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41.
Two processes are generally explained as causes of temporal changes in the stoichiometric silicon/nitrogen (Si/N) ratios of
sinking particles and of nutrient consumption in the surface water during the spring diatom bloom: (1) physiological changes
of diatom under the stress of photosynthesis of diatom and (2) differences of regeneration between silicon and nitrogen. We
investigated which process plays an important role in these changes using a one-dimensional ecosystem model that explicitly
represents diatom and the other non-silicious phytoplankton. The model was applied to station A7 (41°30′ N, 145°30′ E) in
the western North Pacific, where diatom regularly blooms in spring. Model simulations show that the Si/N ratios of the flux
exported by the sinking particles at 100 m depth and of nutrient consumptions in the upper 100 m surface water have their
maxima at the end of the spring diatom bloom, the values and timings of which are significantly different from each other.
Analyses of the model results show that the differences of regeneration between silicon and nitrogen mainly cause the temporal
changes of the Si/N ratios. On the other hand, the physiological changes of diatoms under stress can hardly cause these temporal
changes, because the effect of the change in the diatom's uptake ratio of silicon to nitrogen is cancelled by that in its
sinking rate. 相似文献
42.
Several large deployments of neutrally buoyant floats took place within the Antarctic Intermediate (AAIW), North Atlantic Deep Water (NADW), and the Antarctic Bottom Water (AABW) of the South Atlantic in the 1990s and a number of hydrographic sections were occupied as well. Here we use the spatially and temporally averaged velocities measured by these floats, combined with the hydrographic section data and various estimates of regional current transports from moored current meter arrays, to determine the circulation of the three major subthermocline water masses in a zonal strip across the South Atlantic between the latitudes of 19°S and 30°S. We concentrate on this region because the historical literature suggests that it is where the Deep Western Boundary Current containing NADW bifurcates. In support of this notion, we find that a net of about 5 Sv. of the 15–20 Sv that crosses 19°S does continue zonally eastward at least as far as the Mid-Atlantic Ridge. Once across the ridge it takes a circuit to the north along the ridge flanks before returning to the south in the eastern half of the Angola Basin. The data suggest that the NADW then continues on into the Indian Ocean. This scheme is discussed in the context of distributions of dissolved oxygen, silicate and salinity. In spite of the many float-years of data that were collected in the region a surprising result is that their impact on the computed solutions is quite modest. Although the focus is on the NADW we also discuss the circulation for the AAIW and AABW layers. 相似文献
43.
With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km2 dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m3 of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m3 of the originally dumped 2.6 million m3 of dredge spoil had already been removed from the dumping site. 相似文献
44.
45.
通过在二维数值水槽内用边界元法直接求解Laplace方程,对规则波在缓坡上的变形及破碎进行了数值计算。分析了不同底坡及采用不同底摩阻系数时规则波的破碎特征,并对规则波破碎的极限坡度进行了研究。重点分析了规则波破碎时海底坡度、底摩阻系数及波形不对称性对破碎指标的影响。 相似文献
46.
This paper presents a numerical model study of the propagation of water waves using the parabolic approximation of the mild-slope equation in the orthogonal coordinate system. Two types of coordinate systems are studied: (a) a general form of orthogonal coordinate system and (b) the conformal system, a special form of orthogonal coordinate system. Two typical examples, namely, expanded breakwaters and a circular channel, are studied to validate the model. First, the examples are studied by use of the general orthogonal coordinates. Then the same examples are computed by use of the confonnal system. The computational results show that the confonnal coordinate system generally gives better predictions than the general orthogonal system. A numerical technique for generating the conformal grid is combined with the numerical model to improve the practicability of the model. The comparison between the result from the numerical grid system and that from the analytical grid system shows that reliable computational results can be obtained by use of the numerical confonnal grid system. 相似文献
47.
基于神经网络的平底结构砰击压力预报 总被引:1,自引:0,他引:1
对利用神经网络预报平底结构入水砰击压力的方法进行了探讨。首先利用仿真软件计算各种情况下平底结构入水所产生的砰击压力,以此形成训练神经网络的数据集。其次利用数据集对三层反馈式网络进行了训练,讨论了不同隐含层节点数对该非线性系统的拟合能力,并且对梯度下降法、动量修正法和基于优化的LM算法的有效性和精度进行了比较,最后得出了适合平底结构入水砰击系统的网络结构。 相似文献
48.
中国近海的天然气勘探 总被引:1,自引:0,他引:1
据最新勘探资料,在综合分析中国近海海域天然气勘探现状、资源潜力及其区域分布规律的基础上,分析了我国近海海域天然气勘探的有利区带及目前比较现实的勘探目标,展示了我国近海海域天然气勘探的良好前景。 相似文献
49.
采用RT-PCR技术和RACE技术成功克隆淡水鱼类斑鳢sGST基因cDNA全序列,推测得到氨基酸序列,初步分析其结构功能域及系统进化关系。结果表明,斑鳢sGST基因cDNA序列全长为898bp,编码225个氨基酸。斑鳢sGST与真鲷、金头鲷、鲽、黑头鲦、川鲽、大口黑鲈等最新定名为ρ型的sGST氨基酸同源性较高,ρ型sGST为水生生物所特有并共同占据进化树上独立的分枝;与大鼠、小鼠、人等哺乳动物sGST现有所有类型同源性均很低,并且在进化树上距离也较远,表明本研究成功克隆的sGST基因应属于ρ型,可能在鱼类等水生生物对水栖环境的适应上有重要作用。 相似文献
50.
2002年2月—2004年11月对胶州湾异养细菌和大肠菌群进行长期调查发现,胶州湾异养细菌丰度在105—106cells/ml之间,其中河口区域和近岸区域数量较高,其它区域相对较低。从季节上来看,夏季、秋季细菌丰度较高(分别为7.4×105、7.2×105cells/ml),冬季和春季丰度较低(分别为4.1×105cells/ml、5.9×105cells/ml),且在一年内呈现出一定的规律性波动。从季节尺度上看异养细菌丰度与温度呈现很好的正相关性(R=0.54)。对大肠菌群的研究表明,河口区域的大肠菌群数量显著高于其它区域,并且河口区域大肠菌群常年处于严重超标状态(最高为1.1×106cells/L,超过国家前三类水质标准的100倍)。根据大肠菌群的数量状况可以将胶州湾分为三个区域,即严重污染区、中度污染区和轻度污染区。该区域划分与通过营养盐对胶州湾区域的划分(富营养区、中度营养区、贫营养区)结果一致。 相似文献