Enrichment of trace metals in surface sediments from the northern part of Point Calimere, SE coast of India   总被引：1，自引：0，他引：1  

V. Stephen-Pichaimani  M. P. Jonathan  S. Srinivasalu  N. Rajeshwara-Rao  S. P. Mohan 《Environmental Geology》2008,55(8):1811-1819

This study deals with the geochemical nature of distribution, enrichment of total trace metals (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn, Cd) in bulk sediments and its association with sediment texture, carbonates and organic carbon. Sixty surface sediment samples were collected during two different seasons in 2002 and 2003 along the coastal regions in three transects from Nagapattinam town, north of Point Calimere in southeast coast of India. The sediments are mostly sandy silt and are dominated by the carbonate content. Organic carbon distribution indicates that they are brought in by the minor river input. Enrichment of trace metals is clearly identified by the domination of Pb, Zn, Cd with high values than the average crustal values and comparison of trace metals from other coastal regions in the southeast coast of India. Statistical analysis clearly indicates that Fe and Mn control the distribution of trace metals and are concentrated in the finer particles and organic carbon fraction. The increase in concentration signifies the need for regular monitoring of the offshore coastal region in southeast coast of India which was recently destroyed by the 2004 December tsunami event, and which is also located near the Sethu Samuthram Ship Canal Project.  相似文献   

Biodegradation effects over different types of coastal rocks     

Murat Gül  Ahmet Özbek  Fahri Karayakar  Mehmet Ali Kurt 《Environmental Geology》2008,55(7):1601-1611

Modern coastal areas have natural and transported rocks (armourstone) on which various types of organisms live. Burrowing, boring and feeding by these organisms can destroy or modify the coastal rocks and hence change the coastal morphology. Two rock types and three dominant types of organisms have been studied in Mersin Bay, Eastern Mediterranean of southern Turkey. In this study area, Plio-Quaternary conglomerates and variously aged limestone armourplates have been affected by Phoronida worms, bivalve Brachidontes pharaonis (Fischer P. 1870) and the limpet Patella sp. Phoronida colonies were found covering the hard substratum as a mat and form tubular endolithes of 35.0 mm depth and 1.5 mm diameter, whilst Brachidontes pharaonis (Fischer P. 1870) form 44 mm deep vase-shaped gastrochaenolites. The bioerosive activity of Limpet Patella sp., found intertidal and within the spray zone, cannot be significantly observed on the rocks over short time periods. The soft sandy matrix of the conglomerates present were found to disintegrate by bioerosional processes, with the released gravels being transported and deposited onto the beach. Within the armourstone limestone blocks, a maximum of 44.0 mm deep holes developed after 50–60 years. However, these biological activities do not threaten the stability of the blocks due to their hard and homogeneous internal structure. Furthermore, the organism colonies that cover these rocks as a strong mat (maximum 29.0 mm) act to protect their surfaces from further biological attack and wave action.  相似文献   

氡及其子体测量方法在滑坡勘查中的应用研究   总被引：1，自引：0，他引：1  

邓居智  叶树林  刘庆成 《地质与勘探》2008,44(1):113-116

从滑坡体上氡及其子体异常形成机理出发,推导了滑坡体边界上氡及其子体测量异常特征,从理论上论证了利用氡及其子体测量勘查滑坡体的可行性.结合在重庆某已知滑坡体上土壤天然热释光测量和210Po测量的试验测量结果,进一步探讨了氡及其子体测量技术在滑坡勘查中的可行性和应用前景.  相似文献   

港仔地裂缝——雷州半岛西部一条纵贯晚全新世砂堤地裂缝的发现          下载免费PDF全文

徐起浩 《第四纪研究》2008,28(4):712-720

港仔地裂缝发生于新生代以来强烈活动的琼雷凹陷北部雷州半岛的西海岸,沿构造带展布,形成于凸起和凹陷交界地区。地裂缝局部纵贯沿海岸展布的晚全新世砂堤,切过中更新世火山岩及其风化土和全新世海成阶地。根据其展布区的构造、地形地貌和形成特征,并与近几十年雷州半岛大量发生的地裂缝比较,认为港仔地裂缝可能属构造蠕变地裂缝。该地裂缝揭示了被纵贯砂堤的沉积学特征和形成于巨砾海滩和高能海浪下的古环境。砂堤上部约海拔5m砂堤岩取样¹⁴C测年为1360±60aB.P.,结合雷州半岛西海岸、西南海岸其他抬升特征,推测该地裂缝是在晚全新世该地海岸抬升或抬升后形成的。  相似文献   

Thermodynamics and Microphysical Characteristics of an Extreme Rainfall Event Under the Influence of a Low-level Jet over the South China Coast     

徐碧裕  黎慧琦  叶朗明  刘显通  饶晓娜  肖辉  徐加民  林青蒲义良  黄青兰 《热带气象学报(英文版)》2023,29(2):216-235

In this paper, the data of Automatic Weather Stations (AWSs), ERA5 reanalysis, sounding, wind profile radar, and dual-polarization radar are used to study an extreme rainfall event in the south China Coast on 11 to 12 May 2022 from the aspects of thermodynamics and microphysical characteristics under the influence of low-level jets (LLJs). Results show that: (1) The extreme rainfall event can be divided into two stages: the first stage (S1) from 0000 to 0600 LST on May 12 and the second stage (S2) from 0700 to 1700 LST on the same day. During S1, the rainfall is mainly caused by the upper-level shortwave trough and the boundary layer jet (BLJ), characterized by strong upward motion on the windward side of mountains. In S2, the combined influence of the BLJ and synoptic-system-related low-level jet (SLLJ) increases the vertical wind shear and vertical vorticity, strengthening the rainstorm. In combination with the effect of topography, a warm and humid southwest flow continuously transports water vapor to farther north, resulting in a significant increase in rainfall over the study area (on the terrain’s windward slope). From S1 to S2, the altitude of a divergence center in the upper air decreases obviously. (2) The rainfalls in the two stages are both associated with the mesoscale convergence line (MCL) on the surface, and the wind field from the mesoscale outflow boundary (MOB) in S1 is in the same direction as the environmental winds. Due to a small area of convergence that is left behind the MOB, convection moves eastward quickly and causes a short duration of heavy rainfall. In S2, the convergence along the MOB is enhanced, which strengthens the rainfall and leads to strong outflows, further enhancing the surface convergence near the MOB and forming a positive feedback mechanism. It results in a slow motion of convection and a long duration of heavy rainfall. (3) In terms of microphysics, the center of a strong echo in S1 is higher than in S2. The warm-rain process of the oceanic type characterizes both stages, but the convective intensity in S2 is significantly stronger than that in S1, featuring bigger drop sizes and lower concentrations. It is mainly due to the strengthening of LLJs, which makes small cloud droplets lift to melting levels, enhancing the ice phase process (riming process), producing large amounts of graupel particles and enhancing the melting and collision processes as they fall, resulting in the increase of liquid water content (LWC) and the formation of large raindrops near the surface.  相似文献   

台湾海峡西岸地应力特征研究     

李冉  陈群策  张重远  孟文  牛琳琳  邱君  陈利忠 《地质学报》2016,90(8):1703-1714

台湾海峡西岸地区受到欧亚板块、太平洋板块和菲律宾板块的共同作用,具有复杂的应力场特征,但本地区现阶段地壳应力状态研究程度较低。为深入了解本区地应力特征,本文采用水压致裂法在福建平潭和广东饶平钻孔中进行了地应力测量,并结合其他实测及震源机制解资料,讨论了台湾海峡西岸构造应力场特征。结果显示平潭和饶平钻孔地应力优势作用方位分别为N19°W和N37°W;由震源机制解资料得到的研究区应力场方向表现为从北向南由NNW方向转向EW方向的扇形分布。地应力状态的水平变化趋势,大致以沙县-南日岛断裂为界,北部为低应力区,南部为高应力区,且南部大致以九龙江下游断裂附近开始,呈现由北向南,地应力水平逐渐降低的趋势。在研究区北部、中部、南部分别选取平潭、泉州、饶平三个钻孔,利用库伦准则对断层活动性进行判断,认为海峡西岸北部地区应力水平较低,断层活动性较弱;泉州所在的海峡西岸中部地区应力已积累到较高的水平,断层失稳滑动的可能性比较大;饶平邻近区域在近期断层失稳滑动的可能性不高。  相似文献   

辽东湾西岸三维海陆风特征的数值模拟   总被引：1，自引：0，他引：1  

王玉国  吴增茂  常志清  江海英 《海洋预报》2009,26(3):12-21

本文所用的数值模式为地形影响修正的三维流体静力的中尺度气象学模式,模式对中尺度的海陆风环流和山谷风环流有较好的模拟效果.利用该模式对一个海陆风个例(1999年7月15～16日)进行了数值模拟,分析了海陆风环流的日变化规律和三维结构特征,以及地形对海陆风环流的影响,模拟结果与实际观测数据和已有研究成果具有较好的一致性.  相似文献   

福建沿岸不同海区夏季浮游植物的组成与分布   总被引：3，自引：0，他引：3  

王雨  林茂  林更铭 《台湾海峡》2009,28(4):496-503

结合福建省“908专项”，于2006年7～8月对福建省沿岸海域水采浮游植物的种属组成、数量分布、生物量进行了大面积科学调查．结果表明，福建沿岸海域浮游植物隶属于6门57属127种，其中硅藻47属107种，甲藻5属15种，蓝藻1属1种，金藻2属2种，隐藻1属1种，裸藻1属1种．硅藻类在种类和数量上均占主导地位，优势种主要是柔弱伪菱形藻（Pseudo—nitzschia delicatissima）、中肋骨条藻（Skeletonema costatum）、旋链角毛藻（Chaetoceros curvisetus）、菱形海线藻（Thalassionema nitzschioides）等．硅藻类广布，甲藻类在闽东海域及东山沿岸分布较多，蓝藻类检出率降低，裸藻类和金藻类检出率增高．表层浮游植物平均细胞密度为3222．59×10^4ind／dm^3，数量分布态势为近岸高、外海低，阂东和闽南高、闽中低．叶绿素a及优势类群的分布与数量分布基本一致．福建沿岸海域赤潮生物种类较多，是引发赤潮的潜在生物因素，一些赤潮生物已在闽南、闽东沿岸局部海域成为优势种．  相似文献   

Modeling the erosion of cohesive clay coasts   总被引：1，自引：0，他引：1  

Alan S. Trenhaile 《Coastal Engineering》2009

A model was developed to study the erosion of cohesive clay coasts in macro- to non-tidal environments. The model shares some of the characteristics of previous models, including the erosion of bare clay surfaces by wave generated bottom shear stresses, and of mobile, sediment-covered surfaces by abrasion. It differs from previous models, however, in several important ways. The morphodynamics of beaches with clay foundations, under different wave conditions, are based on a previously developed model for beaches on rocky shore platforms. Sediment thickness along a beach profile is calculated at regular intervals and compared with the maximum thickness that could be moved at that location under prevailing wave conditions. Wave friction factors are determined, where necessary, according to the occurrence and morphology of ripples on the bottom. In addition to abrasion and the effect of wave induced shear stresses on the clay bottom, erosion by stresses generated by wave impact at the bluff foot and on the intertidal platform is calculated using an expression derived from hard rock coastal models. Tides are represented by their computed tidal duration values, the amount of time each year that the water level falls within each 0.1 m vertical interval. Water depths are modified by wave setup and set-down conditions. Several preliminary model runs were made. The profiles were concave in the submarine zone and roughly linear in the intertidal zone. Equilibrium profiles developed which were maintained as they migrated landwards.  相似文献   

Laboratory study and analysis of the instability of alongshore currents     

REN Chunping  ZOU Zhili 《海洋学报(英文版)》2009,28(4):96-106

A laboratory experiment on the instability of alongshore currents was conducted on a plane beach with slope 1:40. Low-frequency fluctuations of alongshore currents with the period of approximately 100 s were observed. The dominant frequency and amplitudes of the oscillations of alongshore currents were determined using the maximum entropy method and the regression method of trigonometric function. The variations across the beach cross-section of the oscillation amplitudes of the alongshore current were given. The linear shear instability theory was used to analyze the mechanism of the oscillation, and the calculated results agreed with measurements. This confirms that the observed fluctuation of alongshore currents is due to the shear instability of alongshore currents.  相似文献