Airborne dust collected at Barbados

Abstract

Wind-borne dust collections have been made on the island of Barbados; and the day by day amounts have been recorded for several months, commencing August 1965. From mineralogical and biological examinations, this dust is most likely to be derived from the European-African continents. The fungus and magnetic contents of the dust show a marked seasonal variation in accordance with the shift in wind patterns off the African coast. The average concentration of this dust is about 5 × 10 −12 cm 3 per cm 3 of air and making plausible estimates for the fallout rate, its contribution to the deep sea sedimentation of the western tropical Atlantic is about 0·6 mm/1000 yr, suggesting that a goodly fraction of the deep sea clay is indeed wind transported. The size distribution of the Barbados dust, which is mainly below 20 μ, can be argued into agreement with the distribution in the Atlantic sediments. Both the dusts and the deep-sea sediments have similar mineral compositions. The finding of dolomite in the Barbados dusts has led to an explanation of its occurrence in the Atlantic deposits and to a discovery of a dolomite gradient across the ocean. Along with various marine organisms and a great number of fungus hyphae, fresh water diatoms, in particular Melosira granulata, occur in all the Barbados dusts. This diatom is found in Atlantic sediments; and previous studies indicated that in certain core sections it is present in abundance. Occasionally Denticula elegans is also found and, since this fresh water diatom only inhabits cold running waters, there is strong indication that the dusts arriving at Barbados could have come, in part and at various times, from a mountainous region.