黄土碳酸盐碳同位素环境意义讨论          下载免费PDF全文

金雅琪  苗甜  路珂珂  杨雁鹏  梁孔秋  宋垠先  陈忠 《盐湖研究》2022,30(1):87-94

黄土碳酸盐碳同位素广泛应用于第四纪气候环境变化的研究中,以往研究中多利用钙结核、次生碳酸盐或成壤碳酸盐,认为其反映了C4植物的丰度.黄土高原碳酸盐碳同位素表现为黄土层高,古土壤层中低,即黄土层中C4植物丰度高于古土壤层.然而,这样的结果和黄土有机碳同位素得到的结果矛盾,有机碳同位素的结果表明温度对C4植物的分布起到了决...  相似文献   

Lunar atmospheric H₂ detections by the LAMP UV spectrograph on the Lunar Reconnaissance Orbiter     

S. Alan Stern  Jason C. Cook  Jean -Yves Chaufray  Paul D. Feldman  G. Randall Gladstone  Kurt D. Retherford 《Icarus》2013

We report on the detection of H₂ as seen in our analysis of twilight observations of the lunar atmosphere observed by the LAMP instrument aboard NASA’s Lunar Reconnaissance Orbiter. Using a large amount of data collected on the lunar atmosphere between September 2009 and March 2013, we have detected and identified, the presence of H₂ in the native lunar atmosphere, for the first time. We derive a surface density for H₂ of 1.2 ± 0.4 × 10³ cm⁻³ at 120 K. This is about 10 times smaller than originally predicted, and several times smaller than previous upper limits from the Apollo era data.  相似文献   

Comparison of the moments of the Xmax distribution predicted by different cosmic ray shower simulation models     

《Astroparticle Physics》2013

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元素地球化学不活动组份判别--以库布苏金矿中矿带研究为例     

孙华山  高怀忠 《矿产与地质》2000,14(5)

利用 Gresens( 1967)质量平衡方程及 Brimhall等 ( 1987)提出的元素不活动组份ΔX- fv 图解 ,对复杂热液成矿体系的元素不活动组份进行了深入探讨。指出了复杂体系内部各个子体系间元素不活动组份及体积变化上的差异。并结合库布苏金矿中矿带元素不活动组份进行了研究。同时对一些矿床地质现象的形成及成矿物质来源从元素地球化学角度进行了解释和判断。  相似文献   

Upper crustal abundances of trace elements: A revision and update   总被引：7，自引：0，他引：7  

Zhaochu Hu  Shan Gao   《Chemical Geology》2008,253(3-4):205-221

We report new estimates of abundances of rarely analyzed elements (As, B, Be, Bi, Cd, Ge, In, Mo, Sb, Sn, Te, Tl, W) in the upper continental crust based on precise ICP-MS analyses of well-characterized upper crustal samples (shales, pelites, loess, graywackes, granitoids and their composites) from Australia, China, Europe, New Zealand and North American. Obtaining a better understanding of the upper crustal abundance and associated uncertainties of these elements is important in placing better constraints on bulk crust composition and, from that, whole Earth models of element cycling and crust generation. We also present revised abundance estimates of some more commonly analyzed trace elements (Li, Cr, Ni, and Tm) that vary by > 20% compared to previous estimates. The new estimates are mainly based on significant (r² > 0.6) inter-element correlations observed in clastic sediments and sedimentary rocks, which yield upper continental crust elemental ratios that are used in conjunction with well-determined abundances for certain key elements to place constraints on the concentrations of the rarely analyzed elements. Using the well-established upper crustal abundances of La (31 ppm), Th (10.5 ppm), Al₂O₃ (15.40%), K₂O (2.80%) and Fe₂O₃ (5.92%), these ratios lead to revised upper crustal abundances of B = 47 ppm, Bi = 0.23 ppm, Cr = 73 ppm, Li = 41 ppm, Ni = 34 ppm, Sb = 0.075, Te = 0.027 ppm, Tl = 0.53 ppm and W = 1.4 ppm. No significant correlations exist between Mo and Cd and other elements in the clastic sediments and sedimentary rocks, probably due to their enrichment in organic carbon. We thus calculate abundances of these elements by assuming the upper continental crust consists of 65% granitoid rocks plus 35% clastic sedimentary rocks. The validity of this approach is supported by the similarity of SiO₂, Al₂O₃, La and Th abundances calculated in this way with their upper crustal abundances given in Rudnick and Gao [Rudnick, R., Gao, S., 2003. Composition of the continental crust. In: Rudnick, R.L. (Ed.), The Crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, vol. 3. Elsevier–Pergamon, Oxford, pp. 1–64.]. The upper crustal abundances thus obtained are Mo = 0.6 ppm and Cd = 0.06 ppm. Our data also suggest a  20% increase of the Tm, Yb and Lu abundances reported in Rudnick and Gao [Rudnick, R., Gao, S., 2003. Composition of the continental crust. In: Rudnick, R.L. (Ed.), The Crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, vol. 3. Elsevier–Pergamon, Oxford, pp. 1–64.].  相似文献   

Negative ion chemistry in Titan's upper atmosphere     

V. Vuitton  P. Lavvas  M. Galand  G.R. Lewis  A.J. Coates  J.-E. Wahlund 《Planetary and Space Science》2009,57(13):1558-662

The Electron Spectrometer (ELS), one of the sensors making up the Cassini Plasma Spectrometer (CAPS) revealed the existence of numerous negative ions in Titan's upper atmosphere. The observations at closest approach (∼1000 km) show evidence for negatively charged ions up to ∼10,000 amu/q, as well as two distinct peaks at 22±4 and 44±8 amu/q, and maybe a third one at 82±14 amu/q. We present the first ionospheric model of Titan including negative ion chemistry. We find that dissociative electron attachment to neutral molecules (mostly HCN) initiates the formation of negative ions. The negative charge is then transferred to more acidic molecules such as HC₃N, HC₅N or C₄H₂. Loss occurs through associative detachment with radicals (H and CH₃). We attribute the three low mass peaks observed by ELS to CN⁻, C₃N⁻/C₄H⁻ and C₅N⁻. These species are the first intermediates in the formation of the even larger negative ions observed by ELS, which are most likely the precursors to the aerosols observed at lower altitudes.  相似文献   

Two new V-type asteroids in the outer Main Belt?     

R. Duffard  F. Roig 《Planetary and Space Science》2009,57(2):229-1138

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Methane absorption coefficients for the jovian planets from laboratory, Huygens, and HST data     

Erich Karkoschka  Martin G. Tomasko 《Icarus》2010,205(2):674-694

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The ultraviolet reflectance of Enceladus: Implications for surface composition     

Amanda R. Hendrix  Candice J. Hansen 《Icarus》2010,206(2):608-617

The reflectance of Saturn’s moon Enceladus has been measured at far ultraviolet (FUV) wavelengths (115-190 nm) by Cassini’s Ultraviolet Imaging Spectrograph (UVIS). At visible and near infrared (VNIR) wavelengths Enceladus’ reflectance spectrum is very bright, consistent with a surface composed primarily of H₂O ice. At FUV wavelengths, however, Enceladus is surprisingly dark - darker than would be expected for pure water ice. Previous analyses have focused on the VNIR spectrum, comparing it to pure water ice (Cruikshank, D.P., Owen, T.C., Dalle Ore, C., Geballe, T.R., Roush, T.L., de Bergh, C., Sandford, S.A., Poulet, F., Benedix, G.K., Emery, J.P. [2005] Icarus, 175, 268-283) or pure water ice plus a small amount of NH₃ (Emery, J.P., Burr, D.M., Cruikshank, D.P., Brown, R.H., Dalton, J.B. [2005] Astron. Astrophys., 435, 353-362) or NH₃ hydrate (Verbiscer, A.J., Peterson, D.E., Skrutskie, M.F., Cushing, M., Helfenstein, P., Nelson, M.J., Smith, J.D., Wilson, J.C. [2006] Icarus, 182, 211-223). We compare Enceladus’ FUV spectrum to existing laboratory measurements of the reflectance spectra of candidate species, and to spectral models. We find that the low FUV reflectance of Enceladus can be explained by the presence of a small amount of NH₃ and a small amount of a tholin in addition to H₂O ice on the surface. The presence of these three species (H₂O, NH₃, and a tholin) appears to satisfy not only the low FUV reflectance and spectral shape, but also the middle-ultraviolet to visible wavelength brightness and spectral shape. We expect that ammonia in the Enceladus plume is transported across the surface to provide a global coating.  相似文献   

Shape and obliquity effects on the thermal evolution of the Rosetta target 67P/Churyumov-Gerasimenko cometary nucleus     

M.C. De Sanctis  J. Lasue  M.T. Capria  D. Turrini 《Icarus》2010,207(1):341-494

This work is dedicated to the application to 67P/Churyumov-Gerasimenko of a new quasi-3D approach for non-spherically shaped comet nuclei with the aim to interpret the current activity of the comet in terms of initial characteristics and to predict shape and internal stratification evolution of the nucleus. The model is applied to differently shaped nuclei taking into account the characteristics of Comet 67P/Churyumov-Gerasimenko deduced from observations. We focus our attention on the combined effects that shapes and obliquity have on the comet surface and sub-surface evolution. We discuss the results in terms of activity, local dust mantle formation and disruption, erosion of the surface and internal stratigraphy.The results show that differently shaped nuclei can have different internal structures leading to different activity patterns and behaviors. Our calculations have shown that local variations in the dust and gas fluxes can be induced by the nucleus shape. The distribution of “active” areas on Comet 67P/Churyumov-Gerasimenko is different because of different shapes, reflecting the illumination conditions on the surface. These shapes can influence the structure of the inner coma, but the coma far away from the nucleus is only marginally affected by the nucleus shape. However, different comet behaviors can arise from differently shaped comet nuclei, especially in terms of local activity, surface and sub-surface characteristics and properties. The water flux local distribution is the most influenced by the shape as it is directly linked to the illumination. Irregular shapes have large shadowing effects that can result in activity patterns on the comet surface.The effects of different pole directions are discussed to see the relations with the nucleus activity and internal structure. It is shown that the orientation of the rotation axis plays a strong role on the surface evolution of 67P/Churyumov-Gerasimenko, determining seasonal effects on the fluxes. The activity of the comet changes greatly with the nucleus obliquity leading to pre-post-perihelion differences in the activity and seasonal effects. The effects of the dust deposition and crust formation on the cometary activity have also been simulated and are discussed with respect to 67P/Churyumov-Gerasimenko observations. The dust mantling is also strongly obliquity dependent, with different surface distributions of the dust-covered regions according to the different comet pole orientations. Finally, we show that our model can reproduce the fluxes behavior near perihelion in terms of amplitude and asymmetry, and we estimate 20% of the illuminated surface to be active.  相似文献