Chemical variations of magmas at Izu-Oshima volcano,Japan: plagioclase-controlled and differentiated magmas

Systematic analyses of the major-element chemistry of products of several eruptions during syn-and post-caldera stages of Izu-Oshima volcano were compiled. Comparisons of the products of large-scale eruptions in 1338?, 1421? and 1777–1778, of intermediate-scale eruptions in 1950–1951 and 1986, and of small-scale eruptions in 1954, 1964 and 1974 clearly show the existence of two types of magmas. One is “plagioclase-controlled” and the other is “differentiated” magma (multimineral-controlled); i.e. the bulk chemistry of the first magma type is controlled by plagioclase addition or removal, while that of the second type is controlled by fractionation of plagioclase, orthopyroxene, clinopyroxene, and titanomagnetite. Eruptions of Izu-Oshima volcano have occurred at the summit and along the flanks. Summit eruptions tap only plagioclase-controlled magmas, while flank eruptions supply both magma types. It is considered unlikely that both magma types would coexist in the same magma chamber based on the petrology. In the case of the 1986 eruption, the flank magma was isolated sometime in the past from the summit magma chamber or central conduit, and formed small magma pockets, where further differentiation occurred due to relatively rapid cooling. In a period of quiescence prior to the 1986 eruption, new magma was supplied to the summit magma chamber, and the summit eruption began. The dike intrusion or fracturing around the small magma pockets triggered the flank eruption of the differentiated magma. This model can be applied to the large-scale flank eruption in 1338(?) which erupted differentiated magmas. In 1421(?), the flank eruption tapped plagioclase-controlled magma. In this case, the isolated magmas from the summit magma chamber directly penetrated the flank without differentiation.     

Variation of the distribution coefficients of rare earth elements in modern coral-lattices: species and site dependencies

Rare earth element (REE) concentrations in the carbonate lattice of four species of coral have been analyzed and compared with the dissolved REE in ambient seawaters. The corals were from two areas of different salinity, marine (34-34.5) and bay (33-34). The measurement of REE in coral was carried out with inductively coupled plasma mass spectrometry (ICP-MS) after meticulous washing of coral samples, digestion with acetic acid and preconcentration of REE. The concentrations of REE in the two ambient seawaters were quite different, being ten-times higher in the bay area and enriched in light REE. However, the average distribution coefficients (D’s) were almost identical in the two areas. Substantial distribution coefficient differences were observed among the four coral species and the magnitude of inter-species variation in D was also species-dependent. Theoretical calculations imply that pH variation could cause variations in D large enough to account for the small differences between the two areas.     

Deformation structures in shale bed indicate flow direction of overlying Miocene subaqueous pyroclastic flow

Thrusts, pinch-and-swell structures and undulations are present within a 2-m-thick layered shale bed of Miocene age that is overlain by a rhyolite subaqueous pyroclastic flow deposit 2–3 m thick. The deformation structures were caused by loading and lateral compression by the subaqueous pyroclastic flow, probably analogous to those observed in layered muds deformed by a sand mass advancing across them. Prominent thrusts strike east-west and dip south, and the crests of undulations strike east-west, indicating that the subaqeuous pyroclastic flow moved northward.     

Isolation and chemical characterization of dissolved and particulate polysaccharides in Mikawa Bay

Isolation and chemical elucidation of dissolved and particulate polysaccharides in seawater were conducted. The water samples were collected in Mikawa Bay, Japan during a red tide bloom of the dinoflagellate, Prorocentrum minimum.Dissolved polysaccharides were concentrated from 5–101 of seawater with dialysis followed by separation by gel flitration, and isolation by ethanol precipitation. A heteropolysaccharide consisting of glucose, galactose, mannose, xylose, arabinose, fucose and rhamnose and a glucan were isolated from the polysaccharide component having a molecular weight more than 4,000 Dalton and were characterized by several chemical analyses. The heteropolysaccharide is a mucilaginous polysaccharide having a highly branched structure and a molecular weight of 10⁴?5 × 10⁶ Daltons and probably contains a sulfate half ester: the glucan is a polysaccharide with β-1,3- and 1,6-linkages (chrysolaminaran type). Concentrations of these were respectively ca. 20 and 67 μg l^?1 at 1 m, and 2 and 26 μg l^?1 at 6 m.A similar heteropolysaccharide was found in the boiling water extract of the particulate matter, while β-glucan was isolated in a much less purified form than the seawater β-glucan. In addition, a large amount of β-1,4 glucan was found in the strong alkali extract of the particulate matter, indicating that this glucan must be a cell wall polysaccharide derived from phytoplankton. These results strongly suggest that the heteropolysaccharide and chrysolaminaran type polysaccharide dissolved in seawater were derived from water soluble carbohydrates of phytoplankton through extracellular release or cell lysis.     

Asymptotic behaviour of solutions to the problem of wetting fronts in one-dimensional,horizontal and infinite porous media

The asymptotic behavior of solutions to the problem of wetting fronts is studied in one-dimensional, horizontal and infinite porous media with the soil-water diffusivity proportional to some power of the water content. The uniqueness of the similarity solution for the problem is studied and the properties of this solution are presented. It is shown that the similarity solution is an asymptotic solution of a wide class of initial value problems of wetting fronts in the media. The use of the similarity solution is discussed for the experimental determination of the soil-water diffusivity.     

A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSRE and the vertical amplification correction function

Under hypothetical and idealized conditions, the horizontal site amplification factor (HSAF) is defined as the ratio of the horizontal Fourier amplitude spectrum (FAS) at a point on the Earth's surface with respect to the horizontal FAS at the identical location but on the outcropping seismological bedrock. The HSAF reflects the profile of local sedimentary soils and weathered rock formations, indicating site effects. In most cases, such an idealized HSAF is difficult to measure directly. Thus, quantitatively estimating a HSAF value is a crucial task in strong-motion prediction over the last century. Fortunately, many strong-motion stations have been constructed throughout Japan, facilitating the characterization of HSAFs down to seismological bedrock at more than 1600 observational sites by the generalized inversion technique (GIT). First, this study reported the similarity distribution of the HSAF and the horizontal-to-vertical spectral ratio of earthquakes (HVSR_E). Subsequently, we proposed a hybrid method from a novel aspect for estimating HSAF in terms of the observed similarity distribution and the vertical amplification correction function (VACF) proposed previously. Compared with the direct use of HVSR_E for substituting HSAF, the hybrid method proposed herein demonstrated an improvement of greater than 30% in terms of the residuals between estimated HSAFs and those separated from observations.     

Effect of seasonal forcing on global circulation in a world ocean general circulation model

 Effects of the seasonal variation in thermohaline and wind forcing on the abyssal circulation are investigated by using an ocean general circulation model. To isolate effects of the seasonality in the thermohaline forcing from those in the wind forcing, we carry out three experiments with (1) annual-mean wind forcing and perpetual-winter thermohaline forcing, (2) annual-mean wind forcing and seasonal thermohaline forcing, and (3) seasonal wind forcing and seasonal thermohaline forcing. The deep water under the seasonal thermohaline forcing becomes warmer than under the perpetual-winter thermohaline forcing. Although the perpetual-winter thermohaline forcing is widely used and believed to reproduce the deep water better than the annual-mean forcing, the difference between the results of the perpetual-winter and the seasonal thermohaline forcing is significant. The seasonal variation of the Ekman convergence and divergence produces meridional overturning cells extending to the bottom because the period of seasonal cycle is shorter than the adjustment timescale by baroclinic Rossby waves. The heat transport owing to those Ekman flows and temperature anomalies makes the upper water (0–200 m) colder at low to mid-latitudes (40S–40N) and warmer at high latitudes. Also the deep water becomes warmer owing to the warming of the northern North Atlantic, the main source region of North Atlantic Deep Water. The model is also synchronously (i.e., without acceleration) integrated with seasonal forcing for 5400 y. A past study suggested that under seasonal forcing, a sufficient equilibrium state can be achieved after only decades of synchronous integration following more than 10 000 y of accelerated integration. Here, the result so obtained is compared with that of the 5400-y synchronous integration. The difference in the global average temperature is as small as 0.12 °C, and most of the difference is confined to the Southern Ocean. Received: 1 May 1998 / Accepted: 5 January 1999     

Roles of vertical turbulent mixing in the ocean response to Typhoon Rex (1998)

How the role of vertical turbulent mixing (VTM) in sea surface cooling (SSC) varies with the moving speed of a tropical cyclone was examined for Typhoon Rex (1998) by using the Meteorological Research Institute Community Ocean Model (MRI.COM). The MRI.COM well reproduced TRMM/TMI three-day mean sea surface temperature (SST) fields along Rex’s track. During the fast-moving phase of Rex, SSC simulated by the MRI.COM was caused by shear-induced VTM on the right side of the track. During the slowly-moving phase, on the other hand, the Ekman-pumping area mostly overlapped the VTM area right behind Rex’s center. During the recurvature phase, cool water transported by the upwelling was more efficiently entrained into a mixed layer by the VTM for nearly a 1 near-inertial period after the passage of Rex. We then modified the entrainment formulation of Deardorff (1983), which was incorporated into a slab mixed-layer ocean model (SOM) so as to fit to the results simulated by the MRI.COM. The principal modifications are as follows: (1) consideration of turbulent kinetic energy (TKE) production caused by surface wave breaking; (2) increase in the coefficient for estimating dissipation to balance with TKE production due to turbulent transport; and (3) changing the initial guess for the critical Richardson number. These modifications led to an improvement of SST simulations by the SOM. The impact of the modifications on simulated SSTs turned out to be more significant than the impacts of initial mixed-layer depth and the difference between diurnally-varying and daily mean short-wave radiation.     

Seasonal change of oceanographic conditions and chlorophyll <Emphasis Type="Italic">a</Emphasis> vertical distribution in the southwestern Okhotsk Sea during the non-iced season

Seasonal changes in oceanographic conditions related to primary productivity was investigated in the southwestern Okhotsk Sea during non-iced seasons, using the observation data conducted in 2000∼2006. Based on hydrographic characteristics, the studied area could be classified into two regions, the Coastal Region which is influenced under the Soya Warm Current and the Forerunner Water of the Soya Warm Current, and the Offshore Region where the Intermediate Cold Water was located in the subsurface layer. This study is the first report on seasonal change of nutrient and chlorophyll a concentrations in the offshore region of the southwestern Okhotsk Sea. Variability of concentrations of chlorophyll a and nutrients is temporally and regionally high in the Coastal Region. The maximum chlorophyll a concentration in April was observed at the surface layer of both regions. The most remarkable feature on the vertical structure in the Offshore Region was the consistent existence of the Intermediate Cold Water and the development of seasonal thermocline in the subsurface layer during summer and autumn. The stratification formed within the euphotic zone in the Offshore Region resulted in the formation of the subsurface chlorophyll a maximum (SCM) from May to October. Throughout the research period, although less amplitude of nutrients at the surface was observed in the Coastal Region than that in the Offshore Region, comparable amplitude of chlorophyll a concentration was observed between regions. These results suggested differences of environmental conditions for primary production between the two regions. Depending on the presence of SCM, relationships between chlorophyll a concentration at the sea surface and chlorophyll a standing stock within the euphotic layer were different. At most stations with SCM, the surface chlorophyll a concentration was lower than 0.6 mg m-3. This suggests that the presence of SCM and the chlorophyll a standing stock within the euphotic layer may be estimated using the surface chlorophyll a concentration from spring to autumn in the studied area.     

Simple coprecipitation method combined with low-background γ-spectrometry: Determination of 7Be, 137Cs, 210Pb, and radium and thorium isotopes in small-volume coastal water samples

Application of a coprecipitation method combined with low-background γ-spectrometry allowed the isolation of ⁷Be, ¹³⁷Cs, ²¹⁰Pb, and radium and thorium isotopes together with BaSO₄, Fe(OH)₃, or AMP/Cs in 18 L of coastal water. This simple method showed high chemical yields of 77–91% (mean, 85%) for ²¹⁰Pb and radium isotopes, 87–92% (mean, 91%) for 7Be and thorium isotopes, and 98% for ¹³⁷Cs. The activity of the nuclides showed good reproducibility with standard deviations of 1–8%, while the deviation of activity in particle-reactive ²¹⁰Pb (32%) and ⁷Be (21%) in filtered water samples was exceptionally large.