Vienna, Austria
Date: April, 8th - 11th, 2015
Venue: 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.
Vienna, Austria
Date: April, 12th - 17th, 2015
Venue: Austria Center Vienna
The EGU General Assembly 2015 was again a great success with 4,870 oral, 8,489 poster, and 705 PICO presentations. 577 unique scientific sessions together with 310 side events created an interesting programme. At the conference 11,837 scientists from 108 countries participated, of which 23% were students, 15,000 copies of EGU Today distributed, keen media presence and reporting, and thousands of visits to the webstreams as well as to the EGU blog GeoLog.
Effects of particle optical properties on grain size measurements of aeolian dust deposits
Particle size data are holding crucial information on the sedimentary environment at the time the aeolian dust deposits were accumulated. Various aspects of aeolian sedimentation (wind strength, distance to source(s), possible secondary source regions and modes of sedimentation and transport) can be reconstructed from proper grain size distribution data. Laser diffraction methods provide much more accurate and reliable information on the major granulometric properties of wind-blown sediments compared to the sieve and pipette methods.
The Fraunhofer and Mie scattering theories are generally used for laser diffraction grain size measurements. The two different approaches need different ‘background’ information on the medium measured. During measurements following the Fraunhofer theory, the basic assumption is that parcticles are relatively large (over 25-30 µm) and opaque. The Mie theory could offer more accurate data on smaller fractions (clay and fine silt), assuming that a proper, a’priori knowledge on refraction and absorption indices exists, which is rarely the case for polymineral samples. This study is aimed at determining the effects of different optical parameters on grain size distributions (e.g. clay-content, median, mode).
Multiple samples collected from Hungarian red clay and loess-paleosol records have been analysed using a Malvern Mastersizer 3000 laser diffraction particle sizer (with a Hydro LV unit). Additional grain size measurements have been made on a Fritsch Analysette 22 Microtec and a Horiba Partica La-950 v2 instrument to investigate possible effects of the used laser sources with different wavelengths. XRF and XRD measurements have also been undertaken to gain insight into the geochemical/mineralogical compositions of the samples studied.
Major findings include that measurements using the Mie theory provide more accurate data on the grain size distribution of aeolian dust deposits. Significant differences between the Mie and Fraunhofer approaches have been found for the finest grain size fractions, while only slight discrepancies were observed for the medium to coarse silt fractions. Since the two approaches gave similar results for the medium to coarse silt fractions that are the most abundant in loess, the use of the different approaches has no appreciable effect on the mode of the distributions. In conclusion, the two different applied optical parameter settings has had significant effects on the finer tail of the aeolian grain size distributions.
Support of the Hungarian Research Fund OTKA under contracts PD108708 (for G. Varga) and PD108639 (for G. Újvári) are gratefully acknowledged. It was additionally supported (for G. Varga) by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences.
Various environments of interglacials recorded by Pleistocene paleosoils in Hungary (Central Europe)
Based on stable isotope analyses of worldwide reference curves from deep sea, ice core and speleothem records, it has long been apparent that duration, intensity and climatic conditions of different interglacial periods were significantly diverse. As a consequence of negligible fresh, detrital material admixture during interglacials, the soil formation intensity and maturity of various kinds of past soils have been holding vital information on the environmental conditions at the time the soils formed. This, in turn, means that several physical and chemical properties of soils allow us to reconstruct past climatic regimes.
Loess-paleosol sequences in Hungary (Central Europe) provide insight into the cyclic nature of glacial-interglacial variations of the last 1 million years. The paleosoils have been recognized as the product of warmer and moister interglacials, when the (glacial) loess material was altered by chemical weathering and pedogenic processes. 12 pedogene units from MIS-19 to MIS-5 strata were analysed in the course of this study, with a special attention to MIS-11 and MIS-19 periods, because of these can be regarded as analogues of the Holocene interglacial (due to the similarities in obliquity and eccentricity). Grain size, geochemical and (clay)mineralogical studies were elaborated and were gathered from previously published papers to quantify past weathering intensity and paleoenvironmental conditions by geochemical climofunctions.
The Upper and partly, the Middle Pleistocene loess deposits are intercalated by steppe, forest-steppe and brown forest soils, while the older pedogene horizons are different kinds; these are red, Mediterranean-type soils. The MIS-5 pedocomplex consist of three parts at several Hungarian sites, however the pedogene units cannot be correlated unequivocally with the three MIS-5 warmer substages, due to the scarce absolute age data. The MIS-7 and MIS-9 stages are represented by three forest steppe soils. The MIS-11 pedocomplex and MIS-17 and MIS-19 units are thick and well-developed forest soils, formed under a more humid climate compared to the younger pedogene strata. The geochemical data and climofunctions have been supported well these findings. Contrary to the global loess-paleosoil sequences, the MIS-13 and MIS-15 soils are not so dominant in the Hungarian series.
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.
Good to see the Dust World so well represented at IGU Vienna.
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