Dan H. Yaalon Symposium

Bécs, Ausztria
Időpont: 2015. április 8 - 11.
Helyszín: Boku-Vienna/ Universität für Bodenkultur

Multidisciplinary investigations of Saharan dust events in the Mediterranean and in the Carpathian Basin (Central Europe)

Several hundred tons of windblown dust material is transported every year from Saharan dust source areas into direction of Europe, modifying important climatic and other environmental processes of distant areas. Past Saharan dust addition has also played crucial role in the unique Mediterranean terra rossa formation.
NASA’s daily aerosol indices (from 1979 to 2012) were employed to estimate atmospheric dust amount in the investigation areas. Daily geopotential height (at 700 mb), wind vector and meridional flow data of the distinguished dust events were obtained from the NCEP/NCAR Reanalysis project to compile mean synoptic composite maps. In order to identify the transportation routes and source areas, the backward trajectories were plotted on multiple trajectory maps (NOAA HYSPLIT model). 
The main period of the dust transportation into the Mediterranean is in spring and summer, when the thermal convective activity forces the injection of particles to higher atmospheric levels. However, seasonality patterns of the different Mediterranean sub-basins show quite large differences. In western sub-basins, the maxima of Saharan dust outbreaks is in summer, in the eastern basin, dust storms occur typically in spring, while the seasonal distribution of dust events in the central sub-basins show typical bimodal characteristic with a spring and summer peak, indicating a transitional position.
In the Carpathian Basin, the generally spring and summer dust events can be connected to three different synoptic situations: (1) SW flow between a southward moving trough (over the Atlantic coast of Africa) and the eastern cell of the divided subtropical high; (2) southerly winds associated with eastward moving depressions; and (3) long-range transport from the western parts of the Sahara along the western fringe of an anticyclone and by the westerlies. Granulometric properties of recently deposited dust material were analysed by using electron microscope (SEM) and Malvern Mastersizer 3000 (Hydro LV) laser particle size analyser.
Dust activity of Saharan sources has been much more dominant during certain Pleistocene glacial periods, as it is inferred by the widespread aeolian dust deposits of the investigation area with relevant Saharan contribution. The Saharan dust flux has decreased during the interglacials compared to glacials. However, according to Eastern Mediterranean marine drillings, at the end of the Early Pleistocene Saharan dust deposition was also significant during interglacial periods. It was the time of the formation of red paleosoils in the Carpathian Basin. The fine-grained dust originating from the Sahara could be incorporated to the MIS-17 and MIS-19 soils. 
Grain size, geochemical, mineralogical, micromorphological and SEM analyses have been elaborated on major Hungarian red clay-loess-palaeosol sequences to get more information on aeolian dust deposition and its role in syngenetic, accretionary soil development even during periods characterized by relatively higher temperatures and rainfall. The detailed granulometric analyses of the red clays and red paleosoils represent similarity in terms of their bimodal grain-size distribution patterns with loess horizons. The geochemical analyses suggest that climate during the formation of red clays and red paleosoils was considerably more humid and warmer in comparison to younger interglacials or to modern values.
Support of the Hungarian Research Fund OTKA under contract PD108708 (for G. Varga) is gratefully acknowledged. It was additionally supported (for G. Varga) by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences.

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