature error between urban and rural areas. Our results indicate that overall UHI intensity in Japan is 1.5 K and that the intensity is greater in nighttime than in daytime, consistent with the previous studies. This study also shows that root mean square error and the magnitude of systematic error for the annual mean temperature are small (within 1.0 K).     

Mechanism of Nutrient Supply to Warm-Core Ring off Sanriku, Japan

The mechanism by which nutrient is supplied to a warm-core ring (WCR) was investigated in order to understand the greater productivity of WCR than that of the Kuroshio, where the WCR originattes. A single WCR was observed in January and May, 1997. The thermostad (a layer of isothermal and isohaline water) of the WCR had different properties from January to May, the differences: Δwater temperature: −0.698°C, Δsalinity: −0.048, Δsigma θ: +0.072, Δnitrite+nitrate-N: +1.83 μM, Δphosphate: +0.011 μM and Δsilicate: +3.2 μM. We examined three possible mechanisms for nutrient supply to WCR in winter, namely: 1) inflow of the Oyashio surface water into WCR; 2) isopycnal mixing with Oyashio water; 3) entrainment of the water below the WCR into the WCR. The results were as follows: 1) When the decrease of salinity was due to the inflow of the Oyashio surface water, the increase of nutrients (nitrite+nitrate-N, phosphate-P and silicate-Si) was estimated to be only 17–27% of the observed increase. 2) When the decrease of salinity was due to isopycnal mixing, the increase of nutrients was estimated to be 30–42% of the observed increase. 3) When the decrease of salinity in the WCR in May was due to entrainment of the water below the WCR in winter by convection, the mixing depth was calculated be 620 m according to the salt budget. The increase of nutrients in this case was calculated to be 82–95% of the observed increase. The main mechanism of nutrient supply to WCR was concluded to be due to the entrainment of the water below the WCR by winter mixing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sulfur isotopic characteristics of late Cenozoic ore deposits at the arc junction of Hokkaido, Japan

Abstract Sulfide minerals of late Cenozoic vein-type deposits of southwest Hokkaido and Kuril Islands yielded δ³⁴_CDT S values of 2 to 8 permil, which are typical green-tuff values of magnetite-series igneous terrane. Sulfides of the Kitami district of northeast Hokkaido, on the other hand, are characterized by negative δ³⁴S_CDT values, ranging from 0 to - 7 permil. This unique value among ore deposits in the late Cenozoic back-arc terranes in the Japanese Islands is considered to have resulted from extraction of ³²S enriched sulfur from the basement rocks, because of well-developed N-S fracturing in the basement, which is characteristic of the axial belt and Kitami district of Hokkaido.     

Geochemical and Microbiological Analysis of Sambe Hot Springs,Shimane Prefecture,Japan

Microbiological contribution to the formation of the manganese deposits in Sambe hot springs, Shimane, was investigated in combination with water chemistry, characterization of sediments and microbial community structure. Analysis of bacterial and fungal community structure based on DNA extracted from a Mn‐oxidizing enrichment culture indicated close matches with Pseudomonas putida, Phoma sp. and Plectosphaerella cucumerina, all Mn‐oxidizing microorganisms. These sediments were poorly crystalline and formed at neutral pH values, which is characteristic of biogenic precipitates. The EPMA results demonstrated a positive correlation between Mn and Ba contents in well‐crystalline Mn oxide grains. Substantial Ba contents were observed inside Mn oxide grains. These findings indicated that Ba contents in sediments are influenced by not only aqueous Ba²⁺ concentrations but also crystallinity of biogenic birnessite. Barium would be incorporated in birnessite during biomineralization.     

Characterization of drying-induced deformation behaviour of Opalinus Clay and tuff in no-stress regime

The drying-induced deformation behaviour of Opalinus Clay and tuff, which are being investigated under international and local collaborative projects for nuclear waste disposal in Switzerland and Japan, was investigated under a no-stress condition in the laboratory to evaluate their generic susceptibility to the formation of excavation damaged zone. The cylindrical core samples of Opalinus Clay and tuff were prepared to a one-dimensional drying condition and submitted to an uncontrolled laboratory environment. The strain evolution, evaporative water loss and environmental entities, such as temperature and relative humidity, were recorded simultaneously and quasi-continuously. It was observed that the drying phase induced significant strain magnitude and damage in Opalinus Clay samples, which was evidenced by the formation of hairy cracks on the surface parallel to the bedding. On the contrary, the strain occurrences in tuff samples were relatively insignificant, and no tendency of cracking was observed. In addition, the quasi-continuous availability of volumetric strains was further used in poroelastic relation for the estimation of capillary suction evolution. The calculated results were validated with pore size distributions obtained from mercury intrusion porosimetry.     

Uranium-series chronology for sediments of Lake Hovsgol, Mongolia, and the 1-Ma records of uranium and thorium isotopes from the HDP-04 drill core

Uranium and thorium isotopes in an 81-m long sediment core (HDP-04) of Lake Hovsgol, Mongolia, were measured to investigate their downcore distributions and to explore potential linkage to paleoenvironmental changes. Three-dimensional isochron techniques using isotope-ratio diagrams in ²³⁸U–²³⁴U–²³⁰Th–²³²Th system presented by Ludwig and Titterington were applied to age date the lake sediments at the depths of 11.42, 14.71 and 14.83 m in the HDP-04 section, the estimated ages of these horizons are 66 ± 8, 122 ± 11 and 128 ± 22 ka, respectively. The ²³⁸U concentration throughout the entire section fluctuated by a factor of 12, ranging from 19.9 to 232.1 mBq/g with anomalously high ²³⁸U peak at 23.8 m in depth, while the ²³²Th concentration varied only by a factor of about two between 24.3 and 54.0 mBq/g. The discrimination of the bulk ²³⁸U into authigenic and terrigenous ²³⁸U fractions was attempted, based on the measured ²³²Th as a correction index for terrigenous materials. In the upper 24 m corresponding to the last 250 ka, the authigenic ²³⁸U was higher in interglacials and lower in glacials. This depth profile of authigenic ²³⁸U contents was almost identical pattern with that found in a sediment core (VER98-1-6) from the Academician Ridge, Lake Baikal. Further, this profile can be correlated well with that of photosynthetic pigment contents, one of proxies of paleoproductivity, suggesting that the variation of authigenic ²³⁸U contents were associated with the environmental change around Lake Hovsgol.     

Presence of a primary solar-type atmosphere around the earth: evidence of dissolved noble gas

Recent noble gas data of mantle-derived samples show that there are two end members: PLUME-type and MORB-type. The estimated high ³He and ²²Ne abundances of the PLUME source, possibly representing the lower mantle, should reflect the remnant of dissolved solar-type atmosphere. Calculations of the structure of the primary atmosphere and the noble gas dissolution into the magma ocean of the accreting planet suggest that the high ³He and ²²Ne abundances can be explained if the primary atmosphere persisted until M0.4–0.6 M_E (M_E being the present Earth mass). The PLUME source has higher ³He/⁴He and lower ²¹Ne/²²Ne than the MORB source. This is explained by assuming that the lower mantle was less degassed during magma ocean cooling. The carbon abundance in the mantle can be constrained from the estimated abundance of mantle ³He and C/³He data of the present mantle-derived samples. Dissolved solar-type noble gas might explain high noble gas abundance in the present Venus, if the primary atmosphere persisted until the final stage of accretion under lower dust opacity of the atmosphere.     

New polar ring galaxies in rich clusters of galaxies

Four polar ring galaxies discovered in rich clusters of galaxies are presented. Brief comments on their structural properties are given.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Effects of a physical librations of the moon caused by a liquid core,and determination of the fourth mode of a free libration

An analytical theory of lunar physical librations based on its two-layer model consisting of a non-spherical solid mantle and ellipsoidal liquid core is developed. The Moon moves on a high-precision orbit in the gravitational field of the Earth and other celestial bodies. The defined fourth mode of a free libration is caused by the influence of the liquid core, with a long period of 205.7 yr, with amplitude S = 0″0395 and with an initial phase Π₀ = ?134° (for the initial epoch 2000.0). Estimates of dynamic (meridional) oblatenesses of a liquid core of the Moon have been estimated: ?_D = 4.42 × 10^?4, μ_D = 2.83 × 10^?4 (?_D + μ_D = 7.24 × 10^?4). These results have been obtained as a result of comparison of the developed analytical theory of physical librations of the Moon with the empirical theory of librations of the Moon constructed on the basis of laser observations.