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The DUNE project: a DUst experiment in a low Nutrient, low chlorophyll Ecosystem.

Guieu Cécile

The interactions between atmosphere and ocean play a key role if we are to understand what governs elements cycles in the ocean and to which extent climate change plays a role in the biological carbon pump. In this context, atmospheric deposition is now recognized as a significant source of macro and micro nutrients to the upper ocean. Natural and anthropogenic changes in climate can alter the atmospheric input of aerosols to the ocean. Understanding how these modifications cause changes in planktonic productivity and food web structure is a key question in environmental sciences, as they may result in altered carbon partitioning and biogenic air-sea gas fluxes.
We propose in DUNE to study the vulnerability of the oligotrophic Mediterranean ecosystem to climatic change and the consequent increase in natural and anthropogenic atmospheric input. In particular, we will focus on the ecosystem response in terms of biological productivity in order to find the most pertinent and easy-to-check indicators of the trophic structure changes.
In situ large mesocosms representative of a significant body of surface waters will be fertilized with perfectly well physico-chemically characterized natural and/or anthropogenic aerosols. The mesocoms will be setup in a site representative of sensitive Mediterranean coastal environment: the Natural Preservation Area of Scandola (Corsica), a marine and terrestrial zone protected from human activities.
To be able to quantify at best the present atmospheric fluxes and evaluate their possible short-term evolution, we propose also to couple a synthesis on existing data, with atmospheric collection in the vicinity of the seeding experiment location. Atmospheric transport and deposition modelling of Saharan dust will be performed to assess the deposition pattern at the basin scale, and to study the expected changes in dust transport in the climate change perspective.
Describe/quantify the processes involved after atmospheric fertilization is a prerequisite for modelling the evolution of the Mediterranean ecosystem in the perspective of an expected increase in atmospheric input, water stratification and disturbance of the riverine and atmospheric temporal regime (effect of the increase of extreme events frequency - see also poster Dulac et al.).
This 3 years project was partially funded in 2006. A preliminary and short field survey will be performed after the bloom in spring 2007 to establish the exact trophic conditions of the site and to perform a series of tests on 2 large mesocosms (in particular sampling test and contamination controls). The seeding experiment will take place in 2008.