The morphodynamic modelling of tidal sand waves on the shoreface     

P.K. Tonnon  L.C. van Rijn  D.J.R. Walstra 《Coastal Engineering》2007

An artificial sand wave on the Dutch shoreface of the North Sea has been studied in conditions with relatively strong tidal currents in the range of 0.5 to 1 m/s and sediments in the medium sand size range of 0.2 to 0.5 mm. The sand wave is perpendicular to the tidal current and has a maximum height and length of the order of 5 m and 1 km, respectively. The sand wave is dynamically active and shows migration rates of the order of a few metres per year. A numerical morphodynamic model (DELFT3D model) has been used to simulate the morphological behaviour of the sand wave in the North Sea. This model approach is based on the numerical solution of the three-dimensional shallow water equations in combination with a surface wave propagation model (wind waves) and the advection–diffusion equation for the sediment particles with online bed updating after each time step. The model results show that the sand wave grows in the case of dominant bed-load transport (weak tidal currents; relatively coarse sediment; small roughness height; low waves) and that the sand wave decays in the case of dominant suspended transport (strong currents, relatively fine sediment, large roughness height; storm waves).  相似文献   

“大洋一号”勘查技术体系的设计与建设   总被引：1，自引：0，他引：1  

周宁 《海洋学研究》2005,23(4):61-65

介绍了"大洋一号"远洋科学考察船在近1年的改装施工后所建立的现代化船舶勘查技术体系.由于引进了世界先进的调查设备,自主研发和改造了深海浅地层岩芯钻等大型调查设备,自主设计并完成了网络信息集成系统,同时对实验室、住舱等工作、生活环境进行了改造,"大洋一号"远洋科学考察船已集成了具有高精度水下定位、全覆盖地形地貌、可视化海底取样、地球物理(重、磁、震、浅地层)、深拖(声学、光学)、成矿环境(水文、化学)和生物等专业设备的联合探测分析系统,实现了各系统的科学同步作业和信息融合,大大提高了我国海洋科学考察工作的效率和管理水平,使我国的深海探测技术和方法基本实现了与国际接轨.  相似文献   

Roles of Continental Shelves and Marginal Seas in the Biogeochemical Cycles of the North Pacific Ocean   总被引：4，自引：0，他引：4  

Chen-Tung Arthur Chen  Andrey Andreev  Kyung-Ryul Kim  Michiyo Yamamoto 《Journal of Oceanography》2004,60(1):17-44

Most marginal seas in the North Pacific are fed by nutrients supported mainly by upwelling and many are undersaturated with respect to atmospheric CO₂ in the surface water mainly as a result of the biological pump and winter cooling. These seas absorb CO₂ at an average rate of 1.1 ± 0.3 mol C m⁻²yr⁻¹ but release N₂/N₂O at an average rate of 0.07 ± 0.03 mol N m⁻²yr⁻¹. Most of primary production, however, is regenerated on the shelves, and only less than 15% is transported to the open oceans as dissolved and particulate organic carbon (POC) with a small amount of POC deposited in the sediments. It is estimated that seawater in the marginal seas in the North Pacific alone may have taken up 1.6 ± 0.3 Gt (10¹⁵ g) of excess carbon, including 0.21 ± 0.05 Gt for the Bering Sea, 0.18 ± 0.08 Gt for the Okhotsk Sea; 0.31 ± 0.05 Gt for the Japan/East Sea; 0.07 ± 0.02 Gt for the East China and Yellow Seas; 0.80 ± 0.15 Gt for the South China Sea; and 0.015 ± 0.005 Gt for the Gulf of California. More importantly, high latitude marginal seas such as the Bering and Okhotsk Seas may act as conveyer belts in exporting 0.1 ± 0.08 Gt C anthropogenic, excess CO₂ into the North Pacific Intermediate Water per year. The upward migration of calcite and aragonite saturation horizons due to the penetration of excess CO₂ may also make the shelf deposits on the Bering and Okhotsk Seas more susceptible to dissolution, which would then neutralize excess CO₂ in the near future. Further, because most nutrients come from upwelling, increased water consumption on land and damming of major rivers may reduce freshwater output and the buoyancy effect on the shelves. As a result, upwelling, nutrient input and biological productivity may all be reduced in the future. As a final note, the Japan/East Sea has started to show responses to global warming. Warmer surface layer has reduced upwelling of nutrient-rich subsurface water, resulting in a decline of spring phytoplankton biomass. Less bottom water formation because of less winter cooling may lead to the disappearance of the bottom water as early as 2040. Or else, an anoxic condition may form as early as 2200 AD. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

基于荧光原理的叶绿素a传感器校准方法研究     

《海洋技术学报》2024,(1)

利用传感器对水体叶绿素a 浓度进行原位测量是获取实时、连续、长时间序列数据的重要手段。本文在对RBR 传感器和ECO（Environmental Characterization Optics）传感器进行原理分析和线性度、稳定性、重复性等基本性能测试的基础上，利用单一藻种培养液和2020年南海北部海域现场数据校准传感器，并对新的传感器校准系数进行验证。结果表明：两台传感器使用新系数比原出厂系数的叶绿素a 浓度测量准确度有明显提高。RBR 传感器现场数据校准系数的计算结果与叶绿素a 标准值误差最小，平均绝对误差从1.93 μg/L 减小到0.35 μg/L，平均相对误差从55.1%减小到10.9%；ECO 传感器藻液系数明显优于出厂系数和现场数据校准系数的计算结果，平均绝对误差从1.76 μg/L 减小到0.59 μg/L，平均相对误差从50.3%减小到15.1%。传感器测量准确度的提高，可为海洋环境监测、海洋生态灾害预警等工作获取真实可靠数据提供支撑。  相似文献   

Sediment-starved sand ridges on a mixed carbonate/siliciclastic inner shelf off west-central Florida     

S. E. Harrison  S. D. Locker  A. C. Hine  J. H. Edwards  D. F. Naar  D. C. Twichell  D. J. Mallinson 《Marine Geology》2003,200(1-4):171-194

High-resolution side-scan mosaics, sediment analyses, and physical process data have revealed that the mixed carbonate/siliciclastic, inner shelf of west-central Florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms. The sand ridges, mostly oriented obliquely to the shoreline trend, extend from 2 km to over 25 km offshore. They show many similarities to their well-known counterparts situated along the US Atlantic margin in that both increase in relief with increasing water depth, both are oriented obliquely to the coast, and both respond to modern shelf dynamics. There are significant differences in that the sand ridges on the west-central Florida shelf are smaller in all dimensions, have a relatively high carbonate content, and are separated by exposed rock surfaces. They are also shoreface-detached and are sediment-starved, thus stunting their development. Morphological details are highly distinctive and apparent in side-scan imagery due to the high acoustic contrast. The seafloor is active and not a relict system as indicated by: (1) relatively young AMS ¹⁴C dates (<1600 yr BP) from forams in the shallow subsurface (1.6 meters below seafloor), (2) apparent shifts in sharply distinctive grayscale boundaries seen in time-series side-scan mosaics, (3) maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation, (4) sediment textural asymmetry indicative of selective transport across bedform topography, (5) morphological asymmetry of sand ridges and 2D dunes, and (6) current-meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded. Although larger sand ridges are found along other portions of the west-central Florida inner shelf, these smaller sand ridges are best developed seaward of a major coastal headland, suggesting some genetic relationship. The headland may focus and accelerate the N–S reversing currents. An elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf, allowing them to be more easily influenced by currents and surface gravity waves. Tidal currents, storm-generated flows, and seasonally developed flows are shore-parallel and oriented obliquely to the NW–SE trending ridges, indicating that they have developed as described by the Huthnance model. Although inner shelf sand ridges have been extensively examined elsewhere, this study is the first to describe them in a low-energy, sediment-starved, dominantly mixed siliciclastic/carbonate sedimentary environment situated on a former limestone platform.  相似文献   

排铅奶粉对在岗交警体内粪铅排除作用     

于广利  管华诗  李桂玲  李辉  陈娥功  周斌  梁强 《中国海洋大学学报(自然科学版)》1997,(2)

研究了青岛市南、市北、四方三区交警在服用排铅奶粉（ＬｅａｄＥｘｃｒｅｔｉｎｇＭｉｌｋＰｏｗ－ｄｅｒ，ＬＥＭＰ）前后，体内粪铅含量变化情况。实验结果表明，服用ＬＥＭＰ后，粪铅含量先呈上升趋势，达到最高值后，又呈下降趋势。在整个实验过程中，粪铅含量四方区最高，而市南区最低。服用ＬＥＭＰ前，三区交警粪铅平均含量为０．６８７ｍｇ／ｋｇ，服用７ｄ后达到峰值（１．９６ｍｇ／ｋｇ，Ｐ＜０．０１），第１５ｄ降到１．６１（ｍｇ／ｋｇ）（Ｐ＜０．０５），表明ＬＥＭＰ能排除体内铅起到预防铅中毒的作用  相似文献   

Jason-1: Assessment of the System Performances     

J. Perbos  P. Escudier  F. Parisot  G. Zaouche  P. Vincent  Y. Menard  F. Manon  G. Kunstmann  D. Royer  L. -L. Fu 《Marine Geodesy》2003,26(3):147-157

On 7 December 2001, Jason-1 was successfully launched by a Boeing Delta II rocket from the Vandenberg Air Force Base, California. The Jason-1 satellite will maintain the high accuracy altimeter service provided since 1992 by TOPEX/Poseidon (T/P), ensuring the continuity in observing and monitoring the Ocean Dynamics (intraseasonal to interannual changes, mean sea level, tides, etc.). Despite one-fourth the mass and power, the Jason-1 system has been designed to have basically the same performance as T/P, measuring sea surface topography at a centimetric level. This new CNES/NASA mission also provides near real-time data for sea state and ocean forecast. The first two months of the Jason-1 mission have been dedicated to the assessment of the overall system. The goals of this assessment phase were:

1. To assess the behavior of the spacecraft at the platform and payload levels (Jason-1 being the first program to call on the PROTEUS versatile multimission platform for Low and Medium Earth Orbit Missions developed in partnership between Alcatel Space and CNES);

2. To verify that platform performance requirements are met with respect to Jason-1 requirements;

3. To verify that payload instruments performance requirements evaluated at instrument level are met;

4. To assess the performance of the Jason-1 Ground System.

This article will display the main outputs of the assessment of the system. It will demonstrate that all the elements of the onboard and ground systems are within the specifications. Provision of data to the Jason-1 Science Working Team started at the end of March 2002. This is the goal of a six-month phase after closure of the initial assessment phase to derive the error budget of the system in terms of altimetry user products.  相似文献   

Marine tether dynamics: retrieval and deployment from a heaving platform     

R. E. Baddour  W. Raman-Nair 《Ocean Engineering》2002,29(13):550-1661

A tether management system of a winch module in a marine environment is proposed. For the purpose of this study the subsea body is considered as a mass attached at the free end of a long tether which is wrapped around a circular drum controlled by an external torque. The winch is considered mounted on a heaving platform. The effect of the heaving platform on the motions of the drum, tether and attached mass are studied with respect to the longitudinal vibrations of the tether in one dimension. The hydrodynamic effects are considered on the deployed portion of the tether and the tethered mass, both of which are assumed submerged in otherwise still water. The resulting nonlinear system of equations of motion is developed and solved numerically for an example of a marine tether system. The effect of the tether extensibility on the operation threshold of the system is identified. Comparison with an inextensible tether case is provided. The numerical results and their analysis for the retrieval/deployment of the system are presented.  相似文献   

水动力作用下管道稳定性的试验研究   总被引：2，自引：2，他引：2  

高福平  顾小芸等 《海洋工程》2001,19(2):56-60

利用振荡流水槽在以下两种约束条件下，研究波浪作用下直接铺设于砂质海底的管道失稳临界条件：1）管道两端自由；2）管道可水平、垂直自由运动，但流动受到限制。试验结果表明，管重无量纳数G与管道失稳的临界Fr数之间大致呈线性关系，而当G超过一定数值时，管道是侧向稳定的。管道的约束条件、砂床特性和加载速度对管道稳定性均有影响。  相似文献   

细菌对海水中各形态氮的影响   总被引：1，自引：0，他引：1  

王江涛  赵春霞  尹晓楠  王秋璐 《中国海洋大学学报(自然科学版)》2006,36(3):468-472

海洋细菌生长过程中,不但能利用体系中的有机物质,而且也能利用无机营养盐。本论文通过小麦岛细菌接种实验发现,细菌大量繁殖时吸收利用体系中的营养物质,生成颗粒态氮(PN)和溶解有机氮(DON),体系中溶解无机氮(DIN)、总溶解氮(TDN)降低至最低值。进入细菌指数生长期和稳定期后,颗粒态和有机态氮不断降解向体系中释放出无机营养盐,DIN和TDN呈现回升趋势,颗粒氮(PN)与细菌数量变化正相关。体系中,初始氮源的量决定了细菌体内POC/PN的比值,氮源充足,细菌繁殖数量多,POC/PN值低,氮源不足,细菌数量相对较少,POC/PN比值高。  相似文献