Holocene history of fire,vegetation and land use from the central Pyrenees (France)

Located on a mountain pass in the west-central Pyrenees, the Col d'Ech peat bog provides a Holocene fire and vegetation record based upon nine ¹⁴C (AMS) dates. We aim to compare climate-driven versus human-driven fire regimes in terms of frequency, fire episodes distribution, and impact on vegetation. Our results show the mid-Holocene (8500–5500 cal yr BP) to be characterized by high fire frequency linked with drier and warmer conditions. However, fire occurrences appear to have been rather stochastic as underlined by a scattered chronological distribution. Wetter and colder conditions at the mid-to-late Holocene transition (4000–3000 cal yr BP) led to a decrease in fire frequency, probably driven by both climate and a subsequent reduction in human land use. On the contrary, from 3000 cal yr BP, fire frequency seems to be driven by agro-pastoral activities with a very regular distribution of events. During this period fire was used as a prominent agent of landscape management.     

Application of Artificial Neural Network Model for the Prediction of Suspended Sediment Load in the Large River

Water Resources - Predicting the Suspended Sediment Load (SSL) of the river is a very significant and challenging task. Being a non-linearity in the SSL data, it requires a non-linear method to get...     

On the Role of Lightning NOx in the Formation of Tropospheric Ozone Plumes: A Global Model Perspective

A series of ozone transects measured each year from 1987 to 1990 over thewestern Pacific and eastern Indian oceans between mid-November andmid-Decembershows a prominent ozone maximum reaching 50–80 ppbv between 5 and 10 kmin the 20° S–40° S latitude band. This maximum contrasts with ozonemixing ratios lower than20 ppbv measured at the same altitudes in equatorial regions. Analyses witha globalchemical transport model suggest that these elevated ozone values are part ofa large-scale tropospheric ozone plume extending from Africa to the western Pacific acrosstheIndian ocean. These plumes occur several months after the peak in biomassburninginfluence and during a period of high lightning activity in the SouthernHemispheretropical belt. The composition and geographical extent of these plumes aresimilar to theozone layers previously encountered during the biomass burning season in thisregion.Our model results suggest that production of nitrogen oxides from lightningstrokes sustains the NO_x (= NO+NO₂) levels and the ozonephotochemical productionrequired in the upper troposphere to form these persistent elevated ozonelayers emanating from biomass burning regions.     

Heterogeneous distribution of paramagnetic radicals in insoluble organic matter from the Orgueil and Murchison meteorites

An electron paramagnetic resonance (EPR) investigation was performed on the insoluble organic matter from the Orgueil and Murchison meteorites and on terrestrial coals with similar elemental composition. A complementary electron nuclear double resonance (ENDOR) study was also carried out. The measured g-factors of the observed paramagnetic radicals in the meteoritic organic matter exhibit a similar correlation with the chemical composition as for the type III (i.e., hydrogen-poor) terrestrial coals. The main result, obtained from EPR saturation and ¹H ENDOR enhancement measurements, showed that the effective local concentration in radicals of about 3 to 4 × 10¹⁹ spin.g⁻¹ in the meteoritic organic matter is much higher than the average concentration, hence the occurrence of radical-rich regions accounting for 5% and 20% of the total volume for Murchison and Orgueil, respectively. This heterogeneity of concentration seems to be unique among natural organic macromolecules. It is proposed that these radical-rich regions correspond to pristine parts of the organic matter synthesized in conditions close to those prevailing in the interstellar medium, and which have survived the hydrothermal process on the parent body.     

Response scenarios for the deltaic plain of the Rhône in the face of an acceleration in the rate of sea-level rise with special attention to<Emphasis Type="Italic">Salicornia</Emphasis>-type environments

One of the most critical problems facing many deltaic wetlands is a high rate of relative sea-level rise due to a combination of eustatic sea-level rise and local subsidence. Within the Rhône delta, the main source of mineral input to soil formation is from the river, due to the low tidal range and the presence of a continuous sea wall. We carried out field and modeling studies to assess the present environmental status and future conditions of the more stressed sites, i.e.,Salicornia-type marshes with a shallow, hypersaline groundwater. The impacts of management practices are considered by comparing impounded areas with riverine areas connected to the Rhône River. Analysis of vegetation transects showed differences between mean soil elevation ofArthrocnemum fruticosum (+31.2 cm),Arthrocnemum glaucum (+26.5 cm), bare soil (+16.2 cm), and permanently flooded soil (?12.4 cm). Aboveground and belowground production showed that root:shoot ratio forA. fruticosum andA. glaucum was 2.9 and 1.1, respectively, indicating more stressful environmental conditions forA. glaucum with a higher soil salinity and lack of soil drainage. The annual leaf litter production rate of the two species is 30 times higher than annual stem litter production, but with a higher long-term decomposition rate associated with leaves. We developed a wetland elevation model designed to predict the effect of increasing rates of sea-level rise on wetland elevation andSalicornia production. The model takes into account feedback mechanisms between soil elevation and river mineral input, and primary production. In marshes still connected to the river, mineral input decreased quickly when elevation was over 21 cm. Under current sea-level rise conditions, the annual amount of riverine mineral input needed to maintain the elevation of the study marshes is between 3,000 and 5,000 g m^?2 yr^?1. Simulations showed that under the Intergovernmental Panel on Climate Change best estimate sea-level rise scenario, a mineral input of 6,040 g m^?2 yr^?1 is needed to maintain marsh elevation. The medium term response capacity of the Rhône deltaic plain with rising sea level depends mainly on the possibility of supplying sediment from the river to the delta, even though the Rhône Delta front is wave dominated. Within coastal impounded marshes, isolated from the river, the sediment supply is very low (10 to 50 g m^?2 yr^?1), and an increase of sea-level rise would increase the flooding duration and dramatically reduce vegetation biomass. New wetland management options involving river input are discussed for a long-term sustainability of low coastal Mediterranean wetlands.     

A three-scale model for pH-dependent steady flows in 1:1 clays

A new three-scale model to describe the coupling between electro-chemistry and hydrodynamics in non-swelling kaolinite clays in steady-state conditions is proposed. The medium is characterized by three separate nano-micro and macroscopic length scales. At the pore (micro)-scale the portrait of the clay consists of micro-pores saturated by an aqueous solution containing four monovalent ions (Na⁺, H⁺, Cl⁻, OH⁻) and charged solid particles surrounded by thin electrical double layers. The movement of the ions is governed by the Nernst–Planck equations and the influence of the double layers upon the hydrodynamics is modeled by a slip boundary condition in the tangential velocity governed by the Stokes problem. To capture the correct form of the interface condition we invoke the nanoscopic modeling of the thin electrical double layer based on Poisson–Boltzmann problem with varying surface charge density ruled by the protonation/deprotonation reactions which occur at the surface of the particles. The two-scale nano/micro model is homogenized to the macroscale leading to a precise derivation of effective governing equations. The macroscopic model is discretized by the finite volume method and applied to numerically simulate desalination of a clay sample induced by an external electrical field generated by the placement of electrodes. Numerical results indicate strong pH-dependence of the electrokinetics.     

Deformation measurements using SAR interferometry: potential and limitations

Most applications of Synthetic Aperture Radar (SAR) make only use of the amplitude information in just one image. Interferometric SAR (InSAR) makes use mainly of the phase measurements in two or more SAR images of the same scene, acquired at two different moments and/or at two slightly different locations. By interference of the two images, very small slant-range changes of the same surface can be inferred. These slant-range changes can be related to topography and/or surface deformations. InSAR thus has the potential of mapping centimeter-scale ground displacements over a region many tens of kilometers in size at a resolution of a few meters making it one of the most promising space-geodetic techniques for monitoring Earth's surface deformations. The goal of this paper is to discuss some of the potential new applications of InSAR for the monitoring of deformations, and to show its major limitations. Some potential new applications of InSAR related to surface-change detection including earthquake and crustal studies, the monitoring of volcanoes and anthropogenic effects, and the monitoring of glaciers and ice sheets are presented. The discussion on the limitations of InSAR for surface-change detection focuses on atmospheric perturbations and the problem of temporal decorrelation.     

Composition and spatial organization of a cold seep community on the South Barbados accretionary prism: Tectonic, geochemical and sedimentary context

Deep faunal assemblages were observed on cold seeps, between 1000 and 2000m depth, along the southern termination of the Barbados accretionary prism, during the Caracolante II and Diapicar cruises. Faunal composition and microdistribution of a cold seep community were analyzed at one site using deep-sea photographs and seismic (3.5 Kz) profiles. The community is dominated by large mussels up to 20cm long (possibly related to the genus Bathymodiolus), tiny vesicomyid clams, and vestimentiferan clusters in which animals are up to 2m long. There is a high density of sponges (three species), bryozoans and gorgonians. Other taxa occasionally associated with this assemblage include galatheid crabs, anemones, holothurians and possibly pennatulaceans which are numerous at boundaries of the site. A typical deep-sea fauna of fish, asteroids and ophiuroids is also scattered about the vicinity. This seep community is distributed as a band of discontinuous colonies, 40–50m in width and more than 10km in length. Living colonies alternate with accumulations shells and bare areas. The substratum is hard mud covered by a ferrugineous crust and cemented by carbonates. The early diagenetic character of the bottom and the occurrence of biological assemblages indicate that seepages of sulphur and/or methane, which have been revealed along the decollement zone of the Barbados prism, must diffuse through the sea floor. These biological and geological features are located on the crests of NE-SW anticlinal ridges and mud volcanoes which have been built by diaprism.     

Cenomanian vertebrate assemblages from southwestern France: a new insight into the European mid-Cretaceous continental fauna

Cenomanian paralic deposits of Charentes (southwestern France) have yielded abundant vertebrate microremains, including rather diversified continental taxa (e.g., frogs, turtles, crocodilians, dinosaurs, pterosaurs, lizards, and mammals). In this short report, the succession of faunal assemblages observed is briefly described in relation to palaeoenvironmental change resulting from the Cenomanian-early Turonian transgressive episode. Continental forms occur commonly in estuarine and shallow marine rocks of the lower part of the Cenomanian stage, but seem to be lacking in younger strata deposited in more open marine settings. Among an unexpected biodiversity, several non-marine groups (e.g., ziphodont crocodilians, carcharodontosaurid and troodontid dinosaurs, marsupial-like mammals) are recorded for the first time in the lower Upper Cretaceous of Europe, thus providing new palaeobiogeographical indications for this poorly documented part of the world.