Sequentially sampled gas hydrate water,coupled with pore water and bottom water isotopic and ionic signatures at the Kukuy mud volcano,Lake Baikal: ambiguous deep-rooted source of hydrate-forming water

The isotopic and ionic composition of pure gas hydrate (GH) water was examined for GHs recovered in three gravity cores (165–193 cm length) from the Kukuy K-9 mud volcano (MV) in Lake Baikal. A massive GH sample from core St6GC4 (143–165 cm core depth interval) was dissociated progressively over 6 h in a closed glass chamber, and 11 sequentially collected fractions of dissociated GH water analyzed. Their hydrogen and oxygen isotopic compositions, and the concentrations of Cl^– and HCO₃ ^– remained essentially constant over time, except that the fraction collected during the first 50 minutes deviated partly from this pattern. Fraction #1 had a substantially higher Cl^– concentration, similar to that of pore water sampled immediately above (135–142 cm core depth) the main GH-bearing interval in that core. Like the subsequent fractions, however, the HCO₃ ^– concentration was markedly lower than that of pore water. For the GH water fractions #2 to #11, an essentially constant HCO₃ ^–/Cl^– ratio of 305 differed markedly from downcore pore water HCO₃ ^–/Cl^– ratios of 63–99. Evidently, contamination of the extracted GH water by ambient pore water probably adhered to the massive GH sample was satisfactorily restricted to the initial phase of GH dissociation. The hydrogen and oxygen isotopic composition of hydrate-forming water was estimated using the measured isotopic composition of extracted GH water combined with known isotopic fractionation factors between GH and GH-forming water. Estimated δD of ?126 to ?133‰ and δ¹⁸O of ?15.7 to ?16.7‰ differed partly from the corresponding signatures of ambient pore water (δD of ?123‰, δ¹⁸O of ?15.6‰) and of lake bottom water (δD of ?121‰, δ¹⁸O of ?15.8‰) at the St6GC4 coring site, suggesting that the GH was not formed from those waters. Observations of breccias in that core point to a possible deep-rooted water source, consistent with published thermal measurements for the neighboring Kukuy K-2 MV. By contrast, the pore waters of core St6GC4 and also of the neighboring cores GC2 and GC3 from the Kukuy K-9 MV show neither isotopic nor ionic evidence of such a source (e.g., elevated sulfate concentration). These findings constrain GH formation to earlier times, but a deep-rooted source of hydrate-forming water remains ambiguous. A possible long-term dampening of key deep-water source signatures deserves further attention, notably in terms of diffusion and/or advection, as well as anaerobic oxidation of methane.     

Behavior of warm water flowing into a cold ocean

Behavior of warm water flowing into a model ocean with flat bottom filled with cold water is investigated numerically with a three-dimensional level model in a rotating system.The warm water which flows through the southern opening into the ocean is found to progress in two directions. The east front of the warm water progresses along the east coast and reaches the northern opening. And an eastern boundary current associated with this density structure is formed. The west front progresses along the west coast with the speed much less than that of the eastside front. However, the progression of the west front slows down remarkably half way between the southern and northern boundaries due to-effect, and a baroclinic western boundary current system is formed. Unstable waves whose scales are 200–400 km are found in the region of the eastern boundary current and propagate toward the west. These waves seem to be caused by the baroclinic instability.The boundary currents obtained in the present model are considered to represent some characteristics of the Tsushima Current system in the Japan Sea.     

Hydraulic and numerical study on the generation of a subaqueous landslide-induced tsunami along the coast

By carrying out the hydraulic experiments in a one-dimensional open channel and two-dimensional basin, we clarified the process of how a landslide on a uniform slope causes the generation of a tsunami. The effect of the interactive force that occurs between the debris flow layer and the tsunami is significant in the generation of a tsunami. The continuous flow of the debris into the water makes the wave period of the tsunami short. The present experiments apply numerical simulation using the two-layer model with shear stress models on the bottom and interface, and the results are compared. The simulated debris flow shows good agreement with the measured results and ensures the rushing process into the water. We propose that the model use a Manning coefficient of 0.01 for the smooth slope and 0.015 for the rough slope, and a horizontal viscosity of 0.01 m²/s for the landslide; an interactive force of 0.2 for each layer is recommended. The dispersion effect should be included in the numerical model for the propagation from the shore.     

Theoretical analysis of luminosity drop in red giant branch evolution

Recent evolutionary computations of stars in the globular clusters show that the star ascending up the red giant branch decreases its luminisity temporarily when the outward advancing hydrogen-burning shell passes over the discontinuity in the chemical compositions, which is the trace of maximum inward penetration of the convective envelope in the previous subgiant stage. To understand the physical circumstance of this luminosity drop, the semi-analytical approach using the classical red giant model was applied. The difference of the present analysis from those with usual models of the red giant is that the gradient and the discontinuity in the hydrogen profile, which were usually neglected in the classical red giant model, in the region into which the hydrogen-burning shell advances were taken into account explicitly. It was found that the luminosity would always drop at the critical stage, the stage when the hydrogen-burning shell just passes over the discontinuity. It was also pointed out that the luminosity drop depends on the time step chosen for constructing the stellar evolutionary models and computations with crude time step would fail to catch up this phenomenon.     

A 100 m laser strainmeter system installed in a 1 km deep tunnel at Kamioka, Gifu, Japan

We have installed a laser strainmeter system in a deep tunnel about 1,000 m below the ground surface at Kamioka, Gifu, Japan. The system consists of three types of independent interferometers: (1) an EW linear strainmeter of the Michelson type with unequal arms, (2) an NS-EW differential strainmeter of the Michelson type with equal arms and (3) a NS absolute strainmeter of the Fabry–Perot type. These are configured in L-shaped vacuum pipes, each of which has a length of 100 m. (1) and (2) are highly sensitive (order of 10⁻¹³ strain) and have wide dynamical range (10⁻¹³–10⁻⁶). Observations with strainmeters (1) and (2) started on June 11, 2003. (3) is a new device for absolute-length measurements of the order of 10⁻⁹ of a long-baseline (100 m) Fabry–Perot cavity by the use of phase-modulated light. This third strainmeter will be ready for operation before the end of 2004. The laser source of strainmeters (1) and (2) is a frequency-doubled YAG laser with a wavelength of 532 nm. The laser frequency is locked onto an iodine absorption line and a stability of 2 × 10⁻¹³ is attained. The light paths of the laser strainmeter system are enclosed in SUS304 stainless steel pipes. The inside pressure is kept to be 10⁻⁴ Pa. Consequently, quantitative measurement of crustal strains of the order of 10⁻¹³ can be attained by employing the laser strainmeter system of (1) and (2) at Kamioka. This resolving power corresponds to that of a superconducting gravimeter. Using the laser strainmeter system, we expect to determine parameters related to fluid core resonance, core modes and core undertone as well as other geodynamic signals such as slow strain changes caused by silent earthquakes or slow earthquakes.     

激光雷达在沙尘观测中的应用——2004年春季北京和呼和浩特沙尘天气的解析

2004年春季（2003年12月至2004年5月）利用激光雷达在北京和呼和浩特对沙尘天气进行了连续观测。利用激光雷达的数据导出了沙尘和大气污染物气溶胶消光系数的关系,对两个地点的沙尘天气特征和大气污染特征进行了探讨。该期间在呼和浩特观测到较大型的沙尘事件（消光系数大于0.3·km-1）有9次,这些起源于蒙古国/内蒙古的沙尘事件晚于呼和浩特6~10 h在北京被观测到。在呼和浩特观测到的沙尘云块的高度普遍较低（由地表至高空1~2 km）,而在北京较高一般可达到2~4 km,同一沙尘事件的最高浓度（消光系数）是呼和浩特高于北京。在北京观测到的沙尘天气共有17次,其中包括数次小规模的沙尘事件在呼和浩特未观测到。从北京及呼和浩特的观测结果可以看出,北京地区3~5月沙尘的背景浓度高于呼和浩特,北京地区具有明显的区域规模大气污染特征,而呼和浩特只具有局部规模的大气污染特征。     

Methane in the western North Pacific

The concentration of methane in about 400 seawater samples collected in the western North Pacific, mostly from 40°N to 5°S along 165°E was determined. While the concentration of methane in the surface water was slightly greater in the high-latitudes, it did not widely vary with a standard deviation of 0.29 n mol/l for a mean value of 2.49 n mol/l. The 90% confidence limit of the mean was 0.08 n mol/l. The degree of oversaturation in 1991 (31±4%) was not different from that in circa 1970. If we assume that this degree of oversaturation occurs in the entire oceans, the annual flux of methane becomes 6×10¹²g CH₄. Both the concentrations of methane and chlorophylla were higher in the surface 100 m layer. However, the correlation between them was not well in the entire surface waters. This may indicate that the production of methane is not directly related to the photosynthetic process. The concentration of methane decreased gradually with increasing depth down to 1000 m. Its horizontally and vertically uniform concentration in the abyssal water suggests that the turnover time of methane in the oxic pelagic water is in the range between a few years and a few hundred years.     

Timing of the cataclastic deformation along the Akaishi Tectonic Line,central Japan

This paper describes K-Ar ages of cataclasites and fault gouges from the Akaishi Tectonic Line (ATL), central Japan. Petrological and mineralogical features of these rocks are also examined. Based on the results, we test the hypothesis that the K-Ar ages of these rocks represent the age of hydrothermal alteration associated with the fault movement. Intensity of deformation and alteration increase passing from host rock into cataclasite and finally into fault gouge. This increase corresponds to an increase of the value of crystallinity index (Kübler index) of the micaceous minerals contained in these rocks. Furthermore, the degree of rejuvention of K-Ar ages of the micaceous minerals increases in the same sense. A correlation of K-Ar ages (plotted on the y axis) versus Kübler index (plotted on the x axis) yields a concave curve asymptotically parallel with the x axis at approximately 15 Ma. This curve is interpreted to represent the mode of decrease of the relative amounts of inherited argon in the K-Ar system of the micaceous minerals, corresponding to an increase in the intensity of deformation and alteration. Inclination of the curve becomes zero if all the inherited argon is lost from the K-Ar system of the micaceous minerals. Thus, it is concluded that the hydrothermal alteration occurred at approximately 15 Ma. The strike-slip basin along the ATL formed the middle Miocene. The K-Ar dating of ATL gouges indicates that the ATL was active simultaneously with formation of the strike-slip basin along its trace during the middle Miocene.