Lars G. Franzén

The ‘yellow snowepisode’ of northern Fennoscandia, march 1991—A case study of long-distance transport of soil, pollen and stable organic compounds

Abstract The present paper describes a vast dustfall with snow in northern Fennoscandia, 10 March 1991. The area affected by dust deposition was at least 320,000 km2. and the particulate mass received amounted to between 50 and 200 mgm−2. The total amounts of dust deposited in the investigated area sum up to approximately 50,000 tonnes. The dust consisted of soil particles, i.e. single mineral grains and loose ferric aggregates of mineral grains in addition to pollen and spores. Mineralogically, the dust was dominated by small rounded quartz grains. Median size of the dust particles was 2.72 μm. The total pollen concentration varied from 327 to 1172 pollen cm−2. The pollen types identified were divided in “Nordic/Central European” taxa and “Exotic” taxa. Pollen from the former group, e.g. Betula, Alnus and Corylus were believed to originate in the Alps and in the northern parts of Central Europe where these species were flowering. The latter category was considered to originate in more remote areas, many of them belonging to the taxa growing only around the Mediterranean. From a paleo-ecological point of view, long-distance transport such as this would count for an important potential source of error whenever interpreting Holocene pollen diagrams. The content of stable organic compounds showed that the dust was relatively clean, compared to other episodes, when the dust deposited had originated in heavily polluted regions. The small amounts of chlorinated hydrocarbons, polychlorinated biphenyles (PCB), polyaromated 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 conclusion that the material originated in North Africa. Dust mobilization was reported in Tunisia as well as in Algeria. This means that the dust was transported at least 7000 km before deposition.

Inland transport of marine aerosols in southern Sweden

Abstract The transport of marine aerosols across southern Sweden was studied using six meteorological stations in a transect from west- to east-coast. Measurements were made during dry westerlies on 10 occasions during 1995. The concentration and flux of salt in the air was measured using “salt vanes”. It is concluded that marine salt is transported along the whole transect at all occasions and that the concentration and flux of salt decrease with downwind distance from the coast as an inversed power function. The two easternmost stations show a slight increase towards the east-coast. Variability of the data is high on the west coast due to strong influence from the coastal production of aerosols. This effect diminishes along downwind forming lower, less variable concentration further inland. Statistical models based on the data are in relatively good agreement with previous models and data. Further, salt content on Scots Pine (Pinus sylvestris, L) needles after two westerly gale occasions, in profiles from west- to east-coast, were analysed. The Cl−/Na+, Ca2+/Na+, K+/Na+, Mg2+/Na+ and SO42−/Na+ ratios were studied revealing a clear downwind decrease in Ca2+/Na+ and Mg2+/Na+, a close to sea water ratio for Cl−/Na+ and an excess of SO42− along the profile. Also, the importance of degree of exposure was studied concluding that the roughness of the upwind surface is an important factor for the deposition onto trees in forest edges.

Implications of recent long-distance pollen transport events for the interpretation of fossil pollen records in Fennoscandia

Abstract Under favourable conditions, a considerable amount of long-distance transported pollen can be deposited far from its place of origin. In Fennoscandia, in most cases, such situations occur when there is a strong southerly air circulation from South-Europe and/or North-Africa. Soil particles and pollen grains associated with the top soil or the present vegetation, can be lifted up by strong surface winds and brought up to higher levels, where further transportation takes place. During the last few years several of these events have been reported. The pollen analysis of three events with coloured precipitation from different parts of Fennoscandia provides information about such exotic pollen rain and its extent. The quantity of exotic pollen in the snow samples analysed is high, generally in the range of 500–2000 pollen grains cm −2 per episode. However, the amount of transported pollen can even be as great as that deposited during local anthesis in the same year, and influx values can exceed 30, 000 pollen grains cm −2 per few hours of snowfall. The results are analysed in relation to trajectory calculations, the actual phenological data, and pollen concentrations monitored by volumetric sampling from the air. Since the long-distance transport of pollen grains depends mainly on climatological factors, the hypothesis that exotic pollen deposition was common throughout the whole of the Holocene in Fennoscandia is presented. Long-distance transport of pollen grains can, therefore, be regarded as a potential source of error in the interpretation of Holocene pollen diagrams from Fennoscandia.

A coloured snow episode on the Swedish west coast, january 1987 a quantitative and qualitative study of air borne particles

The authors have made an analysis of particles brought down by snow on the Swedish west coast in January 1987. The analyses included a quantitative study of the deposition and its organic/inorganic...

THE PEATLAND/ICE AGE HYPOTHESIS REVISED, ADDING A POSSIBLE GLACIAL PULSE TRIGGER

Abstract Carbon sequestering in peatlands is believed to be a major climate‐regulating mechanism throughout the late Phanerozoic. Since plant life first evolved on land, peatlands have been significant carbon sinks, which could explain significant parts of the large variations in atmospheric carbon dioxide observed in various records. The result is peat in different degrees of metamorphosis, i.e. lignite, hard coal and graphite. During phases of extensive glaciations such as the 330–240 Ma Pangea Ice Age, atmospheric carbon dioxide was critically low. This pattern repeats itself during the Pleistocene when carbon dioxide oscillates with an amplitude of c. 200–300 ppmv. This paper suggests that the ice age cycles during the Pleistocene are generated by the interglacial growth of peatlands and the subsequent sequestering of carbon into this terrestrial pool. The final initiation of ice age pulses towards the end of inter‐glacials, on the other hand, is attributed to the cyclic influx of cosmic dust to the Earth surface, which in turn regulates cloud formation and the incoming shortwave radiation. These shorter cycles have a frequency of c. 1000‐1250 years and might be connected to sunspot or other low frequency solar variations. In a wider context the ice age cycling could be regarded as an interplay between terrestrial life on the high latitudes of the northern hemisphere and the marine subsurface life in the southeast. If the results presented here are correct, the present global warming might just be the early part of a new warm period such as the Bronze Age and the Roman and Medieval Warm periods. This could be caused by entry into another phase of decreasing influx rates of cosmic dust. The increasing concentrations of atmospheric carbon dioxide might have contributed to this warming but, most important of all, it might temporarily have saved us from a new ice age pulse.