The morphodynamic modelling of tidal sand waves on the shoreface

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).     

唐山市滨海湿地动态演变特征及其机制分析

利用历史资料和Landsat TM卫星遥感图像,研究了唐山市滨海湿地自建国以来的演变特征,着重对1987~2004年陡河———滦河之间的滨海平原湿地类型进行了识别,绘制了不同时期的景观面解译图。利用Mapinfo制图软件计算出两个时期的面积(比例)转化矩阵,显示该区滨海湿地破碎化加重,其动态演变特征呈明显退化趋势,进而提出引起其退化的原因和发展趋势预测。     

“大洋一号”勘查技术体系的设计与建设

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.     

利用卫星测高技术监测厄尔尼诺和拉尼娜现象

利用美国宇航局和法国空间局联合公布的T／P数据（1993-2000年）和Jason-1数据（2002—2006年），由共线法计算了热带太平洋地区海平面高度的变化。根据T／P和Jason-1数据计算的海面月变化异常图，分别研究了和分析了1997-1998年的厄尔尼诺和拉尼娜现象、2002-2003年厄尔尼诺现象的变化发展过程。     

Roles of Continental Shelves and Marginal Seas in the Biogeochemical Cycles of the North Pacific Ocean

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.     

呼伦湖的近期扩张及其与全球气候变化的关系

通过近２０多年湖泊水量平衡分析发现，湖泊水位变化主要由湖盆内径流补给量的丰枯决定。进一步分析揭示，呼伦湖地区乃至整个东北地区，本世纪以来随气温升高，随水有增加的趋势。降水增加导致入湖径流量，湖水位上升，呼伦湖本世纪以来的扩张与内蒙古东部地区其他内陆湖泊的变化一致，但这在我国乃至整个亚洲内陆干旱或半干旱区是独一无二的，为此成为这一地区气候变化的指示器。     

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

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.     

Jason-1: Assessment of the System Performances

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.     

Marine tether dynamics: retrieval and deployment from a heaving platform

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.     

细菌对海水中各形态氮的影响

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。