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1.
Alexandria-Nile Delta coast,Egypt: update and future projection of relative sea-level rise 总被引：1，自引：1，他引：0
Omran El Sayed Frihy Essam A. Deabes Samy M. Shereet Farid A. Abdalla 《Environmental Earth Sciences》2010,61(2):253-273
Previous studies have indicated that the Nile River deltaic plain is vulnerable to a number of aspects, including beach erosion,
inundation, and relatively high rates of land subsidence. This issue motivates an update and analysis of new tide-gauge records,
from which relative sea-level changes can be obtained. Estimated rates from five tide gauges are variable in terms of magnitude
and temporal trend of rising sea level. Analysis of historical records obtained from tide gauges at Alexandria, Rosetta, Burullus,
Damietta, and Port Said show a continuous rise in mean sea level fluctuating between 1.8 and 4.9 mm/year; the smaller rate
occurs at the Alexandria harbor, while the higher one at the Rosetta promontory. These uneven spatial and temporal trends
of the estimated relative sea-level rise (RSLR) are interpreted with reference to local geological factors. In particular,
Holocene sediment thickness, subsidence rate and tectonism are correlated with the estimated rates of relative sea-level change.
From the relatively weak correlation between them, we presume that tectonic setting and earthquakes, both recent and historical
ones, contribute more to accelerated RSLR than that of dewatering and compression/dewatering of Holocene mud underlying the
Nile Delta plain. As a result, large areas of the coastal plain have been subsided, but some sectors have been uplifted in
response to tectonic activities of thick underlying older strata. Projection of averaged sea-level rise trend reveals that
not all the coastal plain of the Nile Delta and Alexandria is vulnerable to accelerated sea-level rise at the same level due
to wide variability of the land topography, that includes low-lying areas, high-elevated coastal ridges and sand dunes, accretionary
beaches, and artificially protective structures. Interaction of all aspects (tectonic regime, topography, geomorphology, erosion
rate, and RSLR rate) permitted to define risk areas much vulnerable to impacts of sea incursion due to accelerated sea-level
rise. 相似文献
2.
Relative sea levels recorded by tide gauges during the past century in northern Europe are dominated by isostatic readjustment of the land following the latest deglaciation of Scandinavia and Scotland. Maximum relative uplift of the land is centered near the northern Gulf of Bothnia (at a rate of 6–7 mm/yr), with a smaller secondary maximum over Scotland (also at a rate of 6–7 mm/yr). Although there probably is a relaxing peripheral bulge surrounding the regions of maximum uplift, such a former bulge is poorly defined by coastal tide gauges; in the North Sea evidence for sinking of a former peripheral bulge of glacial origin is complicated by post-Carboniferous basin deepening with sediment loading and possible rejuvenation associated with glaciation. Other data (gravity, radiocarbon, geomorphology) support the interpretation that glacial isostasy controls the structure of relative sea-level change. Included in this pattern of relative rise of land is a eustatic signal that biases the estimates of glacial rebound. Such a eustatic signal could not be isolated from the isostatic signal using the present data, but glacial isostasy clearly is a major control for relative sea levels of the region.
Absence of significant higher frequency (2–50 yr) cycles in mean annual sea levels of northern Europe reflects the complex hydrologic/oceanographic forces to which sea levels must respond. Whereas other coastal regions show significant higher frequency peaks in the energy spectra of relative sea levels, the many marginal seas in northern Europe preclude a clear relation between hydrologic/oceanographic forcing and relative sea levels, although this relation must exist on a more local scale. 相似文献
3.
揭示晚全新世以来的海平面变化过程对于理解海平面所处的现状和变化的趋势等具有重要意义。构造活动相对稳定的雷州半岛珊瑚礁区蕴藏着丰富的海平面变化信息,文中对该区晚全新世发育的海滩沉积序列研究表明,距今约1.7～1.2Cal.kaBP(14C年代为2.1～1.7kaBP)期间总体上是一个海平面持续上升的时期,其中在距今约1.5Cal.kaBP时海平面有过短暂的下降波动,约1.2Cal.kaBP时的海平面比现在的至少高128cm;之后海平面开始下降,至今海岸线后退了约210m,形成现代海滩-沙堤地貌体系。结合本区珊瑚礁记录的全新世其他时段海平面的变化特征,本文认为全新世海平面与气候变化一样,也存在千年、百年、年代际尺度的波动特征。 相似文献
4.
利用对深圳西冲湾两个岬角之间的海蚀地貌及其海滩沉积物的野外调查资料,鉴定出三级海蚀平台,对其分别进行了高程换算,并借助于海蚀拱门和海蚀刻槽的测定,以及对典型沙层沉积剖面序列的分析和14C测年,认为：虽然西冲湾海蚀平台的岩石类型是不易被侵蚀的花岗岩,但是此处的海蚀地貌（主要是海蚀平台）以及海滩沉积物（主要是海滩岩）可以作为全新世存在高海平面的证据。此外,针对我国海岸带人口密度大,人类活动对海岸影响程度大的现况,提出了未来研究南海北部海岸新构造运动存在的问题以及其解决方案。研究成果对于认识南海北部海岸全新世的构造运动、海平面变化以及与其他地区新构造运动的对比研究都具有重要的意义。 相似文献
5.
6.
五千年来南海海平面变化的研究 总被引：13，自引：0，他引：13
大型块状滨珊瑚的生长上限充其量只能达到大潮低潮面,礁坪面成为古高海面的极好标志。多数学者认为,５０００ａＢ．Ｐ．以来南海周边曾有３—６ｍ的高海面。但南海曾否有古高海面有着两种截然相反的意见。作者对南沙群岛、西沙群岛、海南岛、雷州半岛和台湾恒春半岛珊瑚礁的考察,实测礁顶面的高程,钻取岩芯样品做(１４)Ｃ测年,并收集大量古高海面礁的资料,进一步证实了南海同它的周边情况一样,确实出现过至少比现今高２—３ｍ的高海面。 相似文献
7.
Sedimentary Features of Shallow Ancient River Channels on the Northern Shelf of the South China Sea 总被引：1，自引：0，他引：1
Kou Yangqi Du Deli nd Marine Geological Investigation Party MGMR Guangzhou Guangdong Jiang M inxi 《《地质学报》英文版》1995,69(1)
Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand -body types, and discusses thei 相似文献
8.
Sedimentary Features of Shallow Ancient River Channels on the Northern Shelf of the South China Sea1
Abstract Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand-body types, and discusses their formational setting and evolutionary model, with the main purpose to render a service to the hydrocarbon resources exploration and development and marine engineering in the northern shelf of the South China Sea. 相似文献
9.
Microatoll record for large century-scale sea-level fluctuations in the mid-Holocene 总被引：2，自引：0，他引：2
Coral microatolls have been long used as precise indicators of past sea level, but their use for precise definition of detailed sea-level fluctuations is still rare. Here we report twelve high-precision thermal ionization mass spectrometric 230Th ages for twelve rims of five mid-Holocene microatolls from an emerged reef terrace at Leizhou Peninsula, northern South China Sea. This is a tectonically stable area, enabling us to reconstruct both the timing and trajectory of local sea-level fluctuations accurately. The elevations of these microatoll rims and cores were accurately determined relative to the surface of modern living microatolls at the same site. The results indicate that the sea level during the period of 7050–6600 yr bp (years before AD 1950) was about 171 to 219 cm above the present, with at least four cycles of fluctuations. Over this 450 yr interval, sea level fluctuated by 20–40 cm on century scales. 相似文献
10.
以南海北、西、南部3个沉积速率相对较高而且连续的沉积柱状样MD2904,MD2901和MD2897为基础,通过粒度、碳酸盐、有机地球化学和元素分析,并综合前人研究成果,对南海MIS3期进行探讨。结果显示,南海MIS3是末次冰期中的弱暖期,海水表层古温度比相邻的MIS2和MIS4期略高,但是明显比MIS1和MIS5期低。MIS3的最大特点就在于其气候的不稳定性,发生了多次气候快速变化事件。在格陵兰冰芯中记录的千年尺度快速气候变化事件（D/O事件和Heinrich事件）基本上在南海北、西、南部都有响应,具有与全球同步的特征。南海MIS3古生产力都显示出较高的特点,这与东亚季风有着密切的关系,北部主要受冬季风影响,西部和南部主要受夏季风影响。南海南部MIS3表现出比MIS5更高的古生产力和更强的夏季风强度,这一特点有待更进一步深入研究。 相似文献
11.
南海北部大陆架莺琼盆地新生代海平面变化 总被引：4，自引：0，他引：4
南海北部大陆架莺琼盆地是建立西太平洋新生代海平面变化的关键地区之一。基于有孔虫和钙质超微化石资料所建立的莺歌海盆地和琼东南盆地新生代相对分辨率较高的年代地层格架,通过南海海域表层建立的浮游有孔虫含量与水深的定量关系,辅以古生态、成因相及特征沉积构造分析和反射地震剖面的海岸上超分析,编制了海平面变化曲线。识别出包含三个完整二级海平面变化旋回和半周期的海平面上升旋回。海平面变化幅度在0～200 m之间。海水最深的时期在早中新世晚期至中中新世早期以及上新世早期,与Haq曲线较为吻合。 相似文献
12.
近海陆架区内潮观测研究进展 总被引：3，自引：1，他引：2
内潮是近海陆架区内最常见的海洋内波,一般是由正压潮经过特殊地形或海况激发产生,内潮由此具有天文潮周期且出现频率相对稳定。频繁出现的内潮对人类海上活动的影响有弊也有利,它可引发强烈的海水混合或产生上升流,使深层营养盐提升从而形成丰富的渔场;而大振幅内潮或由其演变出的强孤立内波会干扰海洋工程作业,对建成的石油钻井平台和海底油气管道构成严重的威胁;内潮导致的水体扰动还会对海上舰船的行驶产生不利影响。所以对近海陆架区内潮的观测研究一直为人们所重视。对内潮的一些相关特点做了简要介绍,主要论述了国际上近海陆架区内潮观测研究的进展情况,以及近几年来观测方法的最新发展趋势;并着重分析了南海北部海区内潮研究现状,讨论了目前南海内潮观测研究中存在的一些问题,进而提出今后开展进一步观测研究的思路。 相似文献
13.
南海北部边缘盆地油气勘探现状与深水油气资源前景 总被引：18，自引：0，他引：18
自20世纪60年代初开展浅海油气苗调查及浅井钻探以来,南海北部边缘盆地迄今在陆架浅水区已勘探发现多个油气田,建成了一定储量规模的油气产能,基本构成了南海北部油气富集区的格[JP2]局。然而,如何保持油气可持续发展,尽快寻找油气储量接替的新领域,这是该区油气勘探所面临的关键问题。南海北部陆坡深水区与世界深水盆地一样,颇具油气资源潜力和勘探前景,近期LW311深水探井钻探的新发现表明,其应是该区油气资源接替非常现实的战略选区和勘探靶区。 相似文献
14.
在高分辨率１４Ｃ测年、岩石、生物、化学、同位素、气候及磁性地层学研究成果基础上,通过不同沉积背景典型钻孔的沉积学分析,运用层序地层学理论,对东海陆架全新统进行了高分辨率层序划分及对比;建立了全新世层序地层格架及海平面变化过程;提出了相应的层序成因模式。研究结果表明,东海陆架全新统相当于一个发育中的六级（１～１０ｋａ）层序,可进一步划分为３个七级（０．１～１ｋａ）层序和若干个更次级层序。代表１个六级或３个七级周期相对海平面变化过程中叠加有若干更次级的海平面波动,它们与地球旋回谱系中的太阳带、历法带密切相关。七级层序具有与三级层序相近的内部构型和成因格架。在东海陆架全新世沉积演化过程中,长江三角州至少有３次不同程度地越过东海陆架进入冲绳海槽,并滞留有至少３层海侵改造“残积砂”沉积。在东海陆架全新世海平面变化期间,最大海平面时期为约距今６～５ｋａ,大致高于现今海平面２～４ｍ,最低海平面在距今１０ｋａ左右,大约低于现今海平面１３０ｍ。目前,由于温室效应的影响,海平面仍呈小幅度波浪式上升。事实证明,层序地层学不仅丰富了现代海洋沉积学的内容,而且解决了许多海洋沉积学未能解决的问题。 相似文献
15.
缺氧条件是形成和保存优质烃源岩的重要条件。古氧相的研究对查明海相优质烃源岩时空分布、恢复地史时期古环境演化具有重要意义。泥盆纪时期,南华海受陆内裂陷作用影响,形成台地(滨岸台地和孤立台地)与台沟间列的盆地格局。不同的控制因素控制了古氧相的类型。在台沟和钦防裂陷海槽中,海水分层控制了泥盆纪的古氧相类型和变化。台沟和钦防裂陷海槽以厌氧相与准厌氧相为主。在台地相区,海平面变化控制了古氧相的类型和分布。台地相区的古氧相主要是常氧相和贫氧相。南华海中、晚泥盆世硅质沉积、磷质沉积发育,有机质丰富,形成了有机质-硅质-磷质沉积三位一体的特征,指示上升流作用明显。南华海地区泥盆纪位于赤道附近的信风带,向西的表面洋流越过南华海在西部形成离岸流,海底海水向东补充形成上升的底流,也说明了泥盆纪南华海上升流存在的可能性。 相似文献
16.
Omran E. Frihy 《Natural Hazards》1984,5(1):65-81
Studies of the Nile Delta coast have indicated wide values of local subsidence, ranging from 0.4 to 5 mm/yr. Trend analysis of sea-level rise and shoreline retreat at two Nile Delta promontories have been studied. Records from tide gauges at Alexandria (1944–1989) and Port Said (1926–1987), north of the Nile delta coast, indicate a submergence of the land and/or a rise of the sea-level of 2 and 2.4 mm/yr, respectively.Dramatic erosion has occurred on some beaches of the Nile Delta. This is greatest at the tips of the Rosetta and Damietta promontories, with shoreline retreat up to 58 m/yr. Relationship between the shoreline retreat and sea level trends in terms of correlation analysis and application of the Bruun Rule indicates that the sea level rise has, by itself, a relatively minor effect on coastal erosion. The sea-level trend at the Nile delta coast is found to be only one of several effects on shoreline retreat. Major recent effects include a combination of cut-off of sediment supply to the coast by damming the River Nile and local hydrodynamic forces of waves and currents. Estimates of local future sea-level rise by the year 2100 at Alexandria and Port Said, respectively, is expected to be 37.9 and 44.2 cm. These expectations, combined with other factors, could accelerate coastal erosion, inundate wetlands and lowlands, and increase the salinity of lakes and aquifers. 相似文献
17.
A new sea-level curve (MHW, mean high water level) for the southern North Sea is presented, spanning the last 10 000 years and based on new data recently obtained along the German coast. The 118 dates were selected from basal as well as intercalated peats of the Holocene sequence and archaeological dates from the last 3000 years. Because of different MHW levels along the German North Sea coast, all data were corrected to the standard tide gauge at Wilhelmshaven to make them comparable. Special advantages of this area for sea-level reconstructions are negligible tectonic and isostatic subsidence and the absence of coastal barrier systems that might have mitigated or masked sea-level changes. Changes of water level had therefore immediate consequences for the facies and could be dated exactly. The chronostratigraphic Calais-Dunkirk system has been improved and adapted to the new data. Altogether seven regressions (R 1-R 7) have been identified, each of them characterized by a distinct decline in sea level. These fluctuations are in accord with the evidence from other parts of the North Sea region. A draft of former North Sea shorelines is presented on the basis of this sea-level curve. 相似文献
18.
Analysis of extreme low-temperature events during the warm season in Northeast China 总被引：2，自引：0，他引：2
The trends of global warming are increasingly significant, especially in the middle and high latitude regions of the northern
hemisphere, where the impact of climate change on extreme events is becoming more noticeable. Northeast China is located in
a high latitude region and is sensitive to climate change. Extreme minimum temperatures causing cold damage during the warm
season is a major type of agro-meteorological disaster in Northeast China, which causes serious reductions in crop yield.
In this paper, we analyzed the temporal and spatial trends in the frequency of extreme minimum temperatures during the warm
season (from May to September) during 1956–2005 in Northeast China. Abrupt climatic changes were identified using the Mann–Kendall
test. The results show that the frequency of extreme minimum temperature days during the warm season in Northeast China decreases
significantly from 1956 to 2005 with a background of climate warming. The highest number of extreme minimum temperature days
occurred in the 1970s and 1980s, and there was an abrupt climatic change in 1993. The spatial analysis identified that the
north and southeast of the region experienced a larger decrease in the number of extreme low temperature days than the west
and south of the region. Rice, sorghum, corn, and soybeans are most vulnerable to cold damage. In severe low temperature years,
the average crop yield was reduced by 15.2% in Northeast China. 相似文献
19.
An efficient approach for evaluating storm tide return levels along the southeastern coastline of Australia under present
and future climate conditions is described. Storm surge height probabilities for the present climate are estimated using hydrodynamic
model simulations of surges identified in recent tide gauge records. Tides are then accounted for using a joint probability
method. Storm tide height return levels obtained in this way are similar to those obtained from the direct analysis of tide
gauge records. The impact of climate change on extreme sea levels is explored by adding a variety of estimates of mean sea
level rise and by forcing the model with modified wind data. It is shown that climate change has the potential to reduce average
recurrence intervals of present climate 1 in 100 year storm tide levels along much of the northern Bass Strait coast to between
1 and 2 years by the year 2070. 相似文献
20.
晚三叠-中侏罗世华南陆缘发生多期海侵-海退旋回.元素地球化学特征指示的古盐度高低和古水深深浅记录了海平面的相对升降.华南陆缘存在3个级别的海平面变化.其中, Ⅲ级海平面波动频繁, 由晚三叠世3次波动、早侏罗世4次波动和早、中侏罗世2次波动构成了此间大规模海侵-海退旋回.华南陆缘Ⅰ级海平面相对升降曲线与全球海平面长周期曲线, 在诺利克阶早期-辛涅缪尔阶晚期变化同步, 在辛涅缪尔阶晚期-阿连阶变化相悖.Ⅲ级海平面相对升降曲线与全球海平面短周期曲线, 在瑞替阶-辛涅缪尔阶晚期同发生4次波动, 时间上近乎同步.Sr/Cu值指示的元素迁移与富集反映了气候的温湿与干热.粤中-粤东地区晚三叠-早、中侏罗世经历了温湿-干热-温湿的气候变化. 相似文献