A Numerical Simulation of the Seasonal Cycle of Temperature, Salinity and Velocity Fields in Tokyo Bay

To understand when oxygen-depleted waters occur, how they develop and when they dissipate in inner Tokyo Bay, realistic simulations were attempted with fine spatial and temporal resolution by applying realistic time dependent external forcing. A 3D hydrodynamic model was driven by time-dependent external forcing factors/parameters such as solar radiation, air temperature, relative humidity, wind velocity, and fluvial discharge, under the open boundary conditions of 1995. A simulated time series of salinity and temperature agreed fairly well with observed data, except in summer. The model failed to reproduce the development of the surface mixed layer in summer. Several sensitivity analyses on the external forcing parameters such as wind velocity and vertical diffusivity were conducted to reproduce the mixed layer. However, changing these parameter values did not improve the model results.     

Pressure dependence of electrical conductivity of (Mg,Fe)SiO<Subscript>3</Subscript> ilmenite

The electrical conductivity of (Mg_0.93Fe_0.07)SiO₃ ilmenite was measured at temperatures of 500–1,200 K and pressures of 25–35 GPa in a Kawai-type multi-anvil apparatus equipped with sintered diamond anvils. In order to verify the reliability of this study, the electrical conductivity of (Mg_0.93Fe_0.07)SiO₃ perovskite was also measured at temperatures of 500–1,400 K and pressures of 30–35 GPa. The pressure calibration was carried out using in situ X-ray diffraction of MgO as pressure marker. The oxidation conditions of the samples were controlled by the Fe disk. The activation energy at zero pressure and activation volume for ilmenite are 0.82(6) eV and −1.5(2) cm³/mol, respectively. Those for perovskite were 0.5(1) eV and −0.4(4) cm³/mol, respectively, which are in agreement with the experimental results reported previously. It is concluded that ilmenite conductivity has a large pressure dependence in the investigated P–T range.     

Contamination by Persistent Organochlorines in Small Cetaceans from Hong Kong Coastal Waters

Blubber samples of 2 cetacean species, the Indo-Pacific hump-backed dolphin (Sousa chinensis) (n=11) and finless porpoise (Neophocaena phocaenoides) (n=9), collected from Hong Kong coastal waters were analysed for persistent organochlorines. Mean concentration in the blubber of DDTs was ranked first (46 μg/g wet wt.), followed by PCBs (24 μg/g wet wt.), HCHs (0.76 μg/g wet wt.), chlordane compounds (0.38 μg/g wet wt.) and HCB (0.07 μg/g wet wt.). The present cetacean species may potentially be faced with high risk due to the elevated level of DDTs and PCBs. Relatively high concentrations of PCBs and DDTs can be attributed to the continuous environmental input of these compounds in the Far East region including Hong Kong. Highly chlorinated PCBs such as IUPAC Nos. 138, 153, 180 were the prominent congeners, accounting for 39% of the total PCBs. Mean concentrations of 6 non- and mono-ortho coplanar congeners were 2.1 and 2.8 μg/g wet wt. in the hump-backed dolphin and finless porpoise, respectively. Among highly toxic coplanar PCBs, mono-ortho congener IUPAC No. 118 and non-ortho congener IUPAC No. 126 were estimated to have the greatest toxicity contribution. Tris(4-chlorophenyl) methane (TCPMe) and tris(4-chlorophenyl) methanol (TCPMeOH), which have been the most recently identified microcontaminants, were also detected with the highest concentration of 290 and 300 ng/g (wet wt. basis), respectively. The concentrations of TCPMe relative to TCPMeOH in cetaceans from Hong Kong coastal waters were significantly higher than those found in various seals collected from other parts of the world, suggesting the different metabolic system of these two compounds between seals and cetaceans. Correlations between the concentrations of tris-chlorophenyl compounds with other persistent organochlorines such as HCHs, CHLs, DDTs and PCBs were significant, suggesting their accumulation nature similar to these organochlorines.     

Probing the evolution of early-type galaxies using multicolour number counts and redshift distributions

We investigate pure luminosity evolution models for early-type (elliptical and S0) galaxies (i.e. no number density change or morphological transition), and examine whether these models are consistent with observed number counts in the B , I and K bands, and redshift distributions of two samples of faint galaxies selected in the I and K bands. The models are characterized by the star formation time-scale τ _SF and the time t _gw when the galactic wind starts to blow, in addition to several other conventional parameters. We find that the single-burst model ( τ _SF=0.1 Gyr and t _gw=0.353 Gyr), which is known to reproduce the photometric properties of early-type galaxies in clusters, is inconsistent with the redshift distributions of early-type galaxies in the field environment, owing to overpredictions of the number of galaxies at z ≳1.4 even with strong extinction which is at work until t _gw. In order for dust extinction to be more effective, we treat τ _SF and t _gw as free parameters, and find that models with τ _SF≳0.5 Gyr and t _gw>1.0 Gyr can be made consistent with both the observed redshift distributions and the number counts, if we introduce strong extinction [ E ( B − V )≥1 as a peak value]. These results suggest that early-type galaxies in the field environment do not have the same evolutionary history as described by the single-burst model.     

Upwelling of oxygen-depleted water (Sumishio) in Omura Bay,Japan

Wind-induced circulation and the distribution of hypoxia corresponding to the upwelling of oxygen-depleted water (called “Aoshio” in Japan and “Sumishio” locally in Omura Bay) in Omura Bay, Japan, was examined field observations and by three-dimensional modeling. During the calm weather in summer, well-mixed strait water, in rich oxygen at the mouth of the bay intruded into the middle layer of the bay, southward and northward along the west and east coast, respectively, forming basin-scale cyclonic circulation. A stagnant water mass was formed below the center of this cyclonic circulation, and it became hypoxic water. As a result of the prevailing strong southeast (northeast) wind, the bottom hypoxia moved in a southeasterly (northeasterly) direction. This induces the upwelling of hypoxic water, accompanied by mass mortality of marine organisms.     

Interannual variations of the planktonic ecosystem in the slope water and Kuroshio south of Japan in February in the years 1990–2002

To determine recent interannual variations in the planktonic ecosystem of the slope water south of Japan, an area between 1000 m isobath on the continental slope and assumable Kuroshio front, in reference to preceding reports on the Kuroshio, we examined interannual variations of physical factors, sea surface chlorophyll concentration (SSChl), size-fractioned copepod biomass and the abundance of Calanus sinicus, one of the dominant copepods in the region, in February from 1990 to 2002. In the slope water, SSChl concentration had generally shown a higher value than in the Kuroshio and increase of the SSChl in both areas started in February but lasted longer in the slope water. The regional distribution of copepod biomass and C. sinicus abundance was similar to that of phytoplankton in that they were distributed more densely in the slope water than in the Kuroshio, reflecting assumed higher nutrient supply. The interannual variation in sea surface temperature in the slope water was explained by the rise of air temperature in 1998, a strong El Niño year, and subsequent change in the Kuroshio path (1999–2001). The interannual variation of the planktonic community, i.e. sea surface chlorophyll concentration and copepod biomass, was attributed to the effects of those physical events through the direct effect of local temperature and/or variation in surface irradiance, except for a prominent increase of copepods in the slope water in 2000. The effect of interannual change in the vertical mixing, suggested in previous studies, was not apparent in February, when the primary production is not limited by nutrient concentration which would be more important in regulating biological production in later months.     

Petrological variation of large-volume felsic magmas from Hakkoda-Towada caldera cluster: Implications for the origin of high-K felsic magmas in the Northeast Japan Arc

Abstract The Hakkoda‐Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high‐K (HK‐) type and medium‐ to low‐K (MLK‐) type based on their whole‐rock chemistry. The HK‐type magmas are characterized by higher K₂O and Rb contents and higher ⁸⁷Sr/⁸⁶Sr ratios than MLK‐type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation‐fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK‐type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK‐type magmas. Although MLK‐type magmas were erupted throughout HTCC activity, HK‐type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK‐type magmas. Subsequently, the repeated supply of mantle‐derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK‐type magmas with lesser crustal components. The MLK‐type magmas are common and HK‐type magmas are exceptional during the Pliocene–Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK‐type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK‐type felsic magmas.     

Abundance of nauplii and protein synthesis activity of adult female copepods in the Kuroshio front during the Japanese sardine spawning season

In order to point out the potential importance of the Kuroshio front as a feeding ground for the early post larvae of the Japanese sardine, distributions of copepod nauplii—the principal food for the larvae—were investigated.Nauplii were abundant in and near the front and in a warm water mass off Ensyu-nada, where the concentration of chlorophylla was high. Adult females ofParacalanus sp. were dominant in the copepod group there, and the protein synthesis activity shown by the RNA/DNA ratio was high. It is expected that copepod egg productivity is enhanced in the area where food phytoplankton is abundant, because the RNA/DNA ratio showed a positive correlation to chlorophylla in situ.In and near the front, high chlorophylla concentration—which is probably supported by nutrient supply caused by local upwelling and/or eddies at the front—contributes to the high RNA/DNA ratio of the copepods. The relatively large biomass of copepod nauplii at the front may be supported by female's high egg productivity. It is supposed, as a result, that food availability for the early post larvae of the Japanese sardine is increased in and near the Kuroshio front.     

Impacts of vehicles on natural terrain at seven sites in the San Francisco Bay area

The impacts of off-road vehicles on vegetation and soil were investigated at seven representative sites in the San Francisco Bay area. Plant cover of grass and chaparral (with shrubs to 4 m tall) have been stripped by the two- and four-wheel vehicles in use. Impacts on loamy soils include increased surface strength (as much as 275 bars), increased bulk density (averaging 18%) to depths of 90 cm or more, reduction of soil moisture by an average 43% to 30 cm depths, greatly reduced infiltration, extension of the diurnal temperature range by as much as 12°C, and reduction of organic carbon by an average 33% in exposed soils. Very sandy soils respond similarly to vehicular use except that moisture is increased and surface strength of beach sand is decreased. These physical and chemical impacts reduce the land's capability of restoring its vegetative cover, which in turn adversely affects animal populations. Both the loss of plant cover and the physical changes caused by vehicles promote erosion. Measured soil and substrate losses from vehicular use zones range from 7 to 1180 kg/m². The estimated erosion rate of the Chabot Park site exceeds the rate of erosion considered a serious problem by a factor 30, it exceeds United States Soil Conservation Service tolerance values by a factor of 46, and it exceeds average San Francisco Bay area erosion rates by a factor of 17. The resulting soil losses are effectively permanent. Neither the increased sediment yield nor the increased runoff is accomodated on the sites of use, and both are causing adverse effects to neighboring properties.