Open boundary value problems in ocean dynamics by finite elements

This paper presents recent results of application of the finite element models to wave overtopping and wave run-up problems in ocean dynamics. Open boundaries are prescribed as natural boundary condition obtained from the continuity equation of the Galerkin finite element formulation. The numerical results are, in general, reasonably good agreements with the histrical field data.     

On the number ratio of horizontal branch stars to red giant stars in globular clusters

The number ratios of horizontal branch stars to red giant stars were obtained for globular clusters and Draco dwarf galaxy and the helium abundance was estimated using model results without semiconvection zone (SCZ) and with fully developed one. The analysis was confined to the four clusters (M4, M5, M13, and 47 Tuc) and the Draco galaxy, for which fairly precise star counts had been carried out. The effect of the difference in radial distribution between horizontal and red giant branch stars were taken into account, if necessary. The statistically significant difference inR exists among these objects. The cause may be the difference in the helium abundance and/or in the development of the SCZ. In the case of the fully developed SCZ, the helium abundance for M5 and Draco is appreciably smaller than the value given by the big-bang cosmology. It may be taken as an evidence against the full development of the SCZ for the horizontal branch stars in these objects.     

Antifouling herbicides in the coastal waters of western Japan

Residue analyses of some antifouling herbicides (Diuron, Irgarol 1051 and the latter's degradation product M1, which is also known as GS26575), were conducted in waters collected along the coast of western Japan. In total, 142 water samples were collected from fishery harbours (99 sites), marinas (27 sites), and small ports (16 sites) around the Seto Inland Sea, the Kii Peninsula, and Lake Biwa, in August 1999. A urea-based herbicide, Diuron, was positively identified for the first time in Japanese aquatic environments. Diuron was detected in 121 samples (86%) up to a highest concentration of 3.05 microg/l, and was found in 86% of samples from fishery harbours, 89% from marinas, and 75% from ports. Four freshwater samples out of 11 collected at Lake Biwa contained Diuron. Neither Irgarol 1051 nor M1 was found in the lake waters, but both were found in many coastal waters. Irgarol 1051 was found in 84 samples (60%) at a highest concentration of 0.262 microg/l. The concentrations detected were of similar magnitude to those in our previous surveys, taken in 1997 and 1998. M1 was found in 40 samples (28%) up to a highest concentration of 0.080 microg/l. The concentrations detected were generally lower than those found in our previous surveys. The detection frequency among fishery harbours, marinas, and ports was 57-70% for Irgarol 1051 and 25-30% for M1. Ninety-five per cent of the coastal waters in which M1 was detected also contained Irgarol 1051, and 93% of the samples in which Irgarol 1051 was detected also contained Diuron. These results clearly suggest that commercial ship-bottom paints containing both Diuron and Irgarol 1051 are used extensively in the survey area.     

Implication of the temporal sulphur isotopic variation during the 2000 eruption of Miyakejima Volcano, Japan

Abstract   The variation of sulphur isotopic composition during the 2000 eruption of the Miyakejima Volcano was examined in order to monitor the temporal change of the volcanic activity. The δ³⁴S values of water-soluble sulphate leached from volcanic ash effused during intermittent eruptions from July to September 2005 range from +5 to +11‰ with a fluctuation of ca 3‰ within a single eruption. The δ³⁴S value of sulphuric acid mist collected with 'Cu-metal trap' placed on the flank of the volcano from December 2000 to January 2001 is +6.2‰. These sulphur isotopic compositions of sulphate, which were isotopically equilibrated in the subvolcanic hydrothermal system, indicate that the temperature of the hydrothermal system beneath the caldera increased after the period of intermittent phreatic and phreatomagmatic eruptions. Then, the δ³⁴S value of sulphuric acid trapped from January to March 2001 was +9.0‰ and the δ³⁴S value of water-soluble sulphate on volcanic ash emitted with minor eruption in May 2001 was +11.0‰, suggesting a decrease in temperature of the subvolcanic hydrothermal system.     

Chemical reaction diversity of geofluids revealed by hydrothermal experiments under sub- and supercritical states

Abstract   Hydrothermal experiments of dissolution of granite and quartz with pure water up to 600°C and 60 MPa were carried out in order to evaluate chemical reaction under sub- and supercritical conditions. The supercritical region beyond the critical point for water has been inferred to be a homogeneous state, which does not correspond to either a true liquid phase, or a true vapor phase. Results of dissolution experiments of granite and quartz in a supercritical state (artificially defined as higher pressures and temperatures than the critical point), show this fluid can be subdivided into two apparent phases comprising a 'liquid-like' region and a 'vapor-like' region. Chemical phenomena with respect to dissolution reactions in the 'liquid-like' region are more similar to those of subcritical water, whilst those reactions in the 'vapor-like' region even in the supercritical state are considered to be weak. The critical point of various kinds of geofluids, composed of solutions in the H₂O-CO₂-NaCl system was experimentally determined using a visible type autoclave. Chemical reaction diversity, depending on location of the critical point for a given solution and apparent phase boundary in terms of chemical reaction within the supercritical state, was recognized by hydrothermal experiments.     

S-33 constraints on the seawater sulfate contribution in modern seafloor hydrothermal vent sulfides

Sulfide sulfur in mid-oceanic ridge hydrothermal vents is derived from leaching of basaltic-sulfide and seawater-derived sulfate that is reduced during high temperature water rock interaction. Conventional sulfur isotope studies, however, are inconclusive about the mass-balance between the two sources because ³⁴S/³²S ratios of vent fluid H₂S and chimney sulfide minerals may reflect not only the mixing ratio but also isotope exchange between sulfate and sulfide. Here, we show that high-precision analysis of S-33 can provide a unique constraint because isotope mixing and isotope exchange result in different Δ³³S (≡δ³³S-0.515 δ³⁴S) values of up to 0.04‰ even if δ³⁴S values are identical. Detection of such small Δ³³S differences is technically feasible by using the SF₆ dual-inlet mass-spectrometry protocol that has been improved to achieve a precision as good as 0.006‰ (2σ).Sulfide minerals (marcasite, pyrite, chalcopyrite, and sphalerite) and vent H₂S collected from four active seafloor hydrothermal vent sites, East Pacific Rise (EPR) 9-10°N, 13°N, and 21°S and Mid-Atlantic Ridge (MAR) 37°N yield Δ³³S values ranging from −0.002 to 0.033 and δ³⁴S from −0.5‰ to 5.3‰. The combined δ³⁴S and Δ³³S systematics reveal that 73 to 89% of vent sulfides are derived from leaching from basaltic sulfide and only 11 to 27% from seawater-derived sulfate. Pyrite from EPR 13°N and marcasite from MAR 37°N are in isotope disequilibrium not only in δ³⁴S but also in Δ³³S with respect to associated sphalerite and chalcopyrite, suggesting non-equilibrium sulfur isotope exchange between seawater sulfate and sulfide during pyrite precipitation. Seafloor hydrothermal vent sulfides are characterized by low Δ³³S values compared with biogenic sulfides, suggesting little or no contribution of sulfide from microbial sulfate reduction into hydrothermal sulfides at sediment-free mid-oceanic ridge systems. We conclude that ³³S is an effective new tracer for interplay among seawater, oceanic crust and microbes in subseafloor hydrothermal sulfur cycles.     

Oxygen isotopic and chemical compositions of cosmic spherules collected from the Antarctic ice sheet: Implications for their precursor materials

Bulk chemical compositions and oxygen isotopic compositions were analyzed for 48 stony cosmic spherules (melted micrometeorites) collected from the Antarctic ice sheet using electron- and ion-microprobes. No clear correlation was found between their isotopic compositions and textures. The oxygen isotopic compositions showed an extremely wide range from −28‰ to +93‰ in δ¹⁸O and from −21‰ to +13‰ in Δ¹⁷O. In δ¹⁸O-δ¹⁷O space, most samples (38 out of 48) plot close to the terrestrial fractionation line, but 7 samples plot along the carbonaceous chondrite anhydrous mineral (CCAM) line. Three samples plot well above the terrestrial fractionation line. One of these has a Δ¹⁷O of +13‰, the largest value ever found in solar system materials. One possible precursor for this spherule could be ¹⁶O-poor planetary material that is still unknown as a meteorite. The majority of the remaining spherules are thought to be related to carbonaceous chondrites.     

Estimation of methane emission from whole waste landfill site using correlation between flux and ground temperature

A methodology to estimate a methane emission in a waste landfill site was developed. The methane flux at a waste landfill site in summer, autumn, and winter was within the following ranges: from −1.3×10⁻² to 16, from −6.4×10⁻² to 7.5, and from −1.6×10⁻³ to 1.5×10⁻² g-CH₄ m⁻² h⁻¹, respectively. In those seasons, the mean methane emission rate and coefficient of variation were 1.1 g-CH₄ m⁻² h⁻¹ ±290%, 0.57 g-CH₄ m⁻² h⁻¹ ±347%, and 5.4×10⁻² g-CH₄ m⁻² h⁻¹ ±370%, respectively. These results simultaneously showed that fluctuations of methane emission from the landfill surface were both of spatial and temporal variability. In each season, an exponential relationship was observed between the methane flux density and the ground temperature. Total methane emissions were estimated to be 5.7×10⁻², 7.1×10⁻³, and 1.7×10⁻³ g-CH₄ m⁻² h⁻¹ in the summer, autumn, and winter surveys, respectively, using a temperature surrogated-kriging method. The results of this study would improve upon the labor-intensive closed-chamber method, and could be a more practical way to estimate methane emissions from waste landfills.     

THE RELATIONSHIP BETWEEN THE MOVEMENT OF THE MEIYU/BAIU RAIN BELT AND THE PERIODIC NORTHWESTWARD PROPAGATION OF THE CONVECTIVE ACTIVITY FROM TROPICAL WEST PACIFIC*

In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,a diagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We found that (1) when the tropical convective activity moves westward to 10.5-15.5'N/140°E from east side of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)the main factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thought as the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific.Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics could sometimes shift Baiu rain belt southward;(3) the onsets of Meiyu in China of both cases tend to take place just when the convective activity around lower latitudes moves westward through about 140°E with the 8,18 and 30 day oscillation periods firstly coming to June.