Storm-driven shelf-to-canyon suspended sediment transport at the southwestern Gulf of Lions     

A. Palanques  J. Guillén  P. Puig  X. Durrieu de Madron 《Continental Shelf Research》2008

Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves H_s>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H_s: 8.4 m) and the second on 20–22 February 2004 (max H_s: 7 m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events.  相似文献   

Macroinvertebrate patterns along environmental gradients and hydrological connectivity within a regulated river-floodplain     

Belinda Gallardo  Mercedes García  Álvaro Cabezas  Eduardo González  María González  Cecilia Ciancarelli  Francisco A. Comín 《Aquatic Sciences - Research Across Boundaries》2008,70(3):248-258

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Electrical structure of the upper mantle beneath Central Europe: Results of the CEMES project     

Vladimir Yu. Semenov  Josef Pek  Antal Ádám  Waldemar Jóźwiak  Boris Ladanyvskyy  Igor M. Logvinov  Pavel Pushkarev  Jan Vozar 《Acta Geophysica》2008,56(4):957-981

In the years 2001–2003, we accomplished the experimental phase of the project CEMES by collecting long-period magnetotelluric data at positions of eleven permanent geomagnetic observatories situated within few hundreds kilometers along the south-west margin of the East European Craton. Five teams were engaged in estimating independently the magnetotelluric responses by using different data processing procedures. The conductance distributions at the depths of the upper mantle have been derived individually beneath each observatory. By averaging the individual cross-sections, we have designed the final model of the geoelectrical structure of the upper mantle beneath the CEMES region. The results indicate systematic trends in the deep electrical structure of the two European tectonic plates and give evidence that the electrical structure of the upper mantle differs between the East European Craton and the Phanerozoic plate of west Europe, with a separating transition zone that generally coincides with the Trans-European Suture Zone.  相似文献   

Arguments for ionic nature of the Carpathian electric conductivity anomaly   总被引：1，自引：0，他引：1  

Jerzy Jankowski  Waldemar Jóźwiak  Jan Vozár 《Acta Geophysica》2008,56(2):455-465

This publication is a contribution to discussion on the geometry and petrography of the rock complex responsible for the Carpathian conductivity anomaly. We analysed arguments showing that this anomaly is caused by induction in the sedimentary basin, and make a critical review of various data to find out whether the good conductivity is connected with a rock complex containing graphite or mineralized water. We conclude that a more likely mechanism is the ionic one, i.e., the existence of fluids, although a final decision can only be made on the basis of deep drillings.  相似文献   

Seed germination of wild,in situ-managed,and cultivated populations of columnar cacti in the Tehuacán-Cuicatlán Valley,Mexico     

S. Guillén  J. Benítez  M. Martínez-Ramos  A. Casas 《Journal of Arid Environments》2009,73(4-5):407-413

Seed germination was compared among wild, in situ-managed (wild plants let standing in areas cleared for agriculture), and cultivated populations of the columnar cacti Stenocereus pruinosus, Polaskia chichipe, Myrtillocactus schenckii, and Polaskia chende, species representing a gradient from higher to lower management intensity, respectively. We hypothesized that seeds from cultivated populations have higher water requirements to germinate than seeds of other populations, and that such difference is stronger in species more intensely managed. Germination was evaluated under water potential treatments at 0.0, ?0.2, and ?0.4 MPa. Interspecific differences were identified; germination rates markedly decreased in S. pruinosus and P. chichipe as water potential reduced. M. schenckii seeds germinated better at ?0.2 MPa, and seeds of P. chende in all treatments. Seed germination of wild and cultivated populations was similar in all cases and, therefore, at the population level domestication does not appear to have influenced variations in germination of the studied cacti species. However, experiments to test whether germination of seeds from plants with clear signs of domestication differs with seeds from other plants and their differential germination and seedling survival in wild, in situ-managed and cultivated environments could help to precise the influence of domestication on these plants.  相似文献   

Removal of Pilosocereus leucocephalus (Cactaceae,tribe Cereeae) seeds by ants and their potential role as primary seed dispersers     

M.A. Munguía-Rosas  M.E. Jácome-Flores  V.J. Sosa  L.M. Quiroz-Cerón 《Journal of Arid Environments》2009,73(4-5):578-581

Myrmecochory sensu stricto is uncommon in Neotropical forests. In these ecosystems the role of ants as secondary dispersers of non-myrmecochorous seeds is well known, however, the primary dispersal of this type of seed by ants has been poorly documented. Only a few anecdotal observations scattered throughout the literature report the removal of these seeds from fruit on the plant by ants. We show experimentally that ants are able to remove more pulp and seeds from fruit on the branches than do flying vertebrates in Pilosocereus leucocephalus, a columnar cactus bearing typically ornithochorous fruit. In addition, experiments emulating seed cleaning revealed that cleaned seeds germinate earlier. These results suggest a possible role of ants as primary cactus dispersers; one that requires more extensive research on seed fate and seedling establishment success.  相似文献   

The fissure swarm of the Askja volcanic system along the divergent plate boundary of N Iceland   总被引：1，自引：1，他引：0  

Ásta Rut Hjartardóttir  Páll Einarsson  Haraldur Sigurdsson 《Bulletin of Volcanology》2009,71(9):961-975

Divergent plate boundaries, such as the one crossing Iceland, are characterized by a high density of subparallel volcanic fissures and tectonic fractures, collectively termed rift zones, or fissure swarms when extending from a specific volcano. Volcanic fissures and tectonic fractures in the fissure swarms are formed during rifting events, when magma intrudes fractures to form dikes and even feeds fissure eruptions. We mapped volcanic fissures and tectonic fractures in a part of the divergent plate boundary in northern Iceland. The study area is ~1,800 km², located within and north of the Askja central volcano. The style of fractures changes with distance from Askja. Close to Askja the swarm is dominated by eruptive fissures. The proportion of tectonic fractures gets larger with distance from Askja. This may indicate that magma pressure is generally higher in dikes close to Askja than farther away from it. Volcanic fissures and tectonic fractures are either oriented away from or concentric with the 3–4 identified calderas in Askja. The average azimuth of fissures and fractures in the area deviates significantly from the azimuth perpendicular to the direction of plate velocity. As this deviation decreases gradually northward, we suggest that the effect of the triple junction of the North American, Eurasian and the Hreppar microplate is a likely cause for this deviation. Shallow, tectonic earthquakes in the vicinity of Askja are often located in a relatively unfractured area between the fissure swarms of Askja and Kverkfjöll. These earthquakes are associated with strike-slip faulting according to fault plane solutions. We suggest that the latest magma intrusions into either the Askja or the Kverkfjöll fissure swarms rotated the maximum stress axis from being vertical to horizontal, causing the formation of strike-slip faults instead of the dilatational fractures related to the fissure swarms. The activity in different parts of the Askja fissure swarm is uneven in time and switches between subswarms, as shown by a fissure swarm that is exposed in an early Holocene lava NW of Herðubreið but disappears under a younger (3500–4500 BP) lava flow. We suggest that the location of inflation centres in Askja central volcano controls into which part of the Askja fissure swarm a dike propagates. The size and amount of fractures in the Kollóttadyngja lava shield decrease with increasing elevation. We suggest that this occurred as the depth to the propagating dike(s) was greater under central Kollóttadyngja than under its flanks, due to topography.  相似文献   

Classification of seismic signals at Villarrica volcano (Chile) using neural networks and genetic algorithms     

Gloria Curilem  Jorge Vergara  Gustavo Fuentealba  Gonzalo Acuña  Max Chacón 《Journal of Volcanology and Geothermal Research》2009

Each volcano has its own unique seismic activity. The aim of this work is to construct a system able to classify seismic signals for the Villarrica volcano, one of the most active volcanoes in South America. Since seismic signals are the result of particular processes inside the volcano's structure, they can be used to forecast volcanic activity. This paper describes the different kinds of seismic signals recorded at the Villarrica volcano and their significance. Three kind of signals were considered as most representative of this volcano's activity: the long-period, the tremor, and the energetic tremor signals. A classifier is implemented to read the seismic registers at 30-second intervals, extract the most relevant features of each interval, and classify them into one of the three kinds of signals considered as most representative of this particular volcano. To do so, 1033 different kinds of 30-s signals were extracted and classified by a human expert. A feature extraction process was applied to obtain the main characteristics of each of them. This process was developed using criteria which have been shown by others to effectively classify seismic signals, based on the experience of a human expert. The classifier was implemented with a Multi-Layer Perceptron (MLP) artificial neural network whose architecture and training process were optimized by means of a genetic algorithm. This technique searched for the most adequate MLP configuration to improve the classification performance, optimizing the number of hidden neurons, the transfer functions of the neurons, and the training algorithm. The optimization process also performed a feature selection to reduce the number of signal features, optimizing the number of network inputs. The results show that the optimized classifier reaches more than 93% exactitude. identifying the signals of each kind. The amplitude of the signals is the most important feature for its classification, followed by its frequency content. The described methodology can be used to classify more seismic signals to improve the study of the activity of this volcano or to extend the study to other active volcanoes of the region.  相似文献   

Potential impact of climate change on aquatic insects: A sensitivity analysis for European caddisflies (Trichoptera) based on distribution patterns and ecological preferences   总被引：1，自引：1，他引：0  

Daniel Hering  Astrid Schmidt-Kloiber  John Murphy  Sofie Lücke  Carmen Zamora-Muñoz  Manuel Jesús López-Rodríguez  Thomas Huber  Wolfram Graf 《Aquatic Sciences - Research Across Boundaries》2009,71(1):3-14

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The life history of Serratella ignita (Poda, 1761) (Insecta: Ephemeroptera) in a temporary and permanent Mediterranean stream     

Manuel J. López-Rodríguez  J. Manuel Tierno de Figueroa  Javier Alba-Tercedor 《Aquatic Sciences - Research Across Boundaries》2009,71(2):179-188

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