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141.
长江口潮滩有机质稳定碳同位素时空分布与来源分析 总被引:5,自引:0,他引:5
通过测定长江口潮滩悬浮颗粒有机质和表层沉积有机质在枯水季节 (2006年2月 )和洪水季节 (2006年8月 )的稳定碳同位素值,对有机质潜在来源及局部岸段改造作用进行了分析。结果显示,悬浮颗粒有机质稳定碳同位素值在2月明显低于8月,变化范围分别在-25.8‰~-23.4‰和-25.1‰~-22.9‰,主要是受径流量枯洪季变化和浮游生物生长季节变化两种因素的叠加作用。表层沉积有机质2月和8月的稳定碳同位素分别为-25.0‰~-20.4‰和-24.7‰~-19.5‰,季节变化不明显,主要来自悬浮颗粒物的沉降。除受大背景环境因素影响,局部环境对潮滩有机质也有一定的改造作用,污水、支流河水的输入对悬浮颗粒有机质碳同位素有一定的影响,埋藏的潮滩植物和底栖微藻则对沉积有机质有部分贡献。 相似文献
142.
Luminescence dating has long been used for chronological constraints on marine sediments due to the ubiquitous dating materials (quartz and feldspar grains) and its applicability over a relatively long time range. However, one of the main difficulties in luminescence dating on marine sediments is partial bleaching, which causes age overestimations. Especially, partial bleaching is typically difficult to be detected in the fine grain fraction (FG) of marine sediments. The recently developed feldspar post-IR IRSL (pIRIR) protocol can detect non-fading signals and thus avoid feldspar signal instability. In the current study, fine grains were extracted from a gravity core in the northern Sea of Japan, and the aim is to test the feasibility of using different luminescence signals with various bleaching rates to explore the bleaching conditions of fine grain fraction in marine sediments. The results suggest that the quartz OSL signal and polymineral pIRIR signals at stimulation temperatures of 150 °C and 225 °C (pIRIR150 and pIRIR225) of FG were well bleached prior to deposition. The OSL ages were used to establish a chronology for this sedimentary core and the resulting age-depth relationship is self-consistent and comparable with radiocarbon dates. We conclude that different luminescence signals with various bleaching rates can be used to test the bleaching conditions of fine grain fraction in marine sediments; and the luminescence dating can be applied to marine sediments with great potential. 相似文献
143.
海南岛东南部海岸砂丘风暴冲越沉积记录 总被引:1,自引:0,他引:1
通过海南岛东南部海岸详细的古风暴学考察,在尖岭海岸发现了含有风暴冲越沉积物的海岸沙丘剖面,分别命名为JL-1和JL-2剖面,试图从海岸沙丘沉积记录中提取历史上的风暴事件信息。沉积物粒度、磁化率等参数的指标分析表明,这两个剖面含有典型的风暴冲越沉积物,利用放射性核素AMS14C测年、OSL测年分析,并结合历史文献记载,确定这些风暴沉积层是多次台风作用的产物,其形成机制与风暴浪越过海岸沙丘的堆积有关,风暴流越过沙丘顶部后不能回流,导致风暴流携带的沉积物迅速沉积。此外,依据Stockdon经验公式计算结果,该地点沉积记录所代表的最大风暴事件相当于100到200年一遇的重现期。研究表明,该处海岸沙丘冲越沉积含有南海台风强度与重现期的重要信息。 相似文献
144.
Adequately analyzing and modeling the extreme rainfall events is of great importance because of the effects that their magnitude and frequency can have on human life, agricultural productivity and economic aspects, among others. A single extreme event may affect several locations, and their spatial dependence has to be appropriately taken into account. Classical geostatistics is a well-developed field for dealing with location referenced data, but it is largely based on Gaussian processes and distributions, that are not appropriate for extremes. In this paper, an exploratory study of the annual maximum of monthly precipitation recorded in the northern area of Portugal from 1941 to 2006 at 32 locations is performed. The aim of this paper is to apply max-stable processes, a natural extension of multivariate extremes to the spatial set-up, to briefly describe the models considered and to estimate the required parameters to simulate prediction maps. 相似文献
145.
146.
基于古地磁和AMS14C定年结果,对长江三角洲太湖平原的WJ孔进行岩性特征、矿物磁学、粒度分析及有孔虫化石研究,拟重建WJ孔记录的晚第四纪以来沉积环境演变过程与海侵事件,并探讨环境磁学参数对河口三角洲地区沉积环境演化的指示意义.研究结果表明,WJ孔可以划分为中更新世阶段I、中更新世阶段II、晚更新世、全新世四个阶段,沉积地貌环境分别为:河湖、滨海-阶地、河口坝-河口湾-潮滩与阶地、湖沼平原.WJ孔揭示了三次海侵事件,分别为中更新世晚期海侵,晚更新世MIS5海侵和晚更新世MIS3海侵.其中记录的MIS5e海侵最为强盛,MIS3后期也存在一次海侵加强事件.另外,滨海潮滩-河口坝环境的沉积物磁性特征明显,χlf、SIRM、HIRM等为显著高值. 相似文献
147.
148.
探讨使用长江口的河口海岸数据,提出一套数据结构标准和服务框架,构建一个具有多源数据统一集成管理,适用于本地存储及网络呈现的数据服务平台。基于XML技术通过数据库实现数据的集中存储管理,基于FLEX通过WebGIS实现各种数据在线管理,从而提供一个具有统一的组织结构的综合数据管理服务的解决方案,给长江口的河口海岸的学科基... 相似文献
149.
150.
This study focuses on suspended sediments and in situ flocculation in the Yangtze River, with the goal of improving our understanding of the relationship between freshwater and estuarine flocculation. A field survey with state-of-the-art instruments was carried out in January 2008 in the reach from downstream of the Three Gorges Dam to the estuary. The data show that in situ floc mean diameters range from 22 to 182???m in the river, whereas the median dispersed grain sizes are 4.4?C11.4???m. This demonstrates that flocculation is an important process during the transport of suspended sediments along the river. The flocculation characteristics, suspended sediment concentration and dispersed grain sizes all vary longitudinally in the main stream of the Yangtze River. Biochemical factors are likely be more significant in the freshwater flocculation than in the estuary, where hydrodynamics and biochemical factors are both important. Flocculation is found in the freshwater river, in the estuary and in coastal waters, which indicates that dynamic break-up/reflocculation processes take place during the suspended sediment transport. The freshwater flocs may behave as parent flocs to the estuarine flocculation. This study enhances our understanding of flocculation from estuarine and coastal areas to fresh river systems and provides insights into the effects of input of riverine flocs to the estuarine flocculation and into the sources and fate of flocs. 相似文献