Lead-210 in the Japan Sea     

Yoshiyuki Nozaki  Shizuo Tsunogai  Masakichi Nishimura 《Journal of Oceanography》1973,29(6):251-256

This is the first detailed study on the distribution of lead-210 in the Japan Sea water. The content of lead-210 ranged from 9.3±2.1 dph/l in the surface water to 3.4+-0.8 dph/l in the deep water—a quite low content as compared to that in the deep water of the North Pacific. Vertical profiles show that the content of lead-210 abruptly decreases below the seasonal thermocline (10–20 m in depth) and nearly uniform in the deep water. It is suggested that a significant amount of air-borne lead-210 deposited over the Japan Sea is transported along with the Tsushima Current to the open ocean. The budget of lead-210 is calculated by using a simple box-model and the mean residence time of lead-210 in the Japan Sea is estimated to be 15 yr.  相似文献   

A new method of evaluating the mineralization of particulate and dissolved photoassimilated organic matter     

Masanobu Ishikawa  Hajime Nishimura 《Journal of Oceanography》1983,39(2):29-42

A new method of evaluating the rate of mineralization of photoassimilated organic matter is described. This method enables us to compare the rate of direct mineralization of particulate organic carbon (POC) to CO₂ with the rate of solubilization of photoassimilated organic carbon followed by the mineralization of the resultant dissolved organic carbon (DOC) under the same conditions. The direct mineralization of photoassimilated carbon from POC to CO₂ is a more significant process compared with the mineralization of extracellular released organic carbon. The first-order rate coefficients range from 0.132 to 0.434 day^–1 for direct mineralization and 0.034 to 0.189 day^–1 for solubilization.  相似文献   

Mercury concentration in the ocean     

Masakichi Nishimura  Shigeki Konishi  Katsuhiko Matsunaga  Kohtaro Hata  Tsuneo Kosuga 《Journal of Oceanography》1983,39(6):295-300

Seventy percent of 342 seawater samples collected in the Bering Sea, North and South Pacific, Japan Sea, East and South China Seas, and Indian Ocean had concentrations of “total” mercury ranging from 3 to 6 ng Hg l^?1 with an arithmetic mean of 5.3 ng l^?1 and a geometric mean of 5.0 ng l^?1. In some cases, a higher concentration was observed at the surface, at the halocline or thermocline, or in the bottom water. But in general, there was no consistent correlation between mercury concentration and depth, except for a statistical tendency for mercury concentration to be slightly higher in the surface water. This tendency suggests that mercury in the ocean is supplied from the atmosphere by rain washout. The latitudinal variation of surface mercury concentrations showed that the maximum concentration at each latitude decreased from 40°N to 30°S. This variation provides evidence that atmospheric mercury is emitted mainly from continental areas naturally or anthropogenically.  相似文献   

Volcanic and Seismic Swarm Events on the Reykjanes Ridge and Their Similarities to Events on Iceland: Results of a Rapid Response Mission     

Kathleen Crane  Lynn Johnson  Bruce Appelgate  Clyde Nishimura  Roger Buck  Chris Jones  Peter Vogt  Rubin Kos’yan 《Marine Geophysical Researches》1997,19(4):319-338

On 21 May 1989, a major earthquake swarm on the Reykjanes Ridge at59°44 N, 29°32 W at a water depth of about 1000 m andabout 500 km southwest of Iceland was detected on both the WorldwideStandard Seismic Network (WWSSN) and Icelandic seismic networks. As part ofa multi-institutional response to this swarm, the Naval ResearchLaboratory arranged for a P3 Orion Aircraft to deploy sonobuoys and AXBTs inthe immediate vicinity of the swarm activity. The detection of the swarmmotivated a survey of the region in 1990, using the towed SeaMARC IIside-looking sonar system. In 1990–1991 the Russian ShirshovInstitute of Oceanology offered the use of its MIR deep-divingsubmersibles to investigate the rise axis for recent volcanism. During 1992,a scientific team comprised of five US and ten Russian scientists mobilizedthe twin, deep diving Russian submersibles to study the spreading axis ofthe Reykjanes Ridge. The resulting data analyses allows us to conclude thatthe 1989 seismic swarm event occurred adjacent to and east of the largeaxial high in the center of our survey area. The length, width and depthrange of the earthquakes were very similar to major seismic swarm eventsconfined to fissure systems in the Krafla region of Iceland. It is likelythat the earthquake swarm was located on a fresh, well-defined systemof fissures and faults extending south of the northernmost axial highstudied. The earthquake swarm was probably associated with an emanation oflava creating a region of high backscatter, located just to the east of thecentral axial high. In addition, the region of high-backscatterremains unsampled because it lay underneath the nadir of the processedSeaMARC tracks used to plan the submersible survey. However many sampleswere taken and structural studies of the evolving Reykjanes Ridge werecarried out.  相似文献   

A new method to detect viable bacteria in natural seawater using 16SrRNA oligonucleotide probe     

Masahiko Nishimura  Kumiko Kita-Tsukamoto  Kazuhiro Kogure  Kouichi Ohwada  Usio Simidu 《Journal of Oceanography》1993,49(1):51-56

Fluorescent oligonucleotide probes were used to detectVibrio cholerae directly under epifluorescence microscope. The probe which is complementary to the specific 16SrRNA sequence ofVibrio cholerae was labelled with Texas-Red, whereas the universal probe was labelled with Fluorescein. These probes allowed the distinctionVibrio cholerae from other eubacteria under the same microscopic field. In order to detect and enumerate specific bacteria in natural seawater, this method was combined with the direct viable count (DVC) technique. The combined method increased intracellular rRNA levels in the sample, and made it possible to detect the target bacteria with the specific gene probe. The applicability of this new method was confirmed both for the laboratory mixed culture system and natural seawater.  相似文献   

Some regular patterns in the distribution of sediment contamination in the coastal waters along Japan     

Yasushi Hiraizumi  Takehiko Manabe  Hajime Nishimura 《Journal of Oceanography》1978,34(5):222-232

Observations of sediment contamination along the coast of Japan were analyzed. When the pollutant concentration is divided by the fine particle fraction in the sediment, a regular pattern is observed in the quantitative relationship among the degree and the area of contamination and the discharge rate of pollutant released continuously into the water along the coast. This regularity was observed with respect to COD,n-hexane soluble substances and heavy metals, and could be expressed by a formula.Polluted particles were supposed to disperse through suspension in the bottom water layer, and thus their distribution in the surface sediment is expected to become similar to effluent dispersion in the surface water.  相似文献   

Coupling simulation of microbially induced carbonate precipitation and bacterial growth using reaction–diffusion and homogenisation systems     

Nishimura  Ibuki  Matsubara  Hitoshi 《Acta Geotechnica》2021,16(5):1315-1330

Acta Geotechnica - Soil improvement techniques have been developed experimentally and empirically from various geotechnical standpoints based on physical, chemical, and biological findings. The...  相似文献   

Tracking dynamics of magma migration in open-conduit systems     

Sébastien Valade  Giorgio Lacanna  Diego Coppola  Marco Laiolo  Marco Pistolesi  Dario Delle Donne  Riccardo Genco  Emanuele Marchetti  Giacomo Ulivieri  Carmine Allocca  Corrado Cigolini  Takeshi Nishimura  Pasquale Poggi  Maurizio Ripepe 《Bulletin of Volcanology》2016,78(11):78

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Volcanic tremor during eruptions: Temporal characteristics,scaling and constraints on conduit size and processes     

Stephen R. McNutt  Takeshi Nishimura 《Journal of Volcanology and Geothermal Research》2008

We investigated characteristics of eruption tremor observed for 24 eruptions at 18 volcanoes based on published reports. In particular, we computed reduced displacements (D_R) to normalize the data and examined tremor time histories. We observed: (a) maximum D_R is approximately proportional to the square root of the cross sectional area of the vent, however, with lower than expected slope; (b) about one half of the cases show approximately exponential increases in D_R at the beginnings of eruptions, on a scale of minutes to hours; (c) one half of the cases show a sustained maximum level of tremor; (d) more than 90% of the cases show approximately exponential decay at the ends of eruptions, also on a scale of minutes to hours; and (e) exponential increases, if they occur, are commonly associated with the first large stage of eruptions. We estimate the radii of the vents using several methods and reconcile the topographic estimates, which are systematically too large, with those obtained from D_R itself and theoretical considerations. We compare scaling of tremor D_R with that for explosions and find that explosions have large absolute pressures and scale with vent radius squared, whereas tremor consists of pressure fluctuations that have lower amplitudes than the absolute pressure of explosions, and the scaling is different. We explore several methods to determine the appropriate scaling. This characteristic helps us to distinguish the type of eruptions: explosive (Vulcanian or Strombolian) eruptions versus sustained or continuous ash (e.g. Plinian) eruptions. Average eruption discharge, estimated from the total volume of tephra and the total duration of eruption tremor, is well correlated with peak discharge calculated from cross sectional area of the vent and velocity of volcanic ejecta. These results suggest similar scaling between different eruption types and the overall usefulness of monitoring tremor for evaluating volcanic activity.  相似文献   

近岸波生流数值计算的一种新方法   总被引：9，自引：5，他引：4  

包四林  西村仁嗣 《海洋学报》2000,22(5):115-123

运用Hardy-Cross法的基本原理建立了一种波生流计算的数值模型.本方法在维持计算稳定性方面表现出色,解决了以往的计算方法所存在的计算不稳定的根本缺陷,但是运用这一方法进行实际问题计算时还明显存在计算收敛缓慢的现象,对此,在探讨计算收敛原因的基础上,提出了同心矩形回路补正、粗网格计算初始值等对策.运用这些对策成功地提高了计算的效率和精度.最后通过计算例验证表明,运用本方法既能有效地维持计算的稳定,又能有效地解决局部缓和法所固有的计算效率低的问题,从而为研究和预测海岸工程对地形及环境变化影响问题提供了合理、实用的方法.  相似文献