Modelling the contribution of short-range atmospheric and hydrological transfers to nitrogen fluxes, budgets and indirect emissions in rural landscapes

Spatial interactions within a landscape may lead to large inputs of reactive nitrogen (N<sub>r</sub>) transferred from cultivated areas and farms to oligotrophic ecosystems and induce environmental threats such as acidification, nitric pollution or eutrophication of protected areas. The paper presents a new methodology to estimate N<sub>r</sub> fluxes at the landscape scale by taking into account spatial interactions between landscape elements. This methodology includes estimates of indirect N<sub>r</sub> emissions due to short-range atmospheric and hydrological transfers. We used the NitroScape model which integrates processes of N<sub>r</sub> transformation and short-range transfer in a dynamic and spatially distributed way to simulate N<sub>r</sub> fluxes and budgets at the landscape scale. Four configurations of NitroScape were implemented by taking into account or not the atmospheric, hydrological or both pathways of N<sub>r</sub> transfer. We simulated N<sub>r</sub> fluxes, especially direct and indirect N<sub>r</sub> emissions, within a test landscape including pig farms, croplands and unmanaged ecosystems. Simulation results showed the ability of NitroScape to simulate patterns of N<sub>r</sub> emissions and recapture for each landscape element and the whole landscape. NitroScape made it possible to quantify the contribution of both atmospheric and hydrological transfers to N<sub>r</sub> fluxes, budgets and indirect N<sub>r</sub> emissions. For instance, indirect N<sub>2</sub>O emissions were estimated at around 21% of the total N<sub>2</sub>O emissions. They varied within the landscape according to land use, meteorological and soil conditions as well as topography. This first attempt proved that the NitroScape model is a useful tool to estimate the effect of spatial interactions on N<sub>r</sub> fluxes and budgets as well as indirect N<sub>r</sub> emissions within landscapes. Our approach needs to be further tested by applying NitroScape to several spatial arrangements of agro-ecosystems within the landscape and to real and larger landscapes

A comparison of numerical surface topography calculations in geodynamic modelling: an evaluation of the ‘sticky air' method

Calculating surface topography in geodynamic models is a common numerical problem. Besides other approaches, the so-called ‘sticky air' approach has gained interest as a free-surface proxy at the top boundary. The often used free slip condition is thereby vertically extended by introducing a low density, low viscosity fluid layer. This allows the air/crust interface to behave in a similar manner to a true free surface. We present here a theoretical analysis that provides the physical conditions under which the sticky air approach is a valid approximation of a true free surface. Two cases are evaluated that characterize the evolution of topography on different timescales: (1) isostatic relaxation of a cosine perturbation and (2) topography changes above a rising plume. We quantitatively compare topographies calculated by six different numerical codes (using finite difference and finite element techniques) using three different topography calculation methods: (i) direct calculation of topography from normal stress, (ii) body-fitting methods allowing for meshing the topography and (iii) Lagrangian tracking of the topography on an Eulerian grid. It is found that the sticky air approach works well as long as the term (ηst/ηch)/(hst/L)3 is sufficiently small, where ηst and hst are the viscosity and thickness of the sticky air layer, and ηch and L are the characteristic viscosity and length scale of the model, respectively. Spurious lateral fluctuations of topography, as observed in some marker-based sticky air approaches, may effectively be damped by an anisotropic distribution of markers with a higher number of markers per element in the vertical than in the horizontal directio

Resolving thermomechanical coupling in two and three dimensions: spontaneous strain localization owing to shear heating

International audienceNumerous geological processes are governed by thermal and mechanical interactions. In particular,tectonic processes such as ductile strain localization can be induced by the intrinsiccoupling that exists between deformation, energy and rheology. To investigate this thermomechanicalfeedback, we have designed 2-D codes that are based on an implicit finite-differencediscretization. The direct-iterative method relies on a classical Newton iteration cycle andrequires assembly of sparse matrices, while the pseudo-transient method uses pseudo-timeintegration and is matrix-free. We show that both methods are able to capture thermomechanicalinstabilities when applied to model thermally activated shear localization; they exhibitsimilar temporal evolution and deliver coherent results both in terms of nonlinear accuracyand conservativeness. The pseudo-transient method is an attractive alternative, since it candeliver similar accuracy to a standard direct-iterative method but is based on a much simpleralgorithm and enables high-resolution simulations in 3-D. We systematically investigate thedimensionless parameters controlling 2-D shear localization and model shear zone propagationin 3-D using the pseudo-transient method. Code examples based on the pseudo-transientand direct-iterative methods are part of the M2Di routines (R¨ass et al., 2017) and can bedownloaded from Bitbucket and the Swiss Geocomputing Centre website

Quantitative monitoring of tamoxifen in human plasma extended to 40 metabolites using liquid-chromatography high-resolution mass spectrometry: new investigation capabilities for clinical pharmacology.

Liquid-chromatography (LC) high-resolution (HR) mass spectrometry (MS) analysis can record HR full scans, a technique of detection that shows comparable selectivity and sensitivity to ion transitions (SRM) performed with triple-quadrupole (TQ)-MS but that allows de facto determination of "all" ions including drug metabolites. This could be of potential utility in in vivo drug metabolism and pharmacovigilance studies in order to have a more comprehensive insight in drug biotransformation profile differences in patients. This simultaneous quantitative and qualitative (Quan/Qual) approach has been tested with 20 patients chronically treated with tamoxifen (TAM). The absolute quantification of TAM and three metabolites in plasma was realized using HR- and TQ-MS and compared. The same LC-HR-MS analysis allowed the identification and relative quantification of 37 additional TAM metabolites. A number of new metabolites were detected in patients' plasma including metabolites identified as didemethyl-trihydroxy-TAM-glucoside and didemethyl-tetrahydroxy-TAM-glucoside conjugates corresponding to TAM with six and seven biotransformation steps, respectively. Multivariate analysis allowed relevant patterns of metabolites and ratios to be associated with TAM administration and CYP2D6 genotype. Two hydroxylated metabolites, α-OH-TAM and 4'-OH-TAM, were newly identified as putative CYP2D6 substrates. The relative quantification was precise (<20 %), and the semiquantitative estimation suggests that metabolite levels are non-negligible. Metabolites could play an important role in drug toxicity, but their impact on drug-related side effects has been partially neglected due to the tremendous effort needed with previous MS technologies. Using present HR-MS, this situation should evolve with the straightforward determination of drug metabolites, enlarging the possibilities in studying inter- and intra-patients drug metabolism variability and related effects

Pseudo pyoderma gangrenosum à Scedosporium apiospermum

International audienc

Garnet xenocryst from petit-spot lavas as an indicator for off-axis mantle refertilization at intermediate spreading ridges

Studies of lithospheric mantle from (ultra)slow spreading ridges have shown that melt extraction at mid-ocean ridges may be incomplete, producing metasomatism/refertilization of the shallow lithospheric mantle. However, it remains unclear whether similar processes operate off axis and could affect the cooling lithosphere. Here, we report the discovery of a garnet xenocryst in a petit-spot lava sampled on the top of the downgoing Pacific plate in front of Japan. The trace-element composition of this garnet xenocryst, in particular the low chromium, excludes a peridotitic origin, while the flat mid– to heavy rare earth element pattern does not support direct crystallization from melt percolating through the oceanic lithosphere. Garnet formation is therefore interpreted as formed by a subsolidus reaction of a plagioclase-bearing cumulate during the progressive off-axis cooling of the lithosphere. Combining lithosphere cooling models and the specific physical conditions required for subsolidus formation of garnet in tholeiitic systems (0.7–1.2 GPa) indicates that melt percolation to produce plagioclase-bearing cumulate occurs >150 km off axis. These conditions support that some low-degree melts produced off axis are not collecting to form mid-oceanic ridge basalt (MORB), but percolate and crystallize during the cooling and thickening of the lithospheric mantle. The demonstration of mantle refertilization affecting Pacific lithosphere off axis is critical because such a process could explain the presence of metasomatic domains with distinct physical and chemical properties in the depleted oceanic lithosphere

Les nappes et séries post-nappes. Obduction : l'ophiolite d'Oman portée aux nues

National audienc

Les nappes et séries post-nappes. Obduction : l'ophiolite d'Oman portée aux nues

National audienc