秦皇岛市海岸风成沙丘的研究

秦皇岛市北戴河向南直至滦河河口发育着我国最长的沙丘海岸，沙丘高约20～30m，最高42m。在沙丘发育最充分的地区自岸向陆，沙丘按形态可分成岸前沙丘，沿岸主沙丘链，斜向沙丘链和平坦沙席等4种类型。沙丘由分选极好的中细砂组成，具有微弱的负偏态和双跃移特征。沙丘内部发育有高角度板状交错层理、低角度楔状交错层理等层理构造。滦河新三角洲和沿岸海滩的丰富沙源、向岸和离岸两盛行风的频繁交替以及适宜的空旷地形空间是塑造沙丘的主要条件。加强管理，保护沙丘的自然面貌是当务之急。     

西地中海陆架砂质底形

西地中海加的斯湾、埃布罗湾、巴塞罗那岸外和利翁湾等外陆架和陆坡上部分布大片的砂质水下沙丘、沙带、沙脊以及沙席等砂质底形。沙丘长为150～760m,最长为3km;高一般为0.1～5.0m,最高为20m。背流坡指向SW,丘长与丘高相关斜率为H=0.934L0.006 3,低于1978年世界标准的F氏斜率线;沙脊长为4～24km,宽为1～2.3km,高出海底10～30m。砂层厚约12～30m,其成因与冰消期古岸线相关。以水深350m的直布罗陀海峡为中心,大西洋低盐水团和地中海高盐水团相交换而形成的地中海环流是导致海底砂质底形发育的主要动力,陆架外侧普遍分布的垂岸沟谷及顺谷流也起一定作用。据14C年代测定,大型沙丘沙脊形成于距今13～11ka的冰消期,当时海面波动式趋稳。现代洋流只能在暴风浪期间、底流速较大时才能带动泥沙运动且进行局部修饰、破坏和蚀低原砂质底形。     

东山岛以东近岸海域水下沙丘及其环境

1990～1991年，我所对东山岛海域进行海底地形、底质调查、水文泥沙测验时发现：1）沿东山岛一古雷半岛的NNE、NE向断裂在海域呈现为落差可达20m左右“V”字型深糟；2）在东山岛东部10m等深线以东海域发育众多的水沙丘群，水深15m左右有一地形坡折线，水深20～25m海底为水下一级阶地。据底质粒度、石英电镜扫描、重矿物、地球化学指标等分析表明，水下沙丘群分布区的沉积为准残留沉积，水下一级阶地及水下沙丘为早期滨岸的准残留地貌作，又受到后期现代水动力的改造。     

河北昌黎典型海岸沙丘的沉积构造及其发育模式

采用探地雷达探测了昌黎海岸沙丘区典型横向沙脊和新月形沙丘的沉积构造,据此初步揭示了研究区海岸沙丘的沉积序列特征和发育过程。结果表明,昌黎海岸带在2 000 a BP波浪作用下发育滨岸沙坝,沙坝主要以向海向陆缓倾斜的沉积构造为主,现今的风成沉积发育于滨海相沙坝之上。海岸带向海一侧经历了潮上带前丘到横向沙脊的过程,横向沙脊在东北风的作用下主要发育向陆倾斜的高角度交错层理,同时由于向岸合成风力的阶段性变化,这些层理的倾角略有差异,记录了海岸带风沙活动的周期性变化;内侧新月形沙丘由4组倾角不同的层理组成,被较大规模的二级界面分隔,复合新月形沙丘(链)经历了由盾状沙堆到典型新月形沙丘的加积发育并遭受风蚀的过程。     

基于GPR图像的福建长乐海岸沙丘沉积构造与海岸环境演变

为了探讨福建长乐东部海岸环境演变,运用探地雷达(GPR)探测了研究区海岸沙丘的沉积构造,初步得出以下结论:(1)研究区海岸沙丘沉积构造主要由海滩沉积和海岸沙丘沉积构成,其中下伏沉积为海滩波浪作用形成的波状交错层理,上覆沉积为风成大角度倾斜的交错层理以及局部的水平层理;(2)上部发育的倾向向背的大角度风成交错层理,反映了研究区丰富的沙源、宽阔的海滩、植被扩张的进积海岸特点;(3)从沉积序列分析,研究区海岸地貌环境演变经历了早期的滨岸浅海到晚期的海岸沙丘带两个阶段,反映了海岸向东的进积过程中,外力作用由波浪作用为主演变为风沙沉积作用为主。     

南海湄公河水下三角洲上大沙丘的分布特征

根据2003和2004年冬季风之后的2次侧扫声呐调查结果,解释了湄公河水下三角洲上5个区85个水下大沙丘。沙丘尺度,高1.4～13.2m,长72～672m的属于Ash-ley(1990)分类的大和特大水下沙丘。沙丘普遍具有不对称的外形,陡坡指向W—SW。南海冬季季风引起的冬季环流汇同黑潮(分支)逆流是塑造沙丘的主要动力,据实测,金兰湾外冬季环流表层流速达1～1.4m/s。水下沙丘形成于冰消期低海面时期,如今仍然顺南海冬季环流西侧自N向W—SW迁移,沙丘迁移速率约为2.78×10-5 m/s量级(按流速1.1m/s计算)。     

国外海岸沙丘形成与演化的研究

自20世纪80年代以来，国外对海岸沙丘的研究已从主要对其地貌形态的研究转向海岸海丘与海岸变迁尤其是全球变化关系的研究上，海岸沙丘形成与演化的研究倍受关注，进行了大量研究并取得了一定的研究成果。这里介绍了国外在海岸沙丘形成与演化研究方面的主要进展及其成果，并以此探讨了国内今后开展海岸沙丘形成与演化研究的主要方向与问题。     

河北七里海外海岸沙丘群成因新探

七里海有中国第一大潟湖之称,多数学者认为七里海外的海岸沙丘群是在滨外沙坝的基础上发育形成的。研究认为,七里海外的海岸沙丘群是在末次冰期时期风成沙丘群的基础上演化形成的继承性沙丘综合体。七里海也不是科学意义上的潟湖,它没有形成海岸沙坝这一潟湖形成的过程,其前身是晚更新世末期由风暴活动形成的风蚀洼地。应加强七里海外海岸沙丘群的形成、发育类型及演化过程的研究,从多角度探究七里海外海岸沙丘群的演化机理和发育趋势。     

甘肃青土湖地区不同类型沙丘的表沙理化特征及其环境意义

沙丘表层沉积物的理化特征在揭示风沙的来源、沉积过程、风化作用等方面具有重要作用。本研究采用野外实地采样和实验室分析方法分析了甘肃青土湖地区不同类型沙丘表层沉积物的粒度和地球化学特征。结果表明：(1)青土湖地区沙丘表层沉积物以细砂为优势粒级,平均含量达72.08%,其次为极细砂,黏粒成分很少。频率分布曲线为单峰分布,概率累积曲线表现为三段式,反映出沉积环境较为稳定。(2)研究区沙丘表层沉积物常量元素以SiO₂为主,平均含量为76.40%,其次为Al₂O₃和CaO,平均含量分别为5.05%、3.74%。微量元素以Cr、Mn、Co、Sr、Ba、Ti、Ce和P为主,平均含量均>100 mg/L。(3)Y、Zr和Y/Zr、Rb/Zr双变量图、A-CNK-FM图解表明巴丹吉林沙漠和腾格里沙漠为其沙源。风沙搬运过程中的磨蚀、风选作用是研究区富集Fe、Mg元素的主要原因。此外,下伏湖相沉积物就地起砂,石羊河冲积物也为其提供了部分沙物质。(4)A-CN-K和A-CNK-FM三角模式图表明研究区风化程度较弱,处于初期脱Na、Ca阶段。...     

福建长乐东部海岸沙丘风蚀坑研究

沙丘风蚀坑是沙质海岸常见的风成地貌形态,是固定沙丘开始活化的明显标志.福建长乐东海岸风沙规模大、地貌类型多样,发育了许多典型的海岸沙丘地貌.由于各种自然和人为因素的作用,部分海岸沙丘发育了风蚀坑.根据对研究区风蚀坑的实地调查,本文论述了风蚀坑的形态特征、风蚀坑内的风速与风向变化,以及风蚀坑的风沙搬运与沉积过程,并对风蚀坑的成因和风蚀坑的演化阶段进行了讨论.文中得出以下几点结论:(1)研究区主要发育槽形风蚀坑,风蚀坑中轴线的方位多介于NE40°～NE65°之间,两侧侵蚀壁坡度介于35°～40°之间.(2)大型风蚀坑,风速在顶部最大.小型风蚀坑,较狭窄部位的风速可能大于项部.(3)大型风蚀坑,沿着中轴线上风向基本上保持不变,近侵蚀壁的风向则发生不同程度的改变.小型风蚀坑,从坑口到坑顶的风向变化明显.     

Microbial Biomass and Organic Nutrients in the Deep-Sea Sediments of the Central Indian Ocean Basin

In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance.     

Assessing the Validity of Seismo-Acoustic Predictor Equations for Obtaining Seabed and Sub-Surface Sediment Physical Properties

The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths.     

A Review of Some Environmental Issues Affecting Marine Mining

This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested.     

Increased Particle Fluxes at the INDEX Site Attributable to Simulated Benthic Disturbance

Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement.     

Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification

An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm.     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

Determination of In Situ Sediment Shear Strength from Advanced Piston Corer Pullout Forces

The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments.     

Interannual Sea Level Variations and Annual Tides in the Northwestern Pacific

Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone.     

Flow Cytometric Analysis of Coastal Lagoon Bacterioplankton and Picophytoplankton: Fixation and Storage Effects

The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics.