On the role of desert dust and dust storms in environmental processes

Dust storms and related atmospheric mineral particles have been in the focus of environmental and climatic studies for the last two decades (Stout et al., 2009). Previous investigations confirmed that windblown dust is an active component of the climate system, and can modify its elements via both direct and indirect effects (Harrison et al., 2001, Kohfeld and Tegen, 2007, Maher et al., 2010 and Pósfai and Buseck, 2010). Dust particles affect the Earth's energy balance directly through absorption, scattering and reflection of incoming shortwave and outgoing longwave radiation or by changing the albedo of (bright) surfaces (e.g. Arimoto, 2001). Indirectly, by acting as cloud condensation nuclei, mineral particles have also an effect on atmospheric moisture balance (Rosenfeld et al., 2001 and Sassen et al., 2003). Particles rich in Fe have major impact on iron-limited oceanic ecosystems, and thus, dust can influence the primary phytoplankton production and the carbon cycle through biogeochemical interactions (Ridgwell, 2002).

The global annual input of mineral dust deflated from arid-semiarid areas can be set in the range between 1 and 3 billion of tons (Tegen et al., 1996, Mahowald et al., 1999, Mahowald et al., 2006, Ginoux et al., 2001 and Mahowald et al., 2006). Most important sources are situated in Saharan and Sahel regions, which are responsible for 50–70% of the global emission (Ginoux et al., 2001 and Miller et al., 2004). Four main pathways of Saharan dust transport can be distinguished: (1) southward to Gulf of Guinea; (2) westward over the North Atlantic Ocean; (3) eastward to Middle East; and (4) northward to Europe (for more details, see Engelstaedter et al., 2006 and Goudie and Middleton, 2006).
The several hundred thousand tons of dust derived from Saharan sources influence numerous constituents of European environmental systems (D'Almeida, 1986 and Prospero, 1996). During heavy dust-outbreaks, atmospheric dust concentration often exceed PM10 standards of the European Union in Spain (Rodríguez et al., 2001), in Italy (Matassoni et al., 2011) and in Greece (Gerasopoulos et al., 2006), thereby affecting human health (Griffin et al., 2001). The strongly alkaline dust particles increase the pH of precipitation, thus reduce the frequency of acid rains (Roda et al., 1993, Rogora et al., 2004 and Špoler Čanić et al., 2009). As proposed by Psenner (1999), permanent Saharan dust contributions to low-alkalinity European lakes prevented them to become acidic during the late twentieth century. The accumulated dust particles are even capable of modifying soil properties of a given region (Yaalon, 1997). As such, terra rossa soils in Portugal (Jahn et al., 1991), in Spain (Muhs et al., 2010), in Italy (Jackson et al., 1982), in Croatia (Durn et al., 1999), in Greece (MacLeod, 1980) and in Turkey (Atalay, 1997) have been shown to be an alteration product of local material and far-travelled African mineral dust.
Fine-grained particles lift to higher levels of the atmosphere and have a long atmospheric residence time up to a few weeks (Pye, 1987). Aeolian dust from North Africa can often be detected in Europe's high-latitude areas e.g. in British Isles (Wheeler, 1986), in Germany (Klein et al., 2010), in Scandinavia (Franzén et al., 1994 and Barkan and Alpert, 2010) and even in our study area, the Carpathian Basin (CB) (Central Europe) (Borbély-Kiss et al., 2004, Koltay et al., 2006 and Szoboszlai et al., 2009). Nowadays the CB is generally not regarded as a dusty place, except for episodic dust storms related to cold fronts invading the region at the beginning of the vegetation period in the early spring. Still, Central Europe is lying in the D1b zone of the “Saharan dust-fall map” of Stuut et al. (2009), implying that recent Saharan dust material can be incorporated into the soil system and may increase its fine silt content (Stuut et al., 2009). However, dust activity of the region was much more significant during the Plio–Pleistocene periods, as it is shown by thick aeolian dust deposits covering more than half of the area (e.g. Pécsi and Schweitzer, 1993, Kovács et al., 2008, Újvári et al., 2010, Kovács et al., 2011 and Varga, 2011). It has been recognized that mineral dust particles of these aeolian sediments originate mainly from local sources (e.g. alluvial plains), and only the clay and fine-silt fractions may be linked to Saharan sources (Rózycki, 1991, Rousseau et al., 2007 and Újvári et al., 2012), similarly to Italian loess deposits (Cremaschi, 1990a and Cremaschi, 1990b).

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