Late Holocene estuarine–inner shelf interactions; is there evidence of an estuarine retreat path for Tampa Bay, Florida?     

B. T. Donahue  A. C. Hine  S. Tebbens  S. D. Locker  D. C. Twichell   《Marine Geology》2003,200(1-4):219-241

The purpose of this study was to determine if and how a large, modern estuarine system, situated in the middle of an ancient carbonate platform, has affected its adjacent inner shelf both in the past during the last, post-glacial sea-level rise and during the present. An additional purpose was to determine if and how this inner shelf seaward of a major estuary differed from the inner shelves located just to the north and south but seaward of barrier-island shorelines. Through side-scan sonar mosaicking, bathymetric studies, and ground-truthing using surface grab samples as well as diver observations, two large submarine sand plains were mapped – one being the modern ebb-tidal delta and the other interpreted to be a relict ebb-tidal delta formed earlier in the Holocene. The most seaward portion of the inner shelf studied consists of a field of lobate, bathymetrically elevated, fine-sand accumulations, which were interpreted to be sediment-starved 3D dunes surrounded by small 2D dunes composed of coarse molluscan shell gravel. Additionally, exposed limestone hardbottoms supporting living benthic communities were found as well. This modern shelf sedimentary environment is situated on a large, buried shelf valley, which extends eastward beneath the modern Tampa Bay estuary. These observations plus the absence of an incised shelf valley having surficial bathymetric expression, and the absence of sand bodies normally associated with back-tracking estuarine systems indicate that there was no cross-shelf estuarine retreat path formed during the last rise in sea level. Instead, the modern Tampa Bay formed within a mid-platform, low-relief depression, which was flooded by rising marine waters late in the Holocene. With continued sea-level rise in the late Holocene, this early embayment was translated eastward or landward to its present position, whereby a larger ebb-tidal delta prograded out onto the inner shelf. Extensive linear sand ridges, common to the inner shelves to the north and south, did not form in this shelf province because it was a low-energy, open embayment lacking the wave climate and nearshore zone necessary to create such sand bodies. The distribution of bedforms on the inner shelf and the absence of seaward-oriented 2D dunes on the modern ebb-tidal delta indicate that the modern estuarine system has had little effect on its adjacent inner shelf.  相似文献   

陕西河谷盆地生态系统服务协同与权衡时空差异分析   总被引：6，自引：1，他引：5  

孙艺杰  任志远  赵胜男  张静 《地理学报》2017,72(3):521-532

陕西河谷盆地是区域主要粮食基地和社会经济中心,人口增长、城镇化和工业化的加快发展,使得该地区生态环境受到人类活动的强烈冲击,生态环境面临着潜在的巨大危机,严重影响社会经济的可持续发展。本文选取西北地区经济中心—关中盆地和陕西省生态保护指定区—汉中盆地进行对比研究,以1990-2010年的生态系统服务数据（NPP、保水服务、食物供给）分析生态服务时空差异,通过相关分析、线性和幂函数回归等方法分析了生态系统服务协同与权衡的时空差异。结果表明：NPP与保水是协同关系,NPP与食物供给、保水与食物供给是权衡关系;21年中,两大盆地的协同关系均呈减弱趋势,权衡关系为加强趋势,且关中盆地的变化速度要高于汉中盆地;NPP与保水的协同程度,在关中盆地东部的耕地区域以及汉中盆地的宁强县与略阳县西部最强,以关中的铜川市和汉中的西乡县最弱;NPP与食物供给的权衡程度,在关中盆地的铜川市和西安市境内的秦岭区域以及汉中盆地的西乡县南部制约关系更为突出,以关中的宝鸡市及汉中的略阳县最弱。  相似文献   

Emplacement of sandstone intrusions during contractional tectonics     

《Journal of Structural Geology》2016

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2007年夏季江淮强降水过程中10~30d低频变化及其与对流层上层波包活动的联系          下载免费PDF全文

陈丹萍  管兆勇  侯俊  奚子惠 《大气科学学报》2016,39(2):177-188

利用NCEP/NCAR再分析和全国740站逐日降水资料,运用一点滞后相关等方法,对2007年夏季江淮流域强降水期间低频振荡的波动活动特征及其与降水低频变化的联系进行了分析。结果表明,在2007年夏季降水中,降水低频分量起着重要作用。降水的低频振荡主周期为10~30d,降水距平时间序列与10~30d低频分量具有较好的对应关系。低频扰动在对流层上层和低层都呈现波列状分布,且在降水活跃位相时,低频环流在高、低层具有斜压结构。在对流层上层,低频扰动有缓慢的东移倾向,相速度为每天2~3个经度。西风带中存在多次移动性波列向下游的传播,且在120°E以西以每天14经度的群速度向下游频散能量,表明10~30d低频波动具有明显的下游发展特征。在强降水开始5d前,低频波动与能量可起源于高纬的乌拉尔山附近,沿着西北-东南向的路径向下游传播。下游发展的低频波动为江淮流域带来了能量,为强降水的发生提供了条件。这些结果加深了人们对低频波动在江淮流域强降水过程中所起作用的认识,可为寻找江淮流域强降水过程预报线索提供科学依据。  相似文献   

两种温室气体排放情景下中国汛期江淮暴雨低涡特征研究     

苗春生  徐方姝  王坚红  余钟奇  高义梅  张旭 《大气科学》2016,40(2):257-270

本文基于一个水平分辨率为50 km的区域气候模式RegCM4(Regional Climate Model,version 4.0)的模拟与预估结果,对我国汛期江淮暴雨低涡在气候变化背景下的统计特征与合成结构进行分析,进一步对两种温室排放情景下未来中国汛期的江淮暴雨低涡特征进行预估。结果表明:RegCM4模式对环境要素及低涡都具有一定的模拟能力,低涡的伸展高度、生命期及暴雨位置模拟结果与观测较为接近,但模拟的低涡个数、最大暖区高度以及温、湿要素分布均比实际略偏低,而风速和低涡的强度模拟则偏强;在未来两种温室排放情景预估方面, RCP4.5(Representative Concentration Pathways,简称RCP)典型浓度排放情景下,暴雨低涡数量比例减少,强度减弱,但低涡发展高度仍以850 hPa为主,生命期多为2 d以内,低涡雨区分布及最大暖区高度均与历史时段相近;RCP8.5情景下,暴雨低涡比例明显大于RCP4.5情景,低涡发展高度以700 hPa为主,生命期达3 d的增多,强度增强,最大暖区厚度范围显著伸展。两种情景下均有低涡中温度锋区减弱,而湿度锋区增强,但RCP8.5情景减弱与增强更显著,显示更高的温室气体排放将导致未来出现更强的暴雨低涡,造成伴随暴雨的低涡灾害性天气的增加,因此应进一步深化对低涡暴雨灾害性天气发展趋势的研究。  相似文献   

青海共和盆地多石在沟河道沙丘现代风水交互过程   总被引：2，自引：0，他引：2       下载免费PDF全文

马玉凤  严平  宋阳  杜建会  朱孟郡  丁连刚 《第四纪研究》2008,28(4):695-701

选择青海共和盆地多石在沟河道中6道新月形沙丘链作为研究对象,采用Trimble4700DGPS与常规测量手段,结合野外风沙观测与自动气象站数据,初步观测分析了2006年多石在沟河道沙丘在不同季节的形态变化过程,计算出2006年风季前比雨季后多石在沟河道沙丘体积减小了548.3m³,风积量为2351m³,流水的蚀平量为2899m³,2006年风水两相营力对河道沙丘的侵蚀贡献率约为45%∶55%,流水的搬运作用强于风力的堆积作用。但从较长的时间尺度来看,研究区的风力侵蚀作用强于流水侵蚀作用,河道沙丘不断增大。多石在沟河道沙丘是一个典型的风水交互作用系统,河道成为风力与流水交互作用的"中转站",在风水的交替作用下,沉积物由风积环境进入流水环境中。  相似文献   

Late Holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged, hyperarid alluvial Nahal Arava, Israel   总被引：1，自引：0，他引：1  

Yael Jacoby  Tamir Grodek  Yehouda Enzel  Naomi Porat  Eric V. McDonald  Ofer Dahan   《Geomorphology》2008,95(3-4):274-294

The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava–Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flood-damaged tamarix trees (‘Sigafoos trees’) in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700–1800 m³s^− 1. This is a larger magnitude than the largest gauged flood of 1150 m³s^− 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene ( 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of  2000 m³s^− 1 flood magnitudes for Nahal Arava during that interval. This study indicates that in unfavorable areas the combination of hydrology, fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning.  相似文献   

东亚夏季风指数的年际变化与东亚大气环流   总被引：66，自引：9，他引：66  

张庆云  陶诗言  陈烈庭 《气象学报》2003,61(5):559-569

文中从夏季东亚热带、副热带环流系统特点出发 ,定义了能较好表征东亚夏季风环流年际变化的特征指数 ,并分析了东亚夏季风指数的年际变化与东亚大气环流及夏季中国东部降水的关系。文中定义的东亚夏季风指数既反映了夏季东亚大气环流风场的变化特征 ,也较好地反映了夏季中国东部降水的年际变化特征。此外 ,还探讨了东亚夏季风指数变化的先兆信号  相似文献   

关于创建川滇水库地震监测预报研究实验场的建议     

牟雅元 《地震地磁观测与研究》2005,26(5):39-45

川滇两省水能资源开发量位居全国前茅,尤其是川滇交界区域的雅砻江、大渡河、金沙江流域的水能资源富甲全国,在西部大开发中的战略地位极其重要,国家即将在此建成一个位于全球破坏性地震多发区域的巨型水库密集区。具有全球难寻的监测、预报、研究水库地震的资源优势。建议用完全开放的创新思维,在此区域创建水库地震监测预报研究实验场,具有重要的防震减灾现实意义和历史意义。  相似文献   

海河流域地下水生态水位研究     

张鑫  盖美 《地质灾害与环境保护》2005,16(1):85-88

针对海河流域的生态环境问题,提出海河流域地下水生态水位的概念。本文就山前平原区、中部平原区和东部滨海平原区地下水的不同特点,开发和利用现状的不同,分别提出了海河流域各地区深层和浅层的地下水生态水位,并根据海河流域地下水位现状,提出保持或恢复地下水生态水位的措施。  相似文献