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81.
Sedimentary and igneous rocks of the Swaziland Sequence of South Africa (>3,200 my. old) contain total carbon (0.09–8.28%), organic carbon (0.04–1.95%) and sulfur (9–53,000 ppm). Amounts of organic carbon are generally high in the lower part of the Sequence (based on two samples from the Theespruit Formation). Sulfur content varies widely with no obvious correlations or trends. These rocks may contain clues to the early carbon and sulfur cycles on earth. 相似文献
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84.
T. J. T. Moore D. E. Bretherton T. Fujiyoshi N. A. Ridge J. Allsopp M. G. Hoare S. L. Lumsden J. S. Richer 《Monthly notices of the Royal Astronomical Society》2007,379(2):663-673
We have surveyed a ∼0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to 2500 M⊙ . Part of the W3 GMC is subject to an interaction with the H ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5–13 per cent in the undisturbed cloud but ∼25–37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation. 相似文献
85.
Robert M. Moore Stephen Punshon Claire Mahaffey David Karl 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1449-1458
Fixed nitrogen is a key nutrient involved in regulating global marine productivity and hence the global oceanic carbon cycle. Oceanic nitrogen (N2) fixation is estimated to supply 8×1012 moles N y?1 to the ocean, approximately equal to current riverine and the atmospheric inputs of fixed N, and between 50 and 100% of current estimates of oceanic denitrification. However, the spatial and temporal variability of N2 fixation remains uncertain, mostly because of the normal low resolution sampling for diazotroph distribution and fixation rates. It is well established that N2 fixation, mediated by the enzyme nitrogenase, is a source of hydrogen (H2), but the extent to which it leads to supersaturation of H2 in oceanic waters is unresolved. Here, we present simultaneous measurements of upper ocean dissolved H2 concentration (nmol L?1), and rates of N2 fixation (μmol N m?3 d?1), determined using 15N2 tracer techniques (at 7 or 15 m), on a transect from Fiji to Hawaii. We find a significant correlation (r=0.98) between dissolved H2 and rates of N2 fixation, with the greatest supersaturation of H2 and highest rates of N2 fixation being observed in the subtropical gyres at the southern (~18°S) and northern (18°N) reaches of the transect. The lowest H2 saturation and N2 fixation were observed in the equatorial region between 8°S and 14°N. We propose that an empirical relationship between H2 supersaturations and N2 fixation measurements could be used to guide sampling for 15N fixation measurements or to aid the spatial interpolation of such measurements. 相似文献
86.
Although water- and ammonia-ices have been observed or postulated as important components of the icy surfaces of planetary satellites in the outer Solar System, significant gaps exist in our knowledge of the spectra and behavior of such mixtures under astrophysical conditions. To that end, we have completed low-temperature spectroscopic studies (1-20 μm) of water-ammonia mixtures, with an emphasis on features in the near-IR, a region which is accessible to ground-based observations. The influences of composition, formation temperature, thermal- and radiation-processing, and phase (crystalline or amorphous) of the components were examined. Spectra of both pure NH3 and H2O-NH3 icy mixtures with ratios from 0.7 to 57 were measured at temperatures from 10 to 120 K. Conditions for the formation and thermal stability of the ammonia hemihydrate (2NH3⋅H2O) and the ammonia monohydrate (NH3⋅H2O) have been examined. Band positions of NH3 in different H2O-ices and major band positions of the hydrates were measured. We report spectral shifts that depend on concentration and temperature. The radiation-induced amorphization of the hemihydrate was observed and the radiation destruction of NH3 in H2O-ices was measured. Implications of these results for the formation, stability, and detection of ammonia on outer satellite surfaces are discussed. 相似文献
87.
The radiation chemistry, thermal stability, and vapor pressure of solid-phase carbonic acid (H2CO3) have been studied with mid-infrared spectroscopy. A new procedure for measuring this molecule’s radiation stability has been used to obtain intrinsic IR band strengths and half-lives for radiolytic destruction. We report, for the first time, measurements of carbonic acid’s vapor pressure (0.290-2.33 × 10−11 bar for 240-255 K) and its enthalpy of sublimation (71 ± 9 kJ mol−1). We also report the first observation of a chemical reaction involving solid-phase carbonic acid. Possible applications of these findings are discussed, with an emphasis on the outer Solar System icy surfaces. 相似文献
88.
西天山喇嘛苏铜矿成矿斑岩的岩石学、地球化学特征及成因探讨 总被引:7,自引:3,他引:4
位于西天山别珍套-科古琴晚古生代岛弧西段的喇嘛苏铜矿床是区内最大的铜矿床,与成矿作用有着密切关系的斑岩体为英云闪长斑岩、花岗闪长斑岩,是同源岩浆分异演化的产物,且花岗闪长斑岩可能属于岩浆演化晚期的产物。本区成矿斑岩的主量、微量元素和Sr-Nd同位素地球化学特征表明,其富集大离子亲石元素,而相对亏损高场强元素,出现了较为明显的Ta、Nb负异常,初始锶同位素ISr和εNd(t=390Ma)值分别为0.7072~0.7076和-0.32~0.17,显示壳幔混合源的特征,利用Sr和Nd同位素估算其源区物质约有50%来源于地壳。岩石地球化学特征指示了其为典型钙碱性火山弧花岗岩,暗示其形成于大陆弧环境。结合区域地质背景,推测本区成矿斑岩是在洋壳俯冲作用下发生部分熔融,交代原先的地幔楔,并混合了部分下地壳的物质,经历分离结晶作用的产物,其形成可能与晚古生代准噶尔洋板块向南的俯冲作用有关。结合东西天山的成矿斑岩的地球化学特征对比研究,岩浆源区的差别可能导致不同类型斑岩型矿床的形成,斑岩型铜矿床的形成较斑岩型钼矿床可能有更少的地壳物质贡献。 相似文献
89.
Nitrate contamination in irrigation groundwater,Isfahan, Iran 总被引:1,自引:1,他引:0
Groundwater is one of the major sources of water in Isfahan. Efficient management of these resources requires a good understanding of its status. This paper focuses on the hydrochemistry and also it wants to assess the nitrate concentration in irrigation groundwater of Isfahan suburb. All the groundwater samples are grouped into three categories, including Na-Cl + Ca-Cl (63 %), Na-SO4 + Ca-SO4 (23 %) and Ca-HCO3 (14 %). According to the EC and SAR, the most dominant classes are C3S1, C4S2 and C4S3. 55 % of samples indicate very high salinity and medium to very high alkalinity that is not suitable for irrigation. 84 % of the groundwater samples show nitrate contents higher than HAV (13 mg l?), while more than 25 % exceeded the maximum contamination level (44.27 mg l?) according to EPA regulations. The horizontal and vertical distribution patterns of nitrate in groundwater samples show a surficial origin for nitrate contamination. The high nitrate content can be attributed to the agricultural activities along with domestic sewage and industrial wastewaters in populated area. Based on results, using high nitrate groundwater for irrigation can minimize the requirement for inorganic fertilizers and reduce the cost of cultivation and nitrate contamination. 相似文献
90.
Brian J. Harshburger Karen S. Humes Von P. Walden Troy R. Blandford Brandon C. Moore Raymond J. Dezzani 《水文研究》2010,24(10):1285-1295
As demand for water continues to escalate in the western Unites States, so does the need for accurate monitoring of the snowpack in mountainous areas. In this study, we describe a simple methodology for generating gridded‐estimates of snow water equivalency (SWE) using both surface observations of SWE and remotely sensed estimates of snow‐covered area (SCA). Multiple regression was used to quantify the relationship between physiographic variables (elevation, slope, aspect, clear‐sky solar radiation, etc.) and SWE as measured at a number of sites in a mountainous basin in south‐central Idaho (Big Wood River Basin). The elevation of the snowline, obtained from the SCA estimates, was used to constrain the predicted SWE values. The results from the analysis are encouraging and compare well to those found in previous studies, which often utilized more sophisticated spatial interpolation techniques. Cross‐validation results indicate that the spatial interpolation method produces accurate SWE estimates [mean R2 = 0·82, mean mean absolute error (MAE) = 4·34 cm, mean root mean squared error (RMSE) = 5·29 cm]. The basin examined in this study is typical of many mid‐elevation mountainous basins throughout the western United States, in terms of the distribution of topographic variables, as well as the number and characteristics of sites at which the necessary ground data are available. Thus, there is high potential for this methodology to be successfully applied to other mountainous basins. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献