Impacts of sea-level rise on deltas in the Gulf of Mexico and the Mediterranean: The importance of pulsing events to sustainability     

John W. Day  Didier Pont  Philippe F. Hensel  Carlès Ibañez 《Estuaries and Coasts》1995,18(4):636-647

In deltas, subsidence leads to a relative sea-level rise (RSLR) that is often much greater than eustatic rise alone. Because of high RSLR, deltaic wetlands will be affected early by an acceleration of eustatic sea-level rise. If there is sufficient vertical accretion, wetlands can continue to exist with RSLR; however, lack of sediment input eventually leads to excessive water logging and plant death. Areas with low tidal range, such as the Mediterranean and Gulf of Mexico, are especially vulnerable to rising water levels because the elevational growth range of coastal vegetation is related to tide range. Reduction of suspended sediments in rivers and prevention of wetland flooding by river dikes and impoundments have reduced sediment input to Mediterranean and Gulf of Mexico deltaic wetlands. This sediment deficit will become more important with an acceleration in sea-level rise from global warming. Most sediment input occurs during strong pulsing events such as river floods and storms, and management policies and decisions are especially designed to protect against such events. Management approaches must be reoriented to take advantage of pulsing events to nourish marsh surfaces with sediments. We hypothesize that deltas can be managed to withstand significant rates of sea-level rise by taking advantage of pulsing events leading to high sediment input, and that this type of management approach will enhance ecosystem functioning.  相似文献   

Atacamite formation by deep saline waters in copper deposits from the Atacama Desert,Chile: evidence from fluid inclusions,groundwater geochemistry,TEM, and <Superscript>36</Superscript>Cl data   总被引：2，自引：2，他引：0  

Martin Reich  Carlos Palacios  Miguel A. Parada  Udo Fehn  Eion M. Cameron  Matthew I. Leybourne  Alejandro Zúñiga 《Mineralium Deposita》2008,43(6):663-675

The presence of large amounts of atacamite in oxide zones from ore deposits in the Atacama Desert of northern Chile requires saline solutions for its formation and hyperarid climate conditions for its preservation. We investigated the nature and origin of atacamite-forming solutions by means of coupling groundwater geochemical analyses with fluid inclusion data, high-resolution mineralogical observations, and chlorine-36 (³⁶Cl) data in atacamite from the Mantos Blancos and Spence Cu deposits. In both deposits, the salinities of fluid inclusions in atacamite are comparable to those measured in saline groundwaters sampled from drill holes. The average salinity of fluid inclusions in atacamite for the Mantos Blancos and Spence deposits (~7–9 and 2–3 wt.% NaCl_eq, respectively) are strongly correlated to the salinities at which gypsum supersaturates from groundwaters in both deposits (total dissolved solids ~5–9 and 1–3 wt.% NaCl_eq, respectively). This correlation is confirmed by transmission electron microscopy observations of atacamite-bearing samples, revealing an intimate association between atacamite and gypsum that can be traced down to the nanometer scale. ³⁶Cl data in atacamite provide new lines of evidence concerning the origin and age of the saline waters that formed atacamite in various stratabound and porphyry Cu deposits from the Atacama Desert. All atacamite samples show very low ³⁶Cl-to-Cl ratios (11 × 10⁻¹⁵ to 28 × 10⁻¹⁵ at at⁻¹), comparable to previously reported ³⁶Cl-to-Cl ratios of deep formation waters and old groundwaters. In addition, ³⁶Cl-to-Cl ratios in atacamite correlate with U and Th concentration in the host rocks but are independent from distance to the ocean. This trend supports an interpretation of the low ³⁶Cl-to-Cl ratios in atacamite as representing subsurface production of fissiogenic ³⁶Cl in secular equilibrium with the solutions involved in atacamite formation. Therefore, ³⁶Cl in atacamite strongly suggest that the chlorine in saline waters related to atacamite formation is old (>1.5 Ma) but that atacamite formation occurred more recently (<1.5 Ma) than suggested in previous interpretations. Our data provide new constraints on the origin of atacamite in Cu deposits from the Atacama Desert and support the recent notion that the formation of atacamite in hyperarid climates such as the Atacama Desert is an ongoing process that has occurred intermittently since the onset of hyperaridity.  相似文献   

Updating channel morphology in digital elevation models: lahar assessment for Tenenepanco-Huiloac Gorge, Popocatépetl volcano, Mexico     

Esperanza Muñoz-Salinas  C. S. Renschler  D. Palacios  L. M. Namikawa 《Natural Hazards》2008,45(2):309-320

In contrast to dramatic flow regime changes by less frequent large-scale volcanic eruptions, those caused by more frequent small-scale processes in volcanic landscapes may also drastically change the direction and dynamics of flow in a drainage system formed solely by fluvial processes. During such periods of channel morphology change, it is necessary to frequently update channel flow parameters to assess preventive measures for civil protection purposes. Often aerial photography is impracticable, since parts of the channels are covered by dense vegetation, while total station and laser topographic surveys are often too slow and costly, particularly during a high frequency of events. This article introduces and validates a new methodology for updating the representation of channel morphology in Digital Elevation Models (DEM) used specifically for assessing the dangers of frequently occurring lahars along gorges in volcanic landscapes during eruptive and non-eruptive periods. The updating of channel cross-sections was achieved by inserting more detailed representative profiles of homogeneous channel sectors in DEMs derived from existing less detailed topographic maps. The channel profiles were surveyed along the thalweg in equidistant points according to Universal Transverse Mercator (UTM) (x,y) coordinates and elevation derived from the existing DEM. The proposed technique was applied at Tenenepanco-Huiloac Gorge on Popocatépetl volcano, Mexico, in an area affected by major lahars during the volcano’s most recent eruptive period from 1994 to 2005. The proposed method can reduce the cost and person-hours of a regular channel topographic survey dramatically and the enhanced DEM can determine volume parameters and flood zones associated with the 1 July 1997 and 21 January 2001 lahars, respectively. In addition, the updated DEM with better channel representation allowed a more realistic fluid flow and lahar simulation with the process-based TITAN2D model.  相似文献   

粤北下庄矿田晚白垩世辉绿玢岩的地球化学特征及其构造意义   总被引：4，自引：0，他引：4  

朱捌  凌洪飞  沈渭洲  陆建军  邓平  谭正中 《地质论评》2008,54(1):26-36

晚白垩世太平奄组辉绿玢岩位于粤北贵东复式岩体东部,呈NNE向展布。 它具有相对富硅(SiO2=5391% ~ 5603%)、富K(K2O=178 %~ 302%)、富集大离子亲石元素,Nb、Ta、Zr、Ti亏损明显,LREE富集(LREE/HREE=935 ~ 1024),基本无Eu异常(δEu=084 ~ 100), 低的εNd(91Ma)值(-58 ~ -98)、较高的［n(87Sr)/n(86Sr)］i值(070899 ~ 071525)和典型的Dupal异常铅等特征,这些明显的岛弧火山岩的地球化学特征与其所处的板内环境具有明显的不协调性。这种不协调性反映,在太平奄组辉绿玢岩形成之前的漫长时期内,由于古太平洋板块及其沉积物俯冲过程中产生的流体对上覆地幔楔的交代作用而形成具有岛弧火山岩特征的富集地幔源区。太平奄组辉绿玢岩正是在晚白垩世时期地壳伸展和岩石圈减薄的构造环境下,由这种具有EMⅠ和EMⅡ混合特征的富集地幔源区部分熔融形成的。  相似文献   

SHRIMP U–Pb zircon dating of anatexis in high-grade migmatite complexes of Central Spain: implications in the Hercynian evolution of Central Iberia     

Pedro Castiñeiras  Carlos Villaseca  Luis Barbero  Cristina Martín Romera 《International Journal of Earth Sciences》2008,97(1):35-50

U–Pb SHRIMP ages obtained in zircons from the Sotosalbos and Toledo anatectic complexes in Central Spain give new constraints to the evolution of the inner part of the Hercynian Iberian belt. Pre-Hercynian ages in zircons from the Sotosalbos complex (∼464 Ma) are well preserved and reveal that an age diversity of the Lower Paleozoic magmatism in the area exists, as previous data on westernmost orthogneisses yield significant older ages. Zircon ages in the pelite-derived granites from the Toledo complex also show an important Neoproterozoic age component which points to a metasedimentary protolith deposited maximally 560 Ma ago. Younger zircon populations in both complexes at ∼330 Ma in the Sotosalbos region and ∼317 Ma in the Toledo complex indicate an important diachronism between the anatectic processes in both areas but also that these processes are mainly unrelated to the generation of the later Hercynian granite batholith of Central Spain, which could be of deeper crustal derivation. In addition, as migmatization occurred late in the metamorphic cycle, after peak conditions were attained, the age of anatexis is younger than the age of the main Hercynian metamorphic event, which still is not well constrained. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

A continuous deployment-based approach for the collaborative creation,maintenance, testing and deployment of CityGML models     

Iñaki Prieto  Jose Luis Izkara  Rubén Béjar 《International journal of geographical information science》2018,32(2):282-301

Georeferenced 3D models are an increasingly common choice to store and display urban data in many application areas. CityGML is an open and standardized data model, and exchange format that provides common semantics for 3D city entities and their relations and one of the most common options for this kind of information. Currently, creating and maintaining CityGML models is costly and difficult. This is in part because both the creation of the geometries and the semantic annotation can be complex processes that require at least some manual work. In fact, many publicly available CityGML models have errors. This paper proposes a method to facilitate the regular maintenance of correct city models in CityGML. This method is based on the continuous deployment strategy and tools used in software development, but adapted to the problem of creating, maintaining and deploying CityGML models, even when several people are working on them at the same time. The method requires designing and implementing CityGML deployment pipelines. These pipelines are automatic implementations of the process of building, testing and deploying CityGML models. These pipelines must be run by the maintainers of the models when they make changes that are intended to be shared with others. The pipelines execute increasingly complex automatic tests in order to detect errors as soon as possible, and can even automate the deployment step, where the CityGML models are made available to their end users. In order to demonstrate the feasibility of this method, and as an example of its application, a CityGML deployment pipeline has been developed for an example scenario where three actors maintain the same city model. This scenario is representative of the kind of problems that this method intends to solve, and it is based on real work in progress. The main benefits of this method are the automation of model testing, every change to the model is tested in a repeatable way; the automation of the model deployment, every change to the model can reach its end users as fast as possible; the systematic approach to integrating changes made by different people working together on the models, including the possibility of keeping parallel versions with a common core; an automatic record of every change made to the models (who did what and when) and the possibility of undoing some of those changes at any time.  相似文献   

Impacts of the atmospheric apparent heat source over the Tibetan Plateau on summertime ozone vertical distributions over Lhasa          下载免费PDF全文

Wenjun Liang  Zhen Yang  Jiali Luo  Hongying Tian  Zhixuan Bai  Dan Li  Qian Li  Jinqiang Zhang  Haoyue Wang  Bian Ba  Yang Yang 《大气和海洋科学快报》2021,14(3):66-71

青藏高原(TP)是一个对气候变化敏感的地区,其上空的臭氧分布影响着青藏高原及其周边地区的大气环境,北半球夏季青藏高原上空臭氧柱总量相对较低的现象,及其时空变化受到广泛关注.本研究利用北半球夏季5年的拉萨上空臭氧的气球测量数据,研究高原上空大气视热源(Q1)对臭氧垂直分布的影响并探讨了该过程的机制.结果表明,当TP上空对流层整体的Q1相对较高时,拉萨上空对流层臭氧浓度下降.大气更强的上升运动伴随着TP主体区域上空的Q1的增大.因此,当夏季Q1较高时,由于近地表低浓度臭氧空气向上输送,拉萨上空的对流层臭氧浓度下降.  相似文献   

Self-organization maps (SOM) in the definition of a “transfer function” for a diatoms-based climate proxy     

Acevedo-Acosta  Juan David  Martínez-López  Aída  Morales-Acoltzi  Tomás  Albáñez-Lucero  Mirtha  Verdugo-Díaz  Gerardo 《Climate Dynamics》2021,56(1-2):423-437

Climate Dynamics - This study utilizes self-organizing maps (SOM) —a particular type of artificial neural network (ANN) — as a nonlinear analysis tool for identifying species that can...  相似文献   

Evidence for high velocity gas in giantHii regions     

J. M. Vilchez  C. Esteban  H. Castañeda  M. G. Edmunds 《Astrophysics and Space Science》1989,156(1-2):237-242

Spectroscopy of selected areas of the two GiantHii Regions (GHR) NGC 5471 and NGC 604 shows convincing evidence for the existence of ionised gas at high velocities (1000 km s^–1) from the analysis of the profile of the Balmer (in NGC 604) and the [Oiii] (in NGC 5471) lines. The association of these effects with the presence of WR clusters and possible SNR inside the complex are analysed and the results are compared with previous indications in the literature for 30 Dor (in front of R 136) as well as with recent evidence from high-dispersion spectroscopy for some GHRs in M101.  相似文献   

Mass outflow and its consequences in the circumnuclear zones of galaxies     

C. Muñoz-Tuñon  J. E. Beckman 《Astrophysics and Space Science》1988,147(1):173-187

The distribution of hydrogen gas, atomic plus molecular, in the discs of spiral galaxies, takes two characteristic extreme alternative forms. In one, the density peaks at the nucleus, and falls radially monotonically and roughly exponentially with radius. In the other there is a hole in the gas distribution in the circumnuclear region. In this paper we examine the distributions of gas, and the kinematics in the central zones of a number of spirals which have been observed both spectroscopically and with photometric mapping. We find in addition to a ring structure in the gas, there is often measurable expansion with higher radial velocities occurring near the nucleus. Associated with the more expanded of these ring structures there appear annuli of younger stars with enhanced metallicities; and inside the gaseous ring older, less metallic populations. A strong correlation exists between the absence of central gas and the size of the nuclear bulge of a galaxy: Sa's and Sb's have lower ratios of gas to stars than Sc's and Sd's. We show that radially progressive bursts of star formation can account for a wide range of these observed phenomena and could be related to the presence ofliners in the interstellar medium close to the nucleus. The energetics and dynamical balance within the burst are considered in terms of three sources of outflow: supernovae, stellar winds, and radiation from massive stars, with the probability that all these mechanisms contribute to the collective phenomenon.  相似文献