Climate transitions during the Late Glacial and the Early Holocene reconstructed from moraine records in the Austrian Alps

Glaciers provide an excellent natural laboratory for reconstructing the climate of the past as they respond sensitively to climate oscillations with advance or retreat. Therefore, we study glacier systems and their behavior during the transition from colder to warmer climate episodes in glaciated valleys of the Silvretta Massif in the Austrian Alps.  

Using a combination of geomorphological mapping and beryllium-10 surface exposure dating, we reconstruct ice extents of the past and find that glaciers stabilized during the Pre-Bølling to Bølling transition (14.4 ± 1.0 ka, n=3), during the Younger Dryas (ca. 12.9-11.7 ka; n=7), and during the earliest Holocene (ca. 12-10 ka; n=2). The first, (pre)-Bølling age group indicates a stable ice margin that postdates the Gschnitz stadial (ca. 17-16 ka) and predates the Younger Dryas. It shows that local inner-alpine glaciers prevailed until the onset of the Bølling warm phase (ca. 14.6 ka) or possibly even into the Bølling. The second Younger Dryas age group captures the spatial and temporal fine structure of glacier retreat during the Egesen stadial prior to Holocene warming. It evidences ice surface lowering of several tens of meters throughout the Younger Dryas, which is indicative of milder climate conditions at the end of the stadial compared to its beginning. The third age group falls into a period of substantial warming, the Younger Dryas-Holocene transition. The deposition of moraines during a period of abrupt warming implies centennial-scale cold snaps that were probably caused by feedback in the climate system. An explanation proposed in the Younger Dryas-Holocene context is the deglaciation of ice sheets in the Northern hemisphere and resulting freshwater input into the Atlantic ocean, which in turn slowed down ocean circulations and thus reduced heat transport toward (Northern) Europe.

The new geochronologies synthesized with pre-existing moraine records from the Silvretta Massif show that the transition from glacial to interglacial climate conditions occurred within a few centuries and illustrate the sensitive response of Silvretta glaciers to abrupt warming events in the past. Our ice-margin reconstructions provide an example of the response of glaciers and the climate system in a warming world.