First Detection of Cosmic Microwave Background Lensing and Lyman-{\alpha} Forest Bispectrum

We present the first detection of a correlation between the Lyman-$\alpha$ forest and cosmic microwave background (CMB) lensing. For each Lyman-$\alpha$ forest in SDSS-III/BOSS DR12, we correlate the one-dimensional power spectrum with the CMB lensing convergence on the same line of sight from Planck. This measurement constitutes a position-dependent power spectrum, or a squeezed bispectrum, and quantifies the non-linear response of the Lyman-$\alpha$ forest power spectrum to a large-scale overdensity. The signal is measured at 5~$\sigma$ and is consistent with the $\Lambda$CDM expectation. We measure the linear bias of the Lyman-$\alpha$ forest with respect to the dark matter distribution, and constrain a combination of non-linear terms including the non-linear bias. This new observable provides a consistency check for the Lyman-$\alpha$ forest as a large-scale structure probe and tests our understanding of the relation between intergalactic gas and dark matter. In the future, it could be used to test hydrodynamical simulations and calibrate the relation between the Lyman-$\alpha$ forest and dark matter.Comment: 8 pages, 7 figures; accepted for publication in Phys. Rev.

L'ambivalence des filières biocarburants

D'une situation de faible importance dans la sole agricole française (324 000 hectares en 2004 dont 300 000 hectares de colza), les cultures énergétiques devraient connaître un rapide accroissement de leur surface afin de permettre d'atteindre un niveau d'incorporation de 5,75% de biocarburants dans les carburants fossiles à l'horizon 2010 (valeur recommandée par la Directive 2003/30/CE, dite "promotion des biocarburants"). Le gouvernement français a d'ailleurs récemment augmenté les autorisations de production. Dans le contexte actuel où le prix du pétrole côtoie les 70$ par baril et où la lutte contre le réchauffement climatique devient une priorité, les biocarburants sont présentés sous un angle très favorable. Cependant, compte tenu de leur rendement énergétique par hectare de terre dans l'ensemble très moyen et de leurs coûts élevés, on est amené à tempérer les analyses très optimistes qui les entourent. Présentés essentiellement comme des filières énergétiques, on oublie de souligner que les biocarburants sont également un moyen indirect de soutien de l'agro-industrie et de l'agriculture, sous la responsabilité de chaque pays. Les principaux résultats résumés ici concernent la France. Ils sont obtenus en utilisant un modèle d'équilibre partiel et dynamique, OSCAR, mis au point par l'INRA (encadré 1). Les points forts de ce modèle consistent en une formalisation détaillée des offres agricoles, alimentaire et non alimentaire, compte tenu des évolutions de la PAC et des impacts des biocarburants sur les revenus ainsi que sur les emplois agricoles.

Les enjeux du développement des biocarburants dans l’Union européenne

En mars 2007, le Conseil européen a annoncé qu’à l’horizon 2020, une proportion minimale de 10 % de biocarburants devrait être incorporée dans les carburants utilisés pour le transport routier. Les pouvoirs publics communautaires mettent en avant trois facteurs principaux pour justifier une telle ambition : la réduction des émissions de gaz à effet de serre (GES), la diversification des approvisionnements énergétiques et le soutien des revenus agricoles. Alors qu’on s’interroge sur les conditions dans lesquelles les 5,75 % d’incorporation fixés par le cadre législatif actuel pourraient être atteints en 2010, ce nouvel élan donné à la politique communautaire des biocarburants suscite plusieurs interrogations.

Molecular biogeography of planktonic and benthic diatoms in the Yangtze River

Background: Diatoms are of great significance to primary productivity in oceans, yet little is known about their biogeographic distribution in oligotrophic rivers. Results: With the help of metabarcoding analysis of 279 samples from the Yangtze River, we provided the first integral biogeographic pattern of planktonic and benthic diatoms over a 6030 km continuum along the world's third largest river. Our study revealed spatial dissimilarity of diatoms under varying landforms, including plateau, mountain, foothill, basin, foothill-mountain, and plain regions, from the river source to the estuary. Environmental drivers of diatom communities were interpreted in terms of photosynthetically active radiation, temperature, channel slope and nutrients, and human interference. Typical benthic diatoms, such as Pinnularia, Paralia, and Aulacoseira, experienced considerable reduction in relative abundance downstream of the Three Gorges Dam and the Xiluodu Dam, two of the world's largest dams. Conclusions: Our study revealed that benthic diatoms are of particular significance in characterizing motile guild in riverine environments, which provides insights into diatom biogeography and biogeochemical cycles in large river ecosystems

Killing two birds with one stone: US and EU biofuel programmes

The United States and the European Union have been implementing sizeable biofuel support programmes since the beginning of the decade. Supporting the biofuel industry raises the price of the agricultural feedstock, and hence increases the farmer revenue and reduces the need for direct income support. Thus, for a given objective of agricultural income, the regulator is able to operate a partial substitution between agricultural decoupled payments and the support to the biofuel industry (subsidies or mandatory blending). We detail these effects and derive the biofuel and the environmental policies that maximise social welfare. We also show that for high levels of biofuel production, cross-compliance provisions are a more expensive way of enforcing the environmental policy than fining farmers. Oxford University Press and Foundation for the European Review of Agricultural Economics 2010; all rights reserved. For permissions, please email [email protected], Oxford University Press.

Moving beyond ‘more crop per drop’: insights from two decades of research on agricultural water productivity

Concern over increasing water scarcity has led to the introduction of the concept of agricultural water productivity and an emphasis on interventions to achieve ‘more crop per drop’. Yet, a strong debate continues on how the concept is to be defined and used. Drawing largely from the irrigation literature, the origins of the concept and its methodological developments are reviewed, and its use in applied work over two decades is discussed. Based on this analysis of conceptual and applied research, key insights into the concept’s contributions and limitations are presented, as well as opportunities for further refinements

Ambivalence of biofuel chains in France

From a situation of little importance in French crops (324,000 hectares in 2004 including 300,000 hectares of rapeseed), the surface area of energy crops should quickly grow in order to increase the level of incorporation of biofuels in fossil fuels to 5.75% by 2010 (recommended value of Directive 2003/30/EC, “promotion of biofuels”). The French government recently increased the authorized quantities of biofuel production. In the present context where oil prices are close to 70$ a barrel and where the fight against global warming has become a priority, biofuels are shown in quite a favourable light. However, considering, on the whole, their very poor energy yield per hectare of land and their high costs, we are led to temper the very optimistic analyses carried out on them. Essentially presented as energy chains, it should not be forgotten that biofuels are also an indirect way of supporting agribusiness and agriculture, under the responsibility of each country. The main results summarised here concern France. They are obtained by using a dynamic and partial equilibrium model, OSCAR (Optimisation of the Economic Surplus of Renewable Agricultural Biofuels), developed by the INRA (France) (frame 1). The strong points of this model consist in a detailed formalization of food and non-food agricultural supplies, considering CAP evolutions and the impacts of biofuels on farming incomes as well as on farming jobs

THE SILICA CYCLE IN THE ANTARCTIC OCEAN - IS THE WEDDELL SEA ATYPICAL

International audienceThe lowest biogenic silica production rates in the Southern Ocean (average of 2.59 mmol Si m-2 d-1) have been recorded in an area of heavy ice cover along a transect through the Weddell Sea from Joinville Island to Cap Norvegia (November-December 1990). The associated biomass was also very low (concentrations less-than-or-equal-to 0.6 mumol l-1 for biogenic silica and less-than-or-equal-to 0.8 mug l-1 for chlorophyll a). Based upon these direct measurements of biogenic silica production rates and other data available from the marginal ice zone and open ocean areas, we estimated the annual production of biogenic silica in the northern Weddell Sea to be 810 to 870 mmol m-2 yr-1. This leads to a revised estimate of the total annual biogenic silica production in the Southern Ocean of between 11 and 32 Tmol Si yr-1. Comparing our annual production estimate to previous estimates of vertical flux of opal in the Weddell Sea, we conclude that no more than 1 % of the silica produced annually by phytoplankton in the upper water column reaches a depth of 800 m. This is consistent with the general distribution of high accumulation rates of opal in Southern Ocean sediments which evidence an unexplained gap in the Weddell Sea. Thus, regarding the cycling of biogenic silica in the Southern Ocean, the Weddell Sea appears to be atypical