Holocene dynamics of Arsine Glacier (Ecrins Massif, French Alps) inferred from cosmogenic 10Be dating

Due to the sensitivity of mountain glacier dynamics to climate change, reconstruction of Holocene glacier chronologies allows us to better understand the evolution of the natural climate system during the current interglacial. However, records of glacier variations spanning from the Early Holocene to the Little Ice Age (LIA) and based on direct dating of glacial deposits remain scarce. The forefield of Arsine glacier, located in the Ecrins Massif of the Western Alps (France; 45°N), is characterized by the existence of abundant glacio-geomorphologic markers bearing witness of numerous past glacier extents of different size. Cosmogenic 10Be dating of the most distal moraines in the study area provides evidence for multiple glacier extensions during the Early Holocene, while dating several of the crests on the proximal massive vegetation-free moraine complex yields ages of ~3 ka and a few hundred years. These glacier extensions are thus in accordance with the Neoglacial and the LIA, respectively. No moraines are preserved from between ~10 ka to ~3 ka ago. These results are in very good agreement with Holocene-spanning 10Be moraine records in the Swiss Western and Central Alps, suggesting that glacier fluctuations during the Holocene were regionally synchronous at least on millennial timescales. The glacio-geomorphic peculiarity at the study site of Arsine glacier consists in the existence of a 1-km-wide and 0.5-km-long rockglacier-like deposit mostly composed of big sub-concentric blocky lobes and stratigraphically located between the Early Holocene moraines and the Neoglacial/LIA moraine complex. It could testify to a major glacier extent that must have occurred sometime between ~10 ka and 3 ka ago, but at present further age constraints are missing. 10Be dating of boulders from this deposit are currently ongoing to complement the chronology of Arsine glacier’s behaviour during the Holocene and to put the origin of the peculiar deposit in the context of the Holocene climate evolution.