Glacier response to Holocene warmth inferred from in situ 10Be and 14C bedrock analyses in Steingletscher’s forefield (central Swiss Alps)

Mid-latitude mountain glaciers sensitively respond to local summer temperature changes. Chronologies of past glacier fluctuations based on the investigation of glacial landforms therefore allows for a better understanding of warm-season climate variability at local scale. In this study, we focus on the Holocene, the current interglacial of the last 11,700 years, which remains matter of dispute regarding its temperature evolution and underlying driving mechanisms. In particular, the nature and significance of the transition from the early to mid-Holocene and of the Holocene Thermal Maximum (HTM) are still debated. Here, we apply a new approach by combining in situ cosmogenic 10Be moraine and 10Be-14C bedrock dating from the same site, the forefield of Steingletscher (European Alps), and reconstruct the glacier’s millennial recession and advance periods. The results suggest that subsequent to the final deglaciation at ~10 ka, the glacier was mostly smaller than its 2000 CE extent until ~3 ka, followed by the predominant occurrence of glacier advances until the end of the Little Ice Age in the 19th century. These findings agree with existing proxy records of Holocene summer temperature and glacier evolution in the Alps, showing that glaciers throughout the region retreated beyond modern extents for most of the Early and mid-Holocene. This implies that at least the summer climate of the HTM was warmer than that of the end of the 20th century for several millennia. Further investigations are necessary to refine the magnitude of warming and the potential HTM seasonality.