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1.
A prograding chenier plain on the west side of Broad Sound is up to 5 km wide and individual beach ridges (cheniers) are up to 5 km long. The cheniers are believed to have formed during periods of low sediment supply, leading to the erosion of mangrove deposits and the attendant development of a beach ridge. Radiocarbon dating of two sequences, revealed that cheniers formed at about 5000, 4500, 3550, 2500, 1600 and 700 years B.P. There is no significant change in the elevation of the cheniers during this 5000 year interval and it would seem from the Broad Sound evidence that sea level stabilized at about the present level approximately 5000 years B.P. Since that time mean sea level has varied by no more than ± 1 m. 相似文献
2.
The low chenier coast of northeastern of South America bears Holocene cheniers which are considered as useful features because they protect the coast against marine erosion as sites for human settlement, and the transportation network. The relationship between chenier formation and the morphology of the coast is striking. Most cheniers in Guyana are old features. It is believed that clusters of cheniers were formed when large quantities of sand were available during periods of dry climatic conditions. When fine particles were transported by the streams towards the sea during pluvial climates, chenier formation naturally decreased. A similar cycle of shorter duration based on the movements of mud shoals in the nearshore area of the continental shelf affects the coastal process, resulting in the formation or destruction of cheniers. On the Guyana coast chenier formation is not as active as on the Suriname coast. Much research is necessary to survey and protect these important features. 相似文献
3.
本文通过对鲁北沿岸现代贝壳堤岛的分析认为:贝壳堤发育在冲淤变化不大的粉砂淤泥质岸段,暴风浪是其形成的主要动力;完整的贝壳堤体系应包括海岸贝类生长带(潮滩下部和潮下带)—潮滩侵蚀带—贝壳堤—堤后泻湖;贝壳堤贝壳~(14)C测年资料应当慎用,也不宜把古贝壳堤看成全新世海平面变化的确切标志。 相似文献
4.
Nineteen cheniers formed in the middle and late Holocene have been distinguished and studied. In fair weather the wave action along the Yangtze Delta is weak, with a wave height of 0.5–1.0 m and average wave energy of 0.127 erg/s. However, in late summer and early autumn the coastal area is usually swept by typhoons, which sometimes are extremely violent. The development of cheniers is mainly controlled by these strong typhoons. As a result, a number of the sedimentary characteristics of the cheniers are related to the typhoon-generated high-energy environment. Moreover, the study shows that the top elevation of a fully developed chenier indicates the spring high water level during a violent typhoon (11–12 on the Beaufort scale). 相似文献
5.
In various regions along the east and southeast coast of China and on the outer shelf of the East China Sea, series of cheniers have been found and studied. Their geomorphological and sedimentological features have been described and the main conditions for their formation established. The development of cheniers in China can be divided into three periods: 24,000-15,000 yrs B.P., 7000-5000 yrs B.P. and 5000 yrs B.P. onwards. These periods have been based on 14C datings of 80 shell samples. The chenier groups of the three periods are distributed throughout various geomorphological locations. Using the geomorphological locations of the cheniers in combination with their age of formation, the palaeopositions of the Chinese coastline in the various periods since 24,000 yrs B.P. are described. The history of the position of the east coast of China, including the features attesting to sealevel changes during this era, is briefly discussed. 相似文献
6.
Three to four cheniers are found in the coastal areas of the Bohai Sea and west Yellow Sea. They are formed in the sheltered low tidal flat coast with low to medium wave energy, large quantity of fine sediment supply and shells, and a coastal slope of 0.9–3.0 ‰. The Huanghe River played a major role in controlling the chenier development by either providing sediment supply or cutting off the supply through shifting of its course. Cheniers may be used to determine the coastal development and dynamic processes. 相似文献
7.
B_2孔揭示海河口地区全新世海侵层厚达19.2m,自下往上依次出现潮间滩、近岸浅海、前三角洲、三角洲湾、河口砂坝及河口边滩六个亚相,下部两个亚相呈海进层序,上部四个亚相呈海退层序。除河口边滩亚相底界外,其他所有亚相间的界面均为不连续面,显示海侵层为不连续沉积。研究表明该不连续沉积与海面波动有关.在全新世海侵高峰后,海面一直处于幅度不大(约1m 左右)的振荡运动状态,一次振荡波就在海岸线上留下一道贝壳堤,近5000余年来发生了5次振荡波,在海退平原中就有5道贝克堤与之对应。B_2孔海退层序中曲不连续面与贝壳堤基底侵蚀面相对应,也与振荡波的上升坡段相对应。海退层序所表现出来的海岸向海推进现象不是海面大幅度下降的反映,而主要是河口区沉积物迅速加积的结果。 相似文献
8.
The Holocene coastal plain of Suriname is part of the extensive chenier plain between the Amazon River and the Orinoco River. The development began approximately 6000 yrs B.P. and was interrupted twice by periods of erosion or non-deposition. Along the present coastline large shoreface-attached mudbanks migrate continually to the west. Cheniers are formed in the interbank areas. The geological development and stratigraphy of the Suriname chenier plain and the morphodynamic development of the modern coastline are discussed. Some hypothetical explanations of the geological development from the actual morphodynamics are briefly discussed. A new approach has been developed involving the analysis of aerial photographs using a geographical information system. This was used to analyse the geomorphological changes of the Suriname coastline. 相似文献
9.
The coast of northern Sierra Leone, between the Scarcies and Mellacoree estuaries, forms a prograding muddy Holocene plain comprising two separate, as yet undated, clusters of sand cheniers. The general coastal morpho-stratigraphy and available data on regional climatic and sealevel history suggest that alternations between muddy progradation and chenier cluster formation have been controlled by a probable conjunction of several factors, including the local geomorphic framework, a climatically induced change in mud supply, and relative sealevel oscillations since the middle Holocene. The inner chenier cluster was apparently elaborated under conditions of efficient wave action over a deep, largely unfilled Mellacoree estuary and at a time of reduced mud availability. It peters out seaward, probably in response to several factors, including an increase in mud supply from the upland, a negative sealevel pulse resulting in higher rates of mud export from accreted inner tidal flats, increased muddy sedimentation over a shallower nearshore zone, and attenuated wave action as a result of energy capture by accreted estuarine shoals. The outer cluster, which partly fringes the coast, was formed in a mayor embayment representing the terminus of longshore sand drift. It is suggested that its formation may have been favoured by a higher sealevel resulting in efficient winnowing of sands from subtidal muds, a greater propensity for accretion of tidal flats landwards and, consequently, a lower mud supply to the foreshore. Although the timing of muddy progradation and chenier formation has not been determined, the foregoing interpretation suggests a complex sequence of events, reflecting as much the influence of local morphodynamic factors as external factors. 相似文献
10.
The paper deals with the question of Holocene transgression on the southern plain of the Changjiang Delta.At the beginning of the transgression, the paleovalleys of the Changjiang and Qiantang Rivers were covered by sea water at first.The shoreline of 8000-7500 yr BP coincided with the -7m isobath of paleotopography. Sea level had already been the present level about 7000-6500 years ago, and the Holocene transgression reached its maximum extent. During the period, the Changjiang and Qiantang Rivers and the Dongtiaoxi valley were turned into estuaries; the eastern area of Shanghai became a shallow sea; some of the bays and lagoons were distributed on the Hang-Jia-Hu and Tao-Ge Plain; the hilly region around the Taihu Lake was coastal marsh and freshwater swamp. Gangshen on the west of Shanghai was formed 7000-4000 yr BP, and during the last 4000 years, the eastern coastal plain of Shanghai advanced quickly toward the sea, and partial clear land of the western Taihu Lake was enclosed and charged into a fre 相似文献
11.
利用 2 0 0 1— 2 0 0 2年 4个季度月航次调查资料 ,研究了长江口海域浮游植物的分布及其与长江径流的关系 ,共鉴定浮游植物 1 5 4种 (含变种和变型 ) ,其中属硅藻类的有 1 1 3种 ,甲藻类 36种 ,近岸低盐性的中肋骨条藻 (Skeletonemacostatum)是最重要的优势种。夏季浮游植物密集区位于长江口海域的北部及靠近浙江近海的上升流区 ,春季和秋季密集区出现在调查区的南部。浮游植物数量高峰出现在夏季 (平均为 9 2 7× 1 0 6 个 /m3) ;冬季 (枯水期 )数量最少(平均为 2 91× 1 0 5 个 /m3) ,且分布相对较均匀 ,显示出该海域浮游植物种类组成与数量的季节变化同长江径流量有明显的关系。由于大量营养盐被长江径流携带入海 ,造成河口区严重富营养化 ,这为赤潮生物大量孳生提供了适宜的环境条件 ,长江口海域已成为我国沿海赤潮多发区之一。 相似文献
12.
对赣北黄茅潭近代湖泊沉积岩芯进行了~(137)Cs、~(210)Pb测试和SCP(球状碳粒)计数分析,阐述了~(137)Cs蓄积特征,结合SCP计数、粒度指标及降水记录厘定了一些事件性沉积层位。研究表明,1986年前后是沉积环境中~(137)Cs行为的转折点;在这之前,~(137)Cs以大气散落为主,其蓄积行为大致与降水存在正相关关系,在这之后,~(137)Cs以流域侵蚀为主,其蓄积行为与降水呈负相关关系。1953—1954年、1974—1975年、1998—1999年,流域降水丰沛,相应沉积层位~(137)Cs比活度低,这与流域强烈侵蚀稀释了进入湖泊的~(137)Cs有关。1963—1964年沉积层位~(137)Cs蓄积峰稳定而显著,与高通量的大气散落有关,也与当时降水量低,大雨、暴雨次数少,流域侵蚀强度低造成较低的沉积速率等密切相关,是可靠的定年时标。1986年存在同样的气候环境特点,其蓄积峰可能也是存在的,但需要进一步确认。基于~(210)Pb方法,利用多种计年模式计算了沉积岩芯的年代,发现与这些事件性沉积层位具有较大差异。研究认为,在长江中游这种降水高、流域侵蚀强度高的较为复杂的沉积环境中,~(210)Pb计年存在较大误差。复杂沉积环境中近代沉积的定年,有必要深度挖掘~(137)Cs环境行为,在全面阐述其蓄积特点的基础上,辅以SCP计数、粒度指标及降水等识别事件性沉积层位,矫正~(210)Pb计年,是精确建立近代沉积时标的必要方法。 相似文献
13.
通过研究长江口及邻近海域溶解无机氮(DIN=NO 3-+NO 2-+NH 4+)、磷酸盐(PO 43-)、硅酸盐(SiO 32-)所表征的营养盐区域结构特征及影响因素,在分析营养盐绝对限制情况的基础上,划分了潜在相对营养限制区域。结果表明,123°E以西近岸表层区域DIN/P比值全年均高于16,而Si/DIN除秋季外基本小于1,显示出长江冲淡水影响下"过量氮"的特征。春夏季河口锋面区(31°~32.5°N,122.5°~124°E)硅藻的大量生长可使DIN/P异常升高和Si/DIN异常降低。秋季研究区域北部DIN/P西低东高且Si/DIN西高东低是由于在高DIN、低PO 43-的长江冲淡水影响下,近岸受相对低DIN、高SiO 32-的苏北沿岸流南下入侵影响而被分割而成。冬季长江口门东北部存在的高DIN/P和低Si/DIN区则主要由于寡营养盐的黑潮水深入陆架,向东北输送的部分长江冲淡水和增强的苏北沿岸流共同作用造成DIN升高所致。利用Redfield比值进行了不同站位表层潜在相对营养限制情况的区分。近岸123°E以西受高DIN、SiO 32-长江冲淡水影响,四季多呈现PO 43-潜在相对限制,而在春夏季由于浮游植物的大量吸收PO 43-,造成局部PO 43-绝对限制及潜在相对限制。春夏季氮限(DIN潜在相对限制)一般发生在外海部分站位,但较为零散。秋季除了东南外海大部分站位外,受苏北沿岸流影响在长江口北部近岸也存在氮限。随着低DIN/P的黑潮表层水(KSW)的入侵加强,冬季外海氮限站位增多。硅限(SiO 32-潜在相对限制)在夏季发生在赤潮高发区,而冬季南部存在较多硅限站位表明KSW中SiO 32-相对较为缺乏。 相似文献
14.
Variation in the summer nanoflagellate community on the continental shelf ecosystem of East China Sea (ECS) is closely coupled with environmental variation due to extension of the Changjiang River plume. Spatial patterns of nanoflagellate abundance were studied in June and August 2003, June 2006 and July 2007 over the ECS shelf. The Changjiang River plume was smaller during the August 2003 and July 2007 cruises than during the rest other 2 cruises. Total nanoflagellates densities varied between 1 and 120 × 10 2 cells ml −1 with the highest abundances occurring within the Changjiang River plume during large plume periods. In the small plume periods, the range of nanoflagellates abundance was 3–33 × 10 2 cells ml −1 and the highest abundances were observed during these periods either within the Changjiang River plume or the Yellow Sea Coastal Water (YSCW). During large plume periods, nanoflagellate abundance closely related to changes in salinity and during the small period, abundance was most related to water temperature. The pigmented nanoflagellate community (PNF) within Changjiang River plume, especially in the <3 μm size class, appears to increase in response to terrestrial or anthropogenic inorganic nutrient loading in the discharge of fresh water from the Changjiang River. The PNF abundance pronounced increase caused the variation of nanoflagellate community of ECS in summer. We suggest that the discharge of fresh water from Changjiang River has significant ecological impacts on spatial variations in nanoflagellate community in the ECS. 相似文献
15.
本文基于2016年长江口海域(舟山绿华山)的连续观测数据,分析了该海域水文环境要素分布,并估算了溶解氧跨跃层垂向输运。本次观测发现,水体的温度、盐度和溶解氧剖面具有明显的分层结构,三者跃层具有相同的变化趋势且主要受潮流变化影响。通过计算,得到跃层浮性频率的平方(N2)在10–3—10–2/s2之间,剪切的平方(S2)介于10–5—10–2/s2。潮流活动会激发水体剪切不稳定促进水体中溶解氧的垂向交换。最后,采用简化的一维溶解氧垂向输运模型,得到观测周期内跨跃层输运的溶解氧的含量为4.75mmol/(m2·d),佐证层化是长江口海域出现氧亏损现象的主要原因之一。 相似文献
16.
采用CTD、多参数环境监测系统 YSI等仪器设备 ,于 2 0 0 0年 8月在长江口外海区对长江冲淡水结构、羽状锋等进行了现场观测。 2 0 0 0年 8月长江冲淡水出口门后 ,朝东北偏北流动 ,而当年 8月为长江径流量偏小的月份。通过动力分析指出了近口门段长江冲淡水分布类型与径流量的关系。长江冲淡水主流在近口门附近朝东北偏北扩展后 ,在科氏力作用下朝东南扩展 ,在转向区域为沿水下河谷北上的高盐台湾暖流水。高盐的台湾暖流水和长江冲淡水混合 ,生成口外羽状锋 ,强度大 ,阻挡了长江冲淡水向东扩展 ,并使冲淡水在当年径流量偏小情况下朝东北偏北运动。部分台湾暖流水在中下层能穿越长江口外而向北流动。羽状锋主要存在于长江口外 1 2 2 .6°E附近的 1 5m水层之上。在浙江沿岸、长江口外水下低谷西侧、吕泗近岸存在着上升流现象 相似文献
17.
于1994年4月8－30日运用14C,15N同位素示踪法现场观测东海的初级生产力和新生产力。结果表明,初级生产力变化在200-2770mg／（m2·d）之间,高值出现于开阔深水区和近海富营养区,低值出现于近岸浑水区和外海贫营养区;东海初级生产力的主要限制因子是营养盐可得性和光照条件,在不同海区二者的作用地位有所不同。新生产力的变动范围在15－1372mg／（m2·d）山之间;剧烈的波动主要取决于氧化态、还原态氮的供给比例。f比变化在0．05－0．70。 相似文献
18.
从长江口及邻近海域10 个站点采集表层海水, 通过DAPI 染色计数和克隆文库构建的方法, 对细菌的多样性及群落结构进行初步研究。DAPI 染色计数结果显示长江口及邻近海域表层海水中 细菌丰度总体较高, 生物量变化较大, 从1.16×10 5(A04 站点)到 1.48×10 6 cells/mL (B03 站点); 总体 趋势从长江口向外海增加。细菌克隆文库的系统发育分析表明: 细菌序列以变形菌门为主(占总文库 的60.61%), 其中α-变形菌纲是绝对优势类群(50.62%); 其次是拟杆菌门(15.18%)、放线菌门(14.79%) 和蓝细菌门(4.61%), 还有少量厚壁菌门、绿弯菌门、酸杆菌门、浮霉菌门、纤维杆菌门、疣微菌门 等; 另外柔膜菌门和SAR 类群也有发现。文库多样性分析结果显示长江口及邻近海域部分站点表层 海水中细菌多样性显著, 与研究区海域水产养殖活动有关, 并受到区域洋流和海洋化学环境(如低氧 带)的影响。 相似文献
19.
The Holocene coastal plain of French Guiana is an open chenier plain. The shoreline is characterized by vast migrating shoreface-attached mudbanks. Cheniers develop within the interbank zone. These sandbodies, which rest on the Demerara marine clays, have also been observed in the inner parts of the coastal plain. This paper deals with the coastal area between Mahuri and the Maroni Rivers in French Guiana. An overview of the present state of knowledge regarding the coastal research in this area is given, and based on new evidence the problem of the provenance of the sandy accumulations will be discussed and further defined. 相似文献
20.
根据2011年春季(4月)夏季(8月)两个航次调查的CTD温盐资料,获得观测期间黄、东海主要水团特征:(1)夏季黄海冷水团10℃等温线在黄海海域中部30m以深,影响范围西至122°E南至34°N,最低温度为6.2℃,比气候态平均冷水团温度低约2℃;(2)夏季冲淡水以长江口为中心,呈半圆形向外扩展,并无明显NE转向,30.00等盐线在32°N断面上东至124°E,南至29.5°N,扩展范围与往年相比偏西1°左右,而在SE方向较往年有明显延伸扩展。水文结构特征为:(1)春季,温跃层主要在南黄海中部以西,跃层强度仅为0.10—0.40℃/m;密跃层主要在长江口以东,跃层强度0.20—0.30kg/m4;(2)夏季,温跃层强度最高值在长江口东北,跃层强度达到2.41℃/m,上界深度5.5m,厚度2.5m;黄海温跃层强度普遍强于东海,主要是冷水团区域表底显著的温度差异造成;密跃层强度高值区在33°N断面西侧海区,强度达到1.38kg/m4,上界深度5.5m,厚度约为1.5m;沿长江冲淡水舌轴方向的密跃层强度为0.30—0.60kg/m4,自西向东逐渐减弱。 相似文献
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