Onset of Neoglaciation in the Alps – assessing Holocene minimum Alpine glacier extent

For the Alps, knowledge about maximum Holocene glacier coverage prior to the Little Ice Age is relatively comprehensive, although restricted to lower elevations. Alpine glacier advance and maximum extent can be derived from mapped and dated moraines, while findings of archeological objects, fossil wood or the “Tyrolian iceman” emerging under melted ice allow pointwise constraint of past glacier extent similar as of today. Still little is known about the timing of lower ice cover or even ice-free conditions at high-elevations. Thanks to a more recent analytical development to micro-radiocarbon (14C) date ice using entrapped organic carbonaceous particles (constituent of the contemporary aerosol), this gap can now be filled. Unique in its possibility to determine the age of alpine glacier ice older than a few hundred years (0.5 to 20-30 kyrs), this approach has already been widely applied to date ice cores from various mid- and low-latitude regions. The determination of the age of the oldest ice frozen to the bedrock thereby yielding additional information about the period of glacier formation at the respective sites. Representative spatial data, covering a range of elevations is emerging for some regions (European Alps, Tibetan Plateau) and first studies demonstrated the great potential to access valuable information about the connection between warm periods, elevation and ice coverage. The proposed project focusing on the European Alps, aims to increase the regional and vertical (elevation) density of the available data of Holocene minimum Alpine glacier extent. Ice cores from three so far unexplored locations in the Swiss Alps will be extracted. The proposed study sites are characterized by low ice flow dynamics due to their summit ice-cap like geometry, a rather rare feature in the Alps. These are the summit glaciers of Tödi (Glarus, drill site ~3570 m asl.), Mont Collon (Valais, ~3600 m asl.) and Alphubel (Valais, ~4180 m asl.). All sites experienced a loss in ice thickness over the past few decades. Still, the existence of old perennial ice from the time of glacier formation can be expected at the bottom, because of low glacier flow and, at least until recently, this ice being frozen to the underlying bedrock. Aside from micro-radiocarbon dating of the old bottom ice, investigations of the sites and ice cores will be complemented by measurements of ice temperature (field) and glacio-chemical analysis in the ice including ions and trace elements, stable isotopes of water, black carbon, 210Pb and 3H. It is important to note that with the ongoing warming, the ice at the proposed sites is under great thread of soon being lost as a valuable archive of the past forever.