Seston fatty acid composition and copepod RNA:DNA ratio with respect to the underwater light climate in fluvial Lac Saint-Pierre   总被引：1，自引：0，他引：1  

Julien Pommier  Jean-Jacques Frenette  Philippe Massicotte  Jean-Fran?ois Lapierre  Hélène Glémet 《Aquatic Sciences - Research Across Boundaries》2012,74(3):539-553

The relationship between the underwater light availability at different wavelengths (from 351 to 700?nm) and the fatty acid (FA) composition of seston, as well as the trophic transfer of fatty acids from producers to consumers and its influence on copepod growth condition, were investigated throughout fluvial Lac Saint-Pierre (Québec, Canada). Seston and zooplankton were collected at 11 sampling sites located within distinct water masses discriminated according to their underwater spectral characteristics. Diffuse light attenuation coefficients (K_d(??)) varied among sampling sites and wavelengths (??) and were negatively correlated to seston composition in some essential fatty acids. Particularly, the relationships between K_d(??) and the seston concentration in 20:5n3 and 22:6n3 differed and were wavelength dependent, being stronger for ?? close to the absorption maxima of chlorophyll a, suggesting a potential link with photosynthetic processes. The concentrations of 16:1n7, 18:3n3 and 20:5n3 in copepods were strongly correlated to those in the seston, which points towards the trophic transfer of these fatty acids between primary producers and herbivorous consumers. Moreover, the growth condition of copepods, as expressed by their RNA:DNA ratio, was correlated to the concentrations of 16:1n7, 18:3n3 and 20:5n3 in the seston and in copepods. Our field study sheds light on the potential importance, yet to be precised, of specific wavelengths as a driver of Lac Saint-Pierre??s productivity through their influence on fatty acids composition of seston and its nutritional quality for primary consumers.  相似文献   

Ocean response to strong precipitation events in the Gulf of Lions (northwestern Mediterranean Sea): a sensitivity study     

Cindy Lebeaupin Brossier  Karine Béranger  Philippe Drobinski 《Ocean Dynamics》2012,62(2):213-226

The Mediterranean Sea is a region of intense air–sea interactions, with in particular strong evaporation over sea which drives the thermohaline circulation. The Mediterranean region is also prone to strong precipitation events characterized by low spatial extent, short duration, and high temporal variability. The impacts of intense offshore precipitation over sea, in the Gulf of Lions which is a spot for winter deep convection, are investigated using four sensitivity simulations performed at mesoscale resolution with the eddy-resolving regional ocean model NEMO-MED12. We use various atmospheric fields to force NEMO-MED12, downscaled from reanalyses with the non-hydrostatic mesoscale Weather Research and Forecasting model but differing in space resolutions (20 and 6.7 km) or in time frequencies (daily and three-hourly). This numerical study evidences that immediate, intense, and rapid freshening occurs under strong precipitation events. The strong salinity anomaly induced extends horizontally (≃50 km) as vertically (down to 50 m) and persists several days after strong precipitation events. The change in the space resolution of the atmospheric forcing modifies the precipitating patterns and intensity, as well as the shape and the dynamics of the low-salinity layer formed are changed. With higher forcing frequency, shorter and heavier precipitation falls in the ocean in the center of the Gulf of Lions, and due to a stronger vertical shear and mixing, the low-salinity anomaly propagates deeper.  相似文献   

Erratum to: Lava discharge during Etna’s January 2011 fire fountain tracked using MSG-SEVIRI     

Mathieu Gouhier  Andrew Harris  Sonia Calvari  Philippe Labazuy  Yannick Guéhenneux  Franck Donnadieu  Sébastien Valade 《Bulletin of Volcanology》2012,74(5):1261-1261

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Temporal variability of suspended sediment sources in an alpine catchment combining river/rainfall monitoring and sediment fingerprinting     

Oldrich Navratil  Olivier Evrard  Michel Esteves  Cédric Legout  Sophie Ayrault  Julien Némery  Ainhoa Mate‐Marin  Mehdi Ahmadi  Irène Lefèvre  Alain Poirel  Philippe Bonté 《地球表面变化过程与地形》2012,37(8):828-846

Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905‐km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment. Sediment exports at the river catchment outlet (330 ± 100 t km^‐2 yr^‐1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra‐ and inter‐flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Preface     

Philippe Gourbesville 《Physics and Chemistry of the Earth》2008,33(5):277

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Inversion of a Lagrangian time domain random walk (TDRW) approach to one-dimensional transport by derivation of the analytical sensitivities to parameters     

Frederick Delay  Anne Kaczmaryk  Philippe Ackerer 《Advances in water resources》2008

Lagrangian approaches are well suited to transport in contrasted media but have been considered irrelevant when inversion is envisioned. The randomness of results for the same transport scenario adds to the rough evaluation by perturbation of the sensitivities, yielding an inaccurate search of parameters. It is shown here how a Time Domain Random Walk (TDRW) method can be inverted by deriving the sensitivities analytically. The calculations are very rapid and provide a precise evaluation of the descent directions followed by a Gauss–Newton optimizer. The method handles advection–dispersion + retention by matrix diffusion or sorption with first-order kinetics and proves its worth in all cases. Since analytical sensitivities are available, calculations are rigorous and allow discussing the inversion feasibility, the accuracy of the sought parameters, according to the predominant mechanism involved in the transport scenario.  相似文献   

The present-day atmosphere of Mars: Where does it come from?     

Cédric Gillmann  Philippe Lognonné  Eric Chassefière  Manuel Moreira 《Earth and Planetary Science Letters》2009,277(3-4):384-393

Recent observations and missions to Mars have provided us with new insight into the past habitability of Mars and its history. At the same time they have raised many questions on the planet evolution. We show that even with the few data available we can propose a scenario for the evolution of the Martian atmosphere in the last three billion years. Our model is obtained with a back integration of the Martian atmosphere, and takes into account the effects of volcanic degassing, which constitutes an input of volatiles, and atmospheric escape into space. We focus on CO₂, the predominant Martian atmospheric gas.Volcanic CO₂ degassing rates are obtained for different models of numerical model crust production rates [Breuer, D., Spohn, T. 2003. Early plate tectonics versus single-plate tectonics on Mars: Evidence from magnetic field history and crust evolution. J. Geophys. Res. - Planets, 108, E7, 5072, Breuer, D., Spohn, T., 2006. Viscosity of the Martian mantle and its initial temperature: Constraints from crust formation history and the evolution of the magnetic field. Planet. Space Sci. 54 (2006) 153–169; Manga, M., Wenzel, M., Zaranek, S.E., 2006. Mantle Plumes and Long-lived Volcanism on Mars as Result of a Layered Mantle. American Geophysical Union Fall Meeting 2006, Abstract #P31C-0149.] and constrained on observation. By estimating the volatile contents of the lavas, the amount of volatiles released in the atmosphere is estimated for different scenarios. Both non-thermal processes (related to the solar activity) and thermal processes are studied and non-thermal processes are incorporated in our modelling of the escape [Chassefière, E., Leblanc, F., Langlais, B., 2006, The combined effects of escape and magnetic field history at Mars. Planet. Space Sci. Volume 55, Issue 3, Pages 343–357.]. We used measurements from ASPERA and Mars Express and these models to estimate the amount of lost atmosphere.An evolution of the CO₂ pressure consistent with its present state is then obtained. A crustal production rate of at least 0.01 km³/year is needed for the atmosphere to be at steady state. Moreover, we show that for most of the scenarios a rapid loss of the primary (and primordial) atmosphere due to atmospheric escape is required in the first 2 Gyr in order to obtain the present-day atmosphere. When CO₂ concentration in the mantle is high enough (i.e. more than 800 ppm), our results imply that present-day atmosphere would have a volcanic origin and would have been created between 1 Gyr and 2 Gyr ago even for models with low volcanic activity. If the volcanic activity and the degassing are intense enough, then the atmosphere can even be entirely secondary and as young as 1 Gyr. However, with low activity and low CO₂ concentration (less than 600 ppm), the present-day atmosphere is likely to be for the major part primordial.  相似文献   

Field observations of an evolving rip current on a meso-macrotidal well-developed inner bar and rip morphology   总被引：1，自引：0，他引：1  

Nicolas Bruneau  Bruno Castelle  Philippe Bonneton  Rodrigo Pedreros  Rafael Almar  Natalie Bonneton  Patrice Bretel  Jean-Paul Parisot  Nadia Snchal 《Continental Shelf Research》2009,29(14):1650-1662

The Aquitanian Coast (France) is a high-energy meso-macrotidal environment exhibiting a highly variable double sandbar system. The inner and the outer bar generally exhibit a bar and rip morphology and persistent crescentic patterns, respectively. In June 2007, an intense five-day field experiment was carried out at Biscarrosse Beach. A large array of sensors was deployed on a well-developed southward-oriented bar and rip morphology. Daily topographic surveys were carried out together with video imaging to investigate beach morphodynamic evolution. During the experiment, offshore significant wave height ranged from 0.5 to 3 m, with a persistent shore-normal angle. This paper identifies two types of behavior of an observed rip current: (1) for low-energy waves, the rip current is active only between low and mid tide with maximum mean rip current velocity reaching 0.8 m/s for an offshore significant wave height (H_s) lower than 1 m; (2) for high-energy waves (H_s≈ 2.5–3 m), the rip current was active over the whole tide cycle with the presence of persistent intense offshore-directed flows between mid and high tide. For both low and high-energy waves, very low-frequency pulsations (15–30 min) of the mean currents are observed on both feeder and rip channels.A persistent slow shoreward migration of the sandbar was observed during the experiment while no significant alongshore migration of the system was measured. Onshore migration during the high-energy waves can be explained by different sediment transport processes such as flow velocity skewness, wave asymmetry or bed ventilation. High-frequency local measurements of the bed evolution show the presence of significant (in the order of 10 cm) fluctuations (in the order of 1 h). These fluctuations, observed for both low- and high-energy waves, are thought to be ripples and megaripples, respectively and may play an important but still poorly understood role in the larger scale morphodynamics. The present dataset improves the knowledge of rip dynamics as well as the morphological response of strongly alongshore non-uniform meso-macrotidal beaches.  相似文献   

Distributed hydrologic and hydraulic modelling with radar rainfall input: Reconstruction of the 8–9 September 2002 catastrophic flood event in the Gard region,France     

Laurent Bonnifait  Guy Delrieu  Matthieu Le Lay  Brice Boudevillain  Arielle Masson  Philippe Belleudy  Eric Gaume  Georges-Marie Saulnier 《Advances in water resources》2009

On 8–9 September 2002, an extreme rainfall event caused by a stationary mesoscale convective system (MCS) occurred in the Gard region, France. Distributed hydrologic and hydraulic modelling has been carried out to assess and compare the various sources of data collected operationally and during the post-event field surveys. Distributed hydrological modelling was performed with n-TOPMODELs and assessed for ungauged basins with the discharge estimates of the post-event surveys. A careful examination of the occurrence in time and space of the flash floods over the head watersheds indicates that flooding was controlled by the trajectory of the convective part of the MCS. Stationarity of the MCS over the Gardon watershed (1858 km² at Remoulins) for 28 h was responsible for the exceptional magnitude of the flood at this scale. The flood dynamics were characterized by an extensive inundation of the Gardonnenque plain upstream of the Gardon Gorges resulting in a significant peak flow reduction downstream. One-dimensional unsteady-flow hydraulic modelling was found to be required to reproduce these dynamics. Hydraulic modelling also proved to be potentially useful for the critical analysis and extrapolation of operational discharge rating curves.  相似文献   

The Planeterrella,a pedagogic experiment in planetology and plasma physics     

Jean Lilensten  Mathieu Barthélemy  Cyril Simon  Philippe Jeanjacquot  Guillaume Gronoff 《Acta Geophysica》2009,57(1):220-235

We present here a plasma physics experiment which makes it possible to simulate, in a naive yet useful way, the formation of polar lights. It involves shooting electrons at a magnetized sphere placed in a vacuum chamber. This experiment, inspired by K. Birkeland’s Terrella, built at the turn of 19th century, allows the visualization of very many geophysical and astrophysical situations. Although delicate, it is feasible at undergraduate level.  相似文献