Analytical Study of Longitudinal Mass Flux Due to the Shear Effect in a Tidal Basin     

Hidekazu Yasuda 《Journal of Oceanography》2004,60(3):587-596

The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient. The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical diffusing and the settling flux. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A simple method for calibrating optical backscatter sensors in high concentrations of non-cohesive sediments     

Tony Butt  Jon MilesPeter Ganderton  Paul Russell 《Marine Geology》2002,192(4):419-424

A new method is introduced for calibrating optical backscatter sensors for suspended quartz sand concentrations of up to 200 kg m⁻³. Due to the high settling velocity of quartz sand in water, considerable difficulties have arisen in the past to maintain a spatially and temporally homogeneous suspension suitable for calibration. Traditional methods are clumsy and prone to errors. Here, the sediment is calibrated in glycerol, a clear fluid with a higher viscosity than water. The settling velocity is reduced by three orders of magnitude. An empirical relationship is obtained which is used to correct for any optical differences in response of the sensors in the two fluids. Any extra errors introduced by calibrating with a different fluid from that found in the field are outweighed by the simplicity and reliability of this method.  相似文献   

Contrasts in sedimentation flux below the southern California Current in late 1996 and during the El Niño event of 1997–1998     

Norman Silverberg  Aida Martínez  Sergio Aguíiga  Jos D. Carriquiry  Nancy Romero  Evgeni Shumilin  Soledad Cota 《Estuarine, Coastal and Shelf Science》2004,59(4):575-587

The vertical flux of particulate matter at 330 m depth in San Lázaro Basin off southern Baja California ranged from 63 to 587 mg m⁻² d⁻¹ between August and November 1996. Organic carbon contents were between 5.6 and 14.8%, yielding flux rates of 9–40 mgC m⁻² d⁻¹. In December 1997 and January 1998, at the height of the strong El Niño event, the respective fluxes (47–202 mg m⁻² d⁻¹ and 3–8 mgC m⁻² d⁻¹) were comparable. The February–June 1998 records, however, revealed sharply reduced mass (1–6 mg m⁻² d⁻¹) and organic carbon (0.2–0.8 mgC m⁻² d⁻¹) fluxes. The organics collected in 1996 were predominantly autochthonous (δ¹³C=−22‰; C/N=8). The variations in δ¹⁵N (8.3–11.0‰) suggest an alternation of new and regenerated production, possibly associated with fluctuations in the intensity of deep mixing during that autumn. The relatively high organic matter fluxes in December 1997 appear to be associated with regenerated production. The average composition from February to June 1998 (δ¹³C=−23.6‰; ¹⁵N=11.7‰; C/N=10.5) indicates degraded material of marine origin. The maximum δ¹⁵N value found (14‰) suggests that deeper, denitrified waters were brought to the surface and possibly advected laterally. Regime changes in the waters of the basin occur at 6–10 week intervals, evidenced by concurrent shifts in most of the measured parameters, including fecal pellet types and metal chemistry. The marine snow-dominated detritus collected showed a shift from a mixed diatom-rich-radiolarian-coccolith assemblage in late 1996 to a coccolith-dominated assemblage, including the contents of fecal pellets, during the 1997–1998 El-Niño period. T–S profiles, plankton analysis and chlorophyll contents of the upper water column indicated that the strong phytoplankton bloom, normally associated with seasonal upwelling along the Pacific coast of Baja, did not occur during the spring of 1998. The persistence of oligotrophic conditions during the 1997–1998 El Niño event favored the dominance of nanoplankton and reduced the vertical flux of particles.  相似文献   

Particulate Flux and Cd/P Ratio of Particulate Material in the Pacific Ocean     

Shinichiro Noriki  Kazuhiro Hamahara  Koh Harada 《Journal of Oceanography》1999,55(6):693-703

Time-series Mark 7 sediment traps were deployed at three stations at 0°N, 13°N and 48°N along 175°E to investigate seasonal and spatial variations of particulate material flux. Chemical analysis of particulate material was performed for four major chemical components, viz. opal, CaCO₃, organic material and clay minerals, Cd and P in the particulate material were also determined. We discuss the characteristics of particulate material at each site and the transportation of Cd and P to deep water by the particulate material. The total mass fluxes and variation of fluxes at each site reflect oceanographic conditions, such as biological productivity and kind of major planktonic organisms. At the northern site, large mass fluxes with a spring bloom and high ratios of opal are characteristic. Relatively small mass fluxes with high ratios of CaCO₃ are distinct, and dissolution of CaCO₃ due to sinking is recognized in the middle latitude and 0°N sites. The larger flux at the lower trap than the upper trap at the equatorial site suggests influence by lateral transport in the deep water. Distinctive decreasing Cd/P ratio and CaCO₃ concentrations in the particulate material with increasing depth suggests that the change of Cd/P ratio in the intermediate and deep water occurs through the dissolution of CaCO₃. The dissolved Cd/P ratios in the deep water are proportional to the age of the deep water in the Atlantic but not in the Pacific. This is explained by the difference of kinds of particulate material transporting Cd and P in the deep water between the oceans. That is, the major planktonic organisms are planktons of CaCO₃ tests in the Atlantic Ocean and diatoms of opal tests in the North Pacific Ocean.  相似文献   

长江河口区边界层参数的观测与分析   总被引：1，自引：0，他引：1  

汪亚平  高建华  潘少明 《海洋地质前沿》2006,22(7):16-20

2003年11月在长江口南槽用ADCP进行定点水文观测,结果表明研究区为不规则半日潮,在水流转向期流速较低时常出现悬沙浓度峰值。根据流速对数剖面分布模型与悬沙分布模型,分别计算了海底边界层参数,其中潮周期内摩阻流速可达0.15 m/s,粗糙长度为0.01~1.2 m,拖曳系数为10-3~10-4,边界层厚度为2~4 m,悬沙的沉降速率为0.2~6 mm/s。  相似文献   

海口市区地面沉降监测结果初步分析     

麦照秋  李富强 《测绘信息与工程》2009,34(3):31-32

分析了海口市区地面沉降的多期重复观测成果,找出了海口市区地面沉降的基本规律,提供了市区中长期地震预报的基础数据。  相似文献   

长江口北槽黏性细颗粒泥沙特性的试验研究   总被引：2，自引：0，他引：2  

杨扬  庞重光  金鹰  周晶晶 《海洋科学》2010,34(1):12-24

选用长江口北槽黏性细颗粒泥沙,在不同盐度的人工海水中通过静水沉降、动水沉降等各种试验手段了解其基本特性。在静水沉降管中观测了胶粒的电化学絮凝过程和重力碰并过程,于不同盐度条件下找出最佳絮凝盐度;并通过黏性细颗粒泥沙在流动海水中絮凝的试验研究,揭示其在动水中絮凝的机理和规律,及不同条件下的起动流速、不淤流速、沉降速度等特征值,从而分析其落淤情况。研究结果表明,长江口北槽细颗粒黏性泥沙的最佳絮凝盐度约为15,起动流速为15~20 cm/s,这与泥沙的淤积固结时间有关,而不淤流速约为60 cm/s。并由试验得到了挟沙力与流速之间的经验关系,以及用于估算不同流速条件下泥沙沉降速度及淤积量的经验公式。这些结果可用于长江口航道的疏浚、整治工作中,具有一定的理论指导意义。  相似文献   

The use of grain size trend analysis in macrotidal areas with breakwaters: Implications of settling velocity and spatial sampling density   总被引：1，自引：0，他引：1  

T.A. Plomaritis  D. Paphitis  M. Collins   《Marine Geology》2008,253(3-4):132-148

In a macrotidal environment with offshore breakwaters (Elmer, West Sussex) a new approach for the identification of the sediment transport pathways with grain size trend analysis (GSTA) was undertaken using statistical parameters (mean, sorting and skewness) directly derived from settling velocities distributions. The same samples were analysed with sieving (quarter- and half-phi resolution) and GSTA was performed again in order to directly compare the resultant sediment transport directions derived with the two analytical techniques. Furthermore, both regular and irregular sampling distributions were used to recalculate GSTA. Hydrodynamic data were collected in different locations around the breakwaters and net sediment transport directions were calculated in order to assess the accuracy of the sediment transport pathway directions derived with the different analytical techniques.The accuracy of settling velocity in determining the statistical parameters of the grain size distribution is identified, especially for the fine-medium sand sediments. Settling velocities produced better results than the sieving; the quarter-phi resolution producing the poorer results in comparison with the coarser half-phi resolution. The results for the different spatial sampling strategies are found to depend upon the number of samples utilised; that shows that the accuracy of the GSTA is based upon the ability of representing, adequately, the spatial distribution of the sediment parameters.  相似文献   

哈密市近30a家燕停留时间与气象因子的关系     

白素琴  李兰 《沙漠与绿洲气象(新疆气象)》2009,3(5):40-43

通过对哈密气象站1980-2008年家燕物候资料和气象资料的分析,得出当地家燕物候变化规律及停留时间与气象因子的关系。结果表明：（1）家燕始见日期均在4月,其中4月中旬较多,平均日期为4月16日,绝见日期均在9月且集中于中旬,平均日期为9月16日;（2）家燕停留期为4—9月,平均停留153d;（3）停留期与同期≥0℃积温和日照时数均呈显著的正相关关系,而随降水量的变化在不同时段呈现或同向或反向的趋势;（4）≥0℃积温和日照时数均为增加趋势,总体上家燕停留期变化与二者变化趋势一致,但近6a停留期缩短。  相似文献   

黄海秋季典型站位沉降颗粒物的垂直通量   总被引：3，自引：0，他引：3  

张岩松  章飞军  郭学武  张曼平 《地球化学》2005,34(2):123-128

2002年9月,在海州湾外侧(E1站)、黄海冷水团(E2站)和黄、东海毗邻水域(E3站)分别放置沉积物捕获器采集沉降颗粒物,研究其垂直通量.结果显示,E1、E2和E3站底层颗粒物沉降通量分别为215.44 g/(m2·d)、165.51 g/(m2·d)、873.91 g/(m2·d),POC沉降通量分别为3.15 g/(m2·d)、2.22 g/(m2·d)、10.49 g/(m2·d).生源颗粒物是E1站位次表层POC的主要来源.E3站水体底层的大量悬浮颗粒物主要来自沉积物的再悬浮,再悬浮强烈程度及影响深度均高于E1站.通过模型计算出E2站底层颗粒物再悬浮比率平均(±SD)为95.65(±2.14)%,底表沉积物再悬浮通量占总再悬浮通量的百分比(X值)为89.53%,显示秋季底部平流对黄海冷水团区再悬浮通量影响不大,但这种影响在夏季相对较强.E2站POC净沉降通量为192 mg/(m2·d),生源颗粒物是此站位POC通量的主要贡献者.由于温跃层的长期存在,营养盐贫乏,生物生长受到抑制,导致黄海冷水团区秋季POC通量小于夏季.  相似文献