A Late Winter Hydrography in Hidaka Bay, South of Hokkaido, Japan

Hydrographic observations in Hidaka Bay, south of Hokkaido, Japan were carried out in late winter 1996 and 1997 to examine the spatial distributions and circulation features of two different water masses, i.e., Coastal Oyashio Water (COW) and Tsugaru Warm Water (TWW), and their modifications. It is known that COW is mostly composed of cold and low-salinity water of the melted drift ice coming from the Okhotsk Sea and flows into Hidaka Bay from winter to spring and TWW with high-salinity continuously supplies from the Tsugaru Strait to the North Pacific. Cold surface mixed layers (<26.2σ_θ, 0–100 m depth) were found mainly over the shelf slope, confirming that anti-clockwise flow of COW was formed. TWW was relatively high in salinity and low in potential vorticity, and had some patch-like water masses with a temperature and salinity maximum in the limited area in the further offshore at the deeper density levels of 26.6–26.8σ_θ. The fine structure of vertical temperature and salinity profiles appeared between TWW and COW is an indication of enhanced vertical mixing (double-diffusive mixing), as inferred from the estimated Turner angles. At a mouth of the Tsugaru Strait in late winter 1997, a significant thermohaline front between TWW and the modified COW was formed and a main path of TWW spreaded south along the Sanriku coast, probably as the bottom controlled flow. Hence, the patch-like TWW observed in late winter is isolated from the Tsugaru Warm Current and then rapidly modified due to a diapycnal mixing. This revised version was published online in August 2006 with corrections to the Cover Date.     

Soil pore characteristics of evergreen and deciduous forests of the tropical monsoon region in Cambodia

Both evergreen and deciduous forests (Efs and Dfs) are widely distributed under similar climatic conditions in tropical monsoon regions. To clarify the hydraulic properties of the soil matrix in different forest types and their effects on soil water storage capacity, the soil pore characteristics (SPC) were investigated in Ef and Df stands in three provinces in Cambodia. Soils in the Ef group were characterized in common by large amounts of coarse pores with moderate pore size distribution and the absence of an extremely low K_s at shallow depths, compared to Df group soils. The mean available water capacity of the soil matrix (AWC_sm) for all horizons of the Ef and Df group soils was 0·107 and 0·146 m³ m^?3, respectively. The mean coarse pore volume of the soil matrix (CPV_sm) in the Ef and Df groups was 0·231 and 0·115 m³ m^?3, respectively. A water flow simulation using a lognormal distribution model for rain events in the early dry season indicated that variation in SPC resulted in a larger increase in available soil water in Ef soils than in Df soils. Further study on deeper soil layers in Ef and each soil type in Df is necessary for the deeper understanding of the environmental conditions and the hydrological modelling of each forest ecosystem. Copyright © 2010 John Wiley & Sons, Ltd.     

越南东北部Cat Ba岛泥盆系-石炭系过渡层的初探

The Pho Han Formation is exposed on southern Cat Ba Island, Hai Phong Province in northeastern Vietnam, and intercalates the Devonian and Carbonif-erous (D-C) boundary (Ta and Doan, 2007; Komatsu et al., 2012). The D-C boundary section consists mainly of limestone beds, numbered from 1 to 167, interca-lated with alternating black organic-rich shales. The limestone yields abundant brachiopods, crinoid-stems and conodonts. Preliminary investigations on strati-graphy (conodont biostratigraphy and δ13C) and sedi-mentology of beds 113-133 were undertaken in this study.     

Mobilization and speciation of arsenic from hydrothermally altered rock containing calcite and pyrite under anoxic conditions

The effects of water residence time and anoxic conditions on the mobilization and speciation of As in a calcite- and pyrite-bearing altered rock excavated during a road-tunnel project has been evaluated using batch and column laboratory experiments. Higher infiltration rates (i.e., shorter water residence times) enhanced the leaching of As due to the higher pH values of the effluents and more rapid transport of dissolved As through the columns. The concentration of As in the effluent also increased under anoxic conditions regardless of the water residence time. This enhanced leaching of As under anoxic conditions could be attributed to a significant pH increase and decreased Fe oxyhydroxide/oxide precipitation compared to similar experiments done under ambient conditions. Processes that controlled the evolution of pH and the temporal release mechanisms of As under anoxic conditions were identical to those previously observed under ambient conditions: the dissolution of soluble phases, pyrite oxidation, co-precipitation and/or adsorption/desorption reactions. Speciation of As in the column experiments could partly be attributed to the pH-dependent adsorption of As species onto Fe oxyhydroxide/oxide precipitates. Moreover, apparent equilibrium of the total As and As[III] concentrations was delayed under anoxic conditions in both batch and column experiments.     

Tracking flux melting and melt percolation in supra-subduction peridotites (Josephine ophiolite,USA)

Here, we investigate the scale and nature of melting and melt percolation processes recorded by 17 supra-subduction peridotites collected in a ~70 km² area in the northern portion of the Josephine ophiolite (Western USA). We present major and trace element variations in whole rocks; major elements in olivine, orthopyroxene, clinopyroxene and spinel; and trace elements [including rare earth element (REE)] in clinopyroxene and orthopyroxene. In the Josephine peridotites, compositional variability occurs at different scales. On the one hand, large systematic changes from depleted to fertile peridotites occur on large kilometer scales. Field, petrological and geochemical data can be consistently explained if the Josephine mantle experienced variable degrees of hydrous flux melting (10 to >20–23 %), and we argue that small fractions of subduction-derived fluids (0.015–0.1 wt%) were pervasive in the ~70 km² studied area, and continuously supplied during wedge melting. Fluid localization probably led to increased extent of flux melting in the harzburgitic areas. On the other hand, in single outcrops, sharp transitions from dunite to harzburgite to lherzolite and olivine websterite can be found on meter to centimeter scales. Thus, some fertile samples may reflect limited degrees of refertilization at the outcrop scale. In addition, clinopyroxene and orthopyroxene in ultra-depleted harzburgites (Spinel Cr# > 58) show variable degrees of LREE enrichment, which reflect percolation of and partial re-equilibration with, small fractions of boninite melt. Because the enriched samples also show the highest spinel Cr#, we argue that these enrichments are local features connected to the presence of dunite channels nearby. Lastly, trace element concentrations of pyroxenes in Josephine harzburgites show that they are one of the most depleted harzburgites among worldwide ophiolitic peridotites, indicating particularly high degrees of melting, potentially past the exhaustion of clinopyroxene.     

The Hinode (Solar-B) Mission: An Overview

The Hinode satellite (formerly Solar-B) of the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science (ISAS/JAXA) was successfully launched in September 2006. As the successor to the Yohkoh mission, it aims to understand how magnetic energy gets transferred from the photosphere to the upper atmosphere and results in explosive energy releases. Hinode is an observatory style mission, with all the instruments being designed and built to work together to address the science aims. There are three instruments onboard: the Solar Optical Telescope (SOT), the EUV Imaging Spectrometer (EIS), and the X-Ray Telescope (XRT). This paper provides an overview of the mission, detailing the satellite, the scientific payload, and operations. It will conclude with discussions on how the international science community can participate in the analysis of the mission data. T. Kosugi deceased 26 November 2006.     

Bedform response to flow variability

Laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed. The simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated, followed by a short high‐flow period with double the original discharge, during which the morphology of the bedforms adjusts, followed in turn by a relatively long period of the original low discharge. For the grain size and hydraulic conditions selected, the Froude number remains subcritical during the experiment, and sediment moves predominantly as bedload. Observations show rapid development of quasi‐two‐dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low‐flow period. When the flow increases, the bedforms rapidly increase in wavelength and height, as expected from other empirical results. When the flow decreases back to the original discharge, the height of the bedforms quickly decreases in response, but the wavelength decreases much more slowly. Computational results using an unsteady two‐dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high‐flow period. However, the computational model predicts a much slower rate of wavelength increase, and also performs less accurately during the final low‐flow period, where the wavelength remains essentially constant, rather than decreasing. In addition, the numerical results show less variability in bedform wavelength and height than the measured values; the bedform shape is also somewhat different. Based on observations, these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach. Experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process. Assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment‐transport process, which appears to result in predicted bedform wavelength changes smaller than those observed. However, observations also suggest that three‐dimensional effects play at least some role in the decrease of bedform wavelength, so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions. Published in 2011. This article is a US Government work and is in the public domain in the USA.     

A geochemical study on mud volcanoes in the Junggar Basin, China

A comprehensive study was performed to characterize, for the first time, the mud, water, and gases released from onshore mud volcanoes located in the southern margin of the Junggar Basin, northwestern China. Chemical compositions of mud, along with the geology of the basin, suggest that a source of the mud is Mesozoic or Cenozoic shale. Oxygen and H isotope compositions of the released water suggest a local meteoric origin. Combined with the positive Eu anomalies of the water, a large ¹⁸O shift of the water suggests extensive interaction with rocks. Gases discharged from the mud volcanoes are predominantly thermogenic hydrocarbons, and the high δ¹³C values (>+20‰ VPDB) for CO₂ gases and dissolved carbonate in muddy water suggest secondary methanogenesis with CO₂ reduction after oil biodegradation.The enrichments of Eu and ¹⁸O in water and the low thermal gradient of the area suggest that the water-rock interactions possibly occur deeper than 3670 ± 200 m. On the other hand, considering the relationship to the petroleum reservoir around the mud volcanoes, the depth of the gases can be derived from about 3600 m, a depth that is greater than that generally estimated for reservoirs whose gas is characterized by ¹³C-enriched CO₂. Oil biodegradation with CO₂ reduction likely occurs at a shallower depth along the seepage system of the mud volcano. The results contribute to the worldwide data set of gas genesis in mud volcanoes. Moreover, they further support the concept that most terrestrial mud volcanoes release thermogenic gas produced in very deep sediments and may be early indicators of oil biodegradation, an important problem in the petroleum industry.