Seasonal occurrence of Lepeophtheirus salmonis and Caligus elongatus (Copepoda: Caligidae) on sea trout (Salmo trutta), off southern Norway   总被引：1，自引：0，他引：1  

Schram  T. A.; Knutsen  J. A.; Heuch  P. A.; Mo  T. A. 《ICES Journal of Marine Science》1998,55(2):163-175

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鄂尔多斯盆地中奥陶统马五₆亚段高频旋回层序研究:论海平面升降与横山凸起沉积分异效应^*          下载免费PDF全文

钟寿康  谭秀成  聂万才  张道锋  杨梦颖  卢子兴  张欣玥  肖笛 《古地理学报》1999,24(2):245-260

高频旋回分析有利于揭示浅水碳酸盐岩台地海平面升降、沉积物响应、古地理单元演化及对盆地内沉积分异影响等诸多沉积学信息。依据鄂尔多斯盆地横山地区丰富的钻井取心资料,通过岩石类型、典型五级旋回结构等分析,对中奥陶统马家沟组马五₆亚段开展了高频旋回研究。研究表明: (1)基于研究区内马五₆亚段碳酸盐岩与蒸发岩共生组合的9种岩石类型,识别出5种典型T-R单旋回,其中旋回Ⅰ、Ⅱ、Ⅲ为云质潟湖—颗粒滩—灰泥丘沉积,Ⅳ、Ⅴ为膏盐质潟湖沉积,并以5种单旋回为基本单元搭建骨架井五级高频旋回结构剖面;(2)依据五级高频旋回结构剖面建立的Fischer图解,认为马五₆亚段处于三级旋回晚期,内部发育“2个”四级旋回,具有初次海退—快速海侵—再次海退的相对海平面变化趋势;(3)结合五级旋回厚度统计,认为第1套四级旋回沉积期处于隆拗格局发育阶段,该时期横山凸起作为水下高地,对东西两侧海水封隔明显;至第2套四级旋回沉积阶段,填平补齐作用导致横山凸起影响减弱,海水循环得到改善,凸起东西两侧盐度明显下降。以马五₆亚段为例的高频旋回研究,在横山地区马五₆亚段地层学、沉积学研究中取得了较好的效果,以期在鄂尔多斯盆地马家沟组未来研究中得到进一步推广和实践。  相似文献   

Precise dating of the Dansgaard-Oeschger event 4 and its sub-cycles: Evidence from a stalagmite from Xianyun Cave in Longyan City,Fujian Province     

Che Yin-Ping  Xiao Hai-Yan  Jiang Xiu-Yang  Cai Bing-Gui 《古地理学报》1999,22(2):377-384

The Dansgaard-Oeschger event 4(DO4 event) is a significant warming event that occurred in the late Marine Isotope Stage 3. At present,there are different understandings about the detailed characteristics and internal structures of the DO4 event. Based on 6 precisely-dated ²³⁰Th ages and 188 oxygen isotope data of a stalagmite(No.XYⅢ-28)from the Xianyun Cave,Fujian Province,we present δ¹⁸O time series with an average resolution of 7 yr from 29.13 to 27.94 kyr B.P. Our new stalagmites δ¹⁸O records uncover the detailed processes of the DO4 event. The onset and end time of the DO4 event recorded by the stalagmite δ¹⁸O is 28.83±0.06 and 28.46±0.06 kyr B.P.,respectively, and the duration is 0.37±0.06 kyr. Differential with abrupt change of NGRIP ice core δ¹⁸O record at the onset of DO4 based on the GICC05 layer count time scale,the Xianyun Cave δ¹⁸O shows a relatively slow change. The Xianyun stalagmite δ¹⁸O values negatively shift by 0.4‰ within 145±60 yr,which indicates that the Xianyun Cave was likely affected by the ocean-atmosphere coupling of the tropical. In addition,the Xianyun stalagmite δ¹⁸O reveals a series of sub-million-scale summer monsoon enhancement events in and around the DO4 event,corresponding to the NGRIP ice core δ¹⁸O record and the Arabian Sea basin record. Our results suggest that the East Asian summer monsoon is related to the north-high latitude temperature and the ITCZ position changes on the sub-millennium-scale event.  相似文献   

Earth nutation influence on the temperature regime of the Barents Sea   总被引：1，自引：1，他引：0  

Yndestad  H. 《ICES Journal of Marine Science》1999,56(3):381-387

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Effects of variation in loading protocol on the strength and deformation capacity of ductile reinforced concrete beams          下载免费PDF全文

Kai J. Marder  Christopher J. Motter  Kenneth J. Elwood  G. Charles Clifton 《地震工程与结构动力学》2018,47(11):2195-2213

Understanding the impact of prior earthquake damage on residual capacity is important for postearthquake damage assessment of buildings; however, interpretation of such impact is challenging when based on tests using traditional reversed‐cyclic loading protocols. A new loading protocol, consisting of a dynamic earthquake displacement history followed by quasi‐static reversed‐cyclic loading to failure, is presented as an alternative to traditional simulated seismic loading protocols. Data are analyzed from a set of 12 nominally identical ductile reinforced concrete beams that were tested by using variations of this protocol and traditional reversed‐cyclic and monotonic protocols. Differences in the cycle content of the earthquake displacement histories applied to the test specimens allowed for the effects of load history variation below 2.2% drift to be isolated. It is found that such variation had no effect on the beam deformation capacities. The effects of dynamic loading rates are also analyzed and compared against control quasi‐static specimens. Relative strength increases due to dynamic loading are found to be more significant at yield than at ultimate. Dynamic loading rates led to modest reductions in the beam deformation capacities, but the presence of causality between these variables remains uncertain.  相似文献   

冻融循环对土体强度变形参数的影响          下载免费PDF全文

张渭军 《探矿工程》2020,47(6):86-91

在寒区工程建设中,冻融循环会引起土强度和变形特性发生改变。为了研究多次冻融循环后土的强度和变形参数的变化量,本文以冻融和非冻融的粉质粘土饱和试样为研究对象,通过固结排水三轴剪切试验、三轴等向压缩试验和弹性模量试验,比较了冻融循环对土样强度参数和变形参数的影响。试验结果显示：冻融和非冻融试样的应力—应变关系曲线均呈应变硬化型,对于原状试样冻融作用破坏了其结构性;冻融作用导致土体强度的降低,主要体现在粘聚力的降低,约降低了55.6%;冻融循环对变形参数有明显的影响,其中最明显的是弹性模量的降低,降低了31.2%。该研究结论可为工程冻害处理提供参考,也可为相关研究的数值计算提供试验参数。  相似文献   

冻融循环下花岗岩剪切蠕变试验与模型研究     

张峰瑞  姜谙男  杨秀荣  申发义 《岩土力学》2020,41(2):509-519

为探讨冻融对寒区工程岩石剪切蠕变特性的影响,以吉林省辉白隧道花岗岩为研究对象,对经历不同冻融循环次数的试样开展细观特征分析和剪切蠕变试验。试验结果表明：（1）随着冻融次数的增加,试样裂隙、孔隙不断扩展,岩石表面损伤现象愈发明显;（2）试样主要以中小孔隙为主,孔隙度随着冻融次数的增加呈非线性增长趋势;（3）随着冻融循环次数增加,蠕变变形量和蠕变速率逐渐增大,而蠕变时长、破坏应力和长期强度均呈现明显降低趋势。根据试验结果,进行冻融岩石非定常蠕变参数的表达,提出了冻融岩石损伤黏性元件,构建了花岗岩冻融剪切蠕变本构模型。将蠕变试验曲线和理论模型拟合曲线进行对比,验证了模型的正确性和适用性。通过对蠕变参数进行敏感性分析,研究了其对花岗岩蠕变变形的影响,并给出了蠕变参数随冻融循环次数的变化规律。该研究结果对于寒区岩体工程长期稳定性评价具有指导意义。  相似文献   

DO4事件的精确定年及亚旋回特征: 来自福建龙岩仙云洞石笋的证据^*          下载免费PDF全文

车印平  肖海燕  姜修洋  蔡炳贵 《古地理学报》2020,22(2):377-384

DO4事件(Dansgaard-Oeschger event 4,简称DO4事件)是发生在MIS3阶段后期的1次明显升温事件。根据福建仙云洞石笋(编号XYⅢ-28)300~500 mm层段6个高精度²³⁰Th年龄和188个氧同位素数据,获得了29.13~27.94 kyrB.P.时期平均分辨率达7 yr的东亚夏季风强度的演变过程数据。该石笋 δ¹⁸O 记录的DO4事件起止时间为28.83±0.06~28.46±0.06 kyr B.P.,持续时间为0.37±0.06 kyr。相对基于GICC05年层计数时标NGRIP冰芯 δ¹⁸O 记录在DO4开始阶段的突变特征,仙云洞石笋记录的DO4事件开始阶段 δ¹⁸O 值在145±60 yr内偏负0.4‰,表现为相对缓慢的变化特征,这说明仙云洞所处的中国东南沿海地区有可能受到热带低纬海气耦合的影响。此外,仙云洞石笋 δ¹⁸O 记录揭示了在DO4事件内部及附近存在一系列的百年至十年际尺度夏季风增强事件,与格陵兰冰芯 δ¹⁸O 记录、阿拉伯海海盆反照率记录的DO4事件亚旋回结构在定年误差范围内相对应,表明东亚夏季风强度与北高纬温度变化和ITCZ(赤道辐合带)位置移动在百年至十年际尺度上存在紧密的联系。  相似文献   

Facies character and geochemical signature in the late Quaternary meteoric diagenetic carbonate succession at the Xisha Islands,South China Sea     

Wanli Chen  Xiaoxia Huang  Shiguo Wu  Gang Liu  Haotian Wei  Jiaqing Wu 《海洋学报(英文版)》2021,40(3):94-111

The late Quaternary shallow-water carbonates have been altered by a variety of diagenetic processes, and further influenced by high-amplitude global and regional sea level changes. This study utilizes a new borehole drilled on the Yongxing Island, Xisha Islands to investigate meteoric diagenetic alteration in the late Quaternary shallowwater carbonates. Petrographic, mineralogical, stable isotopic and elemental data provide new insights into the meteoric diagenetic processes of the reef limestone. The results show the variation in the distribution of aragonite,high-Mg calcite(HMC) and low-Mg calcite(LMC) divides the shallow-water carbonates in Core SSZK1 into three intervals, which are Unit I(31.20–55.92 m, LMC), Unit II(18.39–31.20 m, aragonite and LMC) and Unit III(upper 18.39 m of core, aragonite, LMC and HMC). Various degrees of meteoric diagenesis exist in the identified three units. The lowermost Unit I has suffered almost complete freshwater diagenesis, whereas the overlying Units II and III have undergone incompletely meteoric diagenesis. The amount of time that limestone has been in the freshwater diagenetic environment has the largest impact on the degree of meteoric diagenesis. Approximately four intact facies/water depth cycles are recognized. The cumulative depletion of elements such as strontium(Sr),sodium(Na) and sulphur(S) caused by duplicated meteoric diagenesis in the older reef sequences are distinguished from the younger reef sequences. This study provides a new record of meteoric diagenesis, which is well reflected by whole-rock mineralogy and geochemistry.  相似文献   

干旱半干旱地区草原灌丛荒漠化及其 生物地球化学循环     

金钊  齐玉春  董云社 《地理科学进展》2007,26(4):23-32

干旱和半干旱地区草地生态系统木本植物入侵及其导致的草原灌丛化已经成为全球范 围普遍发生的现象， 是草地沙化和荒漠化的一个重要标志。干旱生态系统中， 此种类型的植被变 化将对区域和全球生物地球化学循环产生显著影响。过度放牧、区域气候干旱化和自然火过程是 导致灌丛入侵和发展的主要控制因子。草原灌丛化过程中， 草地生态系统分布较为均匀的土壤养 分及相关元素在水平和垂直方向发生分异， 关键生命元素C、N、P 、S 生物地球化学循环的变化 将对全球气候变化产生显著作用。全球气候变化与草原灌丛荒漠化之间存在潜在的反馈机制， 人 类扰动的影响将使这种反馈作用变得更加迅速和灵敏。  相似文献