The transport history of two Saharan dust events archived in an Alpine ice core

Mineral dust from the Saharan desert can be transported across the Mediterraneantowards the Alpine region several times a year. Occasionally, the dust is depositedwith snowfall on Alpine glaciers and appears then as yellow or red layers in ice cores.Two such significant dust events were identified in an ice core drilled at the high-accumulation site Piz Zup ́o in the Swiss Alps (46◦22′N, 9◦55′E, 3850m a.s.l.). Fromstable oxygen isotopes and major ion concentrations, the events were approximatelydated as October and March 2000. In order to link the dust record in the ice core tothe meteorological situation that led to the dust events, a novel methodology basedon back-trajectory analysis was developed. It allowed for the identification of source regions, the atmospheric transport pathways, and wet deposition periods for both dustevents. Furthermore, differences in the chemical signature of the two dust events couldbe interpreted with respect to contributions from the dust sources and aerosol scaveng-ing during the transport.The dust deposition during the October event took place during 13–16 October 2000. Mobilisation areas of dust were mainly identified in the Algerian and Libyan deserts. Acombination of an upper-level potential vorticity streamer and a midlevel jet across Al-geria first brought moist Atlantic air and later mixed air from the tropics and Saharandesert across the Mediterranean towards the Alps. The March event consisted of twodifferent deposition phases which took place during 18–20 and 23–26 March 2000. The first phase was associated with an exceptional transport pattern past Iceland andtowards the Alps from northerly directions. The second phase was similar to the Oc-tober event. A significant peak of methanesulphonic acid associated with the Marchdust event was most likely caused by incorporation of biogenic aerosol while passingthrough the marine boundary layer of the western Mediterranean during a local phyto-plankton bloom. From this study, we conclude that the whole sequence of mobilisation,transport, and deposition of mineral aerosol should be considered for a detailed under-standing of the chemical signal recorded in the ice core at Piz Zup ́o.ISSN:1680-7375ISSN:1680-736