Continuous measurement of nitrate concentration in a highly event-responsive agricultural catchment in south-west of France: is the gain of information useful?

A nitrate sensor has been set up to measure every 10 min the nitrate signal in a stream draining a small agricultural catchment dominated by fertilized crops during a 2-year study period (2006–2008) in the south-west of France. An in situ sampling protocol using automatic sampler to monitor flood events have been used to assume a point-to-point calibration of the sensor values. The nitrate concentration exhibits nonsystematic concentration and dilution effects during flood events. We demonstrate that the calibrated nitrate sensor signal gathered from the outlet is considered to be a continuous signal using the Nyquist–Shannon sampling theorem. The objectives of this study are to quantify the errors generated by a typical infrequent sampling protocol and to design appropriate sampling strategy according to the sampling objectives. Nitrate concentration signal and flow data are numerically sampled to simulate common sampling frequencies. The total fluxes calculated from the simulated samples are compared with the reference value computed on the continuous signal. Uncertainties are increasing as sampling intervals increase; the method that is not using continuous discharge to compute nitrate fluxes bring larger uncertainty. The dispersion and bias computed for each sampling interval are used to evaluate the uncertainty during each hydrological period. High underestimation is made during flood periods when high-concentration period is overlooked. On the contrary, high sampling frequencies (from 3 h to 1 day) lead to a systematic overestimation (bias around 3%): highest concentrations are overweighted by the interpolation of the concentration in such case. The in situ sampling protocol generates less than 1% of load estimation error and sample highest concentration peaks. We consider useful such newly emerging field technologies to assess short-term variations of water quality parameters, to minimize the number of samples to be analysed and to assess the quality state of the stream at any time

Dynamique du glacier émissaire des processus à l'application sur un glacier école, Astrolabe, Antarctique de l'Est

Le bilan de masse de l'Antarctique dépend de deux contributions principales: le bilan de masse de surface constitué par l'ensemble des processus de perte et de gain de masse agissant en surface (précipitations, fonte, sublimation, tranport par le vent...) et le transfert dynamique de glace de la calotte vers la mer. Ce transfert a lieu au niveau des glaciers émissaires côtiers et représente 90% de la perte du volume total de glace de la calotte. Ces systèmes côtiers constituent ainsi les principaux régulateurs de l'évolution du bilan de masse de la calotte et de la contribution de cette dernière à l'élévation du niveau des mers. Les observations récentes révèlent une diminution accrue du bilan de masse en certaines zones de la calotte polaire telle que la partie Ouest et une contribution à l'élévation du niveau des mers de la part de la calotte qui augmente progressivement par rapport à l'expansion thermique. L'étude de la dynamique des glaciers émissaires par modélisation permet ainsi de mieux comprendre leur fonctionnement, de prédire leur réponse à une quelconque sollicitation, et d'évaluer l'impact potentiel sur l'élévation du niveau des mers. Ce travail de thèse vise à apporter de nouveaux éléments pour mieux contraindre ces modèles d'écoulement de la calotte antarctique. Il se scinde en deux axes principaux. La première partie s'intéresse à l'implémentation des processus physiques dans le modèle numérique, en particulier représenté par la migration de la ligne d'échouage qui sépare la partie posée de la partie flottante. Elle se base sur des cas synthétiques 2D. Nous mettons en évidence dans cette partie la diversité des modèles d'écoulement de calotte impliqués et les différences et similitudes associées. En particulier, la majorité de ces modèles repose sur deux hypothèses fortes que sont la stationnarité et la prédominance du glissement basal sur l'écoulement dont le bien-fondé est remis en question. L'étude d'intercomparaison révèle certaines divergences entre les modèles en terme de contribution à l'élévation du niveau des mers, les résultats nécessitent donc d'être pris avec précaution et les efforts doivent se concentrer sur la validité des hypothèses et l'implémentation du processus de migration de la ligne d'échouage. La deuxième partie consiste à appliquer le modèle Elmer/ice, qualifié de 'full-stokes', au cas réel 3D du Glacier de l'Astrolabe situé en Terre Adélie en Antarctique de l'Est.Cette application nous a permis de tester la sensibilité du modèle full-Stokes aux incertitudes sur les données d'entrées telles que la description du socle rocheux. Cette sensibilité s'avère significative recommandant une bonne connaissance de l'élévation du socle sous jacent à la glace et des méthodes appropriées pour sa détermination sur les noeuds du maillage associé au modèle.Two main contributions dominate the mass balance of Antarctica: surface mass balance, represented by all processes of gain and loss of mass acting at the upper surface (precipitations, melting, sublimation, wind transport...) and dynamical transport from grounded ice to the sea. This transfer takes place through outlet glaciers and represents 90% of the total loss of the whole ice sheet volume. These coastal systems act as regulators for the evolution of the ice sheet mass balance and for its contribution to sea level rise. Recently, observations emphasize a relevant decrease of mass balance in certain zones of Antarctica such as the West Coast, and an associated contribution to sea level rise from the ice sheet which increases significantly with respect to thermal expansion. Studying dynamics of outlet glaciers by modelisation thus participates at a better understanding of involved processes and enables to predict their response to any external sollicitations and to assess their potential impact on sea level budget. This work aims at providing with new elements for constraining these ice flow models for Antarctica. It is composed of two main parts. The first one concerns the implementation of physical processes into numerical models, in particular represented by grounding line migration, delimitating the grounded part from the floating one. It is based on 2 dimensionnal synthetic cases. The diversity of flow line ice sheet models is emphasized, with the associated differences and similarities. Most of these models lie on two strong assumptions, e.g. steadyness and dominance of basal sliding on ice flow, which are not always fulfilled. Moreover, the intercomparison work reveals discrepancies between models in terms of sea level contribution suggesting particular caution to be taken when considering corresponding results. Efforts have now to converge towards the validity of assumptions and on methods for implementing grounding line migration. The second part consists in applying the so-called 'full-Stokes' Elmer/Ice model to the 3D real case of the Astrolabe Glacier situated in Adélie Land in the east part of Antarctica. This application allows us to conduct sensitivity tests of the model to input incertainties such as the ones of bedrock description. This sensitivity appears to be significant, recommending a good knowledge of bedrock elevations and appropriate methods for its determination on the mesh nodes associated to the model.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Ultra-strong coupling of molecular materials: spectroscopy and dynamics

We report here a study of light–matter strong coupling involving three molecules with very different photo-physical properties. In particular we analyze their emission properties and show that the excitation spectra are very different from the static absorption of the coupled systems. Furthermore we report the emission quantum yields and excited state lifetimes, which are self-consistent. The above results raise a number of fundamental questions that are discussed and these demonstrate the need for further experiments and theoretical studie

Pyrethroid insecticide exposure and cognitive developmental disabilities in children: The PELAGIE mother–child cohort

International audiencePyrethroid insecticides are widely used in agriculture and in homes. Despite the neurotoxicity of these insecticides at high doses, few studies have examined whether lower-level exposures could adversely affect children's neurodevelopment. The PELAGIE cohort included 3421 pregnant women from Brittany, France between 2002 and 2006. When their children reached their sixth birthday, 428 mothers from the cohort were randomly selected, successfully contacted and found eligible. A total of 287 (67%) mothers agreed to participate with their children in the neuropsychological follow-up. Two cognitive domains were assessed by the Wechsler Intelligence Scale for Children: verbal comprehension and working memory. Five pyrethroid and two organophosphate insecticide metabolites were measured in maternal and child first-void urine samples collected between 6 and 19 gestational weeks and at 6 years of age, respectively. Linear regression models were used to estimate associations between cognitive scores and urinary pyrethroid metabolite concentrations, adjusting for organophosphate metabolite concentrations and potential confounders. Maternal prenatal pyrethroid metabolite concentrations were not consistently associated with any children's cognitive scores. By contrast, childhood 3-PBA and cis-DBCA concentrations were both negatively associated with verbal comprehension scores (P-trend = 0.04 and P-trend < 0.01, respectively) and with working memory scores (P-trend = 0.05 and P-trend < 0.01, respectively). No associations were observed for the three other childhood pyrethroid metabolite concentrations (4-F-3-PBA, cis-DCCA, and trans-DCCA). Low-level childhood exposures to deltamethrin (as cis-DBCA is its principal and selective metabolite), in particular, and to pyrethroid insecticides, in general (as reflected in levels of the 3-PBA metabolite) may negatively affect neurocognitive development by 6 years of age. Whatever their etiology, these cognitive deficits may be of importance educationally, because cognitive impairments in children interfere with learning and social development. Potential causes that can be prevented are of paramount public health importanc

Urinary Biomarkers of Prenatal Atrazine Exposure and Adverse Birth Outcomes in the PELAGIE Birth Cohort

Background: Despite evidence of atrazine toxicity in developing organisms from experimental studies, few studies—and fewer epidemiologic investigations—have examined the potential effects of prenatal exposure

Une nécropole du second âge du fer à Ambrussum, Hérault

Ambrussum doit sa notoriété aux recherches menées depuis les années 1970 sur l’oppidum du second Âge du Fer et son rempart, sur la ville du Haut-Empire, ainsi que sur l’agglomération gallo-romaine qui s’est développée à son pied, le long de la voie Domitienne reliant l’Italie à l’Espagne. Ce livre présente un nouveau volet de ce site majeur de l’archéologie languedocienne, un secteur du cimetière de l’oppidum gaulois qui a fait l’objet d’une fouille programmée de 1999 à 2003. L’intérêt de cette découverte dépasse le cadre régional puisqu’il s’agit d’une des très rares nécropoles du second Âge du Fer actuellement connues dans le Sud de la France. L’étude des vingt-deux tombes à incinération et des deux aires de crémation, qui s’inscrivent entre le second quart du IIIe siècle et les environs de 200 av. J.-C., fait une large place aux défunts eux-mêmes, aux objets et restes animaux et végétaux qui les accompagnent sur le bûcher, puis, de manière fragmentaire, dans la tombe. Des chapitres de synthèse concernent le mobilier, les pratiques funéraires déployées et le reflet de la société que celles-ci renvoient, mais aussi mettent en perspective ces coutumes dans le contexte de la Gaule méridionale. Ces usages des habitants d’Ambrussum s’inscrivent dans une tradition funéraire régionale bien définie, que l’on peut suivre, avec certaines évolutions, depuis le début du dernier millénaire avant J.-C., tandis que l’influence de la colonisation grecque, pourtant bien perceptible alors dans l’économie et le mode de vie des Indigènes, n’apparaît aucunement dans cette gestion de la mort

Assessment of sub-shelf melting parameterisations using the ocean–ice-sheet coupled model NEMO(v3.6)–Elmer/Ice(v8.3)

Oceanic melting beneath ice shelves is the main driver of the current mass loss of the Antarctic ice sheet and is mostly parameterised in stand-alone ice-sheet modelling. Parameterisations are crude representations of reality, and their response to ocean warming has not been compared to 3-D ocean–ice-sheet coupled models. Here, we assess various melting parameterisations ranging from simple scalings with far-field thermal driving to emulators of box and plume models, using a new coupling framework combining the ocean model NEMO and the ice-sheet model Elmer/Ice. We define six idealised one-century scenarios for the far-field ocean ranging from cold to warm, and representative of potential futures for typical Antarctic ice shelves. The scenarios are used to constrain an idealised geometry of the Pine Island glacier representative of a relatively small cavity. Melt rates and sea-level contributions obtained with the parameterised stand-alone ice-sheet model are compared to the coupled model results. The plume parameterisations give good results for cold scenarios but fail and underestimate sea level contribution by tens of percent for warm(ing) scenarios, which may be improved by adapting its empirical scaling. The box parameterisation with five boxes compares fairly well to the coupled results for almost all scenarios, but further work is needed to grasp the correct number of boxes. For simple scalings, the comparison to the coupled framework shows that a quadratic as opposed to linear dependency on thermal forcing is required. In addition, the quadratic dependency is improved when melting depends on both local and non-local, i.e. averaged over the ice shelf, thermal forcing. The results of both the box and the two quadratic parameterisations fall within or close to the coupled model uncertainty. All parameterisations overestimate melting for thin ice shelves while underestimating melting in deep water near the grounding line. Further work is therefore needed to assess the validity of these melting parameteriations in more realistic set-ups

Experimental design for three interrelated marine ice sheet and ocean model intercomparison projects: MISMIP v. 3 (MISMIP +), ISOMIP v. 2 (ISOMIP +) and MISOMIP v. 1 (MISOMIP1)

Coupled ice sheet–ocean models capable of simulating moving grounding lines are just becoming available. Such models have a broad range of potential applications in studying the dynamics of marine ice sheets and tidewater glaciers, from process studies to future projections of ice mass loss and sea level rise. The Marine Ice Sheet–Ocean Model Intercomparison Project (MISOMIP) is a community effort aimed at designing and coordinating a series of model intercomparison projects (MIPs) for model evaluation in idealized setups, model verification based on observations, and future projections for key regions of the West Antarctic Ice Sheet (WAIS). Here we describe computational experiments constituting three interrelated MIPs for marine ice sheet models and regional ocean circulation models incorporating ice shelf cavities. These consist of ice sheet experiments under the Marine Ice Sheet MIP third phase (MISMIP+), ocean experiments under the Ice Shelf-Ocean MIP second phase (ISOMIP+) and coupled ice sheet–ocean experiments under the MISOMIP first phase (MISOMIP1). All three MIPs use a shared domain with idealized bedrock topography and forcing, allowing the coupled simulations (MISOMIP1) to be compared directly to the individual component simulations (MISMIP+ and ISOMIP+). The experiments, which have qualitative similarities to Pine Island Glacier Ice Shelf and the adjacent region of the Amundsen Sea, are designed to explore the effects of changes in ocean conditions, specifically the temperature at depth, on basal melting and ice dynamics. In future work, differences between model results will form the basis for the evaluation of the participating models

Sea-level rise: from global perspectives to local services

Coastal areas are highly diverse, ecologically rich, regions of key socio-economic activity, and are particularly sensitive to sea-level change. Over most of the 20th century, global mean sea level has risen mainly due to warming and subsequent expansion of the upper ocean layers as well as the melting of glaciers and ice caps. Over the last three decades, increased mass loss of the Greenland and Antarctic ice sheets has also started to contribute significantly to contemporary sea-level rise. The future mass loss of the two ice sheets, which combined represent a sea-level rise potential of ∼65 m, constitutes the main source of uncertainty in long-term (centennial to millennial) sea-level rise projections. Improved knowledge of the magnitude and rate of future sea-level change is therefore of utmost importance. Moreover, sea level does not change uniformly across the globe and can differ greatly at both regional and local scales. The most appropriate and feasible sea level mitigation and adaptation measures in coastal regions strongly depend on local land use and associated risk aversion. Here, we advocate that addressing the problem of future sea-level rise and its impacts requires (i) bringing together a transdisciplinary scientific community, from climate and cryospheric scientists to coastal impact specialists, and (ii) interacting closely and iteratively with users and local stakeholders to co-design and co-build coastal climate services, including addressing the high-end risks