Mineral dust and elemental black carbon records from an Alpine ice core (Colle Gnifetti glacier) over the last millennium

Abstract

Black carbon (BC) and mineral dust aerosols were analyzed in an ice core from the Colle Gnifetti glacier (Monte Rosa, Swiss-Italian Alps, 45°55′N, 7°52′E, 4455 m above sea level) using chemical and optical methods. The resulting time series obtained from this summer ice record indicate that BC transport was primarily constrained by regional anthropogenic activities, i.e., biomass and fossil fuel combustion. More precisely, the δ 13 C composition of BC suggests that wood combustion was the main source of preindustrial atmospheric BC emissions (C3:C4 ratio of burnt biomass of 75:25). Despite relatively high BC emissions prior to 1570, biomass burning activity and especially C4 grassland burning abruptly dropped between 1570 and 1750 (C3:C4 ratio of burnt biomass of 90:10), suggesting that agricultural practices strongly decreased in Europe during this cold period of the "Little Ice Age" (LIA). On the other hand, optical analysis revealed that the main source for atmospheric dust transport to the southern parts of the Alps during summer months was driven by large-scale atmospheric circulation control on the dust export from the northern Saharan desert. This southern aerosol source was probably associated with global-scale hydrologic changes, at least partially forced by variability in solar irradiance. In fact, periods of enhanced Saharan dust deposition in the ice core (around 1200-1300, 1430-1520, 1570-1690, 1780-1800, and after 1870) likely reflect drier winters in North Africa, stronger North Atlantic southwesterlies, and increased spring/summer precipitation in west-central Europe. These results, therefore, suggest that the climatic pejorations and the resulting socioeconomic crises, which occurred in Europe during periods of the LIA, could have been indirectly triggered by large-scale meridional advection of air masses and wetter summer climatic conditions. Copyright 2009 by the American Geophysical Union.