Numerical modelling of 137Cs content in the pelagic species of the Japanese Pacific coast following the Fukushima Dai-ichi Nuclear Power Plant accident using a size-structured food-web model

International audienceAs result of the great east Japan earthquake on March 2011 and the damages of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), huge amount of radionuclides, especially 137Cs, were released to the Japanese Pacific coast. By consequence, several marine species have been contaminated by direct uptake of radionuclides from seawater or through feeding on contaminated preys. In the present study we propose a novel radioecological modelling approach aiming to simulate the radionuclides transfer to pelagic marine species by giving to the organism body-size a key role in the model. We applied the model to estimate the 137Cs content in 14 commercially important species of the North-Western Pacific Ocean after the FDNPP accident. Firstly, we validated the model and evaluated its performance using various observed field data, and we demonstrated the importance of using such modelling approach in radioecological studies. Afterwards, we estimated some radioecological metrics, such as the maximum activity concentration, its corresponding time and the ecological half-life, which are important in assessment of the previous, current and future contamination levels of the studied species. Finally, we estimated the time duration required for each species to reach the pre-accident 137Cs activity concentrations. The results showed that the contamination levels in the planktivorous species have generally reached the preaccident levels since about 5 years after the accident (since 2016). While in the case of the higher trophic level species, although the activity concentrations are much lower than the regulatory limit for radiocesium in seafood in Japan (100 Bq kg-1), these species still require another 6–14 years (2018–2026) to reach the pre-accident levels

Sediment dynamics in the Gulf of Lion (NW Mediterranean Sea) during two autumn–winter periods with contrasting meteorological conditions

International audienceA simulation based on a hydro-sedimentary model was conducted for the period between summer 2010 and spring 2012 in the Gulf of Lion (northwestern Mediterranean Sea) to understand the spatial and temporal variability of sediment transport, erosion and deposition on the continental shelf and slope. Datasets of both simulated and observed current, temperature and suspended matter from the shelf and the Cap de Creus Canyon which is the main export route towards the continental slope, were first compared to assess the reliability of the simulation. The simulation shows the massive sediment accumulation near the Rhone River mouth (∼56 % of the inputs), the accretion along the mid-shelf mud belt, and the impact of dense shelf water cascading on sediment resuspension and erosion inside the Cap de Creus Canyon. The two studied autumn–winter periods were strongly contrasted in terms of meteorological conditions and subsequent impacts on the sediment dynamics. During the first period (2010–2011) dominated by marine storms, the shelf sediment underwent strong changes, the Rhone River sediment load accumulated in a relatively small area, stock of littoral sands moved to the inner shelf (20–40 m) while inner shelf fine particles fed the mid-shelf mud belt and the upper Cap de Creus Canyon. During the second period (2011–2012) with very little marine wind and a particularly cold winter, sediment on the shelf underwent little change except for a southwestward growth of the Rhone River prodeltaic deposit. Sediment from the southwestern end of the shelf as well as from the upper Cap de Creus Canyon was flushed toward deeper reaches by dense shelf water cascading. Cascading also had a more moderate impact in the various canyons incising the continental shelf. Our work supports the view of an unbalanced sedimentary system, with a deficit mainly over the inner shelf, whose main driver is probably the strong and fast reduction of particulate matter inputs from the Rhone River (by a factor of 4 in less than one century)

Archives, archivistes, archivistique dans l'Europe du Nord-Ouest du Moyen Âge à nos jours

Le colloque tenu au Centre des archives du monde du travail, l’un des cinq centres d’archives dépendant des Archives nationales, du 2 au 4 décembre 2004, est né du souhait de la section régionale Nord-Pas-de-Calais-Picardie de célébrer, au plan local, le centenaire de l’Association des archivistes français. Organisé avec la coopération du Centre de recherches historiques sur l’Europe du Nord-Ouest (Université de Lille 3), ce colloque a fondé son projet scientifique sur une démarche pluridisciplinaire mêlant archivistes et universitaires, professionnels et utilisateurs, aux liens naturellement étroits et aux finalités complémentaires. L’appel à communications, diffusé dès 2002, privilégiait une période chronologique large, allant de l’Antiquité à nos jours, et un espace géographique ouvert, comprenant les régions du nord-ouest de la France (Nord, Pas-de-Calais, Picardie, Normandie), la Belgique, les Pays-Bas, le nord de l’Allemagne, le Danemark, la Finlande, la Suède, la Norvège, l'Islande, le Royaume-Uni et l’Irlande. Dans cet espace sans cohérence historique apparente se sont tissés des liens politiques à géométrie variable et des relations économiques polymorphes, dont l’Union européenne forme la dernière représentation. Dans ce cadre aussi, par leur richesse ou par leur indigence, les archives sont le témoin privilégié du rapport entre l’espace et le temps, du flux et du reflux des activités et de l’autorité, mais aussi de la relation indéfectible entre la gouvernance et la mémoire, dont la nature et le mouvement demandent à être jalonnés de balises chronologiques et phénoménologiques. Les interventions devaient fournir aux chercheurs, aux historiens généalogistes comme aux amateurs, des clés d’accès à cette mémoire, afin d’éclairer le contexte de production et le contenu du matériau produit, transmis, légué et exploité. Elles ont été réparties en trois thèmes, appréhendant dans leur dimension historique l’objet mémoriel - les archives, - issu de l’action primaire des structures et des individualités qui le génèrent ; l’agent - les archivistes -, qui veille à la pérennité de la mémoire ; l’action - l’archivistique -, nécessaire à la préservation et fondée sur une science dont les principes se sont progressivement forgés