Anaerobic methane oxidation and a deep H₂S sink generate isotopically heavy sulfides in Black Sea sediments     

Bo Barker Jørgensen  Michael E. Böttcher  Lev N. Neretin 《Geochimica et cosmochimica acta》2004,68(9):2095-2118

The main terminal processes of organic matter mineralization in anoxic Black Sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2-4 m and methanogenesis below the sulfate zone. The modern marine deposits comprise a ca. 1-m-deep layer of coccolith ooze and underlying sapropel, below which sea water ions penetrate deep down into the limnic Pleistocene deposits from >9000 years BP. Sulfate reduction rates have a subsurface maximum at the SO₄²⁻-CH₄ transition where H₂S reaches maximum concentration. Because of an excess of reactive iron in the deep limnic deposits, most of the methane-derived H₂S is drawn downward to a sulfidization front where it reacts with Fe(III) and with Fe²⁺ diffusing up from below. The H₂S-Fe²⁺ transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur. The pore water gradients respond dynamically to environmental changes in the Black Sea with relatively short time constants of ca. 500 yr for SO₄²⁻ and 10 yr for H₂S, whereas the FeS in the black band has taken ca. 3000 yr to accumulate. The dual diffusion interfaces of SO₄²⁻-CH₄ and H₂S-Fe²⁺ cause the trapping of isotopically heavy iron sulfide with δ³⁴S = +15 to +33‰ at the sulfidization front. A diffusion model for sulfur isotopes shows that the SO₄²⁻ diffusing downward into the SO₄²⁻-CH₄ transition has an isotopic composition of +19‰, close to the +23‰ of H₂S diffusing upward. These isotopic compositions are, however, very different from the porewater SO₄²⁻ (+43‰) and H₂S (−15‰) at the same depth. The model explains how methane-driven sulfate reduction combined with a deep H₂S sink leads to isotopically heavy pyrite in a sediment open to diffusion. These results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth’s history.  相似文献   

自适应空间信息移动服务   总被引：4，自引：0，他引：4  

张海堂罗睿  张永生李波 《测绘学院学报》2004,21(1):34-37,41

空间信息移动服务系统是空间信息系统继由传统PC计算环境向有线Web分布式计算环境扩展后，向移动计算环境的新发展。文中在分析移动计算环境概念和特点的基础上，讨论了空间信息移动服务的若干特点及关键技术，研究了自适应空间信息移动服务方案。  相似文献   

自动气象站雨量资料的获取与转换     

余卫东  任光辉董博 杨君健 《河南气象》2005,(4):41-42

分析了自动气象站分钟雨量资料获取与转换的必要性,介绍了雨量资料获取的思路与具体方法.通过这种方法,实现了商丘市所有自动气象站雨量资料的共享,并与GPRS、GSM乡级自动雨量站资料进行融合.  相似文献   

Spatial damage distribution of August 16,2003,Inner Mongolia,China,M_S=5.9 earth-quake and analysis     

高孟潭  许力生  郭文生  万波  俞言祥 《地震学报(英文版)》2005,18(2)

Introduction The ground motion is generally estimated by attenuation relation in seismic hazard assesment.The attenuation relation is usually the function of earthquake magnitude and distance.Actually the focal mechanism and other source parameters may also have significant impacts on the ground motion,especially in the near-source region.Recent post-earthquake investigations show that the damages have close relation with the closest fault-plane distance.On August16,2003,a MS=5.9earthquake o…  相似文献   

桩底注浆钻孔灌注桩承载力的研究     

李连营  林波  邵建 《岩土工程技术》2005,19(1):24-27

通过天津地区几例钻孔灌注桩桩底注浆的静载荷试桩结果 ,分析天津地区钻孔灌注桩桩底注浆单桩竖向极限承载力标准值的估算方法  相似文献   

工程破坏区植被发育动态过程的研究 --以古尔班通古特沙漠为例     

倪萍  牛博  刘江 《云南地理环境研究》2005,17(3):13-17

通过样方法及植被调查法,从纵向和横向两个不同方向对工程破坏后的沙地植被进行比较研究。在纵向上,由于植被恢复时间的不同,其恢复的程度也不同。植被恢复状况可明显的分3个阶段:定居前期(1～6a)主要以多年生羽叶三芒草和小半灌木绢蒿为主;中期(7～11a)主要以多年生小半灌木青杆沙蒿为主;后期(12～16a)主要生长着多年生麻黄及草本沙苔,地表出现大面积的生物结皮。在横向上,将恢复后期的植被与原始植被进行比较。通过对植被发育不同阶段过程中物种重要值、物种多样性、丰富度及生活型的变化等方面的调查,发现在不同阶段,各物种的重要值发生了不同的变化,物种多样性指数,均匀度指数,丰富度指数到后期均增大。  相似文献   

Rb2Ca[B4O5(OH)4]2·8H2O溶解及相转化过程的研究   总被引：2，自引：0，他引：2       下载免费PDF全文

王奖  朱黎霞  李淑妮  王波  夏树屏 《盐湖研究》2005,13(1):25-30

利用IR光谱和Raman光谱等实验手段,对25℃时Rb2Ca[B4O5(OH)4]2·8H2O的溶解及相转化过程进行了初步探索,结果表明,Rb2Ca[B4O5(OH)4]2·8H2O溶于水后,硼在溶液中主要以B(OH)3和[B(OH)4]-的形式存在,残留固相由开始的无定形水合三硼酸钙,最终部分转变为Ca2[B3O3(OH)5]2·8H2O晶体。  相似文献   

Damage evolution of tunnel portal during the longitudinal propagation of Rayleigh waves     

Dong Wu  Bo Gao  Yusheng Shen  Jiamei Zhou  Guihong Chen 《Natural Hazards》2015,75(3):2519-2543

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Seasonal variations in infiltrability of moss‐dominated biocrusts on aeolian sand and loess soil in the Chinese Loess Plateau     

Bo Xiao  Fuhai Sun  Xiaomeng Yao  Kelin Hu  Giora J. Kidron 《水文研究》2019,33(18):2449-2463

Biocrust effects on soil infiltration have attracted increasing attention in dryland ecosystems, but their seasonal variations in infiltrability have not yet been well understood. On the Chinese Loess Plateau, soil infiltrability indicated by saturated hydraulic conductivity (K_s) of biocrusts and bare soil, both on aeolian sand and loess soil, was determined by disc infiltrometer in late spring (SPR), midsummer (SUM), and early fall (FAL). Then their correlations with soil biological and physiochemical properties and water repellency index (RI) were analysed. The results showed that the biocrusts significantly decreased K_s both on sand during SPR, SUM, and FAL (by 43%, 66%, and 35%, respectively; P < .05) and on loess (by 42%, 92%, and 10%, respectively; P <.05). As compared with the bare soil, the decreased K_s in the biocrusted surfaces was mostly attributed to the microorganism biomass and also to the increasing content of fine particles and organic matter. Most importantly, both the biocrusts and bare soil exhibited significant (F ≥ 11.89, P ≤ .003) seasonal variations in K_s, but their patterns were quite different. Specifically, the K_s of bare soil gradually decreased from SPR to SUM (32% and 42% for sand and loess, respectively) and FAL (29% and 39%); the K_s of biocrusts also decreased from SPR to SUM (59% and 92%) but then increased in FAL (36% and 588%). Whereas the seasonal variations in K_s of the biocrusts were closely correlated with the seasonal variations in RI, the RI values were not high enough to point at hydrophobicity. Instead of that, the seasonal variations of K_s were principally explained by the changes in the crust biomass and possibly by the microbial exopolysaccharides. We conclude that the biocrusts significantly decreased soil infiltrability and exhibited a different seasonal variation pattern, which should be carefully considered in future analyses of hydropedological processes.  相似文献   

A two‐dimensional coupled hydromechanical discontinuum model for simulating rock hydraulic fracturing          下载免费PDF全文

Yu‐Yong Jiao  Huan‐Qiang Zhang  Xiu‐Li Zhang  Hai‐Bo Li  Qing‐Hui Jiang 《国际地质力学数值与分析法杂志》2015,39(5):457-481

Within the framework of our discontinuous deformation analysis for rock failure algorithm, this paper presents a two‐dimensional coupled hydromechanical discontinuum model for simulating the rock hydraulic fracturing process. In the proposed approach, based on the generated joint network, the calculation of fluid mechanics is performed first to obtain the seepage pressure near the tips of existing cracks, and then the fluid pressure is treated as linearly distributed loads on corresponding block boundaries. The contribution of the hydraulic pressure to the initiation/propagation of the cracks is considered by adding the components of these blocks into the force matrix of the global equilibrium equation. Finally, failure criteria are applied at the crack tips to determine the occurrence of cracking events. Several verification examples are simulated, and the results show that this newly proposed numerical model can simulate the hydraulic fracturing process correctly and effectively. Although the numerical and experimental verifications focus on one unique preexisting crack, because of the capability of discontinuous deformation analysis in simulating block‐like structures, the proposed approach is capable of modeling rock hydraulic fracturing processes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献