Modeling non-steady state radioisotope transport in the vadose zone - A case study using uranium isotopes at Peña Blanca, Mexico     

T.L. Ku  S. Luo  M.T. Murrell  P.F. Dobson 《Geochimica et cosmochimica acta》2009,73(20):6052-6064

Current models using U- and Th-series disequilibria to study radioisotope transport in groundwater systems mostly consider a steady-state situation. These models have limited applicability to the vadose zone (UZ) where the concentration and migratory behavior of radioisotopes in fluid are often transitory. We present here, as a first attempt of its kind, a model simulating the non-steady state, intermittent fluid transport in vadose layers. It provides quantitative constraints on in-situ migration of dissolved and colloidal radioisotopes in terms of retardation factor and rock-water interaction (or water transit) time. For uranium, the simulation predicts that intermittent flushing in the UZ leads to a linear relationship between reciprocal U concentration and ²³⁴U/²³⁸U ratio in percolating waters, with the intercept and slope bearing information on the rates of dissolution and α-recoil of U isotopes, respectively. The general validity of the model appears to be borne out by the measurement of uranium isotopes in UZ waters collected at various times over a period during 1995-2006 from a site in the Peña Blanca mining district, Mexico, where the Nopal I uranium deposit is located. Enhanced ²³⁴U/²³⁸U ratios in vadose-zone waters resulting from lengthened non-flushing time as prescribed by the model provide an interpretative basis for using ²³⁴U/²³⁸U in cave calcites to reconstruct the regional changes in hydrology and climate. We also provide a theoretical account of the model’s potential applications using radium isotopes.  相似文献   

An empirical model for estimating hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan     

Cheng-Yu Ku  Shih-Meng Hsu  Lin-Bin Chiou  Gwo-Fong Lin 《Engineering Geology》2009,109(3-4):213-223

This paper presents the establishment of an empirical HC model for estimating rock mass hydraulic conductivity of highly disturbed clastic sedimentary rocks in Taiwan using high-resolution borehole acoustic televiewer and double packer hydraulic tests. Four geological parameters including rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI) were adopted for establishing the empirical HC model. To verify rationality of the proposed HC model, 22 in-situ hydraulic tests were carried out to measure the hydraulic conductivity of the highly disturbed clastic sedimentary rocks in three boreholes at two different locations in Taiwan. Besides, the model verification using another borehole data with four additional in-situ hydraulic tests from similar clastic sedimentary rocks was also conducted to further verify the feasibility of the proposed empirical HC model. The field results indicated that the rock mass in the study area has a conductivity between the order of 10^− 10 m/s and 10^− 6 m/s at the depth between 34 m and 275 m below ground surface. Results demonstrate that the empirical HC model may provide a useful tool to predict hydraulic conductivity of the highly disturbed clastic sedimentary rocks in Taiwan based on measured HC-values.  相似文献   

Trace element contents and C-O isotope geochemistry of the different originated magnesite deposits in Lake District (Southwestern Anatolia), Turkey     

Mustafa Kuşcu  Oya Cengiz  Asuman Kahya 《Arabian Journal of Geosciences》2017,10(15):339

Vein-stockwork magnesite in the Madenli area, sedimentary huntite-magnesite in the A?a??t?rtar area, and lacustrine hydromagnesite in the Salda Lake area are located in the Bey?ehir-Hoyran and Lycian nappe rocks around Isparta and Burdur, Southwest Anatolia. The aim of this study is to understand trace element contents and carbon-oxygen isotope ratios in different originated magnesite, magnesite bearing huntite, and hydromagnesite deposits. Also, the element contents and isotope ratios of the magnesite occurrences are to compare with each other and similar magnesite occurrences in Turkey and world. It is found that the Madenli magnesite occurrences in the ?arkikaraa?aç ophiolites, A?a??t?rtar magnesite bearing huntite deposits in the lacustrine rocks of the Miocene-Pliocene, and the Salda hydromagnesite deposits in lacustrine basin on the Ye?ilova ophiolites. The paragenesis contains a common carbonate mineral magnesite, less calcite, serpentine, smectite, dolomite, and talc in the Madenli magnesite occurrences, mostly huntite and locally magnesite, dolomite, calcite, illite, quartz, and smectite in the A?a??t?rtar huntite-magnesite occurrences, and only hydromagnesite mineral in the Salda Lake hydromagnesite occurrences. Vein and stockwork Madenli magnesite deposits were recognized by higher total iron oxide concentrations (mean 1.10 wt%) than sedimentary A?a??t?rtar magnesite bearing huntite (mean 0.13 wt%) and lacustrine Salda hydromagnesite (mean 0.22 wt%) deposits. It is suggested that high Fe content (up to 5%) in the magnesite associated with ultramafic rocks than those from sedimentary environments (≤1% Fe). Based on average Ni, Co, Ba, Sr, As and Zr contents in the magnesite deposits, average Ni (134.63 ppm) and Co (15.19 ppm) contents in the Madenli magnesite and Salda hydromagnesite (36.85 ppm for Ni, 3.15 ppm for Co) have higher values than A?a??t?rtar huntite + magnesite (7.67 ppm for Ni and 0.89 ppm for Co). Average Ni-Co contents of these deposits can have close values depending on ophiolite host rock. Average Ba values of the Madenli (108.09 ppm) and A?a??t?rtar (115.88 ppm) areas are higher than those of Salda hydromagnesite (13.15 ppm). Sediment-hosted A?a??t?rtar magnesite-huntite deposits have the highest Sr contents (mean 505.81 ppm) as reasonably different from ultrabasic rock-related Madenli magnesite (mean 38.76 ppm) and Salda hydromagnesite (mean 36.70 ppm). The highest Sr content of sedimentary A?a??t?rtar deposits reveals that Sr is related to carbonate rocks. As and Zr contents have the highest average values (As 52.76 ppm and Zr 9.67 ppm) in the A?a??t?rtar deposits different from Madenli magnesite (As 0.54 ppm and Zr 1.67 ppm) and Salda hydromagnesite (As 0.5 ppm and Zr 2.58 ppm) deposits. High As and Zr concentrations in the A?a??t?rtar magnesite-huntite deposits may come from volcanic rocks in near country rocks. The δ ¹³C (PDB) isotope values vary between ?10.1 and ?11.4‰ in the Madenli magnesite, 7.8 to 8.8‰ for huntite, 1.7 to 8.3‰ for huntite + magnesite and 4.0‰ for limestone + magnesite in the A?a??t?rtar huntite-magnesite deposits, and 4.4 to 4.9‰ for Salda Lake hydromagnesite. The sources of the CO₂ are hydrothermal solutions, meteoric waters, groundwater dissolved carbon released from fresh water carbonates and marine limestone, soil CO₂, and plant C3 in the Madenli magnesite, and may be deep seated metamorphic reactions in limestone and shales of rich in terms of organic matter. The sources of CO₂ in A?a??t?rtar huntite and Salda hydromagnesite were meteoric water, groundwater dissolved inorganic carbon, fresh water carbonates, and marine limestone. The δ ¹⁸O (SMOW) isotope composition ranges from 26.8 to 28.1‰ in the Madenli magnesite, 30.4 to 32.4‰ for huntite and 29.8 to 35.5‰ for huntite + magnesite and 26.9‰ for limestone + magnesite in the A?a??t?rtar area, and 36.4 to 38.2‰ in the Salda Lake hydromagnesite. The Salda Lake hydromagnesite has heavier oxygen isotopic values than others. The sources of oxygen in the Madenli magnesite deposits are hydrothermal solutions, meteoric water, freshwater carbonates, and marine limestone, but the sources of oxygen of the A?a??t?rtar magnesite-huntite are meteoric water, fresh water carbonates, and marine limestone. The Salda Lake hydromagnesite has very high δ¹⁸O isotope values indicating a strong evaporitic environment. Magnesium (Mg⁺²) and silica are released by disintegration of very weathered-serpentinized ultrabasic rocks of all magnesite deposits and from partly dolomite and dolomitic limestone in the A?a??t?rtar magnesite bearing huntite deposits. In the A?a??t?rtar area, calcium (Ca⁺²) for huntite mineralization is provided by surrounding carbonate rocks. Based on isotopic data, host rocks, petrographic properties of the Madenli magnesite can be described as an ultramafic-associated hydrothermal vein mineralization corresponding to “Kraubath type” deposits, but A?a??t?rtar ve Salda Lake deposits are sedimentary mineralization (lacustrine/evaporitic) corresponding to “Bela Stena type” deposits. The estimated temperature using average δ¹⁸O isotope values is about 33.51 °C for Madenli magnesite, 48.33 °C for A?a??t?rtar huntite-magnesite, and 25 °C for Salda hydromagnesite. Based on isotope data, we can be say that the Madenli magnesite, A?a??t?rtar magnesite-huntite, and Salda hydromagnesite occur at low to moderate-low temperature water and alkaline (pH 8.5–10.5) under surface or near-surface conditions.  相似文献   

西太平洋副热带高压异常进退的对比分析   总被引：4，自引：4，他引：0  

喻世华  赵库 《热带气象学报》1993,(1):12-19

对1980年7月29日—8月16日西太平洋副高位置持续偏南和1983年7月16日—8月12日西太平洋副高位置持续偏北的两次季节内副高中期进退过程的环流特征和加热差异作了对比分析,讨论了东亚季风与对流活动、副高进退之间的关系.   相似文献   

Globular Clusters in the Large Magellanic Cloud: An Impact from GAIA Photometry     

Arūnas Kučinskas  Audrius Bridžius  Vladas Vansevičius 《Astrophysics and Space Science》2002,280(1-2):159-163

The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the Large Magellanic Cloud with ESA's astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective temperatures (Δ T _eff<10%) can be obtained from GAIA photometry down to V ∼ 18 for stars in populations within the studied metallicity range ([M/H] = -0.4 ... -1.7). GAIA will also provide photometric metallicities (Δ [M/H] ≲ 0.3 dex) for the cluster giants brighter than V ∼ 17.5. The knowledge of the effective temperature sand metallicities will allow to obtain accurate ages of stellar populations younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations (≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better understanding of stellar and galactic evolution in different astrophysical environments. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Seasonal and interannual variability of the planktic foraminiferal flux in the vicinity of the Azores Current     

David Storz  Hartmut Schulz  Joanna J. Waniek  Detlef E. Schulz-Bull  Michal Kučera 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(1):107-124

Planktic foraminiferal (PF) flux and faunal composition from three sediment trap time series of 2002–2004 in the northeastern Atlantic show pronounced year-to-year variations despite similar sea surface temperature (SST). The averaged fauna of the in 2002/2003 is dominated by the species Globigerinita glutinata, whereas in 2003/2004 the averaged fauna is dominated by Globigerinoides ruber. We show that PF species respond primarily to productivity, triggered by the seasonal dynamics of vertical stratification of the upper water column. Multivariate statistical analysis reveals three distinct species groups, linked to bulk particle flux, to chlorophyll concentrations and to summer/fall oligotrophy with high SST and stratification. We speculate that the distinct nutrition strategies of strictly asymbiontic, facultatively symbiontic, and symbiontic species may play a key role in explaining their abundances and temporal succession. Advection of water masses within the Azores Current and species expatriation result in a highly diverse PF assemblage. The Azores Frontal Zone may have influenced the trap site in 2002, indicated by subsurface water cooling, by highest PF flux and high flux of the deep-dwelling species Globorotalia scitula. Similarity analyses with core top samples from the global ocean including 746 sites from the Atlantic suggest that the trap faunas have only poor analogs in the surface sediments. These differences have to be taken into account when estimating past oceanic properties from sediment PF data in the eastern subtropical North Atlantic.  相似文献   

Modeling crack propagation path of anisotropic rocks using boundary element method     

Chien‐Chung Ke  Chao‐Shi Chen  Cheng‐Yu Ku  Chih‐Hao Chen 《国际地质力学数值与分析法杂志》2009,33(9):1227-1253

In a cracked material, the stress intensity factors (SIFs) at the crack tips, which govern the crack propagation and are associated with the strength of the material, are strongly affected by the crack inclination angle and the orientation with respect to the principal direction of anisotropy. In this paper, a formulation of the boundary element method (BEM), based on the relative displacements of the crack tip, is used to determine the mixed‐mode SIFs of isotropic and anisotropic rocks. Numerical examples of the application of the formulation for different crack inclination angles, crack lengths, and degree of material anisotropy are presented. Furthermore, the BEM formulation combined with the maximum circumferential stress criterion is adopted to predict the crack initiation angles and simulate the crack propagation paths. The propagation path in cracked straight through Brazilian disc specimen is numerically predicted and the results of numerical and experimental data compared with the actual laboratory observations. Good agreement is found between the two approaches. The proposed BEM formulation is therefore suitable to simulate the process of crack propagation. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Baseline data of subtropical coral communities in Hoi Ha Wan Marine Park, Hong Kong, obtained by an underwater remote operated vehicle (ROV)     

Lam K  Shin PK  Bradbeer R  Ku KK  Hodgson P  Cheung SG 《Marine pollution bulletin》2007,54(1):107-112

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Radiochemical,scanning electron microscope (SEM) and X-ray dispersive energy (EDAX) studies of a FAMOUS hydrothermal deposit     

Claude Lalou  Evelyne Brichet  Teh Lung Ku  Celestine Jehanno 《Marine Geology》1977,24(4):245-258

During the French-American Mid-Oceanic Undersea Survey (FAMOUS) the French team participating in the mission explored the active A transform fault with the diving saucer CYANA, and discovered a characteristic hydrothermal deposit. The results presented here concern the structural and radiochemical study of three samples: two metalenriched samples and one sample of consolidated calcareous sediment recovered from the area.It is shown that there is a chemical segregation between silica and iron on one hand, and manganese in the other hand, and that on such deposits the layer-by-layer radio-chemical analysis of the uranium series is not applicable.Three different age estimations may be made:In the managanese encrustation, thorium 230 is depleted towards equilibrium with its parent uranium 234, suggesting a maximum age of 45,000 years to the deposit.On the contrary, the outermost layer, 0.1 cm thick, formed essentially with loose sediment stained with oxides, presents an excess of thorium 230. The Σ²³⁰Th_(excess)/cm² may be used to calculate a minimum age of 20 years.Such a sediment thickness, in this area, corresponds to a time span of 50 years.  相似文献   

Comparative inverse analysis of satellite (MODIS) and ground (PM10) observations to estimate dust emissions in East Asia     

Bonyang Ku  Rokjin J. Park 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(1):3-17

Soil dust aerosol is the largest contributor to aerosol mass concentrations in the troposphere and has considerable effects on air quality and climate. Arid and semi-arid areas of East Asia are one of the important dust source regions thus it is crucial to understand dust mobilization and accurately estimate dust emissions in East Asia. However, present dust models still contain large uncertainties with dust emissions that remain a significant contributor to the overall uncertainties in the model. In this study, we attempt to reduce these uncertainties by using an inverse modeling technique and obtain optimized dust emissions. We use Moderate Resolution Imaging Spectrometer (MODIS) aerosol optical depths (AODs) and groundbased mass concentrations of particles less than 10 μm in aerodynamic diameter (PM₁₀) observations over East Asia in May 2007. The MODIS AODs are validated with AErosol RObotic NETwork (AERONET) AODs. The inversion uses the maximum a posteriori method and the GEOS-Chem chemical transport model (CTM) as a forward model. The model error is large over dust source regions including the Gobi Desert and Mongolia. We find that inverse modeling analyses from the MODIS and PM₁₀ observations consistently result in decrease of dust emissions over Mongolia and the Gobi Desert. Whereas over the Taklamakan Desert and Manchuria, the inverse modeling analyses from both observations yield contrast results such as increase of dust sources using MODIS AODs, while decrease of those using PM₁₀ observations. We discuss some limitations of both observations to obtain the optimized dust emissions and suggest several strategies for the improvement of dust emission estimates in the model.  相似文献