河流-河口-近海连续体碳循环研究进展          下载免费PDF全文

陈建芳  翟惟东  王斌  李德望  熊天琦  金海燕  李宏亮  刘沁宇  苗燕熠 《海洋学研究》2021,39(4):11-21

河流-河口-近海连续体(简称连续体)是连接陆地和大洋的过渡地带,也是目前全球碳收支估算的薄弱环节。这个复杂的海陆交互生态系统不仅可以通过光合作用、溶解作用吸收大气中的CO2,陆地和流域光合作用或化学风化作用固定的碳也可以被横向输送到陆架和大洋中。本文以国际上著名的切萨皮克湾以及长江-长江口-东海等为例,综述了连续体碳循环研究的进展,并指出通过陆海统筹、海空一体、点线面结合的系统观测,结合动力-生态数值模拟、沉积记录开展多时空尺度过程机制分析研究,是阐明气候变化与人类活动双重压力下,河流-河口-近海连续体碳交换的演变规律及其对碳收支的影响的可行途径。  相似文献   

Snowmelt characteristics in a pristine mountain catchment of the Jalovecký Creek,Slovakia, over the last three decades     

Ladislav Holko  Michal Danko  Patrik Sleziak 《水文研究》2021,35(4):e14128

The Jalovecký Creek catchment, Slovakia (area 22.2 km², mean elevation 1500 m a.s.l.), is likely the last big valley complex in the Carpathian Mountains, in which the hydrological cycle is still governed by natural processes. Hydrological research is conducted there since the end of the 1980s. The overall mission of the research is to increase the knowledge about the hydrological cycle in the highest part of the Carpathians. The research agenda, briefly introduced in the first part of this article, is focused on water balance, snow accumulation and melt and runoff formation. Recent analysis of precipitation, discharge, snow cover and isotopic data from period 1989–2018 indicates that hydrological cycle has become more dynamic since 2014. Although several indicators suggest that it could be related to the cold part of the year, direct links with snow storage and the contribution of snowmelt water to catchment runoff were not confirmed. The second part of the article is therefore focused on an analysis of daily cycles in streamflow in March to June 1988–2018 to obtain a deeper insight into the snowmelt process. We describe characteristics of the cycles and examine their variability over the study period. The results indicate that less snow at the lowest elevations (800–1150 m a.s.l.) since 2009 could have influenced the cessation of the cycles in June since 2010. The possible role of the decreased amount of snow at the lowest elevations in changes in runoff characteristics is also suggested by an increase in time lags between maximum discharges during the events and maximum air temperatures preceding discharge maxima measured near the catchment outlet (at 750 m a.s.l.) in spring 2018 compared to springs with a similar number of streamflow cycles in the years 1988, 2000 and 2009. Wavelet analysis did not indicate changes in global power spectra in hourly discharge and air temperature data.  相似文献   

Laboratory and field performance of recycled aggregate base in a seasonally cold region     

Tuncer B. Edil  Bora Cetin  Ali Soleimanbeigi 《寒旱区科学》2017,9(3):183-191

The objective of this project was to characterize the freeze-thaw properties of recycled concrete (RCA) and asphalt (RAP) as unbound base and to assess how they behaved in the field for nearly 8 years. This paper includes an examination of existing information, laboratory studies of freeze-thaw behavior, and evaluation of data from MnROAD field-test sections in a seasonally cold region, i.e., in Minnesota, USA. Test sections were constructed using recycled materials in the granular base layers at the MnROAD test facility. One test section included 100% RAP, another 100% RCA, a third one a 50/50 blend of RCA/natural aggregate, and a fourth one only natural aggregate (Class 5) as a control. The stiffness (i.e., elastic modulus) was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation, along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance. The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a, as well as by field-scale tests incorporating a falling-weight deflectometer. Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory, and the change in their resilient modulus was measured. In the field-test sections constructed with the same materials as the base course, temperature, moisture, and field modulus (from falling-weight deflectometer tests) were monitored seasonally for nearly 8 years. From the temperatures in the base course layer, the number of freeze-thaw cycles experienced in the field was determined for each test section. Inferences were made relative to modulus change versus freeze-thaw cycles. Conclusions were drawn for long-term field performances of the recycled base (RAB) in comparison to natural aggregate.  相似文献   

贵州织纳煤田晚二叠世海进海退旋回及煤聚积   总被引：3，自引：0，他引：3  

解习农  程守田 《煤田地质与勘探》1992,20(5):1-6

黔西南上二叠统为以碎屑沉积为主的含煤层序。该层序包括3个沉积体系域,下部体系域为海湾-泻湖体系沉积,中部体系域为三角洲体系和障壁坝-泻湖体系沉积,上部体系域为碎屑海岸体系沉积,总体反映海平面上升过程。煤层分布范围随海平面上升不断由东向西后退,主要煤层富集与最大进积期有关,即赋存于下部体系域上部和中部体系域。因此,利用海平面升降旋回可较好地预测煤层分布范围及主要煤层赋存规律。   相似文献   

地球公转轨道偏心率变化的构造运动响应   总被引：5，自引：0，他引：5  

吴锡浩  蒋复初  肖华国 《地质力学学报》1995,1(1):8-14

最近3Ma发生的主要构造运动和气候变化事件,在准0.4Ma周期上与地球轨道偏心率变化存在一致性。据黄土高原地层记录划分的构造气候旋回界限,日历年龄分别为0.07、0.46、0.83、1.32、1.70、2.08、2.74MaBP,对应于偏心率曲线波动幅度由大变小时段的特定转折位置。文中分析了地球公转运动变速的基本数据及其对地球自转运动和圈层相互作用的可能影响,探讨了轨道偏心率变化对构造运动的驱动机制,并指出了构造气候旋回研究可为地质力学理论发展展示良好的前景。   相似文献   

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