Climate Change and the European Water Dimension - Agri ...

gradient with 4 to 10 times greater inputs in the coastal oceans of the northern
hemisphere (Seitzinger and Kroese 1998). Such an excess of nitrogen stimulates
microbial processes such as nitrification and denitrification in the coastal margins,
which contribute to 33% of the total greenhouse gas N2O emission from aquatic
environments.
IV.C.4. Atmospheric Inputs
Another source of inorganic nutrients, and particularly iron, is found in the mineral
dust transported from semi-arid and arid continental regions to the ocean via the
atmosphere, as demonstrated by Duce and Tindale (1991) from a network of aerosol
sampling stations. Iron availability is very important to support phytoplankton growth
and biomass in different parts of the world ocean (Boyd et al. 2000, Bishop et al.
2002) and in coastal systems. According to Prospero et al. (1989), 50 % of the dust
material is lost within 500km distance, suggesting a potentially large impact on the
coastal ecosystem (see below). Two major systems are transporting hundreds of
millions of tons of dust derived from mineral soil annually. The African Sahara and
Sahel systems affect the Mediterranean basin (Figure IV.C.6), and Europe and
transport dust material across the tropical Atlantic to the American continent. The
Gobi and Takla Makan system occurs in Northwest Asia and transports dust across
Korea, Japan and the North Pacific up to North America.
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Figure IV.C.6. (Left) Massive dust flow from Africa to Italy. MODIS-Terra image
acquired on May 04, 2004. (Source:NASA Earth Observatory;
http://earthobservatory.nasa.gov/NaturalHazards/ natural_hazards_v2.php3?img_id=12108)
(Right) Main point sources of Saharan dust particles in the Mediterranean Sea and repartition
of dust events per source for the 1998-2001periods (Source: Martiny and Hoepffner, 2003).
Dust storms have always occurred as a natural phenomenon. Global warming, i.e.
drier climate, and higher winds, changes in land-use practices have modified the dust
input in the oceans and, thus, the controlling role of iron and other nutrients in
plankton blooms (de Baar and La Roche 2002). In turn, an intensification of
atmospheric dust storms will act to reflect more sun light away from the Earth’s
surface, causing a cooling effect. The variability of exported dust from North Africa is
coupled with the NAO index, with greater flux during positive NAO anomalies,
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