Study of the soil–atmosphere moisture exchanges through convective drying tests in non‐isothermal conditions

This paper deals with the moisture exchanges occurring between soils and the surrounding atmosphere. Convective drying tests are performed on Awans silts at different drying temperatures and air relative humidities in order to reproduce the natural drying conditions. The experiments improve the understanding of the vapour transfers kinetics between the soil samples and the atmosphere. The experimental results are analysed assuming that the transfers take place in a boundary layer existing at the surface of the porous medium. The influence of the thermal conditions on the evaporation is also taken into account. In our model, coupled vapour and energy exchanges are controlled by mass and heat transfer coefficients characterizing the boundary layer. These coefficients are determined from the drying experiments. The modelling of the drying tests in non‐isothermal conditions is performed in order to validate the formulation of the vapour and heat exchanges. The numerical results present a good agreement with the kinetic of the materials desaturation determined during the tests. The analysis of the moisture transport mechanisms into the sample and at the boundary shows that at the beginning of the test, the drying is first achieved by the transport of moisture in its liquid form and its evaporation at the sample outer boundary in contact with the atmosphere. In a second step, vapour diffusion becomes predominant into the sample and it corresponds to the most important decrease of relative humidity. Copyright © 2009 John Wiley & Sons, Ltd.     

A conceptual framework for the integral management of marine protected areas

A general conceptual framework for the management of marine protected areas (MPAs) was developed. The driver-pressure-state-impacts-response (DPSIR) framework was used to determine the elements affecting MPAs. The developed evaluation framework helped to select an appropriate suite of indicators to support an ecosystem approach, an assessment of the MPAs functioning and policy decisions. Gaps derived from the management and policy responses in the MPAs were also outlined. It was concluded that the DPSIR framework can help to simplify the complexity of MPA management. This document is a tool for policy makers, scientists and general public on the relevance of indicators to monitor changes and MPAs management.     

History Matching Geostatistical Model Realizations Using a Geometrical Domain Based Parameterization Technique

Reservoir characterization needs the integration of various data through history matching, especially dynamic information such as production or 4D seismic data. Although reservoir heterogeneities are commonly generated using geostatistical models, random realizations cannot generally match observed dynamic data. To constrain model realizations to reproduce measured dynamic data, an optimization procedure may be applied in an attempt to minimize an objective function, which quantifies the mismatch between real and simulated data. Such assisted history matching methods require a parameterization of the geostatistical model to allow the updating of an initial model realization. However, there are only a few parameterization methods available to update geostatistical models in a way consistent with the underlying geostatistical properties. This paper presents a local domain parameterization technique that updates geostatistical realizations using assisted history matching. This technique allows us to locally change model realizations through the variation of geometrical domains whose geometry and size can be easily controlled and parameterized. This approach provides a new way to parameterize geostatistical realizations in order to improve history matching efficiency.     

Thermo‐tectonic evolution of the south‐central Pyrenees from rifting to orogeny: insights from detrital zircon U/Pb and (U‐Th)/He thermochronometry

Constraining the thermal and denudational evolution of continental margins from extensional episodes to early orogenic stages is critical in the objective to better understand the sediment routing during the growth of orogenic topography. Here, we report 160 detrital zircon U/Pb ages and 73 (U‐Th)/He ages from Albian, Upper Cretaceous and Eocene sandstones from the south‐central Pyrenees. All samples show dominant zircon U/Pb age peaks at 310–320 Ma, indicating a primary contribution from Variscan granites of the central Pyrenean Axial Zone. A secondary population at 450–600 Ma documents zircon grains sourced from the eastern Pyrenees. Zircon (U‐Th)/He ages recovered from older samples document, a Triassic age peak at ca. 241 Ma, corresponding to denudation coeval with the initiation of Atlantic rifting. An Early Cretaceous cooling event at ca. 133 Ma appears consistent with rift‐related exhumation and thermal overprint on the Iberian margin. The (U‐Th)/He age peaks from ca. 80 Ma to ca. 68 Ma with decreasing depositional ages are interpreted to reflect the southward‐migrating thrust‐related exhumation on the pro‐wedge side of the Pyrenean orogen. The increase in lag times, from ca. 15 Ma in the Tremp Formation (ca. 65 Ma) to 28 Ma in the Escanilla Formation (ca. 40 Ma), suggests decreasing exhumation rates from 0.4 km Myr^–1 to 0.2 km Myr^–1. The apparent inconsistency with convergence rates is used to infer that rocks cooled at 68 Ma may have resided in the crust before final exhumation to the surface. Finally, the cooling event observed at 68 Ma provides support to the inferred acceleration of convergence, shortening and exhumation during Late Cretaceous times.     

Reversible and irreversible impacts of greenhouse gas emissions in multi-century projections with the NCAR global coupled carbon cycle-climate model

The legacy of historical and the long-term impacts of 21st century greenhouse gas emissions on climate, ocean acidification, and carbon-climate feedbacks are investigated with a coupled carbon cycle-climate model. Emission commitment scenarios with zero emissions after year 2100 and 21st century emissions of 1,800, 900, and 0 gigatons of carbon are run up to year 2500. The reversibility and irreversibility of impacts is quantified by comparing anthropogenically-forced regional changes with internal, unforced climate variability. We show that the influence of historical emissions and of non-CO₂ agents is largely reversible on the regional scale. Forced changes in surface temperature and precipitation become smaller than internal variability for most land and ocean grid cells in the absence of future carbon emissions. In contrast, continued carbon emissions over the 21st century cause irreversible climate change on centennial to millennial timescales in most regions and impacts related to ocean acidification and sea level rise continue to aggravate for centuries even if emissions are stopped in year 2100. Undersaturation of the Arctic surface ocean with respect to aragonite, a mineral form of calcium carbonate secreted by marine organisms, is imminent and remains widespread. The volume of supersaturated water providing habitat to calcifying organisms is reduced from preindustrial 40 to 25% in 2100 and to 10% in 2300 for the high emission case. We conclude that emission trading schemes, related to the Kyoto Process, should not permit trading between emissions of relatively short-lived agents and CO₂ given the irreversible impacts of anthropogenic carbon emissions.     

Impact of Boundary-Layer Processes on Near-Surface Turbulence Within the West African Monsoon

High frequency measurements of near-surface meteorological data acquired in north Benin during the 2006 West African monsoon seasonal cycle, in the context of the African Monsoon Multidisciplinary Analysis (AMMA) experiment, offer insight into the characteristics of surface turbulence in relation to planetary boundary-layer (PBL) processes. A wide range of conditions is encountered at the lower and upper limits of the PBL: (i) from water-stressed to well-fed vegetation, and (ii) from small to large humidity and temperature jumps at the PBL top inversion, due to the Saharan air layer overlying the monsoonal flow. As a result, buoyant convection at the surface and entrainment at the PBL top play very different roles according to the considered scalar. We show that, when the boundary-layer height reaches the shear level between the monsoonal and Harmattan flows, the temperature source and humidity sink at the boundary-layer top are sufficient to allow the entrainment to affect the entire boundary layer down to the surface. This situation occurs mainly during the drying and moistening periods of the monsoon cycle and affects the humidity statistics in particular. In this case, the humidity turbulent characteristics at the surface are no longer driven solely by buoyant convection, but also by entrainment at the boundary-layer top. Consequently, the Monin–Obukhov similarity theory appears to fail for the parameterisation of humidity-related moments.     

Ionic surfactants adsorption on heterogeneous surfacesAdsorption de tensioactifs ioniques sur les surfaces hétérogènes

The adsorption of surfactants from aqueous solution is a phenomenon of major importance in applications ranging from ore flotation and paint technology to enhanced oil recovery. As this paper will illustrate, the process is very complex and of high scientific interest; its results can be extended to the retention of organic compounds (humic and fulvic acids, pollutants...) on solids in the biosphere. For a good understanding of the mechanisms involved in surfactants adsorption at the hydrophilic solid–aqueous solution interface, thermodynamic models have to take into account: (i) the physical chemistry of the surfactant in aqueous solution for choosing the appropriate reference phase, (ii) the surface heterogeneity of the adsorbing solid, (iii) the intensity of normal adsorbate–adsorbent bonds responsible for adsorption, (iv) the intensity of lateral bonds that favour the formation of surface aggregates through cooperative process and finally, (v) suitable theoretical models to describe adsorption phenomena. Once this has been achieved, two systems can be discussed: systems characterised by strong normal adsorbate–adsorbent bonds, currently used in ore flotation, which lead, in the case of heterogeneous surfaces, to the formation of lamellar aggregates at monolayer concentration and bilayer formation for higher concentrations. Systems characterised by weak normal adsorbate–adsorbent bonds, currently used in enhanced oil recovery and hydrocarbon (bio)remediation, which correspond to: (i) formation of globular micelles at the solid surface near the CMC when the temperature is higher than the Krafft point, (ii) formation of bilayered lamellar aggregates in the opposite case, (iii) three-dimensional condensation on substrate (T<T_Krafft) if the ionic surfactant interacts with cations in the bulk. To cite this article: J.-M. Cases et al., C. R. Geoscience 334 (2002) 675–688.     

Surface heterogeneity of mineralsAnalyse de l'hétérogénéité superficielle des minéraux

The precise study of adsorption mechanisms at solid–liquid interfaces requires a good analysis of the surface heterogeneity of the studied solids. For that purpose, molecular probe technique is one of the most powerful, especially at solid–gas interfaces. Indeed, low-pressure gas adsorption coupled to modelling of derivative adsorption isotherms as a function of logarithm of pressure allows to study qualitatively and quantitatively the effect of surface heterogeneity on the energy distribution of adsorption centres. The present review points out the interests of that approach to determine the shape of particles, the presence of high-energy adsorption sites and the surface polarity. Results comparing adsorption at solid–gas and solid–liquid interfaces are also mentioned. To cite this article: F. Villiéras et al., C. R. Geoscience 334 (2002) 597–609.     

Les ensembles fluviatiles néogènes du bassin subandin d'Équateur et implications dynamiquesThe Neogene fluvial systems of the Ecuadorian foreland basin and dynamic inferences

A sedimentological study of the Neogene continental infill of the Subandean foreland basin of Ecuador led us to define an evolution of the fluvial system from an alluvial plain to an alluvial fan with an increasing slope in the same time as the drainage changed from mostly longitudinal to transverse. Combined with the data presently available on palaeotopography, exhumation, tectonic evolution and geomorphology, these results enable us to infer that, in contrast with the other Subandean foreland basins of Bolivia and Peru, the progradation of the Neogene alluvial fans proceeded by an overall expansion, associated with a relatively small tectonic shortening and not as a result of the development of successive thrust-related depocentres. This also indicates that the surrection of the Cordillera progressed in Ecuador throughout the Neogene. To cite this article: F. Christophoul et al., C. R. Geoscience 334 (2002) 1029–1037.