长江河口潮波传播机制及阈值效应分析   总被引：1，自引：0，他引：1  

张先毅  黄竞争  杨昊  欧素英  刘锋  蔡华阳  杨清书 《海洋与湖沼》2019,50(4):788-798

河口潮波传播过程受沿程地形(如河宽辐聚、水深变化)及上游径流等诸多因素影响,时空变化复杂。径潮动力非线性相互作用研究有利于揭示河口潮波传播的动力学机制,对河口区水资源高效开发利用具有重要指导意义。本文基于2007—2009年长江河口沿程天生港、江阴、镇江、南京、马鞍山、芜湖的逐日高、低潮位数据及大通站日均流量数据,统计分析不同河段潮波衰减率与余水位坡度随流量的变化特征,结果表明潮波衰减率绝对值与余水位坡度随流量增大并不是单调递增,而是存在一个阈值流量和区域,对应潮波衰减效应的极大值。为揭示这一阈值现象,采用一维水动力解析模型对研究河段的潮波传播过程进行模拟。结果表明,潮波传播的阈值现象主要是由于洪季上游回水作用随流量加强,余水位及水深增大,导致河口辐聚程度减小,而余水位坡度为适应河口形状变化亦有所减小,从而形成相对应的阈值流量和区域。  相似文献   

南海北部陆坡西部海域“海马”冷泉甲烷渗漏及其海底表征     

赵静  梁前勇  尉建功  陶军  杨胜雄  梁金强  陆敬安  王建军  方允鑫  龚跃华  何雪宝 《地球化学》2020,(1):108-118

2015年3月"海马"号遥控无人潜水器(ROV)在南海北部陆坡西部海域首次发现活动冷泉,并命名为"海马"冷泉,此后中国地质调查局广州海洋地质调查局先后组织了3个航次,对"海马"冷泉开展进一步勘查和研究。本次研究在综合分析4个航次调查数据的基础上,初步阐述"海马"冷泉的分布范围、地形地貌、生物群落、自生碳酸盐岩和流体活动等特征。总体而言,"海马"冷泉区地势平缓,气体渗漏现象非常发育,是以CH4为主要气体渗漏形成的活动冷泉区,且气体渗漏活动具有时空迁移性。气体碳同位素组成表明,海马冷泉区的CH4为混合成因气,且以微生物成因为主;"海马"冷泉区发育有多种类型的化能自养冷泉生物群落,冷泉区种类丰富,目前已报道了多个冷泉生物新种。这些发现为研究南海北部陆坡西部海域天然气水合物分解及其环境效应、冷泉生物生命起源与演化和南海与印度洋及太平洋物种迁移贯通等科学问题提供重要依据。  相似文献   

全球主要河流流域碳酸盐岩风化碳汇评估   总被引：7，自引：0，他引：7  

李朝君  王世杰  白晓永  谭秋  李汇文  李琴  邓元红  杨钰杰  田诗琪  胡泽银 《地理学报》2019,74(7):1319-1332

碳酸盐岩风化吸收的大气CO₂主要以HCO₃ ^-形式连续地经由河流从大陆输送到海洋,成为陆地生态系统的重要碳汇。目前主要河流流域的碳酸盐岩风化碳汇估算存在不确定性,分布格局尚不清晰。基于GEMS-GLORI全球河流数据库提供的全球10万km ²以上主要河流流域多年平均监测数据,利用水化学径流法估算出全球主要河流流域碳酸盐岩对CO₂的吸收速率为0.43±0.15 Pg CO₂ yr ^-1,平均CO₂吸收通量为7.93±2.8 t km ^-2 yr ^-1。CO₂吸收通量在不同气候带下差异显著,热带和暖温带CO₂年吸收速率占全球主要河流流域年吸收速率的62.95%。冷温带CO₂年吸收速率占全球主要河流流域的33.05%,仅次于热带地区。本文划分出全球CO₂吸收通量的9个关键带,关键带的交汇处CO₂吸收通量较高。喀斯特出露流域碳酸盐岩对CO₂吸收通量的均值为8.50 t km ^-2 yr ^-1,约为非喀斯特流域的3倍。全球喀斯特出露流域碳酸盐岩风化碳汇在全球碳循环、水循环及碳收支平衡估算研究方面占据重要地位。  相似文献   

Are carbonate barrier islands mobile? Insights from a mid to late-Holocene system,Al Ruwais,northern Qatar     

John Rivers  Max Engel  Robert Dalrymple  Ruqaiya Yousif  Christian J. Strohmenger  Ismail Al-Shaikh 《Sedimentology》2020,67(1):534-558

Barrier islands are important landforms in many coastal systems around the globe. Studies of modern barrier island systems are mostly limited to those of siliciclastic realms, where the islands are recognized as mobile features that form on transgressive coastlines and migrate landward as sea-level rises. Barrier islands of the ‘Great Pearl Bank’ along the United Arab Emirates coast are the best-known carbonate examples. These Holocene islands, however, are interpreted to be anchored by older deposits and immobile. The mid-Holocene to late-Holocene depositional system at Al Ruwais, northern Qatar, provides an example of a mobile carbonate barrier island system, perhaps more similar to siliciclastic equivalents. Sedimentological and petrographic analyses, as well as ¹⁴C-dating of shells and biogenic remains from vibracored sediments and surface deposits, show that after 7000 years ago a barrier system with a narrow back-barrier lagoon formed along what is now an exposed coastal zone, while, contemporaneously, a laterally-extensive coral reef was forming immediately offshore. After 1400 years ago the barrier system was forced to step ca 3 km seaward in response to a sea-level fall of less than 2 m, where it re-established itself directly on the mid-Holocene reef. Since that time, the barrier has retreated landward as much as 1000 m to its current position, exposing previously-deposited back-barrier lagoonal sediment at the open-coast shoreline. In modern neritic warm-water carbonate settings mobile barrier island systems are rare. Their construction and migration may be inhibited by reef formation, early cementation, and the relative inefficiency of sourcing beach sediments from open carbonate shelves. Carbonate barrier island systems likely formed more commonly during geological periods when ramps and unrimmed shelves predominated and in calcite seas, when meteoric cementation was minimized as a result of initial calcitic allochem mineralogy. As with their siliciclastic analogues, however, recognition of the influence of these transient landforms in the rock record is challenging.  相似文献   

山东莱芜盆地碳酸盐岩热液溶蚀特征及水文地质意义   总被引：1，自引：0，他引：1  

刘元晴  周乐  李伟  王新峰  马雪梅  吕琳  邓启军  陈晨 《现代地质》2020,34(1):199-206

鲁中山区莱芜盆地在燕山期发生大规模岩浆侵入活动,岩浆岩体外围碳酸盐岩区分布有水源地、富水块段等岩溶发育富水区,且靠近岩体含水层多发生大理岩化。富含CO₂、H₂S等酸性成分的岩浆热液流体,能对碳酸盐岩产生明显的溶蚀作用。基于岩石样品化学组分分析、水文地质调查及数据统计分析、热液溶蚀地质点详细观测,构建热液溶蚀模式,对莱芜盆地及外围热液溶蚀特征及机理进行研究。结果表明:高温高压岩浆侵入使得接触带碳酸盐岩发生热液变质大理岩化;沿渗透性断裂、裂缝以及不整合面等运移的热液流体,对碳酸盐岩地层产生酸性热液溶蚀和混合溶蚀作用,形成不同规模溶蚀孔洞,构成地下水富集空间,为寻找城镇地下水后备水源地提供新方向。  相似文献   

Adding the missing third and fourth dimensions to trajectory analysis in carbonate systems     

Philipp Tesch  Robert S. Reece  James R. Markello  Juan Carlos Laya  Michael C. Pope 《Basin Research》2020,32(2):388-401

We developed a seismic geomorphology-based procedure to enhance traditional trajectory analysis with the ability to visualize and quantify lateral variability along carbonate prograding-margin types (ramps and rimmed shelves) in 3D and 4D. This quantitative approach analysed the shelf break geometric evolution of the Oligo-Miocene carbonate clinoform system in the Browse Basin and delineated the feedback between antecedent topography and carbonate system response as controlling factor on shelf break rugosity. Our geometrical analysis identified a systematic shift in the large-scale average shelf break strike direction over a transect of 10 km from 62° to 55° in the Oligo-Miocene interval of the Browse Basin, which is likely controlled by far-field allogenic forcing from the Timor Trough collision zone. Plotting of 3D shelf break trajectories represents a convenient way to visualize the lateral variability in shelf break evolution. Shelf break trajectories that indicate contemporaneous along-strike progradation and retrogradation correlate with phases of autogenic slope system re-organization and may be a proxy for morphological stability of the shelf break. Shelf break rugosity and shelf break trajectory rugosity are not inherited parameters and antecedent topography does not dictate long-term differential movement of the shelf margin through successive depositional sequences. The autogenic carbonate system response to antecedent topography smooths high-rugosity areas by filling accommodation and maintains a relatively constant shelf break rugosity of ~150 m. Color-coding of the vertical component in the shelf break trajectory captures the creation and filling of accommodation, and highlights areas of the transect that are likely to yield inconsistent 2D sequence stratigraphic interpretations.  相似文献   

天山南坡高冰川覆盖率的木扎提河流域水文过程对气候变化的响应   总被引：5，自引：5，他引：0  

赵求东  赵传成  秦艳  苌亚平  王建 《冰川冻土》2020,42(4):1285-1298

木扎提河是天山南坡冰川面积覆盖率最大（48.2%）的河流， 流域径流过程对气候变化极为敏感， 为了合理管理和规划水资源， 确保水资源的可持续利用， 亟需定量评估气候变化对该流域水文过程的影响。以VIC-CAS分布式水文模型为计算平台， 利用实测的径流和两次冰川编目间的冰川面积变化数据开展了模型的多目标参数化校正和验证， 有效提高了模拟结果的“真实性”， 然后通过数值模拟结果结合观测数据定量解析了流域径流的组成、 变化特征及对气候变化的响应机理。结果表明： 木扎提河总径流集中在暖季（5 - 9月）， 占全年总径流量的77.9%， 冰川径流、 融雪径流和降雨径流分别占总径流量的66.6%、 26.4%和7.0%。1971 - 2010年木扎提河流域气温和降水呈显著增加趋势， 由于降水的增加， 降雨和融雪径流均呈增加趋势， 但冰川径流呈现明显减少趋势， 导致总径流呈现下降趋势。在RCP4.5情景下， 未来该流域气温呈现明显升高趋势， 降水表现为微弱下降趋势； 气候变暖后， 更多降水以降雨形式发生， 未来降雨径流将明显增加， 降雪和融雪径流已于20世纪90年代达到峰值， 随后明显减少； 冰川面积将持续萎缩， 冰川径流于21世纪10年代达到拐点， 随后明显减少， 导致河道总径流量也将明显减少。  相似文献   

SIMULATION STUDY OF ROAD-CUT EFFECTS ON SLOPE STABILITY     

CHEN Xiao-li  WANG Ming-ming  ZHANG Ling 《地震地质》2018,40(6):1390-1401

Landslides and rock falls along the highway are common geological hazards in Southwest China. As an influencing factor on potential landslides behavior, roads or distance to roads have been successfully used in landslide susceptibility assessments in mountainous area. However, the relationship between the road-cut and the slope stability is not clear. Therefore, we performed two-dimensional slope stability calculation using the general limit equilibrium (GLE)method incorporated in the software SLOPE/W of GeoStudio for stability analysis of slopes. Our studies show that the man-made roads influence on the slope stability mainly exists in two ways:One is to create a new steep slope, which will result in rock falls and shallow landslides along the roads; the other is to influence the stability of the original slope, which will result in comparatively huge landslides. For the latter, our simulation study reveals that the road location, namely at which part of a natural slope to construct a road is important for the slope stability. For a natural slope with a potential slip surface, if a road is constructed at or near the slope toe where the potential slip surface surpasses, it will greatly degrade the slope's factor of safety (Fs) and make the slope unstable; however, if a rode-cut is near the top of the slope, it will increase the slope's Fs and make the slope more stable. The safety location is different for different slope angle, steeper slope needs a higher location for a safety road-cut in comparison with gentle slopes. Moreover, the slope stability decreases when loading a seismic force and it varies with the slope angle. Firstly, the Fs decreases when the slope angle increasing, and when the slope angle reaches 45°, the Fs then becomes greater with the slope angle increasing.  相似文献   

南海IODP 349航次基底玄武岩中碳酸盐岩脉的岩石学特征*     

许佳锐  陈毅凤  王宝云 《热带海洋学报》2018,37(6):63-73

国际大洋发现计划(International Ocean Discovery Program, IODP)349航次在南海东部次海盆和西南次海盆残留扩张脊附近的U1431和U1433站位首次钻取基底玄武岩, 通过对16块基底玄武岩内的碳酸盐岩脉薄片镜下观察以及激光拉曼光谱分析, 揭示碳酸盐矿物为方解石和文石, 为典型的洋壳低温热液蚀变次生矿物。U1431站位碳酸盐岩脉为独立的方解石脉、文石脉交替出现; 而U1433站位则存在方解石脉、文石脉和方解石-文石共生脉三种情况。此外, U1431站位在基底~42.1m处出现了平行的方解石脉和文石脉, 揭示U1431存在不同来源热液的多期活动, 即可能存在多次或多阶段不同的热液注入。U1431和U1433站位的碳酸岩脉中, 文石的矿物集合体形状基本一致, 呈块状、纤维状和放射纤维状; 而方解石存在差异, U1431的方解石以斑块状、块状、粒状和纤维状出现, 而U1433的方解石仅出现块状。U1431站位的碳酸盐岩脉的丰度明显高于U1433站位。这些均揭示U1431站位的低温热液活动强, 而U1433站位则相对弱。两个站位的热液活动不同很可能是由于区域地质环境的差异造成——U1431附近的巨大海山为其提供了热液补给, 而U1433远离热液的补给/渗漏点。  相似文献   

2016年夏季南海海盆水体颗粒物粒径分布特征*     

郑文迪  周雯  曹文熙  王桂芬  邓霖  徐文龙  许占堂  李彩  蔡建南 《热带海洋学报》2018,37(5):74-85

颗粒物粒径分布(Particle Size Distribution, PSD)代表了颗粒物浓度与颗粒物粒径之间的关系, 影响着海洋生态环境和水体光学特性等。文章基于2016年夏季航次调查的生物光学剖面数据, 研究了南海海盆海域PSD的分布特征。研究发现, 幂律函数可以较好地拟合南海海盆区域的PSD, 对数空间中的实测的PSD与模拟的PSD平均决定系数高达0.95。PSD斜率(ξ)的分布范围为[1.27, 7.65], 均值为3.93±0.56。南海海盆区域表层水体的ξ均值与全球大洋表层水体的ξ均值相近, 但高于海湾等表层水体的ξ均值。ξ能较好地表征颗粒物平均粒径D_A的大小, 两者存在明显负相关关系, 即ξ值越高, D_A越小; 反之, D_A越大。通过分析T1断面的生物光学剖面数据及总体平均的PSD剖面数据, 发现PSD剖面分布特征如下: 1)表层水体的ξ值相对较高, 且D_A值相对较低, 推测可能是由于微微型藻类为主导颗粒物所致; 2) ξ值极小值层出现在次表层叶绿素浓度极大值层(Subsurface Chlorophyll Maximum Layer, SCML)中, 并伴随D_A极大值层的出现, 其原因可能是SCML中的大粒径浮游植物占比显著增加; 3)弱光层中的ξ值较SCML中的高, 但略低于表层的ξ值, 而D_A则位于表层与SCML的D_A之间, 这可能与浮游植物及其碎屑的絮凝、分解、沉降等过程相关。PSD特征影响着海水的固有光学特性, 分析发现: 由于SCML中的叶绿素浓度增加, 颗粒物散射系数(b_p(532))和颗粒物后向散射系数(b_bp(532))也相应呈现显著增加的趋势。弱光层中的平均b_p(532)与平均b_bp(532)最小。ξ与颗粒物衰减光谱斜率之间呈高分散性, Boss 等(2001b)的模型适合用于粗略估算区域性的ξ分布范围及均值。  相似文献