Applications of C and N stable isotopes to ecological and environmental studies in seagrass ecosystems   总被引：2，自引：0，他引：2  

Lepoint G  Dauby P  Gobert S 《Marine pollution bulletin》2004,49(11-12):887-891

Stable isotopes of carbon and nitrogen are increasingly used in marine ecosystems, for ecological and environmental studies. Here, we examine some applications of stable isotopes as ecological integrators or tracers in seagrass ecosystem studies. We focus on both the use of natural isotope abundance as food web integrators or environmental tracers and on the use of stable isotopes as experimental tools. As ecosystem integrators, stable isotopes have helped to elucidate the general structure of trophic webs in temperate, Mediterranean and tropical seagrass ecosystems. As environmental tracers, stable isotopes have proven their utility in sewage impact measuring and mapping. However, to make such environmental studies more comprehensible, future works on understanding of basic reasons for variations of N and C stable isotopes in seagrasses should be encouraged. At least, as experimental tracers, stable isotopes allow the study of many aspects of N and C cycles at the scale of a plant or at the scale of the seagrass ecosystem.  相似文献   

A Parameterization of Dry Thermals and Shallow Cumuli for Mesoscale Numerical Weather Prediction   总被引：3，自引：1，他引：2  

Julien Pergaud  Valéry Masson  Sylvie Malardel  Fleur Couvreux 《Boundary-Layer Meteorology》2009,132(1):83-106

For numerical weather prediction models and models resolving deep convection, shallow convective ascents are subgrid processes that are not parameterized by classical local turbulent schemes. The mass flux formulation of convective mixing is now largely accepted as an efficient approach for parameterizing the contribution of larger plumes in convective dry and cloudy boundary layers. We propose a new formulation of the EDMF scheme (for Eddy Diffusivity\Mass Flux) based on a single updraft that improves the representation of dry thermals and shallow convective clouds and conserves a correct representation of stratocumulus in mesoscale models. The definition of entrainment and detrainment in the dry part of the updraft is original, and is specified as proportional to the ratio of buoyancy to vertical velocity. In the cloudy part of the updraft, the classical buoyancy sorting approach is chosen. The main closure of the scheme is based on the mass flux near the surface, which is proportional to the sub-cloud layer convective velocity scale w _*. The link with the prognostic grid-scale cloud content and cloud cover and the projection on the non- conservative variables is processed by the cloud scheme. The validation of this new formulation using large-eddy simulations focused on showing the robustness of the scheme to represent three different boundary layer regimes. For dry convective cases, this parameterization enables a correct representation of the countergradient zone where the mass flux part represents the top entrainment (IHOP case). It can also handle the diurnal cycle of boundary-layer cumulus clouds (EUROCS\ARM) and conserve a realistic evolution of stratocumulus (EUROCS\FIRE).  相似文献   

Organic matter quality in reclaimed boreal forest soils following oil sands mining     

Isabelle Turcotte  Sylvie A. Quideau  Se-Woung Oh 《Organic Geochemistry》2009,40(4):510-519

Following surface mining of the Athabasca Oil Sands deposits in northeastern Alberta, Canada, land reclamation entails the reconstruction of soil-like profiles using salvaged soil materials such as peat and mining by-products. The overall objective of this research was to assess soil organic matter (SOM) quality in different reclamation practices as compared to undisturbed soils found in the region. Soil samples (0–10 cm) were taken from 45 plots selected to represent undisturbed reference ecosites and reclamation treatments. Soil OM pools were isolated using a combination of acid hydrolysis and physical separation techniques. Chemical composition of the low density fractions was characterized using ramped cross polarization (RAMP-CP) ¹³C nuclear magnetic resonance (NMR). Differences between disturbed and undisturbed sites reflected the influence of different botanical inputs (peat vs. forest litter) to SOM composition. Reconstructed soils were characterized by significantly lower alkyl over O-alkyl carbon (ALK/O-ALK) ratios (0.3) than undisturbed sites (0.5). For these reconstructed soils, a significantly higher proportion of soil carbon was present in the sand associated (Heavy sand) pool (49.2 vs. 37.3) and in the acid-unhydrolyzable residue (AUR) fraction (61.3 vs. 54.7). These SOM parameters were significantly related to time since reconstruction, with the AUR (p value = 0.012) and Heavy sand (p value = 0.05) fractions decreasing with time since reconstruction, while the ALK/O-ALK ratio increased (p value = 0.006). These findings suggest that the ALK/O-ALK, AUR, and Heavy sand parameters are suitable indicators for monitoring SOM quality in these reconstructed soils following oil sands mining.  相似文献   

Molecular study of insoluble organic matter in Kainsaz CO3 carbonaceous chondrite: Comparison with CI and CM IOM     

Laurent REMUSAT  Corentin Le GUILLOU  Jean‐Noël ROUZAUD  Laurent BINET  Sylvie DERENNE  François ROBERT 《Meteoritics & planetary science》2008,43(7):1099-1111

Abstract— Kainsaz CO3 insoluble organic matter (IOM) was studied using Curie point pyrolysis, electronic paramagnetic resonance (EPR), and high‐resolution transmission electron microscopy (HRTEM) to determine the effect of thermal metamorphism on molecular chondritic fingerprints. Pyrolysis released a very low amount of products that consist of one‐ and two‐ring aromatic units with methyl, dimethyl, and ethyl substituents. Moreover, Kainsaz IOM contains two orders of magnitude fewer radicals than Orgueil, Murchison, and Tagish Lake IOM. In addition, no diradicaloids were found in Kainsaz, although they are thought to constitute a specific signature for weakly organized extraterrestrial organic compounds in contrast to terrestrial ones. HRTEM reveals a very heterogeneous structure, with microporous disordered carbon, mesoporous graphitic carbons and graphite. Graphitization likely occurs and explains the differences between Kainsaz and CI or CM IOM. Heating stress experienced by Kainsaz IOM, on the parent body and/or prior its accretion, is likely responsible for the differences in molecular and structural organizations compared with those of CI and CM IOM.  相似文献   

Changes in heat wave characteristics over Extremadura (SW Spain)     

Acero  Francisco Javier  Fernández-Fernández  María Isabel  Carrasco  Víctor Manuel Sánchez  Parey  Sylvie  Hoang  Thi Thu Huong  Dacunha-Castelle  Didier  García  José Agustín 《Theoretical and Applied Climatology》2018,133(1-2):605-617

Theoretical and Applied Climatology - Heat wave (HW) events are becoming more frequent, and they have important consequences because of the negative effects they can have not only on the human...  相似文献   

Gas-driven lava lake fluctuations at Erta ’Ale volcano (Ethiopia) revealed by MODIS measurements     

Sylvie Vergniolle  Emmanuella Bouche 《Bulletin of Volcanology》2016,78(9):60

The long-lived lava lake of Erta ’Ale volcano (Ethiopia) is remotely monitored by moderate resolution imaging spectroradiometers (MODIS) installed on satellites. The Normalised Thermal Index (NTI) (Wright et al. Remote Sens Environ 82:135–155 2002) is shown to be proportional to the volume of the lava lake based on visual observations. The lava lake’s variable level can be plausibly related to a stable foam, i.e. a mixture composed of densely packed non-coalescing bubbles in suspension within a liquid. This foam is trapped at the top of the magma reservoir, and its thickness changes in response to the gas flux feeding the foam being successively turned on and off. The temporal evolution of the foam thickness, and the resulting variation of the volume of the lava lake, is calculated numerically by assuming that the gas flux feeding the foam, initially constant and homogeneous since December 9, 2002, is suddenly stopped on December 13, 2002 and not restarted before May 2003. The best fit between the theoretical foam thickness and the level of the lava lake deduced from the NTI provides an estimate of both the reservoir radius, 155–170 m, and the gas flux feeding the foam, 5.5×10^?3–7.2×10^?3 m ³ s ^?1 when existing. This is in agreement with previous estimates from acoustic measurements (Bouche et al. Earth Planet Sci Lett 295:37–48 2010). The very good agreement between the theoretical foam thickness and that deduced from MODIS data shows for the first time the existence of a regime based on the behaviour of a stable foam, whose spreading towards the conduit (“wide” conduit condition), can explain the long-lived activity. Our predictive model, which links the gas flux at the vent to the foam spreading, could potentially be used on any volcano with a long-lived activity. The underlying gas flux and the horizontal surface area of the magma reservoir can then be deduced by combining modelling to continuous measurements of gas flux. The lava lake, when high, often shows regular rise and fall of its level. We have recognised a minimum of 26 very well marked cycles between January 2001 and December 13, 2002, corresponding to a typical return time of 10.8 ± 2.3 days and a gas volume of 8.3×10⁵ ± 2.0×10⁵ m ³. This corresponds to a gas volume fraction in the reservoir equal to 0.023–0.063 %. The yearly gas flux, estimated between December 13, 2002 and September 27, 2004, varies between 2.3×10^?6 and 5.9×10^?6 m ³ s ^?1 at the depth of the reservoir. The long-time series provided by infra-red sensors mounted on satellites could be used on any persistent volcano to detect potential periodic variations in the level of lava lakes or lava columns, providing that the vent has a funnel shape, as often, and is sufficiently large.  相似文献   

Biradical character of D-rich carriers in the insoluble organic matter of carbonaceous chondrites: A relic of the protoplanetary disk chemistry     

Olivier Delpoux  Hervé Vezin  Sylvie Derenne 《Geochimica et cosmochimica acta》2011,75(1):326-7965

The insoluble organic matter (IOM) of the Orgueil meteorite contains deuterium-rich radicals detectable by Electron Paramagnetic Resonance (EPR) techniques (Gourier et al., 2008). However the structure of these deuterium carriers remains poorly constrained. In this work, their electronic structure is deduced from the measurement of the spin states S by transient nutation in pulsed-EPR. It is shown that these deuterium-rich radicals are dominated by biradicaloids (species with S = 0 ground state and thermally accessible S = 1 state) and biradicals (species with S = 1 ground state) representing ∼61% and ∼31% of the radicals in the IOM of Orgueil, respectively, while single radicals (S = 1/2) contribute only to ∼8%. This is definitely different from mature terrestrial IOMs, which are known to contain almost exclusively S = 1/2 radicals. A structural model is proposed, whereby the occurrence of dominant biradicaloids and biradicals is the direct consequence of the structure of the IOM, made of a network of small aromatic moieties linked by branched and short aliphatic units. This implies that the formation of stable biradicaloids and biradicals by C-H breaking and their deuterium enrichment are produced after the formation of the IOM in the primitive solar system. These results reinforce the idea that the formation of the IOM and the deuterium-rich hotspots are the product of ion chemistry in the solar disk.  相似文献   

Upper mantle anisotropy of southeast Arabia passive margin [Gulf of Aden northern conjugate margin], Oman     

Ali Al-Lazki  Cindy Ebinger  Michael Kendall  George Helffrich  Sylvie Leroy  Christel Tiberi  Graham Stuart  Khalfan Al-Toobi 《Arabian Journal of Geosciences》2011,5(5):925-934

In this study, we used data recorded by two consecutive passive broadband deployments on the Gulf of Aden northern margin, Dhofar region, Sultanate of Oman. The objective of these deployments is to map the young eastern Gulf of Aden passive continental margin crust and upper mantle structure and rheology. In this study, we use shear-wave splitting analysis to map lateral variations of upper mantle anisotropy beneath the study area. In this study, we found splitting magnitudes to vary between 0.33 and 1.0 s delay times, averaging about 0.6 s for a total of 17 stations from both deployment periods. Results show distinct abrupt lateral anisotropy variation along the study area. Three anisotropy zones are identified: a western zone dominated by NW–SE anisotropy orientations, an eastern zone dominated with NE–SW anisotropy orientations, and central zone with mixed anisotropy orientations similar to the east and west zones. We interpret these shorter wavelength anisotropy zones to possibly represent fossil lithospheric mantle anisotropy. We postulate that the central anisotropy zone may be representing a Proterozoic suture zone that separates two terranes to the east and west of it. The anisotropy zones west and east were being used indicative of different terranes with different upper mantle anisotropy signatures.  相似文献   

Molecular evidence for life in the 3.5 billion year old Warrawoona chert   总被引：1，自引：1，他引：0  

Sylvie Derenne  Franois Robert  Audrey Skrzypczak-Bonduelle  Didier Gourier  Laurent Binet  Jean-Noël Rouzaud 《Earth and Planetary Science Letters》2008,272(1-2):476-480

The biological origin of organic matter in the oldest siliceous sediments (cherts) is still debated. To address this issue, the insoluble organic matter (kerogen) was isolated from a chert of the Warrawoona group. The chemical structure of the kerogen was investigated through a combination of analytical techniques including solid-state ¹³C nuclear magnetic resonance and pyrolysis. Although dominated by aromatic hydrocarbons, the pyrolysate comprises a homologous series of long chain aliphatic hydrocarbons characterized by odd-over-even carbon number predominance. This distribution is only consistent with a biological origin. As kerogen must be contemporaneous of the solidification of the chert, this observation should be regarded as an evidence for the presence of life on Earth, 3.5 By ago.  相似文献   

Numerical simulation of the propagation of P waves in fractured media   总被引：1，自引：0，他引：1  

Sylvie Kelner  Michel Bouchon  & Olivier Coutant 《Geophysical Journal International》1999,137(1):197-206

We study the propagation of P waves through media containing open fractures by performing numerical simulations. The important parameter in such problems is the ratio between crack length and incident wavelength. When the wavelength of the incident wavefield is close to or shorter than the crack length, the scattered waves are efficiently excited and the attenuation of the primary waves can be observed on synthetic seismograms. On the other hand, when the incident wavelength is greater than the crack length, we can simulate the anisotropic behaviour of fractured media resulting from the scattering of seismic waves by the cracks through the time delay of the arrival of the transmitted wave. The method of calculation used is a boundary element method in which the Green's functions are computed by the discrete wavenumber method. For simplicity, the 2-D elastodynamic diffraction problem is considered. The rock matrix is supposed to be elastic, isotropic and homogeneous, while the cracks are all empty and have the same length and strike direction. An iterative method of calculation of the diffracted wavefield is developed in the case where a large number of cracks are present in order to reduce the computation time. The attenuation factor Q ⁻¹ of the direct waves passing through a fractured zone is measured in several frequency bands. We observe that the attenuation factor Q ⁻¹ of the direct P wave peaks around kd = 2, where k is the incident wavenumber and d the crack length, and decreases proportionally to ( kd ) ⁻¹ in the high-wavenumber range. In the long-wavelength domain, the velocity of the direct P wave measured for two different crack realizations is very close to the value predicted by Hudson's theory on the overall elastic properties of fractured materials.  相似文献