不同时间尺度下长江口海域表层悬浮体浓度变化

长江入海泥沙是中国东部陆架海沉积物的主要来源之一。本文基于MODIS-Aqua卫星的遥感资料并结合实测悬浮体浓度,建立了基于颗粒物后向散射系数的悬浮体浓度的反演方法,获取了2002—2017年长江口海域的表层悬浮体浓度分布,并分析其在潮周期、季节内以及年际等不同时间尺度下的变化特征。结果表明,在潮周期内,长江口122.3°E以西海域表层悬浮体浓度大潮高于小潮,落潮大于涨潮,高潮大于低潮;在季节尺度内.6—8月表层悬浮体浓度逐渐增加。而122.3°E以东海域,则出现相反的情况;长江口122.3°E以西海域的夏季平均表层悬浮体浓度年际变化明显,主要受长江入海水沙量年际变化的影响。长江口122.3°E以东海域表层悬浮体浓度的年际变化几乎不受长江入海泥沙的影响。风向对悬浮体浓度的扩散具有显著的作用,南风有利于高浓度悬浮体向外海扩散,东风则抑制扩展。     

Gradual downslope change in high-resolution acoustic characters and geometry of large-scale submarine debris lobes in Ulleung Basin, East Sea (Sea of Japan), Korea

A detailed analysis of high-resolution seismic data (Chirp, 2–7 kHz) in the Ulleung Basin reveals spatial variation in echo characteristics and geometry of large-scale debris lobes. In the proximal part, the debris lobes are dominated by hummocky surface echoes and gradually transitional downslope to seafloor-tangent hyperbolic and smooth prolonged bottom echoes, reflecting progressive decrease in size, spacing, and relief of surface forms. The strongly convex-upward upper surface with steep blunt margins in the proximal part is gradually transitional downslope to slightly convex- upward or nearly flat form with less blunt margins. The gradual downslope decrease in both scale and spacing of surface forms and convexity of upper surface within each debris lobe is suggestive of progressive dilution in flow concentration within a debris flow, probably due to mixing of ambient water and removal of suspended sediment by deposition during downslope movement. Received: 3 February 1999 / Revision received: 27 April 1999     

黄河口悬浮泥沙时空动态及其驱动机制

受径流输沙、风浪、潮汐等影响,河口近岸海域悬浮泥沙具有显著的时空变化。本文基于小时分辨率的GOCI遥感影像,利用最优遥感反演算法,结合空间分析和统计方法,深入研究黄河口及邻近海域悬沙时空动态特征及驱动机制。结果表明,径流输沙对悬沙浓度的影响以河口近岸区为主,高径流输沙对悬沙浓度分布影响可达距岸约20 km,并向孤东近岸方向扩散。大风可引起清水沟老河口区泥沙强烈再悬浮,形成高浓度悬沙区。涨落潮对小时尺度的悬沙浓度影响显著,并影响悬沙的南北扩散。大潮悬沙浓度变化和扩散范围均大于小潮,潮流流速不同是造成该差异的主要原因。水深与悬沙浓度之间存在较明显的负相关关系,根据不同驱动因素的差异,悬沙浓度随着水深的增加呈现出指数型、幂函数型、线性3种关系。     

Coupled penetrometer, MBES and ADCP assessments of tidal variations in surface sediment layer characteristics along active subaqueous dunes, Danish Wadden Sea

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ∼1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1–3 kPa in the top layer, 20–140 kPa in the underlying sediment; thickness of the top layer ca. 5–8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 ± 2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.     

闽江口入海悬沙输运的数值模拟

闽江河口位于福建省东部，本文利用欧拉-拉格朗日差分方法模拟闽江口及附近海域在不同径流下的潮流场，并建立拉格朗日水质点跟踪方法近似模拟了悬沙在海域中的迁移过程．水质点运动轨迹计算结果表明，闽江口悬沙在外海主要向南方或东南方输运，其轨迹呈现螺旋线．在洪峰流量下，悬沙运移距离较远．     

基于神经网络和TM图像的大连湾海域悬浮物质量浓度的反演

水体中的悬浮物是评价海洋水质的重要指标之一。采用卫星遥感方法可以获得大范围连续的悬浮物质量浓度。以1999年5月10日大连湾海上现场-卫星同步实验数据为基础,采用神经网络模型技术模拟了陆地卫星TM传感器中心波长分别为485,560和660nm3个波段的辐射亮度值与在该海域现场获取的悬浮物质量浓度之间的传递机理。以TM图像的3个可见光波段作为输入的神经网络模型的相关系数达0．79,在反演海水表层悬浮物质量浓度方面比传统的统计分析方法表现要好。这说明神经网络方法在模拟非线性关系进行遥感反演方面更具应用前景。     

Sediment discharge of the Yellow River,China: past,present and future——A synthesis

The Yellow River cut through Sanmenxia Gorge and discharged into the sea via the North China Plain in 150 ka BP; since then, around 86 000 × 108 t sediment has been transported passing Sanmenxia Gorge. Based on land use and land cover changes in Loess Plateau and other available evidence, an estimate of the Yellow River sediment budget is presented here: about 72% of the sedimentary material was trapped in the North China Plain and the remainder(i.e., 26%) escaped to the sea. At the present stage, 0.2×108 t/a suspended sediment of the Yellow River enter the northern Yellow Sea. The transport pattern is determined mainly by the shelf current system. Annually 0.2×108–0.3×108 t of suspended particles are carried to the East China Sea; the materials are derived mainly from coastal and subaqueous delta erosion associated with the abandoned Yellow River on the Jiangsu coast. Since 1972, the lower Yellow River started to have a situation of continuous no-flow. During 1996–2000, the annual water flow and sediment discharge are only 19%, as compared with normal years(i.e., average for 1950–1979). In response to global warming and increase of water diversion from the Yellow River for industrial and urban use, the sediment flux of the Yellow River to the sea will most likely remain small in the next two to three decades.     

Water quality and sediment and nutrient export from New Zealand hill‐land catchments of contrasting land use

Measurements were made of suspended sediment (SS), volatile suspended solids, dissolved organic carbon (DOC), nitrogen (N) and phosphorus (P) concentrations, turbidity, black disk visibility, pH, alkalinity, and temperature, at monthly intervals for 2–5 years on nine streams draining catchments with pasture, pine plantation, and native forest land uses. Stream flow and flow‐weighted concentrations of SS, N, and P were also measured for up to 2 years from pasture, native forest, and mixed land‐use catchments enabling calculation of export (kg ha^‐1 yr^‐1). During 1996–97, export from the pasture stream was 2.5‐ to 7‐fold higher for SS (988), total P (1.50), total Kjeldahl N (5.65), nitrate N (4.37), and ammoniacal N (0.34) than from the stream draining native forest. In contrast, export of DOC (25.5) and dissolved reactive P (DRP) (0.25) from the pasture stream were within 20% of the native stream's values. Export of SS and nutrients (except DRP) from the pasture catchment was 4‐ to 15‐fold higher during the winters of 1995 and 1996 than winter 1997 when rainfall was half the normal level. Streams draining native forest had lower temperature, sediment, and nutrient concentrations (except DRP), and higher water clarity, than those draining pine forest and pasture. A pine/scrub stream had the highest SS and turbidity and lowest DRP, pH, and alkalinity. Pasture streams had the highest concentrations of all N species (geometric means 2‐to 4‐fold > native), total P, and DOC, and also showed the greatest variation in water quality attributes in relation to season and flow. The influences of land use were attributable to differences in both source materials of sediment and nutrients available for transport and changes in rates of in‐stream processing.     

Bulk density calibration for X-ray tomographic analyses of marine sediments

A calibration procedure is presented for generating bulk density profiles of intact marine sediment cores using X-ray computed tomography (CT). Developed using both artificial and natural marine sediment samples, the correlation is strong with an R ² value of 0.98. Similar experiments with carbonate sediments were also strongly linear, but offset from the terrigenous curve, illustrating the influence of sediment chemistry on scanner response. Comparison between newly computed densities for both sediment types with those from individually calibrated cores during our previous CT studies reveals good correspondence between the data sets. Received: 22 November 1998 / Revision received: 4 March 1999     

Preferential settling of smectite on the Amazon continental shelf

Seventy-five surface and subsurface sediment samples collected on the Amazon continental shelf were analyzed by X-ray diffraction (XRD) in the grain-size fractions smaller than 2 μm. The groups of clay minerals thus identified were smectite, kaolinite, illite, and mixed-layer illite/smectite. Calculation of relative abundance shows a predominance of smectite (37%) in the whole area, followed by kaolinite (27%), illite (23%), and a small percentage of mixed-layer illite/smectite (12%). The distal, northwest region of the continental shelf is characterized by a high abundance of smectite (41%), high salinity values, and high sediment accumulation rates (10 cm year⁻¹), whereas the proximal region is characterized by a comparatively low abundance of smectite (30%), low salinity values, and low sediment accumulation rates (<1 cm year⁻¹). This trend of increasing abundance northwestwards documents a preferential settling of smectite in the distal and more saline regions of this estuarine system. Received: 17 September 1999 / Revision accepted: 17 January 2000     

Geoacoustic and physical properties of carbonate sediments of the Lower Florida Keys

 Near-surface sediment geoacoustic and physical properties were measured from a variety of unconsolidated carbonate sediments in the Lower Florida Keys. Surficial values of compressional and shear speed correlate with sediment physical properties and near-surface acoustic reflectivity. Highest speeds (shear 125–150 m s^-1; compressional 1670–1725 m s^-1) are from sandy sediments near Rebecca Shoal and lowest speeds (shear 40–65 m s^-1; compressional 1520–1570 m s^-1) are found in soft, silty sediments which collect in sediment ponds in the Southeast Channel of the Dry Tortugas. High compressional wave attenuation is attributed to scattering of acoustic waves from heterogeneity caused by accumulation of abundant shell material and other impedance discontinuities rather than high intrinsic attenuation. Compared to siliciclastic sediments, carbonate sediment shear wave speed is high for comparable values of sediment physical properties. Sediment fabric, rather than changes due to the effects of biogeochemical processes, is responsible for these differences.     

杭州湾三维悬浮泥沙输运模型初始场的伴随法反演研究

在悬沙输运的数值模拟中,初始场的准确给定至关重要。目前诸多确定初始场的方案均存在一定的缺陷,初始场的准确性有待进一步提高。本文基于一个三维悬沙输运伴随同化模型,通过孪生实验和实际实验,对模型初始场进行了伴随法反演研究。在孪生实验中,首先验证了初始场的相对重要性;其次,探讨了初始场的反演结果对优化算法、初始猜测值、卫星遥感数据数量、同化时间窗口宽度和背景流场误差的敏感性;最后,比较了伴随法和插值法重构初始场的能力。孪生实验结果表明:最速下降法对初始场的优化反演效果要优于三种共轭梯度法和有限记忆BFGS法;初始场的反演效果对初始猜测值、卫星遥感数据数量和背景流场误差不敏感,而对同化窗口宽度较为敏感;与插值法相比,伴随法是重构模型初始场更有效的手段。实际实验中,在杭州湾海域同化典型的小潮时期和大潮时期的GOCI卫星遥感资料所得表层悬沙浓度数据,优化反演了初始场。实际实验结果表明:数据同化后,得到了更符合实际的最优初始场,表明伴随法是实现初始场优化反演的有效手段。该研究对进一步改进悬沙输运模型的初始化方案具有一定的参考价值,也对其他数值模型的初始化方案具有一定的借鉴价值。     

基于遥感反演的莱州湾水色变化的多时相分析

悬浮泥沙和叶绿素是海洋水色的重要部分,是反映河口海岸地区生态环境状况的重要指标。本文基于Landsat TM/ETM+/OLI遥感影像,在不依赖地面实测数据的条件下,结合水文气象数据,利用光谱信息建立水色遥感模型对莱州湾1996—2015年不同时期的悬浮泥沙和叶绿素变化进行研究。研究结果表明:(1)此模型可以快速反演出较大空间尺度内的水色时空分布情况。(2)1996—2015年这一时期内悬浮泥沙浓度变化明显,枯水期的悬浮泥沙扩散范围总体大于丰水期,悬浮泥沙高浓度区主要分布在黄河口附近海域和沿岸区域,泥沙主要来源于陆源输沙和海水中的泥沙再悬浮,悬浮泥沙的扩散主要受潮流的影响,风和波浪等动力因素也在一定程度上影响着悬浮泥沙的扩散;(3)此外,莱州湾叶绿素高浓度区主要分布在莱州湾东—南部海域,其分布具有明显的季节性,春季(5月)海水温度升高,水中营养物质垂直混合好使得叶绿素浓度处于较高态势。     

秋季东海内陆架悬浮体分布特征

秋季是处于夏、冬季之交的过渡季节,夏季风减弱、冬季风增强的背景下海洋水文泥沙环境有独特特征,关于该时期悬浮体分布特征的研究较少.本文基于东海内陆架2016、2017与2018年秋季悬浮体及温盐数据,分析该海域秋季悬浮体浓度的水平和垂向分布特征.结果表明:悬浮体浓度近岸高于远岸,浓度等值线大致平行于等深线,近底层悬浮体浓...     

Significant wave height forecasting using wavelet fuzzy logic approach

Wave heights and periods are the significant inputs for coastal and ocean engineering applications. These applications may require to obtain information about the sea conditions in advance. This study aims to propose a forecasting scheme that enables to make forecasts up to 48 h lead time. The combination of wavelet and fuzzy logic approaches was employed as a forecasting methodology. Wavelet technique was used to separate time series into its spectral bands. Subsequently, these spectral bands were estimated individually by fuzzy logic approach. This combination of techniques is called wavelet fuzzy logic (WFL) approach. In addition to WFL method, fuzzy logic (FL), artificial neural networks (ANN), and autoregressive moving average (ARMA) methods were employed to the same data set for comparison purposes. It is seen that WFL outperforms those methods in all cases. The superiority of the WFL in model performances becomes very clear especially in higher lead times such as 48 h. Significant wave height and average wave period series obtained from buoys located off west coast of US were used to train and test the proposed models.     

Discussion on ‘The effect of fresh water flow on siltation in the Humber estuary, Northeast UK’ by Pontee NI, Whitehead PA and Hayes CM (ECSS vol. 60, 241–249)

This discussion identifies and presents recent data which show that suspended sediment concentrations in the macrotidal Humber–Trent–Ouse system are much higher, and extend further upstream, than originally presented. The importance of a link between tidal range, fresh water flow and recorded suspended sediment concentrations, is illustrated by reference to data collected under the UK Natural Environment Research Council (NERC) Land–Ocean Interaction Study (LOIS) initiative (1992–1998). Data recorded at Burringham, on the River Trent upstream of Trent Falls show a clear link between tidal range and suspended sediment concentrations which is strongly influenced by the downstream flushing effects of high fresh water flow events. While the arguments presented in this discussion do not contradict the main findings in the original paper it is proposed that a better understanding of siltation in the Humber system may be promoted by understanding the behaviour of the turbidity maximum in this system and its related mobile sediment population. It is suggested that the rapid reduction in suspended sediment concentration brought about by sudden increases in fresh water flow is probably indicative of the highly canalised nature of the tidal reaches of the Trent and Ouse.     

Acoustic imaging of cohesive sediment resuspension and re-entrainment in the Changjiang Estuary, East China Sea

 Vertical profiles of instantaneous cohesive suspension concentration, obtained from an acoustic suspended sediment monitor in the Changjiang Estuary, indicate that near-bed high-concentration suspensions consist of upper and lower high-concentration suspensions, separated by a natural breakpoint at ca. 2 g l^-1. Acoustic images revealed near-bed high-frequency resuspension events of a few seconds, which contribute mainly to the formation of the lower near-bed high-concentration suspension. Upper and lower lutoclines are also indicative of re-entrainment of lower and upper high concentration suspension, respectively. Near-bed high-frequency resuspension is caused by turbulence, while re-entrainment is probably attributable to internal wave activity. Received: 26 April 1996 / Revision received: 23 July 1996     

Sediment accumulation rates along the inner eastern Brazilian continental shelf

Box cores were collected close to river mouths along the eastern Brazilian shelf at water depths of 10–30 m. One core was taken from more than 1000 m depth at the shelf slope. ²¹⁰Pb and ²²⁶Ra activities were measured to establish sediment accumulation rates. Seven of the 10 cores exhibited an exponential decrease with depth of excess ²¹⁰Pb activities. The sediments from the sheltered Sudeste Channel off Caravelas revealed the highest sediment accumulation rate of 0.81 cm yr⁻¹. The sediments at the shelf slope seaward of the Rio Doce revealed the lowest accumulation rate of 0.13 cm yr⁻¹. Sediment accumulation rates increased towards the Caravelas Bank. Current patterns and the morphology of the seabed favor sediment deposition in this area.     

Seasonal variability of cohesive sediment aggregation in the Bach Dang–Cam Estuary, Haiphong (Vietnam)

In the Bach Dang–Cam Estuary, northern Vietnam, mechanisms governing cohesive sediment aggregation were investigated in situ in 2008–2009. As part of the Red River delta, this estuary exhibits a marked contrast in hydrological conditions between the monsoon and dry seasons. The impact on flocculation processes was assessed by means of surveys of water discharge, suspended particulate matter concentration and floc size distributions (FSDs) conducted during a tidal cycle at three selected sites along the estuary. A method was developed for calculating the relative volume concentration for the modes of various size classes from FSDs provided by the LISST 100X (Sequoia Scientific Inc.). It was found that all FSDs comprised four modes identified as particles/flocculi, fine and coarse microflocs, and macroflocs. Under the influence of the instantaneous turbulent kinetic energy, their proportions varied but without significant modification of their median diameters. In particular, when the turbulence level corresponded to a Kolmogorov microscale of less than ∼235 μm, a major breakup of flocs resulted in the formation of particles/flocculi and fine microflocs. Fluctuations in turbulence level were governed by seasonal variations in freshwater discharge and by the tidal cycle. During the wet season, strong freshwater input induced a high turbulent energy level that tended to generate sediment transfer from the coarser size classes (macroflocs, coarse microflocs) to finer ones (particles/flocculi and fine microflocs), and to promote a transport of sediment seawards. During the dry season, the influence of tides predominated. The turbulent energy level was then only episodically sufficiently high to generate transfer of sediment between floc size classes. At low turbulent energy, modifications in the proportions of floc size classes were due to differential settling. Tidal pumping produced a net upstream transport of sediment. Associated with the settling of sediment trapped in a near-bed layer at low turbulent energy, this causes the silting up of the waterways leading to the harbour of Haiphong.     

Relationship between eddy viscosity of seawater and eddy diffusivity of suspended particles

A method is described to calculate the relationship (β) between the eddy diffusivity of suspended particles and the eddy viscosity of the fluid. The data were obtained while making suspended sediment concentration measurements near the seabed on the British continental shelf. β was calculated for 0.50 size fractions and varies inversely with the suspended sediment concentration. The values were used successfully to calculate suspended sediment transport rates for separate sand fractions through a spring tidal cycle. Finally, specific values of β are suggested for varying concentrations of sand at a reference height of 100 cm above the seabed.