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11.
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 Hs>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max Hs: 8.4 m) and the second on 20–22 February 2004 (max Hs: 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
12.
M.I. Rosi S. Puig M.I. Cona F. Videla E. Méndez V.G. Roig 《Journal of Arid Environments》2009,73(3):273-279
Overgrazing by livestock has caused desertification in the Monte, where ctenomyids and livestock share grasses as main food items. The diet of Ctenomys eremophilus, above-ground food availability and changes related to cattle grazing are analyzed in the arid plain of Mendoza, Argentina. The most available categories were grasses, followed by low shrubs and tall shrubs. Tuco-tucos showed dietary generalism, ate mainly above-ground plant parts, preferred grasses and avoided shrubs at both grazed and ungrazed sites. Plant cover, grass diversity and availability decreased under livestock grazing, which was reflected in the diet by a lower percentage of grasses, a shift toward low shrubs and higher number of frequently used resources. Tuco-tucos in the grazed paddock compensated for lower consumption of vegetative plant parts by increasing the use of Prosopis flexuosa pods stored inside burrows. Moreover, greater dietary variation among individuals suggests foraging restricted to the items closest to burrow holes. These feeding tactics would allow them to reduce above-ground foraging as a response to high raptor predation risk due to increased bare soil. The plant recovery detected during the rest period, favoured by moderate stocking rate and rotational grazing system, would allow coexistence of tuco-tucos and cattle. 相似文献
13.
F. Pags J. Martín A. Palanques P. Puig J.-M. Gili 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2170-2180
One hundred and fifty specimens of the elasipod holothurian Penilpidia ludwigi (von Marenzeller, 1893) were collected in sediment traps moored near the seabed in the La Fonera Canyon (Catalan Sea, north-western Mediterranean) and on the adjacent continental slope. These provide the third record of this apparently endemic Mediterranean species and the first record from the western Mediterranean. This was the only holothurian species trapped and the most abundant macroscopic organism found in the traps between 1200 and 1700 m depth over the whole sampling period (March–November 2001). It was particularly abundant in spring during the main flux of organic particles in the canyon. This coupling suggests that Penilpidia may aggregate at the seafloor during these events, making food availability a plausible explanation of the seasonal occurrence. Lateral transport of material re-suspended locally or up-canyon by near bottom currents appear to be the mechanism behind this uncommon occurrence, although in situ observations have recently been made on the swimming capability of this holothurian. The occurrence of benthic organisms in sediment traps set close to the seabed can provide information on bathyal benthic and benthopelagic populations. 相似文献
14.
Ludovic Puig Göran Pilbratt Astrid Heske Isabel Escudero Pierre-Elie Crouzet Bram de Vogeleer Kate Symonds Ralf Kohley Pierre Drossart Paul Eccleston Paul Hartogh Jeremy Leconte Giusi Micela Marc Ollivier Giovanna Tinetti Diego Turrini Bart Vandenbussche Paulina Wolkenberg 《Experimental Astronomy》2018,46(1):211-239
ARIEL, the Atmospheric Remote sensing Infrared Exoplanet Large survey, is one of the three M-class mission candidates competing for the M4 launch slot within the Cosmic Vision science programme of the European Space Agency (ESA). As such, ARIEL has been the subject of a Phase A study that involved European industry, research institutes and universities from ESA member states. This study is now completed and the M4 down-selection is expected to be concluded in November 2017. ARIEL is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. ARIEL targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to warm zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own Solar System in the context of other planetary systems in the Milky Way. A technical and programmatic review of the ARIEL mission was performed between February and May 2017, with the objective of assessing the readiness of the mission to progress to the Phase B1 study. No critical issues were identified and the mission was deemed technically feasible within the M4 programmatic boundary conditions. In this paper we give an overview of the final mission concept for ARIEL as of the end of the Phase A study, from scientific, technical and operational perspectives. 相似文献
15.
Study of the total lightning activity in a hailstorm 总被引：1，自引：0，他引：1
Joan Montany Serge Soula Nicolau Pineda Oscar van der Velde Pere Clapers Glria Sol Joan Bech D. Romero 《Atmospheric Research》2009,91(2-4):430-437
A thunderstorm that developed over northeastern Spain on 16 June 2006 is analyzed. This severe thunderstorm produced hailstones as large as 40 mm and had a lifetime of 3 h and 30 min. Radar cross-sections show strong vertical development with cloud echo tops reaching an altitude of 13 km. The specific characteristics of the lightning activity of this storm were: (i) a large amount (81%) of negative cloud-to-ground (−CG) flashes with very low peak currents (< 10 kA in absolute value), (ii) a very large proportion of intra-cloud (IC) flashes with an IC/CG ratio reaching about 400, (iii) a large number of “short” IC flashes (with only 1-VHF source according to SAFIR detection), (iv) a large increase of the −CG flash rate and of the CG proportion near the end of the storm. The rate of −CG flashes with a low peak current were observed to evolve similarly to the rates of IC flashes. Most of them have been assumed to be IC flashes misclassified by the Spanish Lightning Detection Network (SLDN). They have been filtered as it is usually done for misclassified +CG flashes. After this filtering, CG flash rates remained very low (< 1 min− 1) with +CG flashes sometimes dominant. All the particular lightning activity characteristics similar to those observed in the Severe Thunderstorm Electrification and Precipitation Study (STEPS) campaigns support the hypothesis that this thunderstorm could have had an inverted-polarity or complex charge structure. The maximum IC flash rate (67 min− 1) peaked 24 min before the presence of reflectivity higher than 60 dBZ. The IC activity abruptly decreased during the period when reflectivity was dramatically increasing. The time of maximum reflectivity observed by radar was consistent with the times of reported hail at the ground. 相似文献
16.
Aníbal Ojeda Kuvvet Atakan Eullia Masana Pere Santanach María-Jos Jimnez Mariano García-Fernndez 《Soil Dynamics and Earthquake Engineering》2002,22(9-12):911-916
In this study, the influence of paleoseismic and geologic data in the seismic hazard estimation for the Catalan coastal ranges is analysed. We computed the probabilistic seismic hazard using area seismic sources with a Poissonian assumption for the earthquake occurrence. For the computations, a previously published attenuation relationship based on European strong motion data was applied. The resulting hazard estimates show similarities to the previous assessments in the region. These results were then used as a reference for comparison with other new models. In order to analyse the influence of the paleoseismic data three different models were tested. Since the number of faults that are investigated in detail are few, the same area sources that were used in the Poissonian assumption were kept in all three new models. In addition, the new paleoseismic data with faults expressed as line sources were used. In this case, a cyclic earthquake occurrence was assumed. The three models were based on the paleoseismic data with different assumptions on the time elapsed since last event. The time elapsed was set to 0, 10 and 85% of the recurrence interval in each model. The results are presented as maps showing the difference between the three models and the reference model with the Poissonian assumption. The results are given in horizontal peak ground acceleration contour maps for different return periods, also taking into account large return periods as high as 25,000 years. This is done to demonstrate the effect of large recurrence intervals found for some of the active faults. In general, we observe that for short return periods (<1000 years), the Poissonian assumption of earthquake occurrence is probably sufficient and provides a robust estimate of the hazard. However, for longer return periods (>5000 years) the effects of the paleoseismic data become increasingly significant. In order to estimate the true seismic hazard potential of this apparently low seismicity area, long-term behaviour of the possible active faults in the region needs to be investigated systematically. 相似文献
17.
J. Aguzzi P. Puig J.B. Company 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(3):366-373
Data on biological rhythms of the Norway lobster Nephrops norvegicus (L.) are compared with new findings on inertial currents, a non-photic geophysical hydrodynamic fluctuation. Laboratory experiments on animal endogenous cardiac activity and locomotor rhythms using individuals from the middle slope (400–600 m depth) of the Mediterranean Sea revealed a consistent proportion of ultradian 18-h animals (20.6% and 12.0% of the studied cases for cardiac and locomotor tests, respectively). This characteristic, not reported in similar experiments with individuals from shallower depths (20–200 m) in the Atlantic Ocean, was initially considered meaningless from an ecological point of view. However, a close comparison with in situ oceanographic measurements over 1 year revealed a clear relationship between inertial current fluctuations and the observed 18-h behavioural and physiological rhythms. We propose a novel scenario involving potential non-photic (i.e. hydrodynamic) modulation of Nephrops biorhythms, and suggest that this may provide a paradigm for other benthic species in deep-water areas. 相似文献
18.
Delineating coastal groundwater discharge processes in a wetland area by means of electrical resistivity imaging, 224Ra and 222Rn 
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下载免费PDF全文 Mario Zarroca Rogelio Linares Valentí Rodellas Jordi Garcia‐Orellana Carles Roqué Joan Bach Pere Masqué 《水文研究》2014,28(4):2382-2395
Coastal groundwater discharge (CGD) plays an important role in coastal hydrogeological systems as they are a water resource that needs to be managed, particularly in wetland areas. Despite its importance, identifying and monitoring CGD often presents physical and logistical constraints, restraining the application of more traditional submarine groundwater discharge surveying techniques. Here we investigate the capability of electrical resistivity imaging (ERI) in the Peníscola wetland (Mediterranean coast, Spain). ERI surveying made it possible to identify and delineate an ascending regional groundwater flow of thermal and Ra‐enriched groundwater converging with local flows and seawater intrusion. The continuous inputs of Ra‐rich groundwater have induced high activities of Ra isotopes and 222Rn into the marsh area, becoming among the highest previously reported in wetlands and coastal lagoons. Geoelectrical imaging enabled inferring focused upward discharging areas, leaking from the aquifer roof through a confining unit and culminating as spring pools nourishing the wetland system. Forward modelling over idealized subsurface configurations, borehole datasets, potentiometric records from standpipe piezometers, petrophysical analysis, and four natural and independent tracers (224Ra, 222Rn, temperature and salinity) permitted assessing the geoelectrical model and a derived hydrogeological pattern. The research highlights the potential of ERI to improve hydrogeological characterization of subsurface processes in complex contexts, with different converging flows. Additionally, a hydrogeological conceptual model for a groundwater‐fed coastal wetland was proposed, based on the integration of surveying datasets. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
Pere Blay 《Astrophysics and Space Science》2011,335(1):137-140
High Mass X-Ray Binary systems (HMXRB) are composed by a compact object orbiting around a OB massive star. The mass transfer
which takes place from the massive star onto its compact companion is the responsible of the emission of high energy photons
(X-rays) observed in these systems (to which they owe the name of their class). The presence of a compact object must exert
a clear influence in the outer envelopes of the massive star and, thus, must modify the formation and evolution of its stellar
wind. Tidal interactions, mass capture and high energy radiation heating and pressure are among the possible ways in which
the compact companion and the X-ray emission will influence the stellar wind of the massive counterpart. The status of the
observations of such systems from previous UV missions will be reviewed, and perspectives for the incoming WSO-UV space mission
will be reported. 相似文献
20.
Javier Graciá-Carpio Santiago García-Burillo Pere Planesas 《Astrophysics and Space Science》2008,313(1-3):331-335
The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for
the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation
and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes
involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being
discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample
of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO+, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In
this paper we present the results of our HCO+ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely
questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies. 相似文献