Sources and distribution of trace species in Alpine precipitation inferred from two 60-year ice core paleorecords

Abstract. The Alps represent the largest barrier to meridional air flow in Europe, strongly influencing the weather and hence the distribution of atmospheric trace components. Here for the first time, chemical records from two ice cores retrieved from glaciers located in the northern and southern Swiss Alps were compared in conjunction with an analysis of "weather type", in order to assess geographical and seasonal trends in the deposition of trace species and to identify source regions and transport patterns.

Using a correlation analysis, investigated trace species (NH₄⁺, NO₃⁻, SO₄²⁻, Ca²⁺, Mg²⁺, Na⁺, K⁺, and Cl⁻ were grouped into classes of different origin (anthropogenic, sea salt, or Saharan dust). Over the last 60 years, precipitation chemistry at both sites was dominated by NH₄⁺, NO₄⁻, and SO₄²⁻, all of anthropogenic origin and deposited mainly in summer by way of convective precipitation. The similarity of the SO₄²⁻ profiles with historical records of SO₄ emissions from France and Italy indicated these two countries as key source areas for the anthropogenic species.

In contrast, sea salt and Saharan dust showed major differences in transport pattern and deposition across the Alps. Currently, the sea-salt constituents Na⁺, K⁺, and Cl⁻ are transported to the northern site during advective westerly-wind situations, independent of Saharan dust events. At the southern site, sea salt and Saharan dust are deposited simultaneously, indicating a coupled transport active mainly in summer during south-westerly wind situations.