Large but variable particulate flux in the Antarctic Ocean and its significance for the chemistry of Antarctic water     

Shizuo Tsunogai  Shinichiro Noriki  Koh Harada  Taro Kurosaki  Yasunori Watanabe  Masaru Maedaa 《Journal of Oceanography》1986,42(2):83-90

Settling particles were collected at 1,460 m and 3,760 m depth in the Antarctic Ocean with sediment traps of time series type. The total deployment period of 40 days was divided into four terms of 10 days each. Seawater samples were collected both at deployment and retrieval of the traps at each site. During the 42 days the concentration of silicate in the surface water decreased by 32%, whereas those of nitrate and phosphate decreased by only 4–5%. The total particulate flux in the Antarctic Ocean is the largest among those hitherto observed in the world ocean. The time variation of the particulate flux at 1,460 m depth almost coincided with that at 3,760 m. The settling particles were comprised roughly of 80% biogenic silica, 15% organic matter and 5% other substances including sea salt. The clay fraction was only 0.05% at 1,460 m depth. The settling flux of biogenic silica agrees fairly well with the calculated rate of change in the concentration of silicate in the surface 100 m. Thus it is concluded that preferential propagation of diatoms reduces the concentration of silicate prior to other nutrients in the Antarctic Ocean.  相似文献   

Hydrogeochemistry and environmental isotopes of ground water in Jeju volcanic island,Korea: implications for nitrate contamination     

Dong‐Chan Koh  Ho‐Wan Chang  Kwang‐Sik Lee  Kyung‐Seok Ko  Yongje Kim  Won‐Bae Park 《水文研究》2005,19(11):2225-2245

Ground water from springs and public supply wells was investigated for hydrochemistry and environmental isotopes of ³H, ¹⁸O and D in Jeju volcanic island, Korea. The wells are completed in a basaltic aquifer and the upper part of hydrovolcanic sedimentary formation. Nitrate contamination is conspicuous in the coastal area where most of the samples have nitrate concentrations well above 1 mg NO₃ N/l. Agricultural land use seems to have a strong influence on the distribution of nitrate in ground water. Comparison of stable isotopic compositions of precipitation and ground water show that ground water mostly originates from rainy season precipitation without significant secondary modification and that local recharge is dominant. ³H concentration of ground water ranged from nearly zero to 5 TU and is poorly correlated with vertical location of well screens. The occurrence of the ³H‐free, old ground water is due to the presence of low permeability layers near the boundary of the basaltic aquifer and the hydrovolcanic sedimentary formation, which significantly limits ground water flow from the upper basaltic aquifer. The old ground water exhibited background‐level nitrate concentrations despite high nitrate loadings, whereas young ground water had considerably higher nitrate concentrations. This correlation of ³H and nitrate concentration may be ascribed to the history of fertilizer use that has increased dramatically since the early 1960s in the island. This suggests that ³H can be used as a qualitative indicator for aquifer vulnerability to nitrate contamination. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Silicon flux and distribution of biogenic silica in deep-sea sediments in the western North Pacific Ocean     

Yoko Shibamoto  Koh Harada 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(2):163-174

We investigated biogenic silica, several biological components, and silicate in pore-water in the abyssal sediment to determine silicon flux of western North Pacific during several cruises. The surficial sediment biogenic silica content was high at high latitudes with the boundary running along the Kuroshio Extension, and maximum values (exceeding 20%) were found in the Oyashio region. In the subtropical region to the south, most stations showed less than 5% biogenic silica content. This distribution pattern reflected primary production and ocean currents in the surface layer very well. Pore-water samples were collected from 4 stations along the east coast of Japan. The highest asymptotic silicic acid concentration (670 μmol L^?1) in pore-water was observed at the junction of Kuroshio and Oyashio, followed by samples from the Oyashio region. It is at the southern station that the lowest value (450 μmol L^?1) was observed, and the primary production is low under the influence of Kuroshio there. The diffusive flux followed the same geographic trend as the asymptotic silicic acid concentrations did, ranging 77–389 mmol m^?2 yr ^?1. Multiple sampling of pore-water was conducted throughout the year at one station at high latitude. The average annual biogenic silica rain flux observed using sediment traps was 373 mmol m^?2 yr^?1; the diffusive flux and burial flux at the sediment–water interface were 305 and 9 mmol m^?2 yr^?1, respectively. We concluded that most of the settling silica particles dissolved and diffused at the sediment–water interface and approximately 3% only were preserved in this area. In addition, the obvious time lag observed between the peak rain flux and the maximum diffusive flux suggested that primary production in the surface layer has a great influence on the sedimentation environment of abyssal western North Pacific. These transitions of Si flux at the sediment–water interface were considerably greater in northwestern North Pacific than in southwestern North Pacific. In addition, a station in the Philippine Sea indicated high biogenic silica content because of Ethmodiscus ooze, which are scattered randomly on the sea floor in the subtropical region.  相似文献   

Endocrine disrupting alkylphenols and bisphenol-A in coastal waters and supermarket seafood from Singapore   总被引：2，自引：0，他引：2  

Basheer C  Lee HK  Tan KS 《Marine pollution bulletin》2004,48(11-12):1161-1167

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Re–Os molybdenite dating of granite-related Sn–W–Mo mineralisation at Hnilec, Gemeric Superunit, Slovakia     

M. Kohút  H. Stein 《Mineralogy and Petrology》2005,85(3-4):117-129

Summary Re–Os molybdenite ages from the exocontact of the Hnilec granite-greisen body provide temporal constraints for tin, tungsten and molybdenite mineralisation in the Gemeric Superunit, Slovakia. Two molybdenite separates were taken from a representative sample of the Sn–W–Mo mineralisation at Hnilec and their Re–Os ages of 262.2 ± 0.9 and 263.8 ± 0.8 Ma (2-sigma) are in excellent agreement. The obtained Re–Os molybdenite ages are similar to recent but less precise electron microprobe monazite (276 ± 13 Ma) and U–Pb single zircon (250 ± 18 Ma) ages from the Hnilec granite intrusion, supporting a granite-related greisen origin for the Sn–W–Mo mineralisation. Our precise Re–Os molybdenite ages resolve the long time controversy over the timing of high-temperature mineralisation in the Gemeric Superunit. These Permian ages eliminate suggestions of an Alpine age. The sulphur isotope composition of the studied molybdenite is δ³⁴S_(CDT) = 1.71 ± 0.2‰ and is consistent with a magmatic sulphur source. Field observations indicate the lack of a broad contact aureole in the vicinity of the Hnilec granite body. Shallow level granite emplacement in schistose host rocks was accompanied by alteration and formation of tin-tungsten greisen in the upper part of the granite and exocontact molybdenite mineralisation, both commonly lacking in other granite bodies within the Gemeric Superunit.  相似文献   

Attenuation of peak ground acceleration,velocity and displacement based on multiple regression analysis of japanese strong motion records     

Kazuhiko Kawashima  Koh Aizawa  Kazuyuki Takahashi 《地震工程与结构动力学》1986,14(2):199-215

This paper presents the result of multiple regression analysis of 197 sets of two orthogonal horizontal strong motion acceleration records. They were obtained at 67 free field sites in Japan from 90 earthquakes with focal depth less than 60 km. Because sensitivity of the Japanese SMAC accelerograph is appreciably low at the high frequency range, instrument correction was performed on the original data. Each pair of two orthogonal horizontal components was combined in the time domain to get the maximum peak ground motions in the horizontal plane. The records were classified into three groups due to subsoil condition. With the use of multiple regression analysis, empirical formulae of attenuation of the maximum peak ground acceleration, velocity and displacement were proposed for three subsoil conditions.  相似文献   

Dynamic response of twin circular tunnels due to incident SH-waves     

Thambirajah Balendra  David P. Thambiratnam  Chan Ghee Koh  Seng-Lip Lee 《地震工程与结构动力学》1984,12(2):181-201

The steady-state solution for two parallel under ground tunnels of circular cross-section subjected to incident plane harmonic SH-waves is obtained in closed form, by using the method of wave function expansion. The image technique is employed to account for the reflection of waves at the ground surface. Numerical studies are carried out to determine the influence of spacing between the tunnels on the shear stresses in concrete and steel linings.  相似文献   

Apatite fission track and (U-Th)/He thermochronology of the Rochovce granite (Slovakia) – implications for the thermal evolution of the Western Carpathian-Pannonian region     

Martin Danišík  Milan Kohút  István Dunkl  L’ubomír Hraško  Wolfgang Frisch 《Swiss Journal of Geoscience》2008,101(1):225-233

The thermal evolution of the only known Alpine (Cretaceous) granite in the Western Carpathians (Rochovce granite) is studied by low-temperature thermochronological methods. Our apatite fission track and apatite (U-Th)/He ages range from 17.5 ± 1.1 to 12.9 ± 0.9 Ma, and 12.9 ± 1.8 to 11.3 ± 0.8 Ma, respectively. The data thus show that the Rochovce granite records a thermal event in the Middle to early Late Miocene, which was likely related to mantle upwelling, volcanic activity, and increased heat flow. During the thermal maximum between ~17 and 8 Ma, the granite was heated to temperatures ? 60 °C. Increase of cooling rates at ~12 Ma recorded by the apatic fission track and (U-Th)/He data is primarily related to the cessation of the heating event and relaxation of the isotherms associated with the termination of the Neogene volcanic activity. This contradicts the accepted concept, which stipulates that the internal parts of the Western Carpathians were not thermally affected during the Cenozoic period. The Miocene thermal event was not restricted to the investigated part of the Western Carpathians, but had regional character and affected several basement areas in the Western Carpathians, the Pannonian basin and the margin of the Eastern Alps.  相似文献   

Latitudinal Distribution of CO2 Fugacity along 175°E in the North Pacific in 1992–1996     

Tomonori Watai  Koh Harada  Kouichi Gotoh  Shohei Murayama  Takakiyo Nakazawa 《Journal of Oceanography》1999,55(6):655-665

In order to examine latitudinal distribution and seasonal change of the surface oceanic fCO₂, we analyzed the data obtained in the North Pacific along 175°E during the NOPACCS cruises in spring and summer of 1992–1996. Except for around the equator where the fCO₂ was significantly affected by the upwelling of deep water, the latitudinal distribution of fCO₂ showed distinctive seasonal variation. In the spring, the fCO₂ decreased and then increased going southward with the minimum value of about 300 µatm around 35°N, while in the summer, the fCO₂ displayed high variability, showing minimum and maximum values at latitudes of around 44° and 35°N, respectively. It was also found that the fCO₂ was well correlated with the SST, but the relationship between the two was different for different hydrographic regions. In the subpolar gyre, the frontal regions between the Water-Mass Front and the Kuroshio bifurcation front, and between the Kuroshio bifurcation front and the Kuroshio Extension current, SST, DIC and TA influenced the seasonal fCO₂ change through seasonally-dependent biological activities and vertical mixing and stratification of seawater. In the central subtropical gyre and the North Equatorial current, the seasonal fCO₂ change was found to be produced basically by changes in SST and DIC. The summertime oceanic fCO₂ generally increased with time over the period covered by this study, but the increased rate was clearly higher than those expected from other measurements in the western North Pacific.  相似文献   

Early Variscan magmatism in the Western Carpathians: U–Pb zircon data from granitoids and orthogneisses of the Tatra Mountains (Slovakia)     

U. Poller  M. Janák  M. Kohút  W. Todt 《International Journal of Earth Sciences》2000,89(2):336-349

This study presents the first U–Pb zircon data on granitoid basement rocks of the Tatra Mountains, part of the Western Carpathians (Slovakia). The Western Carpathians belong to the Alpine Carpathian belt and constitute the eastern continuation of the Variscides. The new age data thus provide important time constraints for the regional geology of the Carpathians as well as for their linkage to the Variscides. U–Pb single zircon analyses with vapour digestion and cathodoluminescence controlled dating (CLC-method) were obtained from two distinct granitoid suites of the Western Tatra Mountains. The resulting data indicate a Proterozoic crustal source for both rock suites. The igneous precursors of the orthogneisses (older granites) intruded in Lower Devonian (405 Ma) and were generated by partial melting of reworked crustal material during subduction realated processes. In the Upper Devonian (365 Ma), at the beginning of continent–continent collision, the older granites were affected by high-grade metamorphism including partial melting, which caused recrystallisation and new zircon growth. A continental collision was also responsible for the generation of the younger granites (350–360 Ma). The presented data suggest multi-stage granitoid magmatism in the Western Carpathians, related to a complex subduction and collision scenario during the Devonian and Carboniferous. Received: 19 February 1999 / Accepted: 3 December 1999  相似文献