Undisturbed Strata Succession Sampling Technology and the Engineering Geological Characteristics of an Atoll in the Southern South China Sea

Coral reef calcareous sediment, a special category of rock-soil material, has representative geological structure and environmental characteristics. It is widely distributed in shallow areas of the tropical ocean; therefore the exploration instruments and technologies for engineering geology studies of coral reef calcareous sediments are very different from those used in land or deep-sea. Obtaining undisturbed cores from the Holocene unconsolidated stratum of coral reefs has been a key problem in the field of marine geology and environment surveying. The authors have designed a novel floating drilling platform equipped with a drilling machine, and successfully achieved undisturbed cores from both reef flats (with water depth 0.5 to 2 m) and a enclosed lagoon (with water depth 2–12 m) of Yongshu Reef (9°32–9°42 N, 112°52–113°04 E), southern South China Sea. Based on the detailed observation on the cores and the analysis from engineering geology, Yongshu Reef was split into reef three engineering geological zones: leading edge, reef flat (including outer reef flat, middle reef flat and inner reef flat) and lagoon. The sediments are classified in the stratum as fine sand, medium sand, coarse sand, gravel and weak-cemented reef limestone.     

南沙群岛珊瑚礁岩体结构特征及工程地质分带

珊瑚礁是发育于海洋环境之中、由造礁珊瑚和生物历经生物和地质作用形成的地质体，是一种特殊的岩土介质类型。在南沙群岛珊瑚礁体上，水动力作用和沉积类型、地形地貌都具有成带分布的特点，因而岩体结构和工程地质性质亦具有分带性。在珊瑚礁海洋水动力环境分带的基础上．研究了南沙群岛珊瑚礁的剖面结构、内部结构和浅地层结构特征以及工程地质分层和岩性，将珊瑚礁岩体结构划分为4种类型和5个工程地质相带，并对各分带的工程特性及适宜性进行了评价。     

海南岛鹿回头珊瑚礁研究进展

前人在海南岛鹿回头珊瑚礁区所做的工作主要集中于以下三方面：(1)鹿回头珊瑚礁区地貌的粗略描述;(2)鹿回头珊瑚礁记录的古海平面研究：(3)鹿回头珊瑚礁记录的现代环境信息研究。通过野外实地考察,将鹿回头珊瑚礁分为8个生物地貌带：礁前斜坡活珊瑚带、礁缘砾石突起脊带、外礁坪带、中礁坪带、内礁坪带、海滩、沙堤、洼地,它们是全新世海平呵和气候环境变化的产物。关于本区珊瑚礁的研究,结合全球珊瑚礁与环境的研究来看,许多工作有待于展开和补充,大致可从以下4个方面进行深入研究：(1)珊瑚礁的生物地貌过程;(2)珊瑚及珊瑚礁的高分辨率环境记录;(3)珊瑚对海洋环境污染的记录：(4)珊瑚礁生态系统与社会、经济及人文系统的关系及其可持续发展。     

Effects of reef morphology variations on wave processes over fringing reefs

Many low-lying tropical and sub-tropical atolls fringed by coral reefs are susceptible to coastal inundation during extreme wave events. Previous studies have shown that the infragravity (IG) wave is the dominant component of shoreline run-up compared to the sea and swell (SS) wave and the wave-induced setup. To better understand both the SS and IG wave dynamics over a fringing reef with various morphologies, a series of laboratory experiments were conducted in a wave flume based on an idealized fringing reef profile. The shoreline responses of waves to different reef morphologies with/without the reef crest, the lagoon and the reef surface roughness were examined. IG wave resonance on the reef flat was identified by a spectral analysis of the shoreline wave records. Subsequently, a numerical model based on the Boussinesq equations was validated by the experimental data. The model was then applied to investigate the impacts of varying reef morphologic features (fore-reef slope, reef-crest width, lagoon width, and reef roughness coefficient) on the shoreline wave motions.     

南海九章环礁中牛轭礁和西门礁新生沙洲沉积特征与动态

南沙群岛的珊瑚礁以环礁形式存在, 拥有各具特色的地貌形态。九章环礁中的牛轭礁和西门礁是两座发育有新生沙洲的环礁, 代表灰沙岛形成前一个重要的过渡性地貌演化阶段。这两处新生沙洲表层沉积物样品的粒度分析表明: 沉积物主要组分为珊瑚碎屑, 长轴中值粒径在14~45mm之间, 属于砾石级别; 样品分选系数在4.5~31之间, 分选性很差; 球度值为0.52~0.68, 球度差。粒度特征值中, 中值粒径具有随着到水边线距离的增大而升高的趋势, 而分选性和球度与距水边线距离关系不大。整体上中值粒径与分选系数呈正相关关系, 而与球度呈负相关关系。历史文献记载和卫星图像表明, 牛轭礁和西门礁上的新生沙洲都是近年来才形成的, 与风暴过程及冬季风有关。牛轭礁上沙洲向北迁移, 同时其长轴向东南方向延伸; 西门礁上沙洲整体向东南方向迁移, 并形成回弯形沙嘴形态。新生沙洲的出现与珊瑚碎屑物质供给变化或风暴浪作用变化的关系还需进一步探讨。     

珊瑚礁海岸侵蚀的研究方法

珊瑚礁海岸海滩和礁坪是海岸作用是活跃的部分，也是近几十年来与海岸发育，海岸侵蚀联系最密切的部分，这一部分高潮时被淹没，低潮时完全出露或大部分出露，使得在此进行地质填图成为可能，这样的地质图可以提供许多信息，如沉积物粒度分布规律，沉积物来源和搬运方向，海滩岩所指示的古海岸线位置，人类活动特别是海岸工程对沉积物分布的影响以及海岸线的变化过程和趋势，在礁坪上开挖的人工水道内测流，能够了解水流的性质以及是否有足够的速度搬运沉积物，从而了解人工水道对海岸的影响和预测海岸的状态，这些方法也可以用于大陆泥质和砂质第岸侵蚀的研究。     

南海珊瑚岛礁地貌遥感识别研究

南海珊瑚岛礁总体处于退化状态,卫星遥感可以实现珊瑚礁区底质演变的监测.本文以西沙群岛海域赵述岛为研究区域,以Landsat-8卫星遥感影像为研究数据,对浅海地貌变化进行遥感分析.将影像进行水深校正和波段组合,使用最大似然法进行珊瑚礁地貌分类,可以清晰的识别灰沙岛、礁坪、礁前坡、泻湖坡、暗滩和海面六种地貌类型,以Worl...     

中国海岸湿地退化压力因素的综合分析

对我国海岸湿地类型、特点和分布进行了论述.通过分析指出围垦、城市与港口开发、污染、海岸侵蚀、油气资源开发、生物资源过度利用和海平面上升等环境压力因素是造成湿地退化的主要原因.综合矩阵因子分析表明,不同的海岸湿地类型所承受的环境压力和所遭受的环境退化程度是不同的,其中三角洲、海岸潟湖、砂质海岸、珊瑚礁、淤泥质海岸、滨岸沼泽和红树林等湿地类型遭受的环境压力最大,环境退化也最严重;指出了人为因素是造成海岸湿地环境退化的主要原因.     

Atoll lagoon flushing forced by waves

Water level and current measurements from two virtually enclosed South Pacific atolls, Manihiki and Rakahanga, support a new lagoon flushing mechanism which is driven by waves and modulated by the ocean tide for virtually enclosed atolls. This is evident because the lagoon water level remains above the ocean at all tidal phases (i.e., ruling out tidal flushing) and because the average lagoon water level rises significantly during periods with large waves. Hence, we develop a model by which the lagoons are flushed by waves pumping of ocean water into the lagoon and gravity draining water from the lagoon over the reef rim. That is, the waves on the exposed side push water into the lagoon during most of the tidal cycle while water leaves the lagoon on the protected side for most of the tidal cycle. This wave-driven through flow flushing is shown to be more efficient than alternating tidal flushing with respect to water renewal. Improved water quality should therefore be sought through enhancement of the natural wave pumping rather than by blasting deep channels which would change the system to an alternating tide-driven one.     

西沙群岛珊瑚礁海域浮游动物群落结构初步分析*

为了解西沙群岛珊瑚礁海域浮游动物的群落特征, 于2015年5月末至7月初在西沙群岛8个岛礁(七连屿、永兴岛和东岛3个岛屿以及浪花礁、盘石屿、玉琢礁、华光礁和北礁5个环礁)进行了浮游动物采样, 分析了浮游动物的多样性、丰度和群落结构特征, 并比较了5个环礁潟湖内和向海礁坡区浮游动物群落组成的差异。调查海域共鉴定浮游动物180种(包括浮游幼虫13个类群), 其中桡足类最多, 达83种, 其次是水母类(38种)、浮游软体类(14种)、毛颚类(11种)和浮游被囊类(7种); 浮游动物平均丰度为256.4±117.8个·m^-3, 桡足类占总丰度的51.08%, 其次是浮游幼虫(16.30%)、浮游被囊类(13.22%)和毛颚类(7.70%)。浮游动物种数、多样性和均匀度指数、丰度在岛屿和环礁之间以及环礁的潟湖区和向海礁坡区均存在差异; 浮游动物多样性和丰度在东岛、玉琢礁和华光礁较高, 而在七连屿和北礁较低; 5个环礁向海礁坡区的浮游动物多样性和丰度皆高于潟湖区的。多元统计分析结果表明调查岛礁的浮游动物可划分两个聚群(相似水平85%); 岛屿近岸及环礁的潟湖群落(Ⅰ)和岛屿远岸及环礁的向海礁坡群落(Ⅱ); 两个聚群浮游动物组成差异较显著(r=0.832, p<0.001); 前者的种数、多样性指数、总丰度和主要浮游动物类群如桡足类、毛颚类和浮游幼虫的丰度显著低于后者。环礁潟湖区和向海礁坡区的空间异质性和生态环境差异可能是导致浮游动物群落结构呈现不同特征的主要因素。     

威海典型海滩沉积地貌及质量评价

选择威海双岛湾附近海滩、国际海水浴场海滩、金海滩、青叽岛以西海滩、青叽岛以东海滩、天鹅湖海滩、桑沟湾海滩、楮岛海滩、南海新区海滩和乳山银滩十处代表性岸滩进行了海滩地貌和底质调查,结合沙滩表层样品分析测试数据,对研究区海滩地貌、沉积物粒度分布特征及海滩质量进行了综合评价。结果表明:威海海滩沉积物主要包括砾砂、粗砂、中砂、细砂四种类型,其中中砂分布最广,约占所有点位的35.6%,细砂、粗砂、砾砂分别占34.4%,26.7%和3.3%。岸滩坡度一般较缓,宽度中等以上,岸滩质量整体较好,部分岸滩受沉积物粒度影响,质量稍差。     

On the variation in calcium content of the waters of Laccadives (Arabian Sea)

The concentration of calcium was determined in the samples collected from four stations in the Laccadive Sea and from two lagoons of Kavaratti and Minicoy atolls. The calcium/chlorinity ratio for the open ocean samples was found to be 0.02168 ± 0.000015 with an average calcium concentration of 424.9 mg kg^?1. A maximum in this ratio was observed at about 200 m depth, below the salinity maximum corresponding to Arabian Sea Surface Water mass. No increase in calcium concentration or in calcium/chlorinity ratio was observed down to 1500 m depth, thereby ruling out the possibility of any calcium carbonate dissolution at these depths. Samples from Kavaratti and Minicoy lagoons gave much lower values of the Ca/Cl ratio (0.02145 ± 0.000036 and 0.02142 ± 0.000046, respectively). These low values are apparently the result of calcium utilization by the coral reefs. Using the reduction in the calcium concentration inside the lagoon, in the absence of any chemical precipitation, the annual CaCO₃ production by reef flat and lagoon on Kavaratti Atoll has been estimated as 1 · 10⁷ kg. This gives an average gross production of 1.4 kg CaCO₃ per m² per yr.     

粤东后江湾海进海岸沉积特征和地貌发育

依据地质钻探和海滩观测资料，分析了后江湾海岸在海进作用下，海岸形成海进地层层序。滨面遭受侵蚀并正在后退和变陡。晚更新统陆相杂色粘土层和砾砂层直接暴露于海底。在海域供沙不足的情况下，整个海湾的海滩被侵蚀后退，而海滩各岸段侵蚀程度存在差异。     

Cyclone and bioturbation effects on sediments from coral reef lagoons

Despite the severity of tropical cyclone ‘Winifred’, which crossed the Great Barrier Reef on 1 February 1986, there were little long-term effects on lagoon surface sediments from reefs in its path. Short-term effects were apparent only at one particularly exposed area. These were: an increase in proportion of the coarse fraction, the establishment of sand ripples, and the destruction of the mounds produced by callianassid shrimps (normally the dominant topographic feature). Within six weeks this area was indistinguishable from a typical reef lagoon. This is probably the result of sediment reworking by callianassid shrimp, involving selective burial of the coarse fragments and transport to the surface of finer particles. Sediment turnover rates by callianassids are commensurate with change to the sediment within the relatively short period observed. The sediment fauna responded quickly to the changes in sediment type. Immediately after the cyclone the disturbed area supported a fauna typical of the coarse sediments on the shallow reef flat, as the sediment reverted to a more normal type so the fauna changed back to that typical of a reef lagoon.     

Development of Aggregate Resources in Pacific Tropical Islands

Small tropical Pacific islands suffer from a common problem of acquiring and maintaining an adequate supply of sand and aggregate for infrastructure develop ment, coastal protection, and beach maintenance. This is most critical in countries where atolls predominate, such as the Federated States of Micronesia, and the Republic of Marshall Islands, but presents difficulties in even the largest and most highly developed island communities such as Hawaii and American Samoa. Recent studies by the Marine Minerals Technology Center and others have indicated a Pacific-wide sea-level stillstand about 40,000 years ago which resulted in the formation of coastal terraces with significant sand beaches at depths of about 70 m. It is proposed that such deposits, in water depths of 50-100 m and seaward of the reefs, will serve as resources for sustainable development. Exploration should result in the discovery, throughout the region, of sand deposits containing tens to hundreds of millions of cubic yards of clean sand close to shore. These large deposits should be amenable to dredging by advanced technology at low unit cost. Stockpiles located appropriately throughout the region, integrated with a bulk transportation service, could supply projected needs at a cost which would be affordable to each community.     

Variations in grain‐size and sorting on two kaikoura beaches

Two exposed, high‐energy beaches on the Kaikoura coast of New Zealand are composed of sand and gravel derived from a greywacke terrain. Both beaches can be classified as mixed beaches although the sediment varies from dominantly gravel at the ends of the beach to dominantly sand at the centre, through transition zones in which sand and gravel are mixed. Sixty‐four surface samples were analysed for grain size; two sediment parameters, mean grain size (M_z) and sorting (σ_I), were calculated.

A striking feature of the cumulative frequency curves is that both unimodai and bimodal distributions include median sizes over the whole range of sampled material, even though bimodal samples display two strong modes in the sand and gravel grades. The general deficiency lof sediment dn the very coarse sand and granule classes (0 to — 2 _F ) noted by numerous authors in many parts of the world is apparent in the poorly‐sorted bimodal samples. However, the best‐sorted samples also occur in these two classes.

Mean grain size of samples ranges from medium sand (1.820) to medium pebbles (—4.7 _F ), and sorting ranges from very well sorted (0.250) to very poorly sorted (2.69 _F ). Mean erain size on the northern beach is significantly greater than on the southern beach, but values of sorting are comparable. The greater mean size on one beach compared with the other is thought to be a function of the grade of material supplied by local rivers; the similarity in sorting presumably reflects the similarity of the processes acting on the two beaches.

Mixed sand‐shingle beaches are relatively rare on a world scale but common in New Zealand. Sediment distributions along the Kaikoura beaches do not reveal a regular decrease in size away from the rivers which supply material to shore at present. Instead, the beaches are differentiated into a number of sediment zones composed of either sand, or mixed sand‐gravel, or gravel. On each beach a gravel zone is located furthest from the river outlets. Sorting generally improves toward the Kaikoura Peninsula. Explanations for these trends are not given. Variations in size and sorting across the two beaches do not show a well developed zonation because of the high level of wave energy which continually mixes the material across the beach.     

Non-hydrostatic modelling of regular wave transformation and current circulation in an idealized reef-lagoon-channel system

The wave-induced setup and circulation in a two dimensional horizontal (2DH) reef-lagoon-channel system is investigated by a non-hydrostatic model. The simulated results agree well with observations from the laboratory experiments, revealing that the model is valid in simulating wave transformation and currents over reefs. The effects of incident wave height, period, and reef flat water depth on the mean sea level and wave-driven currents are examined. Results show that the distributions of mean sea level and current velocities on the reef flat adjacent to the channel vary significantly from those in the area close to the side walls. From the wave averaged current field, an obvious alongshore flux flowing from the reef flat to the channel is captured. The flux from the reef flat composes the second source of the offshore rip current, while the first source is from the lagoon. A detailed momentum balance analysis shows that the alongshore current is mainly induced by the pressure gradient between the reef flat and the channel. In the lagoon, the momentum balances are between the pressure and radiation stress gradient, which drives flow towards the channel. Along the channel, the offshore current is mainly driven by the pressure gradient.     

Application of the parabolic bay shape equation to sand and gravel beaches on Mediterranean coasts

The equation most commonly used to describe the bay planform was proposed by Hsu and Evans (1989) and it was obtained through empirical analysis of sand beach planforms.In the last decade interest in gravel sediments increased owing to their greater stability on beaches, compared with sand sediments. Due to the differences between the morphodynamics of sand and gravel beaches, which is strictly influenced by their different hydraulic characteristics, it was necessary to create a predictive instrument for this beach type as well.Therefore, in this study the standard Hsu and Evans equation (1989) was modified in order to make it applicable not only to sand beaches but also to gravel beaches. The shoreline was computed according to a parabolic model in polar coordinates whose coefficients are considered linearly dependent on the wave direction and related to the beach type. The estimation of the free parameters of the model was performed according to a statistical analysis of a shorelines data set of Mediterranean sand and gravel embayed beaches.     

热带风暴过程中珊瑚礁坪示踪砂运移的现场实验研究

１９９５年１０月在小东海珊瑚礁海岸的礁坪上进行了示踪砂运动的现场实验。本次实验对浪,流以及示踪砂采样作了同步观测。根据所获的实验数据,分析在９５１６号热带风暴天气过程礁坪上示踪砂运移的基本规律。在一级近似下,测定并计算了泥沙在波生流作用下的漂移速度与流速比因子０．００２,混合深度小于２ｃｍ。这一结果与其它已往结果相比明显小得多。     

基于类海啸波型的岛礁水动力特性数值模拟研究

基于非静压单相流模型NHWAVE建立了高精度二维数值波浪水槽,采用日本2011年实测真实海啸波型系统研究了海啸波在岛礁上传播变形的规律,并且分析了波高、礁坪淹没水深和礁前斜坡坡度等因素对孤立波和真实海啸传播变形的影响。结果表明,相比孤立波,类海啸波的波长明显大于孤立波波长,在测点处引起的水面变化持续时间更长,同等波高情况下真实海啸波型比孤立波能够携带更多的能量,与岛礁的相互作用也更为复杂,在礁坪上形成的淹没水深约为孤立波的两倍。礁前斜坡坡度和礁坪淹没水深均对类海啸波的反射和透射系数有显著影响。随着礁前斜坡坡度的增加,反射系数和透射系数均逐渐增加。随着礁坪淹没水深的增加,反射系数逐渐减小,而透射系数逐渐增大。但是,反射系数和透射系数均随着入射波高的增加而逐渐减小。