Alpine Ice Cores as Climate and Environmental Archives

The European Alps feature a unique situation with the densest network of long-term instrumental climate observations and anthropogenic emission sources located in the immediate vicinity of glaciers suitable for ice core studies. To archive atmospheric changes in an undisturbed sequence of firn and ice layers, ice core drilling sites require temperatures low enough to minimize meltwater percolation. In the Alps, this implies a restriction to the highest summit glaciers of comparatively small horizontal and vertical extension (i.e., with typical ice thickness not much exceeding 100 m). As a result, Alpine ice cores offer either high-resolution or long-term records, depending on the net snow accumulation regime of the drilling site. High-accumulation Alpine ice cores have been used with great success to study the anthropogenic influence on aerosol-related atmospheric impurities over the last 100 years or so. However, respective long-term reconstructions (i.e., substantially exceeding the instrumental era) from low-accumulation sites remain comparatively sparse. Accordingly, deciphering Alpine ice cores as long-term climate records deserves special emphasis. Certain conditions must exist for Alpine ice cores to serve as climate archives, and this is important in particular regarding the challenges and achievements that have significance for ice cores from other mountain areas: (a) a reliable chronology is the fundamental prerequisite for interpreting any ice core proxy time series. Advances in radiometric ice dating and annual layer counting offer the tools to crucially increase dating precision in the preinstrumental era. (b) Glacier flow effects and spatio-seasonal snow deposition variability challenge linking the ice core proxy signals to the respective atmospheric variability (e.g., of temperature, mineral dust, and impurity concentrations). Here, assistance comes from combining multiple ice cores from one site and from complementary meteorological, glaciological, and geophysical surveys. (c) As Alpine ice cores continue to advance their contribution to Holocene climate science, exploring the link to instrumental, historical, and other natural climate archives gains increasing importance.