Mixed layer depth front and subduction of low potential vorticity water in an idealized ocean GCM   总被引：4，自引：0，他引：4  

Shiro Nishikawa  Atsushi Kubokawa 《Journal of Oceanography》2007,63(1):125-134

It is known that there is a front-like structure at the mixed layer depth (MLD) distribution in the subtropical gyre, which is called the MLD front, and is associated with the formation region of mode water. In the present article, the generation mechanism of the MLD front is studied using an idealized ocean general circulation model with no seasonal forcing. First, it is shown that the MLD front occurs along a curve where u _g ·∇T _s = 0 is satisfied (u _g is the upper ocean geostrophic velocity vector, T _s is the sea surface temperature and ∇ is the horizontal gradient operator). In other words, the front is the boundary between the subduction region (u _g ·∇T _s > 0) and the region where subduction does not occur (u _g ·∇T _s < 0). Second, we have investigated subduction of low potential vorticity water at the MLD front, which has been pointed out by past studies. Since u _g ·∇T _s = 0 at the MLD front, the water particles do not cross the outcrop at the MLD front. The water that is subducted at the MLD front has come from the deep mixed layer region where the sea surface temperature is higher than that at the MLD front. The temperature of the water in the deep mixed layer region decreases as it is advected eastward, attains its minimum at the MLD front where u _g ·∇T _s = 0, and then subducts under the warmer surface layer. Since the deep mixed layer water subducts beneath a thin stratified surface layer, maintaining its thickness, the mixed layer depth changes abruptly at the subduction location.  相似文献   

Response of plant growth to surface water balance during a summer dry period in the Kazakhstan steppe     

Yoshihiro Iijima  Tsuneo Kawaragi  Takehiko Ito  Kanat Akshalov  Atsushi Tsunekawa  Masato Shinoda 《水文研究》2008,22(16):2974-2981

In drylands, water deficit is the primary factor limiting plant growth. In the present study, surface energy balance and plant growth (above‐ground and below‐ground biomass) were measured continuously during the 2002 growing season in semiarid grassland in the northern part of Kazakhstan, Central Asia. Although there was above normal total rainfall during the 2002 growing season (May–November; 244 mm over 183 days), there was a dry period during July and August. Evaporative water was effectively supplied by precipitation and surface soil moisture during the wet season (May and June), during which time above‐ground biomass increased. During the early stages of the dry period, mature plants were likely to tap deeper sources of soil moisture, representing stored snowmelt water. As the soil moisture content decreased during the summer dry period due to the high levels of evapotranspiration and lack of precipitation, the evaporative fraction and above‐ground biomass rapidly decreased, whereas the below‐ground biomass increased. These results suggest that in summer, soil moisture acts to store water, and that soil moisture is essential for plant growth as a direct source of water during the dry period in natural grasslands in the Kazakhstan steppe. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Mineralogical and textural variation of silica minerals in hydrothermal flow-through experiments: Implications for quartz vein formation     

Atsushi Okamoto  Hanae Saishu  Nobuo Hirano  Noriyoshi Tsuchiya 《Geochimica et cosmochimica acta》2010,74(13):3692-3706

We conducted hydrothermal flow-through experiments at 430 °C and 31 MPa to investigate the mechanism of silica precipitation on granite under crustal conditions. Two experiments were performed using different input solutions: a single-component Si solution, and a multi-component solution with minor Al, Na, and K. The degree of supersaturation with respect to quartz, Ω = C_Si/C_Si,Qtz,eq, where C_Si and C_Si,Qtz,eq indicate Si concentration in solutions and the solubility of quartz within water, respectively, decreased from 3-3.5 to <1.1 along the flow path. A variety of silica minerals formed during the experiments (opal-A, opal-C, chalcedony, and quartz), and their occurrences and modal abundances changed in response to Ω and the presence of additives in the solution.For near-equilibrium solutions (Ω < ∼1.2), silica precipitation occurred in a simple way in both experiments, being restricted to overgrowths on pre-existing quartz surfaces in the granite. At higher saturation levels (Ω > ∼1.2), silica minerals were deposited on other surfaces in addition to quartz. In the single-component experiment, the dominant silica minerals changed in the order of opal-A → opal-C → quartz with decreasing Si concentration along the flow path. In contrast, in the multi-component experiment, quartz and minor chalcedony formed throughout the entire reaction vessel. This finding indicates that impurities (Na, K, and Al) in the solutions inhibited the precipitation of opal and enhanced the direct nucleation of quartz. The systematic appearance of metastable silica minerals were examined by nucleation processes and macroscopic precipitation kinetics. Our experimental results indicate that different precipitation mechanisms yield contrasting textures, which in turn suggests that vein textures can be used as indicators of solution chemistry within the fracture.  相似文献   

Assignment of groundwater level at the wastewater collecting pipe for a landfill groundwater simulation: utilization of the two-dimensional saturated–unsaturated groundwater numerical model     

Thuong Huyen Dang  Kenji Jinno  Atsushi Tsutsumi 《Environmental Earth Sciences》2010,60(8):1575-1582

In order to understand the effects of a landfill operation on groundwater flow behavior, a 2D horizontal groundwater simulation model was carried out. The model saved the memory of computer and time consumption, comparing it with the 3D groundwater flow model. However, the greatest difficulty is the assignment of the collecting pipe boundary at the study site. Therefore, a 2D vertical model was applied to calculate the change of the groundwater table above the collecting pipe. This paper focuses on examining the validation of the assignment of the collecting pipe boundary by applying the results of the 2D vertical model. The 2D horizontal model was coupled with the recharge model to solve the partial differential equation of groundwater flow. The finite difference method and iterative successive over relaxation were applied. The drainage volume of leachate collection was summed up in the whole landfill site and compared with the average volume of treated wastewater. The study demonstrated that the results of the 2D vertical model validated and can be applied to the 2D horizontal groundwater flow simulation.  相似文献   

Impact of climate change on runoff from a mid‐latitude mountainous catchment in central Japan     

Yoshinori Shinohara  Tomo'omi Kumagai  Kyoichi Otsuki  Atsushi Kume  Naoya Wada 《水文研究》2009,23(10):1418-1429

Hydrologic balance in high‐altitude, mid‐latitude mountain areas is important in terms of the water resources available to associated lowlands. This study examined how current and historical shifts in precipitation (P) patterns and concurrent increases in temperature (T) affected runoff (Q) and other hydrologic components in a mid‐latitude mountain catchment of central Japan, using a combination of long‐term data and a simplified hydrologic model, along with their stochastic treatment. The availability of intensive meteorological and hydrological data from the period 1997–2001 allowed the derivation of key relationships for the current climate that tie the forcing term to the parameters or state variables. By using the data recorded in the period 1965–2001, the force for driving the historical simulation was generated. Based on this model and historical shifts in P and T, the probability density functions of Q (pdf(Q)) was computed. A main novelty in this study is that such a stochastic representation, which is useful for considering the influence of projected shifts in environmental factors on the hydrologic budget, was provided. Despite the large increase in the rate of T in winter and spring, pdf(Q) in spring and summer varied appreciably during the time studied mainly because of an increase in snowmelt. An interannual change in whole‐year Q was robust to shifts in T because while Q in spring increased, in summer it decreased, implying a crucial effect of global warming on mountain hydrologic regimes is change in the timing of Q. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Liquid Immiscibility of Boninite in Xiangcheng, Southwestern China, and Its implication to Genetic Relationship between Boninite and Komatiitic Basalt     

Tetusro Urabe  Takagi  Naito 《《地质学报》英文版》2001,75(1):74-93

Boninitic rocks and associated high-magnesian basalt and high-iron tholeiite in the Xiangcheng area constitute the basal horizon of the arc volcanic sequence in the Triassic Yidun Island-Arc, southwestern China. The boninite occurs as pillow, massive and ocellar lavas; the last one possesses well-developed globular structure and alternates with the former two. The boninite is characterized by the absence of phenocrysts of olivine and low-Ca pyroxenes and by low CaO/Al2O3 ratios (<0.67) and high Cr (>1000 ppm) and Ni (>250 ppm). The normalized abundance patterns (NAP) of trace elements to primitive mantle are similar to the NAP of low-Ca modern boninites and SHMB in the Archaean and Proterozoic.As a mechanism of ocellar texture, liquid immiscibility in boninite is supported by the following lines of evidence: (a) sharp contact between ocelli and matrix, (b) constant volumetric ratios of ocelli/matrix and common coalescence of ocelli in ocellar rocks, (c) identical micro-spinifex textures and mineral asse  相似文献   

Partition of cadmium and manganese between coexisting sphalerite and galena from some Japanese epithermal deposits     

T. Urabe 《Mineralium Deposita》1977,12(3):319-330

Sphalerites from Japanese epithermal Pb-Zn vein-type deposits, namely, Yatani, Oizumi and Hosokura, contain 2900–3400 ppm cadmium and 760–2100 ppm manganese. And galenas from the same deposits contain cadmium and manganese 19.2–26.9 ppm and 7.8–218.3 ppm, respectively. The temperatures, evaluated from the partition of cadmium between coexisting sphalerite and galena, are consistent within a total range of 150°C at maximum within an individual deposit. No systematic change with depth can be observed at the Shoko-hi vein, Hosokura mine and Hompi vein, Yatani mine. In several samples, the temperatures obtained from the partition of cadmium have been compared with those obtained from sulfur isotope fractionations. Iron content in sphalerite coexisting with pyrite indicates that the deposition of ore minerals at these deposits may have taken place from ore-forming solutions in which H₂S or HS^– was the predominant dissolved sulfur species, and the solutions may have been free from in situ oxidation or reduction.  相似文献   

Mineralogical aspects of the Kuroko deposits in Japan and their implications     

Urabe  T. 《Mineralium Deposita》1974,9(4):309-324

The most remarkable difference in mineralogy of the Kuroko deposits in Japan is shown in their mineral assemblages of wall-rock alteration. They can be divided into three types, namely: (I)kaolinite-pyrophyllite-diaspore type, (II)sericite-chlorite type, and (III)sericite-chlorite-carbonate type. The assemblage of sulfide minerals characteristically differs in each type of the deposits. The distribution of the Kuroko deposits, classified according to the three types, shows regional zoning. At the waning stage of the deposition of black ore of type (II), related mineral assemblages of both types (I) and (III) are found locally. Slight increase in fugacities of oxygen and sulfur, and decrease in temperature took place during the formation of a deposit. Regional zoning of the assemblage of alteration minerals, therefore, corresponds to slight differences in the processes of ore formation during deposition.  相似文献   

Concentrations of Trace Elements in Carbonate Reference Materials Coral JCp-1 and Giant Clam JCt-1 by Inductively Coupled Plasma-Mass Spectrometry   总被引：1，自引：0，他引：1  

Mayuri Inoue  Masato Nohara  Takashi Okai  Atsushi Suzuki  Hodaka Kawahata 《Geostandards and Geoanalytical Research》2004,28(3):411-416

Trace elements in the Geological Survey of Japan carbonate reference materials Coral JCp-1 and Giant Clam JCt-1 were determined by inductively coupled plasma-mass spectrometry after digestion with 2% v/v HNO₃. A standard addition method was adopted in this determination in order to neutralise the Ca matrix effect. In addition, Sc, Y, In and Bi were used as internal standards to control the matrix effect and correct instrumental drift. Of the eighteen elements measured in JCp-1, precisions for fourteen elements, including Cu, Cd and Ba, were better than 10% RSD and concentrations ranged from 0.002 μg g^-1 (Cs) to 8.02 μg g^-1 (Ba). The concentrations of measured trace elements in JCt-1, except for Cu, were lower than those in JCp-1. Precisions for all elements with concentrations higher than 0.04 μg g^-1 in JCt-1 were also better than 10% RSD and concentrations were found to be between 0.001 μg g^-1 (Cs) and 4.84 μg g^-1 (Ba). The concentrations of more than fifteen trace elements in the aragonite reference materials are reported here for the first time. Both reference materials are suitable for use in geochemical studies of environmental reconstruction based upon biogenic carbonate materials.  相似文献   

About This Issue: Kuroko Deposits Revisited after the Discovery of Their Modern Analogues on Submarine Arc Volcanoes     

Tetsuro Urabe  Hiroshi Kubota 《Resource Geology》2004,54(4):385-386

  相似文献