Dirunal variability and its quantification of subsurface sound scatterers in the western equatorial Pacific

A downwardf-looking acoustic Doppler current profiler (ADCP), suspended by a series of surface and subsurface floats and connecte to an anchroed ship, proided a quite stable platform to measure the, vertical profiles of backscatter strenght *BS) and three components of the velocith from 12 to 22 November 1992 at 1°30S and 156°15E, in the Intensive Flux Array (IFA) of TOGA/COARE. While the variability of the horizontal velocity was controlled by the semi-diurnal tide, BS and vertifal velocity were dominated by diurnal variability probably caused by the diel migration of zooplakton. The downward migration occurred early in the moring (0500–0700 in local time) and the upward one late in the afternoon (1700–1900). The average values of about 4 cm s^–1 for the sinking and rising speed were estimated from Doppler shift and BS isopleth displacement. The subsurface chlorophyll maximum (SCM) coincident with the top of the thermocline at 80–100 m was also detectable in the BS data during daytime when almost no migrating zooplankton remained in the upper 300 m. Backscatter signals from the SCM and thermocline were separated by corrlating the BS data with the chlorophylla and temperature data. The maximum contribution of the migrating zooplanktion, passively drifting phytoplankton and temperature gradient on BS was estimated to be 14.8, 7.0, 5.1 dB, respectively.     

Wells turbine with end plates for wave energy conversion

In order to improve the performance of the Wells turbine for wave energy conversion, the effect of end plate on the turbine characteristics has been investigated experimentally by model testing. As a result, it is found that the characteristics of the Wells turbine with end plates are superior to those of the original Wells turbine, i.e., the turbine without end plate and the characteristics are dependent on the size and position of end plate. Furthermore, by using a computational fluid dynamics (CFD), reason of the performance improvement of the turbine has been clarified and the effectiveness of the end plate has been demonstrated.     

Mesoscale eddy effects on temporal variability of surface chlorophyll a in the Kuroshio Extension

We investigated the relationship between chlorophyll a (Chl-a) concentrations estimated from satellite observations and the activity of eddies in the Kuroshio Extension region. High (low) area-averaged Chl-a concentrations were frequently observed in the core of cyclonic (anticyclonic) eddies. Such relationships between Chl-a concentrations and eddy cores were not frequently observed in the southern part of the recirculation gyre, and advection of background meridional gradient of Chl-a by eddy-edge currents accounted for Chl-a spatial variability. Decadal-scale changes of Chl-a concentrations around the Kuroshio Extension were strongly affected by eddy activity and transport but not by large-scale near-surface isopycnal heaving. We also found that decadal changes of nutrient concentrations near the main stream could affect Chl-a concentrations in the southern part of the recirculation gyre via southward transport of eddies and mean flow.     

Comparison of community structures between particle-associated and free-living prokaryotes in tropical and subtropical Pacific Ocean surface waters

The subtropical and tropical regions of the Pacific Ocean are less productive than other oceanic regions. Although particle association should be an important strategy for heterotrophic prokaryotes to survive in such environments, we have little information on particle-associated (PA) prokaryotes in these regions. The specific aim of this study was to determine bacterial and archaeal community structures in the PA assemblage in comparison to the free-living (FL) assemblage in the North Pacific Subtropical Gyre, the South Pacific Subtropical Gyre, and an eastern equatorial region of the Pacific Ocean. Community profiles and phylogenetic identities were obtained by denaturing gradient gel electrophoresis, 454-pyrosequencing, and cloning followed by Sanger sequencing of 16Sr RNA gene amplicons. The distribution patterns of some abundant groups in three regions and two lifestyles (PA and FL) are shown in this study. Also, the PA community structures of bacteria differed from the FL ones and exhibited higher diversity than the FL ones, while the archaeal community structures did not show significant differences between PA and FL assemblages. We found that specific phylotypes of Gammaproteobacteria and Flavobacteria were abundant in PA bacterial assemblages, suggesting that they prefer to attach and consume particulate organic matter. In summary, the surface seawater PA assemblages represent very different bacterial and archaeal community structures between three different oceanic regions, each of which had distinct PA and FL community structures. These results imply that environmental factors determine microbial community structures.     

Interannual and Decadal Variabilities of NPIW Salinity Minimum Core Observed along JMA’s Hydrographic Repeat Sections

We investigated the variation of the North Pacific Intermediate Water (NPIW) distribution in the western North Pacific, focusing on the intermediate salinity minimum (S < 34.2) core observed along the meridional hydrographic sections including the 137°E repeat section by the Japan Meteorological Agency. This core is a cross-section of a low salinity tongue extending westward along the recirculation in the subtropical gyre. The core size shows remarkable variabilities in interannual and decadal time scales. The salinity change in the density layer during the period of core expansion (shrinking) represents the spatial salinity change in the tongue toward the west (east). Thus, we conclude that the core size variation is associated with the zonal wobble of the tongue having thicker distribution to the east, rather than temporal changes of the water mass itself. The core size at 137°E is well correlated with the meridional gradient of the depth in the isopycnal surface at the salinity minimum representing the recirculation intensity, suggesting a relation with the intensity of the subtropical gyre. A significant lag-correlation between the gradient and the wind forcing over the North Pacific suggests that the first mode baroclinic Rossby waves excited in the central North Pacific propagated westward to change the intensity of the recirculation in interannual time scales. In decadal time scales, it is found that the wind stress curl and heat flux fields in the North Pacific precede the recirculation by about 11 years.     

Kinetics of the graphite–diamond transformation in aqueous fluid determined by in-situ X-ray diffractions at high pressures and temperatures

The graphite-diamond transformation was investigated by in situ time-resolved X-ray diffraction experiments using aqueous fluid containing dissolved MgO as the diamond-forming catalyst under conditions of 6.6–8.9 GPa and 1400–1835 °C. The transformed volume fractions of diamond as a function of time under various pressure-temperature conditions were obtained and analyzed using the JMAK rate equation. Variations in the nucleation and growth processes during diamond formation as a function of pressure and temperature were clarified.     

Subhorizontal boundary between ultrahigh-pressure and low-pressure metamorphic units in the Sulu–Tjube area of the Kokchetav Massif, Kazakhstan

Abstract The Kokchetav Massif of Kazakhstan includes high to ultrahigh-pressure (HP–UHP) metamorphic rocks (some of which were recrystallized at depths in excess of 150 km), juxtaposed against much lower pressure metamorphic components. We investigated the relationship between the HP–UHP metamorphic unit and the low pressure (LP) unit (Daulet Suite) in the Sulu–Tjube area, where the metamorphic rocks have previously been interpreted as constituting a megamelange with subvertical structural attitudes. Analyses of fold structures suggest that the HP–UHP metamorphic unit overlies the LP unit across a west-dipping subhorizontal boundary. In addition, kinematic indicators display top-to-the-north senses of shear along the tectonic contact between the two units, indicating that the HP–UHP unit has been extruded northward onto the LP unit. Following the juxtaposition of the two units, upright folds developed in both units, and these are associated with the previously reported steeply dipping metamorphic foliations. These data have important implications for the mode of exhumation of the UHP rocks from upper mantle to shallow crustal depths.     

Integrated colors of globular clusters

Integrated colors of M3, M5, M13, and M92 are calculated from the luminosity function, the color-magnitude diagram, and the two-color diagram to compare them with observed ones. The results show good agreements for M3, M13, and M92 and the discrepancy for M5. Possible causes for this discrepancy are discussed.To study the way in which integrated colors are affected by changes in the distribution of stars in the color-magnitude diagram, we calculate the integrated colors by taking into account changes in the distribution of horizontal branch stars and in the ratio of the number of horizontal branch stars to that of red giant branch stars. The result shows that (B-V) color varies within the range of about 0.1 mag with changes in the distribution of horizontal branch stars, implying that the cluster with a well-developed blue horizontal branch has bluer intrinsic integrated (B-V) color than that with yellow one. This tendency is compared with observation.     

In situ X-ray observations of the decomposition of brucite and the graphite–diamond conversion in aqueous fluid at high pressure and temperature

 An experimental technique to make real-time observations at high pressure and temperature of the diamond-forming process in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments using synchrotron radiation have been performed upon a mixture of brucite [Mg(OH)₂] and graphite as starting material. Brucite decomposes into periclase (MgO) and H₂O at 3.6 GPa and 1050 °C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150 °C, indicating that the solubility of the MgO component in H₂O greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at 7.7 GPa and 1835 °C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained. Received: 17 July 2001 / Accepted: 18 February 2002