Influence of Saharan dust on the rain acidity and atmospheric input to the Mediterranean

Abstract

It has long been recognized that Saharan dust may be transported a long way from its sources, particularly over the ocean¹, and especially over the tropical North Atlantic, as far as the Caribbean^2–7, and over various areas of the Mediterranean^8–10. The eolian transport of desertic aerosols is a major contribution to oceanic sedimentation^11–13 and may have important climatic implications¹⁴. This phenomenon is responsible for episodes of so-called ‘red rain’ or ‘red snow’ which have been identified in various areas of the European continent^15–17. Numerous red rains and red dust falls have been observed in Corsica. From 1984 data on the chemistry of precipitation collected in South Corsica, we show here that due to its CaCO₃ content, Saharan dust significantly increases the pH of rain water. This may counteract the effects of acidic rain. An assessment of African dust deposition indicates that, compared with the sediments discharged by the Rhône river, atmospheric input to the northwestern Mediterranean contributes significantly to sedimentation in that region.