Projet ANR-07-BLAN-0126 – DUNE : a DUst experiment in a low Nutrient, low chlorophyll Ecosystem
Programme : Blanc (BLANC) 2007
Année de financement : 2007
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE COTE D'AZUR (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE COTE D'AZUR)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique; Centre national de la recherche scientifique; Université de Bretagne Occidentale
Montant : 500000.0 euros
Date de début : 2007
Durée : 36 mois
Résumé : The main goal of DUNE is to estimate the impact of atmospheric inputs on an oligotrophic ecosystem submitted to strong atmospheric inputs. Atmospheric deposition is currently recognized as a significant source of macro- and micro-nutrients for the surface ocean, but the quantification of its role on biological carbon pump is still poorly determined. The main difficulty of such a quantification relies mainly on the diversity of the processes occurring: (1) within atmospheric cycling of particles (from emission processes to deposition onto surface ocean, including physical-chemical transformations occurring during transport) and (2) within the water column (uptake by bacteria and phytoplankton of particle-derived elements of biogeochemical interest, and carbon export resulting from fertilisation induced by those inputs). We propose in DUNE to investigate the role of atmospheric inputs on the functioning of an oligotrophic system particularly well adapted to this kind of study: the Mediterranean Sea. The Mediterranean Sea  etymologically, sea surrounded by land, is submitted to atmospheric inputs that are variable both in frequency and intensity. During the stratification period, only atmospheric deposition is prone to fertilise surface waters which had become very oligotrophic due to the nutrient depletion (after the spring bloom). In order to quantify the impact of both natural (Saharan) and anthropogenic (biomass burning, human activity) inputs on productivity and biogenic carbon sequestration  key concern of international scientific community, see for example SOLAS international initiative- it is necessary to parameterise the processes affecting the ecosystem functioning. In particular, it is important to consider the fixation of atmospheric nitrogen N2, for which dissolved iron, which mainly originates from atmospheric deposition, is one of the limiting elements. Realistic fertilisations, aiming to mimic natural and anthropogenic events of known intensity, will be performed onto a set of large mesocosms settled in Scandola Marine Reserve, located in North Corsica. Several biological and chemical parameters will be measured before and up to one month after the fertilisation, in order to quantify bacteria and phytoplankton response. The mesocosms will be installed during two field campaigns throughout the project. With the ambition to develop large mesocosms allowing accurate measurements of trace elements (Fe, P), DUNE constitutes a veritable technological challenge. The main innovation of our approach, relative to traditional use of microcosms or mono-specific cultures, lies on the fact that these ultra-clean systems will allow for the first time to accurately study over time, the processes stimulated by atmospheric deposition and this will be done within an authentic biogeochemical assemblage which natural physico-chemical conditions will be preserved. Moreover, an accurate quantification of exported matter, collected thanks to this device, will allow to achieve an integrated view of ecosystem responses to a selected external forcing, information needed in flux models. The project will take place during 3 years. A first stage will be devoted to the collection of atmospheric end-members and their treatment in order to mimic the physical and chemical modifications during transport and to quantify the release of labile fraction depending on mixing between aerosols sources. This first stage will be followed by two fertilisations campaigns which goal will be to parameterise the processes taking place and the carbon export induced by the stimulation of the natural assemblage after several realistic input scenarios. A final modelling stage (atmosphere and ecosystem) will be, hence, possible by integrating the quantification of atmospheric inputs and the parameterisation of the experimentally described processes. In spite of previous efforts in dedicated programs (EROS, CYCLOPS, ADIOS) the question of the biological response of t..