Clay Minerals in an Active Hydrothermal Field at Iheya‐North‐Knoll,Okinawa Trough

Iheya‐North‐Knoll is one of the small knolls covered with thick sediments in the Okinawa Trough back‐arc basin. At the east slope of Iheya‐North‐Knoll, nine hydrothermal vents with sulfide mounds are present. The Integrated Ocean Drilling Program (IODP) Expedition 331 studied Iheya‐North‐Knoll in September 2010. The expedition provided us with the opportunity to study clay minerals in deep sediments in Iheya‐North‐Knoll. To reveal characteristics of clay minerals in the deep sediments, samples from the drilling cores at three sites close to the most active hydrothermal vent were analyzed by X‐ray diffraction, scanning electron microscope and transmission electron microscope. The sediments are classified into Layer 0 (shallow), Layer 1 (deep), Layer 2 (deeper) and Layer 3 (deepest) on the basis of the assemblage of clay minerals. Layer 0 contains no clay minerals. Layer 1 contains smectite, kaolinite and illite/smectite mixed‐layer mineral. Layer 2 contains chlorite, corrensite and chlorite/smectite mixed‐layer mineral. Layer 3 is grouped into three sub‐layers, 3A, 3B and 3C; Sub‐layer 3A contains chlorite and illite/smectite mixed‐layer mineral, sub‐layer 3B contains chlorite/smectite and illite/smectite mixed‐layer minerals, and sub‐layer 3C contains chlorite and illite. Large amounts of di‐octahedral clay minerals such as smectite, kaolinite, illite and illite/smectite mixed‐layer mineral are found in Iheya‐North‐Knoll, which is rarely observed in hydrothermal fields in mid‐ocean ridges. Tri‐octahedral clay minerals such as chlorite, corrensite and chlorite/smectite mixed‐layer mineral in Iheya‐North‐Knoll have low Fe/(Fe + Mg) ratios compared with those in mid‐ocean ridges. In conclusion, the characteristics of clay minerals in Iheya‐North‐Knoll differ from those in mid‐ocean ridges; di‐octahedral clay minerals and Fe‐poor tri‐octahedral clay minerals occur in Iheya‐North‐Knoll but not in mid‐ocean ridges.     

Study of the initiation and propagation of excavation damaged zones around openings in argillaceous rock

The study of the creation and evolution of the excavation disturbed zone (EDZ) in argillaceous rocks is a major issue for the safety of nuclear wastes underground repositories. In this context, the argillaceous Tournemire site has provided a unique opportunity to study the evolution of the EDZ with time thanks to the existence of three openings of different ages. A thorough characterization of the EDZ has been conducted by different means such as visual observation, analysis of samples extracted from drilled boreholes, EDZ permeability measurements, etc. On the basis of these measurements, a conceptual model of the EDZ initiation and propagation at the Tournemire site has been proposed. In order to validate this model, numerical simulations of increasing complexity have been carried out. In a first attempt, the response of the rock mass to the excavation phase, followed by seasonal cyclic variations of temperature and relative humidity inside the opening, has been simulated by means of a purely mechanical analysis, using a simple elastic material model. The EDZ has been estimated by post-processing the calculated stress states, using a Mohr–Coulomb failure criterion. The results obtained show that no EDZ could be predicted unless adopting a low cohesion value for the rock mass. Moreover, the deferred nature of the EDZ formation in Tournemire could not be reproduced. These limitations have then been suppressed by using a coupled viscoplastic-damaging mechanical model, the parameters of which have been identified from different laboratory experiments. With this model, a time evolution of the EDZ could be predicted, but the EDZ pattern could not match the one observed in situ. Finally, in view of the importance of the hydraulic couplings, unsaturated hydro-mechanical calculations have been carried out to investigate the effect of the numerous seasonal variations cycles and the resulting shrinkage.     

Particle-Image Velocimetry Measurements of Separation and Re-attachment of Airflow over Two-Dimensional Hills with Various Slope Angles and Approach-Flow Characteristics

Airflow over two-dimensional hills was investigated in a wind tunnel using particle image velocimetry. We focus on the flow separation behaviour. A trapezoidal hill shape was used in most of the experimental runs, but the critical slope angle for flow separation was approximately the same as that established for smooth hill shapes. The re-attachment point of the separated flow became farther from the hill as the slope angle $\theta $ increased, reaching a saturation of about seven times the hill height for $\theta \gtrsim 60^\circ $ . Increasing the upwind surface roughness length was found to suppress flow separation. This tendency is analogous to the previous experimental results for turbulent boundary layers on flat plates. The boundary-layer thickness varied by the presence or absence of Counihan-type spires and a castellated fence at the test-section entrance had negligible effect on the flow separation.     

Seismotectonics of the Median Tectonic Line in southwest Japan: Implications for coupling among major fault systems

The relationship between the slip activity and occurrence of historical earthquakes along the Median Tectonic Line (MTL), together with that of the fault systems extending eastward has been examined. The MTL is divided into three segments, each containing diagnostic active faults. No historical earthquakes have been recorded along the central segment, although the segment has faster Quaternary slip rates compared with the other segments that have generated historical earthquakes. This discrepancy between earthquake generation and slip rate can be explained by a microplate model of southwest Japan. The microplate model also provides spatial and temporal coupling of slip on adjacent fault systems. In the context of this model, slip on adjacent faults reduces the normal stress on the MTL. Historical data and paleoseismic evidence indicate that slip on this segment occurs without significant strong ground motion. We interpret this as indicating anomalously slow seismic slip or aseismic slip. Slip on the central segment of the MTL creates transpressional regions at the eastern and western segments where historical earthquakes were recorded. Alternatively, the earthquakes at the eastern and western segments were triggered and concentrated shear stress at the edge of the segments resulted in postseismic slip along the central segment. The sequence of historical events suggests that the MTL characteristically does not produce great earthquakes. The microplate model also provides a tectonic framework for coupling of events among the MTL, the adjacent fault systems and the Nankai trough.     

Metal phases in ordinary chondrites: Magnetic hysteresis properties and implications for thermal history

Magnetic properties are sensitive proxies to characterize FeNi metal phases in meteorites. We present a data set of magnetic hysteresis properties of 91 ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite (both in the cloudy zone as single‐domain grains, and as larger multidomain grains in plessite and in the rim of zoned taenite) dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. The bulk metal contents derived from magnetic measurements are in agreement with those estimated previously from chemical analyses. We evidence a decreasing metal content with increasing petrologic type in ordinary chondrites, compatible with oxidation of metal during thermal metamorphism. Types 5 and 6 ordinary chondrites have higher tetrataenite content than type 4 chondrites. This is compatible with lower cooling rates in the 650–450 °C interval for higher petrographic types (consistent with an onion‐shell model), but is more likely the result of the oxidation of ordinary chondrites with increasing metamorphism. In equilibrated chondrites, shock‐related transient heating events above approximately 500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism and high cooling rates (e.g., following shock reheating or excavation after thermal metamorphism). Our data strengthen the view that the poor magnetic recording properties of multidomain kamacite and the secondary origin of tetrataenite make equilibrated ordinary chondrites challenging targets for paleomagnetic study.     

Deep Flows on the Slope Inshore of the Kuril-Kamchatka Trench Southeast off Cape Erimo, Hokkaido

Deep flows on the slope inshore of the Kuril-Kamchatka Trench southeast off Cape Erimo, Hokkaido were observed for about five years from June 1989 to March 1995, using a mooring system with two current meters. In 1991 and 1993 directionally stable southwestward flows were observed at the upper layer (1000 m). These appear to be typical of the Oyashio because the characteristics of the flows were high mean kinetic energy, low eddy energy and high stability. However, the magnitudes of other mean flows at the upper layer, except for 1991 and 1993, were less than their standard deviations. This suggests that the Oyashio was observed for only a limited period of time. On the other hand, at the lower layer (3000 m) the magnitudes of the mean flows for 10–11 months were 1–3 cm s^-1 and ellipses of their eddy kinetic energy were extremely flattened in the direction of the local isobath. The directions of the mean flows in 1990, 1991 and 1993 were southwestward along the local isobath. The relationships between the upper and the lower flows are discussed in terms of monthly change of kinetic energy, since the low-frequency fluctuations longer than 30-day are predominant from the eddy kinetic energy spectra. The results show that there are cases when the kinetic energy of the monthly mean flows at the lower layers are larger than those at the upper layers. This suggests the possibility that the lower flows are in part a southward deep western boundary current.     

Direct measurements of mid-depth circulation in the Shikoku basin by tracking SOFAR floats

Mid-depth circulation of the Shikoku Basin was measured by tracking four SOFAR floats drifting at the 1,500 m layer. Two floats were released on 17 April 1988 at 30°N, 135°59E and tracked for 433 days. Another two were released on 3 November 1988 at 29°52N and 133°25E, and tracked for 234 days. Two floats flowed clockwise around the Shikoku Warm Water Mass with a diameter of 400 km centered at 31°N and 136°E and a mean drift speed of 4.5 cm sec^–1. One of the floats showed about ten counterclockwise rotations with a period of about 8 days and a maximum speed of 80 cm sec^–1 in the sea area west to the Izu Ridge. In the east to Kyushu, a southward flow was observed under the northward flowing Kuroshio. The southward flow of 4 cm sec^–1 drift speed was considered to be a part of the counterclockwise circulation at deep layers along the perimeter of the Shikoku Basin. One float remained for 234 days in a limited area of 100 km by 150 km in the western part of the basin.     

Phase transition of potassium sulfate,K2SO4 (III); thermodynamical and phenomenological study

The orthorhombic-hexagonal phase transition of K₂SO₄ has been investigated by measurements of the temperature dependencies of the specific heat, expansion, and X-ray intensity of superstructure reflections, correlated with the structural point of view. The values of the net enthalpy and entropy changes are ΔH=4.28 KJ/mol and ΔS=4.98 J/mol·K at the phase transition temperature (587°C), respectively. The thermal expansion along the c axis shows strong anisotropic character above about 300°C and exhibits a very large discontinuous increase at 587°C, whereas those along the a and b axes increase linearly and exhibit small discontinuous decreases at 587°C. The X-ray intensity of superstructure reflections in the low-temperature form gradually decrease with increasing temperature, and come to extinction at 587°C, exhibiting a discontinuity. The observed entropy change and pressure dependence of the phase transition temperature were explained successfully by the use of results of the structural analysis and measured physical properties. The temperature dependencies of the spontaneous strain, X-ray intensity of superstructure reflection, and birefringence were consistently described by introducing a transition parameter on the basis of an instability at the M point in the Brillouin zone of the hexagonal phase.     

Phosphorus content of zooplankton from the Inland Sea of Japan

Measurements of phosphorus content were made for eleven species of copepods, two species of mysids, shrimps (including mysis stage) and chaetognaths, and one species ofNoctiluca, cirriped (naupliar stage) and crab (zoeal stage) from the Inland Sea of Japan. The body phosphorus content (P, inµg) is highly correlated to prosome length (L, inµm) for copepods, which is expressed as logP=2.90 ×logL–9.34. Mean phosphorus content expressed as percent of dry weight is 1.30% for copepods, 1.39% for mysids, 0.63% for a decapod shrimpAcetes japonicus, and 0.80% for chaetognaths.Noctiluca contains phosphorus of only 0.36%. The comparatively higher phosphorus content of suspension-feeding copepods may be related to the constant supply of phosphorus-rich phytoplankton in this region.     

Construction of a genomic DNA library with a TA vector and its application in cloning of the phytoene synthase gene from the cyanobacteriumSpirulina platensis M-135

INTRODUCTIONThesignalproaningschemeofmostpnsentsonarsyStasuChaseChosounder,fishfinder,etc.,deteCtsthesignaIsaanrdingt0theamPlitudethasholdafterthefilter.However,inacomplicatalandfrequenhychangingunderotCfacousticalchanne,thesta-bilityandreiabilityofthiskindofsonarsySteIndroeshamlyasanysySthenoisewhleadt0anindedion.AmplitudefaderesultingfromstrongsignalfluCtuationcauseslossofdata.InsomesyStetnS,suchasndnelocatingsonar,highrangingamCyisneded,soasinglededionschernecann0tadapttoit.Resul…