Particle‐size evidence of barrier estuary regime as a new proxy for ENSO climate variability          下载免费PDF全文

David W. Clarke  John F. Boyle  Andrew J. Plater 《地球表面变化过程与地形》2017,42(10):1520-1534

We investigate a new proxy for ENSO climate variability based on particle‐size data from long‐term, coastal sediment records preserved in a barrier estuary setting. Corresponding ~4–8 year periodicities identified from Wavelet analysis of particle‐size data from Pescadero Marsh in Central Coast California and rainfall data from San Francisco reflect established ENSO periodicity, as further evidenced in the Multivariate ENSO Index (MEI), and thus confirms an important ENSO control on both precipitation and barrier regime variability. Despite the fact that barrier estuary mean particle size is influenced by coastal erosion, precipitation and streamflow, balanced against barrier morphology and volume, it is encouraging that considerable correspondence can also be observed in the time series of MEI, regional rainfall and site‐based mean particle size over the period 1871–2008. This correspondence is, however, weakened after c.1970 by temporal variation in sedimentation rate and event‐based deposition. These confounding effects are more likely when: (i) accommodation space may be a limiting factor; and (ii) particularly strong El Niños, e.g. 1982/1983 and 1997/1998, deposit discrete >cm‐thick units during winter storms. The efficacy of the sediment record of climate variability appears not to be compromised by location within the back‐barrier setting, but it is limited to those El Niños that lead to barrier breakdown. For wider application of this particle size index of ENSO variability, it is important to establish a well‐resolved chronology and to sample the record at the appropriate interval to characterize deposition at a sub‐annual scale. Further, the sample site must be selected to limit the influence of decreasing accommodation space through time (infilling) and event‐based deposition. It is concluded that particle‐size data from back‐barrier sediment records have proven potential for preserving evidence of sub‐decadal climate variability, allowing researchers to explore temporal and spatial patterns in phenomena such as ENSO. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

东北冷涡对海河流域初夏降水异常的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

何丽烨  马宁  郭军 《地球物理学报》2017,60(10):3745-3752

东北冷涡是东亚中高纬度地区的重要天气系统,其频繁活动可能导致显著的气候效应,不仅对东北局地,而且对海河流域地区初夏降水产生影响.本文利用海河流域34个地面气象台站逐日降水资料以及NCEP/NCAR再分析资料,对东北冷涡与海河流域初夏降水的关系进行研究,结果表明:初夏东北冷涡活动与海河流域降水存在显著的相关关系,对其空间分布亦有重要影响.当东北冷涡活动偏多(少)时,海河流域北部地区(尤其是海河下游)初夏降水可能偏多(少),对应时间系数为正(负)时海河流域初夏降水EOF第二模态北多(少)南少(多)的空间分布.在东北冷涡活动偏多年,东北冷涡引导北方"干冷"空气南下推进至海河流域北部,伴随该地区源自西风带水汽输送和水汽辐合的增强,形成了"上干下湿"的不稳定层结,在上升运动的触发下,导致海河流域北部初夏降水偏多;而东北冷涡活动偏少年情况正好相反.东北冷涡活动为海河流域尤其是海河下游地区初夏降水预测提供了具有参考意义的结果,其活动指数与海河下游初夏降水距平的符号一致率在近30年高达83%.  相似文献   

A Detailed Analysis of Sediment Particle Sizes and Clogging in Permeable Pavements     

《洁净——土壤、空气、水》2017,45(4)

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地下核磁共振小尺寸线圈设计和实验   总被引：1，自引：1，他引：0       下载免费PDF全文

林君  张健  易晓峰 《地球物理学报》2017,60(11):4184-4193

很多国家在进行隧道挖掘、地下矿体开采时,经常会遇到突水涌泥事故.核磁共振方法(Magnetic Resonance Sounding,MRS)作为目前唯一一种直接找水的地球物理技术,在探测诱发灾害的水体方面具有明显的优势.本文首先给出了多匝分离式线圈的MRS信号响应和核函数的计算公式,分析了线圈的匝数、边长和含水层位置对MRS信号响应的影响.分析表明,在限定空间内,利用多匝分离式线圈的设计方法可以提高小尺寸线圈的探测能力.同时,对高匝数线圈给探测系统带来的不利因素进行了分析和改进.最后,为了验证本研究所采用的方法,利用6 m边长的方形线圈和改进型MRS探测系统在中国温州一处在建隧道内的地下场地进行实地探测,探测结果与瞬变电磁方法结果对比表明,6 m边长的方形线圈可以对地下30 m内的含水层进行有效探测.  相似文献   

Facies analysis of the Middle and Late Quaternary sediment infill of the northern Weihe Basin,Central China          下载免费PDF全文

Daniël S. Rits  Maarten A. Prins  Simon R. Troelstra  Ronald T. van Balen  Yan Zheng  Christiaan J. Beets  Bin Wang  Xiaoqiang Li  Jie Zhou  Hongbo Zheng 《第四纪科学杂志》2016,31(2):152-165

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东海内陆架EC2005孔沉积物粒度分形特征   总被引：1，自引：0，他引：1       下载免费PDF全文

徐方建  李安春  李铁刚  陈世悦  邱隆伟  操应长  林承焰 《地质学报》2011,85(6):1038-1044

对位于浙-闽沿岸泥质带的EC2005孔沉积物粒度分形特征以及与平均粒径和分选系数的关系进行了探讨.EC2005孔沉积物粒度在累积含量5%～95%的无标度区间内,统计自相似程度高,具有分形特征.沉积物平均粒径与分维值既存在正相关,也有负相关关系.二者正、负相关关系的分界点表现为平均粒径7.0φ左右,＜7.0φ时,平均粒径...  相似文献   

巴丹吉林沙漠高大沙山粒度组成及其意义     

赵景波  张冲  董治宝  邵天杰  李恩菊 《地质学报》2011,85(8):1389-1398

选取巴丹吉林沙漠东南部全球高差最大(约420m)的诺尔图湖东大沙山和较高的苏木巴润吉林湖西大沙山(高差约400m),对其迎风坡沉积物进行系统采样分析,讨论了高大沙山迎风坡沉积物粒度成分特点、变化规律、原因及其活动性.结果表明,全球高差最大的诺尔图东沙山和苏木巴润吉林湖西沙山迎风坡沉积物具有双层结构,表层沉积物的粒度组成...  相似文献   

Linking invertebrate burrow distributions (neoichnology) to physicochemical stresses on a sandy tidal flat: implications for the rock record   总被引：1，自引：0，他引：1  

SHAHIN E. DASHTGARD 《Sedimentology》2011,58(6):1303-1325

Invertebrate burrow distributions (neoichnology) across a modern tidal flat are presented as an analogue for interpreting the ichnology of palaeo‐tidal‐flat successions. Burrow distributions are linked to physical and chemical (physicochemical) stresses to establish the main controls on the distribution of biosedimentary structures. Across the tidal flat, there is clear heterogeneity in both the diversity of traces and the intensity of burrowing. This heterogeneity reflects a myriad of physicochemical stresses, with the sedimentation rate dominating burrow distributions. Across all substrates, the total area occupied by organisms rarely exceeds 3% of the tidal‐flat surface, and is commonly <1%; this equates to a bioturbation index value of one. To reach bioturbation index values of two to six, sediments must be available to biogenic reworking and/or recolonization. With an increasing sedimentation rate, substrates are rapidly buried and re‐exposed, which limits the time when a substrate is available to colonization. For palaeo‐ichnological studies, this research presents several key results. (i) Burrow cross‐cutting relationships in tidal‐flat successions commonly reflect natural heterogeneities in the areal distribution of infaunal communities, rather than infaunal tiering. (ii) Ichnofabric analysis of palaeo‐tidal flats with a high sedimentation rate would yield fabrics that reflect heterogeneities in the areal distribution of infaunal communities rather than variability in the physicochemical stresses of the environment. (iii) The composite trace‐fossil assemblage of tidal flats cannot be attributed to a single ichnofacies, but instead comprises elements typical of multiple ichnofacies. (iv) The main controls on trace assemblages across tidal flats in fully marine settings are sedimentological and include the sedimentation rate and, to a lesser extent, grain size.  相似文献   

Large hatchling size in Cretaceous nautiloids persists across the end-Cretaceous mass extinction: New data of Hercoglossidae hatchlings     

Ryoji Wani  Ken’ichi KuriharaKrishnan Ayyasami 《Cretaceous Research》2011,32(5):618-622

The hatchling sizes of the Cretaceous nautiloids (Hercoglossa forbesianus and Cimomia angustus; Hercoglossidae) are reported here for the first time as ranging between 20.4-22.2 mm in diameter. These new data for Hercoglossidae and the previously reported data for Nautilidae and Cymatoceratidae suggest that all Cretaceous nautiloids had large hatchlings irrespective of their taxonomy relative to those in ammonoids. Based on the relationship between hatching events and the nepionic constriction in modern nautili, the hatchling size of nautiloids can be recognized by the constriction on the shell surface of the innermost whorl. The range of hatchling diameter in all Cretaceous nautiloids (9-35 mm) is comparable to those of modern nautili (20-32 mm), although the Cretaceous nautiloids are characterized by a wider range with the smaller minimum diameter. The large hatchling size in Cretaceous nautiloids stands in marked contrast to those in ammonoids, which had much smaller hatchling size (mostly <2 mm in diameter) and became extinct at the end of the Cretaceous. Such distinct differences in reproductive strategy (i.e., hatchling and egg sizes) suggest that these differences may have played a significant role in the fate of ammonoids and nautiloids through the K/T mass extinction, as previously hypothesized by several paleontologists.  相似文献   

沉积物粒度分析方法的比较   总被引：5，自引：0，他引：5  

冉敬  杜谷  潘忠习 《岩矿测试》2011,30(6):669-676

近年来激光粒度分析法在沉积物粒度分析方面的应用得到了进一步扩展。本文利用美国麦克奇公司生产的S3500型激光粒度分析仪开展沉积物粒度分析方法实验,研究表明:S3500型仪器较优的样品用量约为0.2 g;稀释过程会影响样品的粒度分布;样品分取方式会带来不同的随机误差。与薄片图像法和筛析法两种传统粒度分析方法获得的粒度分布参数比较表明:激光法测得的平均粒径较薄片图像法和筛析法偏细;激光法和筛析法的峰度相关性较好。采用Malvern 2000和Micro S3500两种激光粒度分析仪测量结果的比较表明:Malvern 2000测得的平均粒径较Micro S3500测得的平均粒径偏细,但二者的相关性很好(r=0.9574),研究认为这两种粒度仪的测试结果会给岩石粒度定名带来差异。由于各种粒度分析方法存在差异和局限性,在实际工作中粒度分析应尽可能建立在同一测量体系上,以便资料对比。  相似文献