Bonamia exitiosa epizootic in Ostrea chilensis from Foveaux Strait, southern New Zealand between 1986 and 1992     

Cranfield  H.J.; Dunn  A.; Doonan  I.J.; Michael  K.P. 《ICES Journal of Marine Science》2005,62(1):3-13

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Multiscale Terrain Analysis of Multibeam Bathymetry Data for Habitat Mapping on the Continental Slope   总被引：2，自引：0，他引：2  

Margaret F. J. Wilson  Brian O'Connell  Colin Brown  Janine C. Guinan  Anthony J. Grehan 《Marine Geodesy》2007,30(1):3-35

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Regional variation in springtime ichthyoplankton assemblages in the northeast Pacific Ocean     

Miriam J. Doyle  Kathryn L. Mier  Morgan S. Busby  Richard D. Brodeur   《Progress in Oceanography》2002,53(2-4)

The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log₁₀ (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast.  相似文献   

A note on the seafloor coupling characteristics of the new ONR ocean-bottom seismometer     

Anne M. Trehu  George H. Sutton 《Marine Geophysical Researches》1994,16(2):91-103

A series of transient tests were conducted to determine the seafloor coupling characteristics of a new ocean-bottom seismometer (OBS) developed for the United States Office of Naval Research (ONR). The OBS comprises a large recording package and a separate sensor package that is deployed from the recording package. In addition to the coupling characteristics of both the sensor and the recording packages, the seismic energy radiated from the main recording package as a result of motion of the recording package was measured. The observed vertical coupling resonances of both the recording package and the sensor package are in good agreement with those predicted by a simple model of soil-structure interaction. The most important result of this study is that significant energy is radiated from the recording package in response to horizontal motions of the recording package. When the sensor package is 1 m from the recording package, the amplitude of the recorded signal is similar to that recorded in the recording package. In the field, this effect will result in distortion of seismic signals and increased background noise recorded by the sensor package if the recording package is disturbed by seafloor currents or biological activity. The amplitude of this signal attenuates by approximately a factor of two as sensor/recorder separation is increased from 1 to 6 m, suggesting that an improved response can be achieved by increasing the separation between the recording package and the sensors. This effect is much less severe for vertical disturbances of the recording package.  相似文献   

温度-渗流-应力耦合作用分类     

贺玉龙  杨立中 《四川地质学报》2008,28(3):211-215

根据耦合作用实现方式的不同,将温度-渗流-应力耦合作用分为“力学”耦合和“参数”耦合两大类,“力学”耦合通过场之间的某种力学作用或过程实现,而“参数”耦合则通过场的控制参数的变化而体现出来。  相似文献   

基于GIS组件与ANN耦合技术的矿井构造复杂程度评价     

刘德民  ;张品刚  ;李小明  ;洪益清  ;阎海珠 《中国煤炭地质》2008,(10):74-76

矿井构造是影响煤矿安全生产的主要因素,对瓦斯突出、矿井突水有着明显的控制作用。矿井构造具有空间性和非线性等特点,使矿井构造复杂程度评价的难度较大,据此利用MapObjects的空间分析功能和非线性人工神经网络（ANN）耦合技术,对矿井构造复杂程度进行评价。根据前人的研究成果,将突水系数、底板倾角变异系数、底板标高变异系数、断层强度指数、断层密度等5项指标引入评价体系,经过空间分析统计和模型识别,建立了矿井构造复杂程度评价模型。在开滦矿区东欢矿8煤层构造复杂程度的评价中,共训练及评价了研究区的226个评价单元．评价结果表明研究区西部及西北部构造复杂,中部及东南部构造相对简单。  相似文献   

Influence of submerged aquatic vegetation on size class distribution of perch (Perca fluviatilis) and roach (Rutilus rutilus) in the littoral zone of Lake Geneva (Switzerland)     

Olivier Rossier  Emmanuel Castella  Jean-Bernard Lachavanne 《Aquatic Sciences - Research Across Boundaries》1996,58(1):1-14

The abundance of different size classes of perch and roach in the littoral zone of Lake Geneva was compared between submerged aquatic vegetation and unvegetated zones. Samples were taken with gillnets during four periods between June and October 1993. During the vegetation period (June to September), perch 9 cm and roach 10 cm were more abundant in vegetation whereas roach > 20 cm were more abundant in open water. Perch larger than 18 cm and medium roach were equally distributed in both habitats whatever the period, whereas medium perch distribution fluctuated according to the period. In October, after the decline of the vegetation, no more differences in fish distribution were observed except for small roach, which were always more abundant in the vegetated sites.  相似文献   

热液成矿作用的地质地球化学动力学——以胶东牟平-乳山金矿带为例   总被引：1，自引：0，他引：1       下载免费PDF全文

赵伦山  高大忠  李嘉 《地球科学》1994,3(3)

通过对胶东牟平—乳山热液脉状金,铅锌矿床成矿动力学控制规律的研究,说明了建立热液成矿反应体系的方法,并得出以下认识:（1）区域断裂构造活动,通过影响成矿反应体系的热力学性质和条件,控制元素的富集和分散。（2）热液成矿过程中容矿断裂活动可划分为两种作用方式:脆性破裂和韧—脆性张开,构成热液成矿的两种构造动力学环境。（3）热液成矿反应体系是一种开放的动态的热力学体系。断裂的脆性破裂阶段,使体系处于强烈的过饱和状态,矿质在远离平衡状态下快速结晶,加剧物质分异;在脆—韧性张开阶段,矿质在接近平衡态体系中缓慢晶出。（4）热液演化晚期,金在残余溶液中富集;当断裂再次发生构造脉动震颤时,早期形成的块状黄铁矿矿石碎裂,富金溶液充填其中,形成含裂隙金和晶隙金的富矿石。成矿体系热力学演化与构造动力学条件有利的匹配控制着富矿石的形成。  相似文献   

磁层-电离层电动耦合的中纬电离层效应          下载免费PDF全文

资民筠  沈长寿 《地球物理学报》1992,35(1):17-24

本文通过对1982年磁扰期间琼中、北京两站地磁X分量变化的分析,证实了磁层-电离层电动耦合对中纬电离层电流的影响.分析发现:磁静、磁扰条件下的平均日变化中,两站X分量变化在白天有反向的趋势.这表明它们分处于与动力效应对应的电离层发电机电流圈中心之南北两侧.在磁暴主相期间,X分量变化形态与之明显不同,两站地磁南北分量有同向变化,且变幅相近,甚至有时北京站△X更大.对环电流能量增长指数R小于-25nT/h的21次事件所作的时序叠加分析（以R最负时为零时）进一步证明,这种同向变化是普遍存在的.两站零时之△X大小相近,相关系数高达0.98.该同向变化与R指数突然变负密切相关. 以上对比表明,与发电机电流造成两站X分量反向变化不同,同向变化是磁层源高纬扰动电流向中低纬直接穿透的结果.本文对动力和电动耦合两种过程的不同进行了初步讨论.  相似文献   

Flow and form in rehabilitation of large-river ecosystems: An example from the Lower Missouri River   总被引：2，自引：0，他引：2  

Robert B. Jacobson  David L. Galat   《Geomorphology》2006,77(3-4):249

On large, intensively engineered rivers like the Lower Missouri, the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime. We evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes. The analysis used shallow, slow water (shallow-water habitat, SWH, defined as depths between 0 and 1.5 m, and current velocities between 0 and 0.75 m/s) as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes. Two-dimensional hydrodynamic models for modern and historical channels of the Lower Missouri River at Hermann, Missouri, indicate substantial differences between the two channels in total availability and spatial characteristics of SWH. In the modern channel, SWH is maximized at extremely low flows and in overbank flows, whereas the historical channel had substantially more SWH at all discharges and SWH increased with increasing discharge. The historical channel form produced 3–7 times the SWH area of the modern channel regardless of flow regime. The effect of flow regime is evident in increased within-year SWH variability with the natural flow regime, including significant seasonal peaks of SWH associated with spring flooding. Comparison with other reaches along the Lower Missouri River indicates that a) channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered, and b) rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime. The relative efficacy of managing flow and form in creating SWH is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems.  相似文献