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The main purpose of this work is to propose a mechanism of post-depositional processes affecting chlorine and its chlorine-36 cosmogenic nuclide in the upper snowpack of the High Antarctic Plateau. We suggest that the observed decrease of total chlorine content in the upper meters of the snowpack is due to a progressive release of the HCl content from ice. We also propose a consistent framework, combining diffusion in bulk ice and snow microstructure. The observation of the low chlorine content in ice at depth leads to the robust hypothesis that the chemical equilibrium of chlorine between the ice and the snowpack interstitial air (SIA) is close to zero. HCl is thought to diffuse in ice, and to be progressively released in the SIA, and exported to the Antarctic atmosphere by the wind-ventilation. The time required to expel all the mobile species of chlorine (i.e., HCl) from snow depends on the diffusion coefficient of chlorine in ice combined with the snow grain size and its evolution with depth. This work is synthesised in a model combining the microstructure evolution of the upper meters of a snowpack (changes in mean snow grain size) and the diffusion of chlorine in ice applied to single spherical grains. The variability observed in chloride concentration profiles with depth, at a same site but different sampling time or different snow pits, or among different sites of the High Antarctic Plateau, is mostly due to the variations in initial concentrations in HCl and sodium chloride (NaCl) species and the snow grain size evolution. This model offers a common framework for understanding the fate of chlorine in Antarctica, from coastal to inland locations, including low accumulation sites on the plateau, far from the ocean. Applications of this post-depositional model to chlorine and to 36Cl allows to picture a recycling mechanism of chlorine at the scale of Antarctica. In particular, the 36Cl concentration in the surface snow of the Vostok site illustrates this recycling mechanism and the persistent contamination of inland Antarctica by anthropogenic 36Cl originating from the marine nuclear tests of the 1950s to the 1970s.

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This study aims at providing robust temperature reconstructions for a key oceanographic setting in the North Atlantic and at understanding the nature of the temperature signal recorded by the two biomarkers U-37(k) and TEX86, considering season and depth of production. To do so, high-resolution signals of U-37(k) and TEX86 are determined for the last 70kyr for core MD95-2042, located off Portugal. Signals of U-37(k) and TEX86 present a tight correlation, demonstrating a dominant temperature effect. U-37(k) signals correspond well to the annual mean sea surface temperature (SST), whereas TEX86H-derived temperatures are 5.6 degrees C higher, which is unrealistically warm for this area. Unsuitable TEX86 global linear calibrations on the Iberian Margin may suggest a possible occurrence of archaeal communities with specific temperature response. To assess the impact of different season or depth of production of the biomarkers on the recorded temperature in the sediment, modeled temperature proxies (Tproxies) are introduced in a Regional Oceanic Modeling System and tested for different seasons (annual/summer/winter) and depths (surface and 0-200m) of production for three climate modes (Present Day (PD), Last Glacial Maximum (LGM), and Heinrich Stadials (HS)). Similar temperature amplitudes between climate modes are found at MD95-2042 core site for observations, for both biomarkers, and for modeled annual surface production Tproxy: 5.5-7 degrees C for T(PD-LGM) and 3-4 degrees C for T(LGM-HS). Therefore, we propose a new TEX86H regional calibration to reconstruct present and past annual mean SSTs on the Iberian Margin.

Carbon isotopes in the ocean are frequently used as paleo climate proxies and aspresent-day geochemical ocean tracers. In order to allow a more direct comparisonof climate model results with this large and currently underutilized dataset, we added a carbon isotope module to the ocean model of the Community Earth System Model5(CESM), containing the cycling of the stable isotope13C and the radioactive isotope14C. We implemented the14C tracer in two ways: in the “abiotic” case, the14C tracer isonly subject to air–sea gas exchange, physical transport, and radioactive decay, whilein the “biotic” version, the14C additionally follows the13C tracer through all biogeo-chemical and ecological processes. Thus, the abiotic14C tracer can be run without10the ecosystem module, requiring significantly less computational resources. The car-bon isotope module calculates the carbon isotopic fractionation during gas exchange,photosynthesis, and calcium carbonate formation, while any subsequent biological pro-cess such as remineralization as well as any external inputs are assumed to occurwithout fractionation. Given the uncertainty associated with the biological fractionation15during photosynthesis, we implemented and tested three parameterizations of differ-ent complexity. Compared to present-day observations, the model is able to simulatethe oceanic14C bomb uptake and the13C Suess effect reasonably well compared toobservations and other model studies. At the same time, the carbon isotopes revealbiases in the physical model, for example a too sluggish ventilation of the deep Pacific Ocean., Geoscientific Model Development Discussions, 7 (6), ISSN:1991-962X, ISSN:1991-9611

A regional biogeochemical model is applied to the NW African coastal upwelling between 19° N and 27° N to investigate how a water temperature proxy is produced at the sea surface and recorded in the slope sediments. The biological model has two phytoplankton groups, to distinguish an alkenone producer group (considered as coccolithophores) from other phytoplankton. The Regional Ocean Modelling System (ROMS) is used to simulate the ocean circulation, and takes advantage of the Adaptive Grid Refinement in Fortran (AGRIF) package to set up an embedded griding system. The results show that the alkenone-like temperature records in the sediments are between 1.1 and 2.1°C colder compared to the annual mean SSTs. Despite the seasonality of the coccolithophorid production, this temperature difference is not mainly due to a seasonal bias, nor to the lateral advection of phytoplankton and phytodetritus from the cold water domain to most offshore locations, but to the production depth of the coccolithophores. If core-top sediment alkenone-derived temperatures are effectively recording the annual mean SSTs, the quantitative alkenone production in the water column must be inhomogeneous among the coccolithophore population and depend on physiological factors (growth rate, nutrient stress).

We study the receiver synchronisation in a DVB-S2/S2X beam hopping system. In such a scenario, each beam is illuminated during defined temporal windows. As a consequence, the receivers do not receive a continuous signal which strongly disturbs their synchronisation. To tackle this problem without using a specific format, we introduce a dedicated dummy frame with a synchronisation field that enables the receiver to lock with one frame even with poor channel conditions (a signal-to-noise ratio down to −10 dB). This solution is fully compliant with the existing standards. Through simulations, we present the performance of our scheme and demonstrate its effectiveness for DVB-S2/S2X systems.

International audience; Neodymium isotopic compositions (143Nd/144Nd or εNd) have been used as a tracer of water masses and lithogenic inputs to the ocean. To further evaluate the faithfulness of this tracer, we have updated a global seawater εNd database and combined it with hydrography parameters (temperature, salinity, nutrients and oxygen concentrations), carbon isotopic ratio and radiocarbon of dissolved inorganic carbon. Archive εNd data are also compiled for leachates, foraminiferal tests, deep-sea corals and fish teeth/debris from the Holocene period (< 10,000 years).At water depths ≥ 1500 m, property-property plots show clear correlations between seawater εNd and the other variables, suggesting that large-scale water mass mixing is a primary control of deepwater εNd distribution. At ≥ 200 m, basin-scale seawater T-S-εNd diagrams demonstrate the isotopic evolution of different water masses. Seawater and archive εNd values are compared using property-property plots and T-S-εNd diagrams. Archive values generally agree with corresponding seawater values although they tend to be at the upper limit in the Pacific. Both positive and negative offsets exist in the northern North Atlantic. Applying multiple regression analysis to deep (≥ 1500 m) seawater data, we established empirical equations that predict the main, large-scale, deepwater εNd trends from hydrography parameters. Large offsets from the predicted values are interpreted as a sign of significant local/regional influence. Dominant continental influence on seawater and archive εNd is observed mainly within 1000 km from the continents. Generally, seawater and archive εNd values form gradual latitudinal trend in the Atlantic and Pacific at depths ≥ 600 m, consistent with the idea that Nd isotopes help distinguish between northern/southern sourced water contributions at intermediate and deep water depths.

International audience; This paper deals with a new concept of electrical power distribution system called IMPEC for Integrated Modular Power Electronics Cabinet. The paper defines methods aiming at carrying out an optimal design of IMPEC, the main variables being on one hand the number and size of power electronics module. On the other hand, reconfigurations between these modules and electrical loads are also optimized.The formalization of the problem highlights that designers must deal simultaneously with a combinatorial explosion and a multi-physical system sizing. The main objective of the study is to propose a methodological framework for solving this original optimal design problem. A heuristic-based algorithm is developed to solve this combinatorial optimization problem. A particular attention is paid to develop a weight estimation procedure using generic sizing models. Finally a mapping is performed to identify the best solutions and to highlight the technological components having the most significant sensitivity on the complete system weight.

The oceans cover over 70% of the Earth's surface. Along with the atmosphere, they redistribute the energy that our planet receives from the sun. Figure credit: A. Biastoch GEOMAR-Kiel The joint action of winds and the Coriolis force induce surface currents, most of which have been known to sailors for centuries. However, sailors did not suspect the existence of a much larger system, on a global scale, linked to the circulation of the intermediate and deep layers of the ocean. The ocean can t...

The delta(15)N Signal in marine sediments appears to be a good palaeoceanographic tracer. It records biological processes in the water column and is transferred to and preserved in the sediments. Changes in forcing factors in upwelling systems may be recorded by delta(15)N. These forcing conditions can be of a biogeochemical nature, such as the initial isotopic signal of the nutrients or the trophic structure, or of a physical nature, such as wind stress, insolation, temperature or dynamic recycling. A simple nitrogen-based trophic chain model was used to follow the development of the nitrogen isotopic signal in nutrients, phytoplankton, zooplankton and detritus. Detrital delta(15)N, influenced by the isotopic signature of the upwelled nutrients and isotopic fractionation along the trophic chain (photosynthesis and zooplankton excretion), was then compared to the sedimentary signal measured off Mauritania. In our model, the biological variables are transported at shallow depths by a simple circulation scheme perpendicular to the coast depicting a continental shelf recirculation cell. Because cell length depends on the extension of the continental shelf, modifications of the cell length mimic sea level changes. Long cell length (high sea lever) scenarios produce higher delta(15)N values whereas short cell length scenarios result in lower values as in the glacial low sea level periods. Despite changes in many climatic parameters throughout this period, our results show that changing the sea level is sufficient to reconstruct the main pattern of the sedimentary delta(15)N variations offshore of the Mauritanian upwelling, i.e. an increase from about 3 parts per thousand to 7 parts per thousand during the deglaciation, without invoking any change in nitrogen fixation or denitrification.

A unified framework is presented in order to build lattice constellations matched to both the Rayleigh fading channel and the Gaussian channel. The method encompasses the situations where the interleaving is done on the real components or on two-dimensional signals. In the latter case, a simple construction of lattices congruent to the densest binary lattices with respect to the Euclidean distance is proposed. It generalizes, in a sense to be clarified later, the structural construction proposed by Forney (1991). These constellations are next combined with coset codes. The partitioning rules and the gain formula are similar to those used for the Gaussian channel.

International audience; More and more electric systems are embedded in today aircraft. As a result, the complexity of electrical power system design is increasing and the need of generic and efficient design methods is today required. Among numerous design tasks, the allocation of electric systems on the busbars of the electrical power system is considered as an important one since it has a direct impact on the aircraft mass. But due to the high number of possible allocations and regarding the large diversity of potential sizing cases for the equipments, finding the optimal allocation of electric loads is a hard task. In this paper, the problem is formalized mathematically. Then, four stochastic optimization methods are assessed on complex load allocation problems. Based on this assessment, a genetic algorithm using niching method is considered as the most appropriate algorithm for solving this aircraft design problem.

We introduce here a new approach for designing constellations (signal sets) at high signal-to-noise ratio. It is based on a geometric formulation of the design problem. The sphere packing formulation for the Gaussian case stems as an example and the results that this approach gives on fading channels are surveyed.

francaisCes dernieres annees ont ete marquees par une preoccupation grandissante au sujet du changement climatique, avec un besoin de projections climatiques fiables exprime par les acteurs locaux publics et prives, au service des strategies et actions d'adaptation. Ces acteurs rencontrent des obstacles evidents qui concernent l'acces, la fiabilite (marge d'erreur, traitement des extremes, estimation de l'incertitude) et l'adaptation de ces projections a leurs besoins. Cet article a pour objectif de presenter les differents types de services climatiques qui visent a les rendre accessibles et un inedit, Proclim. Ce dernier facilite l'acces aux projections climatiques a haute resolution issues du projet Cordex, coordonne par le Programme mondial de recherche sur le climat, et progressivement publiees depuis 2014. Une etude pilote menee pour le Programme des Nations unies pour le developpement en Jordanie illustre sa mise en oeuvre. EnglishRecent years have been marked by a growing concern for climate change. In particular there is a need for reliable climate projections, serving future adaptation policies for public and private stakeholders. Indeed, climate data users are facing several barriers, amongst which the access, and reliability of data (e.g., uncertainty management, error margins, management of extreme events) but also the adaptation of climate projections to their needs. This paper aims at presenting the existing range of climate services, and a newcomer, Proclim. This service aims at making more accessible high resolution climate projection, derived from the Cordex datasets (Cordex is a World Climate Research Program initiative). A pilot study conducted for UNDP illustrates its implementation.

International audience; Aircraft electrical power system (EPS), in charge of supplying power to aircraft electric systems, needs a reconfiguration capability in order to overcome cases of EPS component failures. During the design phase, EPS reconfiguration elicitation is a complex task due to the high number of failure combinations and to the aeronautical operational constraints, which are to be taken into account. Therefore a knowledge-based system is developed in order to help designers for such a task. It is based on the implementation of two different types of rules: mandatory and know-how rules. EPS connectivity is managed by graph-theory algorithms. The knowledge-based system is capable of producing several reconfiguration solutions. The knowledge-based system functioning is illustrated in detail on a simplified EPS. Results on an actual and modern EPS are also presented.

Using a regional circulation-ecosystem model subject to a set of boundary conditions that reflect present-day (PD) and Last Glacial Maximum (LGM) conditions, we investigate how changes in preformed subsurface nutrient concentrations as opposed to a local drop in sea level or increase in wind stress influence the biological productivity off the northwest African coastal upwelling area. A reduction of subsurface nutrient concentration at LGM reduced the zonally averaged primary production (PP). The sea level change modifies the shelf morphology, the upwelling circulation, and the productivity and displaces the high-productivity zone. According to our model results, the sedimentary record of PP is best explained by a simulation considering a doubled wind stress over NW Africa. We conclude that production regionally along the coast of NW Africa during the LGM may have been lower than today, despite the fact that most of the sediment cores north of 22°N show local increases in PP during the last glacial period. This paradox may be due to the sea level change and the associated eastward shift of the coastline and upwelling system.

[1] The growing world population increases the demand for water, energy, and land. This demand for natural resources impacts the transport of material and the supply of nutrients in the coastal ocean by rivers. We assess the potential impact of river N, Si, Fe, and organic carbon (OC) fluxes on the global and coastal ocean biogeochemistry, using an ocean biogeochemistry model and observations, in eight different scenarios. We assess two extreme scenarios, one with no river nutrients, corresponding to a complete stop of nutrient input by rivers, and one with high nutrient fluxes, corresponding to a world population of 12 billion people. Compared to today's scenario values, primary production (PP) changes from −5% to +5% for the open ocean, and from −16% to +5% for the coastal ocean. In the coastal ocean the impact of river nutrients on PP depends on regional nutrient limitation. River inputs have a larger impact on PP in areas where upwelling and high runoff are combined. The coastal ocean is typically N- or Si-limited. River Fe not assimilated by the phytoplankton is exported to open ocean areas, and its fertilizing effect depletes coastal and open ocean surface waters from N and Si. The impact on PP is reflected on global ocean low-O2 areas whose extent changes from −16% to +23% across the range of scenarios. River nutrients have a modest impact on the global ocean CO2 sink of up to 0.4 Pg C a−1, depending on the amount of inorganic and organic carbon transported by the rivers.

‡This paper proposes to improve the DVB­S2 standard, developed for the new generation of satellite broadcasting, in case of low cost and mobile equipments. It presents in details the DVB­S2 air interface and associated receiver architecture. It is shown how the latter can be conserved giving better performances at low signal to noise ratio when a regular framing and low efficient coding rates are introduced. The authors conclude that DVB­S2 can be used with mobile portable or hand­held terminals, with slight additions in the standard.

[1] A new model of the marine ecosystem coupled into a global Earth System Climate Model suitable for long-term (multimillennial timescale) simulations is presented. The model is based on nitrate as the sole limiting nutrient. Prognostic equations for nutrients, phytoplankton, zooplankton, and detritus are solved online in the three-dimensional ocean circulation model component. Experiments with different parameterizations of vertical mixing, including a scheme of tidally driven mixing, changes in buoyancy forcing in the Southern Ocean, different particle sinking velocities, and the inclusion of dissolved organic matter are performed, and the results are compared with observations. The results reemphasize the roles of Southern Ocean freshwater forcing and diapycnal mixing in the low-latitude pycnocline in setting the global deep water circulation and properties. The influence of high mixing in the Southern Ocean as inferred from observations is much more limited. The deep water circulation also has a strong influence on the marine ecosystem and nutrient distributions. We demonstrate that larger values of vertical diffusion lead to a shallower nutricline due to increased upwelling. Export production and nutrient distributions respond sensitively to changes in mixing and to the ratio of particle sinking to remineralization in the upper ocean. The best fits to global measurements of temperature, salinity, deep ocean radiocarbon, mixed layer depth, nutrients, and chlorophyll are obtained for values of vertical mixing in the pycnocline of around 0.2–0.3 × 10−4 m2/s and for e-folding depth for particle remineralization of 100–200 m. A simple parameterization of dissolved organic matter dynamics increases primary production and nutrient concentrations in the upper ocean and improves chlorophyll distributions in the subtropical gyres but has no discernible influence on particulate export fluxes. Remaining model deficiencies are identified, and strategies for future model improvement are outlined.

Ecosystem processes are important determinants of the biogeochemistry of the ocean, and they can be profoundly affected by changes in climate. Ocean models currently express ecosystem processes through empirically derived parameterizations that tightly link key geochemical tracers to ocean physics. The explicit inclusion of ecosystem processes in models will permit ecological changes to be taken into account, and will allow us to address several important questions, including the causes of observed glacial-interglacial changes in atmospheric trace gases and aerosols, and how the oceanic uptake of CO2 is likely to change in the future. There is an urgent need to assess our mechanistic understanding of the environmental factors that exert control over marine ecosystems, and to represent their natural complexity based on theoretical understanding. We present a prototype design for a Dynamic Green Ocean Model (DGOM) based on the identification of (a) key plankton functional types that need to be simulated explicitly to capture important biogeochemical processes in the ocean; (b) key processes controlling the growth and mortality of these functional types and hence their interactions; and (c) sources of information necessary to parameterize each of these processes within a modeling framework. We also develop a strategy for model evaluation, based on simulation of both past and present mean state and variability, and identify potential sources of validation data for each. Finally, we present a DGOM-based strategy for addressing key questions in ocean biogeochemistry. This paper thus presents ongoing work in ocean biogeochemical modeling, which, it is hoped will motivate international collaborations to improve our understanding of the role of the ocean in the climate system.

[1] A physical-biogeochemical model is used to simulate the evolution of the δ15N signal during the last glacial-interglacial transition in sedimentary cores offshore from the Mauritanian upwelling. The biological model is a classical nitrogen-based trophic chain model, which also computes the nitrogen isotope fractionation. The 2D physical primitive equation model simulates the coastal upwelling circulation and is applied for different sea level scenarios. The effect of the sea level rise, inducing the shelf immersion, seems to be a main factor explaining the organic nitrogen flux and isotopic signal variations along the last deglaciation. This effect is modulated by an upwelling seasonality that may have been much longer at the Last Glacial Maximum, around 10–11 months instead of 4–5 months at present. Between 15 and 5.5 kyr ago, 60% of the sedimentary δ15N variations could be explained by this local shelf immersion effect. This reconstruction also reproduces the strong isotopic fall occurring between 5.5 kyr and the present.

Sediments on the Namibian Margin in the SE Atlantic between water depths of ∼1000 and ∼3600 m are highly enriched in hydrocarbon-prone organic matter. Such sedimentation has occurred for more than 2 million years and is geographically distributed over hundreds of kilometers along the margin, so that the sediments of this region contain a huge concentrated stock of organic carbon. It is shown here that most of the variability in organic content is due to relative dilution by buried carbonates. This reflects both export productivity and diagenetic dissolution, not differences in either water column or bottom water anoxia and related enhanced preservation of organic matter. These observations offer a new mechanism for the formation of potential source rocks in a well-ventilated open ocean, in this case the South Atlantic. The organic richness is discussed in terms of a suite of probable controls including local wind-driven productivity (upwelling), trophic conditions, transfer efficiency, diagenetic processes, and climate-related sea level and deep circulation. The probability of past occurrences of such organic-rich facies in equivalent oceanographic settings at the edge of large oceanic basins should be carefully considered in deep offshore exploration.

Chemiluminescences emitted during recombination of ground state Cl atoms were studied in the aim of obtaining a laser emission on the B-X electronic transition of the chlorine molecule. Cl atoms were produced by dissociation of pure C12, in a turbulent electric discharge, at pressures between 10 and 50 Torr. Chemiluminescences were observed for the same pressures downstream from the discharge. The experimental spectra were compared to synthetic ones obtained from a modelling of the chlorine afterglow. A population density of Nv'=0 ≈ 1013 molecules/cm3 was estimated for the v' = 0 level of the B state, for an equilibrium vibrational temperature of 700 K. Assuming a long radiative lifetime of the B state, the calculated optical gain is weak, α ≤ 10-5/cm at λ = 1.1 gm.