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101.
福建沿海强潮河口闽江口和九龙江口外均发育有一定规模的线状沉积沙体,通过多波束调查采集数据和浅剖、沉积物资料的分析,对此类沙体特征进行研究,初步认为其为潮流沙脊。结果表明:在平面分布上,闽江口外潮流沙脊走向近SW-NE向,沙脊局部连片;九龙江口外沙脊走向近ENEWSW向,沙脊末端有分叉现象。分析现代海洋环境作用并结合沙脊规模、水深和河口相对关系的研究显示,沙脊主体规模基本稳定,现代水动力仅对沙脊表面有改造作用。在潮流、波浪和近岸余流的共同作用下沙脊脊顶部略显平滑,两翼坡度较缓,其沉积物组成以粒度较粗的古河口砂质浅滩砂为主,沉积主体为全新世海平面上升时期,近岸河口环境的古水下三角洲遭受潮流侵蚀而成。 相似文献
102.
José Tasso Felix Guimarães Marcelo Cancela Lisboa Cohen Marlon Carlos França Luiz Carlos Ruiz Pessenda Eduardo de Jesus Souza Afonso César Rodrigues Nogueira Ronnie Alves 《地球表面变化过程与地形》2013,38(13):1535-1549
The goal of this work was to understand the main hydrodynamic processes acting on tidal flats of the coast of Amapá near the mouth of the Amazon River, and how they change over the short term (~ 20 years). The analysis of morphological and geobotanical units was carried out by applying processing and interpretation methods to optical and synthetic aperture radar (SAR) images, combined with data on water salinity, maximum flood height, sedimentary facies data, rainfall and river discharge. The temporal analysis of morphological and geobotanical units suggests the relative stabilization of savannah, ‘várzea’ and mangrove areas during the drier period and increasing tidal amplitude between 1987 to 1997. The wetter period and decreasing tidal amplitude between 1997 to 2008 led to an increase in the area of ‘várzea’ and lakes over savannah, and the expansion of mangroves mainly over the inundated field and tidal mud/mixed flats. Therefore, the decrease in rainfall index during the drier period is well‐correlated with the reduction of the Calçoene River discharge and jointly with increasing tidal amplitude favored the increase of migration rate of the mud bank and erosion profile along the littoral. It was followed by the increase of the Calçoene River discharge and jointly with decreasing tidal amplitude during the wetter period, favoring the development of mangroves on muddy substrates near the coastline. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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Shear-flow induced secondary circulation in parallel underwater topographic corrugation and its application to satellite image interpretation 总被引:1,自引:0,他引:1
ZHENG Quanan ZHAO Qing YUAN Yeli LIU Xian HU Jianyu LIU Xuehai YIN Liping YE Xiaomin 《中国海洋大学学报(英文版)》2012,11(4):427-435
This study aims to figure out satellite imaging mechanisms for submerged sand ridges in the shallow water region in the case of the flow parallel to the topography corrugation.Solving the disturbance governing equations of the shear-flow yields the analytical solutions of the secondary circulation.The solutions indicate that a flow with a parabolic horizontal velocity shear and a sinusoidal vertical velocity shear will induce a pair of vortexes with opposite signs distributed symmetrically on the two sides of central line of a rectangular canal.In the case of the presence of surface Ekman layer with the direction of Ekman current opposite to(coincident with) the mean flow,the two vortexes converge(diverge) at the central line of canal in the upper layer and form a surface current convergent(divergent) zone along the central line of the canal.In the case of the absence of surface Ekman layer,there is no convergent(divergent) zone formed over the sea surface.The theoretical results are applied to interpretations of three convergent cases,one divergent case and statistics of 27 cases of satellite observations in the submerged sand ridge region of the Liaodong Shoal in the Bohai Sea.We found that the long,finger-like,bright patterns on SAR images are corresponding to the locations of the canals(or tidal channels) formed by two adjacent sand ridges rather than the sand ridges themselves. 相似文献
106.
江苏沿海辐射沙脊群在国内潮成沙体中较为罕见,有关辐射沙脊形成的动力机制已有定论,但对其形成时间和物质来源说法不一。运用长时间尺度动力地貌过程数学模型复演了辐射沙脊群形成演变过程,结果表明:江苏岸外辐聚辐散的流场不依赖于局部海底地形而独立存在;不同初始地形下只要泥沙供给充足,经过150年左右潮流动力对地形不断塑造,辐射状"水道-沙脊"相间的地貌格局都能基本形成;辐射沙脊群是废黄河北归约150年后,随着废黄河水下三角洲不断被侵蚀,辐聚辐散的潮流对不同来源物质重新塑造的结果,是动力-泥沙-地形相互作用的产物。 相似文献
107.
Gravity and bathymetry data have been extensively used to infer the thermo-mechanical evolution of different segments of the
oceanic lithosphere. It is now understood that magmatic fluid processes involved in the accretion of oceanic crust are spatially
complex and episodic. The nature of these processes which are in general nonlinear, can be described using fractal analysis
of marine geophysical data. Fractal analysis has been carried out for gravity and bathymetry profiles over the aseismic Chagos-Laccadive
Ridge and the spreading Carlsberg Ridge. The Iterated Function Systems (IFS) have been used to generate synthetic profiles
of known dimension (D) and these are compared with the observed profiles. The D for the data sets are in the range of 1–1.5.
The D for gravity profiles is less than those of bathymetry and the D for gravity and bathymetry over spreading ridge is higher
than the aseismic ridge. The low fractal dimension indicates that the processes generating them are of low dimensional dynamical
systems. 相似文献
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109.
The seafloor topography of a slow-spreading ridge shows a number of well-documented regularities at the ridge segment scale as the result of the complex interplay between ridge-axis magmatic and tectonic processes. This paper describes the results of a detailed analysis of the seafloor topography of the Mid-Atlantic Ridge near the Atlantis transform, where marine gravity data provide independent, although non-unique, constraints on subseafloor density structure. Using a combined topography and gravity data set, we identified the specific contributions of subseafloor density structure to the seafloor topography. We show that the observed along-axis deepening (0.3–0.8 km) from the midpoint of a ridge segment towards the non-transform offsets in the study area can be explained by the vertical deflection of a zero-age plate in response to along-axis crustal thickness variations. However, this effect can only account for 50–60 per cent of the observed 1.5–1.7 km deepening towards the Atlantis transform, suggesting the presence of significant stresses in the lithosphere near a transform. Results of plate flexural calculations also predict a more elevated rift flank at the inside corner of the ridge–transform intersection than at the conjugate outside corner. Such an asymmetry in rift flank topography is calculated to be greatest near a transform fault with a significant volume of deep transform valley and when adjacent plates across the transform fault are mechanically decoupled or only weakly coupled. Together these results illustrate the complex interplay between various tectonic processes at a slow-spreading ridge. 相似文献
110.