Partitioning and Speciation of Trace Metal Diagenesis in Differing Depositional Environments in the Sediments of the Oman Margin     

Rengasamy?AlagarsamyEmail author  George?A.?Wolff  Roy?Chester 《Aquatic Geochemistry》2005,11(2):195-213

Organic-rich sediment samples collected from a transect within, and below, the Oman Margin oxygen minimum zone (OMZ) were analysed using a sequential leaching technique to characterise the diagenetic behaviour and speciation of Mn and Fe in operationally defined sediment host fractions. Trace metals showed distinct diagenetic behaviour in the two contrasting environments that were sampled. The absence of non-detrital Mn in the cores below the OMZ site is attributed to the lack of easily reducible oxides in surficial sediments and to the reduction and export of any moderately reducible aged oxides. The reactive form of solid phase Mn showed a classic feature of enrichment in the upper layer of the sediments at the abyssal site, reflecting the presence of an oxidising sedimentary layer which acts as a Mn trap during its recycling. The diagenetic Mn enrichment was inferred from typical downcore colour changes and an upward-increasing Mn content in the upper core sections. An easily reducible Fe oxide layer was observed in the abyssal sediments at an identical depth to the Mn enrichment suggesting that Fe associated with Mn oxides also has undergone sub-oxic diagenesis. However, the association of Fe with organic matter did not indicate diagenetic modification; i.e., the binding strength of the metal with organic materials appears to be sufficiently strong to preserve the trace metal. The speciation signature of non-detrital Fe differed from that of Mn. The association of Fe with organic matter suggests that this metal does not undergo diagenetic modification and is preserved in abyssal sediments. The contrasting behaviour of Mn and Fe observed between cores within the OMZ were particularly interesting. Another interesting observation was that, for cores below the OMZ, the iron oxides were associated with the Mn-oxide peak, rather than deeper in the sediments as observed by earlier studies in the Atlantic [Froelich et al. (1979). Geochim. et Cosmochim Acta 43, 1075–1090].This revised version was published online in May 2005 with corrections to the article title.  相似文献   

Influence of glacial retreat on natural hazards of the Palcacocha Lake area, Peru   总被引：1，自引：1，他引：0  

Vít Vilímek  Marco Luyo Zapata  Jan Klimeš  Zdeněk Patzelt  Nelson Santillán 《Landslides》2005,2(2):107-115

In this article we describe natural hazards associated with outburst floods of Palcacocha Lake and landslide events on the slopes of its moraine dam, in Cojup Valley, Cordillera Blanca (Peru). These events occurred in the last 70 years and some of them resulted in disasters, which strongly affected the city of Huarás. Field investigations and reference expression hydrodynamic tests as well as archive satellite images and aerial pictures were used to describe the evolution of hazards connected with Palcacocha Lake. Expression hydrodynamic tests proved a high permeability of sandy gravels glacial sediments, which form the present-day lake dam. Seepage through the natural dam forming small ponds below the overflow spillways occurs. A retreat of the glacial tongue causing an increase of the lake volume and unloading of the slope toe areas are the most important recent processes that influence the potential hazards affecting the Cojup valley. The research has proved that the climate warming and ongoing deglaciation play a very significant role in the change of natural hazards conditions in high mountains.  相似文献   

Reliability of Ambient Noise Horizontal-to-Vertical Spectral Ratio in Urban Environments: The Case of Thessaloniki City (Northern Greece)     

A. A. Panou  N.P. Theodulidis  P.M. Hatzidimitriou  A.S. Savvaidis  C.B. Papazachos 《Pure and Applied Geophysics》2005,162(5):891-912

In the framework of an ambient noise measurement project in the downtown district of the City of Thessaloniki (Northern Greece), several tests and evaluation of noise recordings were performed in selected sites. This data set was processed and compared with previous results for the same sites in terms of horizontal-to-vertical (H/V) spectral ratio obtained from weak and strong motion earthquake data. The recording system used was tested against a reference one. Finally, systematic ambient noise measurements were performed at eight sites in the citys downtown area, to evaluate diurnal and seasonal variations. It was concluded that the recording system used was reliable and the ambient noise H/V spectral ratios were in good agreement with relevant results previously obtained. Diurnal variation of the ambient noise H/V spectral ratio showed that it is preferable to perform measurements during the calm hours of the day, when man-made noise is relatively low. However, no systematic seasonal fluctuation effect on the ambient noise H/V spectral ratio was identified.  相似文献   

云南天文台丽江高美古和昆明的大气视宁度研究   总被引：5，自引：1，他引：4  

钱铜铃  邱春蓉  岑学奋  王建成  许骏  汪从云 《天文学报》2001,42(1):101-111

研究云南天文台昆明凤凰山和丽江高美古两地点的大气视宁度。利用云南天文台于1994年建立的3孔较差视宁度监视仪（3孔DIMM），对这两个地点的视宁度对比观测。还利用云南天文台的1米望远镜所得到的视宁度与3孔DIMM所测的视宁度进行对比。1米望远镜和3孔DIMM同时观测了7个晚上，各取得308组数据，它们的视宁度平均分别为0．90〃和0．84〃。还讨论了3孔DIMM采用不同曝光时间对视宁度测量值的影响，从实验得出3孔DIMM采用20ms曝光比采用8ms曝光所测视宁度的值要好15％左右。从1995年5月－1996年12月，对丽江高美古和昆明凤凰山二地进行了视宁度的对比观测。在高美古和昆明分别观测了234夜和256夜，观测结果是两个点的视宁度平均；丽江为0．70〃，昆明为0．95〃，同时也统计了两个点的月平均视宁度和最好夜的视宁度，并讨论了两地视宁度随时间的变化规律。  相似文献   

使用ASP和ADO技术访问Web数据库   总被引：2，自引：0，他引：2  

徐虹  杜斌 《成都信息工程学院学报》2001,16(4):267-268

通过一个网络购书系统的开发过程，阐述了如何使用ASP和ADO技术访问Web数据库，实现数据库化的动态网站。该系统安全、方便、功能完备，具有一定的实用价值。  相似文献   

On Transpiration and Soil Moisture Content Sensitivity to Soil Hydrophysical Data     

Ferenc?ácsEmail author 《Boundary-Layer Meteorology》2005,115(3):473-497

Sensitivity of evapotranspiration E and root zone soil moisture content θ to the parameterization of soil water retention Ψ(θ) and soil water conductivity K(Ψ), as well as to the definition of field capacity soil moisture content, is investigated by comparing Psi1-PMSURF and Theta-PMSURF models. The core of PMSURF (Penman–Monteith Surface Fluxes) consists of a 3-layer soil moisture prediction module based on Richard’s equation in combination with the Penman–Monteith concept for estimating turbulent heat fluxes. Psi1- PMSURF and Theta-PMSURF differ only in the parameterization of the moisture availability function F_ma. In Psi1,F_ma is parameterized by using Ψ(θ) and K(Ψ) hydrophysical functions; in Theta, F_ma is parameterized by using hydrophysical parameters: the field capacity θ_f and wilting point θ_w soil moisture contents. Both Psi1 and Theta are based on using soil hydrophysical data, that is, there is no conceptual difference between them in the parameterization of E even if in Psi1F_ma depends on 12 parameters, while in Theta only on two soil/vegetation parameters. Sensitivity tests are performed using the Cabauw dataset. Three soil datasets are used: the vG (van Genuchten), CH/vG (Clapp and Hornberger/van Genuchten) and CH/PILPS (Clapp and Hornberger/Project for Intercomparison of Land-surface Parameterization Schemes) datasets. The vG dataset is used in van Genuchten’s parameterization, while in Clapp and Hornberger’s the CH/vG and CH/PILPS datasets are used. It is found that the consistency of soil hydrophysical data in the simulation of transpiration is quite important. The annual sum of E obtained by Psi1E^Psi1, differs from the annual sum of E obtained by Theta, E^Theta, because of the inconsistency between the fitting parameters of Ψ(θ) and K(Ψ) and the θ_f, and not because of the differencies in the parameterization of F_ma. Further, θ_f can be estimated not only on the basis of using soil hydrophysical functions (the θ_f so obtained is θ^Soil_f) but also on the basis of analysing the transpiration process (the θ_fso obtained is θ^tr_f). θ^tr_f values estimated from the condition E^Theta ≈ E^Psi1 are in acceptable accordance with the θ^Soil_f values proposed by Wösten and co-workers. The results are useful in optimizing the parameterization of transpiration in land-surface schemes.  相似文献   

A site effect study in the Verchiano valley during the 1997 Umbria-Marche (Central Italy) earthquakes     

Stéphane Gaffet  Giovanna Cultrera  Michel Dietrich  Françoise Courboulex  Fabrizio Marra  Michel Bouchon  Arrigo Caserta  Cécile Cornou  Anne Deschamps  Jean-Paul Glot  Robert Guiguet 《Journal of Seismology》2000,4(4):525-541

Strong site effects were observed during the two M _W 5.7 and M _W 6.0 main shocks of the Colfiorito seismic crisis which occured on September 26, 1997 in Umbria-Marche (Central Italy).The most obvious indications of these effects are the dramatic differences in damage shown by buildings of similar construction in neighboring villages.Such observations were specifically made in the Verchiano valley in the fault area, 15 km south of Colfiorito where the Verchiano village and the Colle and Camino hamlets were heavily damaged (MCS intensity IX-X) since the first main shock of 1997/09/26,while in contrast, the Curasci village located 2 km eastwards remains almost intact.In order to study the anomalous ground motion amplifications in this area, an array of 11, 3-components seismo- and accelero-meters was set up during the 1997/10/20-24 period, extending from the western side of the valley, up to the top of Mount San Salvatore, going accross the Colle and Curasci hamlets.During the experiment, 67 aftershocks enlightened the valley from the Colfiorito (10 km north) and the Sellano (6 km south) active swarms.Seismic refraction experiments were conducted at the same time in the 500 m wide, 1500 m long Verchiano valley in order to determine the thickness and main characteristics of the alluvial infilling.The main results are: (i) compared to the valley side ground motion, and for all the events, recordings in the central part of the valley (piana di Verchiano) show relative amplification of 10 with a clear lengthening of the seismogram duration by a factor of 2 – (ii) broad band relative amplification of 6–8 is also clearly identified at the top of the Mount San Salvatore overhanging the valley – (iii) any of the site effect measurements done explains by itself the strongly contrasted damage observed at Colle and Curasci: i.e. the modification of the near-field radiation pattern by interaction with the free heterogeneous surface may have induced local shadow zones that saved Curasci.  相似文献   

金沙遗址古环境状况的综合探讨   总被引：1，自引：0，他引：1       下载免费PDF全文

傅 顺叶青培  王成善刘 建 李 奎 《中国地质》2005,32(3):523-528

史期时期，人类社会的生产力还十分低下，自然环境对古人类体质的进化、生产的发展，以及居住范围的变化都产生了重大的影响。通过孢粉分析和对其他植物遗存的研究复原古植被特征，同时结合广汉层古土壤地球化学行为、古河流的水动力等，来综合研究金沙遗址区古环境状况，以期能为古蜀文化研究提供环境背景。研究结果表明，文化期内总体上是热带和亚热带的温暖湿润气候，同时存在着温暖湿润与温暖干旱的气候交替。  相似文献   

高岭石表面酸碱反应的电位滴定实验研究   总被引：2，自引：0，他引：2       下载免费PDF全文

高嵩何广平  吴宏海孙伟亚 《岩石矿物学杂志》2005,24(3):239-244

采用表面酸碱电位滴定法探讨高岭石表面酸碱性质,基于多位模式(即假定高岭石表面存在3种基团Al2 OH 、AlOH 和SiOH ) ,根据实验所得数据对高岭石表面的质子化和去质子化过程的相关参数进行拟合,讨论各个位点所发生的反应,并探讨了支持电解质浓度、高岭石溶解过程对表面酸碱电位滴定结果的影响。高岭石的表面零净质子电荷点(pHPZNPC,5 .2 )不等同于零电荷点,当pH <5 .2时,高岭石表面荷正电荷,主要由于表面富硅贫铝层的形成和Al位的质子化所致;当pH >5 .2时,高岭石表面荷负电荷,以Si位和Al的去质子化反应为主。  相似文献   

中国重要古生物化石及其产地保护浅论   总被引：2，自引：0，他引：2  

张红珍  梁永宁 《云南地理环境研究》2005,17(Z1):70-73

中国古生物化石资源丰富且分布较广,目前在化石的保护与利用上还存在着诸多问题,主要体现在以下几个方面:古生物化石流失严重;古生物化石管理机构不健全;保护法规宣传力度不够;对外交流工作不够;其科普教育价值没有充分发挥;公众保护意识较差等。据此提出如下保护策略及措施:加大相关法律宣传力度;正确处理化石产地、旅游与地方经济的关系;科学规划保护区;积极开展科研工作,大力推广地质科普游;建立健全稳定的资金投入保障机制;加强生态环境的保护;有机整合地质资源,增加吸引力。  相似文献