Saharan dust deposition over Mont Blanc (French Alps) during the last 30 years

Based on continuous and very detailed Al and Ca records along a 70 m long ice core drilled in the Mont Blanc summit area (French Alps, 4270 m asl), continental dust flux at high altitude in the Alps was studied for the past 30 years. From 1955 until 1985, total inputs of 885 and 735 μg/cm-2 were calculated for Al and Ca respectively. Using mineralogical observations and chemical criteria, the relative importance of the local component was estimated close to 10% for Al and to 30% for Ca continental inputs. It was also possible to point out the predominating influence of soil dust sources located in North Africa, which seems to have significantly increased since the early 1970s with very high inputs occurring after 1980. In 1985, which corresponds to the last complete year of our ice record, the North African influence led to A1 and Ca annual deposition rates of 64 and 23 μg cm-2 yr-1.