西沙群岛潮、余流特征研究

对1962、1974、1976、1991、2002年西沙群岛海域实测海流资料分析得出:西沙群岛潮汐特征系数为3.40,是不正规日潮;潮流特征比较复杂,少数为不规则半日潮流型,多数为不规则日潮流型;半日周期的内潮在永兴岛西部特别显著,最大流速可达1.5m/s,对珊瑚生态系统有重要影响;西沙群岛余流,春季4～5月总体方向是东北,最大余流速度66cm/s,出现在中建岛西部;夏初余流方向偏北,速度明显降低,中建岛表、底层流速都不超过50cm/s。结合18a卫星高度计资料统计分析得出,春季和夏季西沙群岛海域处于反气旋式环流的北部,中建岛处于反气旋式环流的西缘,水平压强梯度大,加之地形影响,因此流速最大。     

根据漂流浮标资料对黑潮15m层流路及流轴特征的分析

利用1979-02—2012-03共33a的水帆位于15m层的Argos漂流浮标资料,绘制黑潮流系15m层的多年年平均和月平均流场,运用特征线方法计算得到黑潮流轴,定义黑潮流动路径的边界为流速大小20~30cm/s的过渡性区域。结果显示:黑潮多年年平均流路大致是一个以(13°30′N,142°00′E)为圆心、2 235km为半径的直角弧段,其在吕宋海峡、台湾东北、九州西南及伊豆海岭附近海区发生气旋式弯曲前先进行反气旋式弯曲调整,弯曲处出现的路径开口主要是支流的并入或分支的流出;黑潮流轴整体性偏向黑潮左边界,其中在吕宋岛东北至台湾以东海域最为显著,在本州岛以南海域次之,而在东海段基本居中;黑潮流路上的流速在总体上由南向北呈增大趋势,但并非沿流路持续性逐渐增加,而是呈现出较平直流段的大流速区和弯曲调整流段的低流速区相互交错的状况,其中四国岛以南至伊豆诸岛以西流段的流速为最大。多年月平均流场显示,2月,5月,8月和11月这4个月份是黑潮流路和流轴发生变化的重要转折期,而1月,4月,7月和10月这4个月份则是各季节的代表月份。其中,冬季月份的黑潮流路和流轴最为曲折,向边缘海发生显著入侵;夏季月份的黑潮流路和流轴最为平直,左侧伴随有北向流动;春、秋两季的过渡性特征则比较明显。     

Distribution of calcareous nannoplankton in surface sediments along the northern KwaZulu-Natal Bight,South Africa

The coccolith assemblages from seafloor sediments over the inner shelf in the northern region of the KwaZulu- Natal Bight on the east coast of South Africa were identified and their distribution determined. In all, 29 Recent species and taxonomic groups, as well as 29 reworked species were recorded. The distribution of the Recent species appears to be governed by environmental features that have been documented in other studies: temperature, salinity, nutrient concentration and water circulation pattern, which reveals the long-term existence of a circulation cell in the sector between Durban Bay and the Thukela River. The outer edge of the cell consists of nutrient-enriched mixed layers and is characterised by an enhanced abundance of Gephyrocapsa oceanica, whereas the central region consists of a stratified nutrient-depleted water mass with elevated abundance of Umbilicosphaera sibogae, Florisphaera profunda, and a group of umbelliform species. The elevated levels of G. oceanica, coupled with the rarity of U. sibogae, F. profunda and the umbelliform species, confirm the presence of a permanent upwelling cell off Richards Bay. The maximum abundance of F. profunda found between Richards Bay and Lake Nhlabane indicates a region of nutrient-depleted (except for nitrite) conditions.     

Dynamics and role of the Durban cyclonic eddy in the KwaZulu-Natal Bight ecosystem

The semi-permanent Durban Eddy is a mesoscale, lee-trapped, cold-core cyclonic circulation that occurs off the east coast of South Africa between Durban in the north and Sezela, some 70 km to the south. When present, strong north-eastward countercurrents reaching 100 cm s^–1 are found inshore. It is hypothesised that the cyclone is driven by the strong south-westward flowing Agulhas Current offshore of the regressing shelf edge near Durban. Analysis of ADCP data and satellite imagery shows the eddy to be present off Durban approximately 55% of the time, with an average lifespan of 8.6 days, and inter-eddy periods of 4 to 8 days. After spin-up the eddy breaks loose from its lee position and propagates downstream on the inshore boundary of the Agulhas Current. The eddy is highly variable in occurrence, strength and downstream propagation speeds. There is no detectable seasonal cycle in eddy occurrence, with the Natal Pulse causing more variability than any seasonal signal. A thermistor array deployed in the eddy centre, together with ship CTD data, indicates upward doming of the thermal structure in the eddy core associated with cooler water and nutrients being moved higher in the water column, stimulating primary production. Together with the use of satellite imagery, our findings indicate a second mechanism of upwelling, viz. divergent upwelling in the northern limb of the eddy. Satellite-tracked surface drifters released in the eddy demonstrated the potential for nutrient-rich eddy water to be transported northwards along the inshore regions of the KwaZulu-Natal (KZN) Bight, thus contributing to the functioning of the bight ecosystem, as well as southwards along the KZN and Transkei coasts – both by the eddy migrating downstream and by eddy water being recirculated into the inshore boundary of the Agulhas Current itself.     

水平轴潮流能叶轮尖速比特性分析研究

针对设计尖速比对水平轴潮流能叶轮动力特性的影响问题开展研究工作。基于叶素-动量理论建立叶轮动力特性仿真模型,以叶片数量分别为2、3、4的叶轮为对象,考察设计尖速比对叶轮的功率系数的影响。研究结果表明:设计尖速比越大的叶轮,其最大效率也越高;叶片数量多的叶轮,其功率系数略优于叶片数量少的叶片。结合分析结果,给出了水平轴潮流能叶轮的设计尖速比的选择建议。     

Corrected Formula of Bed Resistance Coefficient for Plane Numerical Simulation of Tidal Current

By means of a logarithm law for the velocity profile,a corrected formula of bed resistancecoefficient,which involves many factors such as gradient of still water depth,variation of surfaceelevation,flow direction,and so on,is derived from the 3D governing equations of tidal current by aver-aging over the whole water depth.Theoretical analysis and application have shown that the 2D plane tidalcurrent numerical model would be more reasonable and could be applied to steep bottom topographywhen the corrected bed resistance coefficient is used,therefore the results of reproduction simulation andengineering calculation would be more scientific and reasonable.     

荣成外海海流特征及影响因素

荣成是我国重要的海产养殖城市,为掌握荣成外海的海流特征,基于2016年1—10月于荣成外海楮岛岬角南侧布放的浮标观测数据,通过谱分析、调和分析等方法,分析了实测流速时间序列剖面及季节变化,分离出该观测点的潮流和余流并进行定性定量分析,探讨了该海域余流的影响因素.结果表明:1)荣成外海浮标观测点流速东西分量总体大于南北分...     

Analysis of southeast Australian zooplankton observations of 1938-42 using synoptic oceanographic conditions

The research vessel Warreen obtained 1742 planktonic samples along the continental shelf and slope of southeast Australia from 1938-42, representing the earliest spatially and temporally resolved zooplankton data from Australian marine waters. In this paper, Warreen observations along the southeast Australian seaboard from 28°S to 38°S are interpreted based on synoptic meteorological and oceanographic conditions and ocean climatologies. Meteorological conditions are based on the NOAA-CIRES 20th Century Reanalysis Project; oceanographic conditions use Warreen hydrological observations, and the ocean climatology is the CSIRO Atlas of Regional Seas. The Warreen observations were undertaken in waters on average 0.45 °C cooler than the climatological average, and included the longest duration El Niño of the 20th century. In northern New South Wales (NSW), week time-scale events dominate zooplankton response. In August 1940 an unusual winter upwelling event occurred in northern NSW driven by a stronger than average East Australian Current (EAC) and anomalous northerly winds that resulted in high salp and larvacean abundance. In January 1941 a strong upwelling event between 28° and 33°S resulted in a filament of upwelled water being advected south and alongshore, which was low in zooplankton biovolume. In southern NSW a seasonal cycle in physical and planktonic characteristics is observed. In January 1941 the poleward extension of the EAC was strong, advecting more tropical tunicate species southward. Zooplankton abundance and distribution on the continental shelf and slope are more dependent on weekly to monthly timescales on local oceanographic and meteorological conditions than continental-scale interannual trends. The interpretation of historical zooplankton observations of the waters off southeast Australia for the purpose of quantifying anthropogenic impacts will be improved with the use of regional hindcasts of synoptic ocean and atmospheric weather that can explain some of the physically forced natural variability.     

An analysis of horizontal dispersion due to the drift current with an Ekman layer

An analytical method for describing horizontal matter dispersion in shear currents is presented using a tensor expression from the point of view that matter dispersion due to the shear effect should be one of the principal mixing dilution processes. Although the behavior of horizontal dispersion is considerably more complicated than common longitudinal dispersion, the present study elucidates the vertical structure of dispersion and the dispersing process from the initial to the stationary stage, besides the usual depth-averaged dispersion coefficient at the stationary stage. As one of the typical applications of horizontal dispersion, dispersion due to the pure drift current with an Ekman layer is examined theoretically using the present method. This examination reveals that the displacement of the centroid and the major axis of dispersion are twisted in the vertical direction more than the direction of the current vector forming the Ekman spiral; that the variance increases in proportion to the third power of the elapsed time; and that the dispersion coefficient at the stationary stage remains constant, independent of the depth normalized by an Ekman layer thickness. Such dependence of the dispersion coefficient in the steady current is shown to be different from that in the oscillatory current, which is inversely proportional to the depth normalized by a Stokes layer thickness. This is considered to be induced by the difference of the vertical profiles of the first order moment in both currents, that is, the shear region of the first order moment is restricted around the floor by the alternation of the current shear in the oscillatory current while it is diffused in the whole depth in the steady current.