THE YELLOW-SNOW EPISODE OF NORTHERN FENNOSCANDIA, MARCH-1991 - A CASE-STUDY OF LONG-DISTANCE TRANSPORT OF SOIL, POLLEN AND STABLE ORGANIC-COMPOUNDS

The present paper describes a vast dustfall with snow in northern Fenn oscandia, 10 March 1991. The area affected by dust deposition was at l east 320,000 km(2). and the particulate mass received amounted to betw een 50 and 200 mg m(-2). The total amounts of dust deposited in the in vestigated area sum up to approximately 50,000 tonnes. The dust consis ted of soil particles, i.e. single mineral grains and loose ferric agg regates of mineral grains in addition to pollen and spores. Mineralogi cally, the dust was dominated by small rounded quartz grains. Median s ize of the dust particles was 2.72 mu m. The total pollen concentratio n varied from 327 to 1172 pollen cm(-2). The pollen types identified w ere divided in ''Nordic/Central European'' taxa and ''Exotic'' taxa. P ollen from the former group, e.g. Betula, Alnus and Corylus were belie ved to originate in the Alps and in the northern parts of Central Euro pe where these species were flowering. The latter category was conside red to originate in more remote areas, many of them belonging to the t axa growing only around the Mediterranean. From a paleo-ecological poi nt of view, long-distance transport such as this would count for an im portant potential source of error whenever interpreting Holocene polle n diagrams. The content of stable organic compounds showed that the du st was relatively clean, compared to other episodes, when the dust dep osited had originated in heavily polluted regions. The small amounts o f chlorinated hydrocarbons, polychlorinated biphenyles (PCB), polyarom ated hydrocarbons (PAH) and other hydrocarbons found, are believed to have been adsorbed by the particle surfaces during transportation. The results of the study, along with meteorological data, lead to the con clusion that the material originated in North Africa. Dust mobilizatio n was reported in Tunisia as well as in Algeria. This means that the d ust was transported at least 7000 km before deposition.