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51.
Nicolas Navarro Christophe Lécuyer Sophie Montuire Cyril Langlois 《Quaternary Research》2004,62(2):172-182
Oxygen isotope compositions of biogenic phosphates from mammals are widely used as proxies of the isotopic compositions of meteoric waters that are roughly linearly related to the air temperature at high- and mid-latitudes. An oxygen isotope fractionation equation was determined by using present-day European arvicoline (rodents) tooth phosphate: δ18Op = 20.98(±0.59) + 0.572(±0.065) δ18Ow. This fractionation equation was applied to the Late Pleistocene karstic sequence of Gigny, French Jura. Comparison between the oxygen isotope compositions of arvicoline tooth phosphate and Greenland ice core records suggests to reconsider the previously established hypothetical chronology of the sequence. According to the δ18O value of meteoric water-mean air temperature relationships, the δ18O value of arvicoline teeth records variations in mean air temperatures that range from 0° to 15°C. 相似文献
52.
53.
Sophie Houzet 《GeoJournal》2007,68(1):5-17
How does the organization of space interfere in the numerical development of territories? Our hypothesis is that information and communication technologies (ICT) are organized by taking into account the existing spatial structures, compared to constraints of distance, spatial position and urban hierarchy. In the context of the liberalization of the sector of telecommunications, ICT spread according to an economic logic of profitability. The concern of network operators collides with the principle of territorial equity in planning policies. To understand the diffusion of ICT in France, a cartographic analysis of their distribution is proposed. It derives from the notion of networks at three levels: infrastructures, services and uses. The research takes into account the difference between regional configurations to identify the spatial factors of the digital divide. For each level, the diffusion of ICT follows a different logic, and characterizes territories with different orientations. Areas with a high density of population and activities are quickly equipped. The democratization of the use of the Internet, notably with the diffusion of public access to the Internet, is present to a greater degree in low-density areas. 相似文献
54.
Schooling behaviour and environmental forcing in relation to anchoveta distribution: An analysis across multiple spatial scales 总被引:3,自引:4,他引:3
Arnaud Bertrand Franois Gerlotto Sophie Bertrand Mariano Gutirrez Luis Alza Andres Chipollini Erich Díaz Pepe Espinoza Jesús Ledesma Roberto Quesqun Salvador Peraltilla Francisco Chavez 《Progress in Oceanography》2008,79(2-4):264
The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO2 sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales. 相似文献
55.
Patterns in the spatial distribution of Peruvian anchovy (Engraulis ringens) revealed by spatially explicit fishing data 总被引:1,自引:0,他引:1
Peruvian anchovy (Engraulis ringens) stock abundance is tightly driven by the high and unpredictable variability of the Humboldt Current Ecosystem. Management of the fishery therefore cannot rely on mid- or long-term management policy alone but needs to be adaptive at relatively short time scales. Regular acoustic surveys are performed on the stock at intervals of 2 to 4 times a year, but there is a need for more time continuous monitoring indicators to ensure that management can respond at suitable time scales. Existing literature suggests that spatially explicit data on the location of fishing activities could be used as a proxy for target stock distribution. Spatially explicit commercial fishing data could therefore guide adaptive management decisions at shorter time scales than is possible through scientific stock surveys. In this study we therefore aim to (1) estimate the position of fishing operations for the entire fleet of Peruvian anchovy purse–seiners using the Peruvian satellite vessel monitoring system (VMS), and (2) quantify the extent to which the distribution of purse–seine sets describes anchovy distribution. To estimate fishing set positions from vessel tracks derived from VMS data we developed a methodology based on artificial neural networks (ANN) trained on a sample of fishing trips with known fishing set positions (exact fishing positions are known for approximately 1.5% of the fleet from an at-sea observer program). The ANN correctly identified 83% of the real fishing sets and largely outperformed comparative linear models. This network is then used to forecast fishing operations for those trips where no observers were onboard. To quantify the extent to which fishing set distribution was correlated to stock distribution we compared three metrics describing features of the distributions (the mean distance to the coast, the total area of distribution, and a clustering index) for concomitant acoustic survey observations and fishing set positions identified from VMS. For two of these metrics (mean distance to the coast and clustering index), fishing and survey data were significantly correlated. We conclude that the location of purse–seine fishing sets yields significant and valuable information on the distribution of the Peruvian anchovy stock and ultimately on its vulnerability to the fishery. For example, a high concentration of sets in the near coastal zone could potentially be used as a warning signal of high levels of stock vulnerability and trigger appropriate management measures aimed at reducing fishing effort. 相似文献
56.
Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers 总被引:1,自引:1,他引:1
Sophie Bertrand Boris Dewitte Jorge Tam Erich Díaz Arnaud Bertrand 《Progress in Oceanography》2008,79(2-4):278
Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management. 相似文献
57.
Sorcha Ní Longphuirt Olivier Ragueneau Laurent Chauvaud Sophie Martin Frédéric Jean Gérard Thouzeau Aude Leynaert 《Estuarine, Coastal and Shelf Science》2009
In shallow coastal areas the amplitude and range of benthic silicic acid fluxes can have a significant influence on benthic–pelagic coupling and the functioning of the pelagic system. To explore the oscillation in fluxes over the diurnal cycle and in particular the influence of microphytobenthos (MPB), an experiment was carried out in a shallow subtidal site in the Bay of Brest (France). Benthic chambers were employed over a 48 h period to measure the variability in silicic acid and oxygen fluxes; MPB migration was investigated using a diving Pulse Amplitude Modulated (PAM) fluorometer and uptake rhythms of silicic acid by natural MPB populations were measured using the 32Si isotope. It was discovered that silicic acid fluxes fluctuated greatly throughout the diurnal period resulting in an oscillation in the availability of this nutrient for phytoplankton communities. The uptake of silicic acid by the MPB was quantified for the first time and highlighted a 2-fold increase in the demand from night to afternoon periods. The combined silicic acid uptake and the concentration of cells at the sediment–water interface, forming a dense biofilm of MPB, were postulated to be the main processes reducing effluxes at midday. Our work highlighted the many processes which influence silicic acid effluxes in shallow coastal areas and the possible interaction between uptake and dissolution processes. The variations in benthic fluxes over the diurnal period were comparable to observations reported at the seasonal scale. Therefore, up-scaling hourly flux observations to daily and annual estimates should be undertaken with caution. Further we suggest that the main processes influencing flux oscillations over the diurnal period should be considered when planning sampling strategies and extrapolating to larger time scales. 相似文献
58.
Aur��lien Bideaud Benoit Belier Alain Benoit Laurent Berg�� Philippe Camus Sophie Collin Louis Dumoulin Christian Hoffmann Stefanos Marnieros Alessandro Monfardini 《Experimental Astronomy》2011,32(2):179-191
Microbolometers are at present the most sensitive detectors for mm and sub-mm Astronomy. They are in use in most of the present instruments in that bandwidth. We have developed filled arrays of NbSi-based planar antenna coupled microbolometers. The fabrication details are given, together with characterization of the NbSi thermometers and optical results. The optical performances are potentially good for ground-based mm-wave astronomy applications, while the overall detectors performances are limited by low-frequency excess noise in the thermometric NbSi high-impedance sensors (Anderson insulator). 相似文献
59.
60.
Aude Lemonsu Sophie Bastin Valéry Masson Philippe Drobinski 《Boundary-Layer Meteorology》2006,118(3):477-501
During the UBL-ESCOMPTE program (June–July 2001), intensive observations were performed in Marseille (France). In particular, a Doppler lidar, located in the north of the city, provided radial velocity measurements on a 6-km radius area in the lowest 3 km of the troposphere. Thus, it is well adapted to document the vertical structure of the atmosphere above complex terrain, notably in Marseille, which is bordered by the Mediterranean sea and framed by numerous massifs. The present study focuses on the last day of the intensive observation period 2 (26 June 2001), which is characterized by a weak synoptic pressure gradient favouring the development of thermal circulations. Under such conditions, a complex stratification of the atmosphere is observed. Three-dimensional numerical simulations, with the Méso-NH atmospheric model including the town energy balance (TEB) urban parameterization, are conducted over south-eastern France. A complete evaluation of the model outputs was already performed at both regional and city scales. Here, the 250-m resolution outputs describing the vertical structure of the atmosphere above the Marseille area are compared to the Doppler lidar data, for which the spatial resolution is comparable. This joint analysis underscores the consistency between the atmospheric boundary layer (ABL) observed by the Doppler lidar and that modelled by Méso-NH. The observations and simulations reveal the presence of a shallow sea breeze (SSB) superimposed on a deep sea breeze (DSB) above Marseille during daytime. Because of the step-like shape of the Marseille coastline, the SSB is organized in two branches of different directions, which converge above the city centre. The analysis of the 250-m wind fields shows evidence of the role of the local topography on the local dynamics. Indeed, the topography tends to reinforce the SSB while it weakens the DSB. The ABL is directly affected by the different sea-breeze circulations, while the urban effects appear to be negligible. 相似文献