湖北宜昌地区下奥陶统生物礁古生态学研究     

肖传桃崔江利  朱忠德李相明龚文平  胡明毅 《地质论评》2004,50(5):520-529

宜昌地区下奥陶统主要为一套台地相碳酸盐沉积,间夹页岩,其中的特征沉积为发育有较多的生物礁。造礁生物主要有海绵类、瓶筐石类、有柄棘皮类、苔藓虫及蓝细菌和Pulchrilamina等。在下奥陶统含礁层系中识别出四种生物相：(1)壳类生物相：发育有Tritoechia-Pelmatozans群落和Tritoechia-Pomatotrema群落;(2)礁生物相：包括Batostoma群落、Calathium--Archaeoscyphia群落、Pelmatozoans--Batostoma群落、Archeoscyphia群落和Calathium--Cyanobacteria群落;(3)静水生物相：发育有Acanthograptus--Dendrogptus群落和Yichangopora群落;(4)异地生物相：产有异地埋藏群,即Nanorthis--Psilocephlina埋藏群。含礁层系存在四个海平面变化旋回,生物礁的发育明显受海平面的升降速率与容纳空间增长速率的控制。生物礁多形成于高海平面时期。由于本区的海平面在上升过程中存在多个次一级旋回,致使生物礁具有数量多、分布广以及厚度薄和规模小等特点。造礁群落存在着演替和取代两种形式,前者有利于生物礁的发育,后者则表现为礁体的衰亡。  相似文献   

Copper and sewage inputs from recreational vessels at popular anchor sites in a semi-enclosed Bay (Qld, Australia): estimates of potential annual loads     

Leon LM  Warnken J 《Marine pollution bulletin》2008,57(6-12):838-845

Environmental impacts of vessels are well documented; Cu pollution as result of Cu based antifouling paints and nutrient pollution (such as N) from marine sewage are two examples of such disturbances. Understanding environmental impacts as well as the use of coastal waterways by recreational vessels is of concern to regulatory authorities, waterway users and local residents. In this study more than 55 aerial surveys were conducted of selected popular anchorages in eastern Moreton Bay, Queensland, Australia. Numbers of recreational vessels at certain times during the year were used in multiple linear regression analyses to develop predictive models for recreational vessel numbers. Over one year approximately 10,000 locally registered recreational craft (>6m length overall) generated an estimated 59,000 vessel nights. With Cu leaching rates from the literature, and estimates of sewage inputs (assuming little or no use of pump-out facilities), load estimates associated with overnight use of 20 popular anchor sites were calculated as 141+/-46 kg of Cu and 1.17+/-0.38 t of nitrogen (N) annually. More importantly, the models showed vessel activity to be highly variable, and focused at peak holiday times, with 14% of vessel activity and associated pollutant loads entering the environment during Christmas and Easter. This study highlighted the inherent difficulties in managing a popular maritime amenity and Marine Parks such as the Moreton Bay Marine Protected Area, Queensland, Australia with its variety of stakeholders and types and intensities of uses.  相似文献   

滇中地区4级调制地震与中强地震的关系     

杨芬  金明培  赵家本 《国际地震动态》2008,(9)

利用1965年1月1日-2006年6月30日云南省地震遥测台网记录的地震正式目录,对正式目录的中强以上地震进行了余震删除.利用已删除余震的正式目录,研究滇中地区4级调制地震与中强地震的三要素关系,总结历史震例得到:滇中地区发生4级调制地震,其后发生中强以上地震的可能性为75%,平均间隔时间为4.7月;而且中强震发震地点与4级调制地震发震地点相关性较好,平均相隔距离为76 km;发生4级孤立型调制地震(无余震发生),其后发生6.5级以上强震的概率为67%;曲江断裂带上发生的4级孤立型调制地震对未来中强震的地点指示意义明确,震级大小与孕震时间相关.  相似文献   

A simulation of the Chilean Coastal Current and associated topographic upwelling near Valparaíso, Chile     

Christopher M. Aiken  Manuel I. Castillo  Sergio A. Navarrete 《Continental Shelf Research》2008,28(17):2371-2381

A 4-year simulation of the surface circulation driven by the local wind on a section of the central Chilean coast is presented. The model is shown to reproduce the major observed features of the circulation. Comparison to observations of sea-surface temperature (SST) taken within the study area suggests that the model captures well coastal upwelling processes in the region. The circulation is shown to have two distinct modes corresponding to spring/summer and autumn/winter. During spring/summer sustained strong south-westerly wind forcing drives an equatorward coastal jet consistent with the Chile Coastal Current (CCC) and coastal upwelling at previously identified locations of intense upwelling at Topocalma Point and Curaumilla Point. Weaker winds during autumn/winter produce a slower CCC and a more homogenous SST field. Upwelling/relaxation and topographic eddies provide the main sources of variability on sub-seasonal time-scales in the model. The mechanisms responsible for each of these are discussed. Upwelling at Topocalma and Curaumilla Points is shown to be produced through generation of an upwelling Ekman bottom boundary layer following acceleration of the CCC close to the coast, reinforced by secondary circulation due to flow curvature around the headlands. Additional upwelling occurs north of Curaumilla Point due to development of shallow wind-driven overturning flow. Wind-sheltering is shown to be an important factor for explaining the fact that Valparaíso Bay is typically an upwelling shadow. Flow separation and eddy formation within Valparaíso Bay is seen to occur on the order of 10 times per year during relaxation after strong wind events and may persist for a number of weeks. Shorter lived topographic eddies are also seen to occur commonly at Topocalma and Toro Points. These eddies are shown to form in response to the surface elevation minima produced at each of these locations during upwelling.  相似文献   

Sub-kilometer length scales in coastal waters     

Shelley M. Blackwell  Mark A. Moline  Andrew Schaffner  Thomas Garrison  Grace Chang 《Continental Shelf Research》2008

Patchiness or spatial variability is ubiquitous in marine systems. With increasing anthropogenic impacts to coastal resources and coastal systems being disproportionately large contributors to ocean productivity, identifying the spatial scales of this patchiness, particularly in coastal waters, is of critical importance to understand coastal ecosystem dynamics. The current work focuses on fine scale structure in three coastal regions. More specifically, we utilize variogram analyses to identify sub-kilometer scales of variability in biological and physical parameters measured by an autonomous underwater vehicle (AUV) in the Mid-Atlantic Bight, Monterey Bay, and in San Luis Obispo Bay between 2001 and 2004. Critical scales of variability in density, turbidity, fluorescence, and bioluminescence are examined as a function of depth and distance offshore. Furthermore, the effects of undersampling are assessed using predictive error analysis. Results indicate the presence of scales of variability ranging from 10s to 100s of meters and provide valuable insight for sampling design and resource allocation for future studies.  相似文献   

Numerical modelling of the suspended sediment transport in Torres Strait     

N. Margvelashvili  F. Saint-Cast  S. Condie 《Continental Shelf Research》2008

One-dimensional vertical and three-dimensional fine-resolution numerical models of sediment transport have been developed and applied to the Torres Strait region of northern Australia. The one-dimensional model, driven by measured waves and currents, was calibrated against measured suspended sediment concentrations using a sequential data assimilation algorithm. The algorithm produced a good match between model and data, but this was achieved only by allowing some temporal variability in parameter values, suggesting that there were underlying uncertainties in the model structure and forcing data. Implications of the assimilation results to the accuracy of the numerical modelling are discussed and the need for observational programmes having an extensive spatial and temporal coverage is highlighted. The three-dimensional sediment model, driven by modelled waves and currents, simulates sediment transport over the shelf during the monsoon and trade-wind seasons covering 1997–2000. The model predicts strong seasonal variability of the sediment transport on the shelf attributed to seasonally varying hydrodynamics, and illustrates significant inter-annual variability of the sediment fluxes driven by extreme events. The developed model provides a platform for testing scientific hypothesis. With additional calibration, including uncertainty analysis, it can also be used in a management context.  相似文献   

CHINA'S FOUR MAJOR METEOROLOGICAL SCIENTIFIC EXPERIMENTS     

马鹤年  汤绪 《Acta Meteorologica Sinica》1999,(2)

China lies in East-Asian monsoon region,which is one of the well-known active monsoonzones around the world.Monsoon anomaly results in frequent natural disasters,such as drought,torrential rain and flood.In 1998,joint intensified observations for 4 major meteorologicalscientific experiments have been carried out over Chinese major monsoon affected areas.A numberof valuable data have been obtained and some observational facts have come out after initialanalysis.The present paper is to give an introduction to the 4 major meteorological scientificexperiments conducted in 1998 in China.including its origin and scientific goals,implementationand planning,equipment and progress,and initial findings from the important observational facts.It aims to provide a comprehensive report on the progress of the above experiments for those whoare interested in.  相似文献   

Equilibrium beach profile model for perched beaches     

M. Gonzlez  R. Medina  M. A. Losada 《Coastal Engineering》1999,36(4):777

A beach profile equilibrium model for perched beaches is presented. The model assumes that wave reflection at the seaward and leeward sides of the breakwater is the most important process that modifies Dean's equilibrium profile model for non-perched beaches. The influence of wave breaking over the submerged structure is also discussed. Several laboratory data sets are used to analyze the merit of the proposed model for describing the equilibrium condition of a perched beach. A good comparison is obtained. Results show that if the ratio between the water depth above the submerged structure, d, and the water depth at the toe of the structure, h_e, is large, d/h_e>0.5, only minor advance of the shoreline is achieved with the construction of a toe structure. A considerable advance is obtained for d/h_e less that 0.1. In these situations, however, resonant effects may result in an inefficient structure. The proposed model is used to provide an estimation for the required sand volume and the associated beach advance for the case of narrow breakwaters.  相似文献   

Effect of sediment size on area of influence during groundwater remediation by air sparging: a laboratory approach   总被引：2，自引：0，他引：2  

J. W. Peterson  P. A. Lepczyk  K. L. Lake 《Environmental Geology》1999,38(1):1-6

 Air sparging is a groundwater remediation technique, in which organic contaminants volatilize into air as it rises from the saturated to vadose zone. An unknown has been the relationship between sediment size and area affected by air. Laboratory experiments were performed on sediments to determine the area affected by air as a function of grain size. For average grain sizes of 1.1 and 1.3-mm diameter, air flow occurs in discrete meandering channels, with a maximum area of sediment column affected of 13%/m² for 1.1-mm and 14%/m² for 1.3-mm sediments. For average grain sizes of 1.84, 2.61 and 4.38-mm diameter, air flow is pervasive, forming a symmetrical cone of influence around the injection point. Maximum areas affected are15%/m² for 1.84-mm, 25%/m² for 2.61-mm, and 9%/m² for 4.38-mm sediments. Optimal sites for air sparging, may be those with grain diameters between about 2–3 mm. Received: 26 June 1998 · Accepted: 27 July 1998  相似文献   

景电灌区新绿洲可持续发展初探   总被引：4，自引：0，他引：4  

刘千枝  王辉 《中国沙漠》1997,17(1):27-31

景电灌区新绿洲是一个完全靠人工力量建立起来的新型荒漠绿洲。根据对新绿洲形成条件和自然环境的分析,认为新绿洲的基本特征为:1.生态系统的脆弱性;2.水资源的有限性;3.潜在高效性。而资源、环境、经济和社会的协调发展是保障和促进新绿洲持续发展的关键。因此,灌区新绿洲要持续发展,必须调整好产业结构,加强环境建设,注意合理开发利用自然资源。  相似文献