Stoichiometries of remineralisation and denitrification in global biogeochemical ocean models

Since the seminal paper of Redfield (1934), constant stoichiometric elemental ratios linking biotic carbon and nutrient fluxes are often assumed in marine biogeochemistry, and especially in coupled biogeochemical circulation models, to couple the global oxygen, carbon and nutrient cycles. However, when looking in more detail, some deviations from the classical Redfield stoichiometry have been reported, in particular with respect to remineralization of organic matter changing with depth or with ambient oxygen levels. We here compare the assumptions about the stoichiometry of organic matter and its remineralization that are used explicitly and implicitly in common biogeochemical ocean models. We find that the implicit assumptions made about the hydrogen content of organic matter can lead to inconsistencies in the modeled remineralization and denitrification stoichiometries. It is suggested that future marine biogeochemical models explicitly state the chemical composition assumed for the organic matter, including its oxygen and hydrogen content

Characterisation of Reaction Products and Mechanisms in Atmospheric Pressure Plasma Deposition of Carbon Films from Ethanol

Atmospheric pressure plasma deposition (APPD) of carbon films from a predominantly ethanol liquid phase was carried out under varying experimental conditions. A solid precipitate formed in the process was characterised by FT-IR and Raman spectroscopy. After each experiment the liquid phase was analysed for by-products by GC-MS. A number of compounds were found and mechanisms for their formation are proposed. These mechanisms involve the production of free radical species under the high energy plasma/discharge conditions of the process. The formation of groups of compounds was found to correlate with the voltage in the cell, but not with any other experimental parameter

Effets d’irradiations électroniques sur le comportement électrique d’un polymère thermoplastique haute-performance à finalité spatiale

International audienceIn space environment, satellite materials are subjected to several environmental constraints like high vacuum, temperature cycling or irradiation by space particles (electrons, protons, …). In case of polymer materials, irradiation by electrons presents two major issues. Since they are electrical insulators, the accumulation of electrons on their surface will lead to electrostatic discharge phenomena that can be responsible of electrical failures. On the other hand, high-energy electrons go through the polymers and transfer part of their energy to the material, which induces different phenomena like Radiation Induced Conductivity or physico-chemical ageing. The initial physical properties of the polymer can then be modified.In this context, numerous studies have investigated these phenomena for many space-used polymers in order to anticipate their behaviour once in orbit [1], [2]. This study focuses on PolyEtherEtherKetone (PEEK), a high-performance thermoplastic polymer which has recently but increasingly been used for space applications. Thus, it is necessary to ana-lyse the effects of electronic irradiation on its physico-chemical structure and on its physical properties

Microplancton des eaux marines et saumâtres de la Guyane et des Antilles françaises

Le microplancton des eaux de la Guyane française a pu être étudié sous les deux aspects qualitatif et taxinomique, durant la période de 1976 à 1979. La partie nomenclaturale a été complétée par des échantillonnages effectués aux Antilles françaises. Le matériel provient de campagnes océanographiques faites en décembre 1977, en mars et en novembre 1978. L'étude de la distribution saisonnière du microplancton et notamment celle des microphytes, met en relief l'importance des particularités climatiques et hydrologiques de cette région. Leur impact sur les facteurs turbidité et salinité est déterminant pour la distribution spatio-temporelle des microorganismes planctoniques. Les investigations ont permis de diviser la région s'étendant depuit le littoral jusqu'au large en trois écosystèmes relativement bien différencié

Characterisation of charging kinetics of dielectrics under continuous electron irradiation through real time electron emission collecting method

Dielectric materials used for spacecraft applications are often characterised under electron irradiation in order to study their physical and electrical mechanisms. For surface potential measurement, a small removable flat device based on the secondary electron spectrometer method has been developed and installed in the CEDRE irradiation test facility at ONERA (Toulouse, France). This technique was developed to get rid off specific issues inherent to the Kelvin Probe technique. This experimental device named REPA (Repulsive Electron Potential Analyser) allows in situ and real time assessment of the surface potential built up on dielectric materials under continuous electron irradiation. A calibration has been performed in order to validate this experimental setup. Furthermore, to optimise its efficiency, the physical behaviour of this device has been modelled and numerically simulated using Particle In Cell (PIC) model and a dedicated numerical code called SPIS (Spacecraft Plasma Interactions System). In a final step, electrical characterisations of a charged dielectric have been carried out under continuous electron irradiation with this new method. These results have been compared with measurements performed in same experimental conditions with conventional Kelvin Probe method. The experimental results have been discussed in this paper. To conclude, advantages of this experimental setup in regard of this application will be emphasised

Notices descriptives des manuscrits du Speculum maius. 1. Le Speculum historiale, Manuscrits de la Biblioteca Apostolica Vaticana

Nous commençons dans ce numéro 4 de Spicae, la publication de notices descriptives des manuscrits contenant le Speculum maius de Vincent de Beauvais, et d'abord le SpecuZum historiale. Il s'agit d'une description sommaire, qui n'entend pas répondre à toutes les exigences d'une description selon les règles codicologiques établies par l'érudition contemporaine . Cependant, pour ce travail, nous avons tenu compte des indications données par le guide publié par l'I.R.H.T pour l'élaboration d'une notice de manuscrit. Des manuscrits du Speculum historiale sont conservés dans les bibliothèques de presque tous les pays d'Europe occidentale et dans quelques bibliothèques américaines . Plus de 200 volumes ont déjà été répertoriés..

Les flores d'auteurs antiques et médiévaux dans le Speculum historiale - suite 1

Le Speculum historiale -et le Speculum maius tout entier- est la compilation organisée de plus de 150 auteurs et textes antiques et médiévaux . L'oeuvre en elle-même est donc un immense florilèg

Experimental investigation and modelling of surface potentials of materials under electron spectra representative of isotropic GEO worst-case environments

International audienceThis paper presents a novel approach used to test surface material charging under electron flux representative of space conditions below 400 keV. A series of severe environments for surface charging at geosynchronous orbit is extracted from Van Allen Probes data and compared to previous Los Alamos National Laboratory measurements. Middle Earth orbit data presented in this paper does not show major differences with respect to geosynchronous orbit data when looking at electron fluxes integrated above 10 keV. Most differences occur below 10 keV. The experimental protocol used to test material properties consists in adapting the electron flux to worst-case conditions. It is shown that the material properties required to predict electrostatic discharges occurrence must be measured with such an adaptive ground setup

Sampling in low oxygen aquatic environments: The deviation from anoxic conditions

Studies of the impact of hypoxic or anoxic environments on both climate and ecosystems rely on a detailed characterization of the oxygen (O-2) distribution along the water column. The former trivial separation between oxic and anoxic conditions is now often redefined as a blurry concentration range in which both aerobic and anaerobic processes might coexist, both in situ and during experimental incubations. The O-2 concentrations during such incubations have often been assumed to be equal to in situ levels, but the concentration was rarely measured. In order to evaluate the actual oxygen concentration in samples collected from low-oxygen environments, a series of measurements were performed on samples collected in the Pacific oxygen minimum zones. Our results show a significant deviation from in situ anoxic conditions in samples collected by Niskin bottles where leakage from the bottle material resulted in O-2 concentrations of up to 1 mu M. Subsequent sampling further increased the O-2 contamination. Sampling and analysis by Winkler method resulted in variable apparent concentrations of 2-4 mu M. Two common procedures to avoid atmospheric contamination were also tested: allowing gentle overflow and keeping the sampling bottle submersed in a portion of the sampled water. Both procedures resulted in similar O-2 contamination with values of 0.5-1.5 mu M when bottles were immediately closed and measurements performed with optical sensors, and 3-4 mu M apparent concentration when analyzed by the Winkler method. Winkler titration is thus not suited for analysis of low-O-2 samples. It can be concluded that incubation under anoxic conditions requires deoxygenation after conventional sampling.We would like to thank Lars B. Pedersen at Aarhus University for the construction of STOX sensors. We are grateful to the cruise leaders Bess B. Ward and Frank Stewart for the invitation to participate in OMZ cruises. We also thank the captains and crews of the R/Vs L'Atalante, New Horizon, Oceanus and Sally Ride. We additionally thank A. Franco-Garcia, M. Giraud, J. Ledesma, F. Baurand, D. Lefevre, B. Dewitte, C. Maes, V. Garcon and the PACOP platform (Toulouse) for operational and experimental support during the AMOP cruise. This work was funded by the Poul Due Jensen Foundation and co-financed by the 2014-2020 ERDF Operational Programme and by the Department of Economy, Knowledge, Business and University of the Regional Government of Andalusia (to EGR, project reference FEDER-UCA18-107225)