At climatological scale, its specific, anti-estuarine circulation is the most probable cause of the West-to-East gradient in nutrient concentrations observed in the globally oligotrophic Mediterranean Sea (Crispi et al. 2001). The exchanges at straits (Gibraltar and Bosphorus) result in a net export of nutrients, 10% for nitrogen (N) and phosphorus (P), and 50% for silicon, approximately (Durrieu de Madron et al. 2011). To sustain biological productivity and heterotrophic activity in Mediterranean waters, a compensation from external sources is generally postulated (e.g., Ribera d’Alcalà et al. 2003). As a common characteristic of semi-enclosed and inland seas where the external physical forcing is strong, the atmospheric deposition plays a major role in supplying nutrients to offshore surface waters (Heimbürger et al. 2011). As well, land-based emission sources of pollutants are intense and numerous along the Mediterranean shores, and the atmospheric pathway is the most efficient transport route to spread a variety of elements and compounds over marine surfaces.
So, atmospheric depositions play a key role in the Mediterranean basin. Their impacts on marine ecosystem are essential for two aspects: (1) atmospheric matter and its impacts on the biological productivity and contamination of terrestrial and marine biosphere, (2) aerosols impacts on the UV/PAR attenuation. Current and future climate change could disrupt wind regimes and consequently change the intensity and pathways of the atmospheric input to the sea. And intensive industrialization and urbanization throughout its periphery, with a marked North-South gradient, make the Mediterranean a particularly sensitive site to the changes induced by human activity, the atmospheric transport covering very effectively all the pelagic zones. The atmospheric input is therefore contrasted and comes from two different sources. Terrigenous inputs, mainly Saharan, as well as dissolved anthropogenic inputs, are likely to have a marked impact on the Mediterranean organic production, given the particularly oligotrophic conditions of this sea. An important source of pollution of the deep-sea environment, but also, sometimes, of the coastal zone, is represented by the atmospheric deposition, too. These inputs essentially correspond to disruptive anthropogenic effects that lead to specific problems for the ecosystem with harmful consequences on ecologically sensitive areas, as observed in Mediterranean coastal regions. The intensification of anthropogenic emissions has introduced, via the atmosphere, large quantities of toxic elements for the marine ecosystem such as lead, cadmium or mercury.
In order to assess the impact of the atmospheric input on marine elemental concentrations, its involvement in biogeochemical marine cycles, and its possible evolution, the MOOSE WP5 implemented an operational homogeneous network of coastal Mediterranean atmospheric stations capable of collecting total (wet + dry) deposition, using the same equipment (MTX™ wet and dry sampler Italia), with a harmonized sampling strategy (14 days of collection for dry deposition – sampling on Tuesday; sampling after every major rain event for wet deposition). At present time, the network comprises 3 stations: from West to East, Cap Béar (42°30’ N – 36°07’ E, altitude 158 m), Frioul Island (43°16’ N – 5°17’ E, altitude 42 m), and Cap Ferrat (43°41′ N – 7°19′30″ E, altitude 130 m). The three stations were not operational at the same time, but a synchronous and harmonized set of data has started in 2012. Such a monitoring will be able to provide an East-West, as well as a coast-open ocean atmospheric gradient, ideal to study the impact of anthropogenic and Saharan dust events on marine ecosystems, but also to improve results from aerosol transport models.
Crispi et al. 2001
Durrieu de Madron et al. 2011
Ribera d’Alcalà et al. 2003
Heimbürger et al. 2011