Field observations of wave refraction and propagation pathways on coral reef platforms     

Philipp G. Mandlier 《地球表面变化过程与地形》2013,38(9):913-925

Field experiments were conducted to investigate the refraction and propagation of ocean waves across two coral reef platforms in the Maldives, central Indian Ocean. A total of seven pressure sensors were deployed on each reef to quantify temporal and spatial variations in wave characteristics across the platform surfaces. Directional wave properties were calculated from high frequency (2 Hz) wave and current records obtained at two locations on each reef and corroborate theoretically predicted propagation pathways derived from an analytical wave refraction model. Results demonstrate that reef geometry critically controls the refraction and propagation behaviour of incident swell across the reef structures. Differences in the magnitude of refraction (approximately 57° and 14°) observed on each reef can be attributed to variations in platform shape and orientation to incident waves. Results demonstrate that reef flat wave patterns define the segmentation of platform surfaces into distinctive high and low wave energy zones. Furthermore, wave focussing has been identified as a major mechanism controlling the transformation of wave energy across the reefs. Results provide the first field‐based validation of wave refraction and convergence on coral reefs and have significant implications for sedimentation processes and the formation of platform deposits. Reef configurations which promote marked wave convergence are more likely to retain sediment on the reef surface, whereas platforms that induce less refraction and changes in the direction of incident waves have a higher potential for the off‐reef evacuation of sediment over leeward reef margins. Results of wave measurements substantiate such projections and provide a first order explanation for the existence and absence of a coral cay on the two study reefs. The study presents empirical evidence of wave refraction and convergence on coral reefs and establishes a baseline for future investigations of hydrodynamic process controls on platform sedimentation and island formation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

基于用岛类型和方式的无居民海岛使用分类体系构建思考     

康婧  李方  王娜  齐玥  李晴  包吉明  吴楠  林雪萍 《海洋通报》2020,39(3):300-308

对申请海岛使用权的无居民海岛开发利用活动进行分类,是制定无居民海岛使用金最低标准定价的基础。2010年《无居民海岛使用金征收使用管理办法》中的海岛分类体系存在与国家和地方分类体系衔接不够、用岛类型与用岛方式概念混杂、对生态用岛引导作用不明显等问题。本文对无居民海岛各类分类体系现状及关联性进行了梳理,分析其存在的主要问题,在继承《全国海岛保护规划》关于适度开发利用海岛的主导用途分类的基础上,充分体现资源有价、生态有价的原则,将原有的10类无居民用岛类型通过合并、新增、保留,调整为9类。根据用岛活动对海岛自然岸线、表面积、岛体和植被等的改变程度,将无居民海岛用岛方式划分为6种。初步构建了基于用岛类型和用岛方式的无居民海岛使用分类体系,为无居民海岛使用金最低价标准调整、分类施策和精细化管理提供依据。  相似文献   

Characteristics of freshly deposited sand and finer sediments along an island-braided, gravel-bed river: The roles of water, wind and trees     

Angela M. Gurnell  Trevor D. Blackall  Geoffrey E. Petts 《Geomorphology》2008,99(1-4):254-269

Over the past two decades there has been a growing interest in the geomorphological mosaic along large floodplain rivers where channel dynamics are seen to drive habitat-patch creation and turnover and to contribute to high biological diversity. This has required a new perspective on fluvial geomorphology that focuses on biological scales of space and time. This study examines the spatial pattern of surface fine sediment accumulations along a reach of a large gravel-bed river, the Tagliamento River in NE Italy; an area with a moist Mediterranean climate and seasonal flow regime. The study investigates changes in sediment characteristics during the summer low-flow period between April and September. Focussing on five areas representing a gradient from open, bar-braided to wooded island-braided morphologies, the paper demonstrates the importance of riparian vegetation and aeolian–fluvial interactions.Significant contrasts in particle size distributions and organic content of freshly deposited sand and finer sediments were found between sampling areas, geomorphological settings, and sampling dates. In particular, wooded floodplain and established islands supported consistently finer sediment deposits than both open bar surfaces and the lee of pioneer islands, and in September significantly finer sediments were also found in deposits located in the lee of pioneer islands than on open bar surfaces. Overall, the September samples had a greater variability in particle size characteristics than those obtained from the same sites in April, with a general coarsening of the D₅ (φ) (i.e., the coarse tail of the particle size distribution). Also in September, crusts of fine sediment (30 μm < D₅₀ < 64 μm) had formed on the surface of some of the open bar and pioneer island deposits within the more open sampling areas along the study reach. These crusts possessed similar particle size characteristics to aeolian crusts found in more arid environments. They were significantly finer than April samples and September subcrust samples obtained from the same sites and had similar particle size characteristics to some samples taken from wooded floodplain, established island surfaces and the lee of pioneer islands that were not crusted.Local climatological and river level data confirm significant wind and rainfall events during a period of consistently low river levels between the April and September sampling periods. These support deflation, deposition and rain wash of finer sediment during the summer, with windblown sediments being deposited on bar surfaces and in the lee of pioneer islands where wood and young trees provide foci for accelerated sedimentation and island growth as well as on marginal floodplains and established islands. We conclude that along braided rivers in moist settings but with a distinct dry season, aeolian reworking of sediment deposits may have a more important role in driving habitat dynamics than previously considered.  相似文献   

浙江海岛植被乔木层种-多度格局及其气候因素分析     

李晓明  吴承祯  古妩  叶然  张海波  齐平  王胜强  周巳颖  魏永杰  蔡燕红 《海洋学报(英文版)》2017,36(9):87-90

采用数理统计方法对浙江海岛植被乔木层种-多度的格局进行研究,并将参数估计法和遗传算法应用于Preston对数正态模型在浙江海岛植被乔木层种-多度格局拟合中,并分析浙江海岛植被（乔木）及其与气候因子的相关关系。结果表明：（1）浙江海岛植被乔木层种-多度格局符合对数正态分布特征,对数正态分布模型在浙江海岛植被乔木层种-多度分布中的适用性与在热带雨林等非海岛群落种-多度格局的适用性一致;（2）浙江海岛植被与毗邻区域的植被同处于相似相近的气候因子下,具有亚热带气候的主要特征,包含了从温带至亚热带地区的针阔混交林、常绿阔叶和落叶阔叶的众多属、种,可作为亚热带气候下植被重要组成部分开展系统生态学研究。  相似文献   

金山三岛滩涂水下地形演变浅析          下载免费PDF全文

王万胜 《海洋开发与管理》2017,34(7):80-84

文章采用GPS-RTK技术进行2016年金山三岛滩涂水下地形测量,绘制金山三岛滩涂水下地形云图,并与2014年和2015年滩涂水下地形测量结果进行对比,得出以下结论:金山三岛连线左右1km之内的地形起伏变化大,小金山岛南北侧各有一条深坑,大小金山岛之间有一条贯穿东西向的深槽,它的形成与涨落潮流不一致以及人为活动有关,大金山岛与浮山岛之间有一类似山脊样的地形,浮山岛南侧也有一深坑存在。近3年金山三岛滩涂水下地形变化不大,局部小范围内有淤积和冲刷。定期对三岛滩涂水下地形进行测量可以掌握其变化规律,为管理部门提供管理基础资料。  相似文献   

大连长山群岛国家级海洋公园建设对我国海岛保护区管理的启示          下载免费PDF全文

康婧  付元宾  杜宇  袁蕾  孙永光  李方  林霞 《海洋开发与管理》2017,34(7):27-32

国家海洋公园是各国目前进行海洋生态保护极为重要的一种形式,以海岛生态系统为核心保护对象的保护区是海洋保护区的重要类型。长山群岛作为北方最大的群岛,在此建立海洋公园,对我国东北地区的经济发展及生态环境保护意义深远。文章在总结分析长山群岛建园优势的基础上,对现有海洋公园的建设方案进行探讨,并结合我国海岛管理的状况,有针对性地提出了我国海岛保护区管理的措施与建议。  相似文献   

胶东半岛海岛旅游资源综合评价——以长岛、养马岛、崆峒岛、刘公岛、镆铘岛、田横岛为例          下载免费PDF全文

向亚武  王永红  徐杨杨 《海洋开发与管理》2017,34(Z2):75-85

以胶东半岛海岛旅游资源系统野外调查成果为基础,运用李悦铮等建立的海岛旅游资源综合评价体系,选取烟台地区长岛(南长岛和北长岛)、养马岛、崆峒岛,威海地区刘公岛、镆铘岛,青岛地区田横岛6个具有代表性的海岛,对海岛旅游资源进行了综合评价。结果显示,长岛、养马岛和刘公岛3个海岛综合得分分别为34.426、33.347和33.191,排名分别列1、2、3位,属于二级海岛旅游区;镆铘岛、崆峒岛和田横岛综合得分分别为25.668、24.272和23.500,排名分别列第4、5、6位,属于三级海岛旅游区,旅游资源条件、区域条件一般,其受自然环境限制较大。基于对6个海岛的评价综合层和评价项目层得分分析,得出胶东半岛海岛旅游资源存在着天然的缺陷,但也具备特色鲜明的旅游资源的结论。从而在海岛旅游开发和旅游产品结构上提出了相应的调整策略。  相似文献   

海岛礁相对重力测量的潮汐影响   总被引：1，自引：0，他引：1  

张宏伟  张松堂  肖凡  刘子旭  刘立加 《测绘信息与工程》2012,37(1):43-45

着重分析固体潮模型、潮汐因子的选取和海洋负荷潮的求定,并利用ETGTAB模型数据详细计算了相对重力测量中的潮汐改正,说明在近海和岛屿地区进行高精度海岛礁相对重力测量时,必须考虑精确的固体潮和海洋负荷潮改正,从而提高相对重力测量的联测精度。  相似文献   

潮汐流影响下珊瑚岛礁附近波浪传播变形和增水试验          下载免费PDF全文

姚宇  唐政江  杜睿超  蒋昌波 《水科学进展》2017,28(4):614-621

为揭示潮汐流影响下珊瑚岛礁附近波浪的运动特征,通过波流水槽试验对潮汐流存在下规则波的传播变形和增水规律进行了研究,测试了一系列的潮汐流流量并对比正向流、反向流以及无流的情况。研究结果表明:反向流使波浪破碎点向远海侧移动,正向流则使其向海岸侧移动,反向流存在时破碎带内的湍流较正向流时更为剧烈;反向流时破碎点附近入射波能量由主频波向高次谐波发生转移更为显著;潮汐流的存在对波浪反射、透射和能量耗散并无明显影响;正向流造成礁坪上波浪增水减少,反向流则促进增水的增长,增水最大值与潮汐流流量间存在显著的线性关系。研究成果可望为岛礁工程的建设和维护提供一定的理论参考。  相似文献   

Detrital record of the denudation of volcanic islands under sub-tropical climate (Cape Verde)     

《Chemie der Erde / Geochemistry》2019,79(2):235-246

This research is focused on the composition of the sediments produced in volcanic islands when the climate does not favour weathering. The XRD mineralogy (bulk sample and fraction finer than 63 μm), petrography and geochemistry of a set of bedload stream and beach samples collected in the “old” Maio and the “young” Fogo islands of Cape Verde archipelago are used to investigate the compositional transformations promoted by exogenous processes during island denudation. The main factor responsible for the variability in sediment composition is the incorporation of biogenic material derived from the evolving shelves; it largely exceeds the effects of the exhumation of different volcanic and basement units. Given the arid climate (and steep land surface in Fogo), only the most labile components of basaltic rocks, such as volcanic glass, are decomposed. The incipient weathering and sorting processes are responsible for the depletion of Al in bedload deposits. The same happens with other elements usually regarded as non-mobile (namely, Nb, Th, REE, etc.), while Mg is concentrated. Thus, weathering indices grounded on the premise that “mobile” elements are lost and “non-mobile” elements are enriched via weathering are useless in Cape Verde bedload sediments. With time, weathering is able to promote Na leaching and the formation of secondary minerals, which tend to retain non-mobile elements released in the earlier stages of alteration (e.g., LREE, Th, Y, Nb, Ta etc.). Sorting processes are responsible for the selective removal of less-dense grains, explaining local differences between beach and stream deposits. Beach placers are enriched in augitic clinopyroxene (occasionally also in olivine in the Fogo island), and Sc, Cr and Co. Niobium and Ta must be hosted in fine-grained particles that are easily windblown and their abundances in dusts may reveal Cape Verde as a source of airborne material crossing the Atlantic Ocean.  相似文献