Spectrophotometric Determination of Zirconium in Thirty-one Geochemical Reference Samples with Xylenol Orange

The zirconium content of 31 geochemical reference samples has been determined by a spectrophotometric method with Xylenol orange after sample decomposition by acid digestion and alkali fusion. The agreement between the present results and published data is generally good.     

Tree ring information and rainfall characteristic for landslide in the Kobe District,Japan

Heavy rainfall on the south side of the Rokko Mountains has often caused severe landslides and debris flows. Analysis of the annual summation of rainfall in excess of 100 mm/day shows that the rainfall in this area has dominant periodicities of about 25–30, 10–13, and 5–7 years. The period of about 25–30 years corresponds to that of occurrence of the natural disasters produced by heavy rainfall; years when the maximum rainfall correspond to years when there have been severe landslides and debris flows in the area. Temporal change in this rainfall may provide a first approximation for erosional force. Analyses of tree ring width from these mountains indicate that the sequences have a dominant periodicity of about 25–30 years. Cross-spectral analyses for rainfall and ring width in this area show high coherency for the periods of about 25–30 years; evidence that variations in the ring width may be used as proxy data for erosional force.     

Along-arc lateral variation of Rb−Sr and K−Ar ages of Cretaceous granitic rocks in Southwest Japan

Cretaceous granitic rocks were emplaced over a distance of 700 km along arc in Southwest Japan. Rb–Sr and K–Ar ages of a major group of these granitic rocks, with ilmenite series ore mineralogy, were examined. Rb–Sr whole rock ages of 92.8±4.0 Ma and Rb–Sr and K–Ar biotite ages of 80–88 Ma were obtained on one group of these granitic rocks from Kamo-Sera area of central Hiroshima Prefecture. The K–Ar ages of various minerals, combined with the Rb–Sr whole-rock age, give a smooth cooling curve, which suggests a 5 to 10 Ma time-lag between intrusion and cooling at 300° C for the Cretaceous granitic rocks. The Rb–Sr whole-rock and Rb–Sr/K–Ar biotite ages of these granitic rocks become younger eastward along the Southwest Japan arc, and the time-lag between the two systems remains constant at 5 to 10 Ma over the entire area. The along-arc age variation does not support the genetical relationship of the Cretaceous granitoids with steady-state subduction. The Cretaceous granitic province at the eastern margin of Eurasian continent was, at least partly, formed by an episodic event such as ridge subduction.     

Distribution of the subsurface chlorophyll maximum and its nutrient-light environment in and around the Euroshio off Japan

Continuous distribution of the subsurface chlorophyll maximum (SCM) was confirmed in the Kuroshio and neighbouring areas in observations at 15 to 40 km intervals. Chlorophyll amounts occurring in and immediately around the SCM constituted 60 to 80% of the total chlorophyll in the water column above the 1% light level. The SCM zone received 1 to 10% of the surface irradiance at its center and contained sufficient macronutrients to support approximately one doubling of the existing phytoplankton biomass at most stations. There were several stations where there were higher nutrient concentrations that would support more than one doubling of the existing biomass around the SCM zone, and this was interpreted as resulting from uplift of the SCM zone due to upwelling.     

Water masses and hydrography in the tropical Pacific during Japanese Pacific Climate Study '91 cruise

Hydrographic measurements by CTD were made in the western-central Equatorial Pacific (160°W–147°E) during the Japanese Pacific Climate Study cruise in January–February 1991. InT-S diagram, three water masses are seen in the layer of kg/m³: salinity water corresponding to the Tropical Water of eastern South Pacific origin, less saline water in the North Pacific, and water with salinity between the above two, found on the equator. In three meridional sections (160°W–160°E), the Tropical Water of eastern South Pacific origin extends further equatorward than the climatological data of Levitus (1982).     

Influence of submarine fumaroles on the distribution of mercury in the sediment of Kagoshima Bay,Japan

To estimate the influence of mercury emitted from submarine fumaroles, the horizontal and vertical distribution of mercury in sediment of Kagoshima Bay was studied. The fumaroles are located in the northern bay head area, and the sediment samples had been taken from 52 points throughout the bay with a gravity core sampler. The core samples obtained were cut at a thickness of 1–2 cm and used for measurements. The total concentration of mercury in surface sediment in the northern and central areas of the bay was 51–679 μg kg^− 1 (average 199 μg kg^− 1, n = 22) and 23–100 μg kg^− 1 (average 55 μg kg^− 1, n = 30), respectively. The highest value was obtained in the vicinity of the fumaroles. The mercury concentration in sediment near the fumaroles varied with depth, which may reflect the variation in fumarolic activity. A successive extraction method was applied to the speciation of mercury in the sediment. The results showed that sediment taken in the vicinity of submarine fumaroles contained a higher percentage of mercury bound with organic matter.