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991.
为探讨北黄海表层沉积物中常量元素分布特征,并进一步分析其控制因素和物质来源,以常量元素为依托,对304个站位表层沉积物常量元素含量分布特征及控制因素进行统计分析,结果表明:沉积物中SiO2、Al2O3、Fe2O3、MgO、K2O、P2O5、TiO2七种元素含量的空间分布具有明显的区域性。其中,SiO2、K2O具有相似的空间分布;Al2O3、Fe2O3、MgO、P2O5、TiO2具有相似的空间分布,但与SiO2、K2O的分布趋势相反;CaO、MnO、Na2O在区域内分布较为均匀,未显示出明显的高低变化趋势。聚类分析显示,表层沉积物的常量元素分布主要受粒度效应的控制。主因子分析提取出3种控制常量元素分布的主成分,分析表明,粒度控制效应、源区风化作用和不同物源输入是影响表层沉积物常量元素空间分布的主要因素,贡献累计方差总和达77.12%。以K2O、CaO、TiO2为指标,通过FD函数识别出北黄海不同海域内的主要物质来源,其主要物源包括黄河、鸭绿江和黄海暖流携带的长江物质。对北黄海沉积物物质来源进行分析,不仅在海洋矿产资源勘探、航道开发、沿岸港口建设与整治等方面具有实际意义,而且在认识海洋环境变迁等方面同样具有理论意义。 相似文献
992.
以2010年11月-2011年3月磨刀门水道挂定角、联石湾、竹排沙、平岗和竹银5个测站的盐度、马口水文站流量、三灶站潮位和竹银站的主流向风速为基本数据,应用偏相干谱估计方法分析了各测站盐度变化对潮汐、流量和风的频率响应。经验诊断分析结果表明:1)马口站入海径流存在准1日、半日、1/4日和1/3日等显著的潮致振荡周期;2)各测站盐度变化与潮汐主要振荡周期并不一致,沿磨刀门水道向上游,潮汐对盐度变化的影响递减,竹银站盐度可作为潮汐直接作用下咸潮上溯的平均上限位置;3)消除潮汐和径流的影响后风对盐度变化的作用明显加强;4)各测站盐度变化对潮汐、流量与风的响应过程存在时间超前或滞后但无特定规律,说明磨刀门水道盐度变化过程十分复杂。 相似文献
993.
Natural weak acidic groundwater occurs in the unconfined and confined aquifers consisting of Quaternary and Neogene unconsolidated sediments near Beihai in southern Guangxi, China. Under natural conditions the groundwater has low TDS(less than 200 mg L-1) and low concentrations of trace elements(less than 100 μg L-1) with a deceasing tend in contents of the Lanthanides(rare earth elements, less than 1 μg L-1) towards higher atomic number. The groundwater ranges in p H from 3.33 to 7.0 with an average value of 5.12(even lower than that of local rainwater, 5.88). p H values in the groundwater are a bit higher in rainy seasons than those in dry seasons and do not show significant increasing or decreasing trend with time. The average p H value in groundwater in the confined aquifers is even a bit lower than that in the unconfined aquifer. Comprehensive analyses of the groundwater environment suggest that H+ in the groundwater may be derived from dissociation of H2CO3, release of the absorbed H3O+ in clay layers and the acidity of rainwater. The H2CO3 in the groundwater may be formed by dissolution of CO2(g). Minerals in the unconsolidated sediment are predominated by quartz with small amount of clay minerals. The sediments undergoing a long-term weathering contain low levels of soluble constitutes. Lack of alkaline substances in the groundwater system is also helpful in the accumulation of acidity of the groundwater. 相似文献
994.
Georg Umgiesser Francesca De Pascalis Christian Ferrarin Carl L. Amos 《Ocean Dynamics》2006,56(3-4):339-351
The origin of the sands in the Venice lagoon has been the subject of an extensive field survey in parallel with numerical modelling. Four transects along Treporti and Burano canals were conducted from which 33 bottom sediment samples were collected. These samples were analysed for grain size and sorting to examine any trends in the granulometry of these sediments that might shed light on transport paths. The modelling study consists of three parts: the sediment transport model sedtrans96 was used with a finite-element hydrodynamic model (Shyfem) and an empirical wave model (US Army Corps of Engineering) to simulate sand transport in the Treporti canal. A type of link box model was created where finite elements of the hydrodynamic model have been combined to macro-boxes on which the water and sediment flux over the sections, and a mass balance has been computed. Several grain size classes were simulated; the distributions before and after the simulation were examined. Idealised wind and tidal values were initially used to force 12 h simulations to test the sediment transport sensitivity. Finally, a full-year simulation (1987) has been carried out using measured tidal and wind data. Only a part of Venice lagoon was covered by the simulation: a major channel (Treporti) running from Lido inlet towards the northern lagoon. The total sand transport through all of the sections was computed for 1 year. Sediment mass balance was determined, and the resulting trends of erosion and deposition were computed. There were no trends in the median grain diameter and sorting of bottom samples from the Treporti canal; all sands were fine (120 μm, one outlier of 300 μm was removed). The absence of a trend in grain size suggests that there is no significant import of sand to the lagoon through the Lido inlet. The results from the simulations seem therefore to confirm the hypothesis of reworking of sand within the lagoon. The computed erosion is some centimeters per year diagnostic of channel scouring and enlargement with time. The Treporti canal is subject to strong current velocities of around 1 m/s, which hold fine sand in suspension and thus prevent sedimentation. 相似文献
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Previous research on climatic change in the Mid-Holocene in China indicates that it was a warm and humid period, accompanied
by stronger summer monsoons, and it is defined as the Megathermal in the Holocene, or the Holocene Optimum period. However,
this conclusion is mainly directed at the monsoonal region in eastern China. In this research, we chose the Gonghe Basin in the
northeastern Qinghai-Tibetan Plateau as the study area. Geochemical analysis of the profiles of paleosols and aeolian sand in the
Santala area in the middle of the Gonghe Basin, along with OSL (optically stimulated luminescence) dating, indicates that the
regional climate has experienced several warm-humid and cold-dry cycles since 11.8 ka. In particular, the Mid-Holocene
(8.1–4.6 ka) was relatively cold and dry as evidenced by drastic fluctuations in chemical weathering degree and humidity, a
higher aridity index, and sparse vegetation, accompanying increased winter monsoonal strength. In order to clarify whether
this is an individual or local signal, we compared our geochemical analysis results with lake and peat records and aeolian deposits
of the monsoonal boundary region. The results indicate that the climate deteriorated widely, with declines in temperature
and moisture, in the Mid-Holocene in the modern monsoonal boundary zone. Furthermore, the duration of climate deterioration
(relatively dry period) generally decreased from west to east in the aforementioned regions. Therefore, this dry phase in
Gonghe Basin may be representative of dry events in Mid-Holocene in northern China. In addition, we discuss the reasons for
this dry climate from several perspectives: (1) it probably can be attributed to a decline in summer monsoonal strength; (2) the
regional evaporation loss (forced by high temperature) was not compensated by regional precipitation; (3) the thermal dynamic
effect of the Qinghai-Tibetan Plateau. 相似文献
1000.
Xavier James Raj 《Planetary and Space Science》2009,57(11):1312-1320
A new non-singular analytical theory for the motion of near-Earth satellite orbits with the air drag effect is developed in terms of uniformly regular KS canonical elements. Diurnally varying oblate atmosphere is considered with variation in density scale height dependent on altitude. The series expansion method is utilized to generate the analytical solutions and terms up to fourth-order terms in eccentricity and c (a small parameter dependent on the flattening of the atmosphere) are retained. Only two of the nine equations are solved analytically to compute the state vector and change in energy at the end of each revolution, due to symmetry in the equations of motion. The important drag perturbed orbital parameters: semi-major axis and eccentricity are obtained up to 500 revolutions, with the present analytical theory and by numerical integration over a wide range of perigee height, eccentricity and inclination. The differences between the two are found to be very less. A comparison between the theories generated with terms up to third- and fourth-order terms in c and e shows an improvement in the computation of the orbital parameters semi-major axis and eccentricity, up to 9%. The theory can be effectively used for the re-entry of the near-Earth objects, which mainly decay due to atmospheric drag. 相似文献